D-link DIR-825AC G1 devices have Insufficient Compartmentalization between a host network and a guest network that are established by the same device. They forward ARP requests, which are sent as broadcast packets, between the host and the guest networks. To use this leakage as a direct covert channel, the sender can trivially issue an ARP request to an arbitrary computer on the network. (In general, some routers restrict ARP forwarding only to requests destined for the network's subnet mask, but these routers did not restrict this traffic in any way. Depending on this factor, one must use either the lower 8 bits of the IP address, or the entire 32 bits, as the data payload.)