PREVENTING DUPLICATE SOURCES FROM CLIENTS SERVED BY A NETWORK ADDRESS PORT TRANSLATOR (NAPT)

Preventing duplicate sources on a protocol connection that uses network addresses, protocols and port numbers to identify source applications that are served by a NAPT. If an arriving packet encapsulates an encrypted packet and has passed through an NAPT en route to the destination host, the encapsulated packet is decrypted to obtain an original source port number and original packet protocol from the decrypted packet. A source port mapping table (SPMT) is searched for an association between the NAPT source address, the original source port, and the original packet protocol associated with the NAPT source address and port number. If an incorrect association is found, the packet is rejected as representing an illegal duplicate source; that is, a second packet from a different host served by a NAPT that is USING the same SOURCE port and protocol.