--- 1/draft-ietf-idr-bgp-ls-segment-routing-msd-04.txt 2019-06-01 11:13:12.429530258 -0700 +++ 2/draft-ietf-idr-bgp-ls-segment-routing-msd-05.txt 2019-06-01 11:13:12.453530863 -0700 @@ -1,53 +1,53 @@ IDR Working Group J. Tantsura Internet-Draft Apstra, Inc. Intended status: Standards Track U. Chunduri -Expires: August 23, 2019 Huawei USA +Expires: December 3, 2019 Futurewei Technologies + K. Talaulikar + Cisco Systems G. Mirsky ZTE Corp. - S. Sivabalan - Cisco N. Triantafillis Apstra, Inc. - February 19, 2019 + June 1, 2019 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link- State - draft-ietf-idr-bgp-ls-segment-routing-msd-04 + draft-ietf-idr-bgp-ls-segment-routing-msd-05 Abstract This document defines a way for a Border Gateway Protocol Link-State (BGP-LS) speaker to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. - Such advertisements allow logically centralized entities (e.g., - centralized controllers) to determine whether a particular SID stack - can be supported in a given network. + Such advertisements allow entities (e.g., centralized controllers) to + determine whether a particular Segment Identifier (SID) stack can be + supported in a given network. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on August 23, 2019. + This Internet-Draft will expire on December 3, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -55,177 +55,239 @@ to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 - 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3 - 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 - 3. MSD supported by a node . . . . . . . . . . . . . . . . . . . 4 - 4. MSD supported on a link . . . . . . . . . . . . . . . . . . . 4 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 - 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 - 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 - 8.2. Informative References . . . . . . . . . . . . . . . . . 6 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 + 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 + 2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 + 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 + 4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 + 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6 + 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 + 9.2. Informative References . . . . . . . . . . . . . . . . . 7 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction - When Segment Routing tunnels are computed by a centralized - controller, it is critical that the controller learns the MSD - "Maximum SID Depth" of the node or link SR tunnel exits over, so the - SID stack depth of a path computed doesn't exceed the number of SIDs - the node is capable of imposing. This document describes how to use - BGP-LS to signal the MSD of a node or link to a centralized - controller. + When Segment Routing (SR) [RFC8402] paths are computed by a + centralized controller, it is critical that the controller learns the + Maximum SID Depth (MSD) that can be imposed at each node/link on a + given SR path. This ensures that the Segment Identifier (SID) stack + depth of a computed path doesn't exceed the number of SIDs the node + is capable of imposing. - PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD - in SR PCE Capability TLV and METRIC Object. However, if PCEP is not - supported/configured on the head-end of a SR tunnel or a Binding-SID - anchor node and controller does not participate in IGP routing, it - has no way to learn the MSD of nodes and links which has been - configured. BGP-LS [RFC7752] defines a way to expose topology and - associated attributes and capabilities of the nodes in that topology - to a centralized controller. + [I-D.ietf-pce-segment-routing] defines how to signal MSD in the Path + Computation Element Protocol (PCEP). The OSPF and IS-IS extensions + for signaling of MSD are defined in [RFC8476] and [RFC8491] + respectively. + + However, if PCEP is not supported/configured on the head-end of a SR + tunnel or a Binding-SID anchor node, and controller does not + participate in IGP routing, it has no way of learning the MSD of + nodes and links. BGP-LS [RFC7752] defines a way to advertise + topology and associated attributes and capabilities of the nodes in + that topology to a centralized controller. This document defines + extensions to BGP-LS to advertise one or more types of MSDs at node + and/or link granularity. Other types of MSD are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] and [I-D.ietf-isis-mpls-elc] define Readable Label Depth Capability (RLDC) that is used by a head-end to insert an Entropy Label (EL) at a depth that can be read by transit nodes. + In the future, it is expected that new MSD-Types will be defined to + signal additional capabilities, e.g., ELs, SIDs that can be imposed + through recirculation, or SIDs associated with another data plane + such as IPv6. MSD advertisements MAY be useful even if SR itself is + not enabled. For example, in a non-SR MPLS network, MSD defines the + maximum label depth. + 1.1. Conventions used in this document 1.1.1. Terminology BGP-LS: Distribution of Link-State and TE Information using Border Gateway Protocol MSD: Maximum SID Depth PCC: Path Computation Client PCE: Path Computation Element PCEP: Path Computation Element Protocol SID: Segment Identifier SR: Segment routing + Label Imposition: Imposition is the act of modifying and/or adding + labels to the outgoing label stack associated with a packet. This + includes: + + o replacing the label at the top of the label stack with a new + label. + + o pushing one or more new labels onto the label stack The number of + labels imposed is then the sum of the number of labels that are + replaced and the number of labels that are pushed. See [RFC3031] + for further details. + 1.1.2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here . -2. Problem Statement +2. Advertisement of MSD via BGP-LS - In existing technology only PCEP has extension to signal the MSD (SR - PCE Capability TLV/ METRIC Object as defined in - [I-D.ietf-pce-segment-routing],If PCEP is not supported by the node - (head-end of the SR tunnel) controller has no way to learn the MSD of - the node/link configured. OSPF and IS-IS extensions are defined in: + This document describes extensions that enable BGP-LS speakers to + signal the MSD capabilities of nodes and their links in a network to + a BGP-LS consumer of network topology such as a centralized + controller. The centralized controller can leverage this information + in computation of SR paths and their instantiation on network nodes + based on their MSD capabilities. When a BGP-LS speaker is + originating the topology learnt via link-state routing protocols like + OSPF or IS-IS, the MSD information for the nodes and their links is + sourced from the underlying extensions as defined in [RFC8476] and + [RFC8491] respectively. The BGP-LS speaker may also advertise the + MSD information for the local node and its links when not running any + link-state IGP protocol e.g. when running BGP as the only routing + protocol. - [RFC8476], [RFC8491] + The extensions introduced in this document allow for advertisement of + different MSD-Types. This document does not define these MSD-Types + but leverages the definition, guidelines and the code-point registry + specified in [RFC8491]. This enables sharing of MSD-Types that may + be defined in the future by the IGPs in BGP-LS. -3. MSD supported by a node +3. Node MSD TLV - Node MSD is encoded in a new Node Attribute TLV, as defined in - [RFC7752] + Node MSD is encoded in a new Node Attribute TLV [RFC7752] using the + following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | Sub-Type and Value ... - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... + | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - Figure 1: Node attribute format + Figure 1: Node MSD TLV Format - Type : A 2-octet field specifying code-point of the new TLV type. - Code-point:(TBD1) from BGP-LS Node Descriptor, Link Descriptor, - Prefix Descriptor, and Attribute TLVs registry + Where: - Length: A 2-octet field that indicates the length of the value - portion + o Type: 266 - Sub-Type and value fields are as defined in corresponding OSPF - [RFC8476] and IS-IS [RFC8491] extensions. + o Length: variable (multiple of 2); represents the total length of + the value field in octets. -4. MSD supported on a link + o Value : consists of one or more pairs of a 1-octet MSD-Type and + 1-octet MSD-Value. - Link MSD is encoded in a New Link Attribute TLV, as defined in - [RFC7752] + * MSD-Type : one of the values defined in the IANA registry + titled "IGP MSD-Types" under the "Interior Gateway Protocol + (IGP) Parameters" registry created by [RFC8491]. + + * MSD-Value : a number in the range of 0-255. For all MSD-Types, + 0 represents the lack of ability to impose an MSD stack of any + depth; any other value represents that of the node. This value + MUST represent the lowest value supported by any link + configured for use by the advertising protocol instance. + +4. Link MSD TLV + + Link MSD is encoded in a new Link Attribute TLV [RFC7752] using the + following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | Sub-Type and Value ... - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... + | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - Figure 2: Link attribute format + Figure 2: Link MSD TLV Format - Type : A 2-octet field specifying code-point of the new TLV type. - Code-point:(TBD2) from BGP-LS Node Descriptor, Link Descriptor, - Prefix Descriptor, and Attribute TLVs registry + Where: - Length: A 2-octet field that indicates the length of the value - portion - Sub-Type and value fields are as defined in corresponding OSPF - [RFC8476] and IS-IS [RFC8491] extensions. + o Type: 267 + o Length: variable (multiple of 2); represents the total length of + the value field in octets. + + o Value : consists of one or more pairs of a 1-octet MSD-Type and + 1-octet MSD-Value. + + * MSD-Type : one of the values defined in the IANA registry + titled "IGP MSD-Types" under the "Interior Gateway Protocol + (IGP) Parameters" registry created by [RFC8491]. + + * MSD-Value : a number in the range of 0-255. For all MSD-Types, + 0 represents the lack of ability to impose an MSD stack of any + depth; any other value represents that of the link when used as + an outgoing interface. 5. IANA Considerations - We request IANA assign code points from the registry BGP-LS Node - Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs, - as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference - TBD1 Node MSD 242/23 (this document) TBD2 Link MSD - (22,23,25,141,222,223)/15 (this document) + This document requests assigning code-points from the registry "BGP- + LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute + TLVs" based on table below. Early allocation for these code-points + have been done by IANA. + + +------------+-----------------+---------------------------+ + | Code Point | Description | IS-IS TLV/Sub-TLV | + +------------+-----------------+---------------------------+ + | 266 | Node MSD | 242/23 | + | 267 | Link MSD | (22,23,25,141,222,223)/15 | + +------------+-----------------+---------------------------+ 6. Security Considerations The advertisement of an incorrect MSD value may have negative consequences. If the value is smaller than supported, path computation may fail to compute a viable path. If the value is larger than supported, an attempt to instantiate a path that can't be supported by the head-end (the node performing the SID imposition) may occur. The presence of this information may also inform an attacker of how to induce any of the aforementioned conditions. This document does not introduce security issues beyond those discussed in [RFC7752], [RFC8476] and [RFC8491] -7. Acknowledgements +7. Contributors + Siva Sivabalan + Cisco Systems Inc. + Canada - We like to thank Acee Lindem, Ketan Talaulikar, Stephane Litkowski - and Bruno Decraene for their reviews and valuable comments. + Email: msiva@cisco.com -8. References +8. Acknowledgements -8.1. Normative References + We like to thank Acee Lindem, Stephane Litkowski and Bruno Decraene + for their reviews and valuable comments. - [I-D.ietf-pce-segment-routing] - Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., - and J. Hardwick, "PCEP Extensions for Segment Routing", - draft-ietf-pce-segment-routing-15 (work in progress), - February 2019. +9. References + +9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, @@ -238,68 +300,65 @@ [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, DOI 10.17487/RFC8476, December 2018, . [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, DOI 10.17487/RFC8491, November 2018, . -8.2. Informative References +9.2. Informative References [I-D.ietf-isis-mpls-elc] - Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. + Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-IS", draft-ietf-isis-mpls- - elc-06 (work in progress), September 2018. - - [I-D.ietf-isis-segment-routing-extensions] - Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., - Gredler, H., and B. Decraene, "IS-IS Extensions for - Segment Routing", draft-ietf-isis-segment-routing- - extensions-22 (work in progress), December 2018. + elc-07 (work in progress), May 2019. [I-D.ietf-ospf-mpls-elc] - Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. + Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label-stack Depth Using OSPF", draft-ietf-ospf- - mpls-elc-07 (work in progress), September 2018. + mpls-elc-08 (work in progress), May 2019. - [I-D.ietf-ospf-segment-routing-extensions] - Psenak, P., Previdi, S., Filsfils, C., Gredler, H., - Shakir, R., Henderickx, W., and J. Tantsura, "OSPF - Extensions for Segment Routing", draft-ietf-ospf-segment- - routing-extensions-27 (work in progress), December 2018. + [I-D.ietf-pce-segment-routing] + Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., + and J. Hardwick, "PCEP Extensions for Segment Routing", + draft-ietf-pce-segment-routing-16 (work in progress), + March 2019. - [I-D.ietf-spring-segment-routing-mpls] - Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., - Litkowski, S., and R. Shakir, "Segment Routing with MPLS - data plane", draft-ietf-spring-segment-routing-mpls-18 - (work in progress), December 2018. + [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol + Label Switching Architecture", RFC 3031, + DOI 10.17487/RFC3031, January 2001, + . + + [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., + Decraene, B., Litkowski, S., and R. Shakir, "Segment + Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, + July 2018, . Authors' Addresses Jeff Tantsura Apstra, Inc. Email: jefftant.ietf@gmail.com Uma Chunduri - Huawei USA + Futurewei Technologies - Email: uma.chunduri@huawei.com + Email: umac.ietf@gmail.com + + Ketan Talaulikar + Cisco Systems + + Email: ketant@cisco.com Greg Mirsky ZTE Corp. Email: gregimirsky@gmail.com - - Siva Sivabalan - Cisco - - Email: msiva@cisco.com - Nikos Triantafillis Apstra, Inc. Email: nikos@apstra.com