VLAN ( Virtual Local Area Network ) | Configure VLAN on Cisco Switch.

VLAN ( Virtual Local Area Network ) 

Using VLAN ( Virtual Local Area Network ) you can divide a network into multiple LAN's without any physical change in the network.

Suppose if you have many departments in your company and you want to separate all the LAN networks from each other then VLAN will help you to divide your network into multiple segments without any physical change in the wires or network.

Also you have the managing authority to make any change in the VLAN. You can allow one VLAN to access the another one in the network. Simply you can say that you can partition your existing network using VLAN without any physical change.

In Above scenario you can see that there are multiple switches created different VLAN. Using a single physical network has divided into multiple networks i.e. Engineering VLAN, Marketing VLAN and Accounting VLAN.

VLAN defines the broadcast domain. A broadcast domain is a set of devices will receive broadcast frames orgniting from a device within the network. All the broadcast domains are bounded with a Routers because router do not generate broadcast. Every layer 2 switches create broadcast domains as per the configuration of the switch. Using VLAN all the broadcast domains can be managed accordingly. Traffic cannot pass directly in two different VLAN's within a single or multiple switches.

If you want to connect two different VLAN's you must needed a router or layer 3 switch because VLAN's are associated with IP networks and to perform routing between VLAN's you must required a Router or layer 3 device as routing is not possible on layer 2 devices.

VLAN Range

VLANs Numbers	Range	Usage
1	Normal	Cisco default. You can use this VLAN, but you cannot modify or delete it.
2—1005	Normal	You can create, use, modify, and delete these VLANs.
1006—4094	Extended	You can create, name, and use these VLANs. You cannot change the following parameters: State is always active. VLAN is always enabled. You cannot shut down these VLANs.
3968—4047 and 4094	Internally allocated	These 80 VLANs, plus VLAN 4094, are allocated for internal use. You cannot create, delete, or modify any VLANs within the block reserved for internal use.

Why use VLAN's.

• To control broadcast domains VLAN can be used. Suppose if you have a broadcast domain and you have 10 users in this broadcast domain but you want to send broadcast traffic only 5 selected users in this case you can create a VLAN and can separate other users in a broadcast domain.

• VLAN's provides the best Security. You can manage every port of the switch and can manage all the broadcast domains. One network will not be able to connect with the another one if they have not permitted.

• Simple Administration- Once the VLAN's are created on a Switch then it can be easy to handle by network administrator. No need to make any physical change in the network. Network paths can be changed logically if there is some changes required.

•  Cost Effective- VLAN's are used to create broadcast domain which is very cheaper in comparison of routers.

• High Performance- VLAN's increase the performance of a network as well because it stops the inneccessory traffic in the network and only the requred traffic is passed within a VLAN.

How to configure a VLAN

To configure a VLAN on Cisco switch follow below commands.

First of all enter in the global configuration mode with command "configure Terminal".

Now use command VLAN "vlan id" to create a VLAN as below.

S1(config)#vlan 10

or

S1(config)#vlan 20

VLAN is created now, use exit command to quit from the VLAN configuration mode.

S1(config-vlan)#exit

If you want to assign a VLAN to your switch port then enter the Ethernet id where you want to assign the VLAN ID as below.

S1(config)#interface fastEthernet 0/1

And now run below command to assign the VLAN.

S1(config-if)#switchport access vlan 10

Now VLAN is created and assigned to the desired port. Follow the same process for other ports with different VLAN's.