[c-nsp] bgp weird issue

Tim Franklin tim at pelican.org
Fri Dec 5 06:45:54 EST 2008

On Fri, December 5, 2008 6:00 am, mm-tech wrote:

> It's weird because the eBGP route has an administrative distance of 20
> and the iBGP has an AD of 200 and it should choose the eBGP route.


The BGP best-path selection happens between *all* of the BGP routes, both
eBGP and iBGP, using all of the normal BGP metric, of which AD is NOT one.
 (E vs I is, but it's a lot further down the tree than local-pref).

Only once you've chosen a BGP best path do you compare the AD of that
route with the ADs of matching routes from other non-BGP routing protocols
to see which one makes it into the routing table, which is where the eBGP
< various-IGP < iBGP distinction comes in.


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