[87667] in North American Network Operators' Group
Re: metric 0 vs 'no metric at all'
daemon@ATHENA.MIT.EDU (Danny McPherson)
Tue Jan 3 09:49:49 2006
In-Reply-To: <20060103080308.GA29748@srv01.cluenet.de>
From: Danny McPherson <danny@tcb.net>
Date: Tue, 3 Jan 2006 07:49:29 -0700
To: nanog@nanog.org
Errors-To: owner-nanog@merit.edu
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
