CDP, Frame-Relay & DMVPN Tunnels

Unanswered Question

I have a few routers that have established DMVPN tunnels on both Frame-Relay and wireless links. EIGRP neighborships are established via the tunnel interfaces and I'm able to ping throughout the network (remote to remote & remote to DMVPN headend routers). CDP is globally enabled on all routers, however I only see CDP neighbors across the wireless media. CDP has been specifically enabled on the Frame-Relay sub-interfaces and tunnel interfaces. Is there any way to see CDP neighbors across NBMA media or the Tunnel interfaces? The headend routers are 3845s using IOS 12.4(4) w/ Advanced IP Services and 2801s (remote sites) using IOS 12.3(8r) w/ Advanced Security. The 'show cdp interface' output indicates that the Frame-Relay sub-interfaces are sending packets, but none of these show up when the 'show cdp neigh' command is issued on either side of the FR link.

I have this problem too.
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Richard Burts Wed, 08/08/2007 - 05:27


As far as CDP and the tunnels is concerned the traditional implementation of GRE did not support CDP over GRE tunnels. Cisco has added that support in recent code. My guess is that your IOS 12.3(8r) does not have this support. If you try upgrading code on one of the 2801s to 12.4 I suspect that you will see CDP work over the GRE tunnel.

As far as Frame Relay is concerned, can you supply some detail of how Frame Relay is configured. In my experience CDP runs on point to point subinterfaces but not so well on physical interfaces (or multipoint subinterfaces). Are your Frame Relay configured as point to point subinterfaces or as multipoint?



Thanks for your reply, Rick.

I will try your suggestion regarding an IOS upgrade on a 2801 and see how it goes.

FR is configured as pt-to-pt.

Assuming the 3845s are running the correct code, shouldn't I see those as cdp neighbors via the Tu interfaces? Even though the code allows me to enable cdp on the Tunnels, those interfaces don't report as sending packets in the 'show cdp int' output. Any thoughts?

Richard Burts Wed, 08/08/2007 - 06:28


If the Frame Relay is configured as point to point subinterfaces and if CDP is enabled I would expect it to work.

Assuming that the 3845s are running the correct code I would expect to see CDP running on the interfaces. I would not expect to see cdp neighbors unless the peer on the other end of the tunnel was also running cdp over the tunnel. On routers that I support which are running CDP over GRE tunnels the show cdp interface does show them as sending packets over the tunnel interfaces. Perhaps you can post the output of show cdp interface and also post the interface configs.




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