External dynamic mapping method for NAT traversal

On the Internet, it is not possible to initiate communication to internal nodes located behind a Network Address Translator (NAT) from external nodes. Therefore, we need to have a NAT traversal technology that can establish a connection between the external and internal nodes. Technologies thus far often depend on specific applications and their usage is rather limited. There are other methods which do not depend on any applications, but their efficiency for end-to-end communication is usually lowered quite a lot because they need a specific server that relays packets. This paper presents an external dynamic mapping method to solve such problems. We also define NAT-free (NAT-f) protocol to realize the method. A NAT mapping is created by a negotiation between an external node and a home gateway at the time when the external node initiates communication with an internal node. The kernel in the external node translates the address and the port number in the sending packet to a mapped-address. We have implemented and evaluated a trial system, and the results show that there is almost no performance degradation.