What kind of failure modes are you protecting against. The most
common reasons for ending a BGP session will usually include a
TCP CLOSE. There is no problem with a "normal" shutdown because
BGP will immediately withdraw the routes. The timers are for
aborts, such as someone unplugged the neighbor.
The reason I see for lowering the BGP timer is enabling an upper layer
protocol to ride through the storm. Does Vern Paxson have any data on
how long typical TCP streams survive during periods of routing instability?
If a TCP application lasts 180 seconds, and it takes 150 seconds to recompute
the route table, wouldn't you set the timeout to 30 seconds? (all numbers
fictional)