BGP Update Report

Randy Bush randy at psg.com
Tue Mar 30 22:30:49 CDT 2010


> It's not just AS_PATH, a lot of the reason so many duplicate updates
> occur (nearly 50% of all updates at times, and often more during the
> busiest times) is because on the other end implementations don't keep
> egress advertisement state per attribute (e.g., if cluster_list length
> just triggered an internal transition then a new update is sent to
> external peers with no new information because the determining
> internal attributes are stripped before transmitting the new update),
> yet those *prefixes* might well be suppressed as a result of the
> implementation and/or network architecture on the other end of the BGP
> connection.
> 
> Then you couple what Joe was pointing out, where intermediate nodes
> with consistently unstable links or "paths" result in penalizing an
> entire prefix, not just the unstable paths, and it makes for more
> brokenness than benefit when route flap damping is employed.
> 
> It's not that people haven't studied and understand why this occurs,
> the issue is that implementation optimizations seem to always win out
> today over systemic state effects (i.e., that "be conservative in what
> you send" thing doesn't seem to apply in practice, unfortunately).

might some of this be that the implementations use router-id to fill in
an unconfigured rr cluster-id?

randy




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