VTP (VLAN Trunking Protocol) maintains VLAN configuration consistency throughout the network by distributing VLAN information to the network. VLAN information is sent to network devices in advertisements that contain the VTP management domain name, the current configuration revision number, the VLANs that the server knows about, and certain VLAN parameters. Any time you change a VLAN, VTP automatically sends an advertisement to update all other network devices.
You can display current VTP information by choosing VLAN > VLAN and clicking the Configure VTP tab on the VLAN window.
Note: Catalyst 2912MF, 2924M, and 3500 XL switches support 250 VLANs; all other Catalyst 1900, 2820, and 2900 switches support 64 VLANs. If you define more than the maximum number of VLANs or if the switch receives an advertisement that contains more than the maximum number of VLANs, the switch automatically enters VTP transparent mode and operates with the VLAN configuration preceding the one that sent it into transparent mode. The count of 250 (or 64) VLANs always includes VLAN 1 but never includes VLANs 1002 to 1005, which are reserved.