On 2011-06-13, Chris Wopat <m...@falz.net> wrote: > On Mon, Jun 13, 2011 at 10:39 AM, Chris Wopat <m...@falz.net> wrote: >> Is there a known issue with OpenBGPD ignoring MED during its path >> selection? Note that the first item listed is best below and it has a >> MED of 12. The others are 10 which should be preferred over 12. I'm >> guessing that it's then going to a later stage of path selection where >> it's choosing hte lowest router ID of 77.171.0.2. > ><snip> > > I guess I should have RTFM: > > > rde med compare (always|strict) > If set to always, the MED attributes will always be compared. > The default is strict, where the MED is only compared between > peers belonging to the same AS. > > This sounds like my problem.
RFC1773 says "BGP version 4 re-defined the old INTER-AS metric as a MULTI-EXIT- DISCRIMINATOR. This value may be used in the tie breaking process when selecting a preferred path to a given address space. The MED is meant to only be used when comparing paths received from different external peers in the same AS to indicate the preference of the originating AS." Most modern BGP implementations allow this to be varied (rde med compare always, bgp always-compare-med, path-selection always-compare-med) but afaik it's always a config option.
