On Wed, 19 Jan 2022 13:07:33 +0000 Chris Vine <vine35792...@gmail.com> wrote: [snip] > As I understand it, with linux IPv6 sockets are dual stack capable, and > in earlier kernel versions this was be enabled by default. I believe > with current versions that is no longer the case, and that you have to > specifically enable dual stack by turning off IPV6_V6ONLY using > setsockopt before binding on the socket. > > Then, if receiving a IPv4 connection from address 1.2.3.4, this would be > mapped as ::::ffff:1.2.3.4. > > I do not know about other OSes. I have half a memory that some earlier > versions of windows did not support dual stack sockets (XP?).
By the way I did use dual stack some years ago, and I cannot now remember all the details, but I think I may have had to bind on in6addr_any (which in dual stack would cover INADDR_ANY) or on :: (which would cover 127.0.0.1) to get dual stack to work. I suggest you play around with it to see. One other correction: when I said there was a mapping to ::::ffff: 1.2.3.4 I meant ::ffff:1.2.3.4.
