notes: BGP Route-Dampening

- Is designed to reduce router processing load caused by unstable routes.
- Defined in RFC 2439.
- Each time an eBGP route flaps, it gets 1000 penalty points (This cannot be configured or changed).
- IGBP routes are not dampened.
- The penalty placed on a route decays according to the exponential decay algorithm.
- When the penalty exceeds the suppress limit, the route is dampened (no longer used or propagated to other neighbors).
- A dampened route is propagated again when the penalty drops below the reuse limit.
- A route is never dampened for more time than the maximum suppress limit.
- An unreachable route with a flap history is put in the history state. It stays in the BGP table but only to maintain the flap history. (marked with 'h' in the BGP table)
- A penalty is applied on the individual path in the BGP table, not on the IP prefix.
- Using a (clear ip bgp *) is regarded as a flap to neighbors, which could cause that path to be suppressed.
- Using a (clear ip bgp * [soft] in) is NOT regarded as a flap to neighbors.




 commands:

 - Displays the dampened routes

sh ip bgp dampened-paths 

- Displays flap statistics for all routes with dampening history

sh ip bgp flap-stat [regexp|filter-list|ip]

 - Clears the flap statistics but does not release dampened routes
clear ip bgp {ip} flap-stat [regexp|filter-list|prefix]

- Releases all the dampened routes or just the specified network
- Flap statistics also cleared when the BGP session with the neighbor is lost

 clear ip bgp dampening [prefix] 

 - Displays the BGP dampening events
debug ip bgp dampening

- Route-map to configure dampening for specifics routes only

route-map name 

match ip addess {acl}

set dampening [half-life][reuse][suppress][max-suppress-time]

bgp dampening [half-life][reuse][suppress][max-suppress-time] [route-map map-name]

[half-life] - Decay time in which the penalty is halved (Def = 15min)
[suppress] - The value at which a route is dampened (Def = 2000)
[reuse] - The value when the dampened route is reused (Def = 750)
[max-suppress-time] - Maximum time to suppress the route (Def = 60Min)
[route-map] - Using route-map to dampen specific routes
- Specified without a route-map applies to all routes