- draft version - Behavior and Classification of NAT devices and implications for NAT Traversal - draft

For a long time, traditional client-server communication was the predominant communication paradigm of the Internet. Network Address Translation devices (NAT) emerged to help with the limited availability of IP addresses and were designed with the hypothesis of asymmetric connection establishment in mind. But with the growing success of peer-to-peer applications, this assumption is no longer true. Consequently NAT Traversal became a field of intensive research and standardization for enabling efficient operation of new services. This article provides a comprehensive overview of Network Address Translation and introduces established NAT Traversal techniques. A new categorization of applications into four NAT Traversal Service Categories helps to determine applicable techniques for NAT Traversal. The Interactive Connectivity Establishment (ICE) framework is categorized and a new framework is introduced that addresses scenarios that are not supported by ICE. Current results from a field test on NAT behavior and the success ratio of NAT Traversal techniques support the feasibility of this classification.