Virtual network device

Virtual network device (venet) is the default network device for a container. This network device looks like a point-to-point connection between container and the host system. It does packet switching based on IP header. This is a default network device for container (an alternative is veth device).

Venet drop ip-packets from the container with a source address, and in the container with the destination address, which is not corresponding to an ip-address of the container.

Venet device is created automatically on container start. Vzctl scripts set up an appropriate IP address and other settings on venet inside a container.

Kernel module

First of all, check that vznetdev module is loaded:

# lsmod | grep vznetdev

If it is not, load the module:

# modprobe vznetdev

You might want to check /etc/init.d/vz script to make sure the module gets loaded during startup.

Adding IP address to a container

vzctl set <CTID> --ipadd <IP1>[,<IP2>,...] [--save]

Note: This option is incremental, so IP addresses are added to already existing ones.

Example

vzctl set 101 --ipadd 10.0.0.1 --save

After executing this command IP address 10.0.0.1 will be added to container 101 and IP configuration will be saved to a container configuration file.

Removing IP address from a container

vzctl set <CTID> --ipdel <IP1>[,<IP2>,...] [--save]
vzctl set <CTID> --ipdel all [--save]

Example

vzctl set 101 --ipdel 10.0.0.1

After executing this command IP address 10.0.0.1 will be removed from container 101, but IP configuration will not be changed in container config file. And after container reboot IP address 10.0.0.1 will be assigned to this container again.

Sysctl

You will need to configure some sysctl parameters to get your venet devices working. Please have a look at the Installation_on_Debian#sysctl section.

IPv6

To setup IPv6 networking with venet you'll need to enable the following in your sysctl.conf:

   # IPv6 Packet Forwarding and Proxy NDP 
   net.ipv6.conf.default.forwarding = 1
   net.ipv6.conf.all.forwarding     = 1
   net.ipv6.conf.default.proxy_ndp = 1
   net.ipv6.conf.all.proxy_ndp = 1

In IPv6 you can't control forwarding per device, forwarding control has to take place in ip6tables, so all interfaces will forward IPv6 traffic.

If you enable IPv6 forwarding for your interfaces, Linux assumes your host to act like a router and will ignore 'Router Advertisments' (see Neighbor Discovery Protocol or Linux IPv6 Howto).

You will as well need to configure a new v6 default gateway for your host:

   ip addr add 2620:0:2d0:1::193/64 dev eth0
   route -6 add default gw 2620:0:2d0:1::1

You can add these commands to your existing network configuration on Debian/Linux:

   iface eth0 inet static
       address 64.131.90.7
       netmask 255.255.255.240
       network 64.131.90.0
       broadcast 64.131.90.15
       gateway 64.131.90.1
       up   ip addr add 2620:0:2d0:1::193/64 dev eth0
       up   route -6 add default gw 2620:0:2d0:1::1
       down ip addr del 3620:0:2d0:1::193/64 dev eth0

Specific aspects of venet network device

No ARP protocol support

Venet network device is explicitly NOARP, so there is no MAC address. Consequently, it's not possible to make broadcasts inside a container, so software like Samba server or DHCP server, will not function (under a container with a venet network device).
Please consider use of veth network device if you need this feature

No bridge support

Venet network device cannot be bridged together and/or with other devices.
Please consider use of veth network device if you need this feature

No possiblity to assign an IP from the CT

With venet device, only OpenVZ hardware node administrator can assign an IP address to a container.
Please consider use of veth network device if you need this feature

See also

• Veth
• Differences between venet and veth