Cisco Systems RJ-45-to-AUX manual VTP Switch Modes, Client Mode, VTP Pruning, 100

Many network administrators make the mistake of using the clear config all command, believing that it will erase the current revision number. Doing so is a bad mistake on the network administrator’s part. This command doesn’t do what it says it does—it doesn’t really “clear all.” VTP has its own NVRAM, so the VTP information as well as the revision number will still be present if you perform the clear config all command. You can take care of this problem two ways. The easiest way is to cycle the power on the switch after placing the switch in client mode. The switch must be in client mode because the switch will store VTP information in special NVRAM when the server is in server mode. As a result, merely powering down the switch will not reset the revision number or cause the switch to lose its VTP database.

The other way is to make the switch a client, connect it to the network to get new revisions, and then configure the switch as a VTP server.

Each time a server sends out an updated advertisement, it increases the revision number by one. If a client switch receives two advertisements simultaneously, it knows which one to use by selecting the advertisement with the highest revision number.

VTP Switch Modes

Three switch modes can be configured on a switch that will be used to participate in a VTP domain. The three switching modes are as follows:

∙Client mode

∙Server mode

∙Transparent mode

Client Mode

Client mode allows the switch to have the same functions as server mode, with the exception that it cannot change any VLAN information. A switch in client mode cannot create, modify, or delete VLANs on any VTP client or switch except when it receives an advertisement from a switch operating in server mode. It can, however, advertise its own VLAN configuration, synchronize the VLAN information with other switches on the network, specify VTP configuration information such as VTP version, and participate in VTP pruning. Client mode switches receive their information from other VTP servers in the VTP management domain. In this mode, the global VLAN information is lost when the switch power is cycled.

VTP Pruning

VLAN Trunk Protocol pruning is used to increase network bandwidth by reducing VLAN traffic across switch trunk links. VTP pruning filters network traffic such as broadcasts, multicasts, and unicasts on trunk links that connect switches that contain no VLAN ports in the particular VLAN the data is destined for.

When VTP pruning is enabled on a VTP server, the information is propagated to all other client and server mode switches in the VTP management domain. This step automatically enables VTP pruning on these switches. By default, VLANs 2 through 1,000 are eligible for VTP pruning, and VLAN 1 is always ineligible. VTP pruning usually takes several seconds to propagate to the other VTP management domain clients after it is enabled or the switch power is cycled.

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