consistent policy != consistent announcements

Vince Fuller wrote:

>From our point of view, we aren't seeing any route which can be used for
shortest-exit to your multi-homed customers. Why? Probably because we don't
peer with the other ISP which serves those customers. The result is that we
have to backhaul traffic to other interconnect points, something which is
expensive for us and inconsistant with our normal peering policy.

I can see why you present inconsistant routes to us but I'm not sure that I
understand why you'd prefer a customer prefix via a direct connection to them
at one point in your network but via a connection to another provider at a
different point in your network. That would seem internally inconsistant to
me. Is this deliberate behavior to do shortest-exit within your network toward
your customer?


The scenario I can think where this would happen is using BGP
route-reflectors internally to reduce the intermeshing requirements for
IBGP peers. Since a route-reflector only propagates the best route, it is
quite easy to get different as-paths in different parts of the network.
Not an ideal situation, to be sure, but "correcting" this behaviour is more
than a simple fix.