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Interdomain Routing Working Group                                  C. Li
Internet-Draft                                                   M. Chen
Intended status: Standards Track                                 J. Dong
Expires: April 25, 2019                                            Z. Li
                                                     Huawei Technologies
                                                        October 22, 2018


     SR Policies for Path Segment and Bidirectional Path in BGP-LS
             draft-li-idr-bgp-ls-sr-policy-path-segment-01

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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   This Internet-Draft will expire on April 25, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
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   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 . . . . . . . . . . . . . . . . .   4
     3.2.  Sub-TLVs for Bidirectional Path . . . . . . . . . . . . .   5
       3.2.1.  SR Bidirectional Path Sub-TLV . . . . . . . . . . . .   5
       3.2.2.  SR Reverse Path Segment List Sub-TLV  . . . . . . . .   6
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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.cheng-spring-mpls-path-segment], new policies carrying Path
   Segment and bidirectional path information are defined in
   [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.cheng-spring-mpls-path-segment]
   , or a Path Segment in SRv6 [I-D.li-spring-srv6-path-segment], or
   other IDs that can identify a path.





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   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].

   As defined in [I-D.li-idr-sr-policy-path-segment-distribution], the
   new SR policies for bidirectional path has the following format:
















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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 1. SR policy for Bidirectional path

   For collecting 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.cheng-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

   TBA

6.  Security Considerations

   TBA







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7.  Acknowledgements

   TBA

8.  References

8.1.  Normative References

   [I-D.cheng-spring-mpls-path-segment]
              Cheng, W., Wang, L., Li, H., Chen, M., Gandhi, R., Zigler,
              R., and S. Zhan, "Path Segment in MPLS Based Segment
              Routing Network", draft-cheng-spring-mpls-path-segment-03
              (work in progress), October 2018.

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen,
              E., and S. Lin, "Advertising Segment Routing Policies in
              BGP", draft-ietf-idr-segment-routing-te-policy-04 (work in
              progress), July 2018.

   [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-09 (work in progress), June 2018.

   [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-01 (work in progress), June 2018.

   [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 Bi-directional Path", draft-
              li-idr-sr-policy-path-segment-distribution-00 (work in
              progress), April 2018.

   [I-D.li-spring-srv6-path-segment]
              Li, C., Chen, M., Dhody, D., Li, Z., Dong, J., and R.
              Gandhi, "Path Segment for SRv6 (Segment Routing in IPv6)",
              draft-li-spring-srv6-path-segment-00 (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>.



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   [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-10 (work in progress),
              September 2018.

Authors' Addresses

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

   Email: chengli13@huawei.com


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

   Email: Mach.chen@huawei.com







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   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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