honoring AS-path prepend from a peer or customer?

Fri Feb 19 08:06:42 UTC 1999

At 10:33 PM 2/18/99 -0500, Avi Freedman wrote:

>FYI, this is dangerous.
>For example -
>
>You have a customer A who has a customer B.
>B is multi-homed to A and 701.
>B's link to A goes down.
>
>So, if A's network is broken, they will send you a given prefix
>with as-path ^701 B$ or ^1239 701 B$ or ..., depending on how B 
>sees 701.
>
>And you will transit it.
>
>Shouldn't cause any major damage, but something to be aware of.

I'm wondering why I shouldn't transit it?

In fact, by prepending certain ASNs to each prefix, you can enforce
selective route propagation through loop detection from networks two or
more hops away.  This is something which is very difficult to do otherwise
without a *very* nice upstream.  Of course, I would never recommend such
practices.  (It's not like I know anyone who has ever done anything even
remotely like that..... ;)

>Avi

TTFN,
patrick

I Am Not An Isp
www.ianai.net
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