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 Modes

You can configure VLANs on Catalyst 2820 and Catalyst 1900 switches when the switch is in VTP server or transparent mode. You can use the CLI, console menus, or the MIB (when using a SNMP management station) to modify a VLAN configuration when the switch is in either server or transparent modes.

A switch configured in VTP server mode advertises VLAN configuration to neighboring switches through its trunks and learns new VLAN configurations from those neighbors. Use the server mode to add or delete VLANs and to modify VLAN information by using either the VTP MIB, the CLI, or the console. For example, when you add a VLAN, VTP advertises the new VLAN, and both servers and clients prepare to receive traffic on their trunk ports.

After the switch automatically transitions to VTP client mode, it transmits advertisements and learns new information from advertisements. However, you cannot add, delete, or modify a VLAN through the MIB, the CLI, or the console. The VTP client does not maintain VLAN information in nonvolatile storage; when it starts, it learns the configuration by receiving advertisements from the trunk ports.

In VTP transparent mode, the switch does not advertise or learn VLAN configurations from the network. When a switch is in VTP transparent mode, you can modify, add, or delete VLANs through the console, the CLI, or the MIB.

shows the maximum number of VLANs stored in nonvolatile RAM (NVRAM), the console or MIB configuration options, the advertisement options, and the maximum number of active VLANs for Catalyst 2820 and Catalyst 1900 switches.

Table 2-6 Catalyst 2820 and Catalyst 1900 VTP Modes