Creating VLANs

Today this tutorial is going to be talking about creating VLANs (Virtual Local Area Networks) with a Cisco Catalyst switch. By creating a VLAN you are separating the network, why would you do this? There are some several reasons, like separating your production network from a guest network, and separating a test environment from a production network. This all adds security to your network. You can separate core critical network components from the rest of the production network for added security, easier troubleshooting along with separating or segmenting your network. This is breaking up the broadcast domains into smaller chucks, which will improve your network performance. Let’s get started!

By default if no configuration is applied to a switch, you just turned it on and plugged in networking devices, all of them are in a VLAN already, called VLAN 1. This is great if you know nothing about switch configuration and want something that works out of the box. But this also provides a security risk and if enough devices are connected this will slow down your network performance.

VLANs separate the network so in order for VLANs to communicate a layer three device (router) is needed in order for VLAN communication. When you dive into VLANs there is a lot of information! For this tutorial we are just going to be creating a VLAN and that’s it.

So let’s create a VLAN on a single switch.

  • For this tutorial we are going to put the ports fa0/1 – 10 into an access mode
  • Then apply a VLAN 2 on ports fa0/1 – 10.

(Sample Output) 


Switch>enable
Switch#configure terminal
Switch(config)#interface range fastEthernet 0/1 - 10
Switch(config-if-range)#switchport mode access
Switch(config-if-range)#switchport access vlan 2

%LINK-5-CHANGED: Interface Vlan2, changed state to up
% Access VLAN does not exist. Creating vlan 2
Switch(config-if-range)#exit

If we issue the command show vlan in privilege EXEC mode we can see that VLAN 2 has been created and the interfaces VLAN 2 is configured to (Sample Output) 


Switch#show vlan

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    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
2    VLAN0002                         active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
                                                Fa0/5, Fa0/6, Fa0/7, Fa0/8
                                                Fa0/9, Fa0/10
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        0      0
2    enet  100002     1500  -      -      -        -    -        0      0
1002 fddi  101002     1500  -      -      -        -    -        0      0  
1003 tr    101003     1500  -      -      -        -    -        0      0  
1004 fdnet 101004     1500  -      -      -        ieee -        0      0  
1005 trnet 101005     1500  -      -      -        ibm  -        0      0  

Remote SPAN VLANs
------------------------------------------------------------------------------
Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------
Switch#

Although numbers are ok, let’s create a named VLAN. A named VLAN helps us remember what the purpose of that VLAN does. The steps are almost the same here is the following, you could also change VLAN 2 into a named VLAN as well by doing lines 3 and 6.

  • For this tutorial we are going to put ports fa0/11 -20 into access mode.
  • Then apply a name VLAN called Support on ports fa0/11 – 20.

(Sample Output)


Switch(config)#interface vlan 3
Switch(config-if)#exit
Switch(config)#vlan 3

%LINK-5-CHANGED: Interface Vlan3, changed state to up
Switch(config-vlan)#name Support
Switch(config-vlan)#exit
Switch(config)#interface range fa0/11 - 20
Switch(config-if-range)#switchport mode access
Switch(config-if-range)#switchport access vlan 3
Switch(config-if-range)#exit
Switch(config)#exit

If we issue the command show vlan in privilege EXEC mode we can see that VLAN 3 (Support) has been created and the interfaces VLAN 3 (Support) is configured to. (Sample Output)


Switch#show vlan

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/21, Fa0/22, Fa0/23, Fa0/24
2    VLAN0002                         active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
                                                Fa0/5, Fa0/6, Fa0/7, Fa0/8
                                                Fa0/9, Fa0/10
3    Support                          active    Fa0/11, Fa0/12, Fa0/13, Fa0/14
                                                Fa0/15, Fa0/16, Fa0/17, Fa0/18
                                                Fa0/19, Fa0/20
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        0      0
2    enet  100002     1500  -      -      -        -    -        0      0
3    enet  100003     1500  -      -      -        -    -        0      0
1002 fddi  101002     1500  -      -      -        -    -        0      0  
1003 tr    101003     1500  -      -      -        -    -        0      0  
1004 fdnet 101004     1500  -      -      -        ieee -        0      0  
1005 trnet 101005     1500  -      -      -        ibm  -        0      0  

Remote SPAN VLANs
------------------------------------------------------------------------------
Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------
Switch#

So in the end we have three VLANs on this switch, VLAN 1, VLAN 2, VLAN 3 (Support). If we connected PCs to these three different VLANs none of them would be able to communicate, because each VLAN is like a different network. So you would need to configure a router in order for inter-vlan commutation to work also called router on a stick. I hope this tutorial was helpful if you have questions, comment below.

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