LDP behaviour on link-shut scenarios
draft-aa-mpls-ldp-link-shut-00

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Network                                                         M. Anush
Internet-Draft                                              T. Anupkumar
Updates: 5036 (if approved)                                     Ericsson
Intended status: Standards Track                       September 3, 2019
Expires: March 6, 2020

                  LDP behaviour on link-shut scenarios
                     draft-aa-mpls-ldp-link-shut-00

Abstract

   This document is intended as clarification of LDP behaviour in link-
   down scenarios.  Base LDP RFC5036 lacks sufficient clarity on what an
   LDP enabled node should be doing when a link down event is received,
   and the only LDP adjacency for an LDP peer is over this link.
   Different vendors have handled this scenario differently, with some
   immediately resetting tcp session with neighbor and some waiting for
   igp recovergence instead of reacting directly to link events.  With
   this document we intend to clarify the expected behaviour explicitly
   so that any interop issues can be avoided.

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 March 6, 2020.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Problem Description . . . . . . . . . . . . . . . . . . . . .   2
   4.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerationss  . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   [RFC5036] details LDP specification and procedures to be followed by
   LDP implementations.  However, for some scenarios like link down, the
   rfc isn't particularly clear as to what an implementation is supposed
   to do.  This could lead to interop issues when routers from different
   vendors are part of the network.  More details are given in the
   problem description section below.  A possible solution is also
   suggested in the subsequent sections.

2.  Terminology

   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.

   o  LDP: Label distribution protocol.

   o  GR: Graceful-restart.

3.  Problem Description

   Consider the following topology:

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                   E
                   |
                   |
                   A --- B
                   |     |
                   |     |
                   C --- D

                    Figure 1: Example topology for LDP

   All the nodes here are LDP enabled and also support GR.  We have an
   lsp from C-E via C-A-E path(this is igp bestpath).  IGP has also
   computed LFA backup for this primary-lsp via C-D-B-A-E path and we
   have LDP lfa backup as well (taking this path).

   Now, lets bring down A-C link.  Node A has detected link-shut event
   and since this link is the only adjacency to LDP-neighbor C, it
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