Abstract. As IPv4 address space approaches exhaustion, large networks are deploying IPv6 or preparing for deployment. However, there is little data available about the quantity and quality of IPv6 connectivity. We describe a methodology to measure IPv6 adoption from the perspective of a Web site operator and to evaluate the impact that adding IPv6 to a Web site will have on its users. We apply our methodology to the Google Web site and present results collected over the last year. Our data show that IPv6 adoption, while growing significantly, is still low, varies considerably by country, and is heavily influenced by a small number of large deployments. We find that native IPv6 latency is comparable to IPv4 and provide statistics on IPv6 transition mechanisms used. 1

The Teredo auto-tunnelling protocol allows IPv6 hosts behind IPv4 NATs to communicate with other IPv6 hosts. It is enabled by default on Windows Vista and Windows 7. But Windows clients are self-constrained: if their only IPv6 access is Teredo, they are unable to resolve host names to IPv6 addresses. We use web-based measurements to investigate the (latent) Teredo capability of Internet clients, and the delay introduced by Teredo. We compare this with native IPv6 and 6to4 tunnelling capability and delay. We find that only 6–7 % of connections are from fully IPv6-capable clients, but an additional 15–16 % of connections are from clients that would be IPv6-capable if Windows Teredo was not constrained. However, Teredo increases the median latency to fetch objects by 1–1.5 seconds compared to IPv4 or native IPv6, even with an optimally located Teredo relay. Furthermore, in many cases Teredo fails to establish a tunnel.