The following illustration shows the actions that occur when a port is in the listening
state.
CPU
Port 2
Port 2
Port 1Port 1
Forwarding
Database
Forwarding
Database
BPDUs
BPDUs
BPDUs
Addresses
Discard
Forwarding
Data
Packets
Data
Packets
Data
Packets
Data
Packets
Network
Management
Packets
Network
Management
Packets
Network SegmentNetwork Segment
Network SegmentNetwork Segment
Switch
Fabric
Switch
Fabric
Listening
Learning state
A port in the learning state prepares to participate in frame forwarding. The port
enters the learning state from the listening state.
A port in the learning state does the following:
v Discards frames received from the network segment to which it is attached
v Discards packets sent from another port on the switch for forwarding
v Adds addresses to its forwarding database
v Receives BPDUs and directs them to the CPU
v Processes and transmits BPDUs received from the CPU
v Receives and responds to network management messages
Appendix D. Understanding and troubleshooting the Spanning Tree Protocol 129
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