metric 0 vs 'no metric at all'

Doug Marschke doug at
Fri Feb 17 11:07:45 UTC 2006

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

-----Original Message-----
From: owner-nanog at [mailto:owner-nanog at] On Behalf Of
Danny McPherson
Sent: Tuesday, January 03, 2006 3:49 PM
To: nanog at
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:

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


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