AS701 peer local-pref?

Mike Leber mleber at he.net
Sun Dec 16 22:40:46 UTC 2001


On Sun, 16 Dec 2001, Randy Bush 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?
> 
> yup.  for a discussion of this with diagrams and all, see a nanog
> conversation between vaf, asp, and me circa '97 or so.

I looked over your posts for all of 1997 and those closest I found was
this in March of 1997 (the ensuing thread had lots diagrams etc):

http://www.merit.edu/mail.archives/nanog/1997-03/msg00250.html

You post is example of why you want to prefer customer routes.  Since I
can't find a reponse from Andrew Partan I'm not sure if I found the thread
you were referring to.  If I missed it please privately send me some
search keywords and I'll dig some more.

While handling equal length routes deterministicly so that you don't drop
your own customer's transit routes (paths longer than just one AS)
somewhat apparent, this is probably unnecessarily confusing for some.  So
instead lets take the case where the customer route is longer than the
peer route.

Most often, when you are paid for transit your customer has the
expectation that you will reannounce their routes including their customer
routes.

Assume you have customer A who has customer R who has customer X.  You
also peer with B who also has X as a customer.

Customer A expects you announce all the routes they are paying you to
announce, namely A R X.  You also hear the shorter route B X.  However,
you MUST prefer A R X in order to ensure that it propagates within your
network so that you announce it uniformly.

The two ways to set path selection prior to path length are local pref and
weights.

The prior post asserted that 701 does not use local pref.  This would
leave weights or nothing.  If they do nothing then this is a big deal for
network A because they can't ensure that R's customer routes will be
announced.

Is there a 701 customer on the list that knows definitely how their
customers customers routes are being handled that can clear this up?

Will the real 701 route selection algorithm stand up?  :)

Mike.

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