Segment Routing IPv6 Prefix-SID
draft-previdi-isis-ipv6-prefix-sid-01

Network Working Group                                    S. Previdi, Ed.
Internet-Draft                                               L. Ginsberg
Intended status: Standards Track                             C. Filsfils
Expires: June 16, 2016                               Cisco Systems, Inc.
                                                       December 14, 2015

                    Segment Routing IPv6 Prefix-SID
                 draft-previdi-isis-ipv6-prefix-sid-01

Abstract

   This document defines the Segment Routing IPv6 Prefix-SID sub-TLV.
   This new sub-TLV allows to specify which of the prefixes advertised
   by a node are to be used as Segment Routing Identifiers (SID) for the
   IPv6 dataplane.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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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   This Internet-Draft will expire on June 16, 2016.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  SRv6 Prefix SID . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   With Segment Routing (SR)[I-D.ietf-spring-segment-routing], a node
   steers a packet through an ordered list of instructions, called
   segments.  Segments are identified through Segment Identifiers (SIDs)
   that are advertised by routing protocols.  The IS-IS extensions for
   SR information advertisement are defined in
   [I-D.ietf-isis-segment-routing-extensions].

   Segment Routing can be directly applied to the IPv6 dataplane through
   the use of the Segment Routing Header defined in
   [I-D.previdi-6man-segment-routing-header].

   When applied to the IPv6 dataplane, the SID is represented by an IPv6
   address.  This document defines a new IS-IS Prefix sub-TLV where
   information related to the IPv6 address used as SR-IPv6 SID is
   conveyed.

2.  SRv6 Prefix SID

   When SR is applied to the IPv6 dataplane, Segment Identifiers (SIDs)
   are regular IPv6 addresses that are advertised in routing protocols.
   When SR is used over IPv6 dataplane, it is desirable to identify
   which of the prefixes originated by a node can be used as SIDs
   compared to any other prefix that the node advertises.  Moreover, and
   in order to provide the same functionalities defined in
   [I-D.ietf-spring-segment-routing] and
   [I-D.ietf-isis-segment-routing-extensions], a new sub-TLV is defined:
   the SRv6-Prefix-SID sub-TLV

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   A SRv6-Prefix-SID sub-TLV is associated to a IPv6 prefix advertised
   by a node and MAY be present in any of the following TLVs:

      TLV-236 (IPv6) defined in [RFC5308].

      TLV-237 (MT-IPv6) defined in [RFC5120].

   The SRv6-Prefix-SID sub-TLV has the following format:

    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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Algorithm   |
   +-+-+-+-+-+-+-+-+

   where:

      Type: To be assigned by IANA (suggested value 5).

      Length: 3 octets.

      Flags: 2 octet field of flags.  None of them is defined at this
      stage.

      Algorithm: the router may use various algorithms when calculating
      reachability to other nodes or to prefixes attached to these
      nodes.  Algorithms identifiers are defined in
      [I-D.ietf-isis-segment-routing-extensions].  Examples of these
      algorithms are metric based Shortest Path First (SPF), various
      sorts of Constrained SPF, etc.  The algorithm field of the SRv6-
      Prefix-SID contains the identifier of the algorithm the router has
      used in order to compute the reachability of the IPv6 prefix that
      is used as a SID.  At origination, the SRv6-Prefix-SID algorithm
      field MUST be set to 0 on all SRv6-Prefix-SIDs of prefixes
      computed using SPF algorithm (Shortest Path First).  On reception
      of the SRv6-Prefix-SID sub-TLV, any non-zero algorithm value MUST
      match what advertised in the SR-Algorithm sub-TLV (as defined in
      [I-D.ietf-isis-segment-routing-extensions]).

   A router advertising an IPv6 prefix with the SRv6-Prefix-SID sub-TLV
   MUST support the Segment Routing Header (SRH, defined in
   [I-D.previdi-6man-segment-routing-header] and its associated
   procedures for packets destined to the advertised prefix.  The
   advertising router MUST also set the H-flag in the SR-Capability sub-
   TLV as defined in [I-D.ietf-isis-segment-routing-extensions].

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   Within an area (or within the level-2 subdomain), a router receiving
   the advertisement of an IPv6 prefix with the SRv6-Prefix-SID sub-TLV
   MUST check whether the originator has set the H-flag in its SR-
   Capability Sub-TLV prior to validate the SRv6-Prefix-SID sub-TLV.

   A router receiving a SRv6-Prefix-SID from a remote node and with an
   algorithm value that such remote node has not advertised in the SR-
   Capability sub-TLV (as defined in
   [I-D.ietf-isis-segment-routing-extensions]) MUST ignore the SRv6-
   Prefix-SID sub-TLV.

   The SRv6-Prefix-SID sub-TLV defines the prefix (it is associated to)
   as an SR-IPv6 Prefix SID.  If the prefix is to be used as a Node-SID:

      The IPv6 prefix MUST be advertised with the SRv6-Prefix-SID sub-
      TLV attached.

      The N-flag defined in [I-D.ietf-isis-prefix-attributes] MUST be
      set.

3.  IANA Considerations

   This document makes the following registrations in the "sub-TLVs for
   TLV 135,235,236 and 237" registry.

      Type: TBD (suggested value 5)

      Description: SRv6 Prefix Segment Identifier

      TLV 135: no

      TLV 235: no

      TLV 236: yes

      TLV 237: yes

      Reference: This document (Section 2)

4.  Security Considerations

   This document doesn't introduce new security considerations.

5.  Acknowledgements

   The authors would like to thank Nagendra Kumar for his review of this
   document.

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6.  References

6.1.  Normative References

   [I-D.ietf-isis-prefix-attributes]
              Ginsberg, L., Decraene, B., Filsfils, C., Litkowski, S.,
              Previdi, S., Xu, X., and U. Chunduri, "IS-IS Prefix
              Attributes for Extended IP and IPv6 Reachability", draft-
              ietf-isis-prefix-attributes-02 (work in progress),
              December 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <http://www.rfc-editor.org/info/rfc5120>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <http://www.rfc-editor.org/info/rfc5308>.

6.2.  Informative References

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., 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-05 (work in progress), June 2015.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and r. rjs@rob.sh, "Segment Routing Architecture", draft-
              ietf-spring-segment-routing-06 (work in progress), October
              2015.

   [I-D.previdi-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
              J., Kosugi, T., Vyncke, E., and D. Lebrun, "IPv6 Segment
              Routing Header (SRH)", draft-previdi-6man-segment-routing-
              header-08 (work in progress), October 2015.

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Authors' Addresses

   Stefano Previdi (editor)
   Cisco Systems, Inc.
   Via Del Serafico, 200
   Rome  00142
   Italy

   Email: sprevidi@cisco.com

   Les Ginsberg
   Cisco Systems, Inc.
   US

   Email: ginsberg@cisco.com

   Clarence Filsfils
   Cisco Systems, Inc.
   Brussels
   BE

   Email: cfilsfil@cisco.com

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