https://fosdem.org/2015/news/2015-01-31-ipv6-only-again/

Last year we turned off IPv4 on our main FOSDEM wireless network. They idea is to confront developers with the IPv6-reality and encourage them to fix bugs. Progress has been made, but there is a lot of work left to do!

FOSDEM is a unique opportunity to confront thousands of developers with an IPv6-only reality. We are hopeful that making our default network IPv6-only will encourage people to fix bugs in applications and devices.

The FOSDEM network has NAT64 and DNS64 transition measures in place for communicating with the legacy internet. For those who need it, the FOSDEM-legacy wireless network provides the same dual stack connectivity we offered on FOSDEM prior to 2014.

While last year we had “seatbelts” in place for flipping FOSDEM back to dual stack, we decided not to implement those this year. If the main network catches fire, we will just have to fix our bugs!

• FOSDEM: IPv6-only, provides NAT64 and DNS64. Recursive DNS resolvers announced with RA and DHCPv6. If you need to configure DNS manually, use 2001:67c:1810:f056::2 and 2001:41d0:2:1959:21c:c0ff:fe88:6f58
• FOSDEM-legacy: provides native IPv6 and legacy IP connectivity. No DNS64.

But still Android has issues
https://code.google.com/p/android/issues/detail?id=32629https://code.google.com/p/android/issues/detail?id=32621