I have three 3560 switches in a fully-meshed scenario, an access switch and 2 distribution switches. when connecting these switches in the triangle topology, since STP running by default one of port go to blocking mode and then loop is prohibited. But when in access switch i set tow ports connected toward distribution switches in trunk mode with command "switch port mode trunk" the Blocked port go to forwarding and i can't understand why?because i think the loop there is yet and spanning tree must block one of ports.
Spanning tree mode is PVST+ and there are 8 VLANs on switches.
The question is how does this situation occur? i couldn't find reason of this situation.