This read-write 512-octet bitmap identifies which VLANs are configured as 'transparent' on a QinQ interface, meaning they pass through without the outer service tag being added, with each octet covering eight VLAN IDs and the most significant bit representing the highest-numbered VLAN in that octet. An admin sets specific bits in this bitmap to exempt certain customer VLANs from QinQ encapsulation on that port, letting some traffic bypass the double-tagging while the rest gets the outer tag applied. For example, setting the bit corresponding to VLAN 10 in the first octet would make VLAN 10 traffic pass through the interface untagged with the outer service TPID, while other VLANs on that port continue to be QinQ-tagged.