-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Sam Stickland Sent: Friday, March 18, 2005 9:05 AM To: nanog@nanog.org Subject: Utilising upstream MED values

Hi,

We're looking at doing outbound traffic values based on upstream ("tier1") MED values. But, of course, there's no standard for MED values. Assuming I can get definations from the upstreams as to what their MED values mean, I have to rebase them into a common range.

You've answered the question right there. Since one provides uses apples for its MEDs, and another uses oranges, comparing them to each other. . .

However, a route-map (cisco, foundry) only allows you to set, add or subtract to an MED value, so this doesn't seem possible.

Theoretically, if you can establish a conversion constant for however you define "far" to however ISP Apple defines it and however ISP Orange defines it, you just have to apply that value. Match all routes learned from AS Orange and add or subtract the conversion value. Only works if the range of values is pretty close, though. You *could*, if the range is small enough, write route maps to match metric and set metric.

Is anyone doing this, and if so how?

Or you can hack a script to do traceroutes to various arbitrary destinations, compare to the routes learned, and evaluate the Round Trip Time (or number of hops, or whatever) to MED, establishing your own locally-significant table. Sounds like a lot of trouble to me, but YMMV.

Sam

Lee