Cisco CISCO1401 Software Guide - Page 107

Chapter 8 Configuring Spanning Tree Protocol Figure 8-1 Spanning-Tree Topology LAN segment A Bridge 1 Bridge 2 Understanding Spanning Tree Protocol Bridge 3 Bridge 4 56612 LAN segment B Spanning-Tree Interface States Propagation delays can occur when protocol information passes through a wireless LAN. As a result, topology changes can take place at different times and at different places in the network. When an interface transitions directly from nonparticipation in the spanning-tree topology to the forwarding state, it can create temporary data loops. Interfaces must wait for new topology information to propagate through the LAN before starting to forward frames. They must allow the frame lifetime to expire for forwarded frames that have used the old topology. Each interface on a bridge using spanning tree exists in one of these states: • Blocking-The interface does not participate in frame forwarding. • Listening-The first transitional state after the blocking state when the spanning tree determines that the interface should participate in frame forwarding. • Learning-The interface prepares to participate in frame forwarding. • Forwarding-The interface forwards frames. • Disabled-The interface is not participating in spanning tree because of a shutdown port, no link on the port, or no spanning-tree instance running on the port. An interface moves through these states: • 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 OL-4059-01 Cisco Aironet 1400 Series Wireless Bridges Software Configuration Guide 8-5