VTP(Vlan Trunking Protocol)

1-1 What is VTP?

VTP is a layer 2 messaging protocol which is a Cisco proprietary protocol that propagates the definition of Virtual Local Area Networks (VLAN) on the whole local area network. VTP minimizes misconfigurations and configuration inconsistencies that can result in a number of problems, such as duplicate VLAN names, incorrect VLAN-type specifications, and security violations.

There are three versions of VTP, namely version 1, version 2, version 3. All feature of 3 versions of VTP is shown in Table1

VTP V1	VTP V2	VTP V3	Feature
		*	VTP password
		*	Private Vlan
		*	Extended Vlan
	*		Token Ring Support

There are three main modes in VTP:

• Server : This is a default mode of VTP. You can create, modify, and delete VLANs and specify other configuration parameters (such as VTP version and VTP pruning) for the entire VTP domain. VTP servers advertise their VLAN configuration to other network devices

• Client: VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.

• Transparent: VTP transparent network devices do not participate in VTP. A VTP transparent network device does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, a transparent network device will forward received VTP advertisements from its trunking LAN ports. In VTP version 3, a transparent network device is specific to an instance.

Example:

We want to make a Vlan in Switch 1 and change its mode to server mode. Between Switch 1 and Switch 2, we use trunk port and then set Switch 2 mode for VTP to client.

switch1(config)# int gi0/1
switch1(config-if)# switchport mode trunk
switch1(config)# vlan 10
switch1(config-if)# name IT
switch1(config-if)# exit
switch1(config)# vlan 20
switch1(config-if)# name Sales
switch1(config-if)# exit

switch1(config)# vtp mode server
switch1(config)# vtp domain HRT

switch2(config)# int gi0/1
switch2(config-if)# switchport mode trunk
switch2(config)# vlan 10
switch2(config-if)# name IT
switch2(config-if)# exit
switch2(config)# vlan 20
switch2(config-if)# name Sales
switch2(config-if)# exit

switch2(config)# vtp mode client
switch2(config)# vtp domain HRT

to see status of VTP:

switch1# show vtp status

Now if you check, switch2 , you can see Vlan 10, 20 are made automatically.

in VTP V3, you can define password VTP. In doing so, just switches with the same password can talk eachother.

switch(config)# vtp password cisco

1-2 VTP Pruning

VTP pruning enhances network bandwidth use by reducing unnecessary flooded traffic, such as broadcast, multicast, unknown, and flooded unicast packets. VTP pruning increases available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to access the appropriate network devices. By default, VTP pruning is disabled.

Without VTP Pruning

With VTP Pruning

As you can see in above pictures, traffic with and without VTP Pruning is demonstrated. To enable VTP pruning:

switch(config)# vtp pruning

To enable VTP V2 or V3, you have to write:

switch(config)# vtp version 2 or 3