Understanding Damping Parameters

Flap damping reduces the number of update messages by marking routes as ineligible for selection as the active or preferable route. Marking routes in this way leads to some delay, or suppression, in the propagation of route information, but the result is increased network stability. You typically apply flap damping to external BGP (EBGP) routes (routes in different ASs). You can also apply flap damping within a confederation, between confederation member ASs. Because routing consistency within an AS is important, do not apply flap damping to internal BGP (IBGP) routes. (If you do, it is ignored.)

You can specify one or more of the damping parameters described in Table 17. If you do not specify a damping parameter, the default value of the parameter is used.

Table 17: Damping Parameters

Damping Parameter	Description	Default Value	Possible Values
half-life minutes	Decay half-life—Number of minutes after which an arbitrary value is halved if a route stays stable.	15 (minutes)	1 through 4
max-suppress minutes	Maximum hold-down time for a route, in minutes.	60 (minutes)	1 through 720
reuse	Reuse threshold—Arbitrary value below which a suppressed route can be used again.	750	1 through 20,000
suppress	Cutoff (suppression) threshold—Arbitrary value above which a route can no longer be used or included in advertisements.	3000	1 through 20,000

To change the default BGP flap damping values, you define actions by creating a named set of damping parameters and including it in a routing policy with the damping action. For the damping routing policy to work, you also must enable BGP route flap damping.

Understanding Damping Parameters

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