Routes Dampening

• ONLY apply to eBGP!

• 以路径为单位，如果某条路由存在多条路径，其中一条浮动时对其它路径不影响

BGP route dampening can be used to reduce the propagation of unstable routes throughout a network. When a prefix flaps it will be assigned a penalty of 1000 and moved into the dampening state “history”. Each flap incurs another penalty (of 1000), which is applied cumulatively. If the penalty reaches the suppress-limit, the route is dampened, meaning it won’t be advertised to any neighbors. The default values for each dampening criteria are stated below:

• Penalty :1000

• Suppress Limit: 2000

• Reuse Limit: 750

• Half-Life: 15 Minutes

• Maximum Suppress-Limit: 60 Minutes

Once a route has been dampened, the penalty must be reduced to a value lower than the reuse limit in order to be advertised once again. The half-life timer does this automatically. After a penalty has been assigned and the prefix has become stable again, the half-life timer starts. When the half-life time has been reached, the penalty will be reduced by half (it decreases exponentially every fifteen minutes).

For example, if the penalty was 3000, then fifteen minutes later, the half-life will have reduced the penalty to 1500. Another 15minutes will reduce the penalty to 750, and so on. Once the penalty goes below half of the re-use limit (375 in this case), the penalty is completely removed.

Cisco的dampening实现中，默认路由路径的penalty为0，翻动一次增加1000，只有属性改变时，增加500