Generally as a developer you just want to bind to "::" when listening as the equivalent of "0.0.0.0" ie all addresses, or "::1" for localhost (and create an ipv6 socket, but most higher level stacks will do that given an ipv6 adddress). In most stacks that is the only userspace change. The usual setup is that this will also map ipv4 connections over to ipv6. That is not always true, eg OpenBSD will never bind to both kinds of address, you have to listen on two sockets, and you can force that behaviour on other systems. This should work so long as the host you are on does not have ipv6 completely disabled in the kernel, even if there is in fact no ipv6 routing.
Most things "just work", though there are minor fixes and things to know, eg the standard notation for ipv6 literals in http is http://[::1]/ as the : might be a port specifier. I think the only thing I used recently that had no idea about ipv6 was Twisted, oh and some Java applications.
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Generally as a developer you just want to bind to "::" when listening as the equivalent of "0.0.0.0" ie all addresses, or "::1" for localhost (and create an ipv6 socket, but most higher level stacks will do that given an ipv6 adddress). In most stacks that is the only userspace change. The usual setup is that this will also map ipv4 connections over to ipv6. That is not always true, eg OpenBSD will never bind to both kinds of address, you have to listen on two sockets, and you can force that behaviour on other systems. This should work so long as the host you are on does not have ipv6 completely disabled in the kernel, even if there is in fact no ipv6 routing.
Most things "just work", though there are minor fixes and things to know, eg the standard notation for ipv6 literals in http is http://[::1]/ as the : might be a port specifier. I think the only thing I used recently that had no idea about ipv6 was Twisted, oh and some Java applications.