Dell Networking N4000 Series Configuration Manual page 752

Figure 22-19. STP Example Network Diagram
Of the four switches in Figure 22-19, the administrator decides that Switch A
is the most centrally located in the network and is the least likely to be moved
or redeployed. For these reasons, the administrator selects it as the root bridge
for the spanning tree. The administrator configures Switch A with the highest
priority and uses the default priority values for Switch B, Switch C, and
Switch D.
For all switches, the administrator also configures ports 4–17 in Port Fast
mode because these ports are connected to hosts and can transition directly
to the Forwarding state to speed up the connection time between the hosts
and the network.
752
Configuring the Spanning Tree Protocol