On May 12, 2010, at 9:40 AM, Jay Nakamura wrote:
I just tested this and, yes, with Cisco to Cisco, changing the setting won't reset the connection but you have to reset the connection to have the value take effect. I need to look up what happens when two sides are set to different values and which one takes precedent.
The holdtime isn't technically negotiated, both sides convey their value in the open message and the lower of the two is used by both BGP speakers. IIRC, neither J or C reset the session with the timer change, but the new holdtimer expiry value doesn't take effect until then. One other thing to note is that by default, keepalive intervals in those implementations are {holdtime/3}. Normally, if you're setting holdtime to something really lower (e.g., 10 seconds) you might want to increase the frequency of keepalives such that the probability of getting one through in times of instability rise. In particular, congestion incurred outside of BGP, as update messages themselves will serve as implicit keepalives, and with the amount of churn in BGP, empty updates (keepalives) are rare for most speakers with a global BGP view. -danny