On Feb 19, 2012 1:15 AM, "Michael Mol" <mike...@gmail.com> wrote: > > (Sorry for the top-post...I'm mobile atm.) > > My understanding is that core network operators filter ASs for which they don't have a contract for transit. I.e, if I were to get my own PI space, I'd have to pay tier 1 networks (or pay someone to ride on *their* contract) for a contract to have packets destined for my AS to be able to reach me across their network. >
Well, yes, but it's the other way around. It's an operator saying "I don't want traffic for $AS_LIST" or "I want traffic only for $AS_LIST". The contents of AS_LIST is set by the operator on the receiving side statically, based on the transit contract. The routers, being the workhorse brutes that they are, don't waste time checking on contracts. So, if a neighbor router suddenly advertise it has a 1-hop distance to *any* AS... the router will immediately begin switching packets toward that neighbor. Rgds,
