A method for a first network to receive a packet from a second network is provided, including a router at the first network receiving the packet from the second network, the packet addressed to a client reachable through the first network; the router inspecting the packet for a nonrepudiable marking provided by the second network; if the nonrepudiable marking is present and matches the packet, adding an indicator pointing to the second network in the packet; adding a second nonrepudiable marking to the packet, and transmitting the packet to a destination; and otherwise, dropping the packet.