I like using BGP communities: o filter announcements you receive from downstreams based on your criteria of choice o set a specific BGP community (yourAS:whatever) on announcements which are to be propagated to various places (upstream providers, etc.) o do output filtering based on the communities you set Make sure you clear yourAS:whatever in announcements from your BGP peers.
You can use this same technique for prefixes you originate, so that all your outbound BGP filtering is based on communities.
I am hijacking this thread a bit. Setting communities is excellent advice especially if you are just starting out with downstream ASes. The question is that changing your communities down the road might be a big headache depending on whether you'll come to need more advanced ways of filtering your announcements than coarse communities allow. Especially when going (through growth or acquisition) from a single metro network to a multi-metro or national/international one. What criteria does the community think should be used when specifying communities. IMO, overspecificity [sp?] doesn't hurt, but others may (and have) disagreed. What's the BCP? Thanks, Deepak Jain AINET