There is some confusion and misunderstanding regarding VTP (VLAN Trunking Protocol)+DTP (Dynamic Trunking Protocol) and this article will hopefully make it all clear. Most of the confusion comes from the statement that VTP is always a security threat to your network. There are even some CCIE material which I find to be wrong on this topic so my advice here is to test everything by yourself.
We investigate a special topology condition, where a switch is connected itself on ports Faa0/1 and Fa0/2, and one of the port has BPDUFilter feature applied (i.e. simulating STP is switched off). Both ports are in the same vlan (vlan 1 here). The question is: Is there a topology loop?
Initial state