Virtual LAN

LAN is a type of network. That we have studied.

A computer is considered as the part of the LAN if it is physically connected to the LAN. What happed if we want a virtual connection between two computers belonging to the two different LANs?

We can define the VLAN as:

VLAN stands for virtual local area network. In virtual LAN the Network is configured by software, not by physical wiring.

Let us elaborate this idea by an example:

 A switched LAN in an organization where 10 computers are group in three LANs that are connected through a switch. The first four computers are connected to first LAN group, second three computers are connected to the second LAN group and third three computers are connected to the third LAN group. The LAN is configured to allow the management.

What would happen if the Administration wants to move two computers from first LAN to the third LAN? The LAN configuration would need to be changed. It means to rebuild the network. The problem repeat, if after some weeks the group member wants to join the previous group. In switched LAN change means physical change in network configuration.

the switch LAN divided into VLANs. The whole idea of VLAN is connect the LAN logically not physically.

LANs that are connected logically are called VLANs.

Each VLAN is a working Group in an organization. If a person is move from one group to another, there is no need to change locally. A group membership is defined in software not in hardware. Any computer can be moved locally from one to another.

All members belonging to a VLAN can receive broadcast messages send to that particular VLAN. It means that if a computer is move from VLAN 1 to the VLAN 2 then it receives all the messages from the VLAN 2 not to VLAN 1. It is obvious that all the problems that we faced previous network have solved. It’s easy to move a computer from one LAN to another by software then physically configured the network.

VLAN technology even allows the grouping of computers that are connected to different switches in a VLAN. A backbone local area network with two switches and three VLANs.

Computers of switch A and switch B are belonging to both VLANs. This is also a plus point for the higher  business. For example companies have two branches. Each branch has its own switched LAN. On the basis of this VLAN the people in the one branch and the other branch are in the same work group. 

They are connected to different physical LANs.

From the above three examples, we can define VLAN characteristics:

VLANS create broadcast domain. The computers in a VLAN communicate with one another as though they belong to different physical segment.

Membership:

What characteristics can be used to group computers in a VLAN? Vendors use different characteristics such as port numbers, Mac addresses, IP addresses, IP multicast addresses, or a combination of two or more of these.

Port Number:

Some VLAN vendors use switches port numbers as membership characteristics. For example, the administrator can define that station connecting to ports 1, 2, 3 and 7 belong to VLAN1 station connecting to ports 4, 10, and 12 belong to VLAN2 and so on.

MAC Addresses:

Some VLAN vendors use the 48-bit MAC address as a membership characteristic. For example, the administrator can stipulate that station having MAC addresses E21342A12334 and F2A123BCD341 belong to VLAN1.

IP Addresses:

Some VLAN vendors use the 32-bit IP Addresses as membership characteristics. For example, the administrator can stipulate that station having that IP Addresses 181.34.23.67, 181.34.23.72, 181.34.23.98 and 181.34.23.112 belong to VLAN1.

Multi-cast IP Addresses:

Some VLAN vendors use the multi-cast IP Addresses as membership characteristics. Multicasting at the IP layer in now translates to multi-casting at the data link layer.