University of Southampton Tunneling IPv6 packets over the IPv4 Internet played a major role in the early stages of IPv6 deployment. This was useful because in the early days the routers in the internet did not support IPv6. Nowadays, tunneling is used to get across legacy equipment and ISPs that do not support IPv6. Many different tunneling mechanisms have been invented. This document describes the drivers for IPv6 tunneling, the general architectures of existing mechanisms, and a set of desirable properties against which subsequent analysis of the mechanisms may be made. The document is aimed at small end sites that may typically utilise tunneling methods in an early IPv6 deployment.