Binding to LOOPBACK in IPV6 - IPV4 is bound to ANY?

Question

I swear I've seen this asked before, but I can't hit upon the magic search string to find it for me:

I create a socket for listening using:

s = socket()...
getaddrinfo("::1",...);
bind()...

and I end up with an IPV6 socket bound to "::1" and an IPV4 socket bound to "0.0.0.0". I expect to get the IPV4 socket bound to "127.0.0.1". Why is this happening, and how can I fix it to only accept localhost connections on the ipv4 socket as wel?

This is on Win7 and I've previously turned off IPV6_V6ONLY.

Answer 1

getaddrinfo() and bind() only operate on one IP at a time. IPv4 binds to 0.0.0.0 if you do not specify your own explicit binding. It sounds like you are calling bind() only once for the IPv6 portion of a dual-stack socket and ignoring its IPv4 portion. I do not know if this will work, but try calling bind() twice, once with the IPv6 "::1" address, and again with the IPv6 "::FFFF:127.0.0.1" address (remember that IPv4 addresses on a dual-stack socket must be represented as IPv4-mapped IPv6 addresses).