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.
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
ISPF, The Forum for ISPs by ISPs, <http://www.ispf.com>
"Think of it as evolution in action." - Niven & Pournelle
