Network Working Group                                           K. Zhang
Internet-Draft                                                     Z. Hu
Intended status: Informational                                   J. Dong
Expires: April 23, 2022                                           Huawei
                                                        October 20, 2021


                 BGP SR Policy Extensions for template
                 draft-zhang-idr-sr-policy-template-00

Abstract

   Segment Routing(SR) Policies can be advertised using BGP.  An SR
   Policy may has lots of constraints, and as the application and
   features evolve, the SR Policy may need have more and more attribute
   constraints.  To avoid modifying BGP when constraints are added to an
   SR Policy, we can define a template.  The identifier and content of
   the template are defined by the receiver of the SR Policy.  The
   advertiser of an SR policy only needs to know the ID of the template.
   When advertising SR policy, the advertiser carries the template ID in
   the tunnel encapsulation information of the SR policy.  After
   receiving the SR Policy information, the receiver obtains the
   corresponding template and content according to the template ID,
   thereby obtaining abundant constraint configuration information.

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 BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown
   here.

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."




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   This Internet-Draft will expire on April 23, 2022.

Copyright Notice

   Copyright (c) 2021 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
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Template ID defination  . . . . . . . . . . . . . . . . . . .   3
   4.  SR Policy and Tunnel Encapsulation Attribute Update . . . . .   3
     4.1.  Template ID sub-TLV . . . . . . . . . . . . . . . . . . .   4
   5.  SR Policy Operations  . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Advertisement of SR Policies  . . . . . . . . . . . . . .   5
     5.2.  Reception of an SR Policy . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [I-D.ietf-idr-segment-routing-te-policy]defines some attributes
   encoding of the SR Policy path.  However, in actual applications,
   there are many other constraints of SR Policy path.  These
   constraints are valid only on the device where the SR Policy path is
   installed.  Such constraints may include backup protection,
   Bidirectional Forwarding Detection information, traffic statistics
   collection, or in-situ Flow Information Telemetry detection
   information, etc.  If these constraints are directly delivered
   through BGP, the BGP SR Policy protocol may change frequently.  This
   document defines a general method to carry the path constraints of SR
   Policies.





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2.  Terminology

   SR Policy: An ordered list of segments.

   Candidate Path: the unit for signaling of an SR Policy to a headend
   via protocol extensions like Path Computation Element (PCE)
   Communication Protocol (PCEP) [RFC8664]
   [I-D.ietf-pce-segment-routing-policy-cp] or BGP SR Policy
   [I-D.ietf-idr-segment-routing-te-policy].

   SRPM: SR Policy Module.

   Template: A collection of constraints sets.

   Template ID: The identifier of a template.

3.  Template ID defination

   To support the constraints extension of SR Policies, this document
   defines a constraint template identifier.  The constraint template ID
   is valid only for the recipient.  The SR policy publisher only needs
   to carry the template ID when publishing the SR policy.  The receiver
   of the SR Policy may create a template corresponding to the template
   identifier in advance before receiving the SR Policy, or may define a
   corresponding template after receiving the template definition of the
   SR Policy.  The template can contain any constraints on the SR Policy
   path, including but not limited to backup protection, Bidirectional
   Forwarding Detection information, traffic statistics collection, or
   in-situ Flow Information Telemetry detection information, etc.  After
   receiving the SR Policy information, the receiver matches the
   template information based on the template ID and adds constraints to
   the SR Policy based on the constraints defined in the template.

4.  SR Policy and Tunnel Encapsulation Attribute Update

   As the template ID is defined, the tunnel attribute encapsulation of
   the BGP SR Policy needs to be updated.

   The SR Policy Encoding structure is as follows:

   SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>










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   Attributes:
      Tunnel Encaps Attribute (23)
         Tunnel Type: SR Policy
           Binding SID
           Preference
           Priority
           Policy Name
           Policy Candidate Path Name
           Explicit NULL Label Policy (ENLP)
           Tempate ID
           Segment List
              Weight
              Segment
              Segment
              ....
           ....

   Where Tempate ID indicates the template ID for the SR Policy
   candidate path.

4.1.  Template ID sub-TLV

   A new sub-TLV called Template ID sub-TLV is defined.  Template ID
   sub-TLV specifies the template ID of an SR policy candidate path.
   Each sub-TLV is encoded as shown in Figure 1.

     0               1               2               3
     0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
     |      Type     |    Length     |     Flags     |   RESERVED   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
     |                   Template ID(4 octets)                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                       Figure 1: Template ID Sub-TLV

   Type: Template ID, 1 octet, TBD.

   Length: 6.

   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.

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

   Template ID: a 4-octet value.




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5.  SR Policy Operations

5.1.  Advertisement of SR Policies

   When BGP advertises an SR Policy, different candidate paths of the
   same SR Policy may have different template IDs or the same template
   ID, depending on the constraints required by the candidate paths of
   the SR Policy..

5.2.  Reception of an SR Policy

   When a BGP speaker receives an SR Policy NLRI from a neighbor, BGP
   Speaker determines determine if it's acceptable as described in
   [I-D.ietf-idr-segment-routing-te-policy].  Once BGP on the receiving
   node has determined that the SR Policy NLRI is usable, it passes the
   SR Policy candidate path to the SRPM.  The SRPM then determine how to
   use the template ID in SR Policy.

   The SRPM should find the template by template ID, and determines the
   constraints to use when install the candidate path.  If there is no
   template find, the SRPM should ignore the template ID and use the
   candidate path as there is no template ID.

6.  Acknowledgements

   TBD.

7.  IANA Considerations

   This document requests that IANA allocates a new sub-TLV type as
   defined in Section 4.1 from the "Sub-TLVs for SR Policy" registry as
   specified.

   Value                  Description                  Reference
   ---------------------- ---------------------------- --------------
   TBD                    SR Policy Template ID        This document

                       Figure 2: Template ID sub-TLV

8.  Security Considerations

   These extensions to BGP SR Policy do not add any new security issues
   to the existing protocol.








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9.  References

   [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", draft-ietf-idr-segment-routing-
              te-policy-13 (work in progress), June 2021.

   [I-D.ietf-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
              Bidgoli, "PCEP extension to support Segment Routing Policy
              Candidate Paths", draft-ietf-pce-segment-routing-policy-
              cp-05 (work in progress), May 2021.

   [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>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

Authors' Addresses

   Ka Zhang
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: zhangka@huawei.com


   Zhibo Hu
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: huzhibo@huawei.com




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   Jie Dong
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: jie.dong@huawei.com












































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