Cisco Certified Network Associate (CCNA) Practice Exam

Which command is used to enable Uplink Fast on a Cisco switch?

1. (config)#spanning-tree uplinkfast

2. (config)#enable uplinkfast

3. (config)#set uplinkfast

4. (config)#uplink fast enable

The correct answer is: (config)#spanning-tree uplinkfast

To enable Uplink Fast on a Cisco switch, the command that must be used is "spanning-tree uplinkfast." This command is entered in global configuration mode and is specifically designed to enhance the spanning tree protocol (STP) operation on switches that experience failures or changes in the network path. Uplink Fast is a feature that helps to speed up the transition of a switch from the blocking state to the forwarding state when a primary uplink (the main path to the network) fails. It achieves this by bypassing the normal STP listening and learning states, thus reducing downtime when a link goes down by allowing a backup link to take over quickly. The other options provided do not represent valid commands for enabling Uplink Fast on a Cisco switch. The command "enable uplinkfast" is not recognized as a valid syntax in Cisco IOS, nor is "set uplinkfast" or "uplink fast enable." These terms lack the correct structure and context that the Cisco IOS command line requires for implementing changes related to spanning tree features. Therefore, only "spanning-tree uplinkfast" correctly activates this important functionality for ensuring network resilience.