Cisco 6500 Series Software Configuration Manual page 197

Chapter 15 Configuring STP and IEEE 802.1s MST
Figure 15-2 STP Layer 2 LAN Interface States
Boot-up
initialization
Blocking
state
Listening
state
Learning
state
Forwarding
state
When you enable STP, every port in the Catalyst 6500 series switch, VLAN, and network goes through
the blocking state and the transitory states of listening and learning at power up. If properly configured,
each Layer 2 LAN port stabilizes to the forwarding or blocking state.
When the STP algorithm places a Layer 2 LAN port in the forwarding state, the following process
occurs:
The Layer 2 LAN port is put into the listening state while it waits for protocol information that
1.
suggests it should go to the blocking state.
The Layer 2 LAN port waits for the forward delay timer to expire, moves the Layer 2 LAN port to
2.
the learning state, and resets the forward delay timer.
In the learning state, the Layer 2 LAN port continues to block frame forwarding as it learns end
3.
station location information for the forwarding database.
The Layer 2 LAN port waits for the forward delay timer to expire and then moves the Layer 2 LAN
4.
port to the forwarding state, where both learning and frame forwarding are enabled.
78-14099-04
Disabled
state
Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
Understanding How STP Works
15-7