[e2e] iBGP session break

[Zartash Afzal Uzmi]

>>Greetings everyone
>>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 these
timers
>are set very low, then you might.
> 
>Anoop 

I wonder of there exist scenarios (in real world configurations, maybe!)
when BGP timers are set at such low values that BGP session breaks while IGP
is still re-converging? If setting BGP timers to such low values is not very
common, is it safe to assume that a break in BGP session is also not very
common? Are there other reasons (other than IGP convergence taking longer
than BGP timers) which may cause BGP sessions to break?

Thanks,
Zartash