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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BGP Confederation config problem...
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
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