If three switch connect each other like to triangle. One switch(A) is root, second switch(B) is root secondary, third switch(C) is not enabed STP. Second switch(B) will take BPDU from root switch(A) and send to second Switch(B). this BPDU is spanning...

You can see diagram the attached file.Diagram has three device with triangle BB#1, BB#2 and L2_Switch.BB#1 is a root, BB#2 is a root secondary.L2_Switch is not enabled Spanning-tree protocol.BB#1 and BB#2 is connected to Port-channel 1 and trunk.I ch...