Cisco WS-C4003 Software Guide - Page 134
Configuring PortFast, Enabling Spanning Tree PortFast
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Configuring PortFast Chapter 8 Configuring Spanning Tree PortFast, UplinkFast, and BackboneFast, and Loop Guard Caution PortFast should be used only when connecting a single end station to a switch port. If you enable PortFast on a port connected to another networking device, such as a switch, you can create network loops. When the switch powers up, or when a device is connected to a port, the port normally enters the spanning tree listening state. When the forward delay timer expires, the port enters the learning state. When the forward delay timer expires a second time, the port is transitioned to the forwarding or blocking state. When you enable PortFast on a port, the port is immediately and permanently transitioned to the spanning tree forwarding state. Configuring PortFast These sections describe how to configure spanning tree PortFast on the switch: • Enabling Spanning Tree PortFast, page 8-2 • Disabling Spanning Tree PortFast, page 8-3 Enabling Spanning Tree PortFast Caution PortFast should be used only when connecting a single end station to a switch port. If you enable PortFast on a port connected to another networking device, such as a switch, you can create network loops. To enable PortFast on a switch port, perform this task in privileged mode: Step 1 Step 2 Task Enable PortFast on a switch port connected to a single workstation or server. Verify the PortFast setting. Command set spantree portfast mod_num/port_num enable show spantree mod_num/port_num This example shows how to enable PortFast on port 1 of module 4 and verify the configuration (the PortFast status is shown in the "Fast-Start" column): Console> (enable) set spantree portfast 4/1 enable Warning: Spantree port fast start should only be enabled on ports connected to a single host. Connecting hubs, concentrators, switches, bridges, etc. to a fast start port can cause temporary spanning tree loops. Use with caution. Spantree port 4/1 fast start enabled. Console> (enable) show spantree 4/1 Port Vlan Port-State Cost Priority Fast-Start Group-method 4/1 1 blocking 19 20 enabled 4/1 100 forwarding 10 20 enabled 4/1 521 blocking 19 20 enabled 4/1 522 blocking 19 20 enabled 4/1 523 blocking 19 20 enabled Software Configuration Guide-Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4 8-2 78-12647-02