local_preference for transit traffic?

Keegan Holley keegan.holley at sungard.com
Thu Dec 15 06:33:47 UTC 2011

I suppose so because prepend is so easily defeated, but sometimes you don't
own a prefix shorter than the one you need to advertise.  Assuming I
understand your suggestion correctly.

2011/12/15 Holmes,David A <dholmes at mwdh2o.com>

> For this very reason I have advocated using longest prefix BGP routing for
> some years now, and checking periodically for the expected path, as it
> became obvious from investigating traceroutes that traffic was not being
> routed as intended using AS prepends.
> -----Original Message-----
> From: Keegan Holley [mailto:keegan.holley at sungard.com]
> Sent: Wednesday, December 14, 2011 10:08 PM
> Subject: local_preference for transit traffic?
> 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
> of routes that do not originate locally by default before sending to a
> other larger transit AS's.  Obviously this isn't something that was asked
> of them and it took a few days to find since the customer is not a large
> company and neither them nor my company has a link or business relationship
> with the AS in question.  This seemed strange to me for obvious reasons,
> but I was curious if anyone else was doing this and why.  You obviously
> cannot use prepend to affect transit traffic again for obvious reasons.
> MED is a weak metric but it at least only affects traffic that was already
> going to transit your AS.  The larger transit AS was favoring a lower
> bandwidth link for the customer and causing them to drop packets
> mysteriously.  Just wondering if this practice seemed as strange to others
> as it does to me.
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