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GRE Tunnels Flapping

Hi I'm having a problem establishing a stable GRE tunnel and was wondering if anyone could help?

Both Routers are 7200s. RouterA is running IOS rev 12.3(4r) and RouterB is running IOS rev: 12.2(5d). Both sides of the tunnel show as UP/UP until I enable keepalives on RouterA (RouterB doesn't seem to support them), then RouterA predictably shows the tunnel as UP/DOWN.

I can ping the local interface on RouterA, but RouterB can't seem to ping it's local interface.

I've changed the IPs, but the config on the tunnels is attached (RouterA.txt & RouterB.txt).

Running a debug on the tunnel produces nothing useable. IP ICMP Debug just shows RouterB encapsulating messages, but nothing is returned.

Setting tunnel mode to be ip-ip allows RouterB to ping it's local interface and allows us to ping down the tunnel.

Any ideas are most welcome!

Cisco Employee

Re: GRE Tunnels Flapping

Hi Ray,

Without seeing your routing configuration, I can only think of the recursive routing problem. You can check out this document



Hall of Fame Super Blue

Re: GRE Tunnels Flapping

Can you please post your config? For confidentiality purposes, you can black out the IP Addresses, crypto keys, passwords and other details.

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