8-10
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
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Chapter 8 Configuring Spanning Tree
Understanding How Spanning Tree Protocols Work
Forwarding State
A port in the forwarding state forwards frames, as shown in
Figure 8-6
. The port enters the forwarding
state from the learning state.
Figure 8-6
Port 2 in Forwarding State
A port in the forwarding state performs as follows:
•
Forwards frames received from the attached segment.
•
Forwards frames switched from another port for forwarding.
•
Incorporates 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.
Caution
Use spanning tree PortFast mode only on ports directly connected to individual workstations to allow
these ports to come up and go directly to the forwarding state, instead of having to go through the
entire spanning tree initialization process. To prevent illegal topologies, enable spanning tree on ports
connected to switches or other devices that forward messages. For more information about PortFast,
see
Chapter 9, “Configuring Spanning Tree PortFast, UplinkFast, BackboneFast, and Loop Guard.”
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
