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Network                                                        G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                               P. Shaofu
Expires: April 13, 2019                                  ZTE Corporation
                                                        October 10, 2018


          Unified Identifier in IPv6 Segment Routing Networks
                   draft-mirsky-6man-unified-id-sr-01

Abstract

   Segment Routing architecture leverages the paradigm of source
   routing.  It can be realized in a network data plane by prepending
   the packet with a list of instructions, a.k.a. segments.  A segment
   can be encoded as a Multi-Protocol Label Switching (MPLS) label, IPv4
   address or IPv6 address.  Segment Routing can be applied in MPLS data
   plane by encoding segments in MPLS label stack.  It also can be
   applied to IPv6 data plane by encoding list of segment identifiers in
   IPv6 Segment Routing Extension Header (SRH).  This document extends
   the use of the SRH to segment identifiers encoded as MPLS label and
   IPv4 address.

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 April 13, 2019.

Copyright Notice

   Copyright (c) 2018 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
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   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.  Conventions used in this document . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Segment Routing Extension Header: Benefits and Challenges . .   3
   3.  Support of Multiple SID Lengths in IPv6 Segment Routing
       Extension Header  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Egress SR Tunnel Node . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Segment Routing architecture [RFC8402] leverages the paradigm of
   source routing.  It can be realized in a network data plane by
   prepending the packet with a list of instructions, a.k.a. segment
   identifiers (SIDs).  A segment can be encoded as a Multi-Protocol
   Label Switching (MPLS) label, IPv4 address or IPv6 address.  Segment
   Routing can be applied in MPLS data plane by encoding 20-bits SIDs in
   MPLS label stack [I-D.ietf-spring-segment-routing-mpls].  It also can
   be applied to IPv6 data plane by encoding list of 128-bits SIDs in
   IPv6 Segment Routing Extension Header (SRH)
   [I-D.ietf-6man-segment-routing-header].  Applicability of 32-bits SID
   that may represent an IPv4 address has not been defined.

   SR extensions to Interior Gateway Protocols (IGP), IS-IS
   [I-D.ietf-isis-segment-routing-extensions], OSPF
   [I-D.ietf-ospf-segment-routing-extensions], and OSPFv3
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions], defined how
   20-bits and 32-bits SIDs advertised and bound to SR objects and/or
   instructions.  Extensions to BGP link-state address family
   [I-D.ietf-idr-bgp-ls-segment-routing-ext] enabled propagation of
   segment information of variable length via BGP.





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   This document extends the use of the SRH
   [I-D.ietf-6man-segment-routing-header] to SIDs encoded as MPLS label
   and IPv4 address.

1.1.  Conventions used in this document

1.1.1.  Terminology

   SR: Segment Routing

   SRH: Segment Routing Extension Header

   MPLS: Multiprotocol Label Switching

   MPLS-SR: Segment Routing in MPLS

   SID: Segment Identifier

   IGP: Interior Gateway Protocol

   OAM: Operation, Administration and Maintenance

   TE: Traffic Engineering

   SRv6: Segment Routing in IPv6

1.1.2.  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.

2.  Segment Routing Extension Header: Benefits and Challenges

   Many functions related to Operation, Administration and Maintenance
   (OAM) require identification of the SR tunnel ingress and the path,
   constructed by segments, between the ingress and the egress SR nodes.
   Combination of IPv6 encapsulation [RFC8200] and SRH
   [I-D.ietf-6man-segment-routing-header], referred to as SRv6, comply
   with this requirements while it is challenging when applying SR in
   MPLS networks, also referred to as MPLS-SR.

   On the other hand, the size of IPv6 SID presents a scaling challenge
   to use topological instructions that define strict explicit traffic
   engineered (TE) path in combination with service-based instructions.




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   At the same time, that is where MPLS-SR approach provides better
   results due to smaller SID length.

   [I-D.bryant-mpls-unified-ip-sr] addresses the scaling challenge by
   using more compact SID encoding of MPLS-SR.  Ability to address OAM
   challenge characteristic to MPLS-SR is open for investigation.

3.  Support of Multiple SID Lengths in IPv6 Segment Routing Extension
    Header

   In section 3 of [I-D.ietf-6man-segment-routing-header] SRH format has
   been defined as presented in Figure 1

        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     |              Tag              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |            Segment List[0] (128 bits IPv6 address)            |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                                                               |
                                     ...
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |            Segment List[n] (128 bits IPv6 address)            |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                                                             //
       //         Optional Type Length Value objects (variable)       //
       //                                                             //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                           Figure 1: SRH format

   This document defines the new field Size in the Flags field,
   presented in Figure 2, as a two-bits field with the following values:

      0b00 - 128-bits SID;



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      0b01 - 20-bits SID;

      0b10 - 32-bits SID

      0b11 - reserved for future use.

   When the value of the S field is 0b01, the 20-bit SID is encoded in
   four octets and occupies the 20 rightmost bits.

             0 1 2 3 4 5 6 7
            +-+-+-+-+-+-+-+-+
            |U|P|O|A|H| S |U|
            +-+-+-+-+-+-+-+-+

                       Figure 2: Flags field format

   Entries of the segment list in the SRH MUST be of the same length.

4.  Theory of Operation

   When the SRH is used to include 20-bits or 32-bits SIDs the ingress
   and transit nodes of an SR tunnel act as described in Section 5.1 and
   Section 5.2 of [I-D.ietf-6man-segment-routing-header] respectively.

4.1.  Egress SR Tunnel Node

   TBD

5.  IANA Considerations

   TBD

6.  Security Considerations

   This specification inherits all security considerations of [RFC8402]
   and [I-D.ietf-6man-segment-routing-header].

7.  Acknowledgements

   TBD

8.  Normative References

   [I-D.bryant-mpls-unified-ip-sr]
              Bryant, S., Farrel, A., Drake, J., and J. Tantsura, "MPLS
              Segment Routing in IP Networks", draft-bryant-mpls-
              unified-ip-sr-03 (work in progress), October 2017.




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   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
              d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-14 (work in
              progress), June 2018.

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-08
              (work in progress), May 2018.

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
              segment-routing-extensions-19 (work in progress), July
              2018.

   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
              Psenak, P., Filsfils, C., Previdi, S., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
              Extensions for Segment Routing", draft-ietf-ospf-ospfv3-
              segment-routing-extensions-15 (work in progress), August
              2018.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-25 (work in progress), April 2018.

   [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-14
              (work in progress), June 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>.

   [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>.





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   [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>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


   Peng Shaofu
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing
   China

   Email: peng.shaofu@zte.com.cn


























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