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6man Working Group                                                 C. Li
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                W. Cheng
Expires: May 4, 2021                                        China Mobile
                                                                   Z. Li
                                                                D. Dhody
                                                     Huawei Technologies
                                                        October 31, 2020


                 Encapsulation of Path Segment in SRv6
                draft-li-6man-srv6-path-segment-encap-04

Abstract

   Segment Routing (SR) allows for a flexible definition of end-to-end
   paths by encoding an ordered list of instructions, called "segments".
   The SR architecture can be implemented over an IPv6 data plane,
   called SRv6.  In some use-cases such as end-to-end SR Path Protection
   and Performance Measurement (PM), an SRv6 path needs to be
   identified.  This document defines the encoding of Path Segment in
   SRv6 networks.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on May 4, 2021.

Copyright Notice

   Copyright (c) 2020 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



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   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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Encoding of an SRv6 Path Segment  . . . . . . . . . . . . . .   3
     2.1.  Encapsulation of SRv6 Path Segment  . . . . . . . . . . .   3
   3.  Processing of SRv6 Path Segment . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Segment routing (SR) [RFC8402] is a source routing paradigm that
   explicitly indicates the forwarding path for packets at the ingress
   node by inserting an ordered list of instructions, called segments.

   When segment routing is deployed on an IPv6 data plane, it is called
   SRv6, and it uses a new IPv6 [RFC8200] Routing Header (EH) called the
   IPv6 Segment Routing Header (SRH) [RFC8754] to construct an SRv6
   path.  As per [I-D.ietf-spring-srv6-network-programming], an SRv6
   segment identifier is a 128-bit value, which can be represented as
   LOC:FUNCT, where LOC is the L most significant bits and FUNCT is the
   128-L least significant bits.  Most often the LOC part of the SID is
   routable and leads to the node which instantiates that SID.  The
   FUNCT part of the SID is an opaque identification of a local function
   bound to the SID.

   In several use cases, such as binding bidirectional path
   [I-D.ietf-pce-sr-bidir-path] and end-to-end performance measurement
   [I-D.gandhi-spring-twamp-srpm], the ability to implement path
   identification is a pre-requisite.  In SRv6, it is possible to
   identify a path by the content of the segment list.  However, the
   segment list may not be a good key, since the length of the segment
   list may be too long and flexible according to the number of SIDs.




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   Therefore, [I-D.li-spring-srv6-path-segment] defines an SRv6 Path
   Segment to identify an SRv6 path.

   This document defines the encoding of an SRv6 Path Segment in SRv6
   networks.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.2.  Terminology

   PM: Performance Measurement.

   SID: Segment ID.

   SL: Segment List.

   SR: Segment Routing.

   SRH: Segment Routing Header.

   PSID: Path Segment Identifier.

   PSP: Penultimate Segment Popping.

   Further, this document makes use of the terms defined in [RFC8402]
   and [I-D.ietf-spring-srv6-network-programming].

2.  Encoding of an SRv6 Path Segment

   This section will describe the SRH encoding of an SRv6 Path Segment
   as defined in [I-D.li-spring-srv6-path-segment].  As per
   [I-D.li-spring-srv6-path-segment], an SRv6 Path Segment is a 128-bits
   value, which identifies an SRv6 path.

2.1.  Encapsulation of SRv6 Path Segment

   The SRv6 Path Segment MUST appear only once in a SID list, and it
   MUST appear as the last entry.

   To indicate the existence of a Path Segment in the SRH, this document
   defines a P-bit in the SRH flag field.  The encapsulation of SRv6
   Path Segment is shown 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Last Entry   |     Flags   |P|              Tag              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |            Segment List[0] (128 bits IPv6 address)            |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                                                               |
                                     ...
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |          Segment List[n-1] (128 bits IPv6 address)            |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |    SRv6 Path Segment (Segment List[n],128 bits IPv6 value)    |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                                                             //
       //         Optional Type Length Value objects (variable)       //
       //                                                             //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1. SRv6 Path Segment in SID List

   o  P-bit: set when SRv6 Path Segment is inserted.  It MUST be ignored
      when a node does not support SRv6 Path Segment processing.

3.  Processing of SRv6 Path Segment

   The processing of SRv6 path segment is out of the scope of this
   document and is defined in [I-D.li-spring-srv6-path-segment].

4.  IANA Considerations

   This document requests IANA to allocate bit position TBA within the
   "Segment Routing Header Flags" registry defined in [RFC8402].




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5.  Security Considerations

   TBA

6.  Acknowledgements

   TBA

7.  References

7.1.  Normative References

   [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-24 (work in
              progress), October 2020.

   [I-D.li-spring-srv6-path-segment]
              Li, C., Cheng, W., Chen, M., Dhody, D., and R. Gandhi,
              "Path Segment for SRv6 (Segment Routing in IPv6)", draft-
              li-spring-srv6-path-segment-06 (work in progress),
              September 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>.

   [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>.

   [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>.




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7.2.  Informative References

   [I-D.gandhi-spring-twamp-srpm]
              Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B.
              Janssens, "Performance Measurement Using TWAMP Light for
              Segment Routing Networks", draft-gandhi-spring-twamp-
              srpm-11 (work in progress), October 2020.

   [I-D.ietf-idr-sr-policy-path-segment]
              Li, C., Li, Z., Telecom, C., Cheng, W., and K. Talaulikar,
              "SR Policy Extensions for Path Segment and Bidirectional
              Path", draft-ietf-idr-sr-policy-path-segment-01 (work in
              progress), August 2020.

   [I-D.ietf-pce-sr-bidir-path]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "PCEP Extensions for Associated Bidirectional Segment
              Routing (SR) Paths", draft-ietf-pce-sr-bidir-path-03 (work
              in progress), September 2020.

   [I-D.ietf-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)
              Extension for Path Segment in Segment Routing (SR)",
              draft-ietf-pce-sr-path-segment-01 (work in progress), May
              2020.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-08 (work in progress),
              July 2020.

Authors' Addresses

   Cheng Li
   Huawei Technologies

   Email: c.l@huawei.com


   Weiqiang Cheng
   China Mobile

   Email: chengweiqiang@chinamobile.com






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

   Email: lizhenbin@huawei.com


   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore  560066
   India

   Email: dhruv.ietf@gmail.com



































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