Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 230

Understanding How STP Works Chapter 17 Configuring STP and MST • Forwarding-The Layer 2 LAN port forwards frames. • Disabled-The Layer 2 LAN port does not participate in STP and is not forwarding frames. A Layer 2 LAN port moves through these five states as follows: • From initialization to blocking • From blocking to listening or to disabled • From listening to learning or to disabled • From learning to forwarding or to disabled • From forwarding to disabled Figure 17-2 illustrates how a Layer 2 LAN port moves through the five states. Figure 17-2 STP Layer 2 LAN Interface States Boot-up initialization Blocking state Listening state Disabled state Learning state S5691 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: 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. 17-6 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY OL-11439-03