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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
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Chapter 15 Configuring STP and IEEE 802.1s MST
Understanding How STP Works
Listening State
The listening state is the first transitional state a Layer 2 LAN port enters after the blocking state. The
Layer 2 LAN port enters this state when STP determines that the Layer 2 LAN port should participate
in frame forwarding. Figure 15-4 shows a Layer 2 LAN port in the listening state.
Figure 15-4 Interface 2 in Listening State
A Layer 2 LAN port in the listening state performs as follows:
• Discards frames received from the attached segment.
• Discards frames switched from another LAN port for forwarding.
• Does not incorporate end station location into its address database. (There is no learning at this
point, so there is no address database update.)
• Receives BPDUs and directs them to the system module.
• Receives, processes, and transmits BPDUs received from the system module.
• Receives and responds to network management messages.
Filtering
database
Frame
forwarding
System
module
Port 1
BPDUs
All segment
frames
BPDU and network
mana
ement frames
All segment
frames
Forwarding
Listening
Station
addresses
Network
management
and data frames
Port 2
S5693
Network
management
frames
Data
frames
BPDUs
