VTP Modes Overview
A Cisco switch, configured with Cisco IOS software, can be configured in either server, client, or transparent mode. These modes differ in how they are used to manage and advertise VTP domains and VLANs.
Server Mode
In server mode, you can create, modify, and delete VLANs for the entire VTP domain. VTP server mode is the default mode for a Cisco switch. VTP servers advertise their VLAN configurations to other switches in the same VTP domain and synchronize their VLAN configurations with other switches based on advertisements received over trunk links. VTP servers keep track of updates through a configuration revision number. Other switches in the same VTP domain compare their configuration revision number with the revision number received from a VTP server to see if they need to synchronize their VLAN database.
Client Mode
If a switch is in client mode, you cannot create, change, or delete VLANs. In addition, the VLAN configuration information that a VTP client switch receives from a VTP server switch is stored in a VLAN database, not in NVRAM. Consequently, VTP clients require less memory than VTP servers. When a VTP client is shut down and restarted, it sends a request advertisement to a VTP server for updated VLAN configuration information.
Switches configured as VTP clients are more typically found in larger networks, because in a network consisting of many hundreds of switches, it is harder to coordinate network upgrades. Often there are many network administrators working at different times of the day. Having only a few switches that are physically able to maintain VLAN configurations makes it easier to control VLAN upgrades and to track which network administrators performed them.
For large networks, having client switches is also more cost-effective. By default, all switches are configured to be VTP servers. This configuration is suitable for small scale networks in which the size of the VLAN information is small and the information is easily stored in NVRAM on the switches. In a large network of many hundreds of switches, the network administrator must decide if the cost of purchasing switches with enough NVRAM to store the duplicate VLAN information is too much. A cost-conscious network administrator could choose to configure a few well-equipped switches as VTP servers, and then use switches with less memory as VTP clients. Although a discussion of network redundancy is beyond the scope of this course, know that the number of VTP servers should be chosen to provide the degree of redundancy that is desired in the network.
Transparent Mode
Switches configured in transparent mode forward VTP advertisements that they receive on trunk ports to other switches in the network. VTP transparent mode switches do not advertise their VLAN configuration and do not synchronize their VLAN configuration with any other switch. Configure a switch in VTP transparent mode when you have VLAN configurations that have local significance and should not be shared with the rest of the network.
In transparent mode, VLAN configurations are saved in NVRAM (but not advertised to other switches), so the configuration is available after a switch reload. This means that when a VTP transparent mode switch reboots, it does not revert to a default VTP server mode, but remains in VTP transparent mode.
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