Configuring VLANs

Before you begin creating VLANs, you should determine whether the switch will participate in a VTP domain that will synchronize VLAN configuration with the rest of the network. You must also enable a trunk connection if you want to use VLANs across multiple switches.The steps to configure a VLAN are:
Enable VTP (optional)
Enable Trunking (optional)
Create VLANs
Assign VLANs to ports Verifying VLANs
Verifying the VLAN Configuration
Verifying VLAN Membership
Prevent VLANs from Crossing a Trunk Link
Prevent Individual VLANs from Crossing a Trunk Link
Verifying Trunk Links
Verifying VTP Information
Enabling VTP Pruning Enable VTP
When adding a new switch to an existing domain, it is a good idea to add it in VTP client mode. This will prevent the switch from propagating any incorrect VLAN information to other switches. In this example we will setup a new VTP domain and place the switch into server mode. The password puts VTP into secure mode. Every switch in the management domain must have a password assigned to it for the management domain to function properly in secure mode. Switch1#configure terminalEnter configuration commands, one per line. End with CNTL/ZSwitch1(config)#vtp serverSwitch1(config)#vtp domain ciscotestSwitch1(config)#vtp password ccnaEnable Trunking
The next step is to create a trunk connection with the other switches that will be sharing VLAN information. To enable trunking on a port, enter interface configuration mode for the desired port, and then use the trunk command with the appropriate option: Switch1#configure terminalSwitch1(config)#interface f 0/26Switch1(config-if)#trunk on
trunk Command Options
Option
Function
on
Puts the port into permanent trunking mode and negotiates to convert the link into a trunk link. The port becomes a trunk port even if the neighboring port does not agree to the change.
off
Puts the port into permanent nontrunking mode and negotiates to convert the link into a nontrunk link. The port becomes a nontrunk port even if the neighboring port does not agree to the change.
desirable
Makes the port actively attempt to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to on, desirable, or auto mode.
auto
Makes the port willing to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to on or desirable mode. This is the default mode.
negotiate
Puts the port into permanent trunking mode but prevents the port from generating DTP frames. You must configure the neighboring port manually as a trunk port to establish a trunk link.Create VLANs
To create a VLAN, enter global configuration mode and use the vlan command with the VLAN identifier (1-1005) and its name. Switch1#configure terminalSwitch1(config)#vlan 5 name accountingSwitch1(config)#vlan 6 name management Assign VLANs to Ports
Now that the VLAN has been created, you can statically assign which ports will be members of the VLAN. A port can only belong to one VLAN at a time and by default, all ports are members of VLAN 1. To assign a VLAN to a port, enter interface configuration mode for the port and use the vlan-membership command. Switch1#configure terminalSwitch1(config)#interface e0/4Switch1(config-if)#vlan-membership static 5Switch1(config)#interface e0/5Switch1(config-if)#vlan-membership static 5Switch1(config)#interface e0/6Switch1(config-if)#vlan-membership static 6Verifying the VLAN Configuration
To view the VLANs configured on the switch, use the show vlan command. Switch1#show vlanVLAN Name Status Ports--------------------------------------------------1 default Enabled 1-3, 7-24, AUI, A, B5 accounting Enabled 4, 56 management Enabled 6
Optionally you can view an individual VLAN to see how it's configured by using the show vlan [#] command.Switch1#show vlan 5VLAN Name Status Ports-------------------------------------5 accounting Enabled 2-------------------------------------VLAN Type SAID MTU Parent RingNo BridgeNo Stp Trans1 Trans2---------------------------------------------------------------------5 Ethernet 100005 1500 0 1 1 Unkn 0 0Verifying VLAN Membership
To view which ports are assigned to a VLAN, use the following command: Switch1#show vlan-membership Port VLAN Membership 1 1 Static 2 1 Static 3 1 Static 4 5 Static 5 5 Static 6 6 Static 7 1 Static 8 1 Static [Output Cut]Prevent VLANs from Crossing a Trunk
All VLANs are configured on a trunked link unless you clear it manually. Use the following command if you don't want a trunk to carry VLAN information: Switch1(config)#int f0/26Switch1(config-if)#clear trunkPrevent Individual VLANs from Crossing a Trunk Link
You can clear individual VLANs from crossing a trunk link by using the following command: Switch1(config)#int f0/26Switch1(config-if)#no trunk-vlan 5Verifying Trunk Link
To verify a trunk port use the show trunk [ab] command. The a is for port f0/26 while b represents f0/27. Switch1#show trunk aDISL state: Auto, Trunking: On, Encapsulation type:ISLSwitch1#show trunk allowed-vlans1-4, 6-1004Verifying VTP Information
After VTP has been enabled and configured, you can view the configuration with the following command: Switch1#show vtpVTP Version : 2Configuration Revision : 2Maximum VLANs supported locally : 1005Number of existing VLANs : 2VTP Operating Mode : ServerVTP Password : ccnaVTP Domain Name : ciscotestVTP Pruning Mode : DisabledVTP V2 Mode : DisabledVTP Traps Generation : EnabledMD5 digest : 0xB9 0xC7 0x8D 0xB3 0xD4 0xBA 0x94 0x03Configuration last modified by 192.168.1.86 at 7-25-01 01:22:24Enabling VTP Pruning
If you enable VTP pruning on a VTP server, you will enable it for the entire domain. Enable VTP pruning with the following command: Switch1(config)#vtp pruning enableDisable VTP pruning with: Switch1(config)#vtp pruning disable