Enhanced Topology Independent Loop-free Alternate Fast Re-route
draft-li-rtgwg-enhanced-ti-lfa-00

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RTGWG Working Group                                                C. Li
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: September 12, 2019                               March 11, 2019

    Enhanced Topology Independent Loop-free Alternate Fast Re-route
                   draft-li-rtgwg-enhanced-ti-lfa-00

Abstract

   Topology Independent Loop-free Alternate Fast Re-route (TI-LFA) aims
   at providing protection of node and adjacency segments within the
   Segment Routing (SR) framework.  A key aspect of TI-LFA is the FRR
   path selection approach establishing protection over the expected
   post-convergence paths from the point of local repair.  However, the
   TI-LFA FRR path may skip the node even if it is specified in the SID
   list to be traveled.

   This document defines Enhanced TI-LFA(TI-LFA+) by adding a No-bypass
   indicator for segments to ensure that the FRR route will not bypass
   the specific node, such as firewall.

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 September 12, 2019.

Copyright Notice

   Copyright (c) 2019 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

Li & Hu                Expires September 12, 2019               [Page 1]
Internet-Draft               Enhanced TI-LFA                  March 2019

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

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Overview of Enhanced TI-LFA . . . . . . . . . . . . . . . . .   3
   4.  IGP Protocol Extensions . . . . . . . . . . . . . . . . . . .   4
     4.1.  IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  OSPF  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Segment Routing [RFC8402] enables to steer packets by explicitly
   encoding instructions in the data packets at the source node to
   support services like traffic engineer.  Relying on SR,
   [I-D.ietf-rtgwg-segment-routing-ti-lfa] defines Topology Independent
   Loop-free Alternate Fast Re-route (TI-LFA), a local repair mechanism
   for IGP shortest path that capable of restoring end-to-end
   connectivity in the case of a sudden directly connected failure of a
   network component.

   TI-LFA supports to establish a loop free backup path over the
   expected post-convergence paths from the point of local repair
   irrespective of the topologies used in the network, which provides a
   major improvment compared to LFA [RFC5286], and remote LFA [RFC7490]
   which cannot be applicable in some topologies [RFC6571].

   However, the TI-LFA path may skip the node that the active SID points
   to when protecting [Adjacency, Node] segment lists.  For instance,
   the node that a adjacency SID points to is a very important node and
   can not be skipped, such as a firewall node.  When the link between
   the local repair node and firewall node fails, the packets should be
   steered back to the firewall and then forwarding.  But in TI-LFA, if
   the next SID in the SID list is a node SID, the TI-LFA FRR path MAY
   bypass the node that the active segment points to.  Also, if the