VTP - domain name automatically changes

When configuring VTP on a switch, its initial configuration has an empty VTP domain name. This is considered to be a domain name of NULL. The following output shows an example of what this looks like:

Switch#show vtp status
VTP Version capable : 1 to 2
VTP version running : 2
VTP Domain Name :
VTP Pruning Mode : Disabled
VTP Traps Generation : Disabled
Device ID : 0001.9751.0E00
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00
Local updater ID is 0.0.0.0 (no valid interface found)

Feature VLAN :
--------------
VTP Operating Mode : Server
Maximum VLANs supported locally : 255
Number of existing VLANs : 5
Configuration Revision : 0
MD5 digest : 0x7D 0x5A 0xA6 0x0E 0x9A 0x72 0xA0 0x3A
0xF0 0x58 0x10 0x6C 0x9C 0x0F 0xA0 0xF7
Switch#

Note the domain name is empty. This is the state of a switch as soon as it comes out of the box. In this state, if the switch receives a VTP update, the switch will automatically adopt the VTP domain name of that update. If that domain requires a password, the local switch will not be able to exchange or use any VTP information received. However, if there is no password, any information found within that update will be incorporated into the VLAN database of the local switch.