This read-write TruthValue expresses the operator's preference for whether control-plane traffic may be routed over this trunk. Setting it to True tells PAR to avoid the trunk for control-plane traffic unless every other trunk is unavailable, i.e. not in the added(2) operational state, in which case it is chosen anyway. For example, an administrator would set this True on a low-bandwidth backup trunk to keep node-to-node signaling off it under normal conditions while still allowing it to carry control traffic if all primary trunks go down.