Frequently Asked Questions

Q— If I specify the maximum number of prefixes that will be accepted from a peer as 100, for example, and enable soft reconfiguration inbound for that peer, will this limit the number of unaltered routes to be stored in memory to 100?

A— No. All the routes learned from the peer (the Adj-RIB-In before the Input Policy Engine is applied) will be stored in memory.

Q— My border router is having problems because the link to my provider is oscillating, causing routes to flip-flop. Will configuring route dampening stabilize my router?

A— To a certain extent. In this case, configuring route dampening might help stabilize your AS if you are injecting the BGP routes into your IGP. Your border router will still experience the instabilities caused by your provider. A better approach is to call your provider.

Q— I am advertising my IGP routes into BGP. My IGP routes are very unstable, which causes the BGP routes I am advertising to fluctuate. Will route dampening solve the problem?

A— No. Configuring route dampening on your border router will prevent your routes from being advertised. This will help others but will cause you outages. What you need to do is address the source of your IGP's instability.

Q— Some of my internal routes are flip-flopping, which is causing my provider to dampen them. I can't figure out the problem. What should I do in the meantime?

A— You can always define these routes statically and inject them into BGP. This way, they will always be advertised, irrespective of their up or down state. Even better (if possible), you can define your routes as part of an aggregate route. The aggregate route will not disappear unless all the more-specific routes it represents disappear.

Q— I am a provider. I don't want to penalize all prefixes in the same manner. Is there a way to assign different dampening parameters to different prefixes?

A— Yes. Cisco offers you the flexibility to selectively apply the dampening parameters depending on certain criteria such as IP prefixes, AS_PATH, or community.