The Freenet6 client is a good way for people behind NAT (or in the case of two NATs) to access IPv6-enabled sites. I was also able to access sites from cmd.exe, using ping6 to ping ipv6.com and ftp to connect to the IPv6 only FTP server at ftp6.netbsd.org. The client was running I configured it with the username and password I registered, and I set broker.freenet.net as my Gateway6 address.”]
Source: https://taosecurity.blogspot.com/2009/01/ipv6-tunnel-on-windows-xp-using.html