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Introduction To VLAN Trunking Protocol (VTP)

VLAN Trunking Protocol (VTP) is a technology that allows us to create, delete or modify VLAN’s in one switch and then have that change propagated throughout the switches in the same VTP domain. VTP advertisements that carry this information are only sent on trunk links.

Managing VLANs without using VTP

For example, let’s assume we have a network that consists of five switches as shown in the below figure and we want to create VLAN 777 and extend it across all of our switches. What we can do is configure VLAN 777 on one switch and then move on to the next switch and configure VLAN 777 on this switch. Like that we can go in to the cli of each switch individually and configure VLAN 777. Suppose, in an enterprise environment where we might have about 100s of switches, then we would have to configure on each switch this VLAN. It would be a considerable administrative burden to do so and probably not an efficient way to manage VLANs. This method certainly does not scale very well.



Figure Creating a new VLAN on five individual switches without using VTP


Managing VLANs using VTP

Let’s say we want to create VLAN 777 on all of our switches and this time we’ll let VTP do the heavy lifting. Now all we have to do is create VLAN 777 on one switch as shown below. Then what we can do is have VTP send that VLAN information over the trunk links to neighbouring switches using VTP messages. When the neighbouring switches receive that information about the new VLAN 777 they will add this newly created VLAN to their VLAN database.

Now that they have processed this information they will also send VTP messages out of their trunk ports to neighbouring switches. As a result, the switches at the bottom of our network diagram will also receive details about the newly created VLAN 777 and they will also add VLAN 777 to their respective VLAN databases. Now every switch in our topology knows about VLAN 777 and we only had to add it on one switch. It is obvious VTP can significantly cut down administrative overhead involved in Creating, deleting or modifying VLANs.



Figure Creating a new VLAN on five individual switches using VTP



Furthermore, there are many options we can configure. For example, if we don’t want certain switches to be able to create VLANs we can configure those switches as VTP Clients. They will only learn about VLAN changes and propagate these changes over trunk links. In addition, we can configure some of the switches as VTP server where they will be able to create, modify or delete VLANs.  Also, if we do not want a switch to learn about VLAN changes via VTP messages and change their VLAN database we can configure those switches as VTP Transparent switches.


Let’s have a look at these options in greater detail in our next lesson.