IDR                                                              C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                               W. Cheng
Expires: June 17, 2024                                     China Mobile
                                                                 Y. Liu
                                                                    ZTE
                                                          K. Talaulikar
                                                          Cisco Systems
                                                                M. Chen
                                                   New H3C Technologies
                                                      December 17, 2023


            BGP SR Policy Extensions for Segment List Identifier
                   draft-ietf-idr-sr-policy-seglist-id-00


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

   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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   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on June 17, 2024.




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Copyright Notice

   Copyright (c) 2023 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
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   warranty as described in the Simplified BSD License.

Table of Contents


   1. Introduction...................................................3
      1.1. Requirements Language.....................................3
   2. Segment List Identifier in SR Policy...........................4
      2.1. Segment List ID Sub-TLV...................................5
   3. Security Considerations........................................5
   4. IANA Considerations............................................6
   5. References.....................................................6
      5.1. Normative References......................................6
      5.2. Informative References....................................6
   Authors' Addresses................................................7





















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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-
   segment-routing-te-policy] 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.

   For example, a network controller distributes SR policies to the
   headend nodes, and the headend nodes 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.

   For another example, 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. So,
   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.



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2. Segment List Identifier in SR Policy

   As defined in [I-D.ietf-idr-segment-routing-te-policy], 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:

      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.



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   When signaling SR Policy by PCEP [I-D.ietf-pce-multipath], 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.

   The Segment List ID sub-TLV has 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      |     Flags     |   RESERVED    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Segment List ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o Type: TBD.

   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 octet of ID for the segment list.

3. Security Considerations

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

   This document does not introduce any new security consideration.




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4. IANA Considerations

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

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

5. References

5.1. 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-segment-routing-te-policy] 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-segment-routing-te-policy-
             25, 26 September 2023, <http://www.ietf.org/internet-
             drafts/draft- ietf-idr-segment-routing-te-policy-25.txt>.

5.2. 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>.

   [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-09, 24 July 2023,
             <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
             multipath-09>.




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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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