I have a customer with 3 locations, 3661 routers (12.2.xT IOS), HSSI interfaces toward a carrier IP backbone with 3 Mbps ports. My customer has also a Frame Relay T1 PVC for back up.
I configured GRE tunnels and EIGRP between all the locations. The GRE tunnels were created between loopback interfaces in each router. GRE tunnels are UP, EIGRP updates, everything looks OK.
Sometimes strange things happen with one or all the tunnels. After 2/3 weeks, or few days, or same day, the GRE tunnels show Up, but no EIGRP updates. I am trying to ping the GRE interface at the other end and it is not successful. I am trying to ping the serial over the carrier IP backbone and it goes fine, very good reply time as usual. (60 ms). After a shut down for the tunnel interface and a no shut the GRE tunnels start to pass traffic again. The carrier or my customer did not do any changes.
The MTU on the HSSI is 1400 and I adjusted the Delay/BW on the HSSI also so the EIGRP route over the GRE tunnel to be preferred against the Frame Relay T1 path. What's wrong?
