BGP-LS Extensions for Shorter SRv6 SID
draft-liu-idr-bgp-ls-shorter-srv6-extensions-00

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IDR WG                                                          Yao. Liu
Internet-Draft                                              Shaofu. Peng
Intended status: Standards Track                         ZTE Corporation
Expires: September 29, 2020                               March 28, 2020

                 BGP-LS Extensions for Shorter SRv6 SID
            draft-liu-idr-bgp-ls-shorter-srv6-extensions-00

Abstract

   This document describes the BGP-LS extensions required to support the
   Shorter SRv6 SIDs( Compressing SRv6 SIDs).

Status of This Memo

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   This Internet-Draft will expire on September 29, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Advertising Shorter SRv6 SIDs capabilities  . . . . . . . . .   2
   3.  Advertising SRv6 SID Structure TLV  . . . . . . . . . . . . .   4
   4.  Advertising SRv6 SID Endpoint Behaviors with UET-Flavor . . .   4
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Segment Routing [RFC8402] leverages the source routing paradigm.  An
   ingress node steers a packet through an ordered list of
   instructions,called segments.

   Segment Routing can be directly instantiated on the IPv6 data plane
   through the use of the Segment Routing Header defined in
   [I-D.ietf-6man-segment-routing-header].  SRv6 refers to this SR
   instantiation on the IPv6 dataplane.

   However, the size of the SRv6 SID presents a scalability challenge to
   use topological instructions that define a strict explicitly routed
   path in combination with service-based instructions.  At the same
   time, the size of the SRH/SID may be a challenge for some data plane
   processors and traffic overhead.
   [I-D.cheng-spring-shorter-srv6-sid-requirement] describes a list of
   requirements for the use of a shortened identifier in a segment
   routing network with the IPv6 data plane.

   [I-D.mirsky-6man-unified-id-sr] proposed an extension of SRH that
   enables the use of a shorter segment identifier in dataplane, such as
   32-bits Label format SID or 32-bits IP address format SID.

   This document defines extensions to BGP-LS in order to to support the
   advertisement of Shorter SRv6 SIDs contained in SID list that
   installed in dataplane.

2.  Advertising Shorter SRv6 SIDs capabilities

   A node indicates that it supports the SR Segment Endpoint Node
   functionality as specified in [I-D.ietf-6man-segment-routing-header]
   by advertising a SRv6 Capabilities TLV [I-D.ietf-idr-bgpls-srv6-ext]
   of the node NLRI.

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   This document extends the flags field in the SRv6 Capabilities TLV
   [I-D.ietf-idr-bgpls-srv6-ext] to indicate that the node supports the
   Shorter SRv6 SIDs, where,

        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               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             Flags       | UEC |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: UEC-Flag in SRv6 Capabilities TLV

   UEC: Unified-SID Encapsulation Capability, 3-bits field, refers to
   [I-D.mirsky-6man-unified-id-sr], it indicates the U-SID capabilities
   which the node support.  A node advertised a specific UEC also means
   the node belongs to the related UET domain, so it will have
   capability to install a local SID entry with behavor to get next UET
   related U-SID from SRH.  The value of UEC could be:

      0b000: The node only support to use classical 128-bits SRv6 SID.
      It only belongs to UET-128 domain, and has capability only to get
      next classical 128-bits SID from SRH.

      0b001: The node support to use both classical 128-bits SRv6 SID
      and 32-bits IPv4 U-SID.  It can belongs to both UET-128 domain and
      UET-32 IPv4 domain, and has capability both to get next classical
      128-bits SID and 32-bits IPv4 U-SID from SRH.

      0b010: The node support to use both classical 128-bits SRv6 SID
      and 32-bits MPLS U-SID.  It can belongs to both UET-128 domain and
      UET-32 MPLS domain, and has capability both to get next classical
      128-bits SID and 32-bits MPLS U-SID from SRH.

      0b011: The node support to use both classical 128-bits SRv6 SID,
      32-bits IPv4 U-SID, and 32-bits MPLS U-SID.  It can belongs to
      both UET-128 domain, UET-32 IPv4 domain, and UET-32 MPLS domain,
      and has capability both to get next classical 128-bits SID,
      32-bits IPv4 U-SID, and 32-bits MPLS U-SID from SRH.

      0b100: The node support to use both classical 128-bits SRv6 SID
      and 16-bits U-SID.  It can belongs to both UET-128 domain and
      UET-16 domain, and has capability both to get next classical
      128-bits SID and 32-bits U-SID from SRH.

      0b101: The node support to use both classical 128-bits SRv6 SID,
      32-bits IPv4 U-SID, and 16-bits U-SID.  It can belongs to both

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      UET-128 domain, UET-32 IPv4 domain, and UET-16 domain, and has
      capability both to get next classical 128-bits SID, 32-bits IPv4
      U-SID, and 16-bits U-SID from SRH.

      others: For later defined.

   For typical 32-bits based compression scenario, 0b001 UEC is enough.

   Note that UEC has two meanings.  First, it indicates which UET domain
   does the advertised node belongs to, this will help to outline which
   UET domains the SR path crosses.  The second meanning, it indicates
   the advertised node has capability to install a local SID entry with
   UET related behavor, to get next UET related U-SID from SRH, this
   will help to select appropriate SID with specific UET related behavor
   for an segment list during compression.

3.  Advertising SRv6 SID Structure TLV

   SRv6 SID Structure TLV is an optional TLV use in the BGP-LS Attribute
   for an SRv6 SID NLRI defined in [I-D.ietf-idr-bgpls-srv6-ext].

   As discussed in [I-D.ietf-spring-srv6-network-programming], the node
   with the SRv6 capability will maintain its local SID table.  A Local
   SID is generally composed of two parts, that is, LOC:FUNCT, or may
   carry arguments at the same time, that is, LOC:FUNCT:ARGS.  The
   controller plane protocol can also use B:N to represent an LOC, where
   B is SRv6 SID Locator Block and N to represent node N.  In other
   words, the structure of a complete SID is B:N:FUNCT:ARGS.

   SRv6 SID Structure TLV is used to advertise the length of each
   individual part of the SRv6 SID as defined in
   [I-D.ietf-spring-srv6-network-programming].

   If a node advertised an UEC-FLAG with 0b001/0b011/0b100/0b101, it
   SHOULD advertise the related SIDs with structure information, i.e.,
   contained SRv6 SID Structure TLV in the BGP-LS Attribute for an SRv6
   SID NLRI, otherwise the result optimized SID list will have to
   contain related classical 128-bits SRv6 SID.

4.  Advertising SRv6 SID Endpoint Behaviors with UET-Flavor

   Endpoint behaviors are defined in
   [I-D.ietf-spring-srv6-network-programming].  The codepoints for the
   Endpoint behaviors are defined in the "SRv6 Endpoint Behaviors"
   registry defined in [I-D.ietf-spring-srv6-network-programming].  For
   End, End.X and End.T behaviors, they can also have PSP, USP and USD
   variants.  This document continues to extend the following new
   flavors for End and End.X behaviors:

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      UET-32-IPv4 Flavor: indicate the next SID is 32-bits IP address,
      termed as UET-1 flavor.

      UET-32-MPLS Flavor: indicate the next SID is 32-bits MPLS Label,
      termed as UET-2 flavor.

      UET-16-IP Flavor: indicate the next SID is 16-bits IP address, ,
      termed as UET-3 flavor.

   Other flavors are for later defined.

   We can take regard the traditional behaviors that has not any
   indication of next SID type as behaviors with UET-128-IPv6 flavor,
   termed as UET-0 flavor.

   To extend the above UET related flavors for other endpoint behaviors,
   such as VPN related SID and SFC related SID, is out the scope of this
   document.

   Note that a SID MUST NOT set two or more of the above flavors at the
   same time, because these flavors is used to indicate the next SID
   type in SRH, that is, the local SID entry must provide exact
   indication for this purpose.

   Each of the above UET related flavors can be used combined with
   existing PSP/USP/USD flavors.

   If a node supports an UEC, it SHOULD also allocate related SIDs for
   this UEC, otherwise the result optimized SID list will have to
   contain related classical 128-bits SRv6 SID.

   For example, a node X advertised UCE 0b001, it can allocate a
   classical END SID X1 with endpoint behavior "End (no PSP, no USP)",
   it can also allocate an END SID X2 with endpoint behavior "End (no
   PSP, no USP, UET-32-IPv4)".

   Endpoint Behavior information of SRv6 SID could be advertised within
   SRv6 End.X SID TLV, SRv6 LAN End.X SID TLV, and SRv6 Endpoint
   Behavior TLV that defined in [I-D.ietf-idr-bgpls-srv6-ext].

5.  Operations

   Based on the BGP-LS database which contains UEC capabilities and
   SID(s) per UET related flavors, a headend or controller can firstly
   check which UET domains a computed SR path crossed, then selects UET
   related SID to construct an optimized E2E SID list.

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   The detailed description can refer to [I-D.mirsky-6man-unified-id-sr]
   and [I-D.liu-idr-segment-routing-te-policy-complement].

6.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the security considerations discussed in
   [I-D.ietf-idr-bgpls-srv6-ext].

7.  IANA Considerations

   TBD

8.  Normative References

   [I-D.cheng-spring-shorter-srv6-sid-requirement]
              Cheng, W., Xie, C., Pang, R., Li, Z., Chen, R., Lijun, L.,
              Duan, X., and G. Mirsky, "Shorter SRv6 SID Requirements",
              draft-cheng-spring-shorter-srv6-sid-requirement-01 (work
              in progress), March 2020.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.

   [I-D.ietf-6man-spring-srv6-oam]
              Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
              Chen, "Operations, Administration, and Maintenance (OAM)
              in Segment Routing Networks with IPv6 Data plane (SRv6)",
              draft-ietf-6man-spring-srv6-oam-03 (work in progress),
              December 2019.

   [I-D.ietf-idr-bgpls-srv6-ext]
              Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
              daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link
              State Extensions for SRv6", draft-ietf-idr-bgpls-
              srv6-ext-02 (work in progress), January 2020.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-14 (work in
              progress), March 2020.

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   [I-D.liu-idr-segment-routing-te-policy-complement]
              Yao, L. and S. Peng, "BGP Extensions for Unified SID in TE
              Policy", draft-liu-idr-segment-routing-te-policy-
              complement-01 (work in progress), March 2020.

   [I-D.mirsky-6man-unified-id-sr]
              Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., and
              C. Wei, "Unified Identifier in IPv6 Segment Routing
              Networks", draft-mirsky-6man-unified-id-sr-06 (work in
              progress), March 2020.

   [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>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [RFC7981]  Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
              for Advertising Router Information", RFC 7981,
              DOI 10.17487/RFC7981, October 2016,
              <https://www.rfc-editor.org/info/rfc7981>.

   [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>.

Authors' Addresses

   Liu Yao
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: liu.yao71@zte.com.cn

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   Peng Shaofu
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: peng.shaofu@zte.com.cn

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