



LSR Working Group                                                J. Dong
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: 5 January 2026                                      4 July 2025


      Advertising SRv6 SIDs for Layer 2 Bundle Member Links in IGP
                    draft-dong-lsr-l2bundle-srv6-03

Abstract

   There are deployments where the Layer-3 interface on which IGP
   operates is a Layer-2 interface bundle.  Existing IGP advertisements
   only support advertising link attributes of the Layer-3 interface.
   If entities external to IGP wish to control traffic flows on the
   individual physical links that comprise the Layer-2 interface bundle,
   link attribute information about the bundle members is advertised by
   IGP extensions for Layer-2 (L2) bundle.

   When Segment Routing over IPv6 (SRv6) is used with Layer-2 interface
   bundle to control traffic flows on the individual member links, the
   SRv6 SIDs which represent the Layer 2 member links of the L2 bundle
   needs to be advertised in IGP.

   This document proposes the IGP extensions to advertise the SRv6 SIDs
   of the Layer 2 (L2) bundle member links.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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
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   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."




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Copyright Notice

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   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  SRv6 SIDs for L2 Bundle Member Links  . . . . . . . . . . . .   3
   4.  Advertising SRv6 SIDs for L2 Bundle Members . . . . . . . . .   3
     4.1.  SRv6 SIDs Encodings for IS-IS L2 Bundle . . . . . . . . .   3
       4.1.1.  L2 Bundle Member SRv6 End.X SID Sub-TLV . . . . . . .   3
       4.1.2.  L2 Bundle Member SRv6 LAN End.X SID Sub-TLV . . . . .   5
     4.2.  SRv6 SIDs Encodings for OSPF L2 Bundle  . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   There are deployments where the Layer-3 interface on which an IGP
   adjacency is established is a Layer-2 interface bundle, for instance,
   a Link Aggregation Group (LAG) [IEEE802.1AX].  This reduces the
   number of adjacencies that need to be maintained by the routing
   protocol in cases where there are parallel links between the
   neighbors.  Entities external to IS-IS such as Path Computation
   Elements (PCEs) [RFC4655] may wish to control traffic flows on
   individual members of the underlying Layer-2 bundle.  In order to do
   so, link attribute information about individual bundle members is
   required.





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   [RFC8668] and [RFC9356] specify the IGP extensions to advertise link
   attribute information for each of the L2 Bundle members which
   comprise the Layer-3 interface, in which the encoding and
   advertisement of SR-MPLS adjacency SIDs of each bundle member link is
   defined.  When SRv6 is used with Layer-2 interface bundle, to control
   traffic flows on the individual member links, the SRv6 SIDs which
   represent the Layer-2 member links of the L2 bundle needs to be
   advertised.

   This document proposes the IGP extensions to advertise the SRv6 SIDs
   of the L2 bundle member links.

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
   BCP14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

3.  SRv6 SIDs for L2 Bundle Member Links

   As defined in [RFC8986], the SRv6 End.X behavior means "Endpoint with
   cross-connect to an array of layer-3 adjacencies".  An SRv6 SID
   associated with a Layer 2 bundle member link of an L3 adjacency can
   be considered as an instance of the End.X SID, which identifies a
   subset of the L3 adjacency.  Thus separate End.X SID can be allocated
   for each L2 bundle member link.

4.  Advertising SRv6 SIDs for L2 Bundle Members

4.1.  SRv6 SIDs Encodings for IS-IS L2 Bundle

   This section defines the IS-IS sub-TLVs to advertise SRv6 SIDs for L2
   Bundle Members.  Following the encoding mechanism used in [RFC8668]
   for the advertisement of SR-MPLS adj-SIDs for L2 Bundle Members, this
   allows the advertisement of a set of SRv6 End.X SIDs (one per L2
   Bundle Member) in a single sub-TLV.

4.1.1.  L2 Bundle Member SRv6 End.X SID Sub-TLV

   [RFC9352] defines the SRv6 End.X SID sub-TLV to advertise an SRv6 SID
   associated with a point-to-point adjacency.  This document defines a
   new sub-TLV called "L2 Bundle Member SRv6 End.X SIDs" to advertise
   the SRv6 End.X SIDs for the L2 Bundle Members.  This sub-TLV is
   allowed to be carried in TLV 25 "L2 Bundle Member Attributes" only.
   The format of the sub-TLV is as below:




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   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     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Flags    |   Algorithm   |    Weight     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Endpoint Behavior     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ SID #1 (128 bits)                                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ SID #2 (128 bits)                                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ ...                                                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ SID #n (128 bits)                                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Sub-sub-tlv-len|         Sub-sub-TLVs (variable) . . .         ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   *  Type: TBA.

   *  Length: Variable.

   *  Flags: 1 octet.  The format is the same as the Flags field in the
      SRv6 End.X SID sub-TLV as defined in [RFC9352].

   *  Algorithm: 1 octet.  The algorithm values are defined in the IGP
      Algorithm Type registry.

   *  Weight: 1 octet.  The value represents the weight of the SID for
      the purpose of load balancing.

   *  Endpoint Behavior: 2 octets.  It SHOULD be set to the value of
      End.X behavior.

   *  SIDs.  One or multiple 16-octet SRv6 SIDs.  The number of the SIDs
      is determined by the "Number of L2 Bundle Member Descriptors"
      field as defined in [RFC8668].

   *  Sub-sub-tlv-length: 1 octet.  Number of octets used by sub-sub-
      TLVs.

   *  Optional Sub-sub-TLVs: Supported sub-sub-TLVs are specified in
      Section 11.6 of [RFC9352].




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   Multiple L2 Bundle Member SRv6 End.X SID Sub-TLV may be required in
   order to advertise all the SRv6 End.X SIDs associated with the member
   links of an L2 bundle.

4.1.2.  L2 Bundle Member SRv6 LAN End.X SID Sub-TLV

   [RFC9352] defines the SRv6 LAN End.X SID sub-TLV to advertise an SRv6
   SID associated with a LAN adjacency.  This document defines a new
   sub-TLV called "L2 Bundle Member SRv6 LAN End.X SIDs" to advertise
   the SRv6 LAN End.X SIDs for the L2 Bundle Members.  The format of the
   sub-TLV is as below:

   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    |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |             Neighbor System-ID (ID length octets)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Flags    |   Algorithm   |    Weight     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Endpoint Behavior     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ SID #1 (128 bits)                                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ SID #2 (128 bits)                                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ ...                                                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~ SID #n (128 bits)                                             ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Sub-sub-tlv-len|         Sub-sub-TLVs (variable) . . .         ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   *  Type: TBA.

   *  Length: Variable.

   *  Neighbor System-ID: IS-IS System-ID of length "ID Length" as
      defined in [ISO10589].

   *  Flags: 1 octet, the format is the same as the Flags field in the
      SRv6 End.X SID sub-TLV as defined in [RFC9352].

   *  Algorithm: 1 octet.  The algorithm values are defined in the IGP
      Algorithm Type registry.



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   *  Weight: 1 octet.  The value represents the weight of the End.X SID
      for the purpose of load balancing.

   *  Endpoint Behavior: 2 octets.  It SHOULD be set to the value of
      End.X behavior.

   *  SIDs.  One or multiple 16-octet SRv6 SIDs.  The number of the SIDs
      is determined by the "Number of L2 Bundle Member Descriptors"
      field as defined in [RFC8668].

   *  Sub-sub-tlv-length: 1 octet.  Number of octets used by sub-sub-
      TLVs.

   *  Optional Sub-sub-TLVs: Supported sub-sub-TLVs are specified in
      Section 11.6 of [RFC9352].

4.2.  SRv6 SIDs Encodings for OSPF L2 Bundle

   This section describes the mechanism to advertise SRv6 SIDs for L2
   Bundle Members in OSPF.

   For SR-MPLS data plane, as described in [RFC9356], the SR-MPLS
   Adjacency SID sub-TLVs for the L3 adjacency is used for the
   advertisement of Adjacency SIDs of L2 Bundle Members.  And for
   OSPFv3, the L2 Bundle Member Attributes sub-TLV is an optional sub-
   TLV of the Router-Link TLV of the OSPFv3 E-Router-LSA [RFC8362].

   For SRv6 data plane, the SRv6 related sub-TLVs as defined in
   [RFC9513] can be used under the L2 Bundle Member Attributes sub-TLV
   for the advertisement of SRv6 SIDs of the L2 bundle members in
   OSPFv3.  Table 1 lists the SRv6 related sub-TLVs that are applicable
   to the Router-Link TLV and their applicability for L2 bundle member
   links.

     +=======+=========================================+===============+
     | Value | Description                             | Applicability |
     +=======+=========================================+===============+
     | 31    | SRv6 SID Structure                      |       Y       |
     +-------+-----------------------------------------+---------------+
     | 31    | SRv6 End.X SID                          |       Y       |
     +-------+-----------------------------------------+---------------+
     | 32    | SRv6 LAN End.X SID                      |       Y       |
     +-------+-----------------------------------------+---------------+
   Table 1: Applicability of SRv6 related Sub-TLVs for L2 Bundle Members







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5.  IANA Considerations

   IANA is requested to assign two new code points from the IS-IS "Sub-
   TLVs for TLVs 22, 23, 25, 141, 222, and 223" registry.

    +------+--------------------------+----+----+----+-----+-----+-----+
    | Type | Description              | 22 | 23 | 25 | 141 | 222 | 223 |
    +======+==========================+====+====+====+=====+=====+=====+
    |  TBD | L2 Bundle Member SRv6    | n  | n  | y  |  n  |  n  |  n  |
    |      | End.X SID                |    |    |    |     |     |     |
    +------+--------------------------+----+----+----+-----+-----+-----+
    |  TBD | L2 Bundle Member SRv6    | n  | n  | y  |  n  |  n  |  n  |
    |      | LAN End.X SID            |    |    |    |     |     |     |
    +------+--------------------------+----+----+----+-----+-----+-----+

   In the "OSPFv3 Extended- LSA Sub-TLVs" registry, IANA has already set
   the L2BM flag for the code points 30, 31 and 32 to "Y", per the
   request of [RFC9513].

6.  Security Considerations

   The security considerations in [RFC8668] and [RFC9356] apply.  This
   document introduces no additional security vulnerabilities to IS-IS
   and OSPF.

7.  Acknowledgements

   The authors would like to thank Zhenbin Li for the review and
   discussion of this document.

8.  References

8.1.  Normative References

   [IEEE802.1AX]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Link Aggregation", 2016,
              <https://ieeexplore.ieee.org/document/7055197>.

   [ISO10589] ISO, "Information technology -- Telecommunications and
              information exchange between systems -- Intermediate
              System to Intermediate System intra-domain routing
              information exchange protocol for use in conjunction with
              the protocol for providing the connectionless-mode network
              service (ISO 8473)", November 2002,
              <https://ieeexplore.ieee.org/document/7055197>.





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   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [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>.

   [RFC9352]  Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
              and Z. Hu, "IS-IS Extensions to Support Segment Routing
              over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
              February 2023, <https://www.rfc-editor.org/info/rfc9352>.

   [RFC9356]  Talaulikar, K., Ed. and P. Psenak, "Advertising Layer 2
              Bundle Member Link Attributes in OSPF", RFC 9356,
              DOI 10.17487/RFC9356, January 2023,
              <https://www.rfc-editor.org/info/rfc9356>.

   [RFC9513]  Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
              "OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)",
              RFC 9513, DOI 10.17487/RFC9513, December 2023,
              <https://www.rfc-editor.org/info/rfc9513>.

8.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.





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Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing
   100095
   China
   Email: jie.dong@huawei.com


   Zhibo Hu
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing
   100095
   China
   Email: huzhibo@huawei.com

































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