We have a core switch that was already configured as a VTP server, and had another switched connected to it as a VTP client. They were both up and running fine. I needed to add a 3rd switch, so before connecting it to anything, I set it (new switch) up as a VTP client, gave it the same domain and password as the other 2 switches, configured it for trunking on 2 ports, then connected those 2 ports to the core switch. It seemed like they negotiated, then soon after, all the lights on the core switch turned to orange. I found out that the core switch had lost all its VLANs and VTP was disabled (no domain). Any ideas why this might happen? After that happened, I immediately disconnected the connections from the core switch to the new switch, re-enabled VTP server on the core switch, went to the switch that was originally configured as a VTP client, re-configured VTP on it. After all this, the core switch lost all its VLAN info again. So, I'm not running with VTP on the core switch now. Scratching my head as to what could have caused this. The only thing I can think of is that both the core switch and the switch that was already working had a "VTP V2 Mode", whereas the new switch did not have the line when I did a "show vtp status". But, I made sure I set the new switch to VTP version 2 like the other switches.