North American Network Operators Group

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Re: honoring AS-path prepend from a peer or customer?

  • From: Avi Freedman
  • Date: Thu Feb 18 22:46:32 1999

> done it such that we only did prefix filtering, not any as-path
> filtering, this allows them to prepend as they wish, just not advert
> anything other than what we filtered them at.

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.

> 	- Jared