VLAN

A virtual LAN (Local Area Network) is a logical subnetwork that can group together a collection of devices from different physical LAN.

1-1 Create VLAN

Imagine that we have different departments on your company and you want to separate each department based on their employees. So, with the VLAN concept you can create a VLAN and then assign different ports to these VLANs.

Vlan 10-20-30 in Switch1

In the above picture, we have 3 departments, each of which is assigned to unique VLAN. let's configure switch:

sw# conf t
sw(config)# vlan 10
sw(config-vlan)# name Management
sw(config-vlan)# exit
sw(config)# vlan 20
sw(config-vlan)# name IT
sw(config-vlan)# exit
sw(config)# vlan 30
sw(config-vlan)# name SALES
sw(config-vlan)# exit

For viewing created VLANs, we enter this command:

sw# show vlan 

VLAN 1 is a default VLAN in Cisco devices. VLAN from 1002-1005 are for other protocols. VLAN from 1006- 4094 is called Extended VLAN.

1-2 Access Switch Ports to Vlan

In above picture, a PC in VLAN 10 is connected to port Fa0/1 switch. So, we can write this command to access port Fa0/1 to VLAN 10:

sw(config)# int fa0/1
sw(config-vlan)# switchport mode access
sw(config-vlan)# switchport access vlan 10
sw(config-vlan)# exit

Now, if we enter show vlan:

Now we do it for other ports:

sw(config)# int fa0/2
sw(config-vlan)# switchport mode access
sw(config-vlan)# switchport access vlan 20
sw(config-vlan)# exit
sw(config)# int fa0/3
sw(config-vlan)# switchport mode access
sw(config-vlan)# switchport access vlan 30
sw(config-vlan)# exit

and the result is:

1-3 Native Vlan

By default in Cisco switches , Vlan 1 is a native Vlan. It means, untagged traffic carries in this vlan. We'll know how to change Native Vlan.