The main basis for vtp to synchronize switch is Configuration Revision. When everyone’s domain name and password are the same, whoever has a higher Configuration Revision will be subject to that. According to this principle, when we judge that the VTP information cannot be synchronized, we need to look at the following aspects:
1. First, judge that all switches participating in vtp are consistent with password. Domain name is easy to deal with. You can see through sh vtp stat, but password is not easy to deal with. New switches can be seen through sh vtp password. Some older switches do not have this command. So far, I don’t know how to get this password. The safer way to encounter such old switches is to reset password.
2. Secondly, determine whether the vtp mode of all switches is server or client. If it is transparent mode, the switch will not be synchronized with other switches in the vtp domain. It is worth mentioning that some cisco switches only support a limited number of vlans, such as 2950 only supports 64 vlans. If you configure more than 64 vlans on the vtp server side, in this case, IOS will automatically change the vtp mode of 2950 to transparent. In this case, the vtp information cannot be synchronized.
3. Finally, there is a special situation, that is, the vlan information of several switches in the vtp domain is inconsistent, but everyone's Configuration Revision is the same. In this case, it cannot be synchronized. The solution is to modify the vlan information of a certain switch, force the Configuration Revision to increase, and trigger synchronization. This situation is quite special, and is often the case where you take a switch from different places to build a test environment.
4. Commonly used 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 mismatch in domain passwords
sh vtp password
This command is used to view the current vtp password
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