3825 ISR has a Tunnel0 with an IP but no actual configuration

[Waterbird]

Hi,

I have a router that has a Tunnel0.  This has an IP address visible in show ip interface brief.  However, when I issue the command show run interface Tunnel0, it has no configuration at all on the interface.  However, when I issue the command show interface Tunnel0, I do see an IP address that has been configured on this Tunnel.

Normally I would expect to see an interface configuration on show run, but I don't see it for this Tunnel0.  Yet it has an IP, put there somehow by some previous administrator.

Please explain to me what's going on with this mysterious missing configuration.

[balaji.bandi]

It is hard to say at this stage until we see the configuration bit and output what you referring to that will give some information for us to address and understand the issue.

[Waterbird]

There is no output.  That's the issue.

[Richard Burts]

Are you running anything like WCCP on this router? There are some things as already mentioned that might dynamically create tunnels. Probably the best way to figure this out is to post a sanitized show run.

[Georg Pauwen]

Hello,

the 3825 has been end of sale somewhere around 2010, so I assume you are running an old IOS version. There is a bug where the tunnel interface cannot be deleted to some IPv6 configuration, not sure if you have any IPv6 configured ?

Either way, I would guess the tunnel interface disappears (if that is what you want) when you delete it and then reload the router:

3825#conf t

3825(config)#no interface tunnel0

3825(config)#end

3825#we

3825#reload

[Sergey Lisitsin]

Waterbird,

Some features in IOS configure Tunnel interfaces automatically. For example, a Tunnel interface is created when a router has Multicast routing enabled with PIM and the Rendezvous Point is configured.

[Waterbird]

I can understand Tunnel0 appearing automatically for some reason.  But not sure how it could acquire an IPv4 address from the local network, but still not show that in the running config.