BigIron RX Series Configuration Guide 76553-1002253-01Configuring route flap dampening 26Configuring route flap dampeningRoute Flap Dampening reduces the amount of change propagated by BGP due to routing statecaused by unstable routes. Reducing change propagation will help reduce processingrequirements.To enable route flap dampening using the default values, enter the following command.BigIron RX(config-bgp)# dampeningSyntax: dampening [ ]The parameter specifies the number of minutes after which the route’s penalty becomeshalf its value. The route penalty allows routes that have remained stable for a while despite earlierinstability to eventually become eligible for use again. The decay rate of the penalty is proportionalto the value of the penalty. After the half-life expires, the penalty decays to half its value. Thus, adampened route that is no longer unstable can eventually become eligible for use again. You canconfigure the half-life to be from 1 - 45 minutes. The default is 15 minutes.The parameter specifies how low a route’s penalty must become before the routebecomes eligible for use again after being suppressed. You can set the reuse threshold to a valuefrom 1 – 20000. The default is 750 (0.75, or three-fourths, of the penalty assessed for a one“flap”).The parameter specifies how high a route’s penalty can become before the devicesuppresses the route. You can set the suppression threshold to a value from 1 – 20000. Thedefault is 2000 (more than two “flaps”).The parameter specifies the maximum number of minutes that a route canbe suppressed regardless of how unstable it is. You can set the maximum suppression time to avalue from 1 – 20000 minutes. The default is four times the half-life setting. Thus, if you use thedefault half-life of 15 minutes, the maximum suppression time is 60 minutes.The following example shows how to change the dampening parameters.BigIron RX(config-bgp)# dampening 20 200 2500 40This command changes the half-life to 20 minutes, the reuse threshold to 200, the suppressionthreshold to 2500, and the maximum number of minutes a route can be dampened to 40.NOTETo change any of the parameters, you must specify all the parameters with the command. If youwant to leave some parameters unchanged, enter their default values.Originating the default routeBy default, the device does not originate and advertise a default route using BGP4. A BGP4 defaultroute is the IP address 0.0.0.0 and the route prefix 0 or network mask 0.0.0.0. For example,0.0.0.0/0 is a default route.NOTEThe device checks for the existence of an IGP route for 0.0.0.0/0 in the IP route table before creatinga local BGP route for 0.0.0.0/0.To enable the router to originate and advertise a default BGP4 route, enter the following command.
