RE: Utilising upstream MED values

From: [] On
Behalf Of Sam Stickland
Sent: Friday, March 18, 2005 9:05 AM
Subject: Utilising upstream MED values


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