[c-nsp] AS-prepending

[Pete Templin]

Vincent De Keyzer wrote:
> 
> as an ISP, I need to limit the traffic that I receive *from* one of my two
> upstream providers.
> 
> I was thinking of AS-prepending. Is it the best method ? If yes, can
> somebody point me to a document that gives a recipe for this?

Are the two networks similar in size and peering?  If one is "fully 
peered" (i.e. does not buy full routes from another net) and the other 
isn't, prepending may not work as expected within the network(s) 
providing full routes.  Most providers (me too!) apply a higher local 
preference to customer prefixes than peers.  If you were my customer, 
I'd prefer your announcement than any other identical prefix I learn on 
the 'Net, and I'll announce it to all of my transit providers (who will 
do the same thing).  I've got five transit links, so if you announce a 
prefix to me, by default it'll have customer local preference in those 
five networks (actually, it's nine, because one of those transits is 
InterNAP, who gets customer LP in all of their providers).

That said, your providers should (hopefully) support a community where 
you can request peer-level LP in their transit providers.

pt