Tossing Packets Over the Wall Using Transmit-Only Ethernet Cables

Solutions for transporting packets from an insecure DMZ into an organization’s internal network are described. All of the solutions attempt to prevent the establishment of two-way traffic by physically cutting the transmit wires at the receiving device on the internal network. Because alternate paths to the packet sender could exist, a user-mode packet relay on the internal network is used to accept and re-transmit the packets to the appropriate destination. Applications discussed include relaying of syslog and SNMP trap packets from DMZ systems to receiving hosts on a secure network, and monitoring traffic for IDS and diagnostic purposes using a system conveniently located on the secure internal network.