draft-ietf-rift-rift-08.txt   draft-ietf-rift-rift-09.txt 
RIFT Working Group A. Przygienda, Ed. RIFT Working Group A. Przygienda, Ed.
Internet-Draft Juniper Internet-Draft Juniper
Intended status: Standards Track A. Sharma Intended status: Standards Track A. Sharma
Expires: March 11, 2020 Comcast Expires: May 7, 2020 Comcast
P. Thubert P. Thubert
Cisco Cisco
Bruno. Rijsman Bruno. Rijsman
Individual Individual
Dmitry. Afanasiev Dmitry. Afanasiev
Yandex Yandex
September 8, 2019 November 4, 2019
RIFT: Routing in Fat Trees RIFT: Routing in Fat Trees
draft-ietf-rift-rift-08 draft-ietf-rift-rift-09
Abstract Abstract
This document outlines a specialized, dynamic routing protocol for This document defines a specialized, dynamic routing protocol for
Clos and fat-tree network topologies. The protocol (1) deals with Clos and fat-tree network topologies optimized towards minimization
fully automated construction of fat-tree topologies based on of configuration and operational complexity. The protocol
detection of links, (2) minimizes the amount of routing state held at
each level, (3) automatically prunes and load balances topology deals with no configuration, fully automated construction of fat-
flooding exchanges over a sufficient subset of links, (4) supports tree topologies based on detection of links,
automatic disaggregation of prefixes on link and node failures to
prevent black-holing and suboptimal routing, (5) allows traffic minimizes the amount of routing state held at each level,
steering and re-routing policies, (6) allows loop-free non-ECMP
forwarding, (7) automatically re-balances traffic towards the spines automatically prunes and load balances topology flooding exchanges
based on bandwidth available and finally (8) provides mechanisms to over a sufficient subset of links,
synchronize a limited key-value data-store that can be used after
protocol convergence to e.g. bootstrap higher levels of supports automatic disaggregation of prefixes on link and node
functionality on nodes. failures to prevent black-holing and suboptimal routing,
allows traffic steering and re-routing policies,
allows loop-free non-ECMP forwarding,
automatically re-balances traffic towards the spines based on
bandwidth available and finally
provides mechanisms to synchronize a limited key-value data-store
that can be used after protocol convergence to e.g. bootstrap
higher levels of functionality on nodes.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 11, 2020.
This Internet-Draft will expire on May 7, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 28 skipping to change at page 2, line 44
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 8 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 8
3. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 8 3. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Requirement Considerations . . . . . . . . . . . . . . . . . 14 4. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 14
5. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 17 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1.1. Properties . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Properties . . . . . . . . . . . . . . . . . . . . . 18 4.1.2. Generalized Topology View . . . . . . . . . . . . . . 16
5.1.2. Generalized Topology View . . . . . . . . . . . . . . 18 4.1.2.1. Terminology . . . . . . . . . . . . . . . . . . . 16
5.1.3. Fallen Leaf Problem . . . . . . . . . . . . . . . . . 28 4.1.2.2. Clos as Crossed Crossbars . . . . . . . . . . . . 17
5.1.4. Discovering Fallen Leaves . . . . . . . . . . . . . . 30 4.1.3. Fallen Leaf Problem . . . . . . . . . . . . . . . . . 26
5.1.5. Addressing the Fallen Leaves Problem . . . . . . . . 31 4.1.4. Discovering Fallen Leaves . . . . . . . . . . . . . . 28
5.2. Specification . . . . . . . . . . . . . . . . . . . . . . 32 4.1.5. Addressing the Fallen Leaves Problem . . . . . . . . 29
5.2.1. Transport . . . . . . . . . . . . . . . . . . . . . . 32 4.2. Specification . . . . . . . . . . . . . . . . . . . . . . 30
5.2.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . 33 4.2.1. Transport . . . . . . . . . . . . . . . . . . . . . . 31
5.2.3. Topology Exchange (TIE Exchange) . . . . . . . . . . 35 4.2.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . 31
5.2.3.1. Topology Information Elements . . . . . . . . . . 35 4.2.2.1. LIE FSM . . . . . . . . . . . . . . . . . . . . . 34
5.2.3.2. South- and Northbound Representation . . . . . . 36 4.2.3. Topology Exchange (TIE Exchange) . . . . . . . . . . 40
5.2.3.3. Flooding . . . . . . . . . . . . . . . . . . . . 38 4.2.3.1. Topology Information Elements . . . . . . . . . . 40
5.2.3.4. TIE Flooding Scopes . . . . . . . . . . . . . . . 39 4.2.3.2. South- and Northbound Representation . . . . . . 40
5.2.3.5. 'Flood Only Node TIEs' Bit . . . . . . . . . . . 41 4.2.3.3. Flooding . . . . . . . . . . . . . . . . . . . . 43
5.2.3.6. Initial and Periodic Database Synchronization . . 42 4.2.3.4. TIE Flooding Scopes . . . . . . . . . . . . . . . 50
5.2.3.7. Purging and Roll-Overs . . . . . . . . . . . . . 42 4.2.3.5. 'Flood Only Node TIEs' Bit . . . . . . . . . . . 52
5.2.3.8. Southbound Default Route Origination . . . . . . 43 4.2.3.6. Initial and Periodic Database Synchronization . . 53
5.2.3.9. Northbound TIE Flooding Reduction . . . . . . . . 43 4.2.3.7. Purging and Roll-Overs . . . . . . . . . . . . . 53
5.2.3.10. Special Considerations . . . . . . . . . . . . . 48 4.2.3.8. Southbound Default Route Origination . . . . . . 54
5.2.4. Reachability Computation . . . . . . . . . . . . . . 49 4.2.3.9. Northbound TIE Flooding Reduction . . . . . . . . 54
5.2.4.1. Northbound SPF . . . . . . . . . . . . . . . . . 49 4.2.3.10. Special Considerations . . . . . . . . . . . . . 59
5.2.4.2. Southbound SPF . . . . . . . . . . . . . . . . . 50 4.2.4. Reachability Computation . . . . . . . . . . . . . . 60
5.2.4.3. East-West Forwarding Within a non-ToF Level . . . 50 4.2.4.1. Northbound SPF . . . . . . . . . . . . . . . . . 60
5.2.4.4. East-West Links Within ToF Level . . . . . . . . 50 4.2.4.2. Southbound SPF . . . . . . . . . . . . . . . . . 61
5.2.5. Automatic Disaggregation on Link & Node Failures . . 51 4.2.4.3. East-West Forwarding Within a non-ToF Level . . . 61
5.2.5.1. Positive, Non-transitive Disaggregation . . . . . 51 4.2.4.4. East-West Links Within ToF Level . . . . . . . . 61
5.2.5.2. Negative, Transitive Disaggregation for Fallen 4.2.5. Automatic Disaggregation on Link & Node Failures . . 62
Leafs . . . . . . . . . . . . . . . . . . . . . . 54 4.2.5.1. Positive, Non-transitive Disaggregation . . . . . 62
5.2.6. Attaching Prefixes . . . . . . . . . . . . . . . . . 56 4.2.5.2. Negative, Transitive Disaggregation for Fallen
5.2.7. Optional Zero Touch Provisioning (ZTP) . . . . . . . 65 Leafs . . . . . . . . . . . . . . . . . . . . . . 65
5.2.7.1. Terminology . . . . . . . . . . . . . . . . . . . 66 4.2.6. Attaching Prefixes . . . . . . . . . . . . . . . . . 67
5.2.7.2. Automatic SystemID Selection . . . . . . . . . . 67 4.2.7. Optional Zero Touch Provisioning (ZTP) . . . . . . . 76
5.2.7.3. Generic Fabric Example . . . . . . . . . . . . . 68 4.2.7.1. Terminology . . . . . . . . . . . . . . . . . . . 77
5.2.7.4. Level Determination Procedure . . . . . . . . . . 69 4.2.7.2. Automatic SystemID Selection . . . . . . . . . . 78
5.2.7.5. Resulting Topologies . . . . . . . . . . . . . . 70 4.2.7.3. Generic Fabric Example . . . . . . . . . . . . . 79
5.2.8. Stability Considerations . . . . . . . . . . . . . . 72 4.2.7.4. Level Determination Procedure . . . . . . . . . . 80
5.3. Further Mechanisms . . . . . . . . . . . . . . . . . . . 72 4.2.7.5. ZTP FSM . . . . . . . . . . . . . . . . . . . . . 81
5.3.1. Overload Bit . . . . . . . . . . . . . . . . . . . . 72 4.2.7.6. Resulting Topologies . . . . . . . . . . . . . . 89
5.3.2. Optimized Route Computation on Leafs . . . . . . . . 72 4.2.8. Stability Considerations . . . . . . . . . . . . . . 91
5.3.3. Mobility . . . . . . . . . . . . . . . . . . . . . . 73 4.3. Further Mechanisms . . . . . . . . . . . . . . . . . . . 92
5.3.3.1. Clock Comparison . . . . . . . . . . . . . . . . 74 4.3.1. Overload Bit . . . . . . . . . . . . . . . . . . . . 92
5.3.3.2. Interaction between Time Stamps and Sequence 4.3.2. Optimized Route Computation on Leafs . . . . . . . . 92
Counters . . . . . . . . . . . . . . . . . . . . 74 4.3.3. Mobility . . . . . . . . . . . . . . . . . . . . . . 92
5.3.3.3. Anycast vs. Unicast . . . . . . . . . . . . . . . 75 4.3.3.1. Clock Comparison . . . . . . . . . . . . . . . . 94
5.3.3.4. Overlays and Signaling . . . . . . . . . . . . . 75 4.3.3.2. Interaction between Time Stamps and Sequence
5.3.4. Key/Value Store . . . . . . . . . . . . . . . . . . . 76 Counters . . . . . . . . . . . . . . . . . . . . 94
5.3.4.1. Southbound . . . . . . . . . . . . . . . . . . . 76 4.3.3.3. Anycast vs. Unicast . . . . . . . . . . . . . . . 95
5.3.4.2. Northbound . . . . . . . . . . . . . . . . . . . 76 4.3.3.4. Overlays and Signaling . . . . . . . . . . . . . 95
5.3.5. Interactions with BFD . . . . . . . . . . . . . . . . 76 4.3.4. Key/Value Store . . . . . . . . . . . . . . . . . . . 95
5.3.6. Fabric Bandwidth Balancing . . . . . . . . . . . . . 77 4.3.4.1. Southbound . . . . . . . . . . . . . . . . . . . 95
5.3.6.1. Northbound Direction . . . . . . . . . . . . . . 77 4.3.4.2. Northbound . . . . . . . . . . . . . . . . . . . 96
5.3.6.2. Southbound Direction . . . . . . . . . . . . . . 79 4.3.5. Interactions with BFD . . . . . . . . . . . . . . . . 96
5.3.7. Label Binding . . . . . . . . . . . . . . . . . . . . 80 4.3.6. Fabric Bandwidth Balancing . . . . . . . . . . . . . 97
5.3.8. Segment Routing Support with RIFT . . . . . . . . . . 80 4.3.6.1. Northbound Direction . . . . . . . . . . . . . . 97
5.3.8.1. Global Segment Identifiers Assignment . . . . . . 80 4.3.6.2. Southbound Direction . . . . . . . . . . . . . . 99
5.3.8.2. Distribution of Topology Information . . . . . . 80 4.3.7. Label Binding . . . . . . . . . . . . . . . . . . . . 100
5.3.9. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 81 4.3.8. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 100
5.3.10. Address Family and Multi Topology Considerations . . 81 4.3.9. Address Family and Multi Topology Considerations . . 100
5.3.11. Reachability of Internal Nodes in the Fabric . . . . 81 4.3.10. Reachability of Internal Nodes in the Fabric . . . . 101
5.3.12. One-Hop Healing of Levels with East-West Links . . . 82 4.3.11. One-Hop Healing of Levels with East-West Links . . . 101
5.4. Security . . . . . . . . . . . . . . . . . . . . . . . . 82 4.4. Security . . . . . . . . . . . . . . . . . . . . . . . . 101
5.4.1. Security Model . . . . . . . . . . . . . . . . . . . 82 4.4.1. Security Model . . . . . . . . . . . . . . . . . . . 101
5.4.2. Security Mechanisms . . . . . . . . . . . . . . . . . 84 4.4.2. Security Mechanisms . . . . . . . . . . . . . . . . . 103
5.4.3. Security Envelope . . . . . . . . . . . . . . . . . . 84 4.4.3. Security Envelope . . . . . . . . . . . . . . . . . . 104
5.4.4. Weak Nonces . . . . . . . . . . . . . . . . . . . . . 87 4.4.4. Weak Nonces . . . . . . . . . . . . . . . . . . . . . 107
5.4.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . 88 4.4.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . 108
5.4.6. Key Management . . . . . . . . . . . . . . . . . . . 88 4.4.6. Key Management . . . . . . . . . . . . . . . . . . . 108
5.4.7. Security Association Changes . . . . . . . . . . . . 88 4.4.7. Security Association Changes . . . . . . . . . . . . 108
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 109
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 89 5.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 109
6.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 89 5.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 110
6.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 90 5.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 111
6.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 91 5.4. Northbound Partitioned Router and Optional East-West
6.4. Northbound Partitioned Router and Optional East-West Links . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Links . . . . . . . . . . . . . . . . . . . . . . . . . . 93 6. Implementation and Operation: Further Details . . . . . . . . 113
7. Implementation and Operation: Further Details . . . . . . . . 93 6.1. Considerations for Leaf-Only Implementation . . . . . . . 113
7.1. Considerations for Leaf-Only Implementation . . . . . . . 93 6.2. Considerations for Spine Implementation . . . . . . . . . 114
7.2. Considerations for Spine Implementation . . . . . . . . . 94 6.3. Adaptations to Other Proposed Data Center Topologies . . 114
7.3. Adaptations to Other Proposed Data Center Topologies . . 94 6.4. Originating Non-Default Route Southbound . . . . . . . . 115
7.4. Originating Non-Default Route Southbound . . . . . . . . 95 7. Security Considerations . . . . . . . . . . . . . . . . . . . 115
8. Security Considerations . . . . . . . . . . . . . . . . . . . 95 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 115
8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 95 7.2. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
8.2. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 7.3. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . 116
8.3. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . 96 7.4. Packet Number . . . . . . . . . . . . . . . . . . . . . . 116
8.4. Packet Number . . . . . . . . . . . . . . . . . . . . . . 96 7.5. Outer Fingerprint Attacks . . . . . . . . . . . . . . . . 116
8.5. Outer Fingerprint Attacks . . . . . . . . . . . . . . . . 96 7.6. TIE Origin Fingerprint DoS Attacks . . . . . . . . . . . 116
8.6. TIE Origin Fingerprint DoS Attacks . . . . . . . . . . . 96 7.7. Host Implementations . . . . . . . . . . . . . . . . . . 117
8.7. Host Implementations . . . . . . . . . . . . . . . . . . 97 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 117
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 97 8.1. Requested Multicast and Port Numbers . . . . . . . . . . 117
9.1. Requested Multicast and Port Numbers . . . . . . . . . . 97 8.2. Requested Registries with Suggested Values . . . . . . . 117
9.2. Requested Registries with Suggested Values . . . . . . . 97 8.2.1. Registry RIFT/common/AddressFamilyType . . . . . . . 118
9.2.1. RIFT/common/AddressFamilyType . . . . . . . . . . . . 98 8.2.1.1. Requested Entries . . . . . . . . . . . . . . . . 118
9.2.1.1. Requested Entries . . . . . . . . . . . . . . . . 98 8.2.2. Registry RIFT/common/HierarchyIndications . . . . . . 118
9.2.2. RIFT/common/HierarchyIndications . . . . . . . . . . 98 8.2.2.1. Requested Entries . . . . . . . . . . . . . . . . 118
9.2.2.1. Requested Entries . . . . . . . . . . . . . . . . 98 8.2.3. Registry RIFT/common/IEEE802_1ASTimeStampType . . . . 118
9.2.3. RIFT/common/IEEE802_1ASTimeStampType . . . . . . . . 98 8.2.3.1. Requested Entries . . . . . . . . . . . . . . . . 118
9.2.3.1. Requested Entries . . . . . . . . . . . . . . . . 98 8.2.4. Registry RIFT/common/IPAddressType . . . . . . . . . 119
9.2.4. RIFT/common/IPAddressType . . . . . . . . . . . . . . 98 8.2.4.1. Requested Entries . . . . . . . . . . . . . . . . 119
9.2.4.1. Requested Entries . . . . . . . . . . . . . . . . 98 8.2.5. Registry RIFT/common/IPPrefixType . . . . . . . . . . 119
9.2.5. RIFT/common/IPPrefixType . . . . . . . . . . . . . . 99 8.2.5.1. Requested Entries . . . . . . . . . . . . . . . . 119
9.2.5.1. Requested Entries . . . . . . . . . . . . . . . . 99 8.2.6. Registry RIFT/common/IPv4PrefixType . . . . . . . . . 119
9.2.6. RIFT/common/IPv4PrefixType . . . . . . . . . . . . . 99 8.2.6.1. Requested Entries . . . . . . . . . . . . . . . . 119
9.2.6.1. Requested Entries . . . . . . . . . . . . . . . . 99 8.2.7. Registry RIFT/common/IPv6PrefixType . . . . . . . . . 119
9.2.7. RIFT/common/IPv6PrefixType . . . . . . . . . . . . . 99 8.2.7.1. Requested Entries . . . . . . . . . . . . . . . . 119
9.2.7.1. Requested Entries . . . . . . . . . . . . . . . . 99 8.2.8. Registry RIFT/common/PrefixSequenceType . . . . . . . 120
9.2.8. RIFT/common/PrefixSequenceType . . . . . . . . . . . 99 8.2.8.1. Requested Entries . . . . . . . . . . . . . . . . 120
9.2.8.1. Requested Entries . . . . . . . . . . . . . . . . 99 8.2.9. Registry RIFT/common/RouteType . . . . . . . . . . . 120
9.2.9. RIFT/common/RouteType . . . . . . . . . . . . . . . . 100 8.2.9.1. Requested Entries . . . . . . . . . . . . . . . . 120
9.2.9.1. Requested Entries . . . . . . . . . . . . . . . . 100 8.2.10. Registry RIFT/common/TIETypeType . . . . . . . . . . 120
9.2.10. RIFT/common/TIETypeType . . . . . . . . . . . . . . . 100 8.2.10.1. Requested Entries . . . . . . . . . . . . . . . 121
9.2.10.1. Requested Entries . . . . . . . . . . . . . . . 100 8.2.11. Registry RIFT/common/TieDirectionType . . . . . . . . 121
9.2.11. RIFT/common/TieDirectionType . . . . . . . . . . . . 101 8.2.11.1. Requested Entries . . . . . . . . . . . . . . . 121
9.2.11.1. Requested Entries . . . . . . . . . . . . . . . 101 8.2.12. Registry RIFT/encoding/Community . . . . . . . . . . 121
9.2.12. RIFT/encoding/Community . . . . . . . . . . . . . . . 101 8.2.12.1. Requested Entries . . . . . . . . . . . . . . . 121
9.2.12.1. Requested Entries . . . . . . . . . . . . . . . 101 8.2.13. Registry RIFT/encoding/KeyValueTIEElement . . . . . . 121
9.2.13. RIFT/encoding/KeyValueTIEElement . . . . . . . . . . 101 8.2.13.1. Requested Entries . . . . . . . . . . . . . . . 122
9.2.13.1. Requested Entries . . . . . . . . . . . . . . . 101 8.2.14. Registry RIFT/encoding/LIEPacket . . . . . . . . . . 122
8.2.14.1. Requested Entries . . . . . . . . . . . . . . . 122
9.2.14. RIFT/encoding/LIEPacket . . . . . . . . . . . . . . . 102 8.2.15. Registry RIFT/encoding/LinkCapabilities . . . . . . . 123
9.2.14.1. Requested Entries . . . . . . . . . . . . . . . 102 8.2.15.1. Requested Entries . . . . . . . . . . . . . . . 123
9.2.15. RIFT/encoding/LinkCapabilities . . . . . . . . . . . 103 8.2.16. Registry RIFT/encoding/LinkIDPair . . . . . . . . . . 123
9.2.15.1. Requested Entries . . . . . . . . . . . . . . . 103 8.2.16.1. Requested Entries . . . . . . . . . . . . . . . 123
9.2.16. RIFT/encoding/LinkIDPair . . . . . . . . . . . . . . 103 8.2.17. Registry RIFT/encoding/Neighbor . . . . . . . . . . . 124
9.2.16.1. Requested Entries . . . . . . . . . . . . . . . 103 8.2.17.1. Requested Entries . . . . . . . . . . . . . . . 124
9.2.17. RIFT/encoding/Neighbor . . . . . . . . . . . . . . . 104 8.2.18. Registry RIFT/encoding/NodeCapabilities . . . . . . . 124
9.2.17.1. Requested Entries . . . . . . . . . . . . . . . 104 8.2.18.1. Requested Entries . . . . . . . . . . . . . . . 124
9.2.18. RIFT/encoding/NodeCapabilities . . . . . . . . . . . 104 8.2.19. Registry RIFT/encoding/NodeFlags . . . . . . . . . . 125
9.2.18.1. Requested Entries . . . . . . . . . . . . . . . 104 8.2.19.1. Requested Entries . . . . . . . . . . . . . . . 125
9.2.19. RIFT/encoding/NodeFlags . . . . . . . . . . . . . . . 105 8.2.20. Registry RIFT/encoding/NodeNeighborsTIEElement . . . 125
9.2.19.1. Requested Entries . . . . . . . . . . . . . . . 105 8.2.20.1. Requested Entries . . . . . . . . . . . . . . . 125
9.2.20. RIFT/encoding/NodeNeighborsTIEElement . . . . . . . . 105 8.2.21. Registry RIFT/encoding/NodeTIEElement . . . . . . . . 125
9.2.20.1. Requested Entries . . . . . . . . . . . . . . . 105 8.2.21.1. Requested Entries . . . . . . . . . . . . . . . 126
9.2.21. RIFT/encoding/NodeTIEElement . . . . . . . . . . . . 105 8.2.22. Registry RIFT/encoding/PacketContent . . . . . . . . 126
9.2.21.1. Requested Entries . . . . . . . . . . . . . . . 106 8.2.22.1. Requested Entries . . . . . . . . . . . . . . . 126
9.2.22. RIFT/encoding/PacketContent . . . . . . . . . . . . . 106 8.2.23. Registry RIFT/encoding/PacketHeader . . . . . . . . . 126
9.2.22.1. Requested Entries . . . . . . . . . . . . . . . 106 8.2.23.1. Requested Entries . . . . . . . . . . . . . . . 126
9.2.23. RIFT/encoding/PacketHeader . . . . . . . . . . . . . 106 8.2.24. Registry RIFT/encoding/PrefixAttributes . . . . . . . 127
9.2.23.1. Requested Entries . . . . . . . . . . . . . . . 106 8.2.24.1. Requested Entries . . . . . . . . . . . . . . . 127
9.2.24. RIFT/encoding/PrefixAttributes . . . . . . . . . . . 107 8.2.25. Registry RIFT/encoding/PrefixTIEElement . . . . . . . 127
9.2.24.1. Requested Entries . . . . . . . . . . . . . . . 107 8.2.25.1. Requested Entries . . . . . . . . . . . . . . . 127
9.2.25. RIFT/encoding/PrefixTIEElement . . . . . . . . . . . 107 8.2.26. Registry RIFT/encoding/ProtocolPacket . . . . . . . . 128
9.2.25.1. Requested Entries . . . . . . . . . . . . . . . 107 8.2.26.1. Requested Entries . . . . . . . . . . . . . . . 128
9.2.26. RIFT/encoding/ProtocolPacket . . . . . . . . . . . . 108 8.2.27. Registry RIFT/encoding/TIDEPacket . . . . . . . . . . 128
9.2.26.1. Requested Entries . . . . . . . . . . . . . . . 108 8.2.27.1. Requested Entries . . . . . . . . . . . . . . . 128
9.2.27. RIFT/encoding/TIDEPacket . . . . . . . . . . . . . . 108 8.2.28. Registry RIFT/encoding/TIEElement . . . . . . . . . . 128
9.2.27.1. Requested Entries . . . . . . . . . . . . . . . 108 8.2.28.1. Requested Entries . . . . . . . . . . . . . . . 128
9.2.28. RIFT/encoding/TIEElement . . . . . . . . . . . . . . 108 8.2.29. Registry RIFT/encoding/TIEHeader . . . . . . . . . . 129
9.2.28.1. Requested Entries . . . . . . . . . . . . . . . 108 8.2.29.1. Requested Entries . . . . . . . . . . . . . . . 130
9.2.29. RIFT/encoding/TIEHeader . . . . . . . . . . . . . . . 109 8.2.30. Registry RIFT/encoding/TIEHeaderWithLifeTime . . . . 130
9.2.29.1. Requested Entries . . . . . . . . . . . . . . . 110 8.2.30.1. Requested Entries . . . . . . . . . . . . . . . 130
9.2.30. RIFT/encoding/TIEHeaderWithLifeTime . . . . . . . . . 110 8.2.31. Registry RIFT/encoding/TIEID . . . . . . . . . . . . 130
9.2.30.1. Requested Entries . . . . . . . . . . . . . . . 110 8.2.31.1. Requested Entries . . . . . . . . . . . . . . . 131
9.2.31. RIFT/encoding/TIEID . . . . . . . . . . . . . . . . . 110 8.2.32. Registry RIFT/encoding/TIEPacket . . . . . . . . . . 131
9.2.31.1. Requested Entries . . . . . . . . . . . . . . . 111 8.2.32.1. Requested Entries . . . . . . . . . . . . . . . 131
9.2.32. RIFT/encoding/TIEPacket . . . . . . . . . . . . . . . 111 8.2.33. Registry RIFT/encoding/TIREPacket . . . . . . . . . . 131
9.2.32.1. Requested Entries . . . . . . . . . . . . . . . 111 8.2.33.1. Requested Entries . . . . . . . . . . . . . . . 131
9.2.33. RIFT/encoding/TIREPacket . . . . . . . . . . . . . . 111 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 131
9.2.33.1. Requested Entries . . . . . . . . . . . . . . . 111 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 132
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 111 10.1. Normative References . . . . . . . . . . . . . . . . . . 132
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 112 10.2. Informative References . . . . . . . . . . . . . . . . . 134
11.1. Normative References . . . . . . . . . . . . . . . . . . 112 Appendix A. Sequence Number Binary Arithmetic . . . . . . . . . 136
11.2. Informative References . . . . . . . . . . . . . . . . . 114 Appendix B. Information Elements Schema . . . . . . . . . . . . 137
Appendix A. Sequence Number Binary Arithmetic . . . . . . . . . 116 B.1. common.thrift . . . . . . . . . . . . . . . . . . . . . . 138
Appendix B. Information Elements Schema . . . . . . . . . . . . 117 B.2. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 144
B.1. common.thrift . . . . . . . . . . . . . . . . . . . . . . 118 Appendix C. Constants . . . . . . . . . . . . . . . . . . . . . 152
B.2. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 124 C.1. Configurable Protocol Constants . . . . . . . . . . . . . 152
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 154
Appendix C. Finite State Machines and Precise Operational
Specifications . . . . . . . . . . . . . . . . . . . 132
C.1. LIE FSM . . . . . . . . . . . . . . . . . . . . . . . . . 133
C.2. ZTP FSM . . . . . . . . . . . . . . . . . . . . . . . . . 139
C.3. Flooding Procedures . . . . . . . . . . . . . . . . . . . 147
C.3.1. FloodState Structure per Adjacency . . . . . . . . . 147
C.3.2. TIDEs . . . . . . . . . . . . . . . . . . . . . . . . 149
C.3.2.1. TIDE Generation . . . . . . . . . . . . . . . . . 149
C.3.2.2. TIDE Processing . . . . . . . . . . . . . . . . . 150
C.3.3. TIREs . . . . . . . . . . . . . . . . . . . . . . . . 151
C.3.3.1. TIRE Generation . . . . . . . . . . . . . . . . . 151
C.3.3.2. TIRE Processing . . . . . . . . . . . . . . . . . 151
C.3.4. TIEs Processing on Flood State Adjacency . . . . . . 152
C.3.5. TIEs Processing When LSDB Received Newer Version on
Other Adjacencies . . . . . . . . . . . . . . . . . . 153
C.3.6. Sending TIEs . . . . . . . . . . . . . . . . . . . . 153
Appendix D. Constants . . . . . . . . . . . . . . . . . . . . . 153
D.1. Configurable Protocol Constants . . . . . . . . . . . . . 153
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 155
1. Authors 1. Authors
This work is a product of a list of individuals which are all to be This work is a product of a list of individuals which are all to be
considered major contributors independent of the fact whether their considered major contributors independent of the fact whether their
name made it to the limited boilerplate author's list or not. name made it to the limited boilerplate author's list or not.
Tony Przygienda, Ed. | Alankar Sharma | Pascal Thubert Tony Przygienda, Ed. | Alankar Sharma | Pascal Thubert
Juniper Networks | Comcast | Cisco Juniper Networks | Comcast | Cisco
skipping to change at page 7, line 10 skipping to change at page 7, line 9
network with an irregular topology and low degree of connectivity network with an irregular topology and low degree of connectivity
originally but given they were the only available options, originally but given they were the only available options,
consequently several attempts to apply those protocols to Clos have consequently several attempts to apply those protocols to Clos have
been made. Most successfully BGP [RFC4271] [RFC7938] has been been made. Most successfully BGP [RFC4271] [RFC7938] has been
extended to this purpose, not as much due to its inherent suitability extended to this purpose, not as much due to its inherent suitability
but rather because the perceived capability to easily modify BGP and but rather because the perceived capability to easily modify BGP and
the immanent difficulties with link-state [DIJKSTRA] based protocols the immanent difficulties with link-state [DIJKSTRA] based protocols
to optimize topology exchange and converge quickly in large scale to optimize topology exchange and converge quickly in large scale
densely meshed topologies. The incumbent protocols precondition densely meshed topologies. The incumbent protocols precondition
normally extensive configuration or provisioning during bring up and normally extensive configuration or provisioning during bring up and
re-dimensioning which is only viable for a set of organizations with re-dimensioning. This tends to be viable only for a set of
according networking operation skills and budgets. For the majority organizations with according networking operation skills and budgets.
of data center consumers a preferable protocol would be one that For many IP fabric builders a desirable protocol would be one that
auto-configures itself and deals with failures and misconfigurations auto-configures itself and deals with failures and mis-configurations
with a minimum of human intervention only. Such a solution would with a minimum of human intervention only. Such a solution would
allow local IP fabric bandwidth to be consumed in a 'standard allow local IP fabric bandwidth to be consumed in a 'standard
component' fashion, i.e. provision it much faster and operate it at component' fashion, i.e. provision it much faster and operate it at
much lower costs, much like compute or storage is consumed today. much lower costs than today, much like compute or storage is consumed
already.
In looking at the problem through the lens of data center In looking at the problem through the lens of data center
requirements, an optimal approach does not seem however to be a requirements, RIFT addresses challenges in IP fabric routing not
simple modification of either a link-state (distributed computation) through an incremental modification of either a link-state
or distance-vector (diffused computation) approach but rather a (distributed computation) or distance-vector (diffused computation)
mixture of both, colloquially best described as "link-state towards but rather a mixture of both, colloquially best described as "link-
the spine" and "distance vector towards the leafs". In other words, state towards the spine" and "distance vector towards the leafs". In
"bottom" levels are flooding their link-state information in the other words, "bottom" levels are flooding their link-state
"northern" direction while each node generates under normal information in the "northern" direction while each node generates
conditions a default route and floods it in the "southern" direction. under normal conditions a "default route" and floods it in the
This type of protocol allows naturally for highly desirable "southern" direction. This type of protocol allows naturally for
aggregation. Alas, such aggregation could blackhole traffic in cases highly desirable aggregation. Alas, such aggregation could blackhole
of misconfiguration or while failures are being resolved or even traffic in cases of misconfiguration or while failures are being
cause partial network partitioning and this has to be addressed. The resolved or even cause partial network partitioning and this has to
approach RIFT takes is described in Section 5.2.5 and is basically be addressed by some adequate mechanism. The approach RIFT takes is
based on automatic, sufficient disaggregation of prefixes. described in Section 4.2.5 and is basically based on automatic,
sufficient disaggregation of prefixes in case of link and node
failures.
For the visually oriented reader, Figure 1 presents a first level For the visually oriented reader, Figure 1 presents a first level
simplified view of the resulting information and routes on a RIFT simplified view of the resulting information and routes on a RIFT
fabric. The top of the fabric is holding in its link-state database fabric. The top of the fabric is holding in its link-state database
the nodes below it and the routes to them. In the second row of the the nodes below it and the routes to them. In the second row of the
database table we indicate that partial information of other nodes in database table we indicate that partial information of other nodes in
the same level is available as well. The details of how this is the same level is available as well. The details of how this is
achieved will be postponed for the moment. When we look at the achieved will be postponed for the moment. When we look at the
"bottom" of the fabric, the leafs, we see that the topology is "bottom" of the fabric, the leafs, we see that the topology is
basically empty and they only hold a load balanced default route to basically empty and they only hold a load balanced default route to
the next level. the next level under normal conditions.
The balance of this document details the requirements of a dedicated The balance of this document details a dedicated IP fabric routing
fabric routing protocol, fills in the specification details and protocol, fills in the specification details and ultimately includes
ultimately includes resulting security considerations. resulting security considerations.
. [A,B,C,D] . [A,B,C,D]
. [E] . [E]
. +-----+ +-----+ . +-----+ +-----+
. | E | | F | A/32 @ [C,D] . | E | | F | A/32 @ [C,D]
. +-+-+-+ +-+-+-+ B/32 @ [C,D] . +-+-+-+ +-+-+-+ B/32 @ [C,D]
. | | | | C/32 @ C . | | | | C/32 @ C
. | | +-----+ | D/32 @ D . | | +-----+ | D/32 @ D
. | | | | . | | | |
. | +------+ | . | +------+ |
skipping to change at page 8, line 33 skipping to change at page 8, line 33
. +-+---+ | | +---+-+ . +-+---+ | | +---+-+
. | A +--+ +-+ B | . | A +--+ +-+ B |
. 0/0 @ [C,D] +-----+ +-----+ 0/0 @ [C,D] . 0/0 @ [C,D] +-----+ +-----+ 0/0 @ [C,D]
Figure 1: RIFT information distribution Figure 1: RIFT information distribution
2.1. Requirements Language 2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 8174 [RFC8174].
3. Reference Frame 3. Reference Frame
3.1. Terminology 3.1. Terminology
This section presents the terminology used in this document. It is This section presents the terminology used in this document. It is
assumed that the reader is thoroughly familiar with the terms and assumed that the reader is thoroughly familiar with the terms and
concepts used in OSPF [RFC2328] and IS-IS [ISO10589-Second-Edition], concepts used in OSPF [RFC2328] and IS-IS [ISO10589-Second-Edition],
[ISO10589] as well as the according graph theoretical concepts of [ISO10589] as well as the according graph theoretical concepts of
shortest path first (SPF) [DIJKSTRA] computation and directed acyclic shortest path first (SPF) [DIJKSTRA] computation and DAGs.
graphs (DAG).
Crossbar: Physical arrangement of ports in a switching matrix Crossbar: Physical arrangement of ports in a switching matrix
without implying any further scheduling or buffering disciplines. without implying any further scheduling or buffering disciplines.
Clos/Fat Tree: This document uses the terms Clos and Fat Tree Clos/Fat Tree: This document uses the terms Clos and Fat Tree
interchangeably whereas it always refers to a folded spine-and- interchangeably whereas it always refers to a folded spine-and-
leaf topology with possibly multiple PoDs and one or multiple ToF leaf topology with possibly multiple Points of Delivery (PoDs) and
planes. Several modifications such as leaf-2-leaf shortcuts and one or multiple Top of Fabric (ToF) planes. Several modifications
multiple level shortcuts are possible and described further in the such as leaf-2-leaf shortcuts and multiple level shortcuts are
document. possible and described further in the document.
Directed Acyclic Graph (DAG): A finite directed graph with no
directed cycles (loops). If links in Clos are considered as
either being all directed towards the top or vice versa, each of
such two graphs is a DAG.
Folded Spine-and-Leaf: In case Clos fabric input and output stages Folded Spine-and-Leaf: In case Clos fabric input and output stages
are analogous, the fabric can be "folded" to build a "superspine" are analogous, the fabric can be "folded" to build a "superspine"
or top which we will call Top of Fabric (ToF) in this document. or top which we will call Top of Fabric (ToF) in this document.
Level: Clos and Fat Tree networks are topologically partially Level: Clos and Fat Tree networks are topologically partially
ordered graphs and 'level' denotes the set of nodes at the same ordered graphs and 'level' denotes the set of nodes at the same
height in such a network, where the bottom level (leaf) is the height in such a network, where the bottom level (leaf) is the
level with lowest value. A node has links to nodes one level down level with lowest value. A node has links to nodes one level down
and/or one level up. Under some circumstances, a node may have and/or one level up. Under some circumstances, a node may have
links to nodes at the same level. As footnote: Clos terminology links to nodes at the same level. As footnote: Clos terminology
uses often the concept of "stage" but due to the folded nature of uses often the concept of "stage" but due to the folded nature of
the Fat Tree we do not use it to prevent misunderstandings. the Fat Tree we do not use it to prevent misunderstandings.
Superspine/Aggregation or Spine/Edge Levels: Traditional names in Superspine/Aggregation or Spine/Edge Levels: Traditional names in
5-stages folded Clos for Level 2, 1 and 0 respectively. Level 0 5-stages folded Clos for Level 2, 1 and 0 respectively. Level 0
is often called leaf as well. We normalize this language to talk is often called leaf as well. We normalize this language to talk
about leafs, spines and top-of-fabric (ToF). about leafs, spines and top-of-fabric (ToF).
Zero Touch Provisioning (ZTP): Optional RIFT mechanism which allows
to derive node levels automatically based on minimum configuration
(only ToF property has to be provisioned on according nodes).
Point of Delivery (PoD): A self-contained vertical slice or subset Point of Delivery (PoD): A self-contained vertical slice or subset
of a Clos or Fat Tree network containing normally only level 0 and of a Clos or Fat Tree network containing normally only level 0 and
level 1 nodes. A node in a PoD communicates with nodes in other level 1 nodes. A node in a PoD communicates with nodes in other
PoDs via the Top-of-Fabric. We number PoDs to distinguish them PoDs via the Top-of-Fabric. We number PoDs to distinguish them
and use PoD #0 to denote "undefined" PoD. and use PoD #0 to denote "undefined" PoD.
Top of PoD (ToP): The set of nodes that provide intra-PoD Top of PoD (ToP): The set of nodes that provide intra-PoD
communication and have northbound adjacencies outside of the PoD, communication and have northbound adjacencies outside of the PoD,
i.e. are at the "top" of the PoD. i.e. are at the "top" of the PoD.
skipping to change at page 9, line 47 skipping to change at page 10, line 7
communication and have no northbound adjacencies, i.e. are at the communication and have no northbound adjacencies, i.e. are at the
"very top" of the fabric. ToF nodes do not belong to any PoD and "very top" of the fabric. ToF nodes do not belong to any PoD and
are assigned "undefined" PoD value to indicate the equivalent of are assigned "undefined" PoD value to indicate the equivalent of
"any" PoD. "any" PoD.
Spine: Any nodes north of leafs and south of top-of-fabric nodes. Spine: Any nodes north of leafs and south of top-of-fabric nodes.
Multiple layers of spines in a PoD are possible. Multiple layers of spines in a PoD are possible.
Leaf: A node without southbound adjacencies. Its level is 0 (except Leaf: A node without southbound adjacencies. Its level is 0 (except
cases where it is deriving its level via ZTP and is running cases where it is deriving its level via ZTP and is running
without LEAF_ONLY which will be explained in Section 5.2.7). without LEAF_ONLY which will be explained in Section 4.2.7).
Top-of-fabric Plane or Partition: In large fabrics top-of-fabric Top-of-fabric Plane or Partition: In large fabrics top-of-fabric
switches may not have enough ports to aggregate all switches south switches may not have enough ports to aggregate all switches south
of them and with that, the ToF is 'split' into multiple of them and with that, the ToF is 'split' into multiple
independent planes. Introduction and Section 5.1.2 explains the independent planes. Introduction and Section 4.1.2 explains the
concept in more detail. A plane is subset of ToF nodes that see concept in more detail. A plane is subset of ToF nodes that see
each other through south reflection or E-W links. each other through south reflection or E-W links.
Radix: A radix of a switch is basically number of switching ports it Radix: A radix of a switch is basically number of switching ports it
provides. It's sometimes called fanout as well. provides. It's sometimes called fanout as well.
North Radix: Ports cabled northbound to higher level nodes. North Radix: Ports cabled northbound to higher level nodes.
South Radix: Ports cabled southbound to lower level nodes. South Radix: Ports cabled southbound to lower level nodes.
skipping to change at page 10, line 38 skipping to change at page 10, line 46
East-West Link: A link between two nodes at the same level. East- East-West Link: A link between two nodes at the same level. East-
West links are normally not part of Clos or "fat-tree" topologies. West links are normally not part of Clos or "fat-tree" topologies.
Leaf shortcuts (L2L): East-West links at leaf level will need to be Leaf shortcuts (L2L): East-West links at leaf level will need to be
differentiated from East-West links at other levels. differentiated from East-West links at other levels.
Routing on the host (RotH): Modern data center architecture variant Routing on the host (RotH): Modern data center architecture variant
where servers/leafs are multi-homed and consecutively participate where servers/leafs are multi-homed and consecutively participate
in routing. in routing.
Northbound representation: Subset of topology information flooded
towards higher levels of the fabric.
Southbound representation: Subset of topology information sent Southbound representation: Subset of topology information sent
towards a lower level. towards a lower level.
South Reflection: Often abbreviated just as "reflection" it defines South Reflection: Often abbreviated just as "reflection" it defines
a mechanism where South Node TIEs are "reflected" back up north to a mechanism where South Node TIEs are "reflected" from the level
allow nodes in same level without E-W links to "see" each other. south back up north to allow nodes in the same level without E-W
links to "see" each other's node TIEs.
TIE: This is an acronym for a "Topology Information Element". TIEs TIE: This is an acronym for a "Topology Information Element". TIEs
are exchanged between RIFT nodes to describe parts of a network are exchanged between RIFT nodes to describe parts of a network
such as links and address prefixes, in a fashion similar to ISIS such as links and address prefixes, in a fashion similar to ISIS
LSPs or OSPF LSAs. We will talk about N-TIEs when talking about LSPs or OSPF LSAs. A TIE has always a direction and a type. We
TIEs in the northbound representation and S-TIEs for the will talk about North TIEs (sometimes abbreviated as N-TIEs) when
southbound equivalent. talking about TIEs in the northbound representation and South-TIEs
(sometimes abbreviated as S-TIEs) for the southbound equivalent.
TIEs have different types such as node and prefix TIEs.
Node TIE: This stands as acronym for a "Node Topology Information Node TIE: This stands as acronym for a "Node Topology Information
Element" that contains all adjacencies the node discovered and Element" that contains all adjacencies the node discovered and
information about node itself. information about node itself. Node TIE should NOT be confused
with a N-TIE since "node" defines the type of TIE rather than its
direction.
Prefix TIE: This is an acronym for a "Prefix Topology Information Prefix TIE: This is an acronym for a "Prefix Topology Information
Element" and it contains all prefixes directly attached to this Element" and it contains all prefixes directly attached to this
node in case of a N-TIE and in case of S-TIE the necessary default node in case of a North TIE and in case of South TIE the necessary
the node passes southbound. default routes the node advertises southbound.
Key Value TIE: A S-TIE that is carrying a set of key value pairs Key Value TIE: A South TIE that is carrying a set of key value pairs
[DYNAMO]. It can be used to distribute information in the [DYNAMO]. It can be used to distribute information in the
southbound direction within the protocol. southbound direction within the protocol.
TIDE: Topology Information Description Element, equivalent to CSNP TIDE: Topology Information Description Element, equivalent to CSNP
in ISIS. in ISIS.
TIRE: Topology Information Request Element, equivalent to PSNP in TIRE: Topology Information Request Element, equivalent to PSNP in
ISIS. It can both confirm received and request missing TIEs. ISIS. It can both confirm received and request missing TIEs.
De-aggregation/Disaggregation: Process in which a node decides to De-aggregation/Disaggregation: Process in which a node decides to
advertise certain prefixes it received in N-TIEs to prevent black- advertise certain prefixes it received in North TIEs to prevent
holing and suboptimal routing upon link failures. black-holing and suboptimal routing upon link failures.
LIE: This is an acronym for a "Link Information Element", largely LIE: This is an acronym for a "Link Information Element", largely
equivalent to HELLOs in IGPs and exchanged over all the links equivalent to HELLOs in IGPs and exchanged over all the links
between systems running RIFT to form adjacencies. between systems running RIFT to form 3-way adjacencies.
Flood Repeater (FR): A node can designate one or more northbound Flood Repeater (FR): A node can designate one or more northbound
neighbor nodes to be flood repeaters. The flood repeaters are neighbor nodes to be flood repeaters. The flood repeaters are
responsible for flooding northbound TIEs further north. They are responsible for flooding northbound TIEs further north. They are
similar to MPR in OSLR. The document sometimes calls them flood similar to MPR in OSLR. The document sometimes calls them flood
leaders as well. leaders as well.
Bandwidth Adjusted Distance (BAD): This is an acronym for Bandwidth Bandwidth Adjusted Distance (BAD): This is an acronym for Bandwidth
Adjusted Distance. Each RIFT node calculates the amount of Adjusted Distance. Each RIFT node calculates the amount of
northbound bandwidth available towards a node compared to other northbound bandwidth available towards a node compared to other
skipping to change at page 12, line 5 skipping to change at page 12, line 19
accordingly to allow for the lower level to adjust their load accordingly to allow for the lower level to adjust their load
balancing towards spines. balancing towards spines.
Overloaded: Applies to a node advertising `overload` attribute as Overloaded: Applies to a node advertising `overload` attribute as
set. The semantics closely follow the meaning of the same set. The semantics closely follow the meaning of the same
attribute in [ISO10589-Second-Edition]. attribute in [ISO10589-Second-Edition].
Interface: A layer 3 entity over which RIFT control packets are Interface: A layer 3 entity over which RIFT control packets are
exchanged. exchanged.
Adjacency: RIFT tries to form a unique adjacency over an interface 3-Way Adjacency: RIFT tries to form a unique adjacency over an
and exchange local configuration and necessary ZTP information. interface and exchange local configuration and necessary ZTP
information. An adjacency is only advertised in node TIEs and
used for computations after it achieved 3-way state, i.e. both
routers reflected each other in LIEs including relevant security
information. LIEs before 3-way state is reached may carry ZTP
related information already.
Neighbor: Once a three way adjacency has been formed a neighborship Bi-directional Adjacency: Bidirectional adjacency is an adjacency
where nodes of both sides of the adjacency advertised it in the
node TIEs with the correct levels and system IDs. Bi-
directionality is used to check in different algorithms whether
the link should be included.
Neighbor: Once a 3-way adjacency has been formed a neighborship
relationship contains the neighbor's properties. Multiple relationship contains the neighbor's properties. Multiple
adjacencies can be formed to a neighbor via parallel interfaces adjacencies can be formed to a remote node via parallel interfaces
but such adjacencies are NOT sharing a neighbor structure. Saying but such adjacencies are NOT sharing a neighbor structure. Saying
"neighbor" is thus equivalent to saying "a three way adjacency". "neighbor" is thus equivalent to saying "a 3-way adjacency".
Cost: The term signifies the weighted distance between two Cost: The term signifies the weighted distance between two
neighbors. neighbors.
Distance: Sum of costs (bound by infinite distance) between two Distance: Sum of costs (bound by infinite distance) between two
nodes. nodes.
Metric: Without going deeper into the proper differentiation, a Shortest-Path First (SPF): A well-known graph algorithm attributed
metric is equivalent to distance. to Dijkstra that establishes a tree of shortest paths from a
source to destinations on the graph. We use SPF acronym due to
its familiarity as general term for the node reachability
calculations RIFT can employ to ultimately calculate routes of
which Dijkstra algorithm is one.
North SPF (N-SPF): A reachability calculation that is progressing
northbound, as example SPF that is using South Node TIEs only.
South SPF (S-SPF): A reachability calculation that is progressing
southbound, as example SPF that is using North Node TIEs only.
Security Envelope RIFT packets are flooded within an authenticated
security envelope that allows to protect the integrity of
information a node accepts.
3.2. Topology 3.2. Topology
. +--------+ +--------+ ^ N . +--------+ +--------+ ^ N
. |ToF 21| |ToF 22| | . |ToF 21| |ToF 22| |
.Level 2 ++-+--+-++ ++-+--+-++ <-*-> E/W .Level 2 ++-+--+-++ ++-+--+-++ <-*-> E/W
. | | | | | | | | | . | | | | | | | | |
. P111/2| |P121 | | | | S v . P111/2| |P121 | | | | S v
. ^ ^ ^ ^ | | | | . ^ ^ ^ ^ | | | |
. | | | | | | | | . | | | | | | | |
. +--------------+ | +-----------+ | | | +---------------+ . +--------------+ | +-----------+ | | | +---------------+
. | | | | | | | | . | | | | | | | |
. South +-----------------------------+ | | ^ . South +-----------------------------+ | | ^
skipping to change at page 14, line 40 skipping to change at page 14, line 40
Figure 3: Topology with multiple planes Figure 3: Topology with multiple planes
We will use topology in Figure 2 (called commonly a fat tree/network We will use topology in Figure 2 (called commonly a fat tree/network
in modern IP fabric considerations [VAHDAT08] as homonym to the in modern IP fabric considerations [VAHDAT08] as homonym to the
original definition of the term [FATTREE]) in all further original definition of the term [FATTREE]) in all further
considerations. This figure depicts a generic "single plane fat- considerations. This figure depicts a generic "single plane fat-
tree" and the concepts explained using three levels apply by tree" and the concepts explained using three levels apply by
induction to further levels and higher degrees of connectivity. induction to further levels and higher degrees of connectivity.
Further, this document will deal also with designs that provide only Further, this document will deal also with designs that provide only
sparser connectivity and "partitioned spines" as shown in Figure 3 sparser connectivity and "partitioned spines" as shown in Figure 3
and explained further in Section 5.1.2. and explained further in Section 4.1.2.
4. Requirement Considerations
[RFC7938] gives the original set of requirements augmented here based
upon recent experience in the operation of fat-tree networks.
REQ1: The control protocol should discover the physical links
automatically and be able to detect cabling that violates
fat-tree topology constraints. It must react accordingly to
such mis-cabling attempts, at a minimum preventing
adjacencies between nodes from being formed and traffic from
being forwarded on those mis-cabled links. E.g. connecting
a leaf to a spine at level 2 should be detected and ideally
prevented.
REQ2: A node without any configuration beside default values
should come up at the correct level in any PoD it is
introduced into. Optionally, it must be possible to
configure nodes to restrict their participation to the
PoD(s) targeted at any level.
REQ3: Optionally, the protocol should allow to provision IP
fabrics where the individual switches carry no configuration
information and are all deriving their level from a "seed".
Observe that this requirement may collide with the desire to
detect cabling misconfiguration and with that only one of
the requirements can be fully met in a chosen configuration
mode.
REQ4: The solution should allow for minimum size routing
information base and forwarding tables at leaf level for
speed, cost and simplicity reasons. Holding excessive
amount of information away from leaf nodes simplifies
operation and lowers cost of the underlay and allows to
scale and introduce proper multi-homing down to the server
level. The routing solution should allow for easy
instantiation of multiple routing planes. Coupled with
mobility defined in Paragraph 17 this should allow for
"light-weight" overlays on an IP fabric with e.g. native
IPv6 mobility support.
REQ5: Very high degree of ECMP must be supported. Maximum ECMP is
currently understood as the most efficient routing approach
to maximize the throughput of switching fabrics
[MAKSIC2013].
REQ6: Non equal cost anycast must be supported to allow for easy
and robust multi-homing of services without regressing to
careful balancing of link costs.
REQ7: Traffic engineering should be allowed by modification of
prefixes and/or their next-hops.
REQ8: The solution should allow for access to link states of the
whole topology to enable efficient support for modern
control architectures like SPRING [RFC7855] or PCE
[RFC4655].
REQ9: The solution should easily accommodate opaque data to be
carried throughout the topology to subsets of nodes. This
can be used for many purposes, one of them being a key-value
store that allows bootstrapping of nodes based right at the
time of topology discovery. Another use is distributing MAC
to L3 address binding from the leafs up north in case of
e.g. DHCP.
REQ10: Nodes should be taken out and introduced into production
with minimum wait-times and minimum of "shaking" of the
network, i.e. radius of propagation (often called "blast
radius") of changed information should be as small as
feasible.
REQ11: The protocol should allow for maximum aggregation of carried
routing information while at the same time automatically de-
aggregating the prefixes to prevent black-holing in case of
failures. The de-aggregation should support maximum
possible ECMP/N-ECMP remaining after failure.
REQ12: Reducing the scope of communication needed throughout the
network on link and state failure, as well as reducing
advertisements of repeating or idiomatic information in
stable state is highly desirable since it leads to better
stability and faster convergence behavior.
REQ13: Under normal, fully converged condition, once a packet is
forwarded along a link in a "southbound" direction, it must
not take any further "northbound" links (Valley Free
Routing). Taking a path through the spine in cases where a
shorter path is available is highly undesirable (Bow Tying).
REQ14: Parallel links between same set of nodes must be
distinguishable for SPF, failure and traffic engineering
purposes.
REQ15: The protocol must support interfaces sharing the same
address. Specifically, it must operate in presence of
unnumbered links (even parallel ones) and/or links of a
single node being configured with same addresses.
REQ16: It would be desirable to achieve fast re-balancing of flows
when links, especially towards the spines are lost or
provisioned without regressing to per flow traffic
engineering which introduces significant amount of
complexity while possibly not being reactive enough to
account for short-lived flows.
REQ17: The control plane should be able to unambiguously determine
the current point of attachment (which port on which leaf
node) of a prefix, even in a context of fast mobility, e.g.,
when the prefix is a host address on a wireless node that 1)
may associate to any of multiple access points (APs) that
are attached to different ports on a same leaf node or to
different leaf nodes, and 2) may move and reassociate
several times to a different access point within a sub-
second period.
REQ18: The protocol must provide security mechanisms that allow the
operator to restrict nodes, especially leaf nodes without
proper credentials, from forming a three-way adjacency and
participating in routing.
Following list represents non-requirements:
PEND1: Supporting anything but point-to-point links is not
necessary.
Finally, following are the non-requirements:
NONREQ1: Broadcast media support is unnecessary. However,
miscabling leading to multiple nodes on a broadcast
segment must be operationally easily recognizable and
detectable while not taxing the protocol excessively.
NONREQ2: Purging link state elements is unnecessary given its
fragility and complexity and today's large memory size on
even modest switches and routers.
NONREQ3: Special support for layer 3 multi-hop adjacencies is not
part of the protocol specification. Such support can be
easily provided by using tunneling technologies the same
way IGPs today are solving the problem.
5. RIFT: Routing in Fat Trees 4. RIFT: Routing in Fat Trees
Derived from the above requirements we present a detailed outline of We present here a detailed outline of a protocol optimized for
a protocol optimized for Routing in Fat Trees (RIFT) that in most Routing in Fat Trees (RIFT) that in most abstract terms has many
abstract terms has many properties of a modified link-state protocol properties of a modified link-state protocol
[RFC2328][ISO10589-Second-Edition] when "pointing north" and distance [RFC2328][ISO10589-Second-Edition] when "pointing north" and distance
vector [RFC4271] protocol when "pointing south". While this is an vector [RFC4271] protocol when "pointing south". While this is an
unusual combination, it does quite naturally exhibit the desirable unusual combination, it does quite naturally exhibit the desirable
properties we seek. properties we seek.
5.1. Overview 4.1. Overview
5.1.1. Properties 4.1.1. Properties
The most singular property of RIFT is that it floods flat link-state The most singular property of RIFT is that it floods flat link-state
information northbound only so that each level obtains the full information northbound only so that each level obtains the full
topology of levels south of it. That information is never flooded topology of levels south of it. That information is never flooded
East-West (we'll talk about exceptions later) or back South again. East-West or back South again with some exceptions like south
In the southbound direction the protocol operates like a "fully reflection which will be explained in detail in Section 4.2.5.1 and
summarizing, unidirectional" path vector protocol or rather a east-west flooding at ToF level in multi-plane fabrics outlined in
distance vector with implicit split horizon whereas the information Section 4.1.2. In the southbound direction the protocol operates
propagates one hop south and is 're-advertised' by nodes at next like a "fully summarizing, unidirectional" path vector protocol or
lower level, normally just the default route. However, RIFT uses rather a distance vector with implicit split horizon whereas the
flooding in the southern direction as well to avoid the necessity to information propagates one hop south and is 're-advertised' by nodes
build an update per adjacency. We omit describing the East-West at next lower level, normally just the default route. However, RIFT
direction out for the moment. uses flooding in the southern direction as well to avoid the
necessity to build an update per adjacency. We omit describing the
East-West direction out for the moment.
Those information flow constraints create not only an anisotropic Those information flow constraints create not only an anisotropic
protocol (i.e. the information is not distributed "evenly" or protocol (i.e. the information is not distributed "evenly" or
"clumped" but summarized along the N-S gradient) but also a "smooth" "clumped" but summarized along the N-S gradient) but also a "smooth"
information propagation where nodes do not receive the same information propagation where nodes do not receive the same
information from multiple directions at the same time. Normally, information from multiple directions at the same time. Normally,
accepting the same reachability on any link without understanding its accepting the same reachability on any link without understanding its
topological significance forces tie-breaking on some kind of distance topological significance forces tie-breaking on some kind of distance
metric and ultimately leads in hop-by-hop forwarding substrates to metric and ultimately leads in hop-by-hop forwarding substrates to
utilization of variants of shortest paths only. RIFT under normal utilization of variants of shortest paths only. RIFT under normal
skipping to change at page 18, line 42 skipping to change at page 15, line 44
from multiple directions and its computation principles (south from multiple directions and its computation principles (south
forwarding direction is always prefered) leads to valley-free forwarding direction is always prefered) leads to valley-free
forwarding behavior. And since valley free routing is loop-free it forwarding behavior. And since valley free routing is loop-free it
can use all feasible paths, another highly desirable property if can use all feasible paths, another highly desirable property if
available bandwidth should be utilized to the maximum extent available bandwidth should be utilized to the maximum extent
possible. possible.
To account for the "northern" and the "southern" information split To account for the "northern" and the "southern" information split
the link state database is accordingly partitioned into "north the link state database is accordingly partitioned into "north
representation" and "south representation" TIEs. In simplest terms representation" and "south representation" TIEs. In simplest terms
the N-TIEs contain a link state topology description of lower levels the North TIEs contain a link state topology description of lower
and and S-TIEs carry simply default routes of the level above. This levels and and South TIEs carry simply default routes of the level
oversimplified view will be refined gradually in following sections above. This oversimplified view will be refined gradually in
while introducing protocol procedures aimed to fulfill the described following sections while introducing protocol procedures and state
requirements. machines at the same time.
5.1.2. Generalized Topology View 4.1.2. Generalized Topology View
This section will shed some light on the topologies addresses by RIFT This section will shed some light on the topologies addresses by RIFT
including multi plane fabrics and their related implications. including multi plane fabrics and their related implications.
Readers that are only interested in single plane designs, i.e. all Readers that are only interested in single plane designs, i.e. all
top-of-fabric nodes being topologically equal and initially connected top-of-fabric nodes being topologically equal and initially connected
to all the switches at the level below them can skip this section and to all the switches at the level below them can skip the rest of
resulting Section 5.2.5.2 as well. Section 4.1.2 and resulting Section 4.2.5.2 as well.
It is quite difficult to visualize multi plane design which are It is quite difficult to visualize multi plane design which are
effectively multi-dimensional switching matrices. To cope with that, effectively multi-dimensional switching matrices. To cope with that,
we will introduce a methodology allowing us to depict the we will introduce a methodology allowing us to depict the
connectivity in a two-dimensional plane. Further, we will leverage connectivity in a two-dimensional plane. Further, we will leverage
the fact that we are dealing basically with crossbar fabrics stacked the fact that we are dealing basically with stacked crossbar fabrics
on top of each other where ports align "on top of each other" in a where ports align "on top of each other" in a regular fashion.
regular fashion.
As a word of caution to the reader at this point it should be As a word of caution to the reader at this point it should be
observed that the language used to describe Clos variations, observed that the language used to describe Clos variations,
especially in multi-plane designs varies widely between sources. especially in multi-plane designs varies widely between sources.
This description follows the introduced Section 3.1 and it is This description follows the terminology introduced in Section 3.1
paramount to have it present to follow the rest of this section and it is paramount to have it present to follow the rest of this
correctly. section correctly.
4.1.2.1. Terminology
P: We use P to denote the number of PoDs in a topology.
S: We use S to denote number of ToF nodes in a topology.
K: We use K to denote number of ports in radix of a switch pointing
north or south. We further use K_LEAF to denote number of ports
pointing south, i.e. towards leafs and K_TOP for number of ports
pointing north towards a higher spine level. To simplify the
visual aids, notation and further considerations, we mostly use K
as Radix/2.
ToF Plane: set of ToFs that are aware of each other by means of
south reflection.
N: We use N to denote the number of independent ToF planes in a
topology.
R: We use R to denote a redundancy factor, i.e. number of connections
a spine has towards a ToF plane. In single plane design K_TOP is
equal to R.
Fallen Leaf: A fallen leaf in a plane Z is a switch that lost all
connectivity northbound to Z.
4.1.2.2. Clos as Crossed Crossbars
The typical topology for which RIFT is defined is built of a number P The typical topology for which RIFT is defined is built of a number P
of PoDs, connected together by a number S of ToF nodes. A PoD node of PoDs, connected together by a number S of ToF nodes. A PoD node
has a number of ports called Radix, with half of them (K=Radix/2) has a number of ports called Radix, with half of them (K=Radix/2)
used to connect host devices from the south, and half to connect to used to connect host devices from the south, and half to connect to
interleaved PoD Top-Level switches to the north. Ratio K can be interleaved PoD Top-Level switches to the north. Ratio K can be
chosen differently without loss of generality when port speeds differ chosen differently without loss of generality when port speeds differ
or fabric is oversubscribed but K=R/2 allows for more readable or fabric is oversubscribed but K=R/2 allows for more readable
representation whereby there are as many ports facing north as south representation whereby there are as many ports facing north as south
on any intermediate node. We represent a node hence in a schematic on any intermediate node. We represent a node hence in a schematic
fashion with ports "sticking out" to its north and south rather than fashion with ports "sticking out" to its north and south rather than
by the usual real-world front faceplate designs of the day. by the usual real-world front faceplate designs of the day.
Figure 4 provides a view of a leaf node as seen from the north, i.e. Figure 4 provides a view of a leaf node as seen from the north, i.e.
showing ports that connect northbound and for lack of a better showing ports that connect northbound and for lack of a better
symbol, we have chosen to use the "HH" symbol as ASCII visualisation symbol, we have chosen to use the "oo" or a single "o" symbol as
of a RJ45 jack. In that example, K_LEAF is chosen to be 6 ports. ASCII visualisation of a single RJ45 jack. In that example, K_LEAF
Observe that the number of PoDs is not related to Radix unless the is chosen to be 6 ports. Observe that the number of PoDs is not
ToF Nodes are constrained to be the same as the PoD nodes in a related to Radix unless the ToF Nodes are constrained to be the same
particular deployment. as the PoD nodes in a particular deployment.
Top view Top view
+----+ +----+
| | | |
| HH | e.g., Radix = 12, K_LEAF = 6 | oo | e.g., Radix = 12, K_LEAF = 6
| | | |
| HH | | oo |
| | ------------------------- | | -------------------------
| HH ------- Physical Port (Ethernet) ----+ | oo ------- Physical Port (Ethernet) ----+
| | ------------------------- | | | ------------------------- |
| HH | | | oo | |
| | | | | |
| HH | | | oo | |
| | | | | |
| HH | | | oo | |
| | | | | |
+----+ | +----+ |
|| || || || || || || || || || || || || ||
+----+ +------------------------------------------------+ +----+ +------------------------------------------------+
| | | | | | | |
+----+ +------------------------------------------------+ +----+ +------------------------------------------------+
|| || || || || || || || || || || || || ||
Side views Side views
skipping to change at page 21, line 7 skipping to change at page 19, line 7
leaf node, though more often than not a same type of node is used for leaf node, though more often than not a same type of node is used for
both, effectively forming a square (K*K). In the general case, we both, effectively forming a square (K*K). In the general case, we
could have switches with K_TOP southern ports on nodes at the top of could have switches with K_TOP southern ports on nodes at the top of
the PoD that is not necessarily the same as K_LEAF; for instance, in the PoD that is not necessarily the same as K_LEAF; for instance, in
the representations below, we pick a K_LEAF of 6 and a K_TOP of 8. the representations below, we pick a K_LEAF of 6 and a K_TOP of 8.
In order to form a crossbar, we need K_TOP Leaf Nodes as illustrated In order to form a crossbar, we need K_TOP Leaf Nodes as illustrated
in Figure 5. in Figure 5.
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
Figure 5: Southern View of a PoD, K_TOP=8 Figure 5: Southern View of a PoD, K_TOP=8
The K_TOP Leaf Nodes are fully interconnected with the K_LEAF PoD-top The K_TOP Leaf Nodes are fully interconnected with the K_LEAF PoD-top
nodes, providing a connectivity that can be represented as a crossbar nodes, providing a connectivity that can be represented as a crossbar
as seen from the north and illustrated in Figure 6. The result is as seen from the north and illustrated in Figure 6. The result is
that, in the absence of a breakage, a packet entering the PoD from that, in the absence of a breakage, a packet entering the PoD from
North on any port can be routed to any port on the south of the PoD North on any port can be routed to any port on the south of the PoD
and vice versa. and vice versa.
E<-*->W E<-*->W
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH | | oo oo oo oo oo oo oo oo |
+----------------------------------------------------------------+ +----------------------------------------------------------------+
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH | | oo oo oo oo oo oo oo oo |
+----------------------------------------------------------------+ +----------------------------------------------------------------+
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH | | oo oo oo oo oo oo oo oo |
+----------------------------------------------------------------+ +----------------------------------------------------------------+
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH | | oo oo oo oo oo oo oo oo |
+----------------------------------------------------------------+ +----------------------------------------------------------------+
+----------------------------------------------------------------+ +----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH |<-+ | oo oo oo oo oo oo oo oo |<-+
+----------------------------------------------------------------+ | +----------------------------------------------------------------+ |
+----------------------------------------------------------------+ | +----------------------------------------------------------------+ |
| HH HH HH HH HH HH HH HH | | | oo oo oo oo oo oo oo oo | |
+----------------------------------------------------------------+ | +----------------------------------------------------------------+ |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
^ | ^ |
| | | |
| ---------- --------------------- | | ---------- --------------------- |
+----- Leaf Node PoD top Node (Spine) --+ +----- Leaf Node PoD top Node (Spine) --+
---------- --------------------- ---------- ---------------------
Figure 6: Northern View of a PoD's Spines, K_TOP=8 Figure 6: Northern View of a PoD's Spines, K_TOP=8
skipping to change at page 23, line 49 skipping to change at page 21, line 49
number K of K_POD= K_TOP * K_LEAF, and the design can recurse. number K of K_POD= K_TOP * K_LEAF, and the design can recurse.
It is critical at this junction that the concept and the picture of It is critical at this junction that the concept and the picture of
those "crossed crossbars" is clear before progressing further, those "crossed crossbars" is clear before progressing further,
otherwise following considerations will be difficult to comprehend. otherwise following considerations will be difficult to comprehend.
Further, the PoDs are interconnected with one another through a Top- Further, the PoDs are interconnected with one another through a Top-
of-Fabric at the very top or the north edge of the fabric. The of-Fabric at the very top or the north edge of the fabric. The
resulting ToF is NOT partitioned if and only if (IIF) every PoD top resulting ToF is NOT partitioned if and only if (IIF) every PoD top
level node (spine) is connected to every ToF Node. This is also level node (spine) is connected to every ToF Node. This is also
referred to as a single plane configuration. In order to reach a referred to as a single plane configuration. In order to reach a 1:1
1::1 connectivity ratio between the ToF and the Leaves, it results connectivity ratio between the ToF and the Leaves, it results that
that there are K_TOP ToF nodes, because each port of a ToP node there are K_TOP ToF nodes, because each port of a ToP node connects
connects to a different ToF node, and K_LEAF ToP nodes for the same to a different ToF node, and K_LEAF ToP nodes for the same reason.
reason. Consequently, it takes (P * K_LEAF) ports on a ToF node to Consequently, it takes (P * K_LEAF) ports on a ToF node to connect to
connect to each of the K_LEAF ToP nodes of the P PoDs, as illustrated each of the K_LEAF ToP nodes of the P PoDs, as illustrated in
in Figure 9. Figure 9.
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] <-----+ [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] <-----+
| | | | | | | | | | | | | | | | | |
[=================================] | ----------- [=================================] | -----------
| | | | | | | | +----- Top-of-Fabric | | | | | | | | +----- Top-of-Fabric
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] +----- Node -------+ [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] +----- Node -------+
| ----------- | | ----------- |
| v | v
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ <-----+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ <-----+ +-+
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] ------------------------- | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | |
[ |H| |H| |H| |H| |H| |H| |H| |H<--- Physical Port (Ethernet) | | [ |o| |o| |o| |o| |o| |o| |o| |H<--- Physical Port (Ethernet) | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] ------------------------- | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] -------------- | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] -------------- | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] <--- PoD top level | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] <--- PoD top level | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] node (Spine) ---+ | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] node (Spine) ---+ | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] -------------- | | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] -------------- | | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | |
| | | | | | | | | | | | | | | | -+ +- +-+ v | | | | | | | | | | | | | | | | | | -+ +- +-+ v | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | --| |--[ ]--| | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | ----- | --| |--[ ]--| | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] +--- PoD ---+ --| |--[ ]--| | [ |o| |o| |o| |o| |o| |o| |o| |o| ] +--- PoD ---+ --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | ----- | --| |--[ ]--| | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | --| |--[ ]--| | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | --| |--[ ]--| | [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
| | | | | | | | | | | | | | | | -+ +- +-+ | | | | | | | | | | | | | | | | | | -+ +- +-+ | |
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
Figure 9: Fabric Spines and TOFs in Single Plane Design, 3 PoDs Figure 9: Fabric Spines and TOFs in Single Plane Design, 3 PoDs
The top view can be collapsed into a third dimension where the hidden The top view can be collapsed into a third dimension where the hidden
depth index is representing the PoD number. So we can show one PoD depth index is representing the PoD number. So we can show one PoD
as a class of PoDs and hence save one dimension in our as a class of PoDs and hence save one dimension in our
representation. The Spine Node expands in the depth and the vertical representation. The Spine Node expands in the depth and the vertical
dimensions whereas the PoD top level Nodes are constrained in dimensions whereas the PoD top level Nodes are constrained in
skipping to change at page 25, line 15 skipping to change at page 23, line 15
effectively the class of all the ports at the same position in all effectively the class of all the ports at the same position in all
the PoDs that are projected in its position along the depth axis. the PoDs that are projected in its position along the depth axis.
This is shown in Figure 10. This is shown in Figure 10.
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / ] / / / / / / / / / / / / / / / / ]
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ]] +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ]]
| | | | | | | | | | | | | | | | ] --------------------------- | | | | | | | | | | | | | | | | ] ---------------------------
[ |H| |H| |H| |H| |H| |H| |H| |H| ] <-- PoD top level node (Spine) [ |o| |o| |o| |o| |o| |o| |o| |o| ] <-- PoD top level node (Spine)
[ |H| |H| |H| |H| |H| |H| |H| |H| ] --------------------------- [ |o| |o| |o| |o| |o| |o| |o| |o| ] ---------------------------
[ |H| |H| |H| |H| |H| |H| |H| |H| ]]]] [ |o| |o| |o| |o| |o| |o| |o| |o| ]]]]
[ |H| |H| |H| |H| |H| |H| |H| |H| ]]] ^^ [ |o| |o| |o| |o| |o| |o| |o| |o| ]]] ^^
[ |H| |H| |H| |H| |H| |H| |H| |H| ]] // PoDs [ |o| |o| |o| |o| |o| |o| |o| |o| ]] // PoDs
[ |H| |H| |H| |H| |H| |H| |H| |H| ] // (in depth) [ |o| |o| |o| |o| |o| |o| |o| |o| ] // (in depth)
| |/| |/| |/| |/| |/| |/| |/| |/ // | |/| |/| |/| |/| |/| |/| |/| |/ //
+-+ +-+ +-+/+-+/+-+ +-+ +-+ +-+ // +-+ +-+ +-+/+-+/+-+ +-+ +-+ +-+ //
^ ^
| ---------------- | ----------------
+----- Top-of-Fabric Node +----- Top-of-Fabric Node
---------------- ----------------
Figure 10: Collapsed Northern View of a Fabric for Any Number of PoDs Figure 10: Collapsed Northern View of a Fabric for Any Number of PoDs
This type of deployment introduces a "single plane limit" where the This type of deployment introduces a "single plane limit" where the
bound is the available radix of the ToF nodes, which limits (P * bound is the available radix of the ToF nodes that has to be at least
K_LEAF). Nevertheless, a distinct advantage of a connected or P * K_LEAF. Nevertheless, we will see that a distinct advantage of a
unpartitioned Top-of-Fabric is that all failures can be resolved by connected or non-partitioned Top-of-Fabric is that all failures can
simple, non-transitive, positive disaggregation described in be resolved by simple, non-transitive, positive disaggregation (i.e.
Section 5.2.5.1 that propagates only within one level of the fabric. nodes advertising more specific prefixes with the default to the
In other words unpartitoned ToF nodes can always reach nodes below or level below them that is however not propagated further down the
withdraw the routes from PoDs they cannot reach unambiguously. To be fabric) described in Section 4.2.5.1. In other words non-partitioned
more precise, all failures which still allow all the ToF nodes to see ToF nodes can always reach nodes below or withdraw the routes from
each other via south reflection as explained in Section 5.2.5. PoDs they cannot reach unambiguously. And with this, positive
disaggregation can heal all failures which still allow all the ToF
nodes to see each other via south reflection as, again, explained in
further detail in Section 4.2.5.
In order to scale beyond the "single plane limit", the Top-of-Fabric In order to scale beyond the "single plane limit", the Top-of-Fabric
can be partitioned by a number N of identically wired planes, N being can be partitioned by a number N of identically wired planes, N being
an integer divider of K_LEAF. The 1::1 ratio and the desired an integer divider of K_LEAF. The 1:1 ratio and the desired symmetry
symmetry are still served, this time with (K_TOP * N) ToF nodes, each are still served, this time with (K_TOP * N) ToF nodes, each of (P *
of (P * K_LEAF / N) ports. N=1 represents a non-partitioned Spine K_LEAF / N) ports. N=1 represents a non-partitioned Spine and
and N=K_LEAF is a maximally partitioned Spine. Further, if R is any N=K_LEAF is a maximally partitioned Spine. Further, if R is any
divisor of K_LEAF, then (N=K_LEAF/R) is a feasible number of planes divisor of K_LEAF, then (N=K_LEAF/R) is a feasible number of planes
and R a redundancy factor. If proves convenient for deployments to and R a redundancy factor. If proves convenient for deployments to
use a radix for the leaf nodes that is a power of 2 so they can pick use a radix for the leaf nodes that is a power of 2 so they can pick
a number of planes that is a lower power of 2. The example in a number of planes that is a lower power of 2. The example in
Figure 11 splits the Spine in 2 planes with a redundancy factor R=3, Figure 11 splits the Spine in 2 planes with a redundancy factor R=3,
meaning that there are 3 non-intersecting paths between any leaf node meaning that there are 3 non-intersecting paths between any leaf node
and any ToF node. A ToF node must have in this case at least 3*P and any ToF node. A ToF node must have in this case at least 3*P
ports, and be directly connected to 3 of the 6 PoD-ToP nodes (spines) ports, and be directly connected to 3 of the 6 PoD-ToP nodes (spines)
in each PoD. in each PoD.
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
Plane 1 Plane 1
----------- . ------------ . ------------ . ------------ . -------- ----------- . ------------ . ------------ . ------------ . --------
Plane 2 Plane 2
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ +-| |--| |--| |--| |--| |--| |--| |--| |-+
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
^ ^
| |
| ---------------- | ----------------
+----- Top-of-Fabric node +----- Top-of-Fabric node
"across" depth "across" depth
---------------- ----------------
Figure 11: Northern View of a Multi-Plane ToF Level, K_LEAF=6, N=2 Figure 11: Northern View of a Multi-Plane ToF Level, K_LEAF=6, N=2
skipping to change at page 27, line 8 skipping to change at page 25, line 11
partition the spine with N = K_LEAF and R=1, while maintaining partition the spine with N = K_LEAF and R=1, while maintaining
connectivity between each leaf node and each Top-of-Fabric node. In connectivity between each leaf node and each Top-of-Fabric node. In
that case the ToF node connects to a single Port per PoD, so it that case the ToF node connects to a single Port per PoD, so it
appears as a single port in the projected view represented in appears as a single port in the projected view represented in
Figure 12 and the number of ports required on the Spine Node is more Figure 12 and the number of ports required on the Spine Node is more
or equal to P, the number of PoDs. or equal to P, the number of PoDs.
Plane 1 Plane 1
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ -+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ -+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
----------- . ------------ . ------------ . ------------ . -------- | ----------- . ------------ . ------------ . ------------ . -------- |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
----------- . ------------ . ------------ . ------------ . -------- | ----------- . ------------ . ------------ . ------------ . -------- |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
----------- . ------------ . ------------ . ------------ . -------- +<-+ ----------- . ------------ . ------------ . ------------ . -------- +<-+
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | | +-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | | +-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
----------- . ------------ . ------------ . ------------ . -------- | | ----------- . ------------ . ------------ . ------------ . -------- | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | | +-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | | +-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
----------- . ------------ . ------------ . ------------ . -------- | | ----------- . ------------ . ------------ . ------------ . -------- | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | | +-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | | | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | | +-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ -+ | +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ -+ |
Plane 6 ^ | Plane 6 ^ |
| | | |
| ---------------- -------------- | | ---------------- -------------- |
+----- ToF Node Class of PoDs ---+ +----- ToF Node Class of PoDs ---+
---------------- ------------- ---------------- -------------
Figure 12: Northern View of a Maximally Partitioned ToF Level, R=1 Figure 12: Northern View of a Maximally Partitioned ToF Level, R=1
5.1.3. Fallen Leaf Problem 4.1.3. Fallen Leaf Problem
As mentioned earlier, RIFT exhibits an anisotropic behavior tailored As mentioned earlier, RIFT exhibits an anisotropic behavior tailored
for fabrics with a North / South orientation and a high level of for fabrics with a North / South orientation and a high level of
interleaving paths. A non-partitioned fabric makes a total loss of interleaving paths. A non-partitioned fabric makes a total loss of
connectivity between a Top-of-Fabric node at the north and a leaf connectivity between a Top-of-Fabric node at the north and a leaf
node at the south a very rare but yet possible occasion that is fully node at the south a very rare but yet possible occasion that is fully
healed by positive disaggregation described in Section 5.2.5.1. In healed by positive disaggregation as described in Section 4.2.5.1.
large fabrics or fabrics built from switches with low radix, the ToF In large fabrics or fabrics built from switches with low radix, the
ends often being partioned in planes which makes the occurrence of ToF ends often being partitioned in planes which makes the occurrence
having a given leaf being only reachable from a subset of the ToF of having a given leaf being only reachable from a subset of the ToF
nodes more likely to happen. This makes some further considerations nodes more likely to happen. This makes some further considerations
necessary. necessary.
We define a "Fallen Leaf" as a leaf that can be reached by only a We define a "Fallen Leaf" as a leaf that can be reached by only a
subset of Top-of-Fabric nodes but cannot be reached by all due to subset of Top-of-Fabric nodes but cannot be reached by all due to
missing connectivity. If R is the redundancy factor, then it takes missing connectivity. If R is the redundancy factor, then it takes
at least R breakages to reach a "Fallen Leaf" situation. at least R breakages to reach a "Fallen Leaf" situation.
In a general manner, the mechanism of non-transitive positive In a general manner, the mechanism of non-transitive positive
disaggregation is sufficient when the disaggregating ToF nodes disaggregation is sufficient when the disaggregating ToF nodes
skipping to change at page 28, line 49 skipping to change at page 26, line 49
If the breakage is the last northern link from a Leaf node within If the breakage is the last northern link from a Leaf node within
a plane - there is only one such link in a maximally partitioned a plane - there is only one such link in a maximally partitioned
fabric - that goes down, then connectivity to all unicast prefixes fabric - that goes down, then connectivity to all unicast prefixes
attached to the Leaf node is lost within the plane where the link attached to the Leaf node is lost within the plane where the link
is located. Southern Reflection by a Leaf Node - e.g., between is located. Southern Reflection by a Leaf Node - e.g., between
ToP nodes if the PoD has only 2 levels - happens in between ToP nodes if the PoD has only 2 levels - happens in between
planes, allowing the ToP nodes to detect the problem within the planes, allowing the ToP nodes to detect the problem within the
PoD where it occurs and positively disaggregate. The breakage can PoD where it occurs and positively disaggregate. The breakage can
be observed by the ToF nodes in the same plane through the be observed by the ToF nodes in the same plane through the
flooding of N-TIEs from the ToP nodes, but the ToF nodes need to flooding of North TIEs from the ToP nodes, but the ToF nodes need
be aware of all the affected prefixes for the negative to be aware of all the affected prefixes for the negative,
disaggregation to be fully effective. The problem can also be possibly transitive disaggregation to be fully effective (i.e. a
observed by the ToF nodes in the other planes through the flooding node advertising in control plane that it cannot reach a certain
of N-TIEs from the affected Leaf nodes, together with non-node more specific prefix than default whereas such disaggregation must
N-TIEs which indicate the affected prefixes. To be effective in in extreme condition propagate further down southbound). The
that case, the positive disaggregation must reach down to the problem can also be observed by the ToF nodes in the other planes
nodes that make the plane selection, which are typically the through the flooding of North TIEs from the affected Leaf nodes,
ingress Leaf nodes, and the information is not useful for routing together with non-node North TIEs which indicate the affected
in the intermediate levels. prefixes. To be effective in that case, the positive
disaggregation must reach down to the nodes that make the plane
selection, which are typically the ingress Leaf nodes, and the
information is not useful for routing in the intermediate levels.
If the breakage is a ToP node in a maximally partitioned fabric - If the breakage is a ToP node in a maximally partitioned fabric -
in which case it is the only ToP node serving that plane in that in which case it is the only ToP node serving that plane in that
PoD - that goes down, then the connectivity to all the nodes in PoD - that goes down, then the connectivity to all the nodes in
the PoD is lost within the plane where the ToP node is located - the PoD is lost within the plane where the ToP node is located -
all leaves fall. Since the Southern Reflection between the ToF all leaves fall. Since the Southern Reflection between the ToF
nodes happens only within a plane, ToF nodes in other planes nodes happens only within a plane, ToF nodes in other planes
cannot discover the case of fallen leaves in a different plane, cannot discover the case of fallen leaves in a different plane,
and cannot determine beyond their local plane whether a Leaf node and cannot determine beyond their local plane whether a Leaf node
that was initially reachable has become unreachable. As above, that was initially reachable has become unreachable. As above,
the breakage can be observed by the ToF nodes in the plane where the breakage can be observed by the ToF nodes in the plane where
the breakage happened, and then again, the ToF nodes in the plane the breakage happened, and then again, the ToF nodes in the plane
need to be aware of all the affected prefixes for the negative need to be aware of all the affected prefixes for the negative
disaggregation to be fully effective. The problem can also be disaggregation to be fully effective. The problem can also be
observed by the ToF nodes in the other planes through the flooding observed by the ToF nodes in the other planes through the flooding
of N-TIEs from the affected Leaf nodes, if there are only 3 levels of North TIEs from the affected Leaf nodes, if there are only 3
and the ToP nodes are directly connected to the Leaf nodes, and levels and the ToP nodes are directly connected to the Leaf nodes,
then again it can only be effective it is propagated transitively and then again it can only be effective it is propagated
to the Leaf, and useless above that level. transitively to the Leaf, and useless above that level.
For the sake of easy comprehension let us roll the abstractions back For the sake of easy comprehension let us roll the abstractions back
to a simple example and observe that in Figure 3 the loss of link to a simple example and observe that in Figure 3 the loss of link
Spine 122 to Leaf 122 will make Leaf 122 a fallen leaf for Top-of- Spine 122 to Leaf 122 will make Leaf 122 a fallen leaf for Top-of-
Fabric plane B. Worse, if the cabling was never present in first Fabric plane B. Worse, if the cabling was never present in first
place, plane B will not even be able to know that such a fallen leaf place, plane B will not even be able to know that such a fallen leaf
exists. Hence partitioning without further treatment results in two exists. Hence partitioning without further treatment results in two
grave problems: grave problems:
o Leaf111 trying to route to Leaf122 MUST choose Spine 111 in plane o Leaf 111 trying to route to Leaf 122 MUST choose Spine 111 in
A as its next hop since plane B will inevitably blackhole the plane A as its next hop since plane B will inevitably blackhole
packet when forwarding using default routes or do excessive bow the packet when forwarding using default routes or do excessive
tie'ing, i.e. this information must be in its routing table. bow tie'ing, i.e. this information must be in its routing table.
o any kind of "flooding" or distance vector trying to deal with the o any kind of "flooding" or distance vector trying to deal with the
problem by distributing host routes will be able to converge only problem by distributing host routes will be able to converge only
using paths through leafs, i.e. the flooding of information on using paths through leafs, i.e. the flooding of information on
Leaf122 will go up to Top-of-Fabric A and then "loopback" over Leaf 122 will go up to Top-of-Fabric A and then "loopback" over
other leafs to ToF B leading in extreme cases to traffic for other leafs to ToF B leading in extreme cases to traffic for Leaf
Leaf122 when presented to plane B taking an "inverted fabric" path 122 when presented to plane B taking an "inverted fabric" path
where leafs start to serve as TOFs. where leafs start to serve as TOFs.
5.1.4. Discovering Fallen Leaves 4.1.4. Discovering Fallen Leaves
As we illustrate later and without further proof here, to deal with As we illustrate later and without further proof here, to deal with
fallen leafs in multi-plane designs when aggregation is used RIFT fallen leafs in multi-plane designs when aggregation is used RIFT
requires all the ToF nodes to share the same topology database. This requires all the ToF nodes to share the same topology database. This
happens naturally in single plane design but needs additional happens naturally in single plane design by the means of south
considerations in multi-plane fabrics. To satisfy this RIFT in reflection but needs additional considerations in multi-plane
multi-plane designs relies at the ToF Level on ring interconnection fabrics. To satisfy this RIFT in multi-plane designs relies at the
of switches in multiple planes. Other solutions are possible but ToF Level on ring interconnection of switches in multiple planes.
they either need more cabling or end up having much longer flooding Other solutions are possible but they either need more cabling or end
path and/or single points of failure. up having much longer flooding path and/or single points of failure.
In more detail, by reserving two ports on each Top-of-Fabric node it In more detail, by reserving two ports on each Top-of-Fabric node it
is possible to connect them together in an interplane bi-directional is possible to connect them together by interplane bi-directional
ring as illustrated in Figure 13 (where we show a bi-directional ring rings as illustrated in Figure 13. The rings will exchange full
connecting switches across planes). The rings will exchange full
topology information between planes and with that allow consequently topology information between planes and with that allow consequently
by the means of transitive, negative disaggregation described in by the means of transitive, negative disaggregation described in
Section 5.2.5.2 to efficiently fix any possible fallen leaf scenario. Section 4.2.5.2 to efficiently fix any possible fallen leaf scenario.
Somewhat as a side-effect, the exchange of information fulfills the Somewhat as a side-effect, the exchange of information fulfills the
requirement to present full view of the fabric topology at the Top- ask to present full view of the fabric topology at the Top-of-Fabric
of-Fabric level without the need to collate it from multiple points level without the need to collate it from multiple points by
by additional complexity of technologies like [RFC7752]. additional complexity of technologies like [RFC7752].
+----+ +----+ +----+ +----+ +----+ +----+ +--------+ +----+ +----+ +----+ +----+ +----+ +----+ +--------+
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ | +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
+-| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | Plane A | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | | Plane A
+-| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |-+ |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ | +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
| | | | | | | | | | | | | | | |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ | +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
+-| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | Plane B | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | | Plane B
+-| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |-+ |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ | +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
| | | | | | | | | | | | | | | |
... | ... |
| | | | | | | | | | | | | | | |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ | +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
+-| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | Plane X | | oo | | oo | | oo | | oo | | oo | | oo | | oo | | | Plane X
+-| |--| |--| |--| |--| |--| |--| |-+ | +-| |--| |--| |--| |--| |--| |--| |-+ |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ | +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
+----+ +----+ +----+ +----+ +----+ +----+ +--------+ +----+ +----+ +----+ +----+ +----+ +----+ +--------+
Figure 13: Connecting Top-of-Fabric Nodes Across Planes by Two Rings Figure 13: Connecting Top-of-Fabric Nodes Across Planes by Rings
5.1.5. Addressing the Fallen Leaves Problem 4.1.5. Addressing the Fallen Leaves Problem
One consequence of the Fallen Leaf problem is that some prefixes One consequence of the Fallen Leaf problem is that some prefixes
attached to the fallen leaf become unreachable from some of the ToF attached to the fallen leaf become unreachable from some of the ToF
nodes. RIFT proposes two methods to address this issue, the positive nodes. RIFT proposes two methods to address this issue, the positive
and the negative disaggregation. Both methods flood S-TIEs to and the negative disaggregation. Both methods flood South TIEs to
advertise the impacted prefix(es). advertise the impacted prefix(es).
When used for the operation of disaggregation, a positive S-TIE, as When used for the operation of disaggregation, a positive South TIE,
usual, indicates reachability to a prefix of given length and all as usual, indicates reachability to a prefix of given length and all
addresses subsumed by it. In contrast, a negative route addresses subsumed by it. In contrast, a negative route
advertisement indicates that the origin cannot route to the advertisement indicates that the origin cannot route to the
advertised prefix. advertised prefix.
The positive disaggregation is originated by a router that can still The positive disaggregation is originated by a router that can still
reach the advertised prefix, and the operation is not transitive, reach the advertised prefix, and the operation is not transitive,
meaning that the receiver does not generate its own flooding south as meaning that the receiver does not generate its own flooding south as
a consequence of receiving positive disaggregation advertisements a consequence of receiving positive disaggregation advertisements
from an higher level node. The effect of a positive disaggregation from an higher level node. The effect of a positive disaggregation
is that the traffic to the impacted prefix will follow the prefix is that the traffic to the impacted prefix will follow the prefix
skipping to change at page 32, line 38 skipping to change at page 30, line 38
On the other hand, when the fabric is partitioned in planes, the On the other hand, when the fabric is partitioned in planes, the
positive disaggregation from ToF nodes in different planes do not positive disaggregation from ToF nodes in different planes do not
reach the ToP switches in the affected plane and cannot solve the reach the ToP switches in the affected plane and cannot solve the
fallen leaves problem. In other words, a breakage in a plane can fallen leaves problem. In other words, a breakage in a plane can
only be solved in that plane. Also, the selection of the plane for a only be solved in that plane. Also, the selection of the plane for a
packet typically occurs at the leaf level and the disaggregation must packet typically occurs at the leaf level and the disaggregation must
be transitive and reach all the leaves. In that case, the negative be transitive and reach all the leaves. In that case, the negative
disaggregation is necessary. The details on the RIFT approach to disaggregation is necessary. The details on the RIFT approach to
deal with fallen leafs in an optimal way is specified in deal with fallen leafs in an optimal way is specified in
Section 5.2.5.2. Section 4.2.5.2.
5.2. Specification 4.2. Specification
5.2.1. Transport This section specifies the protocol in a normative fashion by either
prescriptive procedures or behavior defined by Finite State Machines
(FSM).
Some FSM figures are provided as [DOT] description due to limitations
of ASCII art.
"On Entry" actions on FSM state are performed every time and right
before the according state is entered, i.e. after any transitions
from previous state.
"On Exit" actions are performed every time and immediately when a
state is exited, i.e. before any transitions towards target state are
performed.
Any attempt to transition from a state towards another on reception
of an event where no action is specified MUST be considered an
unrecoverable error.
The FSMs and procedures are normative in the sense that an
implementation MUST implement them either literally or an
implementation MUST exhibit externally observable behavior that is
identical to the execution of the specified FSMs.
Where a FSM representation is inconvenient, i.e. the amount of
procedures and kept state exceeds the amount of transitions, we defer
to a more procedural description on data structures.
4.2.1. Transport
All packet formats are defined in Thrift [thrift] models in All packet formats are defined in Thrift [thrift] models in
Appendix B. Appendix B.
The serialized model is carried in an envelope within a UDP frame The serialized model is carried in an envelope within a UDP frame
that provides security and allows validation/modification of several that provides security and allows validation/modification of several
important fields without de-serialization for performance and important fields without de-serialization for performance and
security reasons. security reasons.
5.2.2. Link (Neighbor) Discovery (LIE Exchange) 4.2.2. Link (Neighbor) Discovery (LIE Exchange)
LIE exchange happens over well-known administratively locally scoped LIE exchange happens over well-known administratively locally scoped
and configured or otherwise well-known IPv4 multicast address and configured or otherwise well-known IPv4 multicast address
[RFC2365] and/or link-local multicast scope [RFC4291] for IPv6 [RFC2365] and/or link-local multicast scope [RFC4291] for IPv6
[RFC8200] using a configured or otherwise a well-known destination [RFC8200] using a configured or otherwise a well-known destination
UDP port defined in Appendix D.1. LIEs SHOULD be sent with a TTL of UDP port defined in Appendix C.1. LIEs SHOULD be sent with a TTL of
1 to prevent RIFT information reaching beyond a single L3 next-hop in 1 to prevent RIFT information reaching beyond a single L3 next-hop in
the topology. LIEs SHOULD be sent with network control precedence. the topology. LIEs SHOULD be sent with network control precedence.
Originating port of the LIE has no further significance other than Originating port of the LIE has no further significance other than
identifying the origination point. LIEs are exchanged over all links identifying the origination point. LIEs are exchanged over all links
running RIFT. running RIFT.
An implementation MAY listen and send LIEs on IPv4 and/or IPv6 An implementation MAY listen and send LIEs on IPv4 and/or IPv6
multicast addresses. A node MUST NOT originate LIEs on an address multicast addresses. A node MUST NOT originate LIEs on an address
family if it does not process received LIEs on that family. LIEs on family if it does not process received LIEs on that family. LIEs on
same link are considered part of the same negotiation independent on same link are considered part of the same negotiation independent on
the address family they arrive on. Observe further that the LIE the address family they arrive on. Observe further that the LIE
source address may not identify the peer uniquely in unnumbered or source address may not identify the peer uniquely in unnumbered or
link-local address cases so the response transmission MUST occur over link-local address cases so the response transmission MUST occur over
the same interface the LIEs have been received on. A node CAN use the same interface the LIEs have been received on. A node CAN use
any of the adjacency's source addresses it saw in LIEs on the any of the adjacency's source addresses it saw in LIEs on the
specific interface during adjacency formation to send TIEs. That specific interface during adjacency formation to send TIEs. That
implies that an implementation MUST be ready to accept TIEs on all implies that an implementation MUST be ready to accept TIEs on all
addresses it used as source of LIE frames. addresses it used as source of LIE frames.
A three way adjacency over any address family implies support for A 3-way adjacency over any address family implies support for IPv4
IPv4 forwarding if the `v4_forwarding_capable` flag is set to true forwarding if the `v4_forwarding_capable` flag is set to true and a
and a node can use [RFC5549] type of forwarding in such a situation. node can use [RFC5549] type of forwarding in such a situation. It is
It is expected that the whole fabric supports the same type of expected that the whole fabric supports the same type of forwarding
forwarding of address families on all the links. Operation of a of address families on all the links. Operation of a fabric where
fabric where only some of the links are supporting forwarding on an only some of the links are supporting forwarding on an address family
address family and others do not is outside the scope of this and others do not is outside the scope of this specification.
specification.
Observe further that the protocol does NOT support selective Observe further that the protocol does NOT support selective
disabling of address families, disabling v4 forwarding capability or disabling of address families, disabling v4 forwarding capability or
any local address changes in three way state, i.e. if a link has any local address changes in 3-way state, i.e. if a link has entered
entered three way IPv4 and/or IPv6 with a neighbor on an adjacency 3-way IPv4 and/or IPv6 with a neighbor on an adjacency and it wants
and it wants to stop supporting one of the families or change any of to stop supporting one of the families or change any of its local
its local addresses or stop v4 forwarding, it has to tear down and addresses or stop v4 forwarding, it has to tear down and rebuild the
rebuild the adjacency. It also has to remove any information it adjacency. It also has to remove any information it stored about the
stored about the adjacency such as LIE source addresses seen. adjacency such as LIE source addresses seen.
Unless Section 5.2.7 is used, each node is provisioned with the level Unless Section 4.2.7 is used, each node is provisioned with the level
at which it is operating and its PoD (or otherwise a default level at which it is operating and its PoD (or otherwise a default level
and "undefined" PoD are assumed; meaning that leafs do not need to be and "undefined" PoD are assumed; meaning that leafs do not need to be
configured at all if initial configuration values are all left at 0). configured at all if initial configuration values are all left at 0).
Nodes in the spine are configured with "any" PoD which has the same Nodes in the spine are configured with "any" PoD which has the same
value "undefined" PoD hence we will talk about "undefined/any" PoD. value "undefined" PoD hence we will talk about "undefined/any" PoD.
This information is propagated in the LIEs exchanged. This information is propagated in the LIEs exchanged.
Further definitions of leaf flags are found in Section 5.2.7 given Further definitions of leaf flags are found in Section 4.2.7 given
they have implications in terms of level and adjacency forming here. they have implications in terms of level and adjacency forming here.
A node tries to form a three way adjacency if and only if A node tries to form a 3-way adjacency if and only if
1. the node is in the same PoD or either the node or the neighbor 1. the node is in the same PoD or either the node or the neighbor
advertises "undefined/any" PoD membership (PoD# = 0) AND advertises "undefined/any" PoD membership (PoD# = 0) AND
2. the neighboring node is running the same MAJOR schema version AND 2. the neighboring node is running the same MAJOR schema version AND
3. the neighbor is not member of some PoD while the node has a 3. the neighbor is not member of some PoD while the node has a
northbound adjacency already joining another PoD AND northbound adjacency already joining another PoD AND
4. the neighboring node uses a valid System ID AND 4. the neighboring node uses a valid System ID AND
5. the neighboring node uses a different System ID than the node 5. the neighboring node uses a different System ID than the node
itself itself
6. the advertised MTUs match on both sides AND 6. the advertised MTUs match on both sides AND
7. both nodes advertise defined level values AND 7. both nodes advertise defined level values AND
8. [ 8. [
i) the node is at level 0 and has no three way adjacencies i) the node is at level 0 and has no 3-way adjacencies already
already to HAT nodes with level different than the adjacent to Highest Adjacency Three-Way (HAT) nodes (defined in
node OR Section 4.2.7.1) with level different than the adjacent node
OR
ii) the node is not at level 0 and the neighboring node is at ii) the node is not at level 0 and the neighboring node is at
level 0 OR level 0 OR
iii) both nodes are at level 0 AND both indicate support for iii) both nodes are at level 0 AND both indicate support for
Section 5.3.9 OR Section 4.3.8 OR
iv) neither node is at level 0 and the neighboring node is at iv) neither node is at level 0 and the neighboring node is at
most one level away most one level away
]. ].
The rule in Paragraph 3 MAY be optionally disregarded by a node if The rules checking PoD numbering MAY be optionally disregarded by a
PoD detection is undesirable or has to be ignored. node if PoD detection is undesirable or has to be ignored. This will
not affect the correctness of the protocol expect preventing
detection of certain miscabling cases.
A node configured with "undefined" PoD membership MUST, after A node configured with "undefined" PoD membership MUST, after
building first northbound three way adjacencies to a node being in a building first northbound 3-way adjacencies to a node being in a
defined PoD, advertise that PoD as part of its LIEs. In case that defined PoD, advertise that PoD as part of its LIEs. In case that
adjacency is lost, from all available northbound three way adjacency is lost, from all available northbound 3-way adjacencies
adjacencies the node with the highest System ID and defined PoD is the node with the highest System ID and defined PoD is chosen. That
chosen. That way the northmost defined PoD value (normally the top way the northmost defined PoD value (normally the top spines in a
spines in a PoD) can diffuse southbound towards the leafs "forcing" PoD) can diffuse southbound towards the leafs "forcing" the PoD value
the PoD value on any node with "undefined" PoD. on any node with "undefined" PoD.
LIEs arriving with a TTL larger than 1 MUST be ignored. LIEs arriving with a TTL larger than 1 MUST be ignored.
A node SHOULD NOT send out LIEs without defined level in the header A node SHOULD NOT send out LIEs without defined level in the header
but in certain scenarios it may be beneficial for trouble-shooting but in certain scenarios it may be beneficial for trouble-shooting
purposes. purposes.
LIE exchange uses three way handshake mechanism which is a cleaned up LIE exchange uses 3-way handshake mechanism which is a cleaned up
version of [RFC5303]. Observe that for easier comprehension the version of [RFC5303]. Observe that for easier comprehension the
terminology of one/two and three-way states does NOT align with OSPF terminology of one/two and three-way states does NOT align with OSPF
or ISIS FSMs albeit they use roughly same mechanisms. or ISIS FSMs albeit they use roughly same mechanisms.
5.2.3. Topology Exchange (TIE Exchange) 4.2.2.1. LIE FSM
5.2.3.1. Topology Information Elements This section specifies the precise, normative LIE FSM and can be
omitted unless the reader is pursuing an implemenentation of the
protocol.
Initial state is `OneWay`.
Event `MultipleNeighbors` occurs normally when more than two nodes
see each other on the same link or a remote node is quickly
reconfigured or rebooted without regressing to `OneWay` first. Each
occurence of the event SHOULD generate a clear, according
notification to help operational deployments.
The machine sends LIEs on several transitions to accelerate adjacency
bring-up without waiting for the timer tic.
digraph Ga556dde74c30450aae125eaebc33bd57 {
Nd16ab5092c6b421c88da482eb4ae36b6[label="ThreeWay"][shape="oval"];
N54edd2b9de7641688608f44fca346303[label="OneWay"][shape="oval"];
Nfeef2e6859ae4567bd7613a32cc28c0e[label="TwoWay"][shape="oval"];
N7f2bb2e04270458cb5c9bb56c4b96e23[label="Enter"][style="invis"][shape="plain"];
N292744a4097f492f8605c926b924616b[label="Enter"][style="dashed"][shape="plain"];
Nc48847ba98e348efb45f5b78f4a5c987[label="Exit"][style="invis"][shape="plain"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> N54edd2b9de7641688608f44fca346303
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|MultipleNeighbors|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|ValidReflection|"][color="red"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"][color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|ValidReflection|"][color="red"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> N54edd2b9de7641688608f44fca346303
[label="|LevelChanged|"][color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> N54edd2b9de7641688608f44fca346303
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|MultipleNeighbors|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|ValidReflection|"][color="red"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> N54edd2b9de7641688608f44fca346303
[label="|TimerTick|\n|LieRcvd|\n|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|SendLie|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N292744a4097f492f8605c926b924616b -> N54edd2b9de7641688608f44fca346303
[label=""][color="black"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> N54edd2b9de7641688608f44fca346303
[label="|LevelChanged|"][color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|NewNeighbor|"][color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> N54edd2b9de7641688608f44fca346303
[label="|LevelChanged|\n|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|NeighborDroppedReflection|"]
[color="red"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> N54edd2b9de7641688608f44fca346303
[label="|NeighborDroppedReflection|"][color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
}
LIE FSM DOT
Events
o TimerTick: one second timer tic
o LevelChanged: node's level has been changed by ZTP or
configuration
o HALChanged: best HAL computed by ZTP has changed
o HATChanged: HAT computed by ZTP has changed
o HALSChanged: set of HAL offering systems computed by ZTP has
changed
o LieRcvd: received LIE
o NewNeighbor: new neighbor parsed
o ValidReflection: received own reflection from neighbor
o NeighborDroppedReflection: lost previous own reflection from
neighbor
o NeighborChangedLevel: neighbor changed advertised level
o NeighborChangedAddress: neighbor changed IP address
o UnacceptableHeader: unacceptable header seen
o MTUMismatch: MTU mismatched
o PODMismatch: Unacceptable PoD seen
o HoldtimeExpired: adjacency hold down expired
o MultipleNeighbors: more than one neighbor seen on interface
o SendLie: send a LIE out
o UpdateZTPOffer: update this node's ZTP offer
Actions
on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if
holdtime expired PUSH HoldtimeExpired event
on HALChanged in TwoWay finishes in TwoWay: store new HAL
on MTUMismatch in ThreeWay finishes in OneWay: no action
on HALChanged in ThreeWay finishes in ThreeWay: store new HAL
on ValidReflection in TwoWay finishes in ThreeWay: no action
on ValidReflection in OneWay finishes in ThreeWay: no action
on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no
action
on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE
on MultipleNeighbors in TwoWay finishes in OneWay: no action
on UnacceptableHeader in ThreeWay finishes in OneWay: no action
on MTUMismatch in TwoWay finishes in OneWay: no action
on LevelChanged in OneWay finishes in OneWay: update level with
event value, PUSH SendLie event
on UnacceptableHeader in TwoWay finishes in OneWay: no action
on HALSChanged in TwoWay finishes in TwoWay: store HALS
on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP
FSM
on NeighborChangedLevel in TwoWay finishes in OneWay: no action
on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event
on NeighborChangedAddress in ThreeWay finishes in OneWay: no
action
on HALChanged in OneWay finishes in OneWay: store new HAL
on NeighborChangedLevel in OneWay finishes in OneWay: no action
on HoldtimeExpired in TwoWay finishes in OneWay: no action
on SendLie in TwoWay finishes in TwoWay: SEND_LIE
on LevelChanged in TwoWay finishes in OneWay: update level with
event value
on NeighborChangedAddress in OneWay finishes in OneWay: no action
on HATChanged in TwoWay finishes in TwoWay: store HAT
on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE
on MultipleNeighbors in ThreeWay finishes in OneWay: no action
on MTUMismatch in OneWay finishes in OneWay: no action
on SendLie in OneWay finishes in OneWay: SEND_LIE
on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE
on TimerTick in ThreeWay finishes in ThreeWay: PUSH SendLie event,
if holdtime expired PUSH HoldtimeExpired event
on TimerTick in OneWay finishes in OneWay: PUSH SendLie event
on PODMismatch in ThreeWay finishes in OneWay: no action
on LevelChanged in ThreeWay finishes in OneWay: update level with
event value
on NeighborChangedLevel in ThreeWay finishes in OneWay: no action
on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP
FSM
on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to
ZTP FSM
on HATChanged in OneWay finishes in OneWay: store HAT
on HATChanged in ThreeWay finishes in ThreeWay: store HAT
on HoldtimeExpired in OneWay finishes in OneWay: no action
on UnacceptableHeader in OneWay finishes in OneWay: no action
on PODMismatch in OneWay finishes in OneWay: no action
on SendLie in ThreeWay finishes in ThreeWay: SEND_LIE
on NeighborChangedAddress in TwoWay finishes in OneWay: no action
on ValidReflection in ThreeWay finishes in ThreeWay: no action
on HALSChanged in OneWay finishes in OneWay: store HALS
on HoldtimeExpired in ThreeWay finishes in OneWay: no action
on HALSChanged in ThreeWay finishes in ThreeWay: store HALS
on NeighborDroppedReflection in OneWay finishes in OneWay: no
action
on PODMismatch in TwoWay finishes in OneWay: no action
on Entry into OneWay: CLEANUP
Following words are used for well known procedures:
1. PUSH Event: pushes an event to be executed by the FSM upon exit
of this action
2. CLEANUP: neighbor MUST be reset to unknown
3. SEND_LIE: create a new LIE packet
1. reflecting the neighbor if known and valid and
2. setting the necessary `not_a_ztp_offer` variable if level was
derived from last known neighbor on this interface and
3. setting `you_are_not_flood_repeater` to computed value
4. PROCESS_LIE:
1. if lie has wrong major version OR our own system ID or
invalid system ID then CLEANUP else
2. if lie has non matching MTUs then CLEANUP, PUSH
UpdateZTPOffer, PUSH MTUMismatch else
3. if PoD rules do not allow adjacency forming then CLEANUP,
PUSH PODMismatch, PUSH MTUMismatch else
4. if lie has undefined level OR my level is undefined OR this
node is leaf and remote level lower than HAT OR (lie's level
is not leaf AND its difference is more than one from my
level) then CLEANUP, PUSH UpdateZTPOffer, PUSH
UnacceptableHeader else
5. PUSH UpdateZTPOffer, construct temporary new neighbor
structure with values from lie, if no current neighbor exists
then set neighbor to new neighbor, PUSH NewNeighbor event,
CHECK_THREE_WAY else
1. if current neighbor system ID differs from lie's system
ID then PUSH MultipleNeighbors else
2. if current neighbor stored level differs from lie's level
then PUSH NeighborChangedLevel else
3. if current neighbor stored IPv4/v6 address differs from
lie's address then PUSH NeighborChangedAddress else
4. if any of neighbor's flood address port, name, local
linkid changed then PUSH NeighborChangedMinorFields and
5. CHECK_THREE_WAY
5. CHECK_THREE_WAY: if current state is one-way do nothing else
1. if lie packet does not contain neighbor then if current state
is three-way then PUSH NeighborDroppedReflection else
2. if packet reflects this system's ID and local port and state
is three-way then PUSH event ValidReflection else PUSH event
MultipleNeighbors
4.2.3. Topology Exchange (TIE Exchange)
4.2.3.1. Topology Information Elements
Topology and reachability information in RIFT is conveyed by the Topology and reachability information in RIFT is conveyed by the
means of TIEs which have good amount of commonalities with LSAs in means of TIEs which have good amount of commonalities with LSAs in
OSPF. OSPF.
The TIE exchange mechanism uses the port indicated by each node in The TIE exchange mechanism uses the port indicated by each node in
the LIE exchange and the interface on which the adjacency has been the LIE exchange and the interface on which the adjacency has been
formed as destination. It SHOULD use TTL of 1 as well and set inter- formed as destination. It SHOULD use TTL of 1 as well and set inter-
network control precedence on according packets. network control precedence on according packets.
skipping to change at page 36, line 5 skipping to change at page 40, line 32
design choice is a prefix per TIE which leads to more BGP-like design choice is a prefix per TIE which leads to more BGP-like
behavior where small increments are only advertised on route changes behavior where small increments are only advertised on route changes
vs. deploying with dense prefix packing into few TIEs leading to more vs. deploying with dense prefix packing into few TIEs leading to more
traditional IGP trade-off with fewer TIEs. An implementation may traditional IGP trade-off with fewer TIEs. An implementation may
even rehash prefix to TIE mapping at any time at the cost of even rehash prefix to TIE mapping at any time at the cost of
significant amount of re-advertisements of TIEs. significant amount of re-advertisements of TIEs.
More information about the TIE structure can be found in the schema More information about the TIE structure can be found in the schema
in Appendix B. in Appendix B.
5.2.3.2. South- and Northbound Representation 4.2.3.2. South- and Northbound Representation
A central concept of RIFT is that each node represents itself A central concept of RIFT is that each node represents itself
differently depending on the direction in which it is advertising differently depending on the direction in which it is advertising
information. More precisely, a spine node represents two different information. More precisely, a spine node represents two different
databases over its adjacencies depending whether it advertises TIEs databases over its adjacencies depending whether it advertises TIEs
to the north or to the south/sideways. We call those differing TIE to the north or to the south/sideways. We call those differing TIE
databases either south- or northbound (S-TIEs and N-TIEs) depending databases either south- or northbound (South TIEs and North TIEs)
on the direction of distribution. depending on the direction of distribution.
The N-TIEs hold all of the node's adjacencies and local prefixes The North TIEs hold all of the node's adjacencies and local prefixes
while the S-TIEs hold only all of the node's adjacencies, the default while the South TIEs hold only all of the node's adjacencies, the
prefix with necessary disaggregated prefixes and local prefixes. We default prefix with necessary disaggregated prefixes and local
will explain this in detail further in Section 5.2.5. prefixes. We will explain this in detail further in Section 4.2.5.
The TIE types are mostly symmetric in both directions and Table 2 The TIE types are mostly symmetric in both directions and Table 2
provides a quick reference to main TIE types including direction and provides a quick reference to main TIE types including direction and
their function. their function.
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| TIE-Type | Content | | TIE-Type | Content |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Node N-TIE | node properties and adjacencies | | Node North TIE | node properties and adjacencies |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Node S-TIE | same content as node N-TIE | | Node South TIE | same content as node North TIE |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Prefix N-TIE | contains nodes' directly reachable prefixes | | Prefix North TIE | contains nodes' directly reachable prefixes |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Prefix S-TIE | contains originated defaults and directly | | Prefix South TIE | contains originated defaults and directly |
| | reachable prefixes | | | reachable prefixes |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Positive | contains disaggregated prefixes | | Positive | contains disaggregated prefixes |
| Disaggregation | | | Disaggregation | |
| S-TIE | | | South TIE | |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Negative | contains special, negatively disaggreagted | | Negative | contains special, negatively disaggreagted |
| Disaggregation | prefixes to support multi-plane designs | | Disaggregation | prefixes to support multi-plane designs |
| S-TIE | | | South TIE | |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| External Prefix | contains external prefixes | | External Prefix | contains external prefixes |
| N-TIE | | | North TIE | |
+-------------------+-----------------------------------------------+ +--------------------+----------------------------------------------+
| Key-Value N-TIE | contains nodes northbound KVs | | Key-Value North | contains nodes northbound KVs |
+-------------------+-----------------------------------------------+ | TIE | |
| Key-Value S-TIE | contains nodes southbound KVs | +--------------------+----------------------------------------------+
+-------------------+-----------------------------------------------+ | Key-Value South | contains nodes southbound KVs |
| TIE | |
+--------------------+----------------------------------------------+
Table 2: TIE Types Table 2: TIE Types
As an example illustrating a databases holding both representations, As an example illustrating a databases holding both representations,
consider the topology in Figure 2 with the optional link between consider the topology in Figure 2 with the optional link between
spine 111 and spine 112 (so that the flooding on an East-West link spine 111 and spine 112 (so that the flooding on an East-West link
can be shown). This example assumes unnumbered interfaces. First, can be shown). This example assumes unnumbered interfaces. First,
here are the TIEs generated by some nodes. For simplicity, the key here are the TIEs generated by some nodes. For simplicity, the key
value elements which may be included in their S-TIEs or N-TIEs are value elements which may be included in their South TIEs or North
not shown. TIEs are not shown.
Spine21 S-TIEs: ToF 21 South TIEs:
Node S-TIE: Node South TIE:
NodeElement(level=2, neighbors((Spine 111, level 1, cost 1), NodeElement(level=2, neighbors((Spine 111, level 1, cost 1),
(Spine 112, level 1, cost 1), (Spine 121, level 1, cost 1), (Spine 112, level 1, cost 1), (Spine 121, level 1, cost 1),
(Spine 122, level 1, cost 1))) (Spine 122, level 1, cost 1)))
Prefix S-TIE: Prefix South TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1)) SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 111 S-TIEs: Spine 111 South TIEs:
Node S-TIE: Node South TIE:
NodeElement(level=1, neighbors((Spine21, level 2, cost 1, links(...)), NodeElement(level=1, neighbors((ToF 21, level 2, cost 1, links(...)),
(Spine22, level 2, cost 1, links(...)), (ToF 22, level 2, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)), (Spine 112, level 1, cost 1, links(...)),
(Leaf111, level 0, cost 1, links(...)), (Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...)))) (Leaf112, level 0, cost 1, links(...))))
Prefix S-TIE: Prefix South TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1)) SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 111 N-TIEs: Spine 111 North TIEs:
Node N-TIE: Node North TIE:
NodeElement(level=1, NodeElement(level=1,
neighbors((Spine21, level 2, cost 1, links(...)), neighbors((ToF 21, level 2, cost 1, links(...)),
(Spine22, level 2, cost 1, links(...)), (ToF 22, level 2, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)), (Spine 112, level 1, cost 1, links(...)),
(Leaf111, level 0, cost 1, links(...)), (Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...)))) (Leaf112, level 0, cost 1, links(...))))
Prefix N-TIE: Prefix North TIE:
NorthPrefixesElement(prefixes(Spine 111.loopback) NorthPrefixesElement(prefixes(Spine 111.loopback)
Spine 121 S-TIEs: Spine 121 South TIEs:
Node S-TIE: Node South TIE:
NodeElement(level=1, neighbors((Spine21,level 2,cost 1), NodeElement(level=1, neighbors((ToF 21,level 2,cost 1),
(Spine22, level 2, cost 1), (Leaf121, level 0, cost 1), (ToF 22, level 2, cost 1), (Leaf121, level 0, cost 1),
(Leaf122, level 0, cost 1))) (Leaf122, level 0, cost 1)))
Prefix S-TIE: Prefix South TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1)) SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 121 N-TIEs: Spine 121 North TIEs:
Node N-TIE: Node North TIE:
NodeElement(level=1, NodeElement(level=1,
neighbors((Spine21, level 2, cost 1, links(...)), neighbors((ToF 21, level 2, cost 1, links(...)),
(Spine22, level 2, cost 1, links(...)), (ToF 22, level 2, cost 1, links(...)),
(Leaf121, level 0, cost 1, links(...)), (Leaf121, level 0, cost 1, links(...)),
(Leaf122, level 0, cost 1, links(...)))) (Leaf122, level 0, cost 1, links(...))))
Prefix N-TIE: Prefix North TIE:
NorthPrefixesElement(prefixes(Spine 121.loopback) NorthPrefixesElement(prefixes(Spine 121.loopback)
Leaf112 N-TIEs: Leaf112 North TIEs:
Node N-TIE: Node North TIE:
NodeElement(level=0, NodeElement(level=0,
neighbors((Spine 111, level 1, cost 1, links(...)), neighbors((Spine 111, level 1, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)))) (Spine 112, level 1, cost 1, links(...))))
Prefix N-TIE: Prefix North TIE:
NorthPrefixesElement(prefixes(Leaf112.loopback, Prefix112, NorthPrefixesElement(prefixes(Leaf112.loopback, Prefix112,
Prefix_MH)) Prefix_MH))
Figure 14: example TIES generated in a 2 level spine-and-leaf Figure 14: example TIES generated in a 2 level spine-and-leaf
topology topology
5.2.3.3. Flooding It may be here not necessarily obvious why the node South TIEs
contain all the adjacencies of the according node. This will be
necessary for algorithms given in Section 4.2.3.9 and Section 4.3.6.
4.2.3.3. Flooding
The mechanism used to distribute TIEs is the well-known (albeit The mechanism used to distribute TIEs is the well-known (albeit
modified in several respects to address fat tree requirements) modified in several respects to take advantage of fat tree topology)
flooding mechanism used by today's link-state protocols. Although flooding mechanism used by today's link-state protocols. Although
flooding is initially more demanding to implement it avoids many flooding is initially more demanding to implement it avoids many
problems with update style used in diffused computation such as problems with update style used in diffused computation such as
distance vector protocols. Since flooding tends to present an distance vector protocols. Since flooding tends to present an
unscalable burden in large, densely meshed topologies (fat trees unscalable burden in large, densely meshed topologies (fat trees
being unfortunately such a topology) we provide as solution a close being unfortunately such a topology) we provide as solution a close
to optimal global flood reduction and load balancing optimization in to optimal global flood reduction and load balancing optimization in
Section 5.2.3.9. Section 4.2.3.9.
As described before, TIEs themselves are transported over UDP with As described before, TIEs themselves are transported over UDP with
the ports indicated in the LIE exchanges and using the destination the ports indicated in the LIE exchanges and using the destination
address on which the LIE adjacency has been formed. For unnumbered address on which the LIE adjacency has been formed. For unnumbered
IPv4 interfaces same considerations apply as in equivalent OSPF case. IPv4 interfaces same considerations apply as in equivalent OSPF case.
On reception of a TIE with an undefined level value in the packet On reception of a TIE with an undefined level value in the packet
header the node SHOULD issue a warning and indiscriminately discard header the node SHOULD issue a warning and indiscriminately discard
the packet. the packet.
Precise finite state machines and procedures can be found in 4.2.3.3.1. Normative Flooding Procedures
Appendix C.3.
5.2.3.4. TIE Flooding Scopes This section specifies the precise, normative flooding mechanism and
can be omitted unless the reader is pursuing an implemenentation of
the protocol.
Flooding Procedures are described in terms of a flooding state of an
adjacency and resulting operations on it driven by packet arrivals.
The FSM itself has basically just a single state and is not well
suited to represent the behavior. An implementation MUST behave on
the wire in the same way as the provided normative procedures of this
paragraph.
RIFT does not specify any kind of flood rate limiting since such
specifications always assume particular points in available
technology speeds and feeds and those points are shifting at faster
and faster rate (speed of light holding for the moment). The encoded
packets provide hints to react accordingly to losses or overruns.
Flooding of all according topology exchange elements SHOULD be
performed at highest feasible rate whereas the rate of transmission
MUST be throttled by reacting to adequate features of the system such
as e.g. queue lengths or congestion indications in the protocol
packets.
4.2.3.3.1.1. FloodState Structure per Adjacency
The structure contains conceptually the following elements. The word
collection or queue indicates a set of elements that can be iterated:
TIES_TX: Collection containing all the TIEs to transmit on the
adjacency.
TIES_ACK: Collection containing all the TIEs that have to be
acknowledged on the adjacency.
TIES_REQ: Collection containing all the TIE headers that have to be
requested on the adjacency.
TIES_RTX: Collection containing all TIEs that need retransmission
with the according time to retransmit.
Following words are used for well known procedures operating on this
structure:
TIE Describes either a full RIFT TIE or accordingly just the
`TIEHeader` or `TIEID`. The according meaning is unambiguously
contained in the context of the algorithm.
is_flood_reduced(TIE): returns whether a TIE can be flood reduced or
not.
is_tide_entry_filtered(TIE): returns whether a header should be
propagated in TIDE according to flooding scopes.
is_request_filtered(TIE): returns whether a TIE request should be
propagated to neighbor or not according to flooding scopes.
is_flood_filtered(TIE): returns whether a TIE requested be flooded
to neighbor or not according to flooding scopes.
try_to_transmit_tie(TIE):
A. if not is_flood_filtered(TIE) then
1. remove TIE from TIES_RTX if present
2. if TIE" with same key on TIES_ACK then
a. if TIE" same or newer than TIE do nothing else
b. remove TIE" from TIES_ACK and add TIE to TIES_TX
3. else insert TIE into TIES_TX
ack_tie(TIE): remove TIE from all collections and then insert TIE
into TIES_ACK.
tie_been_acked(TIE): remove TIE from all collections.
remove_from_all_queues(TIE): same as `tie_been_acked`.
request_tie(TIE): if not is_request_filtered(TIE) then
remove_from_all_queues(TIE) and add to TIES_REQ.
move_to_rtx_list(TIE): remove TIE from TIES_TX and then add to
TIES_RTX using TIE retransmission interval.
clear_requests(TIEs): remove all TIEs from TIES_REQ.
bump_own_tie(TIE): for self-originated TIE originate an empty or re-
generate with version number higher then the one in TIE.
The collection SHOULD be served with following priorities if the
system cannot process all the collections in real time:
Elements on TIES_ACK should be processed with highest priority
TIES_TX
TIES_REQ and TIES_RTX
4.2.3.3.1.2. TIDEs
`TIEID` and `TIEHeader` space forms a strict total order (modulo
uncomparable sequence numbers in the very unlikely event that can
occur if a TIE is "stuck" in a part of a network while the originator
reboots and reissues TIEs many times to the point its sequence# rolls
over and forms incomparable distance to the "stuck" copy) which
implies that a comparison relation is possible between two elements.
With that it is implictly possible to compare TIEs, TIEHeaders and
TIEIDs to each other whereas the shortest viable key is always
implied.
When generating and sending TIDEs an implementation SHOULD ensure
that enough bandwidth is left to send elements of Floodstate
structure.
4.2.3.3.1.2.1. TIDE Generation
As given by timer constant, periodically generate TIDEs by:
NEXT_TIDE_ID: ID of next TIE to be sent in TIDE.
TIDE_START: Begin of TIDE packet range.
a. NEXT_TIDE_ID = MIN_TIEID
b. while NEXT_TIDE_ID not equal to MAX_TIEID do
1. TIDE_START = NEXT_TIDE_ID
2. HEADERS = At most TIRDEs_PER_PKT headers in TIEDB starting at
NEXT_TIDE_ID or higher that SHOULD be filtered by
is_tide_entry_filtered and MUST either have a lifetime left >
0 or have no content
3. if HEADERS is empty then START = MIN_TIEID else START = first
element in HEADERS
4. if HEADERS' size less than TIRDEs_PER_PKT then END =
MAX_TIEID else END = last element in HEADERS
5. send sorted HEADERS as TIDE setting START and END as its
range
6. NEXT_TIDE_ID = END
The constant `TIRDEs_PER_PKT` SHOULD be generated and used by the
implementation to limit the amount of TIE headers per TIDE so the
sent TIDE PDU does not exceed interface MTU.
TIDE PDUs SHOULD be spaced on sending to prevent packet drops.
4.2.3.3.1.2.2. TIDE Processing
On reception of TIDEs the following processing is performed:
TXKEYS: Collection of TIE Headers to be send after processing of
the packet
REQKEYS: Collection of TIEIDs to be requested after processing of
the packet
CLEARKEYS: Collection of TIEIDs to be removed from flood state
queues
LASTPROCESSED: Last processed TIEID in TIDE
DBTIE: TIE in the LSDB if found
a. LASTPROCESSED = TIDE.start_range
b. for every HEADER in TIDE do
1. DBTIE = find HEADER in current LSDB
2. if HEADER < LASTPROCESSED then report error and reset
adjacency and return
3. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and
TIE.HEADER < HEADER) into TXKEYS
4. LASTPROCESSED = HEADER
5. if DBTIE not found then
I) if originator is this node then bump_own_tie
II) else put HEADER into REQKEYS
6. if DBTIE.HEADER < HEADER then
I) if originator is this node then bump_own_tie else
i. if this is a North TIE header from a northbound
neighbor then override DBTIE in LSDB with HEADER
ii. else put HEADER into REQKEYS
7. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS
8. if DBTIE.HEADER = HEADER then
I) if DBTIE has content already then put DBTIE.HEADER
into CLEARKEYS
II) else put HEADER into REQKEYS
c. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and
TIE.HEADER <= TIDE.end_range) into TXKEYS
d. for all TIEs in TXKEYS try_to_transmit_tie(TIE)
e. for all TIEs in REQKEYS request_tie(TIE)
f. for all TIEs in CLEARKEYS remove_from_all_queues(TIE)
4.2.3.3.1.3. TIREs
4.2.3.3.1.3.1. TIRE Generation
There is not much to say here. Elements from both TIES_REQ and
TIES_ACK MUST be collected and sent out as fast as feasible as TIREs.
When sending TIREs with elements from TIES_REQ the `lifetime` field
MUST be set to 0 to force reflooding from the neighbor even if the
TIEs seem to be same.
4.2.3.3.1.3.2. TIRE Processing
On reception of TIREs the following processing is performed:
TXKEYS: Collection of TIE Headers to be send after processing of
the packet
REQKEYS: Collection of TIEIDs to be requested after processing of
the packet
ACKKEYS: Collection of TIEIDs that have been acked
DBTIE: TIE in the LSDB if found
a. for every HEADER in TIRE do
1. DBTIE = find HEADER in current LSDB
2. if DBTIE not found then do nothing
3. if DBTIE.HEADER < HEADER then put HEADER into REQKEYS
4. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS
5. if DBTIE.HEADER = HEADER then put DBTIE.HEADER into ACKKEYS
b. for all TIEs in TXKEYS try_to_transmit_tie(TIE)
c. for all TIEs in REQKEYS request_tie(TIE)
d. for all TIEs in ACKKEYS tie_been_acked(TIE)
4.2.3.3.1.4. TIEs Processing on Flood State Adjacency
On reception of TIEs the following processing is performed:
ACKTIE: TIE to acknowledge
TXTIE: TIE to transmit
DBTIE: TIE in the LSDB if found
a. DBTIE = find TIE in current LSDB
b. if DBTIE not found then
1. if originator is this node then bump_own_tie with a short
remaining lifetime
2. else insert TIE into LSDB and ACKTIE = TIE
else
1. if DBTIE.HEADER = TIE.HEADER then
i. if DBTIE has content already then ACKTIE = TIE
ii. else process like the "DBTIE.HEADER < TIE.HEADER" case
2. if DBTIE.HEADER < TIE.HEADER then
i. if originator is this node then bump_own_tie
ii. else insert TIE into LSDB and ACKTIE = TIE
3. if DBTIE.HEADER > TIE.HEADER then
i. if DBTIE has content already then TXTIE = DBTIE
ii. else ACKTIE = DBTIE
c. if TXTIE is set then try_to_transmit_tie(TXTIE)
d. if ACKTIE is set then ack_tie(TIE)
4.2.3.3.1.5. TIEs Processing When LSDB Received Newer Version on Other
Adjacencies
The Link State Database can be considered to be a switchboard that
does not need any flooding procedures but can be given new versions
of TIEs by a peer. Consecutively, a peer receives from the LSDB
newer versions of TIEs received by other peeers and processes them
(without any filtering) just like receving TIEs from its remote peer.
This publisher model can be implemented in many ways.
4.2.3.3.1.6. Sending TIEs
On a periodic basis all TIEs with lifetime left > 0 MUST be sent out
on the adjacency, removed from TIES_TX list and requeued onto
TIES_RTX list.
4.2.3.4. TIE Flooding Scopes
In a somewhat analogous fashion to link-local, area and domain In a somewhat analogous fashion to link-local, area and domain
flooding scopes, RIFT defines several complex "flooding scopes" flooding scopes, RIFT defines several complex "flooding scopes"
depending on the direction and type of TIE propagated. depending on the direction and type of TIE propagated.
Every N-TIE is flooded northbound, providing a node at a given level Every North TIE is flooded northbound, providing a node at a given
with the complete topology of the Clos or Fat Tree network underneath level with the complete topology of the Clos or Fat Tree network
it, including all specific prefixes. This means that a packet underneath it, including all specific prefixes. This means that a
received from a node at the same or lower level whose destination is packet received from a node at the same or lower level whose
covered by one of those specific prefixes may be routed directly destination is covered by one of those specific prefixes may be
towards the node advertising that prefix rather than sending the routed directly towards the node advertising that prefix rather than
packet to a node at a higher level. sending the packet to a node at a higher level.
A node's Node S-TIEs, consisting of all node's adjacencies and prefix A node's Node South TIEs, consisting of all node's adjacencies and
S-TIEs limited to those related to default IP prefix and prefix South TIEs limited to those related to default IP prefix and
disaggregated prefixes, are flooded southbound in order to allow the disaggregated prefixes, are flooded southbound in order to allow the
nodes one level down to see connectivity of the higher level as well nodes one level down to see connectivity of the higher level as well
as reachability to the rest of the fabric. In order to allow an E-W as reachability to the rest of the fabric. In order to allow an E-W
disconnected node in a given level to receive the S-TIEs of other disconnected node in a given level to receive the South TIEs of other
nodes at its level, every *NODE* S-TIE is "reflected" northbound to nodes at its level, every *NODE* South TIE is "reflected" northbound
level from which it was received. It should be noted that East-West to level from which it was received. It should be noted that East-
links are included in South TIE flooding (except at ToF level); those West links are included in South TIE flooding (except at ToF level);
TIEs need to be flooded to satisfy algorithms in Section 5.2.4. In those TIEs need to be flooded to satisfy algorithms in Section 4.2.4.
that way nodes at same level can learn about each other without a In that way nodes at same level can learn about each other without a
lower level, e.g. in case of leaf level. The precise flooding scopes lower level, e.g. in case of leaf level. The precise, normative
are given in Table 3. Those rules govern as well what SHOULD be flooding scopes are given in Table 3. Those rules govern as well
included in TIDEs on the adjacency. Again, East-West flooding scopes what SHOULD be included in TIDEs on the adjacency. Again, East-West
are identical to South flooding scopes except in case of ToF East- flooding scopes are identical to South flooding scopes except in case
West links (rings) which are basically performing northbound of ToF East-West links (rings) which are basically performing
flooding. northbound flooding.
Node S-TIE "south reflection" allows to support positive Node South TIE "south reflection" allows to support positive
disaggregation on failures describes in Section 5.2.5 and flooding disaggregation on failures describes in Section 4.2.5 and flooding
reduction in Section 5.2.3.9. reduction in Section 4.2.3.9.
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| Type / | South | North | East-West | | Type / | South | North | East-West |
| Direction | | | | | Direction | | | |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| node | flood if level of | flood if | flood only if | | node | flood if level of | flood if | flood only if |
| S-TIE | originator is equal | level of | this node is | | South TIE | originator is equal | level of | this node is |
| | to this node | originator is | not ToF | | | to this node | originator is | not ToF |
| | | higher than | | | | | higher than | |
| | | this node | | | | | this node | |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| non-node | flood self- | flood only if | flood only if | | non-node | flood self- | flood only if | flood only if |
| S-TIE | originated only | neighbor is | self-originated | | South TIE | originated only | neighbor is | self-originated |
| | | originator of | and this node | | | | originator of | and this node |
| | | TIE | is not ToF | | | | TIE | is not ToF |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| all | never flood | flood always | flood only if | | all North | never flood | flood always | flood only if |
| N-TIEs | | | this node is | | TIEs | | | this node is |
| | | | ToF | | | | | ToF |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| TIDE | include at least | include at | if this node is | | TIDE | include at least all | include at | if this node is |
| | all non-self | least all | ToF then | | | non-self originated | least all | ToF then |
| | originated N-TIE | node S-TIEs | include all | | | North TIE headers | node South | include all |
| | headers and self- | and all | N-TIEs, | | | and self-originated | TIEs and all | North TIEs, |
| | originated S-TIE | S-TIEs | otherwise only | | | South TIE headers | South TIEs | otherwise only |
| | headers and node | originated by | self-originated | | | and node South TIEs | originated by | self-originated |
| | S-TIEs of nodes at | peer and all | TIEs | | | of nodes at same | peer and all | TIEs |
| | same level | N-TIEs | | | | level | North TIEs | |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| TIRE as | request all N-TIEs | request all | if this node is | | TIRE as | request all North | request all | if this node is |
| Request | and all peer's | S-TIEs | ToF then apply | | Request | TIEs and all peer's | South TIEs | ToF then apply |
| | self-originated | | North scope | | | self-originated TIEs | | North scope |
| | TIEs and all node | | rules, | | | and all node South | | rules, |
| | S-TIEs | | otherwise South | | | TIEs | | otherwise South |
| | | | scope rules | | | | | scope rules |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
| TIRE as | Ack all received | Ack all | Ack all | | TIRE as | Ack all received | Ack all | Ack all |
| Ack | TIEs | received TIEs | received TIEs | | Ack | TIEs | received TIEs | received TIEs |
+-----------+---------------------+---------------+-----------------+ +-----------+----------------------+---------------+-----------------+
Table 3: Flooding Scopes Table 3: Normative Flooding Scopes
If the TIDE includes additional TIE headers beside the ones If the TIDE includes additional TIE headers beside the ones
specified, the receiving neighbor must apply according filter to the specified, the receiving neighbor must apply according filter to the
received TIDE strictly and MUST NOT request the extra TIE headers received TIDE strictly and MUST NOT request the extra TIE headers
that were not allowed by the flooding scope rules in its direction. that were not allowed by the flooding scope rules in its direction.
As an example to illustrate these rules, consider using the topology As an example to illustrate these rules, consider using the topology
in Figure 2, with the optional link between spine 111 and spine 112, in Figure 2, with the optional link between spine 111 and spine 112,
and the associated TIEs given in Figure 14. The flooding from and the associated TIEs given in Figure 14. The flooding from
particular nodes of the TIEs is given in Table 4. particular nodes of the TIEs is given in Table 4.
+-------------+----------+------------------------------------------+ +-----------+----------+--------------------------------------------+
| Router | Neighbor | TIEs | | Router | Neighbor | TIEs |
| floods to | | | | floods to | | |
+-------------+----------+------------------------------------------+ +-----------+----------+--------------------------------------------+
| Leaf111 | Spine | Leaf111 N-TIEs, Spine 111 node S-TIE | | Leaf111 | Spine | Leaf111 North TIEs, Spine 111 node South |
| | 112 | | | | 112 | TIE |
| Leaf111 | Spine | Leaf111 N-TIEs, Spine 112 node S-TIE | | Leaf111 | Spine | Leaf111 North TIEs, Spine 112 node South |
| | 111 | | | | 111 | TIE |
| | | | | | | |
| Spine 111 | Leaf111 | Spine 111 S-TIEs | | Spine 111 | Leaf111 | Spine 111 South TIEs |
| Spine 111 | Leaf112 | Spine 111 S-TIEs | | Spine 111 | Leaf112 | Spine 111 South TIEs |
| Spine 111 | Spine | Spine 111 S-TIEs | | Spine 111 | Spine | Spine 111 South TIEs |
| | 112 | | | | 112 | |
| Spine 111 | Spine21 | Spine 111 N-TIEs, Leaf111 N-TIEs, | | Spine 111 | ToF 21 | Spine 111 North TIEs, Leaf111 North TIEs, |
| | | Leaf112 N-TIEs, Spine22 node S-TIE | | | | Leaf112 North TIEs, ToF 22 node South TIE |
| Spine 111 | Spine22 | Spine 111 N-TIEs, Leaf111 N-TIEs, | | Spine 111 | ToF 22 | Spine 111 North TIEs, Leaf111 North TIEs, |
| | | Leaf112 N-TIEs, Spine21 node S-TIE | | | | Leaf112 North TIEs, ToF 21 node South TIE |
| | | | | | | |
| ... | ... | ... | | ... | ... | ... |
| Spine21 | Spine | Spine21 S-TIEs | | ToF 21 | Spine | ToF 21 South TIEs |
| | 111 | | | | 111 | |
| Spine21 | Spine | Spine21 S-TIEs | | ToF 21 | Spine | ToF 21 South TIEs |
| | 112 | | | | 112 | |
| Spine21 | Spine | Spine21 S-TIEs | | ToF 21 | Spine | ToF 21 South TIEs |
| | 121 | | | | 121 | |
| Spine21 | Spine | Spine21 S-TIEs | | ToF 21 | Spine | ToF 21 South TIEs |
| | 122 | | | | 122 | |
| ... | ... | ... | | ... | ... | ... |
+-------------+----------+------------------------------------------+ +-----------+----------+--------------------------------------------+
Table 4: Flooding some TIEs from example topology Table 4: Flooding some TIEs from example topology
5.2.3.5. 'Flood Only Node TIEs' Bit 4.2.3.5. 'Flood Only Node TIEs' Bit
RIFT includes an optional ECN mechanism to prevent "flooding inrush" RIFT includes an optional ECN mechanism to prevent "flooding inrush"
on restart or bring-up with many southbound neighbors. A node MAY on restart or bring-up with many southbound neighbors. A node MAY
set on its LIEs the according bit to indicate to the neighbor that it set on its LIEs the according bit to indicate to the neighbor that it
should temporarily flood node TIEs only to it. It should only set it should temporarily flood node TIEs only to it. It SHOULD only set it
in the southbound direction. The receiving node SHOULD accomodate in the southbound direction. The receiving node SHOULD accomodate
the request to lessen the flooding load on the affected node if south the request to lessen the flooding load on the affected node if south
of the sender and SHOULD ignore the bit if northbound. of the sender and SHOULD ignore the bit if northbound.
Obviously this mechanism is most useful in southbound direction. The Obviously this mechanism is most useful in southbound direction. The
distribution of node TIEs guarantees correct behavior of algorithms distribution of node TIEs guarantees correct behavior of algorithms
like disaggregation or default route origination. Furthermore like disaggregation or default route origination. Furthermore
though, the use of this bit presents an inherent trade-off between though, the use of this bit presents an inherent trade-off between
processing load and convergence speed since suppressing flooding of processing load and convergence speed since suppressing flooding of
northbound prefixes from neighbors will lead to blackholes. northbound prefixes from neighbors will lead to blackholes.
5.2.3.6. Initial and Periodic Database Synchronization 4.2.3.6. Initial and Periodic Database Synchronization
The initial exchange of RIFT is modeled after ISIS with TIDE being The initial exchange of RIFT is modeled after ISIS with TIDE being
equivalent to CSNP and TIRE playing the role of PSNP. The content of equivalent to CSNP and TIRE playing the role of PSNP. The content of
TIDEs and TIREs is governed by Table 3. TIDEs and TIREs is governed by Table 3.
5.2.3.7. Purging and Roll-Overs 4.2.3.7. Purging and Roll-Overs
RIFT does not purge information that has been distributed by the RIFT does not purge information that has been distributed by the
protocol. Purging mechanisms in other routing protocols have proven protocol. Purging mechanisms in other routing protocols have proven
to be complex and fragile over many years of experience. Abundant to be complex and fragile over many years of experience. Abundant
amounts of memory are available today even on low-end platforms. The amounts of memory are available today even on low-end platforms. The
information will age out and all computations will deliver correct information will age out and all computations will deliver correct
results if a node leaves the network due to the new information results if a node leaves the network due to the new information
distributed by its adjacent nodes. distributed by its adjacent nodes.
Once a RIFT node issues a TIE with an ID, it MUST preserve the ID as Once a RIFT node issues a TIE with an ID, it MUST preserve the ID as
skipping to change at page 43, line 5 skipping to change at page 54, line 7
the nodes that are within the TIE's flooding scope. the nodes that are within the TIE's flooding scope.
TIE sequence numbers are rolled over using the method described in TIE sequence numbers are rolled over using the method described in
Appendix A. First sequence number of any spontaneously originated Appendix A. First sequence number of any spontaneously originated
TIE (i.e. not originated to override a detected older copy in the TIE (i.e. not originated to override a detected older copy in the
network) MUST be a reasonbly unpredictable random number in the network) MUST be a reasonbly unpredictable random number in the
interval [0, 2^10-1] which will prevent otherwise identical TIE interval [0, 2^10-1] which will prevent otherwise identical TIE
headers to remain "stuck" in the network with content different from headers to remain "stuck" in the network with content different from
TIE originated after reboot. TIE originated after reboot.
5.2.3.8. Southbound Default Route Origination 4.2.3.8. Southbound Default Route Origination
Under certain conditions nodes issue a default route in their South Under certain conditions nodes issue a default route in their South
Prefix TIEs with costs as computed in Section 5.3.6.1. Prefix TIEs with costs as computed in Section 4.3.6.1.
A node X that A node X that
1. is NOT overloaded AND 1. is NOT overloaded AND
2. has southbound or East-West adjacencies 2. has southbound or East-West adjacencies
originates in its south prefix TIE such a default route IIF originates in its south prefix TIE such a default route IIF
1. all other nodes at X's' level are overloaded OR 1. all other nodes at X's' level are overloaded OR
2. all other nodes at X's' level have NO northbound adjacencies OR 2. all other nodes at X's' level have NO northbound adjacencies OR
3. X has computed reachability to a default route during N-SPF. 3. X has computed reachability to a default route during N-SPF.
The term "all other nodes at X's' level" describes obviously just the The term "all other nodes at X's' level" describes obviously just the
nodes at the same level in the PoD with a viable lower level nodes at the same level in the PoD with a viable lower level
(otherwise the node S-TIEs cannot be reflected and the nodes in e.g. (otherwise the node South TIEs cannot be reflected and the nodes in
PoD 1 and PoD 2 are "invisible" to each other). e.g. PoD 1 and PoD 2 are "invisible" to each other).
A node originating a southbound default route MUST install a default A node originating a southbound default route MUST install a default
discard route if it did not compute a default route during N-SPF. discard route if it did not compute a default route during N-SPF.
5.2.3.9. Northbound TIE Flooding Reduction 4.2.3.9. Northbound TIE Flooding Reduction
Section 1.4 of the Optimized Link State Routing Protocol [RFC3626] Section 1.4 of the Optimized Link State Routing Protocol [RFC3626]
(OLSR) introduces the concept of a "multipoint relay" (MPR) that (OLSR) introduces the concept of a "multipoint relay" (MPR) that
minimize the overhead of flooding messages in the network by reducing minimize the overhead of flooding messages in the network by reducing
redundant retransmissions in the same region. redundant retransmissions in the same region.
A similar technique is applied to RIFT to control northbound A similar technique is applied to RIFT to control northbound
flooding. Important observations first: flooding. Important observations first:
1. a node MUST flood self-originated N-TIEs to all the reachable 1. a node MUST flood self-originated North TIEs to all the reachable
nodes at the level above which we call the node's "parents"; nodes at the level above which we call the node's "parents";
2. it is typically not necessary that all parents reflood the N-TIEs 2. it is typically not necessary that all parents reflood the North
to achieve a complete flooding of all the reachable nodes two TIEs to achieve a complete flooding of all the reachable nodes
levels above which we choose to call the node's "grandparents"; two levels above which we choose to call the node's
"grandparents";
3. to control the volume of its flooding two hops North and yet keep 3. to control the volume of its flooding two hops North and yet keep
it robust enough, it is advantageous for a node to select a it robust enough, it is advantageous for a node to select a
subset of its parents as "Flood Repeaters" (FRs), which combined subset of its parents as "Flood Repeaters" (FRs), which combined
together deliver two or more copies of its flooding to all of its together deliver two or more copies of its flooding to all of its
parents, i.e. the originating node's grandparents; parents, i.e. the originating node's grandparents;
4. nodes at the same level do NOT have to agree on a specific 4. nodes at the same level do NOT have to agree on a specific
algorithm to select the FRs, but overall load balancing should be algorithm to select the FRs, but overall load balancing should be
achieved so that different nodes at the same level should tend to achieved so that different nodes at the same level should tend to
skipping to change at page 44, line 44 skipping to change at page 55, line 48
arbitrary parent as FR and then a second one for redundancy. The arbitrary parent as FR and then a second one for redundancy. The
computation can be kept relatively simple and completely distributed computation can be kept relatively simple and completely distributed
without any need for synchronization amongst nodes. In a "PoD" without any need for synchronization amongst nodes. In a "PoD"
structure, where the Level L+2 is partitioned in silos of equivalent structure, where the Level L+2 is partitioned in silos of equivalent
grandparents that are only reachable from respective parents, this grandparents that are only reachable from respective parents, this
means treating each silo as a fully connected Clos Network and solve means treating each silo as a fully connected Clos Network and solve
the problem within the silo. the problem within the silo.
In terms of signaling, a node has enough information to select its In terms of signaling, a node has enough information to select its
set of FRs; this information is derived from the node's parents' Node set of FRs; this information is derived from the node's parents' Node
S-TIEs, which indicate the parent's reachable northbound adjacencies South TIEs, which indicate the parent's reachable northbound
to its own parents, i.e. the node's grandparents. A node may send a adjacencies to its own parents, i.e. the node's grandparents. A node
LIE to a northbound neighbor with the optional boolean field may send a LIE to a northbound neighbor with the optional boolean
`you_are_flood_repeater` set to false, to indicate that the field `you_are_flood_repeater` set to false, to indicate that the
northbound neighbor is not a flood repeater for the node that sent northbound neighbor is not a flood repeater for the node that sent
the LIE. In that case the northbound neighbor SHOULD NOT reflood the LIE. In that case the northbound neighbor SHOULD NOT reflood
northbound TIEs received from the node that sent the LIE. If the northbound TIEs received from the node that sent the LIE. If the
`you_are_flood_repeater` is absent or if `you_are_flood_repeater` is `you_are_flood_repeater` is absent or if `you_are_flood_repeater` is
set to true, then the northbound neighbor is a flood repeater for the set to true, then the northbound neighbor is a flood repeater for the
node that sent the LIE and MUST reflood northbound TIEs received from node that sent the LIE and MUST reflood northbound TIEs received from
that node. that node.
This specification proposes a simple default algorithm that SHOULD be This specification proposes a simple default algorithm that SHOULD be
implemented and used by default on every RIFT node. implemented and used by default on every RIFT node.
skipping to change at page 46, line 5 skipping to change at page 57, line 8
The algorithm consists of the following steps: The algorithm consists of the following steps:
1. Derive a 64-bits number by XOR'ing 'N's system ID with RND. 1. Derive a 64-bits number by XOR'ing 'N's system ID with RND.
2. Derive a 16-bits pseudo-random unsigned integer PR(N) from the 2. Derive a 16-bits pseudo-random unsigned integer PR(N) from the
resulting 64-bits number by splitting it in 16-bits-long words resulting 64-bits number by splitting it in 16-bits-long words
W1, W2, W3, W4 (where W1 are the least significant 16 bits of the W1, W2, W3, W4 (where W1 are the least significant 16 bits of the
64-bits number, and W4 are the most significant 16 bits) and then 64-bits number, and W4 are the most significant 16 bits) and then
XOR'ing the circularly shifted resulting words together: XOR'ing the circularly shifted resulting words together:
(W1<<1) xor (W2<<2) xor (W3<<3) xor (W4<<4); A. (W1<<1) xor (W2<<2) xor (W3<<3) xor (W4<<4);
where << is the circular shift operator. where << is the circular shift operator.
3. Sort the parents by decreasing number of northbound adjacencies 3. Sort the parents by decreasing number of northbound adjacencies
(using decreasing system id of the parent as tie-breaker): (using decreasing system id of the parent as tie-breaker):
sort |P(N) by decreasing CN(P), for all P in |P(N), as ordered sort |P(N) by decreasing CN(P), for all P in |P(N), as ordered
array |A(N) array |A(N)
4. Partition |A(N) in subarrays |A_k(N) of parents with equivalent 4. Partition |A(N) in subarrays |A_k(N) of parents with equivalent
cardinality of northbound adjacencies (in other words with cardinality of northbound adjacencies (in other words with
equivalent number of grandparents they can reach): equivalent number of grandparents they can reach):
1. set k=0; // k is the ID of the subarrray A. set k=0; // k is the ID of the subarrray
2. set i=0; B. set i=0;
3. while i < CN(N) do C. while i < CN(N) do
1. set j=i; i) set j=i;
2. while i < CN(N) and CN(|A(N)[j]) - CN(|A(N)[i]) <= S ii) while i < CN(N) and CN(|A(N)[j]) - CN(|A(N)[i]) <= S
1. place |A(N)[i] in |A_k(N) // abstract action, maybe a. place |A(N)[i] in |A_k(N) // abstract action,
noop maybe noop
2. set i=i+1; b. set i=i+1;
3. /* At this point j is the index in |A(N) of the first iii) /* At this point j is the index in |A(N) of the first
member of |A_k(N) and (i-j) is C_k(N) defined as the member of |A_k(N) and (i-j) is C_k(N) defined as the
cardinality of |A_k(N) */ cardinality of |A_k(N) */
4. set k=k+1; set k=k+1;
4. /* At this point k is the total number of subarrays, /* At this point k is the total number of subarrays, initialized
initialized for the shuffling operation below */ for the shuffling operation below */
5. shuffle individually each subarrays |A_k(N) of cardinality C_k(N) 5. shuffle individually each subarrays |A_k(N) of cardinality C_k(N)
within |A(N) using the Durstenfeld variation of Fisher-Yates within |A(N) using the Durstenfeld variation of Fisher-Yates
algorithm that depends on N's System ID: algorithm that depends on N's System ID:
1. while k > 0 do A. while k > 0 do
1. for i from C_k(N)-1 to 1 decrementing by 1 do
1. set j to PR(N) modulo i; i) for i from C_k(N)-1 to 1 decrementing by 1 do
a. set j to PR(N) modulo i;
2. exchange |A_k[j] and |A_k[i]; b. exchange |A_k[j] and |A_k[i];
2. set k=k-1; ii) set k=k-1;
6. For each grandparent G, initialize a counter c(G) with the number 6. For each grandparent G, initialize a counter c(G) with the number
of its south-bound adjacencies to elected flood repeaters (which of its south-bound adjacencies to elected flood repeaters (which
is initially zero): is initially zero):
1. for each G in |G(N) set c(G) = 0; A. for each G in |G(N) set c(G) = 0;
7. Finally keep as FRs only parents that are needed to maintain the 7. Finally keep as FRs only parents that are needed to maintain the
number of adjacencies between the FRs and any grandparent G equal number of adjacencies between the FRs and any grandparent G equal
or above the redundancy constant R: or above the redundancy constant R:
1. for each P in reshuffled |A(N); A. for each P in reshuffled |A(N);
1. if there exists an adjacency ADJ(P, G) in |NA(P) such i) if there exists an adjacency ADJ(P, G) in |NA(P) such
that c(G) < R then that c(G) < R then
1. place P in FR set; a. place P in FR set;
2. for all adjacencies ADJ(P, G') in |NA(P) increment b. for all adjacencies ADJ(P, G') in |NA(P) increment
c(G') c(G')
2. If any c(G) is still < R, it was not possible to elect a set B. If any c(G) is still < R, it was not possible to elect a set
of FRs that covers all grandparents with redundancy R of FRs that covers all grandparents with redundancy R
Additional rules for flooding reduction: Additional rules for flooding reduction:
1. The algorithm MUST be re-evaluated by a node on every change of 1. The algorithm MUST be re-evaluated by a node on every change of
local adjacencies or reception of a parent S-TIE with changed local adjacencies or reception of a parent South TIE with changed
adjacencies. A node MAY apply a hysteresis to prevent excessive adjacencies. A node MAY apply a hysteresis to prevent excessive
amount of computation during periods of network instability just amount of computation during periods of network instability just
like in case of reachability computation. like in case of reachability computation.
2. A node SHOULD send out LIEs that grant flood repeater status 2. A node SHOULD send out LIEs that grant flood repeater status
before LIEs that revoke it on flood repeater set changes to before LIEs that revoke it on flood repeater set changes to
prevent transient behavior where the full coverage of grand prevent transient behavior where the full coverage of grand
parents is not guaranteed. Albeit the condition will correct in parents is not guaranteed. Albeit the condition will correct in
positively stable manner due to LIE retransmission and periodic positively stable manner due to LIE retransmission and periodic
TIDEs, it can slow down flooding convergence on flood repeater TIDEs, it can slow down flooding convergence on flood repeater
status changes. status changes.
3. A node always floods its self-originated TIEs. 3. A node MUST always flood its self-originated TIEs.
4. A node receiving a TIE originated by a node for which it is not a 4. A node receiving a TIE originated by a node for which it is not a
flood repeater does NOT re-flood such TIEs to its neighbors flood repeater does NOT re-flood such TIEs to its neighbors
except for rules in Paragraph 6. except for rules in Paragraph 6.
5. The indication of flood reduction capability is carried in the 5. The indication of flood reduction capability MUST be carried in
node TIEs and can be used to optimize the algorithm to account the node TIEs and CAN be used to optimize the algorithm to
for nodes that will flood regardless. account for nodes that will flood regardless.
6. A node generates TIDEs as usual but when receiving TIREs or TIDEs 6. A node generates TIDEs as usual but when receiving TIREs or TIDEs
resulting in requests for a TIE of which the newest received copy resulting in requests for a TIE of which the newest received copy
came on an adjacency where the node was not flood repeater it came on an adjacency where the node was not flood repeater it
SHOULD ignore such requests on first and first request ONLY. SHOULD ignore such requests on first and first request ONLY.
Normally, the nodes that received the TIEs as flooding repeaters Normally, the nodes that received the TIEs as flooding repeaters
should satisfy the requesting node and with that no further TIREs should satisfy the requesting node and with that no further TIREs
for such TIEs will be generated. Otherwise, the next set of for such TIEs will be generated. Otherwise, the next set of
TIDEs and TIREs MUST lead to flooding independent of the flood TIDEs and TIREs MUST lead to flooding independent of the flood
repeater status. This solves a very difficult incast problem on repeater status. This solves a very difficult incast problem on
nodes restarting with a very wide fanout, especially northbound. nodes restarting with a very wide fanout, especially northbound.
To retrieve the full database they often end up processing many To retrieve the full database they often end up processing many
in-rushing copies whereas this approach should load-balance the in-rushing copies whereas this approach should load-balance the
incoming database between adjacent nodes and flood repeaters incoming database between adjacent nodes and flood repeaters
should guarantee that two copies are sent by different nodes to should guarantee that two copies are sent by different nodes to
ensure against any losses. ensure against any losses.
7. Obviously sine flooding reduction does NOT apply to self 4.2.3.10. Special Considerations
originated TIEs and since all policy-guided information consists
of self-originated TIEs those are unaffected.
5.2.3.10. Special Considerations
First, due to the distributed, asynchronous nature of ZTP, it can First, due to the distributed, asynchronous nature of ZTP, it can
create temporary convergence anomalies where nodes at higher levels create temporary convergence anomalies where nodes at higher levels
of the fabric temporarily see themselves lower than they belong. of the fabric temporarily see themselves lower than they belong.
Since flooding can begin before ZTP is "finished" and in fact must do Since flooding can begin before ZTP is "finished" and in fact must do
so given there is no global termination criteria, information may end so given there is no global termination criteria, information may end
up in wrong layers. A special clause when changing level takes care up in wrong layers. A special clause when changing level takes care
of that. of that.
More difficult is a condition where a node floods a TIE north towards More difficult is a condition where a node floods a TIE north towards
a super-spine, then its spine reboots, in fact partitioning a super-spine, then its spine reboots, in fact partitioning
superspine from it directly and then the node itself reboots. That superspine from it directly and then the node itself reboots. That
leaves in a sense the super-spine holding the "primary copy" of the leaves in a sense the super-spine holding the "primary copy" of the
node's TIE. Normally this condition is resolved easily by the node node's TIE. Normally this condition is resolved easily by the node
re-originating its TIE with a higher sequence number than it sees in re-originating its TIE with a higher sequence number than it sees in
northbound TIEs, here however, when spine comes back it won't be able northbound TIEs, here however, when spine comes back it won't be able
to obtain a N-TIE from its superspine easily and with that the node to obtain a North TIE from its superspine easily and with that the
below may issue the same version of the TIE with a lower sequence node below may issue the same version of the TIE with a lower
number. Flooding procedures are are extended to deal with the sequence number. Flooding procedures are extended to deal with the
problem by the means of special clauses that override the database of problem by the means of special clauses that override the database of
a lower level with headers of newer TIEs seen in TIDEs coming from a lower level with headers of newer TIEs seen in TIDEs coming from
the north. the north.
5.2.4. Reachability Computation 4.2.4. Reachability Computation
A node has three sources of relevant information. A node knows the A node has three possible sources of relevant information for
full topology south from the received N-TIEs. A node has the set of reachability computation. A node knows the full topology south of it
prefixes with associated distances and bandwidths from received from the received North Node TIEs or alternately north of it from the
S-TIEs. South Node TIEs. A node has the set of prefixes with their
associated distances and bandwidths from corresponding prefix TIEs.
To compute reachability, a node runs conceptually a northbound and a To compute prefix reachability, a node runs conceptually a northbound
southbound SPF. We call that N-SPF and S-SPF. and a southbound SPF. We call that N-SPF and S-SPF denoting the
direction in which the computation front is progressing.
Since neither computation can "loop", it is possible to compute non- Since neither computation can "loop", it is possible to compute non-
equal-cost or even k-shortest paths [EPPSTEIN] and "saturate" the equal-cost or even k-shortest paths [EPPSTEIN] and "saturate" the
fabric to the extent desired but we use simple, familiar SPF fabric to the extent desired but we use simple, familiar SPF
algorithms and concepts here due to their prevalence in today's algorithms and concepts here as example due to their prevalence in
routing. today's routing.
5.2.4.1. Northbound SPF 4.2.4.1. Northbound SPF
N-SPF uses northbound and East-West adjacencies in the computing N-SPF MUST use ONLY northbound and East-West adjacencies in the
node's node N-TIEs (since if the node is a leaf it may not have computing node's node North TIEs (since if the node is a leaf it may
generated a node S-TIE) when starting Dijkstra. Observe that N-SPF not have generated a node South TIE) when starting SPF. Observe that
is really just a one hop variety since Node S-TIEs are not re-flooded N-SPF is really just a one hop variety since Node South TIEs are not
southbound beyond a single level (or East-West) and with that the re-flooded southbound beyond a single level (or East-West) and with
computation cannot progress beyond adjacent nodes. that the computation cannot progress beyond adjacent nodes.
Once progressing, we are using the next level's node S-TIEs to find Once progressing, we are using the next higher level's node South
according adjacencies to verify backlink connectivity. Just as in TIEs to find according adjacencies to verify backlink connectivity.
case of IS-IS or OSPF, two unidirectional links are associated Just as in case of IS-IS or OSPF, two unidirectional links MUST be
together to confirm bidirectional connectivity. Particular care MUST associated together to confirm bidirectional connectivity.
be paid that the Node TIEs do not only contain the correct system IDs Particular care MUST be paid that the Node TIEs do not only contain
but matching levels as well. the correct system IDs but matching levels as well.
Default route found when crossing an E-W link is used IIF Default route found when crossing an E-W link SHOULD be used IIF
1. the node itself does NOT have any northbound adjacencies AND 1. the node itself does NOT have any northbound adjacencies AND
2. the adjacent node has one or more northbound adjacencies 2. the adjacent node has one or more northbound adjacencies
This rule forms a "one-hop default route split-horizon" and prevents This rule forms a "one-hop default route split-horizon" and prevents
looping over default routes while allowing for "one-hop protection" looping over default routes while allowing for "one-hop protection"
of nodes that lost all northbound adjacencies except at Top-of-Fabric of nodes that lost all northbound adjacencies except at Top-of-Fabric
where the links are used exclusively to flood topology information in where the links are used exclusively to flood topology information in
multi-plane designs. multi-plane designs.
skipping to change at page 50, line 13 skipping to change at page 61, line 15
default prefix AND default prefix AND
2. the node does not originate a non-default supersuming prefix 2. the node does not originate a non-default supersuming prefix
itself. itself.
i.e. the E-W link can be used as a gateway of last resort for a i.e. the E-W link can be used as a gateway of last resort for a
specific prefix only. Using south prefixes across E-W link can be specific prefix only. Using south prefixes across E-W link can be
beneficial e.g. on automatic de-aggregation in pathological fabric beneficial e.g. on automatic de-aggregation in pathological fabric
partitioning scenarios. partitioning scenarios.
A detailed example can be found in Section 6.4. A detailed example can be found in Section 5.4.
5.2.4.2. Southbound SPF 4.2.4.2. Southbound SPF
S-SPF uses only the southbound adjacencies in the node S-TIEs, i.e. S-SPF MUST use ONLY the southbound adjacencies in the node South
progresses towards nodes at lower levels. Observe that E-W TIEs, i.e. progresses towards nodes at lower levels. Observe that
adjacencies are NEVER used in the computation. This enforces the E-W adjacencies are NEVER used in the computation. This enforces the
requirement that a packet traversing in a southbound direction must requirement that a packet traversing in a southbound direction must
never change its direction. never change its direction.
S-SPF uses northbound adjacencies in node N-TIEs to verify backlink S-SPF MUST use northbound adjacencies in node North TIEs to verify
connectivity. backlink connectivity by checking for presence of the link beside
correct SystemID and level.
5.2.4.3. East-West Forwarding Within a non-ToF Level
Ultimately, it should be observed that in presence of a "ring" of E-W 4.2.4.3. East-West Forwarding Within a non-ToF Level
links in any level (except ToF level) neither SPF will provide a
"ring protection" scheme since such a computation would have to deal
necessarily with breaking of "loops" in generic Dijkstra sense; an
application for which RIFT is not intended. It is outside the scope
of this document how an underlay can be used to provide a full-mesh
connectivity between nodes in the same level that would allow for
N-SPF to provide protection for a single node loosing all its
northbound adjacencies (as long as any of the other nodes in the
level are northbound connected).
Using south prefixes over horizontal links is optional and can Using south prefixes over horizontal links MAY occur if the N-SPF
protect against pathological fabric partitioning cases that leave includes East-West adjacencies in computation. It can protect
only paths to destinations that would necessitate multiple changes of against pathological fabric partitioning cases that leave only paths
forwarding direction between north and south. to destinations that would necessitate multiple changes of forwarding
direction between north and south.
5.2.4.4. East-West Links Within ToF Level 4.2.4.4. East-West Links Within ToF Level
E-W ToF links behave in terms of flooding scopes defined in E-W ToF links behave in terms of flooding scopes defined in
Section 5.2.3.4 like northbound links. Even though a ToF node could Section 4.2.3.4 like northbound links and MUST be used for control
be tempted to use those links during southbound SPF this MUST NOT be plane information flooding ONLY. Even though a ToF node could be
attempted since it may lead in, e.g. anycast cases to routing loops. tempted to use those links during southbound SPF and carry traffic
An implemention could try to resolve the looping problem by following over them this MUST NOT be attempted since it may lead in, e.g.
on the ring strictly tie-broken shortest-paths only but the details anycast cases to routing loops. An implemention MAY try to resolve
are outside this specification. And even then, the problem of proper the looping problem by following on the ring strictly tie-broken
capacity provisioning of such links when they become traffic-bearing shortest-paths only but the details are outside this specification.
in case of failures is vexing. And even then, the problem of proper capacity provisioning of such
links when they become traffic-bearing in case of failures is vexing.
5.2.5. Automatic Disaggregation on Link & Node Failures 4.2.5. Automatic Disaggregation on Link & Node Failures
5.2.5.1. Positive, Non-transitive Disaggregation 4.2.5.1. Positive, Non-transitive Disaggregation
Under normal circumstances, node's S-TIEs contain just the Under normal circumstances, node's South TIEs contain just the
adjacencies and a default route. However, if a node detects that its adjacencies and a default route. However, if a node detects that its
default IP prefix covers one or more prefixes that are reachable default IP prefix covers one or more prefixes that are reachable
through it but not through one or more other nodes at the same level, through it but not through one or more other nodes at the same level,
then it MUST explicitly advertise those prefixes in an S-TIE. then it MUST explicitly advertise those prefixes in an South TIE.
Otherwise, some percentage of the northbound traffic for those Otherwise, some percentage of the northbound traffic for those
prefixes would be sent to nodes without according reachability, prefixes would be sent to nodes without according reachability,
causing it to be black-holed. Even when not black-holing, the causing it to be black-holed. Even when not black-holing, the
resulting forwarding could 'backhaul' packets through the higher resulting forwarding could 'backhaul' packets through the higher
level spines, clearly an undesirable condition affecting the blocking level spines, clearly an undesirable condition affecting the blocking
probabilities of the fabric. probabilities of the fabric.
We refer to the process of advertising additional prefixes southbound We refer to the process of advertising additional prefixes southbound
as 'positive de-aggregation' or 'positive dis-aggregation'. Such as 'positive de-aggregation' or 'positive dis-aggregation'. Such
dis-aggregation is non-transitive, i.e. its' effects are always dis-aggregation is non-transitive, i.e. its' effects are always
contained to a single level of the fabric only. Naturally, multiple contained to a single level of the fabric only. Naturally, multiple
node or link failures can lead to several independent instances of node or link failures can lead to several independent instances of
positive dis-aggregation necessary to prevent looping or bow-tying positive dis-aggregation necessary to prevent looping or bow-tying
the fabric. the fabric.
A node determines the set of prefixes needing de-aggregation using A node determines the set of prefixes needing de-aggregation using
the following steps: the following steps:
1. A DAG computation in the southern direction is performed first, 1. A DAG computation in the southern direction is performed first,
i.e. the N-TIEs are used to find all of prefixes it can reach and i.e. the North TIEs are used to find all of prefixes it can reach
the set of next-hops in the lower level for each of them. Such a and the set of next-hops in the lower level for each of them.
computation can be easily performed on a fat tree by e.g. setting Such a computation can be easily performed on a fat tree by e.g.
all link costs in the southern direction to 1 and all northern setting all link costs in the southern direction to 1 and all
directions to infinity. We term set of those prefixes |R, and northern directions to infinity. We term set of those
for each prefix, r, in |R, we define its set of next-hops to prefixes |R, and for each prefix, r, in |R, we define its set of
be |H(r). next-hops to be |H(r).
2. The node uses reflected S-TIEs to find all nodes at the same 2. The node uses reflected South TIEs to find all nodes at the same
level in the same PoD and the set of southbound adjacencies for level in the same PoD and the set of southbound adjacencies for
each. The set of nodes at the same level is termed |N and for each. The set of nodes at the same level is termed |N and for
each node, n, in |N, we define its set of southbound adjacencies each node, n, in |N, we define its set of southbound adjacencies
to be |A(n). to be |A(n).
3. For a given r, if the intersection of |H(r) and |A(n), for any n, 3. For a given r, if the intersection of |H(r) and |A(n), for any n,
is null then that prefix r must be explicitly advertised by the is null then that prefix r must be explicitly advertised by the
node in an S-TIE. node in an South TIE.
4. Identical set of de-aggregated prefixes is flooded on each of the 4. Identical set of de-aggregated prefixes is flooded on each of the
node's southbound adjacencies. In accordance with the normal node's southbound adjacencies. In accordance with the normal
flooding rules for an S-TIE, a node at the lower level that flooding rules for an South TIE, a node at the lower level that
receives this S-TIE will not propagate it south-bound. Neither receives this South TIE SHOULD NOT propagate it south-bound or
is it necessary for the receiving node to reflect the reflect the disaggregated prefixes back over its adjacencies to
disaggregated prefixes back over its adjacencies to nodes at the nodes at the level from which it was received.
level from which it was received.
To summarize the above in simplest terms: if a node detects that its To summarize the above in simplest terms: if a node detects that its
default route encompasses prefixes for which one of the other nodes default route encompasses prefixes for which one of the other nodes
in its level has no possible next-hops in the level below, it has to in its level has no possible next-hops in the level below, it has to
disaggregate it to prevent black-holing or suboptimal routing through disaggregate it to prevent black-holing or suboptimal routing through
such nodes. Hence a node X needs to determine if it can reach a such nodes. Hence a node X needs to determine if it can reach a
different set of south neighbors than other nodes at the same level, different set of south neighbors than other nodes at the same level,
which are connected to it via at least one common south neighbor. If which are connected to it via at least one common south neighbor. If
it can, then prefix disaggregation may be required. If it can't, it can, then prefix disaggregation may be required. If it can't,
then no prefix disaggregation is needed. An example of then no prefix disaggregation is needed. An example of
disaggregation is provided in Section 6.3. disaggregation is provided in Section 5.3.
A possible algorithm is described last: A possible algorithm is described last:
1. Create partial_neighbors = (empty), a set of neighbors with 1. Create partial_neighbors = (empty), a set of neighbors with
partial connectivity to the node X's level from X's perspective. partial connectivity to the node X's level from X's perspective.
Each entry is a list of south neighbor of X and a list of nodes Each entry in the set is a south neighbor of X and a list of
of X.level that can't reach that neighbor. nodes of X.level that can't reach that neighbor.
2. A node X determines its set of southbound neighbors 2. A node X determines its set of southbound neighbors
X.south_neighbors. X.south_neighbors.
3. For each S-TIE originated from a node Y that X has which is at 3. For each South TIE originated from a node Y that X has which is
X.level, if Y.south_neighbors is not the same as at X.level, if Y.south_neighbors is not the same as
X.south_neighbors but the nodes share at least one southern X.south_neighbors but the nodes share at least one southern
neighbor, for each neighbor N in X.south_neighbors but not in neighbor, for each neighbor N in X.south_neighbors but not in
Y.south_neighbors, add (N, (Y)) to partial_neighbors if N isn't Y.south_neighbors, add (N, (Y)) to partial_neighbors if N isn't
there or add Y to the list for N. there or add Y to the list for N.
4. If partial_neighbors is empty, then node X does not to 4. If partial_neighbors is empty, then node X does not disaggregate
disaggregate any prefixes. If node X is advertising any prefixes. If node X is advertising disaggregated prefixes in
disaggregated prefixes in its S-TIE, X SHOULD remove them and re- its South TIE, X SHOULD remove them and re-advertise its
advertise its according S-TIEs. according South TIEs.
A node X computes reachability to all nodes below it based upon the A node X computes reachability to all nodes below it based upon the
received N-TIEs first. This results in a set of routes, each received North TIEs first. This results in a set of routes, each
categorized by (prefix, path_distance, next-hop-set). Alternately, categorized by (prefix, path_distance, next-hop-set). Alternately,
for clarity in the following procedure, these can be organized by for clarity in the following procedure, these can be organized by
next-hop-set as ( (next-hops), {(prefix, path_distance)}). If next-hop-set as ( (next-hops), {(prefix, path_distance)}). If
partial_neighbors isn't empty, then the following procedure describes partial_neighbors isn't empty, then the following procedure describes
how to identify prefixes to disaggregate. how to identify prefixes to disaggregate.
disaggregated_prefixes = { empty } disaggregated_prefixes = { empty }
nodes_same_level = { empty } nodes_same_level = { empty }
for each S-TIE for each South TIE
if (S-TIE.level == X.level and if (South TIE.level == X.level and
X shares at least one S-neighbor with X) X shares at least one S-neighbor with X)
add S-TIE.originator to nodes_same_level add South TIE.originator to nodes_same_level
end if end if
end for end for
for each next-hop-set NHS for each next-hop-set NHS
isolated_nodes = nodes_same_level isolated_nodes = nodes_same_level
for each NH in NHS for each NH in NHS
if NH in partial_neighbors if NH in partial_neighbors
isolated_nodes = intersection(isolated_nodes, isolated_nodes = intersection(isolated_nodes,
partial_neighbors[NH].nodes) partial_neighbors[NH].nodes)
end if end if
end for end for
if isolated_nodes is not empty if isolated_nodes is not empty
for each prefix using NHS for each prefix using NHS
add (prefix, distance) to disaggregated_prefixes add (prefix, distance) to disaggregated_prefixes
end for end for
end if end if
end for end for
copy disaggregated_prefixes to X's S-TIE copy disaggregated_prefixes to X's South TIE
if X's S-TIE is different if X's South TIE is different
schedule S-TIE for flooding schedule South TIE for flooding
end if end if
Figure 15: Computation of Disaggregated Prefixes Figure 15: Computation of Disaggregated Prefixes
Each disaggregated prefix is sent with the according path_distance. Each disaggregated prefix is sent with the according path_distance.
This allows a node to send the same S-TIE to each south neighbor. This allows a node to send the same South TIE to each south neighbor.
The south neighbor which is connected to that prefix will thus have a The south neighbor which is connected to that prefix will thus have a
shorter path. shorter path.
Finally, to summarize the less obvious points partially omitted in Finally, to summarize the less obvious points partially omitted in
the algorithms to keep them more tractable: the algorithms to keep them more tractable:
1. all neighbor relationships MUST perform backlink checks. 1. all neighbor relationships MUST perform backlink checks.
2. overload bits as introduced in Section 5.3.1 have to be respected 2. overload bits as introduced in Section 4.3.1 have to be respected
during the computation. during the computation.
3. all the lower level nodes are flooded the same disaggregated 3. all the lower level nodes are flooded the same disaggregated
prefixes since we don't want to build an S-TIE per node and prefixes since we don't want to build an South TIE per node and
complicate things unnecessarily. The PoD containing the prefix complicate things unnecessarily. The lower level node that can
will prefer southbound anyway. compute a southbound route to the prefix will prefer it to the
disaggregated route anyway based on route preference rules.
4. positively disaggregated prefixes do NOT have to propagate to 4. positively disaggregated prefixes do NOT have to propagate to
lower levels. With that the disturbance in terms of new flooding lower levels. With that the disturbance in terms of new flooding
is contained to a single level experiencing failures. is contained to a single level experiencing failures.
5. disaggregated prefix S-TIEs are not "reflected" by the lower 5. disaggregated prefix South TIEs are not "reflected" by the lower
level, i.e. nodes within same level do NOT need to be aware level, i.e. nodes within same level do NOT need to be aware
which node computed the need for disaggregation. which node computed the need for disaggregation.
6. The fabric is still supporting maximum load balancing properties 6. The fabric is still supporting maximum load balancing properties
while not trying to send traffic northbound unless necessary. while not trying to send traffic northbound unless necessary.
In case positive disaggregation is triggered and due to the very In case positive disaggregation is triggered and due to the very
stable but un-synchronized nature of the algorithm the nodes may stable but un-synchronized nature of the algorithm the nodes may
issue the necessary disaggregated prefixes at different points in issue the necessary disaggregated prefixes at different points in
time. This can lead for a short time to an "incast" behavior where time. This can lead for a short time to an "incast" behavior where
the first advertising router based on the nature of longest prefix the first advertising router based on the nature of longest prefix
match will attract all the traffic. An implementation MAY hence match will attract all the traffic. An implementation MAY hence
choose different strategies to address this behavior if needed. choose different strategies to address this behavior if needed.
To close this section it is worth to observe that in a single plane To close this section it is worth to observe that in a single plane
ToF this disaggregation prevents blackholing up to (K_LEAF * P) link ToF this disaggregation prevents blackholing up to (K_LEAF * P) link
failures in terms of Section 5.1.2 or in other terms, it takes at failures in terms of Section 4.1.2 or in other terms, it takes at
minimum that many link failures to partition the ToF into multiple minimum that many link failures to partition the ToF into multiple
planes. planes.
5.2.5.2. Negative, Transitive Disaggregation for Fallen Leafs 4.2.5.2. Negative, Transitive Disaggregation for Fallen Leafs
As explained in Section 5.1.3 failures in multi-plane Top-of-Fabric As explained in Section 4.1.3 failures in multi-plane Top-of-Fabric
or more than (K_LEAF * P) links failing in single plane design can or more than (K_LEAF * P) links failing in single plane design can
generate fallen leafs. Such scenario cannot be addressed by positive generate fallen leafs. Such scenario cannot be addressed by positive
disaggregation only and needs a further mechanism. disaggregation only and needs a further mechanism.
5.2.5.2.1. Cabling of Multiple Top-of-Fabric Planes 4.2.5.2.1. Cabling of Multiple Top-of-Fabric Planes
Let us return in this section to designs with multiple planes as Let us return in this section to designs with multiple planes as
shown in Figure 3. Figure 16 highlights how the ToF is cabled in shown in Figure 3. Figure 16 highlights how the ToF is cabled in
case of two planes by the means of dual-rings to distribute all the case of two planes by the means of dual-rings to distribute all the
N-TIEs within both planes. For people familiar with traditional North TIEs within both planes. For people familiar with traditional
link-state routing protocols ToF level can be considered equivalent link-state routing protocols ToF level can be considered equivalent
to area 0 in OSPF or level-2 in ISIS which need to be "connected" as to area 0 in OSPF or level-2 in ISIS which need to be "connected" as
well for the protocol to operate correctly. well for the protocol to operate correctly.
. ++==========++ ++==========++ . ++==========++ ++==========++
. II II II II . II II II II
.+----++--+ +----++--+ +----++--+ +----++--+ .+----++--+ +----++--+ +----++--+ +----++--+
.|ToF A1| |ToF B1| |ToF B2| |ToF A2| .|ToF A1| |ToF B1| |ToF B2| |ToF A2|
.++-+-++--+ ++-+-++--+ ++-+-++--+ ++-+-++--+ .++-+-++--+ ++-+-++--+ ++-+-++--+ ++-+-++--+
. | | II | | II | | II | | II . | | II | | II | | II | | II
. | | ++==========++ | | ++==========++ . | | ++==========++ | | ++==========++
. | | | | | | | | . | | | | | | | |
. .
. ~~~ Highlighted ToF of the previous multi-plane figure ~~ . ~~~ Highlighted ToF of the previous multi-plane figure ~~
Figure 16: Topologically connected planes Figure 16: Topologically connected planes
As described in Section 5.1.3 failures in multi-plane fabrics can As described in Section 4.1.3 failures in multi-plane fabrics can
lead to blackholes which normal positive disaggregation cannot fix. lead to blackholes which normal positive disaggregation cannot fix.
The mechanism of negative, transitive disaggregation incorporated in The mechanism of negative, transitive disaggregation incorporated in
RIFT provides the according solution. RIFT provides the according solution.
5.2.5.2.2. Transitive Advertisement of Negative Disaggregates 4.2.5.2.2. Transitive Advertisement of Negative Disaggregates
A ToF node that discovers that it cannot reach a fallen leaf A ToF node that discovers that it cannot reach a fallen leaf
disaggregates all the prefixes of such leafs. It uses for that disaggregates all the prefixes of such leafs. It uses for that
purpose negative prefix S-TIEs that are, as usual, flooded southwards purpose negative prefix South TIEs that are, as usual, flooded
with the scope defined in Section 5.2.3.4. southwards with the scope defined in Section 4.2.3.4.
Transitively, a node explicitly loses connectivity to a prefix when Transitively, a node explicitly loses connectivity to a prefix when
none of its children advertises it and when the prefix is negatively none of its children advertises it and when the prefix is negatively
disaggregated by all of its parents. When that happens, the node disaggregated by all of its parents. When that happens, the node
originates the negative prefix further down south. Since the originates the negative prefix further down south. Since the
mechanism applies recursively south the negative prefix may propagate mechanism applies recursively south the negative prefix may propagate
transitively all the way down to the leaf. This is necessary since transitively all the way down to the leaf. This is necessary since
leafs connected to multiple planes by means of disjoint paths may leafs connected to multiple planes by means of disjoint paths may
have to choose the correct plane already at the very bottom of the have to choose the correct plane already at the very bottom of the
fabric to make sure that they don't send traffic towards another leaf fabric to make sure that they don't send traffic towards another leaf
using a plane where it is "fallen" at which in point a blackhole is using a plane where it is "fallen" at which in point a blackhole is
unavoidable. unavoidable.
When the connectivity is restored, a node that disaggregated a prefix When the connectivity is restored, a node that disaggregated a prefix
withdraws the negative disaggregation by the usual mechanism of re- withdraws the negative disaggregation by the usual mechanism of re-
advertising TIEs omitting the negative prefix. advertising TIEs omitting the negative prefix.
5.2.5.2.3. Computation of Negative Disaggregates 4.2.5.2.3. Computation of Negative Disaggregates
The document omitted so far the description of the computation The document omitted so far the description of the computation
necessary to generate the correct set of negative prefixes. Negative necessary to generate the correct set of negative prefixes. Negative
prefixes can in fact be advertised due to two different triggers. We prefixes can in fact be advertised due to two different triggers. We
describe them consecutively. describe them consecutively.
The first origination reason is a computation that uses all the node The first origination reason is a computation that uses all the node
N-TIEs to build the set of all reachable nodes by reachability North TIEs to build the set of all reachable nodes by reachability
computation over the complete graph and including ToF links. The computation over the complete graph and including ToF links. The
computation uses the node itself as root. This is compared with the computation uses the node itself as root. This is compared with the
result of the normal southbound SPF as described in Section 5.2.4.2. result of the normal southbound SPF as described in Section 4.2.4.2.
The difference are the fallen leafs and all their attached prefixes The difference are the fallen leafs and all their attached prefixes
are advertised as negative prefixes southbound if the node does not are advertised as negative prefixes southbound if the node does not
see the prefix being reachable within southbound SPF. see the prefix being reachable within southbound SPF.
The second mechanism hinges on the understanding how the negative The second mechanism hinges on the understanding how the negative
prefixes are used within the computation as described in Figure 17. prefixes are used within the computation as described in Figure 17.
When attaching the negative prefixes at certain point in time the When attaching the negative prefixes at certain point in time the
negative prefix may find itself with all the viable nodes from the negative prefix may find itself with all the viable nodes from the
shorter match nexthop being pruned. In other words, all its shorter match nexthop being pruned. In other words, all its
northbound neighbors provided a negative prefix advertisement. This northbound neighbors provided a negative prefix advertisement. This
is the trigger to advertise this negative prefix transitively south is the trigger to advertise this negative prefix transitively south
and normally caused by the node being in a plane where the prefix and normally caused by the node being in a plane where the prefix
belongs to a fabric leaf that has "fallen" in this plane. Obviously, belongs to a fabric leaf that has "fallen" in this plane. Obviously,
when one of the northbound switches withdraws its negative when one of the northbound switches withdraws its negative
advertisement, the node has to withdraw its transitively provided advertisement, the node has to withdraw its transitively provided
negative prefix as well. negative prefix as well.
5.2.6. Attaching Prefixes 4.2.6. Attaching Prefixes
After SPF is run, it is necessary to attach the resulting After SPF is run, it is necessary to attach the resulting
reachability information in form of prefixes. For S-SPF, prefixes reachability information in form of prefixes. For S-SPF, prefixes
from an N-TIE are attached to the originating node with that node's from an North TIE are attached to the originating node with that
next-hop set and a distance equal to the prefix's cost plus the node's next-hop set and a distance equal to the prefix's cost plus
node's minimized path distance. The RIFT route database, a set of the node's minimized path distance. The RIFT route database, a set
(prefix, prefix-type, attributes, path_distance, next-hop set), of (prefix, prefix-type, attributes, path_distance, next-hop set),
accumulates these results. accumulates these results.
In case of N-SPF prefixes from each S-TIE need to also be added to In case of N-SPF prefixes from each South TIE need to also be added
the RIFT route database. The N-SPF is really just a stub so the to the RIFT route database. The N-SPF is really just a stub so the
computing node needs simply to determine, for each prefix in an S-TIE computing node needs simply to determine, for each prefix in an South
that originated from adjacent node, what next-hops to use to reach TIE that originated from adjacent node, what next-hops to use to
that node. Since there may be parallel links, the next-hops to use reach that node. Since there may be parallel links, the next-hops to
can be a set; presence of the computing node in the associated Node use can be a set; presence of the computing node in the associated
S-TIE is sufficient to verify that at least one link has Node South TIE is sufficient to verify that at least one link has
bidirectional connectivity. The set of minimum cost next-hops from bidirectional connectivity. The set of minimum cost next-hops from
the computing node X to the originating adjacent node is determined. the computing node X to the originating adjacent node is determined.
Each prefix has its cost adjusted before being added into the RIFT Each prefix has its cost adjusted before being added into the RIFT
route database. The cost of the prefix is set to the cost received route database. The cost of the prefix is set to the cost received
plus the cost of the minimum distance next-hop to that neighbor while plus the cost of the minimum distance next-hop to that neighbor while
taking into account its attributes such as mobility per Section 5.3.3 taking into account its attributes such as mobility per
necessary. Then each prefix can be added into the RIFT route Section 4.3.3. Then each prefix can be added into the RIFT route
database with the next_hop_set; ties are broken based upon type first database with the next_hop_set; ties are broken based upon type first
and then distance and further attributes and only the best and then distance and further on `PrefixAttributes` and only the best
combination is used for forwarding. RIFT route preferences are combination is used for forwarding. RIFT route preferences are
normalized by the according Thrift [thrift] model type. normalized by the according Thrift [thrift] model type.
An example implementation for node X follows: An example implementation for node X follows:
for each S-TIE for each South TIE
if S-TIE.level > X.level if South TIE.level > X.level
next_hop_set = set of minimum cost links to the S-TIE.originator next_hop_set = set of minimum cost links to the South TIE.originator
next_hop_cost = minimum cost link to S-TIE.originator next_hop_cost = minimum cost link to South TIE.originator
end if end if
for each prefix P in the S-TIE for each prefix P in the South TIE
P.cost = P.cost + next_hop_cost P.cost = P.cost + next_hop_cost
if P not in route_database: if P not in route_database:
add (P, P.cost, P.type, P.attributes, next_hop_set) to route_database add (P, P.cost, P.type, P.attributes, next_hop_set) to route_database
end if end if
if (P in route_database): if (P in route_database):
if route_database[P].cost > P.cost or route_database[P].type > P.type: if route_database[P].cost > P.cost or route_database[P].type > P.type:
update route_database[P] with (P, P.type, P.cost, P.attributes, next_hop_set) update route_database[P] with (P, P.type, P.cost, P.attributes, next_hop_set)
else if route_database[P].cost == P.cost and route_database[P].type == P.type: else if route_database[P].cost == P.cost and route_database[P].type == P.type:
update route_database[P] with (P, P.type, P.cost, P.attributes, update route_database[P] with (P, P.type, P.cost, P.attributes,
merge(next_hop_set, route_database[P].next_hop_set)) merge(next_hop_set, route_database[P].next_hop_set))
else else
// Not preferred route so ignore // Not preferred route so ignore
end if end if
end if end if
end for end for
end for end for
Figure 17: Adding Routes from S-TIE Positive and Negative Prefixes Figure 17: Adding Routes from South TIE Positive and Negative
Prefixes
After the positive prefixes are attached and tie-broken, negative After the positive prefixes are attached and tie-broken, negative
prefixes are attached and used in case of northbound computation, prefixes are attached and used in case of northbound computation,
ideally from the shortest length to the longest. The nexthop ideally from the shortest length to the longest. The nexthop
adjacencies for a negative prefix are inherited from the longest adjacencies for a negative prefix are inherited from the longest
prefix that aggregates it, and subsequently adjacencies to nodes that positive prefix that aggregates it, and subsequently adjacencies to
advertised negative for this prefix are removed. nodes that advertised negative for this prefix are removed.
The rule of inheritance MUST be maintained when the nexthop list for The rule of inheritance MUST be maintained when the nexthop list for
a prefix is modified, as the modification may affect the entries for a prefix is modified, as the modification may affect the entries for
matching negative prefixes of immediate longer prefix length. For matching negative prefixes of immediate longer prefix length. For
instance, if a nexthop is added, then by inheritance it must be added instance, if a nexthop is added, then by inheritance it must be added
to all the negative routes of immediate longer prefixes length unless to all the negative routes of immediate longer prefixes length unless
it is pruned due to a negative advertisement for the same next hop. it is pruned due to a negative advertisement for the same next hop.
Similarily, if a nexthop is deleted for a given prefix, then it is Similarily, if a nexthop is deleted for a given prefix, then it is
deleted for all the immediately aggregated negative routes. This deleted for all the immediately aggregated negative routes. This
will recurse in the case of nested negative prefix aggregations. will recurse in the case of nested negative prefix aggregations.
skipping to change at page 62, line 30 skipping to change at page 73, line 30
| |
| +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 |
+--------+ +--------+
Figure 22: Abstract RIB after negative 2001:db8:1::/48 from S2 Figure 22: Abstract RIB after negative 2001:db8:1::/48 from S2
Negative 2001:db8:1::/48 inherits from 2001:db8::/32 now, so the Negative 2001:db8:1::/48 inherits from 2001:db8::/32 now, so the
positive more specific routes are the complements to S2 in the set of positive more specific routes are the complements to S2 in the set of
next hops for 2001:db8::/32, which are S3 and S4, or, in other words, next hops for 2001:db8::/32, which are S3 and S4, or, in other words,
all entries of the father with the negative holes "punched in" again. all entries of the parent with the negative holes "punched in" again.
After the update, the FIB in T1 shows as illustrated in Figure 23: After the update, the FIB in T1 shows as illustrated in Figure 23:
+---------+ +---------------+ +-----------------+ +---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 | | Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+ +---------+ +---------------+ +-----------------+
| | | | | |
| +--------+ | | | +--------+ | |
+---> | Via S1 | | | +---> | Via S1 | | |
| +--------+ | | | +--------+ | |
| | | | | |
skipping to change at page 65, line 31 skipping to change at page 76, line 31
| +--------+ | +--------+ | +--------+ | +--------+ | +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 | +---> | Via S3 | +---> | Via S3 | +---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+ | +--------+ | +--------+ | +--------+ | +--------+
| | | | | |
| +--------+ | +--------+ | +--------+ | +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 | +---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+ +--------+ +--------+ +--------+
Figure 25: Abstract FIB after negative 2001:db8:2::/48 from S4 Figure 25: Abstract FIB after negative 2001:db8:2::/48 from S4
5.2.7. Optional Zero Touch Provisioning (ZTP) 4.2.7. Optional Zero Touch Provisioning (ZTP)
Each RIFT node can operate in zero touch provisioning (ZTP) mode, Each RIFT node can operate in zero touch provisioning (ZTP) mode,
i.e. it has no configuration (unless it is a Top-of-Fabric at the top i.e. it has no configuration (unless it is a Top-of-Fabric at the top
of the topology or the must operate in the topology as leaf and/or of the topology or the must operate in the topology as leaf and/or
support leaf-2-leaf procedures) and it will fully configure itself support leaf-2-leaf procedures) and it will fully configure itself
after being attached to the topology. Configured nodes and nodes after being attached to the topology. Configured nodes and nodes
operating in ZTP can be mixed and will form a valid topology if operating in ZTP can be mixed and will form a valid topology if
achievable. achievable.
The derivation of the level of each node happens based on offers The derivation of the level of each node happens based on offers
skipping to change at page 66, line 10 skipping to change at page 77, line 10
topologically below it and properly peers with nodes above. topologically below it and properly peers with nodes above.
The fabric is very conciously numbered from the top to allow for PoDs The fabric is very conciously numbered from the top to allow for PoDs
of different heights and minimize number of provisioning necessary, of different heights and minimize number of provisioning necessary,
in this case just a TOP_OF_FABRIC flag on every node at the top of in this case just a TOP_OF_FABRIC flag on every node at the top of
the fabric. the fabric.
This section describes the necessary concepts and procedures for ZTP This section describes the necessary concepts and procedures for ZTP
operation. operation.
5.2.7.1. Terminology 4.2.7.1. Terminology
The interdependencies between the different flags and the configured The interdependencies between the different flags and the configured
level can be somewhat vexing at first and it may take multiple reads level can be somewhat vexing at first and it may take multiple reads
of the glossary to comprehend them. of the glossary to comprehend them.
Automatic Level Derivation: Procedures which allow nodes without Automatic Level Derivation: Procedures which allow nodes without
level configured to derive it automatically. Only applied if level configured to derive it automatically. Only applied if
CONFIGURED_LEVEL is undefined. CONFIGURED_LEVEL is undefined.
UNDEFINED_LEVEL: A "null" value that indicates that the level has UNDEFINED_LEVEL: A "null" value that indicates that the level has
skipping to change at page 66, line 38 skipping to change at page 77, line 38
same time as this flag. It implies CONFIGURED_LEVEL value of 0. same time as this flag. It implies CONFIGURED_LEVEL value of 0.
TOP_OF_FABRIC flag: Configuration flag that MUST be provided to all TOP_OF_FABRIC flag: Configuration flag that MUST be provided to all
Top-of-Fabric nodes. LEAF_FLAG and CONFIGURED_LEVEL cannot be Top-of-Fabric nodes. LEAF_FLAG and CONFIGURED_LEVEL cannot be
defined at the same time as this flag. It implies a defined at the same time as this flag. It implies a
CONFIGURED_LEVEL value. In fact, it is basically a shortcut for CONFIGURED_LEVEL value. In fact, it is basically a shortcut for
configuring same level at all Top-of-Fabric nodes which is configuring same level at all Top-of-Fabric nodes which is
unavoidable since an initial 'seed' is needed for other ZTP nodes unavoidable since an initial 'seed' is needed for other ZTP nodes
to derive their level in the topology. The flag plays an to derive their level in the topology. The flag plays an
important role in fabrics with multiple planes to enable important role in fabrics with multiple planes to enable
successful negative disaggregation (Section 5.2.5.2). successful negative disaggregation (Section 4.2.5.2).
CONFIGURED_LEVEL: A level value provided manually. When this is CONFIGURED_LEVEL: A level value provided manually. When this is
defined (i.e. it is not an UNDEFINED_LEVEL) the node is not defined (i.e. it is not an UNDEFINED_LEVEL) the node is not
participating in ZTP. TOP_OF_FABRIC flag is ignored when this participating in ZTP. TOP_OF_FABRIC flag is ignored when this
value is defined. LEAF_ONLY can be set only if this value is value is defined. LEAF_ONLY can be set only if this value is
undefined or set to 0. undefined or set to 0.
DERIVED_LEVEL: Level value computed via automatic level derivation DERIVED_LEVEL: Level value computed via automatic level derivation
when CONFIGURED_LEVEL is equal to UNDEFINED_LEVEL. when CONFIGURED_LEVEL is equal to UNDEFINED_LEVEL.
LEAF_2_LEAF: An optional flag that can be configured on a node to LEAF_2_LEAF: An optional flag that can be configured on a node to
make sure it supports procedures defined in Section 5.3.9. In a make sure it supports procedures defined in Section 4.3.8. In a
strict sense it is a capability that implies LEAF_ONLY and the strict sense it is a capability that implies LEAF_ONLY and the
according restrictions. TOP_OF_FABRIC flag is ignored when set at according restrictions. TOP_OF_FABRIC flag is ignored when set at
the same time as this flag. the same time as this flag.
LEVEL_VALUE: In ZTP case the original definition of "level" in LEVEL_VALUE: In ZTP case the original definition of "level" in
Section 3.1 is both extended and relaxed. First, level is defined Section 3.1 is both extended and relaxed. First, level is defined
now as LEVEL_VALUE and is the first defined value of now as LEVEL_VALUE and is the first defined value of
CONFIGURED_LEVEL followed by DERIVED_LEVEL. Second, it is CONFIGURED_LEVEL followed by DERIVED_LEVEL. Second, it is
possible for nodes to be more than one level apart to form possible for nodes to be more than one level apart to form
adjacencies if any of the nodes is at least LEAF_ONLY. adjacencies if any of the nodes is at least LEAF_ONLY.
skipping to change at page 67, line 32 skipping to change at page 78, line 32
maintains parallel adjacencies to the neighbor, VOL on each maintains parallel adjacencies to the neighbor, VOL on each
adjacency is considered as equivalent, i.e. the newest VOL from adjacency is considered as equivalent, i.e. the newest VOL from
any such adjacency updates the VOL received from the same node. any such adjacency updates the VOL received from the same node.
Highest Available Level (HAL): Highest defined level value seen from Highest Available Level (HAL): Highest defined level value seen from
all VOLs received. all VOLs received.
Highest Available Level Systems (HALS): Set of nodes offering HAL Highest Available Level Systems (HALS): Set of nodes offering HAL
VOLs. VOLs.
Highest Adjacency Three Way (HAT): Highest neigbhor level of all the Highest Adjacency 3-way (HAT): Highest neigbhor level of all the
formed three way adjacencies for the node. formed 3-way adjacencies for the node.
5.2.7.2. Automatic SystemID Selection 4.2.7.2. Automatic SystemID Selection
RIFT nodes require a 64 bit SystemID which SHOULD be derived as RIFT nodes require a 64 bit SystemID which SHOULD be derived as
EUI-64 MA-L derive according to [EUI64]. The organizationally EUI-64 MA-L derive according to [EUI64]. The organizationally
goverened portion of this ID (24 bits) can be used to generate goverened portion of this ID (24 bits) can be used to generate
multiple IDs if required to indicate more than one RIFT instance." multiple IDs if required to indicate more than one RIFT instance."
As matter of operational concern, the router MUST ensure that such As matter of operational concern, the router MUST ensure that such
identifier is not changing very frequently (or at least not without identifier is not changing very frequently (or at least not without
sending all its TIEs with fairly short lifetimes) since otherwise the sending all its TIEs with fairly short lifetimes) since otherwise the
network may be left with large amounts of stale TIEs in other nodes network may be left with large amounts of stale TIEs in other nodes
(though this is not necessarily a serious problem if the procedures (though this is not necessarily a serious problem if the procedures
described in Section 8 are implemented). described in Section 7 are implemented).
5.2.7.3. Generic Fabric Example 4.2.7.3. Generic Fabric Example
ZTP forces us to think about miscabled or unusually cabled fabric and ZTP forces us to think about miscabled or unusually cabled fabric and
how such a topology can be forced into a "lattice" structure which a how such a topology can be forced into a "lattice" structure which a
fabric represents (with further restrictions). Let us consider a fabric represents (with further restrictions). Let us consider a
necessary and sufficient physical cabling in Figure 26. We assume necessary and sufficient physical cabling in Figure 26. We assume
all nodes being in the same PoD. all nodes being in the same PoD.
. +---+ . +---+
. | A | s = TOP_OF_FABRIC . | A | s = TOP_OF_FABRIC
. | s | l = LEAF_ONLY . | s | l = LEAF_ONLY
skipping to change at page 68, line 47 skipping to change at page 79, line 47
. | | | | | . | | | | |
. ++-++ ++-++ | . ++-++ ++-++ |
. | X +-----+ Y +-+ . | X +-----+ Y +-+
. |l2l| | l | . |l2l| | l |
. +---+ +---+ . +---+ +---+
Figure 26: Generic ZTP Cabling Considerations Figure 26: Generic ZTP Cabling Considerations
First, we must anchor the "top" of the cabling and that's what the First, we must anchor the "top" of the cabling and that's what the
TOP_OF_FABRIC flag at node A is for. Then things look smooth until TOP_OF_FABRIC flag at node A is for. Then things look smooth until
we have to decide whether node Y is at the same level as I, J or at we have to decide whether node Y is at the same level as I, J (and as
the same level as Y and consequently, X is south of it. This is consequence, X is south of it) or at the same level as X. This is
unresolvable here until we "nail down the bottom" of the topology. unresolvable here until we "nail down the bottom" of the topology.
To achieve that we choose to use in this example the leaf flags. We To achieve that we choose to use in this example the leaf flags in X
will see further then whether Y chooses to form adjacencies to F or and Y. In case where Y would not have a leaf flag it will try to
I, J successively. elect highest level offered and end up being in same level as I and
J.
5.2.7.4. Level Determination Procedure 4.2.7.4. Level Determination Procedure
A node starting up with UNDEFINED_VALUE (i.e. without a A node starting up with UNDEFINED_VALUE (i.e. without a
CONFIGURED_LEVEL or any leaf or TOP_OF_FABRIC flag) MUST follow those CONFIGURED_LEVEL or any leaf or TOP_OF_FABRIC flag) MUST follow those
additional procedures: additional procedures:
1. It advertises its LEVEL_VALUE on all LIEs (observe that this can 1. It advertises its LEVEL_VALUE on all LIEs (observe that this can
be UNDEFINED_LEVEL which in terms of the schema is simply an be UNDEFINED_LEVEL which in terms of the schema is simply an
omitted optional value). omitted optional value).
2. It computes HAL as numerically highest available level in all 2. It computes HAL as numerically highest available level in all
skipping to change at page 69, line 30 skipping to change at page 80, line 30
3. It chooses then MAX(HAL-1,0) as its DERIVED_LEVEL. The node then 3. It chooses then MAX(HAL-1,0) as its DERIVED_LEVEL. The node then
starts to advertise this derived level. starts to advertise this derived level.
4. A node that lost all adjacencies with HAL value MUST hold down 4. A node that lost all adjacencies with HAL value MUST hold down
computation of new DERIVED_LEVEL for a short period of time computation of new DERIVED_LEVEL for a short period of time
unless it has no VOLs from southbound adjacencies. After the unless it has no VOLs from southbound adjacencies. After the
holddown expired, it MUST discard all received offers, recompute holddown expired, it MUST discard all received offers, recompute
DERIVED_LEVEL and announce it to all neighbors. DERIVED_LEVEL and announce it to all neighbors.
5. A node MUST reset any adjacency that has changed the level it is 5. A node MUST reset any adjacency that has changed the level it is
offering and is in three way state. offering and is in 3-way state.
6. A node that changed its defined level value MUST readvertise its 6. A node that changed its defined level value MUST readvertise its
own TIEs (since the new `PacketHeader` will contain a different own TIEs (since the new `PacketHeader` will contain a different
level than before). Sequence number of each TIE MUST be level than before). Sequence number of each TIE MUST be
increased. increased.
7. After a level has been derived the node MUST set the 7. After a level has been derived the node MUST set the
`not_a_ztp_offer` on LIEs towards all systems offering a VOL for `not_a_ztp_offer` on LIEs towards all systems offering a VOL for
HAL. HAL.
skipping to change at page 70, line 7 skipping to change at page 81, line 7
are now north or east-west. This will not prevent the correct are now north or east-west. This will not prevent the correct
operation of the protocol but could be slightly confusing operation of the protocol but could be slightly confusing
operationally. operationally.
A node starting with LEVEL_VALUE being 0 (i.e. it assumes a leaf A node starting with LEVEL_VALUE being 0 (i.e. it assumes a leaf
function by being configured with the appropriate flags or has a function by being configured with the appropriate flags or has a
CONFIGURED_LEVEL of 0) MUST follow those additional procedures: CONFIGURED_LEVEL of 0) MUST follow those additional procedures:
1. It computes HAT per procedures above but does NOT use it to 1. It computes HAT per procedures above but does NOT use it to
compute DERIVED_LEVEL. HAT is used to limit adjacency formation compute DERIVED_LEVEL. HAT is used to limit adjacency formation
per Section 5.2.2. per Section 4.2.2.
It MAY also follow modified procedures: It MAY also follow modified procedures:
1. It may pick a different strategy to choose VOL, e.g. use the VOL 1. It may pick a different strategy to choose VOL, e.g. use the VOL
value with highest number of VOLs. Such strategies are only value with highest number of VOLs. Such strategies are only
possible since the node always remains "at the bottom of the possible since the node always remains "at the bottom of the
fabric" while another layer could "invert" the fabric by picking fabric" while another layer could "invert" the fabric by picking
its prefered VOL in a different fashion than always trying to its prefered VOL in a different fashion than always trying to
achieve the highest viable level. achieve the highest viable level.
5.2.7.5. Resulting Topologies 4.2.7.5. ZTP FSM
The procedures defined in Section 5.2.7.4 will lead to the RIFT This section specifies the precise, normative ZTP FSM and can be
omitted unless the reader is pursuing an implemenentation of the
protocol.
Initial state is ComputeBestOffer.
digraph Gd436cc3ced8c471eb30bd4f3ac946261 {
N06108ba9ac894d988b3e4e8ea5ace007
[label="Enter"]
[style="invis"]
[shape="plain"];
Na47ff5eac9aa4b2eaf12839af68aab1f
[label="MultipleNeighborsWait"]
[shape="oval"];
N57a829be68e2489d8dc6b84e10597d0b
[label="OneWay"]
[shape="oval"];
Na641d400819a468d987e31182cdb013e
[label="ThreeWay"]
[shape="oval"];
Necfbfc2d8e5b482682ee66e604450c7b
[label="Enter"]
[style="dashed"]
[shape="plain"];
N16db54bf2c5d48f093ad6c18e70081ee
[label="TwoWay"]
[shape="oval"];
N1b89016876b44cc1b9c1e4a735769560
[label="Exit"]
[style="invis"]
[shape="plain"];
N16db54bf2c5d48f093ad6c18e70081ee -> N57a829be68e2489d8dc6b84e10597d0b
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N57a829be68e2489d8dc6b84e10597d0b
[label="|NeighborDroppedReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Necfbfc2d8e5b482682ee66e604450c7b -> N57a829be68e2489d8dc6b84e10597d0b
[label=""]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|NewNeighbor|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|NeighborDroppedReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|TimerTick|\n|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|\n|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na641d400819a468d987e31182cdb013e
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> N57a829be68e2489d8dc6b84e10597d0b
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> N57a829be68e2489d8dc6b84e10597d0b
[label="|MultipleNeighborsDone|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> Na641d400819a468d987e31182cdb013e
[label="|ValidReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na641d400819a468d987e31182cdb013e
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N57a829be68e2489d8dc6b84e10597d0b
[label="|TimerTick|\n|LieRcvd|\n|NeighborChangedLevel|\n|NeighborChangedAddress|\n|NeighborAddressAdded|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|SendLie|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> Na641d400819a468d987e31182cdb013e
[label="|ValidReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na641d400819a468d987e31182cdb013e
[label="|ValidReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
}
ZTP FSM DOT
Events
o TimerTick: one second timer tic
o LevelChanged: node's level has been changed by ZTP or
configuration
o HALChanged: best HAL computed by ZTP has changed
o HATChanged: HAT computed by ZTP has changed
o HALSChanged: set of HAL offering systems computed by ZTP has
changed
o LieRcvd: received LIE
o NewNeighbor: new neighbor parsed
o ValidReflection: received own reflection from neighbor
o NeighborDroppedReflection: lost previous own reflection from
neighbor
o NeighborChangedLevel: neighbor changed advertised level
o NeighborChangedAddress: neighbor changed IP address
o UnacceptableHeader: unacceptable header seen
o MTUMismatch: MTU mismatched
o PODMismatch: Unacceptable PoD seen
o HoldtimeExpired: adjacency hold down expired
o MultipleNeighbors: more than one neighbor seen on interface
o MultipleNeighborsDone: cooldown for multiple neighbors expired
o SendLie: send a LIE out
o UpdateZTPOffer: update this node's ZTP offer
Actions
on MTUMismatch in OneWay finishes in OneWay: no action
on HoldtimeExpired in OneWay finishes in OneWay: no action
on LevelChanged in ThreeWay finishes in OneWay: update level with
event value
on MultipleNeighbors in MultipleNeighborsWait finishes in
MultipleNeighborsWait: start multiple neighbors timer as 4 *
DEFAULT_LIE_HOLDTIME
on HALChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store new HAL
on NeighborChangedAddress in ThreeWay finishes in OneWay: no
action
on ValidReflection in OneWay finishes in ThreeWay: no action
on MTUMismatch in TwoWay finishes in OneWay: no action
on TimerTick in MultipleNeighborsWait finishes in
MultipleNeighborsWait: decrement MultipleNeighbors timer, if
expired PUSH MultipleNeighborsDone
on MultipleNeighborsDone in MultipleNeighborsWait finishes in
OneWay: decrement MultipleNeighbors timer, if expired PUSH
MultipleNeighborsDone
on HATChanged in ThreeWay finishes in ThreeWay: store HAT
on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP
FSM
on HALSChanged in TwoWay finishes in TwoWay: store HALS
on PODMismatch in TwoWay finishes in OneWay: no action
on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE
on PODMismatch in ThreeWay finishes in OneWay: no action
on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if
holdtime expired PUSH HoldtimeExpired event
on SendLie in TwoWay finishes in TwoWay: SEND_LIE
on SendLie in OneWay finishes in OneWay: SEND_LIE
on TimerTick in OneWay finishes in OneWay: PUSH SendLie event
on HALChanged in OneWay finishes in OneWay: store new HAL
on HALSChanged in ThreeWay finishes in ThreeWay: store HALS
on NeighborChangedLevel in TwoWay finishes in OneWay: no action
on PODMismatch in OneWay finishes in OneWay: no action
on HoldtimeExpired in TwoWay finishes in OneWay: no action
on TimerTick in ThreeWay finishes in ThreeWay: PUSH SendLie event,
if holdtime expired PUSH HoldtimeExpired event
on MultipleNeighbors in TwoWay finishes in MultipleNeighborsWait:
start multiple neighbors timer as 4 * DEFAULT_LIE_HOLDTIME
on UpdateZTPOffer in MultipleNeighborsWait finishes in
MultipleNeighborsWait: send offer to ZTP FSM
on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE
on LevelChanged in MultipleNeighborsWait finishes in OneWay:
update level with event value
on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to
ZTP FSM
on HALChanged in TwoWay finishes in TwoWay: store new HAL
on UnacceptableHeader in OneWay finishes in OneWay: no action
on HALSChanged in OneWay finishes in OneWay: store HALS
on HALSChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HALS
on SendLie in ThreeWay finishes in ThreeWay: SEND_LIE
on MTUMismatch in ThreeWay finishes in OneWay: no action
on HATChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HAT
on NeighborChangedAddress in OneWay finishes in OneWay: no action
on ValidReflection in TwoWay finishes in ThreeWay: no action
on MultipleNeighbors in OneWay finishes in MultipleNeighborsWait:
start multiple neighbors timer as 4 * DEFAULT_LIE_HOLDTIME
on NeighborChangedLevel in OneWay finishes in OneWay: no action
on HATChanged in OneWay finishes in OneWay: store HAT
on NeighborDroppedReflection in OneWay finishes in OneWay: no
action
on HALChanged in ThreeWay finishes in ThreeWay: store new HAL
on NeighborAddressAdded in OneWay finishes in OneWay: no action
on NeighborChangedAddress in TwoWay finishes in OneWay: no action
on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE
on UnacceptableHeader in TwoWay finishes in OneWay: no action
on LevelChanged in TwoWay finishes in OneWay: update level with
event value
on HATChanged in TwoWay finishes in TwoWay: store HAT
on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP
FSM
on ValidReflection in ThreeWay finishes in ThreeWay: no action
on UnacceptableHeader in ThreeWay finishes in OneWay: no action
on HoldtimeExpired in ThreeWay finishes in OneWay: no action
on NeighborChangedLevel in ThreeWay finishes in OneWay: no action
on LevelChanged in OneWay finishes in OneWay: update level with
event value, PUSH SendLie event
on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event
on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no
action
on MultipleNeighbors in ThreeWay finishes in
MultipleNeighborsWait: start multiple neighbors timer as 4 *
DEFAULT_LIE_HOLDTIME
on Entry into OneWay: CLEANUP
Following words are used for well known procedures:
1. PUSH Event: pushes an event to be executed by the FSM upon exit
of this action
2. CLEANUP: neighbor MUST be reset to unknown
3. SEND_LIE: create a new LIE packet
1. reflecting the neighbor if known and valid and
2. setting the necessary `not_a_ztp_offer` variable if level was
derived from last known neighbor on this interface and
3. setting `you_are_not_flood_repeater` to computed value
4. PROCESS_LIE:
1. if lie has wrong major version OR our own system ID or
invalid system ID then CLEANUP else
2. if lie has non matching MTUs then CLEANUP, PUSH
UpdateZTPOffer, PUSH MTUMismatch else
3. if PoD rules do not allow adjacency forming then CLEANUP,
PUSH PODMismatch, PUSH MTUMismatch else
4. if lie has undefined level OR my level is undefined OR this
node is leaf and remote level lower than HAT OR (lie's level
is not leaf AND its difference is more than one from my
level) then CLEANUP, PUSH UpdateZTPOffer, PUSH
UnacceptableHeader else
5. PUSH UpdateZTPOffer, construct temporary new neighbor
structure with values from lie, if no current neighbor exists
then set neighbor to new neighbor, PUSH NewNeighbor event,
CHECK_THREE_WAY else
1. if current neighbor system ID differs from lie's system
ID then PUSH MultipleNeighbors else
2. if current neighbor stored level differs from lie's level
then PUSH NeighborChangedLevel else
3. if current neighbor stored IPv4/v6 address differs from
lie's address then PUSH NeighborChangedAddress else
4. if any of neighbor's flood address port, name, local
linkid changed then PUSH NeighborChangedMinorFields and
5. CHECK_THREE_WAY
5. CHECK_THREE_WAY: if current state is one-way do nothing else
1. if lie packet does not contain neighbor then if current state
is three-way then PUSH NeighborDroppedReflection else
2. if packet reflects this system's ID and local port and state
is three-way then PUSH event ValidReflection else PUSH event
MultipleNeighbors
4.2.7.6. Resulting Topologies
The procedures defined in Section 4.2.7.4 will lead to the RIFT
topology and levels depicted in Figure 27. topology and levels depicted in Figure 27.
. +---+ . +---+
. | As| . | As|
. | 24| . | 24|
. ++-++ . ++-++
. | | . | |
. +--+ +--+ . +--+ +--+
. | | . | |
. +--++ ++--+ . +--++ ++--+
skipping to change at page 72, line 5 skipping to change at page 91, line 37
. | | | . | | |
. +---------+ | | . +---------+ | |
. | | | . | | |
. ++-++ | . ++-++ |
. | X +--------+ . | X +--------+
. | 0 | . | 0 |
. +---+ . +---+
Figure 28: Generic ZTP Topology Autoconfigured Figure 28: Generic ZTP Topology Autoconfigured
5.2.8. Stability Considerations 4.2.8. Stability Considerations
The autoconfiguration mechanism computes a global maximum of levels The autoconfiguration mechanism computes a global maximum of levels
by diffusion. The achieved equilibrium can be disturbed massively by by diffusion. The achieved equilibrium can be disturbed massively by
all nodes with highest level either leaving or entering the domain all nodes with highest level either leaving or entering the domain
(with some finer distinctions not explained further). It is (with some finer distinctions not explained further). It is
therefore recommended that each node is multi-homed towards nodes therefore recommended that each node is multi-homed towards nodes
with respective HAL offerings. Fortuntately, this is the natural with respective HAL offerings. Fortuntately, this is the natural
state of things for the topology variants considered in RIFT. state of things for the topology variants considered in RIFT.
5.3. Further Mechanisms 4.3. Further Mechanisms
5.3.1. Overload Bit 4.3.1. Overload Bit
The overload Bit MUST be respected in all according reachability The overload Bit MUST be respected in all according reachability
computations. A node with overload bit set SHOULD NOT advertise any computations. A node with overload bit set SHOULD NOT advertise any
reachability prefixes southbound except locally hosted ones. A node reachability prefixes southbound except locally hosted ones. A node
in overload SHOULD advertise all its locally hosted prefixes north in overload SHOULD advertise all its locally hosted prefixes north
and southbound. and southbound.
The leaf node SHOULD set the 'overload' bit on its node TIEs, since The leaf node SHOULD set the 'overload' bit on its node TIEs, since
if the spine nodes were to forward traffic not meant for the local if the spine nodes were to forward traffic not meant for the local
node, the leaf node does not have the topology information to prevent node, the leaf node does not have the topology information to prevent
a routing/forwarding loop. a routing/forwarding loop.
5.3.2. Optimized Route Computation on Leafs 4.3.2. Optimized Route Computation on Leafs
Since the leafs do see only "one hop away" they do not need to run a Since the leafs do see only "one hop away" they do not need to run a
"proper" SPF. Instead, they can gather the available prefix "proper" SPF. Instead, they can gather the available prefix
candidates from their neighbors and build the routing table candidates from their neighbors and build the routing table
accordingly. accordingly.
A leaf will have no N-TIEs except its own and optionally from its A leaf will have no North TIEs except its own and optionally from its
East-West neighbors. A leaf will have S-TIEs from its neighbors. East-West neighbors. A leaf will have South TIEs from its neighbors.
Instead of creating a network graph from its N-TIEs and neighbor's Instead of creating a network graph from its North TIEs and
S-TIEs and then running an SPF, a leaf node can simply compute the neighbor's South TIEs and then running an SPF, a leaf node can simply
minimum cost and next_hop_set to each leaf neighbor by examining its compute the minimum cost and next_hop_set to each leaf neighbor by
local adjacencies, determining bi-directionality from the associated examining its local adjacencies, determining bi-directionality from
N-TIE, and specifying the neighbor's next_hop_set set and cost from the associated North TIE, and specifying the neighbor's next_hop_set
the minimum cost local adjacency to that neighbor. set and cost from the minimum cost local adjacency to that neighbor.
Then a leaf attaches prefixes as described in Section 5.2.6. Then a leaf attaches prefixes as described in Section 4.2.6.
5.3.3. Mobility 4.3.3. Mobility
It is a requirement for RIFT to maintain at the control plane a real It is a requirement for RIFT to maintain at the control plane a real
time status of which prefix is attached to which port of which leaf, time status of which prefix is attached to which port of which leaf,
even in a context of mobility where the point of attachement may even in a context of mobility where the point of attachement may
change several times in a subsecond period of time. change several times in a subsecond period of time.
There are two classical approaches to maintain such knowledge in an There are two classical approaches to maintain such knowledge in an
unambiguous fashion: unambiguous fashion:
time stamp: With this method, the infrastructure records the precise time stamp: With this method, the infrastructure records the precise
skipping to change at page 74, line 5 skipping to change at page 93, line 38
heterogeneous sources can be hard to impossible. heterogeneous sources can be hard to impossible.
RIFT supports a hybrid approach contained in an optional RIFT supports a hybrid approach contained in an optional
`PrefixSequenceType` prefix attribute that we call a `monotonic `PrefixSequenceType` prefix attribute that we call a `monotonic
clock` consisting of a timestamp and optional sequence number. In clock` consisting of a timestamp and optional sequence number. In
case of presence of the attribute: case of presence of the attribute:
o The leaf node MAY advertise a time stamp of the latest sighting of o The leaf node MAY advertise a time stamp of the latest sighting of
a prefix, e.g., by snooping IP protocols or the node using the a prefix, e.g., by snooping IP protocols or the node using the
time at which it advertised the prefix. RIFT transports the time time at which it advertised the prefix. RIFT transports the time
stamp within the desired prefix N-TIEs as 802.1AS timestamp. stamp within the desired prefix North TIEs as 802.1AS timestamp.
o RIFT may interoperate with the "update to 6LoWPAN Neighbor o RIFT may interoperate with the "update to 6LoWPAN Neighbor
Discovery" [RFC8505], which provides a method for registering a Discovery" [RFC8505], which provides a method for registering a
prefix with a sequence counter called a Transaction ID (TID). prefix with a sequence counter called a Transaction ID (TID).
RIFT transports in such case the TID in its native form. RIFT transports in such case the TID in its native form.
o RIFT also defines an abstract negative clock (ANSC) that compares o RIFT also defines an abstract negative clock (ANSC) that compares
as less than any other clock. By default, the lack of a as less than any other clock. By default, the lack of a
`PrefixSequenceType` in a Prefix N-TIE is interpreted as ANSC. We `PrefixSequenceType` in a Prefix North TIE is interpreted as ANSC.
call this also an `undefined` clock. We call this also an `undefined` clock.
o Any prefix present on the fabric in multiple nodes that has the o Any prefix present on the fabric in multiple nodes that has the
`same` clock is considered as anycast. ASNC is always considered `same` clock is considered as anycast. ASNC is always considered
smaller than any defined clock. smaller than any defined clock.
o RIFT implementation assumes by default that all nodes are being o RIFT implementation assumes by default that all nodes are being
synchronized to 200 milliseconds precision which is easily synchronized to 200 milliseconds precision which is easily
achievable even in very large fabrics using [RFC5905]. An achievable even in very large fabrics using [RFC5905]. An
implementation MAY provide a way to reconfigure a domain to a implementation MAY provide a way to reconfigure a domain to a
different value. We call this variable MAXIMUM_CLOCK_DELTA. different value. We call this variable MAXIMUM_CLOCK_DELTA.
5.3.3.1. Clock Comparison 4.3.3.1. Clock Comparison
All monotonic clock values are comparable to each other using the All monotonic clock values are comparable to each other using the
following rules: following rules:
1. ASNC is older than any other value except ASNC AND 1. ASNC is older than any other value except ASNC AND
2. Clock with timestamp differing by more than MAXIMUM_CLOCK_DELTA 2. Clock with timestamp differing by more than MAXIMUM_CLOCK_DELTA
are comparable by using the timestamps only AND are comparable by using the timestamps only AND
3. Clocks with timestamps differing by less than MAXIMUM_CLOCK_DELTA 3. Clocks with timestamps differing by less than MAXIMUM_CLOCK_DELTA
are comparable by using their TIDs only AND are comparable by using their TIDs only AND
4. An undefined TID is always older than any other TID AND 4. An undefined TID is always older than any other TID AND
5. TIDs are compared using rules of [RFC8505]. 5. TIDs are compared using rules of [RFC8505].
5.3.3.2. Interaction between Time Stamps and Sequence Counters 4.3.3.2. Interaction between Time Stamps and Sequence Counters
For slow movements that occur less frequently than e.g. once per For slow movements that occur less frequently than e.g. once per
second, the time stamp that the RIFT infrastruture captures is enough second, the time stamp that the RIFT infrastruture captures is enough
to determine the freshest discovery. If the point of attachement to determine the freshest discovery. If the point of attachement
changes faster than the maximum drift of the time stamping mechanism changes faster than the maximum drift of the time stamping mechanism
(i.e. MAXIMUM_CLOCK_DELTA), then a sequence counter is required to (i.e. MAXIMUM_CLOCK_DELTA), then a sequence counter is required to
add resolution to the freshness evaluation, and it must be sized so add resolution to the freshness evaluation, and it must be sized so
that the counters stay comparable within the resolution of the time that the counters stay comparable within the resolution of the time
stampling mechanism. stampling mechanism.
The sequence counter in [RFC8505] is encoded as one octet and wraps The sequence counter in [RFC8505] is encoded as one octet and wraps
around using Appendix A. around using Appendix A.
Within the resolution of MAXIMUM_CLOCK_DELTA the sequence counters Within the resolution of MAXIMUM_CLOCK_DELTA the sequence counters
captured during 2 sequential values of the time stamp SHOULD be captured during 2 sequential values of the time stamp SHOULD be
comparable. This means with default values that a node may move up comparable. This means with default values that a node may move up
to 127 times during a 200 milliseconds period and the clocks remain to 127 times during a 200 milliseconds period and the clocks remain
still comparable thus allowing the infrastructure to assert the still comparable thus allowing the infrastructure to assert the
freshest advertisement with no ambiguity. freshest advertisement with no ambiguity.
5.3.3.3. Anycast vs. Unicast 4.3.3.3. Anycast vs. Unicast
A unicast prefix can be attached to at most one leaf, whereas an A unicast prefix can be attached to at most one leaf, whereas an
anycast prefix may be reachable via more than one leaf. anycast prefix may be reachable via more than one leaf.
If a monotonic clock attribute is provided on the prefix, then the If a monotonic clock attribute is provided on the prefix, then the
prefix with the `newest` clock value is strictly prefered. An prefix with the `newest` clock value is strictly prefered. An
anycast prefix does not carry a clock or all clock attributes MUST be anycast prefix does not carry a clock or all clock attributes MUST be
the same under the rules of Section 5.3.3.1. the same under the rules of Section 4.3.3.1.
Observe that it is important that in mobility events the leaf is re- Observe that it is important that in mobility events the leaf is re-
flooding as quickly as possible the absence of the prefix that moved flooding as quickly as possible the absence of the prefix that moved
away. away.
Observe further that without support for [RFC8505] movements on the Observe further that without support for [RFC8505] movements on the
fabric within intervals smaller than 100msec will be seen as anycast. fabric within intervals smaller than 100msec will be seen as anycast.
5.3.3.4. Overlays and Signaling 4.3.3.4. Overlays and Signaling
RIFT is agnostic whether any overlay technology like [MIP, LISP, RIFT is agnostic whether any overlay technology like [MIP, LISP,
VxLAN, NVO3] and the associated signaling is deployed over it. But VxLAN, NVO3] and the associated signaling is deployed over it. But
it is expected that leaf nodes, and possibly Top-of-Fabric nodes can it is expected that leaf nodes, and possibly Top-of-Fabric nodes can
perform the correct encapsulation. perform the correct encapsulation.
In the context of mobility, overlays provide a classical solution to In the context of mobility, overlays provide a classical solution to
avoid injecting mobile prefixes in the fabric and improve the avoid injecting mobile prefixes in the fabric and improve the
scalability of the solution. It makes sense on a data center that scalability of the solution. It makes sense on a data center that
already uses overlays to consider their applicability to the mobility already uses overlays to consider their applicability to the mobility
solution; as an example, a mobility protocol such as LISP may inform solution; as an example, a mobility protocol such as LISP may inform
the ingress leaf of the location of the egress leaf in real time. the ingress leaf of the location of the egress leaf in real time.
Another possibility is to consider that mobility as an underlay Another possibility is to consider that mobility as an underlay
service and support it in RIFT to an extent. The load on the fabric service and support it in RIFT to an extent. The load on the fabric
augments with the amount of mobility obviously since a move forces augments with the amount of mobility obviously since a move forces
flooding and computation on all nodes in the scope of the move so flooding and computation on all nodes in the scope of the move so
tunneling from leaf to the Top-of-Fabric may be desired. Future tunneling from leaf to the Top-of-Fabric may be desired.
versions of this document may describe support for such tunneling in
RIFT.
5.3.4. Key/Value Store 4.3.4. Key/Value Store
5.3.4.1. Southbound 4.3.4.1. Southbound
The protocol supports a southbound distribution of key-value pairs The protocol supports a southbound distribution of key-value pairs
that can be used to e.g. distribute configuration information during that can be used to e.g. distribute configuration information during
topology bring-up. The KV S-TIEs can arrive from multiple nodes and topology bring-up. The KV South TIEs can arrive from multiple nodes
hence need tie-breaking per key. We use the following rules and hence need tie-breaking per key. We use the following rules
1. Only KV TIEs originated by nodes to which the receiver has a bi- 1. Only KV TIEs originated by nodes to which the receiver has a bi-
directional adjacency are considered. directional adjacency are considered.
2. Within all such valid KV S-TIEs containing the key, the value of 2. Within all such valid KV South TIEs containing the key, the value
the KV S-TIE for which the according node S-TIE is present, has of the KV South TIE for which the according node South TIE is
the highest level and within the same level has highest present, has the highest level and within the same level has
originating system ID is preferred. If keys in the most highest originating system ID is preferred. If keys in the most
preferred TIEs are overlapping, the behavior is undefined. preferred TIEs are overlapping, the behavior is undefined.
Observe that if a node goes down, the node south of it looses Observe that if a node goes down, the node south of it looses
adjacencies to it and with that the KVs will be disregarded and on adjacencies to it and with that the KVs will be disregarded and on
tie-break changes new KV re-advertised to prevent stale information tie-break changes new KV re-advertised to prevent stale information
being used by nodes further south. KV information in southbound being used by nodes further south. KV information in southbound
direction is not result of independent computation of every node over direction is not result of independent computation of every node over
same set of TIEs but a diffused computation. same set of TIEs but a diffused computation.
5.3.4.2. Northbound 4.3.4.2. Northbound
Certain use cases seem to necessitate distribution of essentialy KV Certain use cases seem to necessitate distribution of essentialy KV
information that is generated in the leafs in the northbound information that is generated in the leafs in the northbound
direction. Such information is flooded in KV N-TIEs. Since the direction. Such information is flooded in KV North TIEs. Since the
originator of northbound KV is preserved during northbound flooding, originator of northbound KV is preserved during northbound flooding,
overlapping keys could be used. However, to omit further protocol overlapping keys could be used. However, to omit further protocol
complexity, only the value of the key in TIE tie-broken in same complexity, only the value of the key in TIE tie-broken in same
fashion as southbound KV TIEs is used. fashion as southbound KV TIEs is used.
5.3.5. Interactions with BFD 4.3.5. Interactions with BFD
RIFT MAY incorporate BFD [RFC5881] to react quickly to link failures. RIFT MAY incorporate BFD [RFC5881] to react quickly to link failures.
In such case following procedures are introduced: In such case following procedures are introduced:
After RIFT three way hello adjacency convergence a BFD session MAY After RIFT 3-way hello adjacency convergence a BFD session MAY be
be formed automatically between the RIFT endpoints without further formed automatically between the RIFT endpoints without further
configuration using the exchanged discriminators. The capability configuration using the exchanged discriminators. The capability
of the remote side to support BFD is carried on the LIEs. of the remote side to support BFD is carried on the LIEs.
In case established BFD session goes Down after it was Up, RIFT In case established BFD session goes Down after it was Up, RIFT
adjacency should be re-initialized started from Init. adjacency SHOULD be re-initialized and subsequently started from
Init after it sees a consecutive BFD Up.
In case of parallel links between nodes each link may run its own In case of parallel links between nodes each link MAY run its own
independent BFD session or they may share a session. independent BFD session or they may share a session.
In case RIFT changes link identifiers or BFD capability indication In case RIFT changes link identifiers or BFD capability indication
both the LIE as well as the BFD sessions SHOULD be brought down both the LIE as well as the BFD sessions SHOULD be brought down
and back up again. and back up again.
Multiple RIFT instances MAY choose to share a single BFD session Multiple RIFT instances MAY choose to share a single BFD session
(in such case it is undefined what discriminators are used albeit (in such case it is undefined what discriminators are used albeit
RIFT CAN advertise the same link ID for the same interface in RIFT CAN advertise the same link ID for the same interface in
multiple instances and with that "share" the discriminators). multiple instances and with that "share" the discriminators).
BFD TTL follows [RFC5082]. BFD TTL follows [RFC5082].
5.3.6. Fabric Bandwidth Balancing 4.3.6. Fabric Bandwidth Balancing
A well understood problem in fabrics is that in case of link losses A well understood problem in fabrics is that in case of link losses
it would be ideal to rebalance how much traffic is offered to it would be ideal to rebalance how much traffic is offered to
switches in the next level based on the ingress and egress bandwidth switches in the next level based on the ingress and egress bandwidth
they have. Current attempts rely mostly on specialized traffic they have. Current attempts rely mostly on specialized traffic
engineering via controller or leafs being aware of complete topology engineering via controller or leafs being aware of complete topology
with according cost and complexity. with according cost and complexity.
RIFT can support a very light weight mechanism that can deal with the RIFT can support a very light weight mechanism that can deal with the
problem in an approximate way based on the fact that RIFT is loop- problem in an approximate way based on the fact that RIFT is loop-
free. free.
5.3.6.1. Northbound Direction 4.3.6.1. Northbound Direction
Every RIFT node SHOULD compute the amount of northbound bandwith Every RIFT node SHOULD compute the amount of northbound bandwith
available through neighbors at higher level and modify distance available through neighbors at higher level and modify distance
received on default route from this neighbor. Those different received on default route from this neighbor. Those different
distances SHOULD be used to support weighted ECMP forwarding towards distances SHOULD be used to support weighted ECMP forwarding towards
higher level when using default route. We call such a distance higher level when using default route. We call such a distance
Bandwidth Adjusted Distance or BAD. This is best illustrated by a Bandwidth Adjusted Distance or BAD. This is best illustrated by a
simple example. simple example.
. 100 x 100 100 MBits . 100 x 100 100 MBits
skipping to change at page 79, line 48 skipping to change at page 99, line 48
bandwidth given that the algorithm is distributed and un-synchronized bandwidth given that the algorithm is distributed and un-synchronized
and ultimately, its correct behavior does not depend on uniformity of and ultimately, its correct behavior does not depend on uniformity of
balancing algorithms used in the fabric. E.g. it is conceivable that balancing algorithms used in the fabric. E.g. it is conceivable that
leafs could use real time link loads gathered by analytics to change leafs could use real time link loads gathered by analytics to change
the amount of traffic assigned to each default route next hop. the amount of traffic assigned to each default route next hop.
Observe further that a change in available bandwidth will only affect Observe further that a change in available bandwidth will only affect
at maximum two levels down in the fabric, i.e. blast radius of at maximum two levels down in the fabric, i.e. blast radius of
bandwidth changes is contained no matter its height. bandwidth changes is contained no matter its height.
5.3.6.2. Southbound Direction 4.3.6.2. Southbound Direction
Due to its loop free properties a node CAN take during S-SPF into Due to its loop free properties a node CAN take during S-SPF into
account the available bandwidth on the nodes in lower levels and account the available bandwidth on the nodes in lower levels and
modify the amount of traffic offered to next level's "southbound" modify the amount of traffic offered to next level's "southbound"
nodes based as what it sees is the total achievable maximum flow nodes based as what it sees is the total achievable maximum flow
through those nodes. It is worth observing that such computations through those nodes. It is worth observing that such computations
may work better if standardized but does not have to be necessarily. may work better if standardized but does not have to be necessarily.
As long the packet keeps on heading south it will take one of the As long the packet keeps on heading south it will take one of the
available paths and arrive at the intended destination. available paths and arrive at the intended destination.
5.3.7. Label Binding 4.3.7. Label Binding
A node MAY advertise on its TIEs a locally significant, downstream
assigned label for the according interface. One use of such label is
a hop-by-hop encapsulation allowing to easily distinguish forwarding
planes served by a multiplicity of RIFT instances.
5.3.8. Segment Routing Support with RIFT
Recently, alternative architecture to reuse labels as segment
identifiers [RFC8402] has gained traction and may present use cases
in IP fabric that would justify its deployment. Such use cases will
either precondition an assignment of a label per node (or other
entities where the mechanisms are equivalent) or a global assignment
and a knowledge of topology everywhere to compute segment stacks of
interest. We deal with the two issues separately.
5.3.8.1. Global Segment Identifiers Assignment
Global segment identifiers are normally assumed to be provided by
some kind of a centralized "controller" instance and distributed to
other entities. This can be performed in RIFT by attaching a
controller to the Top-of-Fabric nodes at the top of the fabric where
the whole topology is always visible, assign such identifiers and
then distribute those via the KV mechanism towards all nodes so they
can perform things like probing the fabric for failures using a stack
of segments.
5.3.8.2. Distribution of Topology Information
Some segment routing use cases seem to precondition full knowledge of
fabric topology in all nodes which can be performed albeit at the
loss of one of highly desirable properties of RIFT, namely minimal
blast radius. Basically, RIFT can function as a flat IGP by
switching off its flooding scopes. All nodes will end up with full
topology view and albeit the N-SPF and S-SPF are still performed
based on RIFT rules, any computation with segment identifiers that
needs full topology can use it.
Beside blast radius problem, excessive flooding may present A node MAY advertise on its LIEs a locally significant, downstream
significant load on implementations. assigned, interface specific label. One use of such label is a hop-
by-hop encapsulation allowing to easily distinguish forwarding planes
served by a multiplicity of RIFT instances.
5.3.9. Leaf to Leaf Procedures 4.3.8. Leaf to Leaf Procedures
RIFT can optionally allow special leaf East-West adjacencies under RIFT can optionally allow special leaf East-West adjacencies under
additional set of rules. The leaf supporting those procedures MUST: additional set of rules. The leaf supporting those procedures MUST:
advertise the LEAF_2_LEAF flag in node capabilities AND advertise the LEAF_2_LEAF flag in node capabilities AND
set the overload bit on all leaf's node TIEs AND set the overload bit on all leaf's node TIEs AND
flood only node's own north and south TIEs over E-W leaf flood only node's own north and south TIEs over E-W leaf
adjacencies AND adjacencies AND
skipping to change at page 81, line 30 skipping to change at page 100, line 42
install a discard route for any advertised aggregate in leaf's install a discard route for any advertised aggregate in leaf's
TIEs AND TIEs AND
never form southbound adjacencies. never form southbound adjacencies.
This will allow the E-W leaf nodes to exchange traffic strictly for This will allow the E-W leaf nodes to exchange traffic strictly for
the prefixes advertised in each other's north prefix TIEs (since the the prefixes advertised in each other's north prefix TIEs (since the
southbound computation will find the reverse direction in the other southbound computation will find the reverse direction in the other
node's TIE and install its north prefixes). node's TIE and install its north prefixes).
5.3.10. Address Family and Multi Topology Considerations 4.3.9. Address Family and Multi Topology Considerations
Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC8202] is used Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC8202] is used
today in link-state routing protocols to support several domains on today in link-state routing protocols to support several domains on
the same physical topology. RIFT supports this capability by the same physical topology. RIFT supports this capability by
carrying transport ports in the LIE protocol exchanges. Multiplexing carrying transport ports in the LIE protocol exchanges. Multiplexing
of LIEs can be achieved by either choosing varying multicast of LIEs can be achieved by either choosing varying multicast
addresses or ports on the same address. addresses or ports on the same address.
BFD interactions in Section 5.3.5 are implementation dependent when BFD interactions in Section 4.3.5 are implementation dependent when
multiple RIFT instances run on the same link. multiple RIFT instances run on the same link.
5.3.11. Reachability of Internal Nodes in the Fabric 4.3.10. Reachability of Internal Nodes in the Fabric
RIFT does not precondition that its nodes have reachable addresses RIFT does not precondition that its nodes have reachable addresses
albeit for operational purposes this is clearly desirable. Under albeit for operational purposes this is clearly desirable. Under
normal operating conditions this can be easily achieved by e.g. normal operating conditions this can be easily achieved by e.g.
injecting the node's loopback address into North and South Prefix injecting the node's loopback address into North and South Prefix
TIEs or other implementation specific mechanisms. TIEs or other implementation specific mechanisms.
Things get more interesting in case a node looses all its northbound Things get more interesting in case a node looses all its northbound
adjacencies but is not at the top of the fabric. That is outside the adjacencies but is not at the top of the fabric. That is outside the
scope of this document and may be covered in a separate document scope of this document and may be covered in a separate document.
about policy guided prefixes [PGP reference].
5.3.12. One-Hop Healing of Levels with East-West Links 4.3.11. One-Hop Healing of Levels with East-West Links
Based on the rules defined in Section 5.2.4, Section 5.2.3.8 and Based on the rules defined in Section 4.2.4, Section 4.2.3.8 and
given presence of E-W links, RIFT can provide a one-hop protection of given presence of E-W links, RIFT can provide a one-hop protection of
nodes that lost all their northbound links or in other complex link nodes that lost all their northbound links or in other complex link
set failure scenarios except at Top-of-Fabric where the links are set failure scenarios except at Top-of-Fabric where the links are
used exclusively to flood topology information in multi-plane used exclusively to flood topology information in multi-plane
designs. Section 6.4 explains the resulting behavior based on one designs. Section 5.4 explains the resulting behavior based on one
such example. such example.
5.4. Security 4.4. Security
5.4.1. Security Model 4.4.1. Security Model
An inherent property of any security and ZTP architecture is the An inherent property of any security and ZTP architecture is the
resulting trade-off in regard to integrity verification of the resulting trade-off in regard to integrity verification of the
information distributed through the fabric vs. necessary provisioning information distributed through the fabric vs. necessary provisioning
and auto-configuration. At a minimum, in all approaches, the and auto-configuration. At a minimum, in all approaches, the
security of an established adjacency can be ensured. The stricter security of an established adjacency can be ensured. The stricter
the security model the more provisioning must take over the role of the security model the more provisioning must take over the role of
ZTP. ZTP.
The most security conscious operators will want to have full control The most security conscious operators will want to have full control
skipping to change at page 84, line 22 skipping to change at page 103, line 29
Increasing +--------------+ Less Increasing +--------------+ Less
Provisioning / FAM \ Configuration Provisioning / FAM \ Configuration
| +------------------+ | | +------------------+ |
| / Level Provisioning \ | | / Level Provisioning \ |
| +----------------------+ \|/ | +----------------------+ \|/
| / Zero Configuration \ v | / Zero Configuration \ v
+--------------------------+ +--------------------------+
Figure 30: Security Model Figure 30: Security Model
5.4.2. Security Mechanisms 4.4.2. Security Mechanisms
RIFT Security goals are to ensure authentication, message integrity RIFT Security goals are to ensure authentication, message integrity
and prevention of replay attacks. Low processing overhead and and prevention of replay attacks. Low processing overhead and
efficient messaging are also a goal. Message confidentiality is a efficient messaging are also a goal. Message confidentiality is a
non-goal. non-goal.
The model in the previous section allows a range of security key The model in the previous section allows a range of security key
types that are analogous to the various security association models. types that are analogous to the various security association models.
PAM and NAM allow security associations at the port or node level PAM and NAM allow security associations at the port or node level
using symmetric or asymmetric keys that are pre-installed. FAM using symmetric or asymmetric keys that are pre-installed. FAM
argues for security associations to be applied only at a group level argues for security associations to be applied only at a group level
or to be refined once the topology has been established. RIFT does or to be refined once the topology has been established. RIFT does
not specify how security keys are installed or updated it specifies not specify how security keys are installed or updated it specifies
how the key can be used to achieve goals. how the key can be used to achieve goals.
The protocol has provisions for "weak" nonces to prevent replay The protocol has provisions for "weak" nonces to prevent replay
attacks and includes authentication mechanisms comparable to attacks and includes authentication mechanisms comparable to
[RFC5709] and [RFC7987]. [RFC5709] and [RFC7987].
5.4.3. Security Envelope 4.4.3. Security Envelope
RIFT MUST be carried in a mandatory secure envelope illustrated in RIFT MUST be carried in a mandatory secure envelope illustrated in
Figure 31. Any value in the packet following a security fingerprint Figure 31. Any value in the packet following a security fingerprint
MUST be used only after the according fingerprint has been validated. MUST be used only after the according fingerprint has been validated.
Local configuration MAY allow to skip the checking of the envelope's Local configuration MAY allow to skip the checking of the envelope's
integrity. integrity.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 87, line 28 skipping to change at page 107, line 28
object to protect TIE from modification during flooding. This object to protect TIE from modification during flooding. This
ensures origin validation and integrity (but does not provide ensures origin validation and integrity (but does not provide
validation of a chain of trust). validation of a chain of trust).
Observe that due to the schema migration rules per Appendix B the Observe that due to the schema migration rules per Appendix B the
contained model can be always decoded if the major version matches contained model can be always decoded if the major version matches
and the envelope integrity has been validated. Consequently, and the envelope integrity has been validated. Consequently,
description of the TIE is available to flood it properly including description of the TIE is available to flood it properly including
unknown TIE types. unknown TIE types.
5.4.4. Weak Nonces 4.4.4. Weak Nonces
The protocol uses two 16 bit nonces to salt generated signatures. We The protocol uses two 16 bit nonces to salt generated signatures. We
use the term "nonce" a bit loosely since RIFT nonces are not being use the term "nonce" a bit loosely since RIFT nonces are not being
changed on every packet as common in cryptography. For efficiency changed on every packet as common in cryptography. For efficiency
purposes they are changed at a frequency high enough to dwarf replay purposes they are changed at a frequency high enough to dwarf replay
attacks attempts for all practical purposes. Therefore, we call them attacks attempts for all practical purposes. Therefore, we call them
"weak" nonces. "weak" nonces.
Any implementation including RIFT security MUST generate and wrap Any implementation including RIFT security MUST generate and wrap
around local nonces properly. When a nonce increment leads to around local nonces properly. When a nonce increment leads to
skipping to change at page 88, line 24 skipping to change at page 108, line 24
As a necessary exception, an implementation MUST advertise As a necessary exception, an implementation MUST advertise
`undefined_nonce` for remote nonce value when the FSM is not in 2-way `undefined_nonce` for remote nonce value when the FSM is not in 2-way
or 3-way state and accept an `undefined_nonce` for its local nonce or 3-way state and accept an `undefined_nonce` for its local nonce
value on packets in any other state than 3-way. value on packets in any other state than 3-way.
As optional optimization, an implemenation MAY send one LIE with As optional optimization, an implemenation MAY send one LIE with
previously negotiated neighbor's nonce to try to speed up a previously negotiated neighbor's nonce to try to speed up a
neighbor's transition from 3-way to 1-way and MUST revert to sending neighbor's transition from 3-way to 1-way and MUST revert to sending
`undefined_nonce` after that. `undefined_nonce` after that.
5.4.5. Lifetime 4.4.5. Lifetime
Protecting lifetime on flooding may lead to excessive number of Protecting lifetime on flooding may lead to excessive number of
security fingerprint computation and hence an application generating security fingerprint computation and hence an application generating
such fingerprints on TIEs MAY round the value down to the next such fingerprints on TIEs MAY round the value down to the next
`rounddown_lifetime_interval` defined in the schema when sending TIEs `rounddown_lifetime_interval` defined in the schema when sending TIEs
albeit such optimization in presence of security hashes over albeit such optimization in presence of security hashes over
advancing weak nonces may not be feasible. advancing weak nonces may not be feasible.
5.4.6. Key Management 4.4.6. Key Management
As outlined in the Security Model a private shared key or a public/ As outlined in the Security Model a private shared key or a public/
private key pair is used to Authenticate the adjacency. The actual private key pair is used to Authenticate the adjacency. The actual
method of key distribution and key synchronization is assumed to be method of key distribution and key synchronization is assumed to be
out of band from RIFT's perspective. Both nodes in the adjacency out of band from RIFT's perspective. Both nodes in the adjacency
must share the same keys and configuration of key type and algorithm must share the same keys and configuration of key type and algorithm
for a key ID. Mismatched keys will obviously not inter-operate due for a key ID. Mismatched keys will obviously not inter-operate due
to unverifiable security envelope. to unverifiable security envelope.
Key roll-over while the adjacency is active is allowed and the Key roll-over while the adjacency is active is allowed and the
technique is well known and described in e.g. [RFC6518]. Key technique is well known and described in e.g. [RFC6518]. Key
distribution procedures are out of scope for RIFT. distribution procedures are out of scope for RIFT.
5.4.7. Security Association Changes 4.4.7. Security Association Changes
There in no mechanism to convert a security envelope for the same key There in no mechanism to convert a security envelope for the same key
ID from one algorithm to another once the envelope is operational. ID from one algorithm to another once the envelope is operational.
The recommended procedure to change to a new algorithm is to take the The recommended procedure to change to a new algorithm is to take the
adjacency down and make the changes and then bring the adjacency up. adjacency down and make the changes and then bring the adjacency up.
Obviously, an implementation may choose to stop verifying security Obviously, an implementation may choose to stop verifying security
envelope for the duration of key change to keep the adjacency up but envelope for the duration of key change to keep the adjacency up but
since this introduces a security vulnerability window, such roll-over since this introduces a security vulnerability window, such roll-over
is not recommended. is not recommended.
6. Examples 5. Examples
6.1. Normal Operation 5.1. Normal Operation
This section describes RIFT deployment in the example topology This section describes RIFT deployment in the example topology
without any node or link failures. We disregard flooding reduction without any node or link failures. We disregard flooding reduction
for simplicity's sake. for simplicity's sake.
As first step, the following bi-directional adjacencies will be As first step, the following bi-directional adjacencies will be
created (and any other links that do not fulfill LIE rules in created (and any other links that do not fulfill LIE rules in
Section 5.2.2 disregarded): Section 4.2.2 disregarded):
1. Spine 21 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 1. ToF 21 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122
122
2. Spine 22 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 2. ToF 22 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122
122
3. Spine 111 to Leaf 111, Leaf 112 3. Spine 111 to Leaf 111, Leaf 112
4. Spine 112 to Leaf 111, Leaf 112 4. Spine 112 to Leaf 111, Leaf 112
5. Spine 121 to Leaf 121, Leaf 122 5. Spine 121 to Leaf 121, Leaf 122
6. Spine 122 to Leaf 121, Leaf 122 6. Spine 122 to Leaf 121, Leaf 122
Consequently, N-TIEs would be originated by Spine 111 and Spine 112 Consequently, North TIEs would be originated by Spine 111 and Spine
and each set would be sent to both Spine 21 and Spine 22. N-TIEs 112 and each set would be sent to both ToF 21 and ToF 22. North TIEs
also would be originated by Leaf 111 (w/ Prefix 111) and Leaf 112 (w/ also would be originated by Leaf 111 (w/ Prefix 111) and Leaf 112 (w/
Prefix 112 and the multi-homed prefix) and each set would be sent to Prefix 112 and the multi-homed prefix) and each set would be sent to
Spine 111 and Spine 112. Spine 111 and Spine 112 would then flood Spine 111 and Spine 112. Spine 111 and Spine 112 would then flood
these N-TIEs to Spine 21 and Spine 22. these North TIEs to ToF 21 and ToF 22.
Similarly, N-TIEs would be originated by Spine 121 and Spine 122 and Similarly, North TIEs would be originated by Spine 121 and Spine 122
each set would be sent to both Spine 21 and Spine 22. N-TIEs also and each set would be sent to both ToF 21 and ToF 22. North TIEs
would be originated by Leaf 121 (w/ Prefix 121 and the multi-homed also would be originated by Leaf 121 (w/ Prefix 121 and the multi-
prefix) and Leaf 122 (w/ Prefix 122) and each set would be sent to homed prefix) and Leaf 122 (w/ Prefix 122) and each set would be sent
Spine 121 and Spine 122. Spine 121 and Spine 122 would then flood to Spine 121 and Spine 122. Spine 121 and Spine 122 would then flood
these N-TIEs to Spine 21 and Spine 22. these North TIEs to ToF 21 and ToF 22.
At this point both Spine 21 and Spine 22, as well as any controller At this point both ToF 21 and ToF 22, as well as any controller to
to which they are connected, would have the complete network which they are connected, would have the complete network topology.
topology. At the same time, Spine 111/112/121/122 hold only the At the same time, Spine 111/112/121/122 hold only the N-ties of level
N-ties of level 0 of their respective PoD. Leafs hold only their own 0 of their respective PoD. Leafs hold only their own North TIEs.
N-TIEs.
S-TIEs with adjacencies and a default IP prefix would then be South TIEs with adjacencies and a default IP prefix would then be
originated by Spine 21 and Spine 22 and each would be flooded to originated by ToF 21 and ToF 22 and each would be flooded to Spine
Spine 111, Spine 112, Spine 121, and Spine 122. Spine 111, Spine 111, Spine 112, Spine 121, and Spine 122. Spine 111, Spine 112,
112, Spine 121, and Spine 122 would each send the S-TIE from Spine 21 Spine 121, and Spine 122 would each send the South TIE from ToF 21 to
to Spine 22 and the S-TIE from Spine 22 to Spine 21. (S-TIEs are ToF 22 and the South TIE from ToF 22 to ToF 21. (South TIEs are
reflected up to level from which they are received but they are NOT reflected up to level from which they are received but they are NOT
propagated southbound.) propagated southbound.)
A S-TIE with a default IP prefix would be originated by Node 111 and A South TIE with a default IP prefix would be originated by Node 111
Spine 112 and each would be sent to Leaf 111 and Leaf 112. and Spine 112 and each would be sent to Leaf 111 and Leaf 112.
Similarly, an S-TIE with a default IP prefix would be originated by Similarly, an South TIE with a default IP prefix would be originated
Node 121 and Spine 122 and each would be sent to Leaf 121 and Leaf by Node 121 and Spine 122 and each would be sent to Leaf 121 and Leaf
122. At this point IP connectivity with maximum possible ECMP has 122. At this point IP connectivity with maximum possible ECMP has
been established between the leafs while constraining the amount of been established between the leafs while constraining the amount of
information held by each node to the minimum necessary for normal information held by each node to the minimum necessary for normal
operation and dealing with failures. operation and dealing with failures.
6.2. Leaf Link Failure 5.2. Leaf Link Failure
. | | | | . | | | |
.+-+---+-+ +-+---+-+ .+-+---+-+ +-+---+-+
.| | | | .| | | |
.|Spin111| |Spin112| .|Spin111| |Spin112|
.+-+---+-+ ++----+-+ .+-+---+-+ ++----+-+
. | | | | . | | | |
. | +---------------+ X . | +---------------+ X
. | | | X Failure . | | | X Failure
. | +-------------+ | X . | +-------------+ | X
skipping to change at page 90, line 50 skipping to change at page 110, line 48
.+-------+ +-------+ .+-------+ +-------+
. + + . + +
. Prefix111 Prefix112 . Prefix111 Prefix112
Figure 32: Single Leaf link failure Figure 32: Single Leaf link failure
In case of a failing leaf link between spine 112 and leaf 112 the In case of a failing leaf link between spine 112 and leaf 112 the
link-state information will cause re-computation of the necessary SPF link-state information will cause re-computation of the necessary SPF
and the higher levels will stop forwarding towards prefix 112 through and the higher levels will stop forwarding towards prefix 112 through
spine 112. Only spines 111 and 112, as well as both spines will see spine 112. Only spines 111 and 112, as well as both spines will see
control traffic. Leaf 111 will receive a new S-TIE from spine 112 control traffic. Leaf 111 will receive a new South TIE from spine
and reflect back to spine 111. Spine 111 will de-aggregate prefix 112 and reflect back to spine 111. Spine 111 will de-aggregate
111 and prefix 112 but we will not describe it further here since de- prefix 111 and prefix 112 but we will not describe it further here
aggregation is emphasized in the next example. It is worth observing since de-aggregation is emphasized in the next example. It is worth
however in this example that if leaf 111 would keep on forwarding observing however in this example that if leaf 111 would keep on
traffic towards prefix 112 using the advertised south-bound default forwarding traffic towards prefix 112 using the advertised south-
of spine 112 the traffic would end up on Top-of-Fabric 21 and ToF 22 bound default of spine 112 the traffic would end up on Top-of-Fabric
and cross back into pod 1 using spine 111. This is arguably not as 21 and ToF 22 and cross back into pod 1 using spine 111. This is
bad as black-holing present in the next example but clearly arguably not as bad as black-holing present in the next example but
undesirable. Fortunately, de-aggregation prevents this type of clearly undesirable. Fortunately, de-aggregation prevents this type
behavior except for a transitory period of time. of behavior except for a transitory period of time.
6.3. Partitioned Fabric 5.3. Partitioned Fabric
. +--------+ +--------+ S-TIE of Spine21 . +--------+ +--------+ South TIE of ToF 21
. | | | | received by . | | | | received by
. |ToF 21| |ToF 22| south reflection of . |ToF 21| |ToF 22| south reflection of
. ++-+--+-++ ++-+--+-++ spines 112 and 111 . ++-+--+-++ ++-+--+-++ spines 112 and 111
. | | | | | | | | . | | | | | | | |
. | | | | | | | 0/0 . | | | | | | | 0/0
. | | | | | | | | . | | | | | | | |
. | | | | | | | | . | | | | | | | |
. +--------------+ | +--- XXXXXX + | | | +---------------+ . +--------------+ | +--- XXXXXX + | | | +---------------+
. | | | | | | | | . | | | | | | | |
. | +-----------------------------+ | | | . | +-----------------------------+ | | |
skipping to change at page 92, line 6 skipping to change at page 111, line 50
.| | | | | | | | .| | | | | | | |
.|Leaf111| |Leaf112| |Leaf121| |Leaf122| .|Leaf111| |Leaf112| |Leaf121| |Leaf122|
.+-+-----+ ++------+ +-----+-+ +-+-----+ .+-+-----+ ++------+ +-----+-+ +-+-----+
. + + + + . + + + +
. Prefix111 Prefix112 Prefix121 Prefix122 . Prefix111 Prefix112 Prefix121 Prefix122
. 1.1/16 . 1.1/16
Figure 33: Fabric partition Figure 33: Fabric partition
Figure 33 shows the arguably a more catastrophic but also a more Figure 33 shows the arguably a more catastrophic but also a more
interesting case. Spine 21 is completely severed from access to interesting case. ToF 21 is completely severed from access to Prefix
Prefix 121 (we use in the figure 1.1/16 as example) by double link 121 (we use in the figure 1.1/16 as example) by double link failure.
failure. However unlikely, if left unresolved, forwarding from leaf However unlikely, if left unresolved, forwarding from leaf 111 and
111 and leaf 112 to prefix 121 would suffer 50% black-holing based on leaf 112 to prefix 121 would suffer 50% black-holing based on pure
pure default route advertisements by Top-of-Fabric 21 and ToF 22. default route advertisements by ToF 21 and ToF 22.
The mechanism used to resolve this scenario is hinging on the The mechanism used to resolve this scenario is hinging on the
distribution of southbound representation by Top-of-Fabric 21 that is distribution of southbound representation by Top-of-Fabric 21 that is
reflected by spine 111 and spine 112 to ToF 22. Spine 22, having reflected by spine 111 and spine 112 to ToF 22. ToF 22, having
computed reachability to all prefixes in the network, advertises with computed reachability to all prefixes in the network, advertises with
the default route the ones that are reachable only via lower level the default route the ones that are reachable only via lower level
neighbors that ToF 21 does not show an adjacency to. That results in neighbors that ToF 21 does not show an adjacency to. That results in
spine 111 and spine 112 obtaining a longest-prefix match to prefix spine 111 and spine 112 obtaining a longest-prefix match to prefix
121 which leads through ToF 22 and prevents black-holing through ToF 121 which leads through ToF 22 and prevents black-holing through ToF
21 still advertising the 0/0 aggregate only. 21 still advertising the 0/0 aggregate only.
The prefix 121 advertised by Top-of-Fabric 22 does not have to be The prefix 121 advertised by Top-of-Fabric 22 does not have to be
propagated further towards leafs since they do no benefit from this propagated further towards leafs since they do no benefit from this
information. Hence the amount of flooding is restricted to ToF 21 information. Hence the amount of flooding is restricted to ToF 21
reissuing its S-TIEs and south reflection of those by spine 111 and reissuing its South TIEs and south reflection of those by spine 111
spine 112. The resulting SPF in ToF 22 issues a new prefix S-TIEs and spine 112. The resulting SPF in ToF 22 issues a new prefix South
containing 1.1/16. None of the leafs become aware of the changes and TIEs containing 1.1/16. None of the leafs become aware of the
the failure is constrained strictly to the level that became changes and the failure is constrained strictly to the level that
partitioned. became partitioned.
To finish with an example of the resulting sets computed using To finish with an example of the resulting sets computed using
notation introduced in Section 5.2.5, Top-of-Fabric 22 constructs the notation introduced in Section 4.2.5, Top-of-Fabric 22 constructs the
following sets: following sets:
|R = Prefix 111, Prefix 112, Prefix 121, Prefix 122 |R = Prefix 111, Prefix 112, Prefix 121, Prefix 122
|H (for r=Prefix 111) = Spine 111, Spine 112 |H (for r=Prefix 111) = Spine 111, Spine 112
|H (for r=Prefix 112) = Spine 111, Spine 112 |H (for r=Prefix 112) = Spine 111, Spine 112
|H (for r=Prefix 121) = Spine 121, Spine 122 |H (for r=Prefix 121) = Spine 121, Spine 122
|H (for r=Prefix 122) = Spine 121, Spine 122 |H (for r=Prefix 122) = Spine 121, Spine 122
|A (for Spine 21) = Spine 111, Spine 112 |A (for ToF 21) = Spine 111, Spine 112
With that and |H (for r=prefix 121) and |H (for r=prefix 122) being With that and |H (for r=prefix 121) and |H (for r=prefix 122) being
disjoint from |A (for Top-of-Fabric 21), ToF 22 will originate an disjoint from |A (for Top-of-Fabric 21), ToF 22 will originate an
S-TIE with prefix 121 and prefix 122, that is flooded to spines 112, South TIE with prefix 121 and prefix 122, that is flooded to spines
112, 121 and 122. 112, 112, 121 and 122.
6.4. Northbound Partitioned Router and Optional East-West Links 5.4. Northbound Partitioned Router and Optional East-West Links
. + + + . + + +
. X N1 | N2 | N3 . X N1 | N2 | N3
. X | | . X | |
.+--+----+ +--+----+ +--+-----+ .+--+----+ +--+----+ +--+-----+
.| |0/0> <0/0| |0/0> <0/0| | .| |0/0> <0/0| |0/0> <0/0| |
.| A01 +----------+ A02 +----------+ A03 | Level 1 .| A01 +----------+ A02 +----------+ A03 | Level 1
.++-+-+--+ ++--+--++ +---+-+-++ .++-+-+--+ ++--+--++ +---+-+-++
. | | | | | | | | | . | | | | | | | | |
. | | +----------------------------------+ | | | . | | +----------------------------------+ | | |
skipping to change at page 93, line 32 skipping to change at page 113, line 32
. | | | | | | | | | . | | | | | | | | |
.++-+-+--+ | +---+---+ | +-+---+-++ .++-+-+--+ | +---+---+ | +-+---+-++
.| | +-+ +-+ | | .| | +-+ +-+ | |
.| L01 | | L02 | | L03 | Level 0 .| L01 | | L02 | | L03 | Level 0
.+-------+ +-------+ +--------+ .+-------+ +-------+ +--------+
Figure 34: North Partitioned Router Figure 34: North Partitioned Router
Figure 34 shows a part of a fabric where level 1 is horizontally Figure 34 shows a part of a fabric where level 1 is horizontally
connected and A01 lost its only northbound adjacency. Based on N-SPF connected and A01 lost its only northbound adjacency. Based on N-SPF
rules in Section 5.2.4.1 A01 will compute northbound reachability by rules in Section 4.2.4.1 A01 will compute northbound reachability by
using the link A01 to A02 (whereas A02 will NOT use this link during using the link A01 to A02 (whereas A02 will NOT use this link during
N-SPF). Hence A01 will still advertise the default towards level 0 N-SPF). Hence A01 will still advertise the default towards level 0
and route unidirectionally using the horizontal link. and route unidirectionally using the horizontal link.
As further consideration, the moment A02 looses link N2 the situation As further consideration, the moment A02 looses link N2 the situation
evolves again. A01 will have no more northbound reachability while evolves again. A01 will have no more northbound reachability while
still seeing A03 advertising northbound adjacencies in its south node still seeing A03 advertising northbound adjacencies in its south node
tie. With that it will stop advertising a default route due to tie. With that it will stop advertising a default route due to
Section 5.2.3.8. Section 4.2.3.8.
7. Implementation and Operation: Further Details 6. Implementation and Operation: Further Details
7.1. Considerations for Leaf-Only Implementation 6.1. Considerations for Leaf-Only Implementation
RIFT can and is intended to be stretched to the lowest level in the RIFT can and is intended to be stretched to the lowest level in the
IP fabric to integrate ToRs or even servers. Since those entities IP fabric to integrate ToRs or even servers. Since those entities
would run as leafs only, it is worth to observe that a leaf only would run as leafs only, it is worth to observe that a leaf only
version is significantly simpler to implement and requires much less version is significantly simpler to implement and requires much less
resources: resources:
1. Under normal conditions, the leaf needs to support a multipath 1. Under normal conditions, the leaf needs to support a multipath
default route only. In most catastrophic partitioning case it default route only. In most catastrophic partitioning case it
has to be capable of accommodating all the leaf routes in its own has to be capable of accommodating all the leaf routes in its own
PoD to prevent black-holing. PoD to prevent black-holing.
2. Leaf nodes hold only their own N-TIEs and S-TIEs of Level 1 nodes 2. Leaf nodes hold only their own North TIEs and South TIEs of Level
they are connected to; so overall few in numbers. 1 nodes they are connected to; so overall few in numbers.
3. Leaf node does not have to support any type of de-aggregation 3. Leaf node does not have to support any type of de-aggregation
computation or propagation. computation or propagation.
4. Leaf nodes do not have to support overload bit normally. 4. Leaf nodes do not have to support overload bit normally.
5. Unless optional leaf-2-leaf procedures are desired default route 5. Unless optional leaf-2-leaf procedures are desired default route
origination and S-TIE origination is unnecessary. origination and South TIE origination is unnecessary.
7.2. Considerations for Spine Implementation 6.2. Considerations for Spine Implementation
In case of spines, i.e. nodes that will never act as Top of Fabric a In case of spines, i.e. nodes that will never act as Top of Fabric a
full implementation is not required, specifically the node does not full implementation is not required, specifically the node does not
need to perform any computation of negative disaggregation except need to perform any computation of negative disaggregation except
respecting northbound disaggregation advertised from the north. respecting northbound disaggregation advertised from the north.
7.3. Adaptations to Other Proposed Data Center Topologies 6.3. Adaptations to Other Proposed Data Center Topologies
. +-----+ +-----+ . +-----+ +-----+
. | | | | . | | | |
.+-+ S0 | | S1 | .+-+ S0 | | S1 |
.| ++---++ ++---++ .| ++---++ ++---++
.| | | | | .| | | | |
.| | +------------+ | .| | +------------+ |
.| | | +------------+ | .| | | +------------+ |
.| | | | | .| | | | |
.| ++-+--+ +--+-++ .| ++-+--+ +--+-++
skipping to change at page 95, line 9 skipping to change at page 115, line 9
.+-+ | | | .+-+ | | |
. | L0 | | L1 | . | L0 | | L1 |
. +-----+ +-----+ . +-----+ +-----+
Figure 35: Level Shortcut Figure 35: Level Shortcut
Strictly speaking, RIFT is not limited to Clos variations only. The Strictly speaking, RIFT is not limited to Clos variations only. The
protocol preconditions only a sense of 'compass rose direction' protocol preconditions only a sense of 'compass rose direction'
achieved by configuration (or derivation) of levels and other achieved by configuration (or derivation) of levels and other
topologies are possible within this framework. So, conceptually, one topologies are possible within this framework. So, conceptually, one
could include leaf to leaf links and even shortcut between levels but could include leaf to leaf links and even shortcut between levels As
certain requirements in Section 4 will not be met anymore. As an an example, shortcutting levels illustrated in Figure 35 will lead
example, shortcutting levels illustrated in Figure 35 will lead
either to suboptimal routing when L0 sends traffic to L1 (since using either to suboptimal routing when L0 sends traffic to L1 (since using
S0's default route will lead to the traffic being sent back to A0 or S0's default route will lead to the traffic being sent back to A0 or
A1) or the leafs need each other's routes installed to understand A1) or the leafs need each other's routes installed to understand
that only A0 and A1 should be used to talk to each other. that only A0 and A1 should be used to talk to each other.
Whether such modifications of topology constraints make sense is Whether such modifications of topology constraints make sense is
dependent on many technology variables and the exhausting treatment dependent on many technology variables and the exhausting treatment
of the topic is definitely outside the scope of this document. of the topic is definitely outside the scope of this document.
7.4. Originating Non-Default Route Southbound 6.4. Originating Non-Default Route Southbound
Obviously, an implementation may choose to originate southbound Obviously, an implementation may choose to originate southbound
instead of a strict default route (as described in Section 5.2.3.8) a instead of a strict default route (as described in Section 4.2.3.8) a
shorter prefix P' but in such a scenario all addresses carried within shorter prefix P' but in such a scenario all addresses carried within
the RIFT domain must be contained within P'. the RIFT domain must be contained within P'.
8. Security Considerations 7. Security Considerations
8.1. General 7.1. General
One can consider attack vectors where a router may reboot many times One can consider attack vectors where a router may reboot many times
while changing its system ID and pollute the network with many stale while changing its system ID and pollute the network with many stale
TIEs or TIEs are sent with very long lifetimes and not cleaned up TIEs or TIEs are sent with very long lifetimes and not cleaned up
when the routes vanishes. Those attack vectors are not unique to when the routes vanishes. Those attack vectors are not unique to
RIFT. Given large memory footprints available today those attacks RIFT. Given large memory footprints available today those attacks
should be relatively benign. Otherwise a node SHOULD implement a should be relatively benign. Otherwise a node SHOULD implement a
strategy of discarding contents of all TIEs that were not present in strategy of discarding contents of all TIEs that were not present in
the SPF tree over a certain, configurable period of time. Since the the SPF tree over a certain, configurable period of time. Since the
protocol, like all modern link-state protocols, is self-stabilizing protocol, like all modern link-state protocols, is self-stabilizing
and will advertise the presence of such TIEs to its neighbors, they and will advertise the presence of such TIEs to its neighbors, they
can be re-requested again if a computation finds that it sees an can be re-requested again if a computation finds that it sees an
adjacency formed towards the system ID of the discarded TIEs. adjacency formed towards the system ID of the discarded TIEs.
8.2. ZTP 7.2. ZTP
Section 5.2.7 presents many attack vectors in untrusted environments, Section 4.2.7 presents many attack vectors in untrusted environments,
starting with nodes that oscillate their level offers to the starting with nodes that oscillate their level offers to the
possiblity of a node offering a three way adjacency with the highest possiblity of a node offering a 3-way adjacency with the highest
possible level value with a very long holdtime trying to put itself possible level value with a very long holdtime trying to put itself
"on top of the lattice" and with that gaining access to the whole "on top of the lattice" and with that gaining access to the whole
southbound topology. Session authentication mechanisms are necessary southbound topology. Session authentication mechanisms are necessary
in environments where this is possible and RIFT provides the in environments where this is possible and RIFT provides the
according security envelope to ensure this if desired. according security envelope to ensure this if desired.
8.3. Lifetime 7.3. Lifetime
Traditional IGP protocols are vulnerable to lifetime modification and Traditional IGP protocols are vulnerable to lifetime modification and
replay attacks that can be somewhat mitigated by using techniques replay attacks that can be somewhat mitigated by using techniques
like [RFC7987]. RIFT removes this attack vector by protecting the like [RFC7987]. RIFT removes this attack vector by protecting the
lifetime behind a signature computed over it and additional nonce lifetime behind a signature computed over it and additional nonce
combination which makes even the replay attack window very small and combination which makes even the replay attack window very small and
for practical purposes irrelevant since lifetime cannot be for practical purposes irrelevant since lifetime cannot be
artificially shortened by the attacker. artificially shortened by the attacker.
8.4. Packet Number 7.4. Packet Number
Optional packet number is carried in the security envelope without Optional packet number is carried in the security envelope without
any encryption protection and is hence vulnerable to replay and any encryption protection and is hence vulnerable to replay and
modification attacks. Contrary to nonces this number must change on modification attacks. Contrary to nonces this number must change on
every packet and would present a very high cryptographic load if every packet and would present a very high cryptographic load if
signed. The attack vector packet number present is relatively signed. The attack vector packet number present is relatively
benign. Changing the packet number by a man-in-the-middle attack benign. Changing the packet number by a man-in-the-middle attack
will only affect operational validation tools and possibly some will only affect operational validation tools and possibly some
performance optimizations on flooding. It is expected that an performance optimizations on flooding. It is expected that an
implementation detecting too many "fake losses" or "misorderings" due implementation detecting too many "fake losses" or "misorderings" due
to the attack on the packet number would simply suppress its further to the attack on the packet number would simply suppress its further
processing. processing.
8.5. Outer Fingerprint Attacks 7.5. Outer Fingerprint Attacks
A node can try to inject LIE packets observing a conversation on the A node can try to inject LIE packets observing a conversation on the
wire by using the outer key ID albeit it cannot generate valid hashes wire by using the outer key ID albeit it cannot generate valid hashes
in case it changes the integrity of the message so the only possible in case it changes the integrity of the message so the only possible
attack is DoS due to excessive LIE validation. attack is DoS due to excessive LIE validation.
A node can try to replay previous LIEs with changed state that it A node can try to replay previous LIEs with changed state that it
recorded but the attack is hard to replicate since the nonce recorded but the attack is hard to replicate since the nonce
combination must match the ongoing exchange and is then limited to a combination must match the ongoing exchange and is then limited to a
single flap only since both nodes will advance their nonces in case single flap only since both nodes will advance their nonces in case
the adjacency state changed. Even in the most unlikely case the the adjacency state changed. Even in the most unlikely case the
attack length is limited due to both sides periodically increasing attack length is limited due to both sides periodically increasing
their nonces. their nonces.
8.6. TIE Origin Fingerprint DoS Attacks 7.6. TIE Origin Fingerprint DoS Attacks
A compromised node can attempt to generate "fake TIEs" using other A compromised node can attempt to generate "fake TIEs" using other
nodes' TIE origin key identifiers. Albeit the ultimate validation of nodes' TIE origin key identifiers. Albeit the ultimate validation of
the origin fingerprint will fail in such scenarios and not progress the origin fingerprint will fail in such scenarios and not progress
further than immediately peering nodes, the resulting denial of further than immediately peering nodes, the resulting denial of
service attack seems unavoidable since the TIE origin key id is only service attack seems unavoidable since the TIE origin key id is only
protected by the, here assumed to be compromised, node. protected by the, here assumed to be compromised, node.
8.7. Host Implementations 7.7. Host Implementations
It can be reasonably expected that with the proliferation of RotH It can be reasonably expected that with the proliferation of RotH
servers, rather than dedicated networking devices, will constitute servers, rather than dedicated networking devices, will constitute
significant amount of RIFT devices. Given their normally far wider significant amount of RIFT devices. Given their normally far wider
software envelope and access granted to them, such servers are also software envelope and access granted to them, such servers are also
far more likely to be compromised and present an attack vector on the far more likely to be compromised and present an attack vector on the
protocol. Hijacking of prefixes to attract traffic is a trust protocol. Hijacking of prefixes to attract traffic is a trust
problem and cannot be addressed within the protocol if the trust problem and cannot be addressed within the protocol if the trust
model is breached, i.e. the server presents valid credentials to form model is breached, i.e. the server presents valid credentials to form
an adjacency and issue TIEs. However, in a move devious way, the an adjacency and issue TIEs. However, in a move devious way, the
servers can present DoS (or even DDos) vectors of issuing too many servers can present DoS (or even DDos) vectors of issuing too many
LIE packets, flood large amount of N-TIEs and similar anomalies. A LIE packets, flood large amount of North TIEs and similar anomalies.
prudent implementation hosting leafs should implement thresholds and A prudent implementation hosting leafs should implement thresholds
raise warnings when leaf is advertising number of TIEs in excess of and raise warnings when leaf is advertising number of TIEs in excess
those. of those.
9. IANA Considerations 8. IANA Considerations
This specification requests multicast address assignments and This specification requests multicast address assignments and
standard port numbers. Additionally registries for the schema are standard port numbers. Additionally registries for the schema are
requested and suggested values provided that reflect the numbers requested and suggested values provided that reflect the numbers
allocated in the given schema. allocated in the given schema.
9.1. Requested Multicast and Port Numbers 8.1. Requested Multicast and Port Numbers
This document requests allocation in the 'IPv4 Multicast Address This document requests allocation in the 'IPv4 Multicast Address
Space' registry the suggested value of 224.0.0.120 as Space' registry the suggested value of 224.0.0.120 as
'ALL_V4_RIFT_ROUTERS' and in the 'IPv6 Multicast Address Space' 'ALL_V4_RIFT_ROUTERS' and in the 'IPv6 Multicast Address Space'
registry the suggested value of FF02::A1F7 as 'ALL_V6_RIFT_ROUTERS'. registry the suggested value of FF02::A1F7 as 'ALL_V6_RIFT_ROUTERS'.
This document requests allocation in the 'Service Name and Transport This document requests allocation in the 'Service Name and Transport
Protocol Port Number Registry' the allocation of a suggested value of Protocol Port Number Registry'