Virtual Networks

Virtual Networks covers a vast variety of topics.

Virtual Private Network

VPN, such as:

• OpenVPN

Virtual Local Area Network

VLAN

Virtual Ethernet Bridge

In Linux, the brctl command is used for setting up (Virtual) Ethernet Bridges.

Creating TAP/TUN devices

Assuming the Linux kernel is compiled to support TAP/TUN and the appropriate device node has been created in /dev/net, there are several ways to create TAP/TUN devices:

• using tunctl command (from UML utilities)
• using the openvpn command (from OpenVPN)
• using the ip command (from iproute2):

# ip tuntap add mode tap

will add a new tapX device

The new tapX can be added to a Virtual Ethernet Bridge:

# brctl addif brY tapX
# ip link set tapX up

VirtualBox and Linux Ethernet Bridges

VirtualBox allows a guest to have multiple network interfaces, any of which can be connected to host Ethernet Bridges. However, probably due to the multi-platform nature of VirtualBox, the bridged interfaces do not appear as normal Linux Ethernet Bridge interfaces, eg. when viewed using:

brctl show

Also, the VirtualBox documentation clearly discusses the bridge mode as "connecting to a special interface alongside the physical interface".

External links

• Why does adding a non-VLANed interface to a bridge break the VLANed interfaces? - the answer is a good coverage of setting up tagged VLANs on Virtual Bridges, from unix.stackexchange.com
• Tun/Tap interface tutorial
• Tap Interfaces and Linux Bridge
• my answer to Reach LXC container from a virtualbox guest on the same host at serverfault.com
• Thinking of using a VPN? Check the privacy policy first at EFA.com.au