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This article describes how to use VPN via the TUN/TAP device inside a [[container]].

OpenVZ supports VPN inside a container via kernel TUN/TAP module and device.

To allow container #101 to use the TUN/TAP device the following should be done:

Make sure the '''tun''' module has been already loaded on the [[hardware node]]:

lsmod | grep tun

If it is not there, use the following command to load '''tun''' module:

modprobe tun

To make sure that '''tun''' module will be automatically loaded on every reboot you can also add it or into <code>/etc/modules.conf</code> (on RHEL see <code>/etc/sysconfig/modules/</code> directory).

Allow your container to use the tun/tap device by running the following commands on the host node:

vzctl set $CTID --devnodes net/tun:rw --capability net_admin:on --save

After the configuration steps above are done it is possible to use VPN software working with TUN/TAP inside

container just like on a usual standalone Linux box.

The following software can be used for VPN with TUN/TAP:

* Tinc (http://tinc-vpn.org)

* Virtual TUNnel (http://vtun.sourceforge.net)

In order to reach hosts behind VPN container you must configure it to use a VETH interface instead a VENET one, at least with an OpenVPN server.

With a VENET interface you will only reach the VPN container.

To use a VETH device follow [[Veth]] article.

If you insist on using a VENET interface and need to reach hosts behind the OpenVPN VE then you can use source NAT. You need to mangle source packets so that they appear to originate from the OpenVPN server VE.

Using the default venet0:0 interface on the container, tinc seems to have problems as it complains the port 655 is already used on 0.0.0.0.

Netstat shows that the port 655 is available:

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root@132 / [3]# netstat -l

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Starting the Tincd daemon where it complains that port 655 is not available:

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root@132 / [4]# tincd -n myvpn

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An echo to Bindv6only (see [http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=440150 discussion here]) seems to resolve the problem:

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root@132 / [12]# echo 1 > /proc/sys/net/ipv6/bindv6only

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Or put in your /etc/sysctl.conf file:

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net.ipv6.bindv6only = 1

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Then apply the changes with:

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root@132 / [14]# sysctl -p

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Unfortunately, you are limited to [http://forum.openvz.org/index.php?t=msg&th=4280&goto=22066&#msg_22066 non-persistent tunnels inside the VEs]:

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# tunctl

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Get a patched tunctl [https://github.com/xl0/uml-utilities here], and run it with the -n option. It will create a non-persistent tun device and sleep instead of terminating, to keep the device from deletion. To remove the tunnel, kill the tunctl process.

If NAT is needed within the VE, this error will occur on attempts to use NAT:

iptables v1.4.3.2: can't initialize iptables table `nat': Table does not exist (do you need to insmod?)

Perhaps iptables or your kernel needs to be upgraded.

Solution:

* use recent kernel

: <code>vzctl set $CTID --netfilter full --save</code>

* [http://vtun.sourceforge.net Virtual TUNnel]

* [http://openvpn.net OpenVPN]