draft-ietf-idr-bgp-ls-segment-routing-msd-17.txt   draft-ietf-idr-bgp-ls-segment-routing-msd-18.txt 
IDR Working Group J. Tantsura IDR Working Group J. Tantsura
Internet-Draft Apstra, Inc. Internet-Draft Apstra, Inc.
Intended status: Standards Track U. Chunduri Intended status: Standards Track U. Chunduri
Expires: October 28, 2020 Futurewei Technologies Expires: November 9, 2020 Futurewei Technologies
K. Talaulikar K. Talaulikar
Cisco Systems Cisco Systems
G. Mirsky G. Mirsky
ZTE Corp. ZTE Corp.
N. Triantafillis N. Triantafillis
Amazon Web Services Amazon Web Services
April 26, 2020 May 8, 2020
Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link
State State
draft-ietf-idr-bgp-ls-segment-routing-msd-17 draft-ietf-idr-bgp-ls-segment-routing-msd-18
Abstract Abstract
This document defines a way for a Border Gateway Protocol - Link This document defines a way for a Border Gateway Protocol - Link
State (BGP-LS) speaker to advertise multiple types of supported State (BGP-LS) speaker to advertise multiple types of supported
Maximum SID Depths (MSDs) at node and/or link granularity. Maximum SID Depths (MSDs) at node and/or link granularity.
Such advertisements allow entities (e.g., centralized controllers) to Such advertisements allow entities (e.g., centralized controllers) to
determine whether a particular Segment Identifier (SID) stack can be determine whether a particular Segment Identifier (SID) stack can be
supported in a given network. supported in a given network.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 October 28, 2020. This Internet-Draft will expire on November 9, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 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
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4
2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4
3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Procedures for Defining and Using Node and Link MSD 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6 6. Manageability Considerations . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Manageability Considerations . . . . . . . . . . . . . . . . 6 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
When Segment Routing (SR) [RFC8402] paths are computed by a When Segment Routing (SR) [RFC8402] paths are computed by a
centralized controller, it is critical that the controller learns the centralized controller, it is critical that the controller learns the
Maximum SID Depth (MSD) that can be imposed at each node/link on a 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 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 depth of a computed path doesn't exceed the number of SIDs the node
is capable of imposing. is capable of imposing.
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1-octet MSD-Value. 1-octet MSD-Value.
* MSD-Type : MSD-Type : one of the values defined in the "IGP * MSD-Type : MSD-Type : one of the values defined in the "IGP
MSD-Types" registry defined in [RFC8491]. MSD-Types" registry defined in [RFC8491].
* MSD-Value : a number in the range of 0-255. For all MSD-Types, * 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 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 depth; any other value represents that of the link when used as
an outgoing interface. an outgoing interface.
5. Procedures for Defining and Using Node and Link MSD Advertisements 5. IANA Considerations
When Link MSD is present for a given MSD-type, the value of the Link
MSD MUST take precedence over the Node MSD. When a Link MSD-type is
not signaled but the Node MSD-type is, then the Node MSD-type value
MUST be considered as the MSD value for that link.
In order to increase flooding efficiency, it is RECOMMENDED that
routers with homogenous link MSD values advertise just the Node MSD
value.
The meaning of the absence of both Node and Link MSD advertisements
for a given MSD-type is specific to the MSD-type. Generally it can
only be inferred that the advertising node does not support
advertisement of that MSD-type. However, in some cases the lack of
advertisement might imply that the functionality associated with the
MSD-type is not supported. The correct interpretation MUST be
specified when an MSD-type is defined in [RFC8491].
6. IANA Considerations
This document requests assigning code-points from the registry "BGP- This document requests assigning code-points from the registry "BGP-
LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" based on table below. Early allocation for these code-points TLVs" based on table below. Early allocation for these code-points
have been done by IANA. have been done by IANA.
+------------+-----------------+---------------------------+-------------------+ +------------+-----------------+---------------------------+-------------------+
| Code Point | Description | IS-IS TLV/Sub-TLV | Reference | | Code Point | Description | IS-IS TLV/Sub-TLV | Reference |
+------------+-----------------+---------------------------+-------------------+ +------------+-----------------+---------------------------+-------------------+
| 266 | Node MSD | 242/23 | This document | | 266 | Node MSD | 242/23 | This document |
| 267 | Link MSD | (22,23,25,141,222,223)/15 | This document | | 267 | Link MSD | (22,23,25,141,222,223)/15 | This document |
+------------+-----------------+---------------------------+-------------------+ +------------+-----------------+---------------------------+-------------------+
7. Manageability Considerations 6. Manageability Considerations
The new protocol extensions introduced in this document augment the The new protocol extensions introduced in this document augment the
existing IGP topology information that is distributed via [RFC7752]. existing IGP topology information that is distributed via [RFC7752].
Procedures and protocol extensions defined in this document do not Procedures and protocol extensions defined in this document do not
affect the BGP protocol operations and management other than as affect the BGP protocol operations and management other than as
discussed in the Manageability Considerations section of [RFC7752]. discussed in the Manageability Considerations section of [RFC7752].
Specifically, the malformed attribute tests for syntactic checks in Specifically, the malformed attribute tests for syntactic checks in
the Fault Management section of [RFC7752] now encompass the new BGP- the Fault Management section of [RFC7752] now encompass the new BGP-
LS Attribute TLVs defined in this document. The semantic or content LS Attribute TLVs defined in this document. The semantic or content
checking for the TLVs specified in this document and their checking for the TLVs specified in this document and their
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left to the consumer of the BGP-LS information (e.g. an application left to the consumer of the BGP-LS information (e.g. an application
or a controller) and not the BGP protocol. or a controller) and not the BGP protocol.
A consumer of the BGP-LS information retrieves this information over A consumer of the BGP-LS information retrieves this information over
a BGP-LS session (refer Section 1 and 2 of [RFC7752]). a BGP-LS session (refer Section 1 and 2 of [RFC7752]).
This document only introduces new Attribute TLVs and any syntactic This document only introduces new Attribute TLVs and any syntactic
error in them would result in the BGP-LS Attribute being discarded error in them would result in the BGP-LS Attribute being discarded
[RFC7752]. The MSD information introduced in BGP-LS by this [RFC7752]. The MSD information introduced in BGP-LS by this
specification, may be used by BGP-LS consumer applications like a SR specification, may be used by BGP-LS consumer applications like a SR
path computation engine (PCE) to learn the SR SID stack handling PCE to learn the SR SID stack handling capabilities of the nodes in
capabilities of the nodes in the topology. This can enable the SR the topology. This can enable the SR PCE to perform path
PCE to perform path computations taking into consideration the size computations taking into consideration the size of SID stack that the
of SID stack that the specific head-end node may be able to impose. specific head-end node may be able to impose. Errors in the encoding
Errors in the encoding or decoding of the MSD information may result or decoding of the MSD information may result in the unavailability
in the unavailability of such information to the SR PCE or incorrect of such information to the SR PCE or incorrect information being made
information being made available to it. This may result in the head- available to it. This may result in the head-end node not being able
end node not being able to instantiate the desired SR path in its to instantiate the desired SR path in its forwarding and provide the
forwarding and provide the SR based optimization functionality. The SR based optimization functionality. The handling of such errors by
handling of such errors by applications like SR PCE may be applications like SR PCE may be implementation specific and out of
implementation specific and out of scope of this document. scope of this document.
The extensions specified in this document do not specify any new The extensions specified in this document do not specify any new
configuration or monitoring aspects in BGP or BGP-LS. The configuration or monitoring aspects in BGP or BGP-LS. The
specification of BGP models is an ongoing work based on the specification of BGP models is an ongoing work based on the
[I-D.ietf-idr-bgp-model]. [I-D.ietf-idr-bgp-model].
8. Security Considerations 7. Security Considerations
The advertisement of an incorrect MSD value may have negative The advertisement of an incorrect MSD value may have negative
consequences. If the value is smaller than supported, path consequences. If the value is smaller than supported, path
computation may fail to compute a viable path. If the value is 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 larger than supported, an attempt to instantiate a path that can't be
supported by the head-end (the node performing the SID imposition) supported by the head-end (the node performing the SID imposition)
may occur. The presence of this information may also inform an may occur. The presence of this information may also inform an
attacker of how to induce any of the aforementioned conditions. attacker of how to induce any of the aforementioned conditions.
The procedures and protocol extensions defined in this document do The procedures and protocol extensions defined in this document do
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section of [RFC4271] for a discussion of BGP security. Also, refer section of [RFC4271] for a discussion of BGP security. Also, refer
to [RFC4272] and [RFC6952] for analyses of security issues for BGP. to [RFC4272] and [RFC6952] for analyses of security issues for BGP.
Security considerations for acquiring and distributing BGP-LS Security considerations for acquiring and distributing BGP-LS
information are discussed in [RFC7752]. The TLVs introduced in this information are discussed in [RFC7752]. The TLVs introduced in this
document are used to propagate the MSD IGP extensions defined in document are used to propagate the MSD IGP extensions defined in
[RFC8476] [RFC8491]. It is assumed that the IGP instances [RFC8476] [RFC8491]. It is assumed that the IGP instances
originating these TLVs will support all the required security (as originating these TLVs will support all the required security (as
described in [RFC8476] [RFC8491]) in order to prevent any security described in [RFC8476] [RFC8491]) in order to prevent any security
issues when propagating the TLVs into BGP-LS. The advertisement of issues when propagating the TLVs into BGP-LS. The advertisement of
the node and link attribute information defined in this document the node and link attribute information defined in this document
presents no additional risk beyond that associated with the existing presents no significant additional risk beyond that associated with
node and link attribute information already supported in [RFC7752]. the existing node and link attribute information already supported in
[RFC7752].
9. Contributors 8. Contributors
Siva Sivabalan Siva Sivabalan
Cisco Systems Inc. Cisco Systems Inc.
Canada Canada
Email: msiva@cisco.com Email: msiva@cisco.com
10. Acknowledgements 9. Acknowledgements
We like to thank Acee Lindem, Stephane Litkowski, Bruno Decraene and We like to thank Acee Lindem, Stephane Litkowski, Bruno Decraene and
Alvaro Retana for their reviews and valuable comments. Alvaro Retana for their reviews and valuable comments.
11. References 10. References
11.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752, Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016, DOI 10.17487/RFC7752, March 2016,
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[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018, DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>. <https://www.rfc-editor.org/info/rfc8476>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018, DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>. <https://www.rfc-editor.org/info/rfc8491>.
11.2. Informative References 10.2. Informative References
[I-D.ietf-idr-bgp-model] [I-D.ietf-idr-bgp-model]
Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
YANG Model for Service Provider Networks", draft-ietf-idr- YANG Model for Service Provider Networks", draft-ietf-idr-
bgp-model-08 (work in progress), February 2020. bgp-model-08 (work in progress), February 2020.
[I-D.ietf-isis-mpls-elc] [I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", draft-ietf- Entropy Readable Label Depth Using IS-IS", draft-ietf-
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