This TruthValue controls whether an L2PT transform is performed on eligible frames at egress; L2 Protocol Tunneling lets a carrier transparently tunnel a customer's Spanning Tree, CDP, or other L2 control frames across the carrier network by disguising them as data, and enabling this on egress reverses that disguise back to the original protocol frame before handing traffic to the customer. Getting this wrong can either leak carrier-internal tunneling artifacts to the customer or break their L2 protocol operation entirely. Enabling it so a customer's tunneled STP BPDUs re-emerge correctly formatted as STP frames at the far end is the intended effect.