Hello Heping
If you try to make a change to a VTP client, such as adding a VLAN, it won’t let you make the change. You’ll get an error message like this:
%VTP VLAN configuration not allowed when device is in CLIENT mode.
In order to be allowed to make changes to VLANs from a switch, that switch must be manually configured as a VTP server. For VTPv3, it’s not enough to simply be a VTP server. Only the primary VTP server can make changes to VLANs.
I hope this has been helpful!
Laz