Command:

bgp dampening


Mode:

Router(config-router)#


Syntax:

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

no bgp dampening [half-life reuse suppress max-suppress-time] [route-map map-name]

 

Syntax Description:

half-life

(Optional) Time (in minutes) after which a penalty is decreased. Once the route has been assigned a penalty, the penalty is decreased by half after the half-life period (which is 15 minutes by default). The process of reducing the penalty happens every 5 seconds. The range of the half-life period is 1 to 45 minutes. The default is 15 minutes.

reuse

(Optional) Reuse values based on accumulated penalties. If the penalty for a flapping route decreases enough to fall below this value, the route is unsuppressed. The process of unsuppressing routes occurs at 10-second increments. The range of the reuse value is from 1 to 20000; the default is 750.

suppress

(Optional) A route is suppressed when its penalty exceeds this limit. The range is from 1 to 20000; the default is 2000.

max-suppress-time

(Optional) Maximum time (in minutes) a route can be suppressed. The range is from 1 to 20000; the default is 4 times the half-life. If the half-life value is allowed to default, the maximum suppress time defaults to 60 minutes. When the max-suppress-time is configured, the maximum penalty will never be exceeded, regardless of the number of times that the prefix dampens. The maximum penalty is computed with the following formula:

Max penalty = reuse-limit *2^(maximum suppress time/half time)

route-map map-name

(Optional) Name of route map that controls where BGP route dampening is enabled.

 

Command Description:

To enable BGP route dampening or change various BGP route dampening factors, use the bgp dampening command in address family or router configuration mode. To disable the function or restore the default values, use the no form of this command.

If this command is used with no arguments, it enables BGP route dampening. The half-life, reuse, suppress, and max-suppress-time arguments are position-dependent. Therefore, if any of these arguments are issued, they must all be specified.

When BGP dampening is configured and a prefix is withdrawn, BGP considers the withdrawn prefix as a flap and increases the penalty by a 1000. If BGP receives an attribute change, BGP increases the penalty by 500. If then the prefix has been withdrawn, BGP keeps the prefix in the BGP table as a history entry. If the prefix has not been withdrawn by the neighbor and BGP is not using this prefix, the prefix is marked as dampened. Dampened prefixes are not used in the BGP decision process and not installed to the routing table.


Example:

The following router configuration mode example sets the half life to 30 minutes, the reuse value to 1500, the suppress value to 10000, and the maximum suppress time to 120 minutes:

Router(config)#router bgp 5
Router(config-router)#bgp dampening 30 1500 10000 120


Misconceptions:

None


Related Commands:

clear ip bgp dampening
clear ip bgp flap-statistics
show ip bgp flap-statistics

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