local_preference for transit traffic?

Thu Dec 15 21:02:33 UTC 2011

Jeff Wheeler writes:
>On Thu, Dec 15, 2011 at 1:07 AM, Keegan Holley
><keegan.holley at sungard.com> wrote:
>> Had in interesting conversation with a transit AS on behalf of a customer
>> where I found out they are using communities to raise the local preference
>
>That sounds like a disreputable practice.
>
>While not quite as obvious, some large transit ASes, like Level3,
>reset the origin to I (best) sometime between when they learn it and
>when they announce it to their customers and peers.  This similarly
>causes them to suck in a bit more traffic than they might otherwise.

Once upon a time, UUNET did the opposite by setting origin to unknown
for peer routes, in an attempt to prefer customer routes over peer
routes. We moved to local preference shortly thereafter as it became
clear this was "changing" the routes in some meaningful way; if a
customer was multihomed to us and another provider, this might affect
path selection.

(The original thought was that local pref might be too heavyweight,
but of course later it became the standard.)

Joe