Cisco WS-C2980G-A Software Guide - Page 102

Understanding How STPs Work Chapter 7 Configuring Spanning Tree • Listening • Learning • Forwarding • Disabled A port moves through these states: • From initialization to blocking • From blocking to either listening or disabled • From listening to either listening or disabled • From learning to either forwarding or disabled • From forwarding to disabled Figure 7-2 illustrates how a port moves through the states. Figure 7-2 STP Port States Boot-up initialization Blocking state Listening state Disabled state Learning state S5691 Forwarding state You can modify each port state by using management software, such as the VLAN Trunking Protocol (VTP). When you enable spanning tree, every switch in the network goes through the blocking state and the transitory states of listening and learning at power up. If properly configured, each port stabilizes into the forwarding or blocking state. When the spanning tree algorithm places a port in the forwarding state, the following occurs: • The port is put into the listening state while it waits for protocol information that suggests it should go to the blocking state • The port waits for the expiration of a protocol timer that moves the port to the learning state • In the learning state, the port continues to block frame forwarding as it learns station location information for the forwarding database • The expiration of a protocol timer moves the port to the forwarding state, where both learning and forwarding are enabled Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 7-6 78-15486-01