What is VTP?
Virtual Trunking Protocol. A Cisco Proprietary Protocol that propagates VLAN information on the whole local area network through a VTP domain.
Why do we use VTP?
Last time, we learned about VLANs. We learned that we can divide a network into several sub networks without having to add more equipments. We read about how you can be connected to the same switch as another user but be in a completely different network. That is, having no access to the path, the other user’s packets traverse.
Managing VLANs isn’t very time consuming and doesn’t require administrative overhead. Let’s say, we have a 24 port switch and each access port is on its own VLAN. It doesn’t take that long to configure each port on a separate VLAN.
What if, however, you add another switch. Your network expands and you have to add another. You will have to configure the other switches the same way you did the first – depending on how you’re going to set up your network.
2 or 3, okay, that’s fine.
What if your business grows? You add office branches, regional warehouses, data centers each location having its own network. It’s going to take a while for you to build the VLANs for each switch.
As you can see, the method mentioned above isn’t that scalable. In a consistently changing environment and constantly improving standards, it is ideal to have a centralized control over your VLANs on a network.
This is why VTP exists.
As the number of switches increases on a small- or medium-sized business network, the overall administration required to manage VLANs and trunks in a network becomes a challenge. – CCNA 2
VTP, basically, allows a switch to be able to propagate its VLAN information dynamically to whatever switch its configured to share information with.
This particular switch will be configured as a VTP server. See below a table of VTP modes from Cisco.
|VTP server||In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters (such as the VTP version) for the entire VTP domain. VTP servers advertise their VLAN configurations to other switches in the same VTP domain and synchronize their VLAN configurations with other switches based on advertisements received over trunk links.In VTP server mode, VLAN configurations are saved in nonvolatile RAM (NVRAM). VTP server is the default mode.|
|VTP client||A VTP client behaves like a VTP server, but you cannot create, change, or delete VLANs on a VTP client.In VTP client mode, VLAN configurations are not saved in NVRAM.|
|VTP transparent||VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, transparent switches do forward VTP advertisements that they receive from other switches from their trunk interfaces. You can create, modify, and delete VLANs on a switch in VTP transparent mode. The switch must be in VTP transparent mode when you create extended-range VLANs. See the “Configuring Extended-Range VLANs” section.When the switch is in VTP transparent mode, the VTP and VLAN configurations are saved in NVRAM, but they are not advertised to other switches. In this mode, VTP mode and domain name are saved in the switch running configuration and you can save this information in the switch startup configuration file by entering the copy running-config startup-config privileged EXEC command.
As stated above, there are three modes of VTP: server, client, transparent. By default, Cisco Switches are configured as VTP servers.
How does a Cisco Server share its VLAN information to other servers and VTP Clients?
VTP shares VLAN information with other switches on the same ‘domain’. A VTP domain is a collection of VTP-aware switches that share VLAN information with each other.
When you configure a VTP Server, you will have to set it up on a specific domain by configuring a VTP domain (VTP parameter). This way, you only have to set up the same domain name on all other switches you want to share VLAN info with.
Follow the commands below to enable VTP on a switch.
switch(config)#vtp mode server
switch(config)#vtp domain [domain-name]
Verify VTP status by typing show vtp status on priviledged EXEC mode. See below for a sample output from CCNA 3 Exploration.
Learn more about VTP from Cisco.