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SPRING WG                                                       W. Cheng
Internet-Draft                                              China Mobile
Intended status: Standards Track                                 R. Chen
Expires: August 19, 2020                                          A. Liu
                                                                G. Mirsk
                                                         ZTE Corporation
                                                       February 16, 2020


                     Shorter SRv6 SID Requirements
              draft-cheng-shorter-srv6-sid-requirement-00

Abstract

   This document describes a list of requirement for Shorter SRv6 SID.

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 August 19, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements: . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  The proposal solutions of shorter SRv6 SID  . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   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.

   A segment can be encoded as a Multi-Protocol Label Switching (MPLS)
   label, IPv4 address, or IPv6 address.  Segment Routing can be
   deployed on MPLS data plane by encoding 20-bits SIDs in MPLS label
   stack [I-D.ietf-spring-segment-routing-mpls].  It also can be
   deployed on the IPv6 data plane by encoding a list of 128-bits SIDs
   in IPv6 Segment Routing Extension Header
   (SRH)[I-D.ietf-6man-segment-routing-header].

   The SRv6 Network Programming
   [I-D.ietf-spring-srv6-network-programming]specifies the base set of
   SRv6 behaviors that enables the creation of interoperable overlays
   with underlay optimization.

   However, the size of the IPv6 segment identifier (SID) presents a
   scaling 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.
   Meanwhile, SR-MPLS currently, more often than SRv6, is used in metro
   networks.  With the gradual deployment of SRv6 in the core networks,
   it becomes necessary to support interworking between SR-MPLS and SRv6
   and upgrading to SRv6 from SR-MPLS.It requires some solutions to
   resolve these problems.

2.  Requirements:

   This section list the suggested requirements for Shorter SRv6 SID,
   which have been used to help the WG evaluate against the proposed
   solutions:






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   REQ#1:The Shorter SRv6 solution MUST align with the basic SRv6.
   There are three basic Segment Routing over the IPv6 data-plane (SRv6)
   documents:

   o  The Segment Routing (SR) architecture is defined [RFC8402].

   o  The IPv6 Segment Routing Header (SRH) is defined
      [I-D.ietf-6man-segment-routing-header].

   o  SRv6 Network Programming is defined
      [I-D.ietf-spring-srv6-network-programming].

   The Shorter SRv6 SID solution MUST align with above basic SRv6
   documents.

   REQ#2:The Shorter SRv6 SID solution MUST support Efficient SRv6
   header compression.

   When SRv6 is deployed, the SRv6 header overhead must be considered,
   as the size of the SRH may affect the forwarding performance.  The
   solution MUST reduce the SRv6 SID size effectively.

   REQ#3:The Shorter SRv6 SID solution MUST be easy to implement and
   hardware-friendly

   The Shorter SRv6 SID solution MUST be simple and easy to implement
   and MUST use the mature hardware capabilities

   REQ#4:The Shorter SRv6 SID solution MUST be compatible with SRv6
   header(SRH).

   For support of SRv6 network, Segment Routing Header (SRH) has been
   defined in [I-D.ietf-6man-segment-routing-header].  The Shorter SRv6
   SID solution MUST be compatible with SRH.

   REQ#5:The Shorter SRv6 SID solution MUST support Compressed SRv6
   Network Programming.

   In a SR domain,there will be such the scenario in which some nodes
   support Compressed SRv6 while others only support SRv6, the proposed
   solution must support this scenario.

   REQ#6:The Shorter SRv6 SID solution MUST support super-large-scale
   networking and address planning.

   Note:The operator suggest to reuse the current address assignment and
   planning, thus minimizing the impact on the network.




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   REQ#7:The Shorter SRv6 SID solution MUST have the ability to upgrade
   smooth from SR-MPLS to SRv6.

   2G/3G/4G backhaul networks widely deploy MPLS to connect wireless
   services.  Many operators are already deploying 5G networks.  To
   optimize the operation of the network, many operators intent to adopt
   the segment routing.  Currently, given maturity of SR-MPLS, it has
   been deployed on a large scale.  Meanwhile the requirements of 5G
   super-large-scale number of connections accelerate the deployment of
   IPv6 networks.  Thus, logically, operators consider SRv6 solution to
   fulfill the 5G backhaul requirement.  But the backhaul network could
   not deploy SRv6 in one day, especially if it has already been using
   MPLS and SR-MPLS.  It might be reasonable to upgrade from MPLS to SR-
   MPLS and then to SRv6

   REQ#8:The Shorter SRv6 SID solution MUST support interworking between
   SRv6 and SR-MPLS domains in the network.

   SR-MPLS currently, more often than SRv6, is used in metro networks.
   With the gradual deployment of SRv6 in the core networks, it becomes
   necessary to support interworking between SR-MPLS and SRv6.

3.  The proposal solutions of shorter SRv6 SID

   As we know, there are a number of proposals in the called 'shorter
   SRv6 SID' topic. This document tries to summarize these proposals
   here. Then we can discuss whether all the proposals can meet the
   requirements. And then we can look at merits and costs of each
   solution. After that, we will possibly refine them, possibly
   converge on a single one, and probably drop multiples.

   Here are the solutions that have been proposed:

   o  [I-D.mirsky-6man-unified-id-sr]extends the use the flag of the SRH
      to unified identifiers encoded as shorter SID (such as 32-bits).
      It can be interworking with SR-MPLS. It is the earliest one,
      simple, and compatible well with original SRH.

   o  [I-D.filsfils-spring-net-pgm-extension-srv6-usid] extends SRv6
      Network Programming with a new type of SRv6 SID behavior.  A uSID
      carrier can be encoded in the Destination Address of an IPv6
      header or at any position in the Segment List of an SRH.

   o  [I-D.decraene-spring-srv6-vlsid]extends SRH and SRv6 Network
      Programming to allow for SIDs of variable length, from 1 up to 128
      bits.  It is required to extend the control plane to advertise the
      SID length.




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   o  [I-D.bonica-6man-comp-rtg-hdr]defines two new Routing header
      types.  Collectively, they are called the Compressed Routing
      Headers (CRH).  Individually,they are called CRH-16 and CRH-32.
      In the CRH, the Type-specific data field contains a list of
      Segment Identifiers (SIDs)(16bits/32bits).

   o  [I-D.cl-spring-generalized-srv6-np]proposes Generalized Segment
      Routing over IPv6 (G-SRv6) Networking Programming, which supports
      to encode multiple types of Segments in a SRH, called Generalized
      SRH (G-SRH).  These Segments can be called Generalized Segment,
      and the ID can be Generalized Segment Identifier (G-SID), which
      may include an SRv6 SID(128 bits),C-SIDs, MPLS labels, or IPv4
      tunnel information.

4.  IANA Considerations

   This document has no requests to IANA.

5.  Security Considerations

   This document does not change the security considerations of SRv6,
   please refers to [RFC8402], [I-D.ietf-6man-segment-routing-header]
   and [I-D.ietf-spring-srv6-network-programming].

6.  Normative References

   [I-D.bonica-6man-comp-rtg-hdr]
              Bonica, R., Kamite, Y., Niwa, T., Alston, A., and N. So,
              "The IPv6 Compressed Routing Header (CRH)", draft-bonica-
              6man-comp-rtg-hdr-11 (work in progress), February 2020.

   [I-D.cl-spring-generalized-srv6-np]
              Cheng, W., Li, Z., Li, C., Xie, C., Cong, L., Tian, H.,
              and F. Zhao, "Generalized SRv6 Network Programming",
              draft-cl-spring-generalized-srv6-np-00 (work in progress),
              February 2020.

   [I-D.decraene-spring-srv6-vlsid]
              Decraene, B. and R. Raszuk, "SRv6 vSID: Network
              Programming extension for variable length SIDs", draft-
              decraene-spring-srv6-vlsid-02 (work in progress), February
              2020.









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   [I-D.filsfils-spring-net-pgm-extension-srv6-usid]
              Filsfils, C., Camarillo, P., Cai, D., Voyer, D., Meilik,
              I., Patel, K., Henderickx, W., Jonnalagadda, P., and D.
              Melman, "Network Programming extension: SRv6 uSID
              instruction", draft-filsfils-spring-net-pgm-extension-
              srv6-usid-03 (work in progress), February 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-spring-segment-routing-mpls]
              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-22
              (work in progress), May 2019.

   [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-09 (work in
              progress), February 2020.

   [I-D.mirsky-6man-unified-id-sr]
              Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., Wei,
              C., and S. Shay, "Unified Identifier in IPv6 Segment
              Routing Networks", draft-mirsky-6man-unified-id-sr-04
              (work in progress), November 2019.

   [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>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.







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   [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

   Weiqiang Cheng
   China Mobile

   Email: chengweiqiang@chinamobile.com


   Ran Chen
   ZTE Corporation

   Email: chen.ran@zte.com.cn


   Aihua Liu
   ZTE Corporation

   Email: liu.aihua@zte.com.cn


   Greg Mirsk
   ZTE Corporation

   Email: gregimirsky@gmail.com






















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