This object designates the Layer 2 Protocol Tunneling role of a specific switch port: 'none' for a normal port with tunneling disabled, 'uni' for a port facing a customer site where protocol PDUs get tunneled across the provider network, or 'nni' for a port facing the provider network where tunneled PDUs are restored to their original form. Administrators set this per port when building a provider network that needs to carry customer STP or GVRP traffic transparently between sites. For example, setting a port connecting to a customer's switch to uni(2) means BPDUs arriving there will be encapsulated and tunneled rather than processed locally.