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BGP Extensions of SR Policy for Headend Behavior
draft-lin-idr-sr-policy-headend-behavior-04

Document Type Active Internet-Draft (idr WG)
Authors Changwang Lin , Jiang Wenying , Yisong Liu , Mengxiao Chen , Ran Chen
Last updated 2024-05-15
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draft-lin-idr-sr-policy-headend-behavior-04
IDR Working Group                                                C. Lin
Internet Draft                                     New H3C Technologies
Intended status: Standards Track                               W. Jiang
Expires: November 12, 2024                                       Y. Liu
                                                           China Mobile
                                                                M. Chen
                                                   New H3C Technologies
                                                                R. Chen
                                                        ZTE Corporation
                                                           May 16, 2024

              BGP Extensions of SR Policy for Headend Behavior
                draft-lin-idr-sr-policy-headend-behavior-04

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 November 12, 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
   (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. Security Considerations........................................6
   4. IANA Considerations............................................6
   5. References.....................................................6
      5.1. Normative References......................................6
      5.2. Informative References....................................7
   Authors' Addresses................................................7

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.

   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.ietf-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. 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.

   The SRv6 Binding SID sub-TLV is defined in [I-D.ietf-idr-sr-policy-
   safi] 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

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   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-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 headend behavior is expressed 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)
           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.

   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.

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   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].

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:

    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].

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3. Security Considerations

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

4. IANA Considerations

   Headend Behavior Sub-TLV (TBD)

   L2 Headend Behavior Sub-TLV (TBD)

5. References

5.1. 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-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-01, 4 March 2024,
             <https://datatracker.ietf.org/api/v1/doc/document/draft-
             ietf-idr-sr-policy-safi/>.

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5.2. 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.ietf-idr-ts-flowspec-srv6-policy] Jiang, W., Liu, Y., Zhuang,
             S., Mishra, G., and S. Chen, "Traffic Steering using BGP
             Flowspec with SR Policy", Work in Progress, Internet-
             Draft, draft-ietf-idr-ts-flowspec-srv6-policy-03, 17 June
             2023, <http://www.ietf.org/internet-drafts/draft-ietf-idr-
             ts-flowspec-srv6-policy-03.txt>.

Authors' Addresses

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

   Wenying Jiang
   China Mobile
   China
   Email: jiangwenying@chinamobile.com

   Yisong Liu
   China Mobile
   China
   Email: liuyisong@chinamobile.com

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

   Ran Chen
   ZTE Corporation
   China
   Email: chen.ran@zte.com.cn

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