Communities BCP [was: RE: BGP Path Filtering]

Guy Tal guy at
Fri May 16 22:28:37 UTC 2003

comments inline...

On Fri, 16 May 2003, Stephen J. Wilcox wrote:
> On Fri, 16 May 2003, Danny McPherson wrote:
> > On 5/16/03 1:26 PM, "Jay Ford" <jay-ford at> wrote:
> >
> > > You can & definitely should strip those community values on announcements you
> > > receive from EBGP peers.  Interesting things happen if you let others turn
> > > your routing policy knobs when you think they can't reach them.\
> >
> > Agreed.
> >
> > Likewise, when you receive communities (and MEDs, ugh!) [if possible] you
> > should reset them (v. employing 'additive').  Unnecessary propagation and/or
> Hmm.. assuming you're interconnecting at multiple points with the same ASN they
> will probably want to indicate to you where to send traffic to them using MEDs,
> if you go stripping them out you lose that info, check the peering policy.. this
> may put you in breach.
> Even without a breach of policy the MED will help find the best path to a route
> thats identical at two points and if you take it out you lose that.

All a matter of perspective. I would assume most people want to use
closest exit on their networks. Imagine how nice it would be if you could
hand off traffic to a peer that is your closest exit, then force them to
carry the traffic back to you at that same point from across the country
or across the globe!

> Altho I'd agree if you'd say to clear the communities and MEDs on egress, thats
> an okay thing to do.

Spank me if I'm wrong here, but you don't pass MEDs on transitively
anyway. And if you strip communities off, you limit your
peers/customers/providers from being able to use the same control that you
are asking for.

Guy Tal

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