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


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.

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Table of Contents

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 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.

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


6. Acknowledgements


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", Internet-Draft draft-ietf-isis-segment-routing-extensions-25, May 2019.
[I-D.ietf-rtgwg-segment-routing-ti-lfa] Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., Francois, P.,, d., Clad, F. and P. Camarillo, "Topology Independent Fast Reroute using Segment Routing", Internet-Draft draft-ietf-rtgwg-segment-routing-ti-lfa-01, 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.
[RFC3031] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001.
[RFC8402] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018.

Authors' Addresses

Ran Chen ZTE Corporation EMail:
Shaofu Peng ZTE Corporation EMail:
Jie Han ZTE Corporation EMail: