There are thee different modes of operation within a VTP domain. Figure 4 shows all three.
Server : Is the default for all Catalyst switches. You need at least one server in your VTP domain to propagate VLAN information throughout the domain. The switch must be in server mode to be able to create, add, or delete VLANs in a VTP domain. Changing VTP information must also be done in server mode. Any change made to a switch in server mode is advertised to the entire VTP domain.
Client : Receives information from VTP servers and send and receives updates, but cannot make any changes. No ports on a client switch can be added to a new VLAN before the VTP server notifies the client switch of the new VLAN. If you want a switch to become a server, first make it a client so it receives all the correct VLAN information, then change it to a server.
Transparent : Does not participate in the VTP domain but will still forward VTP advertisements through the configured trunk links. VTP transparent switches can add and delete VLANs as the switch keeps its own database and does not share it with other switches. Transparent is considered only locally significant.
Configuration Revision Number: The revision number is the most important piece in the VTP advertisement. Figure shows an example of how a revision number is used in an advertisement.
This figure shows a configuration revision number as “N.” As a database is modified, the VTP server increments the revision number by 1. The VTP server then advertises the database with the new configuration revision number. When a switch receives an advertisement that has a higher revision number, it overwrites the database in NVRAM with the new database being advertised.
VTP Pruning: You can preserve bandwidth by configuring the VTP to reduce the amount of broadcasts, multicasts, and other unicast packets, which helps preserve bandwidth. This is called pruning. VTP pruning only sends broadcasts to trunk links that must have the information; any trunk link that does not need the broadcasts will not receive them. For example, if a switch does not have any ports configured for VLAN 5, and a broadcast is sent throughout VLAN 5, the broadcast would not traverse the trunk link to this switch. VTP pruning is disabled by default on all switches.
When you enable pruning on a VTP server, you enable it for the entire domain. By default, VLANs 2–1005 are pruning-eligible. VLAN 1 can never prune because it is an administrative VLAN.
Server : Is the default for all Catalyst switches. You need at least one server in your VTP domain to propagate VLAN information throughout the domain. The switch must be in server mode to be able to create, add, or delete VLANs in a VTP domain. Changing VTP information must also be done in server mode. Any change made to a switch in server mode is advertised to the entire VTP domain.
Client : Receives information from VTP servers and send and receives updates, but cannot make any changes. No ports on a client switch can be added to a new VLAN before the VTP server notifies the client switch of the new VLAN. If you want a switch to become a server, first make it a client so it receives all the correct VLAN information, then change it to a server.
Transparent : Does not participate in the VTP domain but will still forward VTP advertisements through the configured trunk links. VTP transparent switches can add and delete VLANs as the switch keeps its own database and does not share it with other switches. Transparent is considered only locally significant.
Configuration Revision Number: The revision number is the most important piece in the VTP advertisement. Figure shows an example of how a revision number is used in an advertisement.
This figure shows a configuration revision number as “N.” As a database is modified, the VTP server increments the revision number by 1. The VTP server then advertises the database with the new configuration revision number. When a switch receives an advertisement that has a higher revision number, it overwrites the database in NVRAM with the new database being advertised.
VTP Pruning: You can preserve bandwidth by configuring the VTP to reduce the amount of broadcasts, multicasts, and other unicast packets, which helps preserve bandwidth. This is called pruning. VTP pruning only sends broadcasts to trunk links that must have the information; any trunk link that does not need the broadcasts will not receive them. For example, if a switch does not have any ports configured for VLAN 5, and a broadcast is sent throughout VLAN 5, the broadcast would not traverse the trunk link to this switch. VTP pruning is disabled by default on all switches.
When you enable pruning on a VTP server, you enable it for the entire domain. By default, VLANs 2–1005 are pruning-eligible. VLAN 1 can never prune because it is an administrative VLAN.