BGP Timers Configuration


We are pursuing some work along the lines of studying BGP
scalability in terms of churn evolution. One of the key mechanisms
used by BGP to dampen the churn is the MRAI timer (Minimum Route
Advertisement Interval).

From different vendors' specifications we find that:

1- Cisco enables MRAI by default for both route announcements and route
2- Juniper has a similar parameter called out-delay which is disabled
by default.

Of course these are default configurations, and we don't know if
ISPs use them without any change. We would appreciate any input on the
following questions:

A- Is it common that ISPs change MRAI default configurations? If yes,
then what decides the MRAI settings for both e-BGP and i-BGP sessions?
B- Does anybody use a configuration where only route announcements are
rate limited, and not explicit route withdrawals?
C- Are there configurations where rate limiting is applied only to a
subset of session?

Best regards,

Ahmed Elmokashfi
Simula Research Laboratory.