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BGP Extensions of SR Policy for Headend Behavior
draft-lin-idr-sr-policy-headend-behavior-03

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Changwang Lin , Jiang Wenying , Yisong Liu , Mengxiao Chen , Hao Li
Last updated 2024-05-08 (Latest revision 2023-12-08)
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draft-lin-idr-sr-policy-headend-behavior-03
IDR Working Group                                                C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                               W. Jiang
Expires: June 5, 2024                                            Y. Liu
                                                           China Mobile
                                                                M. Chen
                                                                  H. Li
                                                   New H3C Technologies
                                                       December 8, 2023

              BGP Extensions of SR Policy for Headend Behavior
                draft-lin-idr-sr-policy-headend-behavior-03

Abstract

   This document defines extensions to Border Gateway Protocol (BGP) to
   distribute SR policies carrying headend behavior.

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
   working documents as Internet-Drafts. The list of current Internet-
   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."

   This Internet-Draft will expire on June 5, 2024.

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
   carefully, as they describe your rights and restrictions with

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   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Headend Behavior in SR Policy..................................3
      2.1. Headend Behavior Sub-TLV..................................4
      2.2. L2 Headend Behavior Sub-TLV...............................5
   3. Extensions of BGP-LS...........................................6
   4. Security Considerations........................................6
   5. IANA Considerations............................................6
   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-
   segment-routing-te-policy] specifies a mechanism by using BGP.

   As described in [RFC9256], a headend can steer a packet flow into an
   SR Policy in various ways, including BSID steering, per-destination
   steering, per-flow steering, and policy-based steering. Moreover,
   [I-D.jiang-idr-ts-flowspec-srv6-policy] describes a way by using BGP
   FlowSpec to steer packets into an SRv6 Policy.

   [RFC8986] defines End.B6.Encaps behavior and End.B6.Encaps.Red
   behavior for SRv6 BSID. [I-D.filsfils-spring-srv6-net-pgm-insertion]
   extends the SRv6 BSID behaviors with End.B6.Insert and
   End.B6.Insert.Red. When receiving packets with an active SID
   matching a local BSID of these kinds, the headend will perform
   corresponding behaviors. Different BSID behaviors are suitable for
   different scenarios. For example, comparing with End.B6.Encaps,
   End.B6.Encaps.Red reduces the size of the SRH by excluding the first
   SID, which can be useful for the devices with lower capacity of SID
   depths, like the switches in data center network. End.B6.Insert
   inserts a new SRH in between the IPv6 Header and the received SRH
   rather than pushing a new IPv6 header, which can be applied to

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   express scalable traffic-engineering policies across multiple
   domains.

   The SRv6 Binding SID sub-TLV is defined in [I-D.ietf-idr-segment-
   routing-te-policy] to signal the SRv6 BSID information along with SR
   Policies. It enables the specified SRv6 BSID behavior to be
   instantiated on the headend node. However, if the packets are
   steering into an SR Policy in some other way than using BSID, the
   headend behavior is not specified during the distributing of SR
   Policy by BGP. The network operator has to use additional tools,
   like NETCONF, to signal the headend behavior.

   This document defines extensions to Border Gateway Protocol (BGP) to
   distribute SR policies carrying headend behavior. So that the
   headend can be instructed to perform specific behavior when packets
   are steered into the SR policy without BSID.

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. Headend Behavior in SR Policy

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

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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
             Segment
             ...
           ...

   SR policy with headend behavior is expressed 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)
           Headend Behavior
           L2 Headend Behavior
           Segment List
              Weight
             Segment
             Segment
             ...
           ...

2.1. Headend Behavior Sub-TLV

   The Headend Behavior sub-TLV encodes the default headend behavior
   associated with the candidate path for L3 traffic. When the headend
   steers L3 packets into that SR Policy and the associated candidate
   path is active, the specific headend behavior should be performed by
   default. In the case of BSID steering, the behavior defined by the
   BSID overrides the default headend behavior.

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   The Headend Behavior sub-TLV is optional, and MUST NOT appear more
   than once in the SR Policy encoding.

   The Headend Behavior 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     |            RESERVED           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Headend Behavior       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o Type: to be assigned by IANA.

   o Length: 4.

   o RESERVED: 2 octets of reserved bits. SHOULD be set to zero on
      transmission and MUST be ignored on receipt.

   o Headend Behavior: a 2-octet value. The following values are
      defined.

      * TBD: H.Encaps. A headend behavior defined in [RFC8986].

      * TBD: H.Encaps.Red. A headend behavior defined in [RFC8986].

      * TBD: H.Insert. A headend behavior defined in [I-D.filsfils-
            spring-srv6-net-pgm-insertion].

      * TBD: H.Insert.Red. A headend behavior defined in [I-
            D.filsfils-spring-srv6-net-pgm-insertion].

2.2. L2 Headend Behavior Sub-TLV

   The L2 Headend Behavior sub-TLV encodes the default headend behavior
   associated with the candidate path for L2 traffic. When the headend
   steers L2 packets into that SR Policy and the associated candidate
   path is active, the specific headend behavior should be performed by
   default.

   The L2 Headend Behavior sub-TLV is optional, and MUST NOT appear
   more than once in the SR Policy encoding.

   The L2 Headend Behavior 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     |            RESERVED           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      L2 Headend Behavior      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o Type: to be assigned by IANA.

   o Length: 4.

   o RESERVED: 2 octets of reserved bits. SHOULD be set to zero on
      transmission and MUST be ignored on receipt.

   o L2 Headend Behavior: a 2-octet value. The following values are
      defined.

      * TBD: H.Encaps.L2. A headend behavior defined in [RFC8986].

      * TBD: H.Encaps.L2.Red. A headend behavior defined in [RFC8986].

3. Extensions of BGP-LS

   [I-D.ietf-idr-bgp-ls-sr-policy] describes a mechanism to collect the
   SR policy information that is locally available in a node and
   advertise it into BGP-LS updates. Extensions of BGP-LS for headend
   behavior of SR Policy will be included in the future version of this
   draft.

4. Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the security considerations discussed in [I-D.ietf-idr-
   segment-routing-te-policy].

5. IANA Considerations

   Headend Behavior Sub-TLV (TBD)

   L2 Headend Behavior Sub-TLV (TBD)

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6. References

6.1. 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>.

   [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-idr-segment-routing-te-policy] Previdi, S., Filsfils, C.,
             Talaulikar, K., Mattes, P., Rosen, E., Jain, D., and S.
             Lin, "Advertising Segment Routing Policies in BGP", Work
             in Progress, Internet-Draft, draft-ietf-idr-segment-
             routing-te-policy-26, 23 October 2023,
             <http://www.ietf.org/internet-drafts/draft-ietf-idr-
             segment-routing-te-policy-26.txt>.

6.2. Informative References

   [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>.

   [I-D.jiang-idr-ts-flowspec-srv6-policy] Jiang, W., Liu, Y., Chen,
             S., and S. Zhuang, "Traffic Steering using BGP Flowspec
             with SRv6 Policy", Work in Progress, Internet-Draft,
             draft-jiang-idr-ts-flowspec-srv6-policy-07, 23 March 2022,
             <http://www.ietf.org/internet-drafts/draft-jiang-idr-ts-
             flowspec-srv6-policy-07.txt>.

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   [I-D.filsfils-spring-srv6-net-pgm-insertion] Filsfils, C.,
             Camarillo, P., Leddy, J., Voyer, D., Matsushima, S., and
             Z. Li, "SRv6 NET-PGM extension: Insertion", Work in
             Progress, Internet-Draft, draft-filsfils-spring-srv6-net-
             pgm-insertion-09, 16 August 2023,
             <http://www.ietf.org/internet-drafts/draft-filsfils-
             spring-srv6-net-pgm-insertion-09.txt>.

   [I-D.ietf-idr-bgp-ls-sr-policy] Previdi, S., Talaulikar, K., Dong,
             J., Gredler, H., and J. Tantsura, "Advertisement of
             Segment Routing Policies using BGP Link-State", Work in
             Progress, Internet-Draft, draft-ietf-idr-bgp-ls-sr-policy-
             03, 5 November 2023,
             <https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
             ls-sr-policy-03>.

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Authors' Addresses

   Changwang Lin
   New H3C Technologies

   Email: linchangwang.04414@h3c.com

   Wenying Jiang
   China Mobile

   Email: jiangwenying@chinamobile.com

   Yisong Liu
   China Mobile

   Email: liuyisong@chinamobile.com

   Mengxiao Chen
   New H3C Technologies

   Email: chen.mengxiao@h3c.com

   Hao Li
   New H3C Technologies

   Email: lihao@h3c.com

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