VTP cannot be synchronized between vswitches.

Configuration Revision is the main basis for vtp synchronization on vswitches. When domain name and password are the same, the Configuration Revision height of vtp is determined by the user. Based on this principle, when determining that vtp information cannot be synchronized, we should look at the following aspects:
1. First, determine that all vswitches involved in vtp have the same domain name and password. The domain name is easy to handle. You can see it through sh vtp stat, but the password is not easy to handle, the new vswitch can be seen through the sh vtp password. Some older vswitches do not have this command. So far, I do not know how to get this password, the safer way to deal with this old switch is to reset the password.

2. Determine whether the vtp mode of all vswitches is server or client. If the vswitch is in transparent mode, the vswitch will not be synchronized with other vtp domain switches. It is worth mentioning that some cisco switches only support a limited number of VLANs. For example, 2950 only supports 64 VLANs. If you have configured more than 64 VLANs on The vtp server, in this case, IOS will automatically change the vtp mode of 2950 to transparent. In this case, the vtp information cannot be synchronized.

3. Another special case is that the vlan information of several vswitches In The vtp domain is inconsistent, but the Configuration Revision is the same. In this case, the vlan information cannot be synchronized, the solution is to modify the vlan information of a vswitch and force the Configuration Revision to be added to trigger synchronization. This situation is special. It is common when a vswitch is taken from different places to build a test environment.
4. Common commands:

Sh vtp stat

Note in this command

Configuration Revision: 106

VTP Operating Mode: Server

VTP Domain Name: test

Sh vtp counter

Note in this command

Number of config revision errors: 25

This error is caused by the same revision.

Number of config digest errors: 0

This error is caused by domain password mismatch.

Sh vtp password

This command is used to view the current vtp password