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Networking Working Group                                       Ran. Chen
Internet-Draft                                              Shaofu. Peng
Intended status: Standards Track                                Jie. Han
Expires: January 6, 2020                                 ZTE Corporation
                                                            July 5, 2019


                         Anycast-SID FRR in SR
                  draft-chen-spring-anycast-sid-frr-01

Abstract

   This document specifies the fast redundancy protection mechanism,
   aimed at providing protection of the links and domain boundary nodes
   for network that use segment routing.

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 January 6, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
   3.  Problem statement . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Proposal  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Domain boundary nodes protection  . . . . . . . . . . . .   3
     4.2.  example . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative references  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   This document extends the use of Anycast-SID FRR to provide links and
   domain boundary nodes that use segment routing.

2.  Conventions used in this document

   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 RFC2119.

3.  Problem statement


     +----------------------------+  +---------------+  +------------------+
     |      SID:20  SID:30        |  |               |  | SID:60           |
     |        A2-----A3--Link311-GW11------C1------GW21------A6            |
     |        / \    /            |  |\     / \     /|  |       \          |
     |       /   \  /          LinkL | \   /   \   / |  |        \         |
     |SID:10/     \/     Adj-SID 3|  |  \ /     \ /  |  |         \ SID:80 |
     |    A1      /\           SID:100   \       /   SID:200       A8      |
     |      \    /  \             |  |  / \     / \  |  |         /        |
     |       \  /    \            |  | /   \   /   \ |  |        /         |
     |        \/      \           |  |/     \ /     \|  |       /          |
     |       A4--------A5---------GW12------C2------GW22-------A7          |
     |      SID:40  SID:50        |  |               |  |   SID:70         |
     +----------------------------+  +---------------+  +------------------+


                                 Figure 1

   The figure above describes a network example with two groups of the
   domain boundary nodes.  The GW11 and GW12 are in the same anycast
   group.  They are all configured with the same anycast prefix and the
   same prefix-sid 100, in addition, GW11 has node-sid 110 and GW12 has



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   node-sid 120.  Suppose that the metric of link between two anycast
   node is large while other links' metirc are small.  From A1/A2/A3
   perspective, GW11 is an active anycast node and GW12 is a standby,
   from A4/A5 perspective, GW12 is active an anycast node , andGW11 is a
   standby.

   On the A3 node, it can select the primary or backup TI-LFA
   FRR[I-D.ietf-rtgwg-segment-routing-ti-lfa] forwarding path (to
   destination node GW12) which not through the active anycast node GW11
   as the backup path to anycast-sid 100.  In this example it will
   select the direct next-hop A2 which is the primary path to
   destination node GW12.

   Supposed that an SID list is {100, 200, 80} which represents the SR-
   TE path from A1 to A8.

   Time1: the active anycast node GW11 DOWN.

   Time2: Anycast FRR take effect in the event of node GW11 has failed,
   the flow will be encapsulated with node-sid of GW12 and directed to
   next-hop A2.

   Time3: route convergence executed, depending on the convergence speed
   of the nodes, A3 may regard GW12 as the new originator source of
   anycast prefix, so that any flow that match the anycast prefix will
   be forwarded to direct next-hop A2 to destination node GW12.
   However, A2 may not converge so quickly, it will still regard GW11 as
   the originator source of the anycast prefix, its forwarding entry of
   anycast-prefix is still to destination GW11 and the next hop is A3.
   There is a loop here.  So A3 has responsibility to generate a micro-
   loop avoided path {GW12, anycast-prefix} to anycast prefix, that is,
   it must insert the new originator source to the unloop path.

4.  Proposal

4.1.  Domain boundary nodes protection

   The solution consists of three parts.

   o  Configure the same anycast prefix and associated prefix-sid for
      each domain boundary node that forms redundant protection, then
      the anycast prefix and associated prefix-sid with Anycast-Group
      flag should be advertised to the neighbor node.

   o  Create the anycast-group forwarding entry (i.e.  FRR entry) after
      the direct neighbor node of the domain boundary nodes receive the
      prefix-sid with Anycast-Group flag advertisement.  The anycast-
      group forwarding entry includes the forwarding information which



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      points to each of the domain boundary node, then the forwarding
      entry pointing to the main domain boundary (one of the direct
      connected boundary nodes from the PLR) is set to the active state,
      and others are set to the backup state.  Only the direct neighbor
      of the domain boundary nodes need to set up the anycast-group
      forwarding entry.  The anycast-group forwarding entry may also be
      created on PLR by default, when it received an anycast-prefix
      advertisement from two or more originator source.

   o  if the neighbor node detects the main domain boundary node
      failure, the neighbor node immediately activates the backup entry.
      Note that the backup entry contains the node-sid of the slave
      boundary node, and the packet will be forwarded based on the node-
      sid, not the anycast prefix-sid again.

4.2.  example

   In figure 1, considering that the GW11 DOWN,then

   Time1:GW11 DOWN.

   Time2: Primary or backup TI-LFA
   [I-D.ietf-rtgwg-segment-routing-ti-lfa]provides protection in the
   event of GW11 has failed on the A3 node.

   Time3: When A3 detects GW11 failure, and the anycast-sid 100 is the
   top Label in the label stack.The anycast-sid 100 is swapped with the
   node-sid 120 (node-sid of the GW12) according to the anycast-group
   forwarding entry.  Pachets is forwarded to next-hop A2.

5.  Security Considerations

   TBD.

6.  Acknowledgements

   TBD.

7.  Normative references

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., and B. Decraene, "IS-IS Extensions for
              Segment Routing", draft-ietf-isis-segment-routing-
              extensions-25 (work in progress), May 2019.






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   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
              Francois, P., daniel.voyer@bell.ca, d., Clad, F., and P.
              Camarillo, "Topology Independent Fast Reroute using
              Segment Routing", draft-ietf-rtgwg-segment-routing-ti-
              lfa-01 (work in progress), March 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>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [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

   Ran Chen
   ZTE Corporation

   Email: chen.ran@zte.com.cn


   Shaofu Peng
   ZTE Corporation

   Email: peng.shaofu@zte.com.cn


   Jie Han
   ZTE Corporation

   Email: han.jie@zte.com.cn











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