STP topology best practices

• Use Router-On-A-Stick Topology. Place the most powerful managed switch between the router and the rest of the LAN to serve as the core switch. Connect additional equipment to the managed switch.

• Set the core switch’s Bridge Priority to 4096.

• Do not put an unmanaged switch between managed switches.

• Increment the Bridge Priority by 4096 at every switch tier. (i.e. 4096 for the core switch, 8192 for the second tier of switches, 12288 for the third tier of switches, etc.)

• Disable Edge Port and Auto Edge on each port.

Note: STP traffic can flow through an unmanaged switch and the devices connected to it, but a device can only benefit from STP by being connected to an STP-enabled port on managed switch.

What happens if the core switch fails?

To make a loop-free environment, the edge switches elect the switch with the lowest priority as the new root bridge. The topology above would break into two separate instances of STP because they have no link between them.

If all the switches in these topologies have the default Bridge Priority, the new topology could create two sub-optimal instances of STP.