Using vlans to logically partition your switches you do away with the need to purchase any further equipment to segment your network.
Lets look at partitioning the switch into logical segments. When the switch first arrives out of the box or is defaulted back to factory defaults all of the ports are in one common vlan known as VLAN 1. This entity is also referred to as the NATIVE VLAN.
When you connect your network hosts into the ports all subsequent traffic which they generate will be placed into the vlan of that connected port, in the default case this would be V1, all devices which are connected to this vlan are going to see all other hosts broadcast traffic, so here we see that by merely placing the devices into a vlan does not mean the broadcasts will cease.
We are going to use and example 24 port switch to see how to configure the device.
In this exercise the task is to create 3 additional vlans and place 8 ports into each vlan, the result ought to be that the switch has 3 new broadcast domain.
Switch#
Switch#configure terminal
Switch(config)#vlan 2
Switch(config-vlan)#exit
Switch(config)#vlan 3
Switch(config-vlan)#exit
Switch(config)#vlan 4
Switch(config-vlan)#exit
In the example above the commands used created and additional 3 vlans on our switch
Switch(config)#interface range fastethernet 0/1 – 8
Switch(config-if-range)#switchport mode access
Switch(config-if-range)#switchport access vlan 2
Switch(config-if-range)#exit
Switch(config)#interface range fastethernet 0/9 – 16
Switch(config-if-range)#switchport mode access
Switch(config-if-range)#switchport access vlan 3
Switch(config-if-range)#exit
Switch(config)#interface range fastethernet 0/17 – 24
Switch(config-if-range)#switchport mode access
Switch(config-if-range)#switchport access vlan 4
In the commands above:
The ports numbered from 1 through 8 were assigned to v2
The ports numbered from 9 through 16 were assigned to v3
The ports numbered from 17 through 24 were assigned to v4
Switch(config-if-range)#end
Switch#copy run start
Finally we save our configuration.
In all our fictional switch now has 3 new broadcast domains, by populating all of our switchports with hosts it would have the effect of securing the visibility of host on one broadcast domain from seeing hosts on one of the other broadcast domains from a security stand point this is ideal and from a performance point of view it achieves exactly what we need
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