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Re: metric 0 vs 'no metric at all'

  • From: Danny McPherson
  • Date: Tue Jan 03 09:50:38 2006


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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