Cisco vtp client not updating
By default all switches are configured as VTP Servers when first powered on.
All VLAN information such as VLAN number and VLAN name is stored locally, on a separate NVRAM from where the 'startup-config' is stored.
Lastly, some people tend to relate the VTP Domain with the Internet Domain name space, however, this is completely incorrect.
Even though the acronym 'DNS' contains the word 'Domain', it is not related in any way with the VTP Domain.
Here (in VTP land), the word 'Domain' is simply used to describe a logical area in which certain hosts (switches) belong to or participate in, and are affected by any changes made within it.
We should also note that all Cisco switches default to VTP Server mode but will not transmit any VLAN information to the network until a VTP Domain is set on the switch.
The VTP protocol is a fairly complex protocol, but easy to understand and implement once you get to know it.
This means that you must ensure that all switches connect to the network backbone via Trunk links, otherwise no VTP updates will get to your switches.