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 <[email protected]> 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? > -- ================================================================ :: :: Kevin Hodle | http://www.linkedin.com/in/kevinhodle :: :: PGP Key ID | fingerprint :: :: 0x803F24BE | 1094 FB06 837F 2FAB C86B E4BE 4680 3679 803F 24BE "Elegance is not a dispensable luxury but a factor that decides between success and failure. " -Edsger Dijkstra ================================================================ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
