Virtual Ethernet device

Virtual Ethernet device is an Ethernet-like device that can be used inside a container. Unlike a venet network device, a veth device has a MAC address. Therefore, it can be used in more configurations. When veth is bridged to a CT0 network interface (e.g., eth0), the container can act as an independent host on the network. The container's user can set up all of the networking himself, including IPs, gateways, etc.

A virtual Ethernet device consist of two Ethernet devices, one in CT0 (e.g., vethN.0) and a corresponding one in CT (e.g., eth0) that are connected to each other. If a packet is sent to one device it will come out the other device.

Virtual Ethernet device usage

Kernel module

The vzethdev module should be loaded. You can check it with the following commands.

# lsmod | grep vzeth
vzethdev                8224  0
vzmon                  35164  5 vzethdev,vznetdev,vzrst,vzcpt
vzdev                   3080  4 vzethdev,vznetdev,vzmon,vzdquota

In case it is not loaded, load it:

# modprobe vzethdev

MAC addresses

The following steps to generate a MAC address are not necessary, since newer versions of vzctl will automatically generate a MAC address for you. These steps are provided in case you want to set a MAC address manually.

You should use a random MAC address when adding a network interface to a container. Do not use MAC addresses of real eth devices, because this can lead to collisions.

MAC addresses must be entered in XX:XX:XX:XX:XX:XX format.

There is a utility script available for generating MAC addresses: http://www.easyvmx.com/software/easymac.sh. It is used like this:

chmod +x easymac.sh
./easymac.sh -R

Adding veth to a CT

vzctl set <CTID> --netif_add <ifname>[,<mac>,<host_ifname>,<host_mac>,<bridge>]

Here

• ifname is the Ethernet device name in the CT
• mac is its MAC address in the CT
• host_ifname is the Ethernet device name on the host (CT0)
• host_mac is its MAC address on the host (CT0)
• bridge is an optional parameter which can be used in custom network start scripts to automatically add the interface to a bridge. (See the reference to the vznetaddbr script below and persistent bridge configurations.)

Note: All parameters except ifname are optional. Missing parameters, except for bridge, are automatically generated, if not specified. This is the preferred method.

Example:

vzctl set 101 --netif_add eth0 --save

If you want to specify everything:

vzctl set 101 --netif_add eth0,00:12:34:56:78:9A,veth101.0,00:12:34:56:78:9B --save

If you want to specify the bridge and autogenerate the other values:

vzctl set 101 --netif_add eth0,,,,vmbr1 --save

Removing veth from a CT

vzctl set <CTID> --netif_del <dev_name>|all

Here

• dev_name is the Ethernet device name in the CT.

Note: If you want to remove all Ethernet devices in CT, use all.

Example:

vzctl set 101 --netif_del eth0 --save

Common configurations with virtual Ethernet devices

Module vzethdev must be loaded to operate with veth devices.

Simple configuration with virtual Ethernet device

Assuming you have 192.168.0.0/24 on your LAN, you will learn how to integrate a container in this LAN using veth.

Start a CT

[host-node]# vzctl start 101

Add veth device to CT

[host-node]# vzctl set 101 --netif_add eth0 --save

This allocates a MAC address and associates it with the host eth0 port.

Configure devices in CT0

The following steps are needed when the CT is not bridged to a CT0 interface. That is because the CT is connected to a virtual network that is "behind" CT0. CT0 must forward packets between its physical network interface and the virtual network interface where CT is located. The first step below to configure the interface is not necessary if the container has been started, since the device will have been initialized.

[host-node]# ifconfig veth101.0 0
[host-node]# echo 1 > /proc/sys/net/ipv4/conf/veth101.0/forwarding
[host-node]# echo 1 > /proc/sys/net/ipv4/conf/veth101.0/proxy_arp
[host-node]# echo 1 > /proc/sys/net/ipv4/conf/eth0/forwarding
[host-node]# echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp

Configure device in CT

[host-node]# vzctl enter 101
[ve-101]# /sbin/ifconfig eth0 0
[ve-101]# /sbin/ip addr add 192.168.0.101 dev eth0
[ve-101]# /sbin/ip route add default dev eth0

Notes:

• Until you ifconfig eth0 it won't appear. When you do it will use the mac address netif_add added earlier
• 192.168.0.101 is chosen to be an unrouteable private ip address. Where 101 reminds you that it is node 101.
• The "ip route" tells all traffic to head to "device eth0"
• In theory you could use dhcpd with OpenVZ and dhclient to pick up an DHCP address from your router instead of hardwiring it
  • http://openvz.org/pipermail/users/2005-November/000020.html

Add route in CT0

[host-node]# ip route add 192.168.0.101 dev veth101.0

Using a directly routed IPv4 with virtual Ethernet device

Situation

Hardware Node (HN/CT0) has 192.168.0.1/24 with router 192.168.0.254.

We also know that IPv4 10.0.0.1/32 is directly routed to 192.168.0.1 (this is called a fail-over IP).

We want to give this directly routed IPv4 address to a container (CT).

Start container

[host-node]# vzctl start 101

Add veth device to CT

[host-node]# vzctl set 101 --netif_add eth0 --save

This allocates a MAC address and associates it with the host eth0 port.

Configure device and add route in CT0

[host-node]# ifconfig veth101.0 0
[host-node]# ip route add 10.0.0.1 dev veth101.0

You can automatize this at VPS creation by using a mount script $VEID.mount.

The problem here is that the veth interface appears in CT0 after VPS has started, therefore we cannot directly use the commands in the mount script. We launch a shell script (enclosed by { }) in background (operator &) that waits for the interface to be ready and then adds the IP route.

Contents of the mount script /etc/vz/conf/101.mount:

#!/bin/bash
# This script source VPS configuration files in the same order as vzctl does

# if one of these files does not exist then something is really broken
[ -f /etc/vz/vz.conf ] || exit 1
[ -f $VE_CONFFILE ] || exit 1

# source both files. Note the order, it is important
. /etc/vz/vz.conf
. $VE_CONFFILE

# Configure veth with IP after VPS has started
{
  IP=X.Y.Z.T
  DEV=veth101.0
  while sleep 1; do
    /sbin/ifconfig $DEV 0 >/dev/null 2>&1
    if [ $? -eq 0 ]; then
      /sbin/ip route add $IP dev $DEV
      break
    fi
  done
} &

Make sure IPv4 forwarding is enabled in CT0

[host-node]# echo 1 > /proc/sys/net/ipv4/ip_forward
[host-node]# echo 1 > /proc/sys/net/ipv4/conf/eth0/forwarding
[host-node]# echo 1 > /proc/sys/net/ipv4/conf/veth101.0/forwarding

You can permanently set this by using /etc/sysctl.conf.

Configure device in CT

1. Configure IP address

2. Add gateway

3. Add default route

[ve-101]# /sbin/ifconfig eth0 10.0.0.1 netmask 255.255.255.255
[ve-101]# /sbin/ip route add 192.168.0.1 dev eth0
[ve-101]# /sbin/ip route add default via 192.168.0.1

In a Debian container, you can configure this permanently by using /etc/network/interfaces:

auto eth0
iface eth0 inet static
        address 10.0.0.1
        netmask 255.255.255.255
        up /sbin/ip route add 192.168.0.1 dev eth0
        up /sbin/ip route add default via 192.168.0.1

Virtual Ethernet device with IPv6

See the VEs and HNs in same subnets article.

Virtual Ethernet devices can be joined in one bridge

Perform steps 1 - 4 from Simple configuration chapter for several containers and/or veth devices

Create bridge device

[host-node]# brctl addbr vzbr0

Add veth devices to bridge

[host-node]# brctl addif vzbr0 veth101.0
...
[host-node]# brctl addif vzbr0 veth101.n
[host-node]# brctl addif vzbr0 veth102.0
...
...
[host-node]# brctl addif vzbr0 vethXXX.N

Configure bridge device

[host-node]# ifconfig vzbr0 0

Add routes in CT0

[host-node]# ip route add 192.168.101.1 dev vzbr0
...
[host-node]# ip route add 192.168.101.n dev vzbr0
[host-node]# ip route add 192.168.102.1 dev vzbr0
...
...
[host-node]# ip route add 192.168.XXX.N dev vzbr0

Thus you'll have more convinient configuration, i.e. all routes to containers will be through this bridge and containers can communicate with each other even without these routes.

Making a veth-device persistent

According to http://bugzilla.openvz.org/show_bug.cgi?id=301 , a bug that stopped the veth device persistent was "Obsoleted now when --veth_add/--veth_del are introduced"

See http://wiki.openvz.org/w/index.php?title=Virtual_Ethernet_device&diff=5990&oldid=5989#Making_a_veth-device_persistent for a workaround that used to be described in this section.

That's it! At this point, when you restart the CT you should see a new line in the output, indicating that the interface is being configured and a new route being added. And you should be able to ping the host, and to enter the CT and use the network.

Making a bridged veth-device persistent

Like the above example, here it is how to add the veth device to a bridge in a persistent way.

vzctl include a 'vznetaddbr' script, which makes use of the bridge parameter of the --netif_add switch.

Just create /etc/vz/vznet.conf containing the following.

#!/bin/bash
EXTERNAL_SCRIPT="/usr/sbin/vznetaddbr"

The script uses 'vmbr0' as default bridge name when no bridge is specified.

Virtual Ethernet devices + VLAN

This configuration can be done by adding vlan device to the previous configuration.

See also

• Virtual network device
• Differences between venet and veth
• Using private IPs for Hardware Nodes
• Patch: Disable venet interface
• Troubleshooting: Bridge doesn't forward packets

External links

• Linux IPv6 HOWTO, a chapter about radvd
• 2 veth with 2 bridges setup