BGP4 COMMUNITY attribute

John W. Stewart III jstewart at
Thu Mar 27 19:34:59 UTC 1997

 > What is the general concensus about passing communities in the "community"?

i could see a reason for a subscriber passing communities
through a mid-level provider to a top-level provider.  but i'm
not sure if it makes sense [yet] for top-levels to pass
communities between themselves

 > > > 1. Is COMMUNITY a transitive attribute only between me and my immediate
 > > > upstream supplier or 
 > > > is it being propagated further into Internet (so I can influence how
 > > > somebody ,say, 5 AS hops 
 > > > away from me sees my routes) ?
 > >
 > >the attribute is defined as transitive (i.e., once associated
 > >with a route it *stays* associated with the route).  however, in
 > Unless an intermediate provider deliberately changes the value, as
 > opposed to appending to it.

these values aren't an end-to-end thing .. it's simply a
way for providers to more easily facilitate routing policies.
your comment implies somebody being a bad guy...

 > >practice, many providers are configured to not send communities
 > >to other providers
 > Is this a conscious decision or just that they have not turned on 
 > "send-community"?

both.  they don't turn on send-community so that others don't
see their communities.  maybe they have some whiz-bang features
that make configing their neat really cool, and they don't want
others to see their communities because it might imply a way for
others to do the same thing without the same amount of work


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