When I run "netstat" on my machine I get some lines like:tcp 0 0 ::ffff:188.8.131.52:80 ::ffff:<remote ip
::ffff is the IPv6 prefix for an IPv4 address mapped into IPv6 space
(something along those lines).
And it means that it is an IPv6 socket that is used for IPv4
communication. Application and socket-wise, it is IPv6 but network and
packet-wise it is IPv4. This is allowed as a transition mechanism if
net.ipv6.bindv6only=0 and the application didn't set the socket option
It seems that some recent OSes disable this option by default so that
IPv6 sockets can handle only real IPv6 communications.