IGP Extensions for Shorter SRv6 SID
draft-chen-lsr-igp-shorter-srv6-extensions-02

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LSR WG                                                         Ran. Chen
Internet-Draft                                              Shaofu. Peng
Intended status: Standards Track                         ZTE Corporation
Expires: November 9, 2020                                    May 8, 2020

                  IGP Extensions for Shorter SRv6 SID
             draft-chen-lsr-igp-shorter-srv6-extensions-02

Abstract

   This document describes the IGP extensions required to support the
   Shorter SRv6 SIDs( Compressing SRv6 SIDs).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on November 9, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Advertising Shorter SRv6 SIDs capabilities. . . . . . . . . .   2
     2.1.  IS-IS Extensions  . . . . . . . . . . . . . . . . . . . .   2
     2.2.  OSPFv3 Extensions . . . . . . . . . . . . . . . . . . . .   4
   3.  Advertising SRv6 SID Structure Sub-Sub-TLV  . . . . . . . . .   5
   4.  Advertising Endpoint Behaviors with U-Flavor  . . . . . . . .   6
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 [RFC8754].
   SRv6 refers to this SR instantiation on the IPv6 dataplane.

   However, the size of the SRv6 SID presents a scalabilities 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 IGP in order to to support the
   Shorter SRv6 SIDs contained in SID list that installed in dataplane.

2.  Advertising Shorter SRv6 SIDs capabilities.

2.1.  IS-IS Extensions

   A node indicates that it supports the SR Segment Endpoint Node
   functionality as specified in [RFC8754] by advertising a new SRv6
   Capabilities sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] of the
   router capabilities TLV [RFC7981].

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   This document extensions the flags field in the SRv6 Capabilities
   sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] to indicate the node
   supports the Shorter SRv6 SIDs.

        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            |U|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Optional sub-sub-TLVs...

               Figure 1: U-Flag in SRv6 Capabilities sub-TLV

   where

   U: U-SID Encapsulation Capability.  When the U flag is set, it
   indicates that the node supports the encapsulate and decapsulate the
   U-SID, that is to say, the SID list composed of multiple classic 128
   bit SIDs can be compressed into an U-SID list containing multiple
   shorter U-SIDs, which is encapsulated in SRH, or the shorter U-SID
   can be obtained from SRH and restored to the classic 128 bit SID.

   Optional sub-sub-TLVs: When the U flag is set, A new U-Domain sub-
   sub-TLV is carried to describe which compression domain (U-Domain)
   the node is in.  If the U-Domain sub-sub-tlv is not carried, it is in
   32-bit compression domain by default.  Note that each node is always
   in the classical 128 bit compression domain, without explicit
   notification.

      The format of the U-Domain sub-Sub-TLV is as below:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | sub-Type=U-D  |     Length    |            Flags        |M|S|T|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2:U-Domain sub-Sub-TLV

      Three flags are currently defined in the U-Domain sub-Sub-TLV:

         T: The node is in 32-bit compression domain.

         S: The node is in 16-bit compression domain.

         M: The node is in MPLS compression domain.

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   Note that the U-SID Encapsulation capability has nothing to do with
   the type of compression domain the node is in.  For example, an N1
   node in a 128 bit compression domain has U-SID Encapsulation
   capability, while an N2 node in the same domain may not have U-SID
   Encapsulation capability.

2.2.  OSPFv3 Extensions

   The SRv6 Capabilities TLV is used by an OSPFv3 router to advertise
   its SRv6 support along with its related capabilities for SRv6
   functionality.  This is an optional top level TLV of the OSPFv3
   Router Information LSA [RFC7770] which MUST be advertised by an SRv6
   enabled router.

   This document extensions the flags field in the SRv6 Capabilities TLV
   [I-D.ietf-lsr-ospfv3-srv6-extensions] to indicate the node supports
   the Shorter SRv6 SIDs.

        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           |U|            Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Sub-TLVs...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: U-Flag in SRv6 Capabilities TLV

   where

   U: U-SID Encapsulation Capability.  When the U flag is set, it
   indicates that the node supports the encapsulate and decapsulate the
   U-SID, that is to say, the SID list composed of multiple classic 128
   bit SIDs can be compressed into an U-SID list containing multiple
   shorter U-SIDs, which is encapsulated in SRH, or the shorter U-SID
   can be obtained from SRH and restored to the classic 128 bit SID.

   Sub-TLVs: When the U flag is set, A new U-Domain sub-TLV is carried
   to describe which compression domain (U-Domain) the node is in.  If
   the U-Domain sub-tlv is not carried, it is in 32-bit compression
   domain by default.  Note that each node is always in the classical
   128 bit compression domain, without explicit notification.

      The format of the U-Domain sub-Sub-TLV is as below:

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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | sub-Type=U-D  |     Length    |            Flags        |M|S|T|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 4: U-Domain sub-TLV

      Three flags are currently defined in the U-Domain sub-TLV:

         T: The node is in 32-bit compression domain.

         S: The node is in 16-bit compression domain.

         M: The node is in MPLS compression domain.

   Note that the U-SID Encapsulation capability has nothing to do with
   the type of compression domain the node is in.  For example, an N1
   node in a 128 bit compression domain has U-SID Encapsulation
   capability, while an N2 node in the same domain may not have U-SID
   Encapsulation capability.

3.  Advertising SRv6 SID Structure Sub-Sub-TLV

   SRv6 SID Structure Sub-Sub-TLV is an optional Sub-Sub-TLV of SRv6 End
   SID Sub-TLV, SRv6 End.U SID Sub-TLV ,and SRv6 LAN End.U SID Sub-TLV .

   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 Sub-Sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] or
   SRv6 SID Structure Sub-TLV [I-D.ietf-lsr-ospfv3-srv6-extensions] is
   used to advertise the length of each individual part of the SRv6 SID.

   If a node advertised the compression domains which the node is in, it
   SHOULD advertise the related SIDs with structure information,
   otherwise the result optimized SID list will have to contain related
   classical 128-bits SRv6 SID.

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4.  Advertising Endpoint Behaviors with U-Flavor

   Endpoint behaviors are defined in
   [I-D.ietf-spring-srv6-network-programming]
   and[I-D.ietf-6man-spring-srv6-oam] . 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:

      U32-Flavor: indicate the next SID is 32-bits IP address.

      U16-Flavor: indicate the next SID is 16-bits IP address.

   We can take regard the traditional behaviors that has not any
   indication of next SID type as behaviors with U128-flavor.

   To extend the above U 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 U related flavors can be used combined with
   existing PSP/USP/USD flavors.

5.  Operations

   Based on the IGP link-state database which contains U-SID
   Encapsulation Capabilities and SID(s) per U-Flavors, a headend or
   controller can firstly check which compression domains a computed SR
   path crossed, then secondly select U-Flavor related SID to construct
   an optimized E2E SID list.

   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-lsr-isis-sr
   v6-extensions]and[I-D.ietf-lsr-ospfv3-srv6-extensions] .

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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-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-04 (work in progress),
              March 2020.

   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extension to Support Segment Routing over
              IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08
              (work in progress), April 2020.

   [I-D.ietf-lsr-ospfv3-srv6-extensions]
              Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
              "OSPFv3 Extensions for SRv6", draft-ietf-lsr-
              ospfv3-srv6-extensions-00 (work in progress), February
              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-15 (work in
              progress), March 2020.

   [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-02 (work in progress), May 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.

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   [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>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

Authors' Addresses

   Ran Chen
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: chen.ran@zte.com.cn

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

   Email: peng.shaofu@zte.com.cn

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