Incorrect Revision Number
There are other factors that can undermine your network even after you have configured the switches in your VTP domain correctly. They can adversely affect the functionality of VTP.
The topology diagram below is configured with VTP. There is one VTP server switch, SW1, and two VTP client switches, SW2 and SW3.
SW1, SW2 and SW3 are configured with the same VTP domain name (Cisco) and same revision number (15)
Incorrect Revision Number
SW4 is added to the network, it has been previously configured as a VTP client with the following configurations:
Domain name= Cisco
Revision number= 25
VLANs 30, 40
When switch SW4 is connected to switch SW3, there will be VTP summary advertisements sent to all other switches on the network announcing the arrival of a VTP-enabled switch with the highest revision number in the network. From The switch SW3, switch SW1, and finally switch SW2 will all reconfigure themselves to the configuration found in switch SW4. As each switch connected to the network reconfigures itself with VLANs that are not supported in the network, the ports will no longer forward traffic from the PCs because they are configured with VLANs that no longer exist on the newly reconfigured switches.
Solution
To solve this problem, the administrator will have to reset each switch back to earlier configuration and reconfigure SW1 with the correct VLANs, 10, AND 20.
Note: Before adding a pre-configured switch to a VTP enabled network, ensure that the switch is reset to it’s default revision number.
