Cisco 7609 Configuration Manual page 199

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 Cisco 7600 series router, 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:
1. 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.
2. 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.
3. 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.
4. 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.
78-14064-04
Disabled
state
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
Understanding How STP Works
15-7