From what I've experience on Cisco routers. The RID isn't the final deciding factor, it has been the route that was first present. I had a router peering with 10.0.0.6 and 10.0.0.7 and if I reset BGP on .6 the .7 route will stick and even though .6 comes back up the .7 route will stay. BGP resets doesn't bring .6 back up. The same applies to resetting .7 Cisco documentation that I've seen has stated the RID is the last criteria. Interesting.

-=Vandy=- -----Original Message----- From: Gustavus, Wayne [mailto:wgustavus@gnilink.net] Sent: Wednesday, June 26, 2002 11:18 AM To: 'Ralph Doncaster'; Jared Mauch Cc: nanog@merit.edu Subject: RE: how is cold-potato done? Ultimately there won't be any ties, since BGP will eventually have to select a best path. If necessary, the decision will come down to RID. If the metrics really are the same then theoretically it doesn't matter which path it takes. If it does matter, you will have to modify your policy to make a decision based on some other criteria that you are also influencing via policy. ___________________________________________________________ Wayne Gustavus, CCIE #7426 Operations Engineering Verizon Internet Services ___________________________________________________________ -----Original Message----- From: Ralph Doncaster [mailto:ralph@istop.com] Sent: Wednesday, June 26, 2002 2:08 PM To: Jared Mauch Cc: nanog@merit.edu Subject: Re: how is cold-potato done?

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If I peer with network X in cities A and B, and receive the same route in both cities with an AS-path of X, how do I know which city to use for an exit? I can understand how if X uses communities to tag the geographic origin of the traffic, but I'm not aware of many networks that do this. Lots of networks claim to use cold-potato routing though, so how do they do it?

they use the MED sent on the route (aka metric) from the other provider to determine which exit where they both interconnect is the "shortest".

this can at times provide undesired results because of aggregation.

Besides aggregation, wouldn't this lead to a lot of ties? Let's say the cities are LA & Manhattan, and the route from X originates in Chicago. I would think that it would be a common occurrance for the route to have the same metric in LA & Manhattan. -Ralph