“If any root switch for the specified VLAN has a switch priority lower than 24576, the switch sets its own priority for the specified VLAN to 4096 less than the lowest switch priority”. This statement is not correct, if for example your current root has priority 24576 and you type “root primary” on another switch, what happens is the following (as you want the new switch to become root):
1. if the “new” root bridge has a lower MAC than the old root, it will set the same priority as the old root, in this case 24576, and it will win election becasue of lower MAC
2. if the “new” root bridge has a higher MAC than old root, it will set the priority to 24576-4096 and will win the election
Good luck with your studies!
UplinkFast cannot be enabled on VLANs that have been configured with a switch priority.
However switch will accept the “spanning-tree uplink” command eventhough priority was already configured manually. It wont throws any error/alert. Even in “sh spanning-tree summay” shows uplink fast is enabled. we can confirm this by checking in the “sh spanning-tree vlan 2” command where priority and cost will not increased. Also you wont see the “uplinkfast enabled”