Since both isis and ospf support a large range of metrics nowadays, the actual mileage itself is an option for the metric too. For example, before isis wide metrics, a route with fiber mileage of 1000 might be given an isis metric of 16(using the method Sush mentioned to get the metric within the isis metric range of 0-63, so 1000/64 = 15.625, round up to 16), but now with wide metrics, the actual mileage can be used. Using the wide metrics also helps reduce/eliminate the equal cost paths that used to crop up in large networks with a limited metric range. and actual mileage of 1000On Fri, 19 Jul 2002, Sush Bhattarai wrote:
Date: Fri, 19 Jul 2002 14:25:16 -0400 From: Sush Bhattarai <netnews@sush.org> To: nanog@merit.edu, Tom Holbrook <tomhol@corp.earthlink.net> Subject: Re: IGP metrics on WAN links
Think most ISPs use actual fiber miles (with an arithmetic factor to get to a certain range of course) as the means for the value of IGP metrics... of course there are always some "twinking" done regularly to give higher priorities to the higher bandwidth, link condition etc.
Sush
----- Original Message ----- From: "Tom Holbrook" <tomhol@corp.earthlink.net> To: <nanog@merit.edu> Sent: Friday, July 19, 2002 12:27 PM Subject: IGP metrics on WAN links
Just curious as to what people are using for metrics in their IGP and what their reasons are; bandwidth? geographical distance? latency? etc...
Thanks -Tom
__________________ Tom Holbrook Sr. Network Engineer Atlanta Earthlink
-sean Spoon!