3Com LANPLEX 2500, Operation Manual

Page: 52 / 139

Spanning Tree and the Bridged Network 5-17
Figure 5-9 illustrates the factors that cause a port to change from one state
to another. The arrows indicate the direction of movement between states.
The numbers correspond to the factors that affect the transition.
For example, for a port in the blocking state to transition to the listening
state, the Spanning Tree algorithm must select that port as a designated or
root port. After the port enters the listening state, forward delay must expire
before the port can transition to the learning state. If a port in listening,
learning, or forwarding state is disabled by the network administrator or by
a failure or initialization, then that port becomes disabled.
Figure 5-9 Factors Involved in Spanning Tree Port State Transitions
Disabled A port is disabled when Spanning Tree Protocol has been turned off
for that specific port or when the port has failed. In the disabled state,
the port does not participate in the Spanning Tree algorithm. If
Spanning Tree has been turned off for a specific port, that port
continues to forward frames only if Spanning Tree Protocol is disabled
for the entire bridge.
Table 5-1 Spanning Tree Port States (continued)
Port State Description
Disabled Blocking Listening Learning Forwarding
port enabled by either network administrator or initialization
port disabled by either network administrator or failure
Spanning Tree algorithm selects port as designated or root
Spanning Tree algorithm does not select port as designated or root
forwarding timer (forward delay) expires
1
4
3
2
5
1
2
5
&
1
2
3
4
5