Re: BGP4 COMMUNITY attribute

["Paul G. Donner" <pdonner () cisco com>]

Actually, along this vein (granted, this may not be the place but since
the subject came up)..

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

See in-line below...

At 01:32 PM 3/27/97 EST, John W. Stewart III wrote:
> many of your questions are for MCI and not nanog
>
> > In the preparation for upcoming 2nd (multihomed) connection to Internet
> > I am looking into
> > COMMUNITY attribute of BGP4 as a way (in conjunction with my own
> > LOCAL_PREF) of load balancing
> > traffic between my two internet links (both T3). After reading CISCO
> > documentation I am still not
> > clear on some issues:
> >
> > 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.

> 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"?

Donner

> > 2. If COMMUNITY propagates into big I, and I set COMMUNITY to 3561:70
> > (for MCI to set 
> > LOCAL_PREF on my routes to 70) and my next hop supplier sets COMMUNITY
> > of my routes to  
> > 3561:80, what happens ? what MCI is going to do ?
>
> is one of your immediate upstream provider's MCI?  if so, then
> you would tag routes with 3561:70 and MCI would immediately see
> and react to that.  however, you imply that your "next hop
> supplier" isn't MCI, which makes it a bit odd for you to be
> sending communities for MCI, but is doable if your "next hop
> supplier" agrees to carry your communities all the way to MCI
>
> > 3. Is COMMUNITY a CISCO only or is it part of RFC ? Has any other router
> > vendor implemented
> > this parameter ?
>
> rfc1997.  i think there's a GateD with communities
>
> /jws
>
> > 4. Which major Internet providers have COMMUNITY/LOCAL_PREF implemented
> >  (I am aware of MCI and Sprint) ?
> >
> > 5. Your experiences, comments, suggestions .....
> >
> >
> > Thanks in advance, Walter
> >
> >
> >
> > Walter Towbin
> > Telus Advanced Communications
> > phone: 403-543-2032, fax: 403-543-2030, cell: 403-620-0019
> > walter.towbin () telus com
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