The switch supports route dampening (route suppression). When you use route dampening, a route accumulates penalties each time the route fails. After the accumulated penalties exceed a threshold, the router no longer advertises the route. The router enters the suppressed routes into the routing table only after the accumulated penalty falls below the reuse threshold.
Route flap dampening suppresses the advertisement of the unstable route until the route becomes stable. For information about how to enable flap-dampening, see Configure BGP. For information about viewing flap dampening configurations, see Viewing global flap-dampening configurations.
Dampening applies only to routes that are learned through an eBGP. Route flap dampening prevents routing loops and protects iBGP peers from having higher penalties for routes external to the AS.
The following paragraph describes the algorithm that controls route flaps.
After the route flaps the first time
the router creates a route history entry
a timer starts (180 seconds)
If the route does not flap again, the router uses this timer to delete the history entry after the 180 seconds expires.
After the route flaps a second time
The penalty is recalculated based on the decay function.
If the penalty is greater than the cut-off value (1536), the route is suppressed and the reuse time is calculated based on the reuse time function.
The reuse timer starts.
After the reuse time expires, the suppressed route is announced again (the reuse time is recalculated if the route flaps again). The penalty decays slower for withdrawn routes than for update routes. The route history entry is kept longer if the route is withdrawn. For update history, the delete time is 90 seconds and the withdrawn history delete time is 180 seconds.