What are the priorities amongst the Interface Binding rules and when are they active?

The Interface Binding rules are prioritized by the order that they have been added with the first rule being the highest priority. They are active only when the WAN line for which the binding is defined has a connection. So, if there are 2 binding rules that match some of the same traffic then the first rule will be active unless there is a loss of connectivity on that WAN, in which case the second rule will be applied to the matched traffic.