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Interdomain Routing Working Group                                  C. Li
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                 H. Chen
Expires: February 9, 2020                                  China Telecom
                                                                 M. Chen
                                                                 J. Dong
                                                                   Z. Li
                                                     Huawei Technologies
                                                          August 8, 2019


SR Policies Extensions for Path Segment and Bidirectional Path in BGP-LS
             draft-li-idr-bgp-ls-sr-policy-path-segment-03

Abstract

   This document specifies the way of collecting configuration and
   states of SR policies carrying Path Segment and bidirectional path
   information by using BPG-LS.  Such information can be used by
   external conponents for many use cases such as performance
   measurement, path re-optimization and end-to-end protection.

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 RFC 2119 [RFC2119].

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on February 9, 2020.







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Copyright Notice

   Copyright (c) 2019 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
   (https://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 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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Carrying SR Path Sub-TLVs in BGP-LS . . . . . . . . . . . . .   3
     3.1.  SR Path Segment Sub-TLV . . . . . . . . . . . . . . . . .   5
     3.2.  Sub-TLVs for Bidirectional Path . . . . . . . . . . . . .   6
       3.2.1.  SR Bidirectional Path Sub-TLV . . . . . . . . . . . .   6
       3.2.2.  SR Reverse Path Segment List Sub-TLV  . . . . . . . .   7
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  BGP-LS SR Segment Descriptors . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Segment routing (SR) [RFC8402] is a source routing paradigm that
   allows the ingress node steers packets into a specific path according
   to the Segment Routing Policy
   [I-D.ietf-spring-segment-routing-policy].

   However, the SR Policies defined in
   [I-D.ietf-spring-segment-routing-policy] only supports unidirectional
   SR paths and there is no path ID in a Segment List to identify an SR
   path.  For identifying an SR path and supporting bidirectional path
   [I-D.ietf-spring-mpls-path-segment], new policies carrying Path
   Segment and bidirectional path information are defined in



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   [I-D.li-idr-sr-policy-path-segment-distribution], as well as the
   extensions to BGP to distribute new SR policies.  The Path Segment
   can be a Path Segment in SR-MPLS [I-D.ietf-spring-mpls-path-segment]
   , or other IDs that can identify a path.

   In many network scenarios, the configuration and state of each TE
   Policy is required by a controller which allows the network operator
   to optimize several functions and operations through the use of a
   controller aware of both topology and state information
   [I-D.ietf-idr-te-lsp-distribution].

   To collect the TE Policy information that is locally available in a
   router, [I-D.ietf-idr-te-lsp-distribution] describes a new mechanism
   by using BGP-LS update messages.

   Based on the mechanism defined in [I-D.ietf-idr-te-lsp-distribution],
   this document describes a mechanism to distribute configuration and
   states of the new SR policies defined in
   [I-D.li-idr-sr-policy-path-segment-distribution] to external
   components using BGP-LS.

2.  Terminology

   This memo makes use of the terms defined in [RFC8402] and
   [I-D.ietf-idr-te-lsp-distribution].

3.  Carrying SR Path Sub-TLVs in BGP-LS

   A mechanism to collect states of SR Policies via BGP-LS is proposed
   by [I-D.ietf-idr-te-lsp-distribution].  The characteristics of an SR
   policy can be described by a TE Policy State TLV, which is carried in
   the optional non-transitive BGP Attribute "LINK_STATE Attribute"
   defined in [RFC7752].  The TE Policy State TLV contains several sub-
   TLVs such as SR TE Policy sub-TLVs.  Rather than replicating SR TE
   Policy sub-TLVs, [I-D.ietf-idr-te-lsp-distribution] reuses the
   equivalent sub-TLVs as defined in
   [I-D.ietf-idr-segment-routing-te-policy].

   [I-D.li-idr-sr-policy-path-segment-distribution] defines the BGP
   extensions for Path Segment.  The Path Segment can appear at both
   segment-list level and candidate path level upon the use case.  The
   encoding is shown below.









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

           Figure 1. Path Segment in SR policy

   Also, [I-D.li-idr-sr-policy-path-segment-distribution] defines SR
   policy extensions for bidirectional SR path, the encoding is shown
   below:






















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

             Figure 2. SR policy for Bidirectional path

   In order to collect configuration and states of unidirectional and
   bidirectional SR policies defined in
   [I-D.li-idr-sr-policy-path-segment-distribution], new sub-TLVs in SR
   TE Policy sub-TLVs should be defined.  Likewise, rather than
   replicating SR Policy sub-TLVs, this document can reuse the
   equivalent sub-TLVs as defined in
   [I-D.li-idr-sr-policy-path-segment-distribution].

3.1.  SR Path Segment Sub-TLV

   This section reuses the SR Path Segment sub-TLV defined in
   [I-D.li-idr-sr-policy-path-segment-distribution] to describe a Path
   Segment , and it can be included in the Segment List sub-TLV as
   defined in [I-D.ietf-idr-te-lsp-distribution] . An SR Path Segment
   sub-TLV can be associated with an SR path specified by a Segment List
   sub-TLV, and it MUST appear only once within a Segment List sub-TLV.
   Also, it can be used for identifying an SR candidate path or an SR
   Policy defined in [I-D.ietf-spring-segment-routing-policy].

   The format of Path Segment TLV is included below for reference.







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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     |    Flag       |      ST       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Path Segment (Variable)                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Figure 2. Path Segment sub-TLV

   All fields, including type and length, are defined in
   [I-D.li-idr-sr-policy-path-segment-distribution].

3.2.  Sub-TLVs for Bidirectional Path

   In some scenarios like mobile backhaul transport network, there are
   requirements to support bidirectional path.  In SR, a bidirectional
   path can be represented as a binding of two unidirectional SR paths
   [I-D.ietf-spring-mpls-path-segment].
   [I-D.li-idr-sr-policy-path-segment-distribution] defines new sub-TLVs
   to describe an SR bidirectional path.  An SR policy carrying SR
   bidirectional path information is expressed in Figure 1.

3.2.1.  SR Bidirectional Path Sub-TLV

   This section reuses the SR bidirectional path sub-TLV defined in
   [I-D.li-idr-sr-policy-path-segment-distribution] to specify a
   bidirectional path, which contains a Segment List sub-TLV
   [I-D.ietf-idr-segment-routing-te-policy] and an associated Reverse
   Path Segment List as defined in
   [I-D.li-idr-sr-policy-path-segment-distribution].  The SR
   bidirectional path 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    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Sub-TLVs (Variable)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 3. SR Bidirectional path sub-TLV

   All fields, including type and length, are defined in
   [I-D.li-idr-sr-policy-path-segment-distribution].








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3.2.2.  SR Reverse Path Segment List Sub-TLV

   This section reuses the SR Reverse Path Segment List sub-TLV defined
   in [I-D.li-idr-sr-policy-path-segment-distribution] to specify an
   reverse SR path associated with the path specified by the Segment
   List in the same SR Bidirectional Path Sub-TLV, and it 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    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Sub-TLVs (Variable)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 4. SR Reverse Path Segment List Sub-TLV

   All fields, including type and length, are defined in
   [I-D.li-idr-sr-policy-path-segment-distribution].

4.  Operations

   No new operation procedures are defined in this document, the
   operations procedures of [RFC7752] can apply to this document.

   Typically but not limited to, the uni/bidirectional SR policies
   carrying path identification information can be distributed by the
   ingress node.

   Generally, BGP-LS is used for collecting link states and
   synchronizing with the external component.  The consumer of the uni/
   bidirectional SR policies carrying path identification information is
   not BGP LS process by itself, and it can be any applications such as
   performance measurement [I-D.gandhi-spring-udp-pm] and path re-
   coputation or re-optimization, etc.  The operation of sending
   information to other precesses is out of scope of this document.

5.  IANA Considerations

5.1.  BGP-LS TLVs

   IANA maintains a registry called "Border Gateway Protocol - Link
   State (BGP-LS) Parameters" with a sub-registry called "Node Anchor,
   Link Descriptor and Link Attribute TLVs".  The following TLV
   codepoints are suggested (for early allocation by IANA):






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          Codepoint   Description                           Reference
          -------------------------------------------------------------
          1212        Path Segment sub-TLV                  This document
          1213        SR Bidirectional Path sub-TLV         This document
          1214        Reverse Segment List sub-TLV          This document


5.2.  BGP-LS SR Segment Descriptors

   This document defines new sub-TLVs in the registry "SR Segment
   Descriptor Types" [I-D.ietf-idr-te-lsp-distribution] to be assigned
   by IANA:

          Codepoint   Description                           Reference
          -------------------------------------------------------------
          14          Path Segment sub-TLV                  This document



6.  Security Considerations

   TBA

7.  Acknowledgements

   Many thanks to Shraddha Hedge for her detailed review and
   professional comments.

8.  References

8.1.  Normative References

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Mattes, P., Rosen, E., Jain,
              D., and S. Lin, "Advertising Segment Routing Policies in
              BGP", draft-ietf-idr-segment-routing-te-policy-07 (work in
              progress), July 2019.

   [I-D.ietf-idr-te-lsp-distribution]
              Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler,
              H., and J. Tantsura, "Distribution of Traffic Engineering
              (TE) Policies and State using BGP-LS", draft-ietf-idr-te-
              lsp-distribution-11 (work in progress), May 2019.








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   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
              "Path Segment in MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment-00 (work in progress),
              March 2019.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-03 (work in progress), May 2019.

   [I-D.li-idr-sr-policy-path-segment-distribution]
              Li, C., Chen, M., Dong, J., and Z. Li, "Segment Routing
              Policies for Path Segment and Bidirectional Path", draft-
              li-idr-sr-policy-path-segment-distribution-01 (work in
              progress), October 2018.

   [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>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [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>.

8.2.  Informative References

   [I-D.gandhi-spring-udp-pm]
              Gandhi, R., Filsfils, C., daniel.voyer@bell.ca, d.,
              Salsano, S., Ventre, P., and M. Chen, "UDP Path for In-
              band Performance Measurement for Segment Routing
              Networks", draft-gandhi-spring-udp-pm-02 (work in
              progress), September 2018.

   [I-D.ietf-mpls-bfd-directed]
              Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Directed Return
              Path", draft-ietf-mpls-bfd-directed-11 (work in progress),
              April 2019.



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Authors' Addresses

   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: chengli13@huawei.com


   Huanan Chen
   China Telecom
   109 West Zhongshan Ave
   Guangzhou
   China

   Email: chenhn8.gd@chinatelecom.cn


   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: Mach.chen@huawei.com


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

   Email: jie.dong@huawei.com


   Zhenbin Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: lizhenbin@huawei.com






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