Virtual network device

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Virtual network device (venet) is the default network device for a container. Due to Layer 3 employed by OpenVZ's venet, 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.

Contents

[edit] Usage

[edit] 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.

[edit] Adding IP address to a container

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

Address can optionally have a netmask specified in the CIDR notation (e.g. 10.1.2.3/25).

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

[edit] Example

vzctl set 101 --ipadd 10.0.0.1  --save
vzctl set 101 --ipadd fd00::101 --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.

[edit] Removing IP address from a container

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

[edit] Example

vzctl set 101 --ipdel 10.0.0.1
vzctl set 101 --ipdel fd00::101

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.

[edit] Specific aspects of venet network device

Yellowpin.svg Note: If you require a feature which venet is lacking (from the list below), please consider using veth device (which have layer 2 support.)

[edit] 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).

[edit] No bridge support

Venet network device cannot be bridged together and/or with other devices.

[edit] 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.

[edit] Limited packet sniffing support

Some applications using libpcap and similar packages will report an error.

[edit] No full support of IPv6 stack

venet devices are not fully IPv6 compliant. They do not properly support MAC addresses and consequently link local addresses and can not play nice with neighbor discovery or router advertisements, router discovery, or auto-conf. They also require additional modifications to the layer 3 forwarding behaviour of the host via sysctl, to get your venet devices working. Please have a look at the Quick installation#sysctl section.

veth devices do require iptables and ip6tables exceptions on the host for each VE address.

You'll need to use the veth bridging device if you want full IPv6 compliance. See the VEs and HNs in same subnets article for an example.

[edit] See also

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