Fao/13 Managing Spanning Tree VLAN0004 32772 000d.edc2.0000 Fa0/13 VLAN0010 32778 000d.edc2.0000 Fa0/13 VLAN0100 32868 000d.edc2.0000 Fa0/13 VLAN0200 32968 000f.8f5c.5a00 There is no equivalent command in CatOS. Additional Spanning Tree Features Spanning tree was originally designed for bridges with few ports. With the advent of Ethernet switches, some enhancements were made to spanning tree. These com- monly seen enhancements helped make spanning tree more palatable by decreasing the time a host needs to wait for a port, and decreasing the convergence time in a layer-2 network. PortFast PortFast is a feature on Cisco switches that allows a port to bypass all of the other spanning tree states (see Figure 8-5) and proceed directly to the forwarding state. PortFast should be enabled only on ports that will not have switches connected. Spanning tree takes about 30 seconds to put a normal port into the forwarding state, which can cause systems using DHCP to time out and not get an IP address (on a Windows machine, a default IP address may be used). Enabling the PortFast feature on a port alleviates this problem, but you should be very careful when using this fea- ture. If a switch were to be connected to a port configured with PortFast active, a loop could occur that would not be detected. To enable PortFast on an IOS switch, use the spanning-tree portfast interface com- mand. The switch will deliver a nice warning about the dangers of PortFast when you enable the feature: Cat-3550(config-if)# spanning-tree portfast %Warning: portfast should only be enabled on ports connected to a single host. Connecting hubs, concentrators, switches, bridges, etc to this interface when portfast is enabled, can cause temporary bridging loops. Use with CAUTION %Portfast has been configured on FastEtherneto/20 but will only have effect when the interface is in a non-trunking mode. To disable PortFast on an interface in IOS, simply negate the command. There is no fanfare when disabling PortFast: Cat-3550(config-if)# no spanning-tree por