[e2e] fast restoration/protection

Olivier Bonaventure Bonaventure at info.ucl.ac.be
Thu Jun 15 08:11:58 PDT 2006


> to clarify - what happens in a link state protocol is that you
> distribute states each epoch to all routers who construct a RIB
> and do a dijkstra to compute a local FIB - what i am saying is
> save the output of the dijkstra for all cases you see, and then 
> when you get a link state delta that _matches_ the FIB for a previous
> case, load the FIB immediately

Yes, but this approach of precomputing FIBs has a few drawbacks :
- you may need to compute a lot of different FIB to cover all possible
failures in the network
- updating a FIB is not necessary fast on current routers. For example,
on a Cisco 12k, updating a FIB requries about 110 microsecond per prefix

If instead of updating completely the FIB you agree to use a tunnel to
reroute the packets around a local failure, then it is possible to
achieve fast  (i.e. sub 50 msec) restoration even for BGP peering links
but using a clever organisation of the FIB, see :


The IETF is also doing some (slow) work on those fast restoration issues
in the rtgwg working group.

Best regards,


CSE Dept. UCL, Belgium - http://www.info.ucl.ac.be/people/OBO/

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