I'm having trouble picturing your network in my head,
but I think what you're describing is that ospf is
prefering intra-area paths over other (inter-area) paths
that have a lower metric.
Yes, I was confused by this when I first saw this behavior
too. At some level we want to believe that the igp metric
is the key element in the path selection, but things are
slightly more complicated -- as you're seeing.
A cisco engineer had a clever workaround. Applied to
your case it would go like this:
build a tunnel over that area 0 ethernet segment, and
put the tunnel in area 1
I'm neither recommending or discouraging that one, but
I did think it was creative. I never tried it, and I
imagine that there could be some weird side effects.
Trying to imagine what the graph of links would look
like to ospf has a certain Escher quality to it.
Hope this helps.
On Thu, Dec 16, 1999 at 10:00:53AM -0600, Dave Bergum wrote:
> Something I never read about OSPF, but that seems *not quite correct*;
>
> I have two ABR routers interconnected with a bunch of other routers over
> atm full mesh on the area 0 side, and connected to the pop mesh in area 1
> via Ethernet. One of the routers carries upstream connections (router A)
> and the other is a customer aggregation router (router B).
>
> They are also IBGP peers.
>
> All the traffic from router B to router A goes via the atm vc in area 0.
>
> No traffic goes via the ethernet media in area 1, even though the ospf cost
> is lower.
>
> The upstream interface is in area 0.
>
> Is this expected protocol behavior? I have had no knowledge about ospf
> path selection biased towards one area over the other where multiple paths
> were concerned.
>
> IOS is 11.1(29)CC1, C7507.
>
> Thanks for any lights you can illuminate!
>
> --
> Thanks and regards,
>
> Dave
> A Onvoy/Internet - Internet in Minnesota since 1987
> -----/|\--------------------------------------------------------------+
> - / | \ Dave Bergum, Sr. Network Engineer <bergum@MR.Net> |
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