[c-nsp] Faster BGP Failover

[Kevin Hodle]

As others have mentioned, your total time to re-converge is bounded by
a number of different variables, and there are multiple aspects to
consider. With regards to rapid failure detection, BFD is the optimal
solution and most competent service providers will run BFD with you on
transit eBGP sessions if you really push them for it. For optimizing
convergence *after* a failure is detected, you will get the biggest
'bang for your buck' with Cisco's prefix independent convergence (PIC)
feature, which takes advantage of a hierarchical RIB design allowing
next-hop pointers for many  BGP RIB entries to be quickly
reprogrammed, as opposed to the flattened RIB structure where total
time to update RIB structures after a failure can be dramatic.
Unfortunately this functionality has only emerged *natively* in IOS
XR. More recent IOS releases for the 7600 series claim to support BGP
PIC, however from what I understand because of architectural
limitations, this is more of a hack and its usefulness is probably
limited.

... That said, depending on your IOS version, you could potentially
optimize the time required to purge all RIB entries whose next-hop
becomes invalid, the configuration knob:

ip routing protocol purge interface

This allows for most routing protocols to be signaled directly after a
link failure and gives them a shortcut to purge all RIB entries they
associate with the downed interface. Without this, the normal behavior
is for IOS to trigger the RIB update process to perform a full table
walk to remove entries with invalidated next-hops.  This delay can be
significant depending on hardware and total RIB size.

Cheers,
Kevin

On Tue, Oct 11, 2011 at 10:25 AM, Vincent Aniello
<vincent.aniello at pipelinefinancial.com> wrote:
> What can be done to reduce the amount of time it takes BGP to detect the failure of an Internet connection and start routing traffic through another Internet connection?
>


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