selection of pool

Priority-based member activation
With the Priority Group Activation feature, you can specify the minimum number of members that must remain available in each priority group in order for traffic to remain confined to that group. This feature is used in tandem with the Priority Group feature for individual pool members.
If the number of available members assigned to the highest priority group drops below the number that you specify, Local Traffic Manager distributes traffic to the next highest priority group, and so on.