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| 3.7 |  | Tuning, Verifying, and Troubleshooting Spanning-Tree Protocol |
| 3.7.2 |  | Configuring UplinkFast |

UplinkFast RSTP incorporates an automatically enabled feature exactly similar to Cisco uplink fast proprietary spanning tree extension. The 802.1w topology change mechanism clears the appropriate entries in the Content Addressable Memory (CAM) tables of the upstream bridges, removing the need for the dummy multicast generation process of uplink fast.

UplinkFast cannot be enabled on VLANs that have been configured for switch priority. To enable UplinkFast on a VLAN with switch priority configured, first restore the switch priority on the VLAN to the default value by using the no spanning-tree vlan vlan-id priority global configuration command.

When UplinkFast is enabled, it affects all VLANs on the switch. UplinkFast cannot be configured on an individual VLAN.

The UplinkFast feature is supported only when the switch is running PVST. Beginning in privileged EXEC mode, follow the steps outlined in Figure to enable UplinkFast.

When UplinkFast is enabled, the switch priority of all VLANs is set to 49152. If the path cost is changed to a value less than 3000 and then UplinkFast is enabled or if UplinkFast is already enabled, the path cost of all interfaces and VLAN trunks is increased by 3000 (if the path cost is changed to 3000 or above, the path cost is not altered). The changes to the switch priority and the path cost reduce the chance that the switch will become the root switch.

When UplinkFast is disabled, the switch priorities of all VLANs and path costs of all interfaces are set to default values unless the defaults had been modified.

To return the update packet rate to the default setting, use the no spanning-tree uplinkfast max-update-rate global configuration command. To disable UplinkFast, use the no spanning-tree uplinkfast command.