Configuring STP and IEEE 802.1s MST
Figure 15-2 STP Layer 2 LAN Interface States
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
The Layer 2 LAN port is put into the listening state while it waits for protocol information that
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
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
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
port to the forwarding state, where both learning and frame forwarding are enabled.
Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
Understanding How STP Works