 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 C Switch C Figure 8-6. UplinkFast example Additional Spanning Tree Features 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 in which 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: 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 (y/n) [n]? y VLANs 1-4094 bridge priority set to 32768. The port cost of all bridge ports set to default value. The portvlancost of all bridge ports set to default value. uplinkfast all-protocols field set to off. uplinkfast disabled for bridge. The values are not necessarily set to what they were before I enabled UplinkFast-they are returned to their de