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RE: metric 0 vs 'no metric at all'
From: "Doug Marschke" <doug () ipath net>
Date: Fri, 17 Feb 2006 12:07:45 +0100


And just to update, those drafts have made it into RFC 4271

http://www.ietf.org/rfc/rfc4271.txt

-----Original Message-----
From: owner-nanog () merit edu [mailto:owner-nanog () merit edu] On Behalf Of
Danny McPherson
Sent: Tuesday, January 03, 2006 3:49 PM
To: nanog () nanog org
Subject: Re: metric 0 vs 'no metric at all'



On Jan 3, 2006, at 1:03 AM, Daniel Roesen wrote:

So the spec is fuzzy about how "no MED vs. MED=0" should be  
treated, but
vendors seem to largely agree to "no MED == MED 0". I know of no
deviation, except the old ERX bug which got fixed (ERX treated "no  
MED"
as best, even better than MED=0 - contrary to documentation).

I recall some earlier implementations from "well known" vendors that
had varying behavior for MED processing as well.

Fortunately, the update to RFC 1771:

http://www.ietf.org/internet-drafts/draft-ietf-idr-bgp4-26.txt

is considerably more explicit about this behavior, as well as a slew
of other previously-left-to-the-implementation items ironed out
through a great deal of  implementation and deployment experience.

The "BGP Experience" and "BGP MED Considerations" Internet-
drafts provide a good bit of additional insight into some of these
behaviors.

-danny



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