When is the Bridge Priority form of STP load balancing useful? What command(s) are used to implement this approach? What makes this technique so confusing?
The Bridge Priority form of STP load balancing can be useful if you are using pre-3.1 code and cannot use Root Bridge placement (because of traffic patterns) or portvlanpri (because the switches are not back-to-back). If you are using 3.1+ code, portvlancost is generally a better choice. The set spantree priority command is used to implement this approach. This technique can be confusing for several reasons:
The Bridge Priority values must be adjusted on devices that are upstream of where the load balancing takes place.
The Bridge Priority values must not be adjusted too low or your Root Bridge placement is disrupted.
It can be difficult to remember why each Bridge Priority was set.