![]() Section 3.2) or a downstream path provides protection against micro. ![]() ![]() Inįigure 2, S would be able to use N as a downstream alternate, but NĬould not use S therefore, N would have no alternate and wouldĭiscard the traffic, thus avoiding the micro-loop.Īs shown above, the use of either a node-protecting LFA (described in Restriction can severely limit the coverage of alternates. Although use of downstream pathsĮnsures that the micro-looping via alternates does not occur, such a To the use of alternates can be avoided by using downstream pathsīecause each succeeding router in the path to the destination must beĬloser to the destination than its predecessor (according to the Selection of only downstream paths as alternates. Micro-looping of traffic via the alternates caused when a moreĮxtensive failure than planned for occurs can be prevented via Mechanisms to handle node failure, a node failure is still a concernįigure 2: Link-Protecting Alternates Causing Loop on Node Failure Second simultaneous correlated failure - another link connected to The key assumption, that all other routers in the network areįorwarding based upon the shortest path, is violated because of a To redirect the traffic to N and N to redirect the traffic to S and However, if router E fails, then both S and N will detect a failureĪnd switch to their alternates. This process can take hundreds of milliseconds.įails, then the link-protecting alternate via N will work correctly. Installed, traffic directed towards the affected prefixes isĭiscarded. Its neighbors via the IGP, recompute new primary next-hops for allĪffected prefixes, and only then install those new primary next-hops When a local link fails, a router currently must signal the event to The mechanism alsoĪssumes that both the primary path and the alternate path are in the Mechanism assumes that routing in the network is performed using a Next-hops based upon the changed network topology. Pre-computed alternate until the router installs the new primary This specification describes such a mechanism thatĪllows a router whose local link has failed to forward traffic to a Repair path, which is minimally affected by any subsequent re-Ĭonvergence. Mechanism for the router adjacent to a failure to rapidly invoke a Milliseconds the application traffic may be sensitive to lossesĪs discussed in, minimizing traffic loss requires a A router'sĬonvergence time is generally on the order of hundreds of IP (VoIP) and pseudowires can be very sensitive to traffic loss, suchĪs occurs when a link or router in the network fails. IntroductionĪpplications for interactive multimedia services such as Voice over RFC 5286 IP Fast Reroute: Loop-Free Alternates September 2008 1. OSPF Example Where LFA Based on Local Area Interactions with IS-IS Overload, RFC 3137, and Costed Broadcast and Non-Broadcast Multi-Access (NBMA) Links. RFC 5286 IP Fast Reroute: Loop-Free Alternates September 2008ġ. The extent to which this goal can be met by this specification isĭependent on the topology of the network. This simple approach does not require any support from other routers. Use until the distributed network convergence process completes. Use of precalculated backup next-hops that are loop-free and safe to Packet loss that happens while routers converge after a topologyĬhange due to a failure. The goal of this technology is to reduce the In the event of a single failure, whether link, node, or shared risk Local protection for unicast traffic in pure IP and MPLS/LDP networks This document describes the use of loop-free alternates to provide Official Protocol Standards" (STD 1) for the standardization stateĪnd status of this protocol. Please refer to the current edition of the "Internet Internet community, and requests discussion and suggestions for This document specifies an Internet standards track protocol for the Atlas, Ed.īasic Specification for IP Fast Reroute: Loop-Free Alternates Updated by: 8518 Errata Exist Network Working Group A. RFC 5286: Basic Specification for IP Fast Reroute: Loop-Free Alternates
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