7-8
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 7 Configuring Spanning Tree
Understanding How Spanning Tree Protocols Work
Figure 7-3
Port 2 in Blocking State
A port in the blocking state performs as follows:
•
Discards frames that are received from the attached segment.
•
Discards frames that are switched from another port for forwarding.
•
Does not incorporate station location into its address database. (There is no learning on a blocking
port, so there is no address database update.)
•
Receives BPDUs and directs them to the system module.
•
Does not transmit BPDUs that are received from the system module.
•
Receives and responds to network management messages.
Listening State
The listening state is the first transitional state that a port enters after the blocking state. The port enters
this state when the spanning tree determines that the port should participate in frame forwarding.
Learning is disabled in the listening state.
Figure 7-4
shows a port in the listening state.
Filtering
database
Frame
forwarding
System
module
Port 1
BPDUs
Segment
frames
Segment
frames
Forwarding
Blocking
BPDUs
Station
addresses
Network
management
and data frames
Port 2
S5692
Network
management
frames
Data
frames
