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Intermediate System to Intermediate System (IS-IS) Transient Blackhole Avoidance (RFC3277)

IP.com Disclosure Number: IPCOM000007869D
Original Publication Date: 2002-Apr-01
Included in the Prior Art Database: 2002-May-01
Document File: 7 page(s) / 13K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D. McPherson: AUTHOR

Abstract

This document describes a simple, interoperable mechanism that can be employed in Intermediate System to Intermediate System (IS-IS) networks in order to decrease the data loss associated with deterministic blackholing of packets during transient network conditions. The mechanism proposed here requires no IS-IS protocol changes and is completely interoperable with the existing IS-IS specification.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 26% of the total text.

Network Working Group                                       D. McPherson

Request for Comments: 3277                                           TCB

Category: Informational                                       April 2002

           Intermediate System to Intermediate System (IS-IS)

                     Transient Blackhole Avoidance

Status of this Memo

   This memo provides information for the Internet community.  It does

   not specify an Internet standard of any kind.  Distribution of this

   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document describes a simple, interoperable mechanism that can be

   employed in Intermediate System to Intermediate System (IS-IS)

   networks in order to decrease the data loss associated with

   deterministic blackholing of packets during transient network

   conditions.  The mechanism proposed here requires no IS-IS protocol

   changes and is completely interoperable with the existing IS-IS

   specification.

1. Introduction

   When an IS-IS router that was previously a transit router becomes

   unavailable as a result of some transient condition such as a reboot,

   other routers within the routing domain must select an alternative

   path to reach destinations which have previously transited the failed

   router.  Presumably, the newly selected router(s) comprising the path

   have been available for some time and, as a result, have complete

   forwarding information bases (FIBs) which contain a full set of

   reachability information for both internal and external (e.g., BGP)

   destination networks.

   When the previously failed router becomes available again, it is only

   seconds before the paths that had previously transited the router are

   again selected as the optimal path by the IGP.  As a result,

   forwarding tables are updated and packets are once again forwarded

   along the path.  Unfortunately, external destination reachability

   information (e.g., learned via BGP) is not yet available to the

   router, and as a result, packets bound for destinations not learned

   via the IGP are unnecessarily discarded.

McPherson                    Informational                      [Page 1]

RFC 3277          IS-IS Transient Blackhole Avoidance         April 2002

   A simple interoperable mechanism to alleviate the offshoot associated

   with this deterministic behavior is discussed below.

2. Discussion

   This document describes a simple, interoperable mechanism that can be

   employed in IS-IS [1, 2] networks in order to avoid transition to a

   newly available path until other associated routing protocols such as

   BGP have had sufficient time to converge.

   The benefits of such a mechanism can be realized when considering the

   following scenario depicted in Figure 1.

                                 D.1

                                  |

                              +-------+

                              | RtrD  |

                              +-------+

                              /      \

                             /        \

                        +-------+    +-------+

                        | RtrB  |    | RtrC  |

                        +-------+    +-------+

                             \        /

                              \      /

                              +-------+

                              | RtrA  |

                              +-------+

                                   |

                                  S.1

                 Figure 1: Example Network Topology

   Host S.1 is transmitting data to destination D.1 via a primary path

   of RtrA->RtrB->RtrD.  Routers A, B and C learn of reachability to

   destination D.1 via BGP from RtrD.  RtrA's primary path to D.1 is

   selected because when calculating the path to BGP NEXT_HOP of RtrD,

   the sum of the IS-IS link metrics o...