i had a somewhat if not entirely similar problem - eigrp preferring the bit
bucket if one of two parallel links is down.
fixed it with a "no auto summmary" i believe, an then i did not spend more
thought
ios version & ip classless settings slipped my memory
well that is all just to say thanks for your post, it had been interesting
for me
--
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"John Neiberger" <[EMAIL PROTECTED]> schrieb im Newsbeitrag
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Ok, to recap, here was the problem. We have two PVCs from router A to
> router B. We have eigrp running on the first PVC but not on the second,
and
> there are static routes forcing certain traffic to use the second PVC.
> These are point-to-point frame relay links. Here are the relevant static
> routes affecting the second PVC, and let's assume the loopback address at
> the router B is 10.50.1.1:
>
> ip route 10.50.1.1 255.255.255.255 10.1.1.2 50
>
> We also have another static route for an entirely separate reason, but it
is
> involved here, as well:
>
> ip route 10.0.0.0 255.0.0.0 Null0
>
> We recently upgraded to 12.1 from 11.2. In 11.2, "no ip classless" was
the
> default. In 12.x, ip classless is the default.
>
> We thought that if the second PVC went down, since the next hop was
> unavailable, the router would pick the next available route with a higher
> administrative distance. Since there is a valid route to router B over
the
> first PVC, we thought it would take this route. The odd thing was, it
> wasn't and we didn't know why. Here's why:
>
> Even though 10.1.1.2 was at the other end of a point-to-point link and
shows
> in the routing table as directly connected, the router never realized that
> that route disappeared! When the PVC was down, if I did a show ip route
> 10.50.1.1, it would show as reachable via 10.1.1.2. Then a show ip route
> 10.1.1.2 would show that it was reachable thanks to the 10.0.0.0 route
> pointing to null0. Isn't that freaky??
>
> I assumed that the router would be smart enough to know that if a point to
> point link is down, the remote IP address is truly unreachable, even if
> there is valid supernet route; apparently, such is not the case. I did
> some testing and proved to myself that this is what was happening.
>
> So, since we don't require classless routing on this router, I've turned
it
> off. Now, the router will not use the 10.0.0.0 supernet route and it will
> correctly decide that the point to point link is down. Then, it will use
> the eigrp-learned route on the other PVC.
>
> If someone understands why a router would choose a supernet route to reach
a
> directly attached down interface, please let me know. I'm sure this will
> come up later!
>
> Thanks,
> John
>
>
>
>
>
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