Cisco WS-C4003 Software Guide - Page 106

How Spanning Tree Protocols Work Chapter 7 Configuring Spanning Tree Forwarding State A port in the forwarding state forwards frames, as shown in Figure 7-6. The port enters the forwarding state from the learning state. Figure 7-6 Port 2 in Forwarding State All segment frames Forwarding Station addresses Port 1 BPDUs Network management and data frames Filtering database System module Frame forwarding S5695 Station addresses BPDUs Port 2 Network management and data frames Forwarding All segment frames A port in the forwarding state performs as follows: • Forwards frames received from the attached segment. • Forwards frames switched from another port for forwarding. • Incorporates station location information into its address database. • Receives BPDUs and directs them to the system module. • Processes BPDUs received from the system module. • Receives and responds to network management messages. Caution Use spanning tree PortFast mode only on ports directly connected to individual workstations to allow these ports to come up and go directly to the forwarding state, instead of having to go through the entire spanning tree initialization process. To prevent illegal topologies, enable spanning tree on ports connected to switches or other devices that forward messages. For more information about PortFast, see Chapter 8, "Configuring Spanning Tree PortFast, UplinkFast, and BackboneFast, and Loop Guard." Disabled State A port in the disabled state does not participate in frame forwarding or STP, as shown in Figure 7-7. A port in the disabled state is virtually nonoperational. 7-10 Software Configuration Guide-Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4 78-12647-02