VLANs can easily be implemented on Cisco switches to improve network layout as well as security and efficiency. With VLANs we are able to, with software, logically separate ports on a switch (or other network device) into discrete groups that function as their own independent LANs. For example, let’s say we are designing a network for a small school that will provide access to the Internet via a 48 port switch. We want to separate the Faculty and Staff network devices from Students and Guests.
For our internal network we will be using a 192.168.1.0/24 network address, and we will divide our network into two subnets, 192.168.1.0/25 for the faculty and staff (Fac/Staff) and 192.168.1.128/25 for students and the Public (Students). Now let’s set up our VLANs on the switch.
In IOS, enter config mode
Switch>;enable Switch#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#
Next we will create the VLANs and give them a name. I don’t think naming the VLAN is required, but it is recommended.
Switch(config)#vlan 10 Switch(config-vlan)#name facstaff Switch(config-vlan)#exit Switch(config)#vlan 20 Switch(config-vlan)#name students Switch(config-vlan)#end %SYS-5-CONFIG_I: Configured from console by console
Let’s take a look at our VLAN set up.
Switch#show vlan brief VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4 Fa0/5, Fa0/6, Fa0/7, Fa0/8 Fa0/9, Fa0/10, Fa0/11, Fa0/12 Fa0/13, Fa0/14, Fa0/15, Fa0/16 Fa0/17, Fa0/18, Fa0/19, Fa0/20 Fa0/21, Fa0/22, Fa0/23, Fa0/24 Gig1/1, Gig1/2 10 facstaff active 20 students active 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active Switch#
VLAN 1 is the default VLAN and all ports are members of it. VLANs 1002 – 1005, are also assigned by default, as show. We are going to split the 24 FastEthernet ports between the two new VLANs. We will take advantage of the ability in IOS to configure a range of interfaces at a time.
Switch#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#interface range fastEthernet 0/1-12 Switch(config-if-range)#switchport mode access Switch(config-if-range)#switchport access vlan 10 Switch(config-if-range)#exit Switch(config)#interface range fastEthernet 0/13-24 Switch(config-if-range)#switchport mode access Switch(config-if-range)#switchport access vlan 20 Switch(config-if-range)#exit Switch(config)#end %SYS-5-CONFIG_I: Configured from console by console Switch# show vlan brief VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1 default active Gig1/1, Gig1/2 10 facstaff active Fa0/1, Fa0/2, Fa0/3, Fa0/4 Fa0/5, Fa0/6, Fa0/7, Fa0/8 Fa0/9, Fa0/10, Fa0/11, Fa0/12 20 students active Fa0/13, Fa0/14, Fa0/15, Fa0/16 Fa0/17, Fa0/18, Fa0/19, Fa0/20 Fa0/21, Fa0/22, Fa0/23, Fa0/24 1002 fddi-default active 1003 token-ring-default active 1004 fddinet-default active 1005 trnet-default active