AS 701 local-pref answer.

Mike Leber mleber at he.net
Mon Dec 17 03:09:40 UTC 2001


Not to be like Columbo... However, there's just one last question
bothering me.  Well ok, more than one :)

If it's like mentzer at mentzer.org said and 701 doesn't deterministicly
prefer customer routes (customers and peer routes at the same local pref)
wouldn't this mean that they wouldn't have consistent route announcments
in various parts of their network?

If a customer doesn't set the community to boost the local pref, and 701
truly by default sets customers and peers to 100, then 701 would be
announcing varying numbers of routes to the same peer at different
locations.

Do they expect consistent route annoucements from their peers?

Many networks out there insist upon this as a requirement when peering.

Mike.

On Sun, 16 Dec 2001, Mike Leber wrote:

> 
> Thank you for pointing that out.  I was being dense and reading way too
> much into the statements:
> 
> smentzer at mentzer.org wrote:
> > All the responses I have gotten indicate that UUnet does indeed set
> > local-pref on both customers and peers to 100 (or leave default in this
> > case).  Thanks for all the responses...
> 
> Especially when the 701 communities were already provided by German
> Martinez.  *DOH*
> 
> In other words, 701 transit customers that actually want to ensure their
> downstream customer routes are announced by 701 had better set the
> appropriate community so that local pref gets set above 100.  By default
> this is not done.
> 
> Pardon me while I get some much needed rest.
> 
> Mike.
> 
> On Sun, 16 Dec 2001, David Barak wrote:
> 
> > Mike Leber wrote:
> > 
> > >If they set local pref for both peers and customers
> > >to 100 how do they
> > >ensure that the customer transit routes are
> > >announced to peers?
> > 
> > >The reason I ask this is because if a customer 
> > >announces a customer of
> > >theirs to you that a peer also has as a customer >you
> > will have equal
> > >length routes for the same destination AS.  While
> > >there are many ways to
> > >deterministicly prefer customer routes, local pref
> > >is the most common.
> > 
> > AS 701 always announces the best route, as their
> > routers know it.  Their average AS-path length is
> > under 2, so it doesn't seem to be a problem.  If a
> > customer of AS 701 wants to insure that his/her route
> > is advertised in all cases, s/he could send a
> > community which AS701 edge devices could use to
> > manipulate local-preference upward.  [this was covered
> > in a previous posting on this topic]  I leave it to
> > your imagination whether peers would be permitted to
> > do this.
> > 
> > -David Barak
> > I only speak for myself.
> > "Quis custodes ipsos custodiet?" - Juvenal
> > 
> > __________________________________________________
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