On Fri, Mar 06, 1998 at 10:01:41AM -0800, Andy McConnell wrote:
The problem is this: How do you get BGP to choose the shortest "AS PATH", since internal AS paths are ignored in selecting BGP routes? Right now, to top router in AS4 will always choose a route through (2 3 1) instead of (1), because it prefers "external" routes (even external confederation routes) over internal routes.
So, when given a choice, the router on the distant side of the AS will ALWAYS prefer the three-AS-hop path, because it is external. Is there a way around this?!?
Avi Freedman suggested using a +1 metric when leaving each member-AS. (Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it right. In fact, it doesn't look like the metrics are adjusted more than 1. for example, from AS2, the lower router sees every route outside of AS2 as having only metric 1! The top router in AS3 does not add 1 to the metrics it readvertises to AS2.
I've been stewing over this problem for some time... I believe there is some clue that I've missed. Any help would be greatly appreciated!
This won't work because Cisco's bgp implementation skips over MED from neighboring sub ASes inside a confederation in its decision process. What you probably need is to get cisco to implement a knob that will evaluate MEDs across sub-ASes inside a confederation. Cisco is working on this, but I'm not sure what the ETA is. -dorian