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RE: how is cold-potato done?

  • From: Gustavus, Wayne
  • Date: Wed Jun 26 14:26:04 2002

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?



> > 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





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