cmEthernetAccPortCpdV2L2PTTunnelMac is a read-write MAC address configured on the Ethernet access port that replaces the destination address of STP, CDP, and VTP frames whenever their control protocol disposition is set to pass-thru-l2pt, and is also used on decapsulation to recognize returning tunneled frames by their protocol signature plus this configured address. An administrator needs this set consistently at both ends of the L2PT tunnel, since a mismatched tunnel MAC would cause the far end to fail to recognize decapsulated STP/CDP/VTP frames as tunneled traffic. For example, a carrier tunneling a customer's spanning-tree BPDUs transparently across its core would configure this access port's tunnel MAC to a value both PE devices agree on before enabling pass-thru-l2pt on the relevant protocol dispositions.