Utilising upstream MED values

Sat Mar 19 07:06:06 UTC 2005

Sam,

On Fri, 18 March 2005 14:05:12 +0000, Sam Stickland wrote:
> 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.

MEDs are pretty much always specific to the network
advertising them. Some base them on round-trip-time,
some on the pipe size (both IGP), and what not. To
compare these is difficult to impossible I'd say
myself.

> However, a route-map (cisco, foundry) only allows you to set, add or 
> subtract to an MED value, so this doesn't seem possible.
> 
> Is anyone doing this, and if so how?

Don't do it... MEDs are perfect when you have two
links to the same provider and want to determine
where to send him the traffic closest to the origin,
but that's pretty much all you can/want to do with
MEDs from your transit supplier.

For peers you can of course use some pre- defined
metrics and 'always-compare-med' or variants of it,
to differentiate the type of peer, but that is not
what you mean as I see it.

Alexander