On: IPv6 is the only way forward

[tonymet]

Having 2 sockets for loopback or multiple interfaces is a huge pain

[BenjiWiebe → tonymet]

Bind to '::' and you can get v4 and v6 traffic on one socket.

[IcePic → BenjiWiebe]

Not on all OSes. And it's not all good to have one less socket, there are still issues with people not expecting v4 traffic on a v6-capable socket, like described here:

https://radar.offseq.com/threat/ipv4-mapped-ipv6-addresses-t...

If you want to handle two protocols, it is not unreasonable to use two sockets.

[tonymet → BenjiWiebe]

Doesn’t work for loopback (you have to listen externally )

[vimredo → tonymet]

It works fine for me on NixOS (Linux), with a recent kernel version and no weird config options - or at least I think so.