A New Method for Symmetric NAT Traversal in UDP and TCP

This paper proposes a new method for Network Address Translator (NAT) Traversal in UDP. Several techniques have been proposed for traversing NAT or firewall boxes in UDP. These techniques can establish UDP communication between hosts behind NATs. However, existing NAT traversal methods, including Universal Plug and Play (UPnP), Simple traversal of UDP over NATs (STUN) and Teredo, cannot traverse symmetric NAT boxes. Our method uses a new port prediction method. It controls ports to traverse symmetric NAT boxes as well as other kinds of NATs. In addition, our new method can be extended for simple NAT traversal in TCP. The method is based on a new UDP hole punching technique. We have tested nine working NAT products in our laboratory. The results show that our method can be practically implemented for successful NAT traversal for real use.