I am trying to hook up a virtual machine to a host using openvpn. When i create a tap interface within the virtual machine using: /usr/sbin/openvpn --mktun --dev tap1 The state of the tap interface is always "NO-CARRIER"

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether fa:16:3e:07:55:b5 brd ff:ff:ff:ff:ff:ff
    inet brd scope global eth0
    inet6 fe80::f816:3eff:fe07:55b5/64 scope link tentative dadfailed 
       valid_lft forever preferred_lft forever
3: br-ex: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN 
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
    inet scope global br-ex
    inet6 fe80::3c23:adff:feb3:6d9d/64 scope link 
       valid_lft forever preferred_lft forever
8: tap1: <NO-CARRIER,BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast state DOWN qlen 100
    link/ether ce:e9:4a:1d:80:55 brd ff:ff:ff:ff:ff:ff

Any ideas why this could be happening? I have checked to see the permissions of /dev/net/tun and it seems fine:

root@ip-10-66-210-99:~# ls -l /dev/net/tun
crw-rw-rw- 1 root root 10, 200 2014-02-15 07:15 /dev/net/tun

On the host itself there seems to be no issues. What am i missing?

  • Figured out the issue. The tap interface needs an application tied to it. Once I start the openvpn service, the tap interface state transitions to "RUNNING" – NetCubist Feb 19 '14 at 7:00
  • If you figured it out, you should write an answer. It is perfectly fine to answer your own questions. – Enno Gröper Feb 19 '14 at 22:20

The issue it turns out was that the tap interface has to have an application associated with it for it to be in the "RUNNING" state. Once i started the Openvpn service binding to tap0, the state moved to "RUNNING"

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