I'm not sure that I understand the problem, but here's my take on it. You have this in your routing table:
D 10.10.26.0/24 [90/297372416] via 10.10.28.1, 00:10:28, Tunnel1
[90/297372416] via 10.10.27.1, 00:10:28, Tunnel2
for the same destination. When one of your links goes down, and you look at the routing table, chances are the other link is still up and routing through that tunnel to get to the same destination. That would explain why you have to bring both sides down because now your other destination doesn't know how to get to it either.
Can you please post the show ip route output of both routers when you shut down the s0/0/1 interface on NIB_Router_BabElouk and both tunnels go down?
I am suspecting a tunnel endpoint reachability problem here but I need more information about it.
One more question: Why are the corresponding Frame Relay subinterfaces on both routers not in the same IP subnet? For example, on NIB_Router_Maadi, the s0/0/0.16 is 10.10.1.5/30 while on NIB_Router_BabElouk, the s0/0/0.16 is 10.10.1.1/30, thus they are in two different networks (10.10.1.4/30 and 10.10.1.0/30, respectively). Why is that? I assume that there is a PVC going directly from one interface to the other - no intermediate router inbetween. Can you confirm this?
I am sorry for replying lately. Can you please post the output of the show ip route commands on both routers after you deactivate the s0/0/1 interface on NIB_Router_BabElouk and both tunnels go down, as I originally asked?
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