SWITCH 300-115 1.6 Configure and verify spanning tree

1.6.a PVST+, RPVST+, MST

STP elects a root bridge (switch) and puts all root bridge interfaces into forwarding state
Each non root bridge (switch) determines which of its ports has the least administrative cost (best) to the root bridge and STP makes that port that switch’s root port.
The switch with the lowest (best) cost  to the root is put in forwarding state.
The lowest cost switch on each segment is the designated bridge (switch) and the interface on that switch is called the designated port.
            The root bridge’s (switch) ports are always in forwarding state and the root switch (bridge) is always the designated bridge on all connected segments.
            The non root bridge root port is always forwarding. This port receives the lowest cost BPDU from the root.
            Each LAN’s designated port is always forwarding and the bridge forwarding the lowest cost BPDU is the segment’s designated bridge (switch)
             All other ports are blocking. No forwarding frames, no receiving frames.
         At first each switch claims to be root by sending BPDU’s that contain:
                 The root bridge ID- a combination switch priority and MAC address, lower number, higher priority
             The cost to reach the root- again the lower, the better

And it’s own bridge ID