BGP4 COMMUNITY attribute

Paul G. Donner pdonner at
Thu Mar 27 23:23:09 UTC 1997

At 02:34 PM 3/27/97 EST, John W. Stewart III wrote:
> > What is the general concensus about passing communities in the
>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
> > > > 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...

Actually, I hadn't necessarily meant to imply "being a bad guy".  
The comment was meant to show that the "intermediate" ISP has this 
kind of control over the attribute.  In any case, if the decision 
about whether or not to pass on an attribute (or to modify it) was 
part of the intermediate ISP's policy, whether or not he/she is a 
bad guy would depend on varying points of view.


> > >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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