Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

I am configuring a GRE tunnel in Linux 2.6.26 and I've been facing a very strange problem for which I could not find any solution.

I have created a GRE tunnel called gre0, but no matter what I do, I am simply unable to delete this tunnel. The command ip tunnel del gre0 fails with the response ioctl: Operation not permitted. Any attempt to change the addresses of the tunnel also fails.

The following commands illustrate the problem:

# ip tunnel del gre0
ioctl: Operation not permitted
# ip tunnel change gre0
# ip tunnel change gre0 remote <some address> local <some address>
ioctl: No such file or directory

I can create, change and delete other tunnels without any problem, but gre0 just sticks there and does not go away, even if I reboot or take the interfaces down.

If I remove the ip_gre module, the tunnel disappears. As soon as I insert the module again, gre0 reappears and the problem continues.

I have two questions:

  1. What can I do to get rid of this pesky tunnel? I suspect this might be a kernel or a module bug.
  2. Where such persistent data (in this case, the information for gre0, but this applies to any other setup I may be even unaware of) is stored?

If any other information is needed, please let me know.

Thanks a lot for any help.

share|improve this question

1 Answer 1

up vote 9 down vote accepted

I believe I've found myself an answer to this problem.

After tinkering for a while, I decided to reproduce the problem in a clean installation.

The ip_gre module is not inserted by default in the kernel after installing Debian. ip tunnel show does not display any tunnel. After inserting the ip_gre module, but without creating any tunnel, gre0 appears and is undeletable and unchangeable as expected. Thus gre0 seems to be a dummy tunnel created by default by the ip_gre module.

The frustrating part is that this 'feature' is totally undocumented, and is even an unexpected one, since it might be natural to attempt to create a gre0 tunnel as the first (and only) GRE tunnel in a system.

share|improve this answer
1  
This is also true for tunl0 and sit0. –  user68296 Apr 6 '11 at 9:01
    
Thank you! It is really what I looked for. –  user141591 Oct 18 '12 at 6:01

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.