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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
Forwarding State
A Layer 2 LAN port in the forwarding state forwards frames, as shown in Figure 15-6. The Layer 2 LAN
port enters the forwarding state from the learning state.
Figure 15-6 Interface 2 in Forwarding State
A Layer 2 LAN port in the forwarding state performs as follows:
• Forwards frames received from the attached segment.
• Forwards frames switched from another port for forwarding.
• Incorporates end station location information into its address database.
• Receives BPDUs and directs them to the system module.
• Processes 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
All segment
frames
Forwarding
Forwarding
BPDUs
Station
addresses
Network
management
and data frames
Port 2
S5695
Network
management
and data frames
Station
addresses
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