Communities BCP [was: RE: BGP Path Filtering]

Daniel Golding dgold at FDFNet.Net
Fri May 16 19:13:56 UTC 2003

To take a crack at it...

- Route origin - customer, peer, transit provider, other (dial, etc)
- Route geography - depends on your network, but some have seperate
communities for POP, Country, Region, etc
- Customer originated information - tweaks by your customers to
selectively prepend, change local pref, not send to peers, or what not
- Source AS - simply your AS:peer AS that the route was learned from

There was an Internet Draft, last year, that summarized some of the
approachs. I suspect overspecificity in this case has never done any harm,
while lack of specificity has probably caused some heartache.

- Daniel Golding

On Fri, 16 May 2003, Deepak Jain wrote:

> > 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

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