Chapter 4: STP and RSTP
sent or received on a the port except for BPDU data. A port with a higher path cost to the root bridge than another on the switch will cause a switching loop and is placed in the blocking state by the Spanning Tree algorithm. The port’s state may change to the forwarding state if the other links in use fail and the Spanning Tree algorithm determines the port may transition to the forwarding state.
Listening - This state occurs on a port during the convergence process. The port in the listening state processes BPDUs and awaits new information that would cause the port to return to the blocking state.
Learning - While the port does not yet forward frames (packets) in this state, the port does learn source addresses from frames received and adds them to the filtering (switching) database.
Forwarding - A port that both receives and sends data. This indicates normal operation. STP continues to monitor the port for incoming BPDUs that indicate the port should return to the blocking state to prevent a loop.
Disabled - This state is not strictly part of STP. However, a network administrator can manually disable a port.
Role - Indicates one of the following port roles:
Disabled - The Disabled Port role is assigned if the port is not operational or is excluded from the active topology by management or it is a network access port (IEEE Std 802.1X) and it is Unauthorized, or its Administrative Bridge Port state is Disabled.
Root - If the least cost path to the root is through this port, then it becomes the root port for this bridge.
Designated - If this is the designated bridge for the LAN and if the root path cost information received on this port is greater than the root port's path cost and less than any other port's received information, then this port becomes the designated port.
Backup - Any operational Bridge Port that is not a Root or
Designated Port is a Backup Port if the Bridge is the Designated
Bridge for the attached LAN.
Alternate - Any operational Bridge Port that is not a Root or a Designated Port is an Alternate Port if that Bridge is not the Designated Bridge for the attached LAN.
STP Status - Indicates if spanning tree protocol (either RSTP or
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