A New Protocol to Determine the NAT Characteristics of a Host

The shortage of IPv4 addresses and the very slow transition to IPv6 leads to well-established pragmatic solutions in the Internet: today many hosts are still using IPv4 and are connected to the Internet over a Network Address Translation router. For many applications, which need inbound connections, like e.g. voice-over-IP or peer-to-peer-based systems it is necessary to determine the characteristics of the surrounding network environment, i.e. the behavior of the used router. In most cases this information is required to successfully establish inbound connections. Therefore, we present in this paper a new protocol to determine the characteristics of the used router. Our protocol is backward compatible to the well known STUN protocol while providing more detailed results. Furthermore, our protocol can be used in a fully decentralized way, i.e. without any centralized servers, making it suitable for pure peer-to-peer-based systems. We complete the presentation of our new protocol with an evaluation through a field experiment.