What is VTP?
VTP is a Cisco Proprietary Layer 2 protoco; that allows switches to get and send VLAN info. You can create VLAN’s in one Switch and send it over to the rest of the switches via VTP. To do this, VTP carries VLAN information to all the switches in a VTP domain. VTP advertisements can be sent over 802.1Q, and ISL trunks.
Advantages of VTP:
It reduces administrative overhead like suppose you have 100 switches in your network and you want to create a new VLAN without VTP, you need to login to 100 switches and create the VLAN whereas with VTP you only need to create VLAN in your VTP server.
Disadvantages of VTP:
VTP can be devastating as well. Suppose your network VTP server is having a revision number of 10. Now you have a switch failure in your network which you are replacing with your LAB switch which belongs to same VTP domain of your network with a higher revision number than your VTP server and having different VLAN.
You can configure a switch to operate in any one of these VTP modes:
- Server—In VTP server mode, 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 switches in the same VTP domain and synchronize their VLAN configuration with other switches based on advertisements received over trunk links. VTP server is the default mode.
- 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 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, but transparent switches do forward VTP advertisements that they receive out their trunk ports in VTP Version 2.
- Off (configurable only in CatOS switches)—In the three described modes, VTP advertisements are received and transmitted as soon as the switch enters the management domain state. In the VTP off mode, switches behave the same as in VTP transparent mode with the exception that VTP advertisements are not forwarded.
VTP uses well-known MAC Address: 01-00-0c-cc-cc-cc to propagate its message.
The VLAN Trunking Protocol (VTP) revision number is important because it determines which updates are to be used when not managed properly this number can cause the deletion of all your networks VLAN information.
When you set a VTP Domain Name, the revision number is set to zero. After which each change to the VLAN database increases the revision number by one. When a switch receives VTP information from a neighboring switch. The first switch processes data only for the same domain when the revision number is higher than its own.
Show vtp counters
Show vtp password
Show vtp status