Indicates if this is a preferential CUG. A value of false means non-preferred CUG. There can be at most one preferential CUG on an interface. When a preferential cug exists, this object has to be set to false before another CUG can become a preferential CUG. For e.g., if CUG X is the preferential CUG and CUG Y has to take the role of preferential CUG, change CUG X to be non-preferential by modifying this object to false and make CUG Y the preferential CUG by modifying this object to true.