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
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 terminal
Enter configuration commands, one per line. End with CNTL/Z
Switch1(config)#vtp server
Switch1(config)#vtp domain ciscotest
Switch1(config)#vtp password ccna
Enable 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 terminal
Switch1(config)#interface f 0/26
Switch1(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 terminal
Switch1(config)#vlan 5 name accounting
Switch1(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 terminal
Switch1(config)#interface e0/4
Switch1(config-if)#vlan-membership static 5
Switch1(config)#interface e0/5
Switch1(config-if)#vlan-membership static 5
Switch1(config)#interface e0/6
Switch1(config-if)#vlan-membership static 6
Verifying the VLAN Configuration
To view the VLANs configured on the switch, use the show vlan
command.
Switch1#show vlan
VLAN Name Status Ports
--------------------------------------------------
1 default Enabled 1-3, 7-24, AUI, A, B
5 accounting Enabled 4, 5
6 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 5
VLAN 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 0
Verifying 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 f0/26
Switch1(config-if)#clear trunk
Prevent 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 f0/26
Switch1(config-if)#no trunk-vlan 5
Verifying Trunk Link
To verify a trunk port use the show trunk [a|b] command. The
a is for port f0/26 while b represents f0/27.
Switch1#show trunk a
DISL state: Auto, Trunking: On, Encapsulation type:ISL
Switch1#show trunk allowed-vlans
1-4, 6-1004
Verifying VTP Information
After VTP has been enabled and configured, you can view the configuration
with the following command:
Switch1#show vtp
VTP Version : 2
Configuration Revision : 2
Maximum VLANs supported locally : 1005
Number of existing VLANs : 2
VTP Operating Mode : Server
VTP Password : ccna
VTP Domain Name : ciscotest
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Enabled
MD5 digest : 0xB9 0xC7 0x8D 0xB3 0xD4 0xBA 0x94 0x03
Configuration last modified by 192.168.1.86 at 7-25-01 01:22:24
Enabling 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 enable
Disable VTP pruning with:
Switch1(config)#vtp pruning disable
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