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VLAN Trunking Protocol Configuration

You must do a few things to configure VTP. You need to configure a port on your switch as a trunk; then you need to enable VTP. You use three operating modes with VTP that you designate in Global Configuration mode:

  • VTP Client mode: When running in Client mode, your switch will only receive configurations from other devices and will not allow changes to VLANs to be made on that specific switch.

  • VTP Server mode: This mode allows you to make changes and propagate those changes out to all other switches in the domain. This is the default mode on your switches when you unpack them. How many servers can you have on your network? Well, as many as you want.

    Your VTP server will send VTP advertisements through 802.1Q trunk links to other switches, keeping them aware of any changes that occur on the switch. VTP Server mode switches will also accept VTP advertisements from other switches and apply revisions that are more recent.

  • VTP Transparent mode: When a switch is running in this mode, you can create and modify VLANs on that switch, but those changes are not sent to other switches on the network. You can pass VTP through the switch, but the switch will not participate with VTP; rather it will have its VLAN configuration set and stored locally.

The default settings for VTP are as follows:

  • VTP Domain Name: Null

  • VTP Mode: Server

  • VTP Version 2 State: Disabled.

    VTP version 2 supports Token Ring: This represents the only difference between version 1 and version 2. If you are not using Token Ring, then you should use version 1.

  • VTP Password: None

  • VTP Pruning: Disabled

The other commands you will want to use in Global Configuration mode are listed here. In order to configure VTP, you only need to specify a domain name and a password. The rest of the options do not need to be changed. These two commands will modify the default options.

Switch1(config)#vtp domain MyVtpDomain
Switch1(config)#vtp password MyVtpPassword

Now, walk through a brief configuration. Note that a switch currently does not have any special VLANs configured, as shown here:

Switch2>enable
Switch2#show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/2, Fa0/3, Fa0/4, Fa0/5
                                                Fa0/6, Fa0/7, Fa0/8, Fa0/9
                                                Fa0/10, Fa0/11, Fa0/12
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

Because you want the entire VLAN configuration copied to this switch, you will want to use VTP. However, you have determined that you will not need to be able to make changes to the overall network VLAN configuration from this switch, which is ideal for VTP Client mode.

You also configure it for the network VTP domain that you are working with here, which includes a password. Notice the status messages you get as you make the configuration changes:

Switch2>enable
Switch2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch2(config)#vtp mode client
Setting device to VTP CLIENT mode.
Switch2(config)#vtp domain edtetz.net
Changing VTP domain name from NULL to edtetz.net
Switch2(config)#vtp password MyVtpPass
Setting device VLAN database password to MyVtpPass
Switch2(config)#end

Even though you made these changes, if you check the VLAN configuration on the switch, you will not see any changes. That is because VTP information passes only through trunk ports, which have not been configured on this switch.

You have already made the necessary changes on your other network switches, like Switch 1, so you just need to make the change here. Now, make sure that all ports that interconnect switches are configured as trunks and are actually trunking:

Switch2>enable
Switch2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch2(config)#interface fastEthernet 0/1
Switch2(config-if)#switchport mode trunk
Switch2(config-if)#end

Wait just a few seconds, and the VTP traffic will start flowing through to this switch. Once that happens, you are able to check the status of the VLANs and see the change based on the VLAN data that comes through from Switch 1. Here is how show vlan brief looks now.

Switch2>enable
Switch2#show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/2, Fa0/3, Fa0/4, Fa0/5
                                                Fa0/6, Fa0/7, Fa0/8, Fa0/9
                                                Fa0/10, Fa0/11, Fa0/12
2    Executives                       active
5    VLAN0005                         active
10   VLAN0010                         active
15   VLAN_15                          active
20   Test_VLAN                        active
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup
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