This read-write enumeration selects how a test plug binds to a network interface: none disables it, pmi binds it to the primary management interface (useful for single-interface devices like IP phones), and ifIndex or ipAddress bind it to a specific interface or address. An admin picks the binding method that matches the device's topology, for instance using pmi on a phone with only one interface. Setting avCnaTpConfBindTo to ifIndex(3) on a multi-interface gateway lets the admin pin a test plug to a specific physical port rather than the management interface.