VLAN for linux

What is VLAN ?

VLAN, Virtual Local Area Network, is somehow a several virtual network co-exist in a same switch port or interface by using the software configurations but not using hardware interface.

In the case whereby all workstations which connected to a same L2 switch in LAN X, are able to communicate within each other. If a workstation from LAN X is wish to communicate with LAN Y, then a router is needed.

VLAN, is actually an act of dividing the communications between few different network virtually by using a single switch device. A single switch port in a VLAN-capable switch can carry packets from multiple virtual LANs and linux can understand the format of these Ethernet frames.

VLAN, is known as IEEE 802.1Q and aslo known as VLAN tagging. More info on Wikipedia.

What are the advantages using VLAN ?

• Performance
• Easy to manage
• Security
• Trunks
• Save the work of 'hardware configurations' whenever there is any changing of physical location for any device.

How to configure VLAN ?

The 802.1Q package has been pre-patch in kernel 2.4. Any distributions which are earlier than this, should download and compile/patch the kernel before proceed.

First of all, you need/must to modprobe the module by :

# modprobe 8021q

Then you should make sure the interface where you want to add the VLAN is UP and RUNNING.

For example,

2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:02:44:73:ed:64 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.254/24 brd 192.168.0.255 scope global eth0
    inet6 fe80::202:44ff:fe73:ed64/64 scope link
       valid_lft forever preferred_lft forever

To bring up the interface

# ifconfig eth0 up

# ip link set eth0 up

To bring down the interface

# ifconfig eth0 up

# ip link set eth0 up

Case 1 : You will want to add an VLAN 8 to interface eth0 and configure as 10.10.10.10/25 for this VLAN interface. Then remove it.

To add a new VLAN

# vconfig add eth0 8

To bring up the VLAN interface and configure IP

# ifconfig eth0.8 up

# ifconfig eth0.8 10.10.10.10 netmask 255.255.255.128 broadcast 10.10.10.127

To remove the VLAN interface

# vconfig rem eth0.8