Root

Provides the best path to the root. This is the port that receives the best BPDU on a bridge.

Designated

Can send the best BPDU on a segment to which it is connected. Bridges connected to a given segment listen to the BPDUs of other bridges and agree on the bridge sending the best BPDU as the designated bridge for that segment and the port as the designated port.

Alternate

Blocked because another port on the bridge received superior information from another bridge. This port corresponds to the blocking state of 802.1w.

Back-up

Blocked because another port received superior information from the same bridge. This port also corresponds to the blocking state of 802.1w.