[c-nsp] BGP routes co-existing with different local-preference

[Oliver Boehmer (oboehmer)]

Kristofer Sigurdsson <> wrote on Tuesday, October 25, 2005 10:25 AM:

> Hi,
> 
> We just hit some weird behavior in a Cisco 7500/RSP8 and RSP4, running
> IOS 12.0(24)S6.  This router is one of two upstream routers for our
> AS. Both of the routers are receiving full routes from their
> respective upstream.  For traffic engineering purposes, both of them
> have a certain set of routes they set to a higher local preference.
> 
> Now, when the 7500 has 2 routes to the same destination, from it's
> upstream and from the other edge router and the route received from
> the other edge router has a higher local preference, the 7500 does
> not advertise his route (the one with the "normal" local preference)
> to other routers within our AS.
> If I set the weight of those routes (in the 7500) to 250, it
> advertises them.
> 
> Now, shouldn't the router advertise it's routes, even if there's
> another route that is preferred?  The outcome from this would be if
> the preferred outgoing edge router lost connectivity, the less
> preferred route would not be in the other routers BGP tables, so no
> connectivity, which is a bad thing (TM).
> 
> Cisco 7200 running 12.2S seems to do this the way I want (advertise
> all routes to the other routers within the AS and let them choose).

a BGP speaker always advertises its best path towards BGP neighbors. If
the best path is learned via iBGP (as your 7500 above), this path is
only advertised to other iBGP peers if the BGP speaker (the 7500) is
acting as route-reflector.
This is the way BGP works..

Are all your iBGP speakers fully-meshed?

	oli