2 bgp tips

What I learned Today about networking

This is a repost from my old blog, but I think they are good tips that I don't want to lose, so I'm reposting them here:

Tip 1 BGP community Best Practice
It is better to set bgp communities on a inbound route-map(or on the redistrabute command) than on an outbound route-map. When you set the communities on the inbound, you know more about the route. For example was this route learned via ebgp or ibgp.

Exception:
Doing an outbound route-map are good if you need to send different cummunities to different peers. Even in this case it may make since to do both inbound and outbound route-map in order not to lose the info about where the route came from.




Tip 2 A eBGP no-no
When you do ebgp multihop toward your peer, and ibgp internally you need to make you sure you don't advertize back to your ebgp peer's addresses back to them.

For example if you redisrabute static routes of your peers networks into your ibgp, then do ebgp multihop else where, they will get their own routes back if you don't use a route filter toward them.