[e2e] iBGP session break
anoop at brocade.com
Wed Apr 11 11:21:44 PDT 2007
From: end2end-interest-bounces at postel.org
[mailto:end2end-interest-bounces at postel.org] On Behalf Of Saqib Ilyas
Sent: Wednesday, April 11, 2007 12:33 AM
To: end2end-interest at postel.org
Subject: [e2e] iBGP session break
My question is: Is it possible for an iBGP session to break even
when the underlying IP topology is not partitioned?
We would expect that IGP maintains connectivity at the IP layer,
and even in case of a failure in the network that doesnt partition the
topology, the IGP should be able to quickly converge to a new
configuration for paths between every possible pair of nodes. This
should result in, perhaps, a few dropped TCP packets for the iBGP
session, but not a session break. Would it, then still be possible for
an iBGP session to break and blackholes to consequently result?
It is certainly possible depending on the configuration. BGP
uses hold and keep-alive
timers. If a session has its hold timer expire because of not
receiving a keepalive, then
the session will be terminated, even though TCP would not
normally have torn down
the connection on its own.
In the typical case (hold timer 180 sec, keep alive timer 60
sec), you probably
wouln't lose the peering while the IGP is reconverging. But if
are set very low, then you might.
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