BGP Session Timers

There are two primary timers in BGP. The first is the Hold Down timer, the other is the Keepalive Interval.

HOLD DOWN TIMER

Cisco default setting: 180 seconds = 3x Keepalive

The Hold Down Timer indicates how long a router will wait between hearing messages from it's neighbor. The Hold Down Timer defaults to 180 seconds on a Cisco router, but can be reconfigured. The timer starts at zero and counts it's way up to the Hold Down Timer value. If either a Keepalive or Update message is not received in that time, then the router declares the peering session dead, places all routes learned from that peer into a 'dampened' state and attempts to reset the session.

KEEPALIVE INTERVAL

Cisco default setting: 60 seconds

To be certain that a BGP session stays up and functional, Keepalive messages are exchanged. The Keepalive Interval counts down to zero and then sends out another Keepalive. There is no timer for route updates, as updates happen dynamically on an incremental basis.