Framework for Loop-Free Convergence Using the Ordered Forwarding Information Base (oFIB) Approach

Thu, 07/17/2014 - 15:01 by Olivier Bonaventure


This document describes an illustrative framework of a mechanism for
use in conjunction with link-state routing protocols that prevents
the transient loops that would otherwise occur during topology
changes. It does this by correctly sequencing the forwarding
information base (FIB) updates on the routers.

This mechanism can be used in the case of non-urgent (management
action) link or node shutdowns and restarts or link metric changes.
It can also be used in conjunction with a fast reroute mechanism that
converts a sudden link or node failure into a non-urgent topology
change. This is possible where a complete repair path is provided
for all affected destinations.

After a non-urgent topology change, each router computes a rank that
defines the time at which it can safely update its FIB. A method for
accelerating this loop-free convergence process by the use of
completion messages is also described.

The technology described in this document has been subject to
extensive simulation using pathological convergence behavior and real
network topologies and costs. However, the mechanisms described in
this document are purely illustrative of the general approach and do
not constitute a protocol specification. This document represents a
snapshot of the work of the Routing Area Working Group at the time of
publication and is published as a document of record. Further work
is needed before implementation or deployment.

M. Shand, S. Bryant, S. Previdi, C. Filsfils, P. Francois and O. Bonaventure
RFC,(6976), July 2013.
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