title: How to delete a network interface?
body: <p>I tried to create an IPIP tunel using the ip tunnel add command. Now I want to delete it but it won't go away!</p>
  
  <pre><code>tunl0     Link encap:IPIP Tunnel  HWaddr   
            NOARP  MTU:1480  Metric:1
            RX packets:0 errors:0 dropped:0 overruns:0 frame:0
            TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0 
            RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
  
  $ sudo ifdown tunl0
  ifdown: interface tunl0 not configured
  $ sudo ifconfig tunl0 down
  $ /sbin/ip tunnel del tunl0
  delete tunnel tunl0 failed: Operation not permitted
  </code></pre>
  
  <p>What should I do?</p>