port fails. This allows the network to recover in five seconds or Additional Spanning Tree Features less. This feature affects all VLANs on the switch. It also sets the bridge priority to 49,152 to all but ensure that the switch will not become the root bridge. Figure 8-6 shows where Uplink Fast would be applied in a simple network. Switches A and B would be either core or distribution switches. Switch C would be an access- layer switch. The only links to other switches on Switch C are to the distribution or core. Root bridge Switch A Switch B Forwarding Forwarding Forwarding Forwarding Forwarding Blocking UplinkFast configured only on Switch Switch C Figure 8-6. UplinkFast example UplinkFast should be configured only on access-layer switches. It should never be enabled on distribution-layer or core switches because it prevents the switch from becoming the root bridge, which is usually counterindicated in core switches. To configure UplinkFast on a CatOS switch, use the set spantree uplinkfast enable command: Catos-6509: (enable) set spantree uplinkfast enable VLANs 1-4094 bridge priority set to 49152. The port cost and portvlancost of all ports set to above 3000. Station update rate set to 15 packets/100ms. uplinkfast all-protocols field set to off. uplinkfast enabled for bridge. When disabling UplinkFast, be careful, and remember that a lot of other values were changed when you enabled the feature: Catos-6509: (enable) set spantree uplinkfast disable uplinkfast disabled for bridge. Use clear spantree uplinkfast to return stp parameters to default. That last line of output is important. If you're moving a switch from an access-layer role to a role where you want it to become the root bridge, you'll need to change the priorities back to their defaults. Here's what happens when I follow the switch's advice: Chapter 8: Spanning Tree Catos-6509: (enable) clear spantree uplinkfast This command will cause all portcosts, portvlancosts, and the bridge priority on all vlans to be set to default. Do you want to continue (