I have four 7206 Routers as my core devices. These routers have HSRP configured in them. We have divided the routers in groups of 2 - 2. Every group's routers are reduntant for each other. The division is done to segregate the branches connected to my core through different service providers.
All of these four routers have point-to-point links which are terminating on the serial ports of my core routers. I have ISDN as my back up connection for every branch connecting through point-to-point links. Rest all branches connects through GRE Tunnels.
Now, whenever any of my point-to-point branch goes down. I do 'no shut' to my dialer interface for that particular site to start the ISDN connectivity.
But I have to manually shut the serial interface of this branch else the other users who have point-to-point connectivity experience extremely high latency. Similarly, I have to shut the dialer interface if the point-to-point link start working.
I had a major outage this week where my backhaul link went down and I had to manually transfer the tunnels to my DR Router.
The point-to-point links were up on ISDN at this time. When the bachaul link issue was resolved. The GRE Tunnels came up and started performing normally but my point-to-point branches started facing same extremely high latency issue. It didn't stop until I shut all the dialer interfaces for these point-to-point links.
Can anyone please explain me the concept behind this?