Communities BCP [was: RE: BGP Path Filtering]

["Deepak Jain" <deepak () ai net>]

> 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