On Sat, Nov 5, 2011 at 12:21 AM, Jakob Heitz <[email protected]> wrote: > On Nov 4, 2011, at 3:41 PM, "Brian Dickson" <[email protected]> > wrote: > >> Once a route crosses a peer connection or goes "downhill", it can no >> longer go "uphill" >> or cross another peering link. > > Why can it not cross a peering link? > > -- > Jakob Heitz.
When two networks peer, they agree to exchange routes for their respective customers. If A announces a route to B, that route is A's customer and _not_ B's customer. So, by the nature of the agreements, B cannot announce that route to another peer, C. Take the worst case - a tier-1 network. All their routes are either customer routes, or peer routes. If they were to send their peers' routes to their peers, they would be sending all routes to everyone. They would be providing transit, for free, to their peers. This would not be good for many reasons. Put another way - when network B sends routes to peer C, it is providing transit to those routes. It generally only wants to do that for customers, especially if that happens to be its primary business. Brian _______________________________________________ sidr mailing list [email protected] https://www.ietf.org/mailman/listinfo/sidr
