BGP SR Policy Extensions for Segment List Identifier
draft-ietf-idr-sr-policy-seglist-id-03

IDR                                                              C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                               W. Cheng
Expires: August 24, 2025                                   China Mobile
                                                                 Y. Liu
                                                                    ZTE
                                                          K. Talaulikar
                                                          Cisco Systems
                                                                M. Chen
                                                   New H3C Technologies
                                                      February 24, 2025

            BGP SR Policy Extensions for Segment List Identifier
                   draft-ietf-idr-sr-policy-seglist-id-03

Abstract

   Segment Routing is a source routing paradigm that explicitly
   indicates the forwarding path for packets at the ingress node. An SR
   Policy is a set of candidate paths, each consisting of one or more
   segment lists. This document defines extensions to BGP SR Policy to
   specify the identifier of segment list.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 24, 2025.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document. Please review these documents
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Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Segment List Identifier in SR Policy...........................3
      2.1. Segment List ID Sub-TLV...................................4
   3. Security Considerations........................................5
   4. Implementation Status..........................................5
      4.1. New H3C Technologies......................................6
      4.2. ZTE Corp..................................................6
   5. IANA Considerations............................................7
   6. References.....................................................7
      6.1. Normative References......................................7
      6.2. Informative References....................................7
   Authors' Addresses................................................9

1. Introduction

   Segment routing (SR) [RFC8402] is a source routing paradigm that
   explicitly indicates the forwarding path for packets at the ingress
   node. The ingress node steers packets into a specific path according
   to the Segment Routing Policy (SR Policy) as defined in [RFC9256].
   In order to distribute SR policies to the headend, [I-D.ietf-idr-sr-
   policy-safi] specifies a mechanism by using BGP.

   However, there is no identifier for segment list in BGP SR Policy,
   which may cause inconvenience for other mechanisms to designate
   segment lists distributed by BGP.

   Consider the case of a network controller distributing SR policies
   to the headend nodes where the headend nodes need to collect traffic
   forwarding statistics per segment list. When a headend node reports
   each statistic to the controller, it needs to specify the segment
   list which the statistic belongs to. Due to the lack of identifier,
   the headend node usually reports all SIDs in the associated segment
   list along with the statistic, and then the controller needs to
   compare the SIDs one by one to recognize which segment list it is.
   The advertisement of all SIDs in the segment list consumes a lot of
   octets, and the comparison of SIDs can be complicated.

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   Consider a second example where a network controller distributes SR
   policies using BGP, and then it uses NETCONF to set some
   configurations of the segment lists which are not suitable to be
   carried in BGP. The controller needs to specify which segment list
   these configurations belong to when it issues them. In this case, a
   simple identifier of segment list can also be helpful.

   An identifier of segment list may also serve as a user-friendly
   attribute for debugging and troubleshooting purposes, such as
   displaying an invalid segment list when its associated BFD session
   is down.

   This document defines extensions to BGP SR Policy to specify the
   identifier of segment list.

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. Segment List Identifier in SR Policy

   As defined in [I-D.ietf-idr-sr-policy-safi], the SR policy encoding
   structure is as follows:

      SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
      Attributes:
         Tunnel Encaps Attribute (23)
            Tunnel Type: SR Policy
                Binding SID
                SRv6 Binding SID
                Preference
                Priority
                Policy Name
                Policy Candidate Path Name
                Explicit NULL Label Policy (ENLP)
                Segment List
                    Weight
                    Segment
                    Segment
                    ...
                ...

   SR policy with segment list identifier is expressed as below:

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      SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
      Attributes:
         Tunnel Encaps Attribute (23)
            Tunnel Type: SR Policy
                Binding SID
                SRv6 Binding SID
                Preference
                Priority
                Policy Name
                Policy Candidate Path Name
                Explicit NULL Label Policy (ENLP)
                Segment List
                    Weight
                    Segment List Identifier
                    Segment
                    Segment
                    ...
                ...

   The segment list identifier can be advertised using the Segment List
   ID sub-TLV, as defined in Section 2.1.

   When signaling SR Policy by PCEP [I-D.ietf-pce-multipath] (see
   section 5.2), a segment list is identified by "Path ID", which is a
   4-octet identifier. In this document, the segment list identifier is
   also represented using a 4-octet ID.

2.1. Segment List ID Sub-TLV

   The Segment List ID sub-TLV specifies the identifier of the segment
   list by a 4-octet number. The Segment List ID is unique within the
   context of a Candidate Path.

   The Segment List ID sub-TLV is optional and it MUST NOT appear more
   than once inside the Segment List sub-TLV. If multiple instances are
   present, then the first one is considered valid and the rest are
   ignored.

   The Segment List ID sub-TLV has the following format:

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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     |   RESERVED    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Segment List ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o Type: TBD(19).

   o Length: 6.

   o Flags: 1 octet of flags. None are defined at this stage. Flags
      SHOULD be set to zero on transmission and MUST be ignored on
      receipt.

   o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
      transmission and MUST be ignored on receipt.

   o Segment List ID: 4 octets which carry a 32-bit unsigned non-zero
      number that serves as the identifier associated with the segment
      list. A value of 0 indicates that there is no identifier
      associated with the Segment List. The scope of this identifier is
      the SR Policy Candidate path.

3. Security Considerations

   The security requirements and mechanisms described in [I-D.ietf-idr-
   sr-policy-safi] also apply to this document.

   This document does not introduce any new security consideration.

4. Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of
   this Internet-Draft, and is based on a proposal described in
   [RFC7942]. The description of implementations in this section is
   intended to assist the IETF in its decision processes in progressing
   drafts to RFCs.  Please note that the listing of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify the information
   presented here that was supplied by IETF contributors.  This is not

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   intended as, and must not be construed to be, a catalog of available
   implementations or their features.  Readers are advised to note that
   other implementations may exist.

   According to [RFC7942], "this will allow reviewers and working
   groups to assign due consideration to documents that have the
   benefit of running code, which may serve as evidence of valuable
   experimentation and feedback that have made the implemented
   protocols more mature. It is up to the individual working groups to
   use this information as they see fit".

4.1. New H3C Technologies

   *  Organization: New H3C Technologies.

   *  Implementation: H3C CR16000, CR19000 series routers
      implementation.

   *  Description: All sections including all the "MUST" and "SHOULD"
      clauses have been implemented in above-mentioned New H3C
      Products(running Version 7.1.099 and above).

   *  Maturity Level: Product

   *  Coverage: All sections.

   *  Version: Draft-03

   *  Licensing: N/A

   *  Implementation experience: Nothing specific.

   *  Contact: linchangwang.04414@h3c.com

   *  Last updated: February 10, 2025

4.2. ZTE Corp

   *  Organization: ZTE Corporation

   *  Implementation: ZTE's ZXR10 core router

   *  Description: The implementation in lab has been completed. The
      commercial implementation is under development.

   *  Maturity Level: Product

   *  Coverage: All

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   *   Version: Draft-03

   *   Licensing: N/A

   *   Implementation experience: Nothing specific.

   *   Contact: feng.jun99@zte.com.cn

   *   Last updated: February 6, 2025

5. IANA Considerations

   This document defines a new Sub-TLV in the registry "SR Policy
   Segment List Sub-TLVs" [I-D.ietf-idr-sr-policy-safi]:

   Value     Description                   Reference
   -------------------------------------------------------
   TBA (19)  Segment List ID sub-TLV       This document

6. References

6.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, May 2017

   [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>.

   [I-D.ietf-idr-sr-policy-safi] Previdi, S., Filsfils, C., Talaulikar,
             K., Mattes, P., and D. Jain, "Advertising Segment Routing
             Policies in BGP", Work in Progress, Internet-Draft, draft-
             ietf-idr-sr-policy-safi-13, 6 February 2025,
             <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
             policy-safi-13>.

6.2. Informative References

   [RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
             A., and P. Mattes, "Segment Routing Policy Architecture",
             RFC 9256, DOI 10.17487/RFC9256, July 2022,
             <https://www.rfc-editor.org/info/rfc9256>.

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   [I-D.ietf-pce-multipath] Koldychev, M., Sivabalan, S., Saad, T.,
             Beeram, V. P., Bidgoli, H., Yadav, B., Peng, S., and G. S.
             Mishra, "PCEP Extensions for Signaling Multipath
             Information", Work in Progress, Internet-Draft, draft-
             ietf-pce-multipath-12, 8 October 2024,
             <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
             multipath-12>.

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Authors' Addresses

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

   Weiqiang Cheng
   China Mobile
   China
   Email: chengweiqiang@chinamobile.com

   Yao Liu
   ZTE
   China
   Email: liu.yao71@zte.com.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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