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Segment Routing BGP Egress Peer Engineering over Layer 2 Bundle
draft-lin-idr-sr-epe-over-l2bundle-05

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Changwang Lin , Zhenqiang Li , Ran Pang , Ketan Talaulikar , Mengxiao Chen
Last updated 2024-04-26 (Latest revision 2024-03-16)
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draft-lin-idr-sr-epe-over-l2bundle-05
IDR Working Group                                                C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                                  Z. Li
Expires: September 13, 2024                                China Mobile
                                                                R. Pang
                                                           China Unicom
                                                          K. Talaulikar
                                                          Cisco Systems
                                                                M. Chen
                                                   New H3C Technologies
                                                         March 17, 2024

      Segment Routing BGP Egress Peer Engineering over Layer 2 Bundle
                   draft-lin-idr-sr-epe-over-l2bundle-05

Abstract

   There are deployments where the Layer 3 interface on which a BGP
   peer session is established is a Layer 2 interface bundle. In order
   to allow BGP-EPE to control traffic flows on individual member links
   of the underlying Layer 2 bundle, BGP Peering SIDs need to be
   allocated to individual bundle member links, and advertisement of
   such BGP Peering SIDs in BGP-LS is required. This document describes
   how to support Segment Routing BGP Egress Peer Engineering over
   Layer 2 bundle.

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
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   This Internet-Draft will expire on September 13, 2024.

Copyright Notice

   Copyright (c) 2024 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

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described in
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   warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Problem Statement..............................................3
   3. Advertising Peer Adjacency Segment for L2 Bundle Member in BGP-LS
   ..................................................................4
      3.1. MPLS-SR...................................................4
      3.2. SRv6......................................................5
   4. Manageability Considerations...................................5
   5. Security Considerations........................................5
   6. IANA Considerations............................................5
   7. References.....................................................6
      7.1. Normative References......................................6
      7.2. Informative References....................................6
   Appendix A. Example...............................................7
   Acknowledgements..................................................9
   Authors' Addresses................................................9

1. Introduction

   Segment Routing (SR) leverages the source routing paradigm.  A node
   steers a packet through an ordered list of instructions called
   "segments". Segment Routing can be instantiated on both MPLS and
   IPv6 data planes, which are referred to as SR-MPLS and SRv6.

   BGP Egress Peer Engineering (BGP-EPE) allows an ingress Provider
   Edge (PE) router within the domain to use a specific egress PE and a
   specific external interface/neighbor to reach a particular
   destination.

   The SR architecture [RFC8402] defines three types of BGP Peering
   Segments that may be instantiated at a BGP node:

   o Peer Node Segment (PeerNode SID): instruction to steer to a
      specific peer node

   o Peer Adjacency Segment (PeerAdj SID): instruction to steer over a
      specific local interface towards a specific peer node

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   o Peer Set Segment (PeerSet SID): instruction to load-balance to a
      set of specific peer nodes

   [RFC9087] illustrates a centralized controller-based BGP-EPE
   solution involving SR path computation using the BGP Peering
   Segments. A centralized controller learns the BGP Peering SIDs via
   Border Gateway Protocol - Link State (BGP-LS) and then uses this
   information to program a BGP-EPE policy. [RFC9086] defines the
   extension to BGP-LS for advertisement of BGP Peering Segments along
   with their BGP peering node information.

   There are deployments where the Layer 3 interface on which a BGP
   peer session is established is a Layer 2 interface bundle (L2
   Bundle), for instance, a Link Aggregation Group (LAG) [IEEE802.1AX].
   BGP-EPE may wish to control traffic flows on individual member links
   of the underlying Layer 2 bundle. In order to do so, BGP Peering
   SIDs need to be allocated to individual bundle member links, and
   advertisement of such BGP Peering SIDs in BGP-LS is required.

   This document describes how to support Segment Routing BGP Egress
   Peer Engineering over Layer 2 bundle.

1.1. 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

   In the network depicted in Figure 1, B and C establish BGP peer
   session on a Layer 2 bundle. Assume that, the link delays of the
   members are different because they are over different transport
   paths, and member link 1 has the lowest delay.

   The operator of AS1 wishes to apply a BGP-EPE policy to steer the
   time-sensitive traffic from AS1 to AS2 via member link 1 of the
   Layer 2 bundle.

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                    L2 Bundle      +--------+
                 /---member 1---\  |        |
               --+---member 2---+--C   AS2  |
   +--------+ /  \---member 3---/  |        |
   |        |/                     +--------+
   A   AS1  B
   |        |\                     +--------+
   +--------+ \                    |        |
               --------------------D   AS3  |
                                   |        |
                                   +--------+

   Figure 1: BGP-EPE over L2 Bundle

   The existing Peer Adjacency SID can be allocated to the Layer 3
   interface between B and C, which is a Layer 2 interface bundle. If
   steered by that Peer Adjacency SID, the traffic will be forwarded by
   load balancing among all the bundle member links. So, the existing
   mechanism cannot meet the requirement of steering traffic flows via
   individual member link.

3. Advertising Peer Adjacency Segment for L2 Bundle Member in BGP-LS

   BGP peering segments are generally advertised in BGP-LS from a BGP
   node along with its peering topology information, in order to enable
   computation of efficient BGP-EPE policies and strategies.

   When a BGP peer session is established over a Layer 2 interface
   bundle, an implementation MAY allocate one or more Peer Adjacency
   Segments for each member link. If so, it SHOULD advertise the Peer
   Adjacency Segments of bundle members in BGP-LS, using the method
   defined in this section.

3.1. MPLS-SR

   For SR-MPLS, Section 5.2 of [RFC9086] described the BGP-LS
   advertisement of the PeerAdj SID for L3 link.

   In order to advertise the PeerAdj SIDs for L2 bundle members in BGP-
   LS, the L2 Bundle Member Attributes TLVs [RFC9085] MUST also be
   included in the Link Attributes. Each L2 Bundle Member Attributes
   TLV identifies an L2 bundle member, and includes the PeerAdj SID TLV
   [RFC9086] to advertise the PeerAdj SID for the associated L2 bundle
   member.

   This document updates [RFC9085] and [RFC9086] to allow the PeerAdj
   SID TLV to be included as a sub-TLV of the L2 Bundle Member
   Attributes TLV.

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   Note that the inclusion of a L2 Bundle Member Attributes TLV implies
   that the identified link is a member of the L2 bundle and that the
   member link is operationally up. If any member link fails, an
   implementation MUST withdraw the L2 Bundle Member Attributes TLV in
   BGP-LS, along with the Peer Adjacency Segments for the failed member
   link.

3.2. SRv6

   For SRv6, according to Section 4.1 of [RFC9514], the advertisement
   of L3 link BGP EPE Peer Adjacency SID is the same as for SR-MPLS,
   except for using the SRv6 End.X SID TLV [RFC9514] instead of the
   PeerAdj SID TLV [RFC9086].

   Similarly, when advertising the SRv6 BGP Peer Adjacency SIDs for L2
   bundle members, the L2 Bundle Member Attributes TLVs [RFC9085] MUST
   also be included in the Link Attributes. The SRv6 End.X SID TLV
   [RFC9514] MUST be carried in the L2 Bundle Member Attributes TLV to
   advertise the SRv6 Peer Adjacency SID for the associated L2 bundle
   member.

4. Manageability Considerations

   The manageability considerations described in [RFC9552] and
   [RFC9086] also apply to this document.

   The operator MUST be provided with the options of configuring,
   enabling, and disabling the advertisement of Peer Adjacency Segment
   for L2 Bundle member links, as well as control of which information
   is advertised to which internal or external peer.

5. Security Considerations

   The security considerations described in [RFC9552] and [RFC9086]
   also apply to this document.

   This document does not introduce any new security consideration.

6. IANA Considerations

   This document has no IANA actions.

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7. References

7.1. 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, <https://www.rfc-
             editor.org/info/rfc2119>.

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
             May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
             H., and M. Chen, "Border Gateway Protocol - Link State
             (BGP-LS) Extensions for Segment Routing", RFC 9085, DOI
             10.17487/RFC9085, August 2021, <https://www.rfc-
             editor.org/info/rfc9085>.

   [RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
             Ray, S., and J. Dong, "Border Gateway Protocol - Link
             State (BGP-LS) Extensions for Segment Routing BGP Egress
             Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
             2021, <https://www.rfc-editor.org/info/rfc9086>.

   [RFC9514] Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
             Bernier, D., and B. Decraene, "Border Gateway Protocol -
             Link State (BGP-LS) Extensions for Segment Routing over
             IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
             2023, <https://www.rfc-editor.org/info/rfc9514>.

   [RFC9552] K. Talaulikar, "Distribution of Link-State and Traffic
             Engineering Information Using BGP", RFC 9552, DOI
             10.17487/RFC9552, December 2023, <https://www.rfc-
             editor.org/info/rfc9552>.

7.2. Informative References

   [IEEE802.1AX] IEEE, "IEEE Standard for Local and metropolitan area
             networks -- Link Aggregation", IEEE 802.1AX,
             <https://ieeexplore.ieee.org/document/7055197>.

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   [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
             M., and E. Aries, "Advertising Layer 2 Bundle Member Link
             Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
             December 2019, <https://www.rfc-editor.org/info/rfc8668>.

   [RFC9087] Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
             and D. Afanasiev, "Segment Routing Centralized BGP Egress
             Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
             2021, <https://www.rfc-editor.org/info/rfc9087>.

Appendix A. Example

   This section shows an example of how Node B in Figure 1 allocates
   and advertises Peer Adjacency Segments for L2 bundle members.

   B allocates a PeerAdj SID for the Layer 2 interface bundle to peer
   C, along with a PeerAdj SID for each member link. B programs its
   forwarding table accordingly:

   +===============================+====================+
   |          PeerAdj SID          | Outgoing Interface |
   +---------------+---------------+                    |
   | IF on SR-MPLS |  IF on SRv6   |                    |
   |   Data Plane  |  Data Plane   |                    |
   +===============+===============+====================+
   |     1010      |     A::A0     | L2 Bundle to C     |
   +---------------+---------------+--------------------+
   |     1011      |     A::A1     | Member link 1 to C |
   +---------------+---------------+--------------------+
   |     1012      |     A::A2     | Member link 2 to C |
   +---------------+---------------+--------------------+
   |     1013      |     A::A3     | Member link 3 to C |
   +---------------+---------------+--------------------+

   B signals the related BGP-LS Link NLRI and Link Attributes including
   the PeerAdj SID for L3 parent link to the BGP-EPE controller, as
   specified in Section 5.2 of [RFC9086]. In addition, B also
   advertises L2 Bundle Member Attribute TLVs carrying the PeerAdj SIDs
   for L2 bundle members.

   For MPLS-SR, the Link Attributes are as follows:

   o PeerAdj SID TLV (Label-1010)

   o L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 1)

      * PeerAdj SID TLV (Label-1011)

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      * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
            member link 1)

   o L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 2)

      * PeerAdj SID TLV (Label-1012)

      * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
            member link 2)

   o L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 3)

      * PeerAdj SID TLV (Label-1013)

      * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
            member link 3)

   For SRv6, the Link Attributes are as follows:

   o SRv6 End.X SID TLV (SID-A::A0)

   o L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 1)

      * SRv6 End.X SID TLV (SID-A::A1)

      * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
            member link 1)

   o L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 2)

      * SRv6 End.X SID TLV (SID-A::A2)

      * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
            member link 2)

   o L2 Bundle Member Attribute TLV (Link Local Identifier describing
      the member link 3)

      * SRv6 End.X SID TLV (SID-A::A3)

      * (Optional) Min/Max Unidirectional Link Delay TLV (Delay of
            member link 3)

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Acknowledgements

   The authors would like to thank Sasha Vainshtein for his review and
   comments of this document.

Authors' Addresses

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

   Zhenqiang Li
   China Mobile
   China
   Email: lizhenqiang@chinamobile.com

   Ran Pang
   China Unicom
   China
   Email: pangran@chinaunicom.cn

   Ketan Talaulikar
   Cisco Systems
   India
   Email: ketant.ietf@gmail.com

   Mengxiao Chen
   New H3C Technologies
   China
   Email: chen.mengxiao@h3c.com

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