Re: consistent policy != consistent announcements
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
> My first concern is the loss of information when the route to M isn't > announced. This causes unfairness when traffic ends up taking the 'long' > route. My peer fears that and would like me to fix it. I don't understand how I can do that in a simple maintainable fashion. > More than likely your peer is doing the same thing unto you. Quite possibly, but they won't 'fess up to it. And I don't want to whine at them unless I know how to constructively address the opportunity (the peer is a Californian:-). A correction: the peer individual is definitely not a native Californian, though he does reside there. As best I can tell, we present consistant routes to all of our peers. How do I know this? Because I set up test routers to peer with our public interconnect points and run periodically run my consistancy checker against them. If my peer does not agree that my policy is reasonable and a consequence of current tools, their reaction may be to reject inconsistent announcements thereby increasing the likelihood that no path is propagated. 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
Vince Fuller writes:
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?
We have some customers that have specifically requested this sort of arrangement. -Hank
Consider the case where a customer has two AS numbers and uses one for his East Coast operations and one for his West Coast operations. Since he only purchases transit, he can use his Internet connections to back up his coast-to-coast link, which he normally prefers. Suppose he has connections to a particular backbone on both coasts and wishes nearest exit to be used. At MAE-E, this backbone will prefer the East Coast AS to reach his IPs. At MAE-W, this backbone will prefer the West Caost AS to reach his IPs. The BGP advertisements this backbone will make to its peers will be 'inconsistent' but also 'optimal'. DS On Thu, 13 Mar 1997, Henry Kilmer wrote:
Vince Fuller writes:
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?
We have some customers that have specifically requested this sort of arrangement.
-Hank
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
participants (4)
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David Schwartz -
Henry Kilmer -
the Riz -
Vince Fuller