Re: consistent policy != consistent announcements

[the Riz <riz () boogers sf ca us>]

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?
>
>       --Vince

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.

+j

-- 
Jeff Rizzo                                         http://boogers.sf.ca.us/~riz
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