连接到IPv4映射的IPv6地址失败

Question

I am attempting to use an IPv6 socket to connect to an IPv4 address using an IPv4 mapped IPv6 address, on linux (debian-lenny-64 2.6.26-2-amd64)

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc, void **argv)
{
    struct addrinfo *sa;
    struct addrinfo *ra;

    int err = getaddrinfo("2001:DB8::2", 0, 0, &sa);

    int fd = socket(sa->ai_family, SOCK_DGRAM, 0);

    int v6only = 0;     

    err = setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (void *)&v6only, sizeof(v6only)); 

    err = bind(fd, sa->ai_addr, sa->ai_addrlen);

    err = getaddrinfo("::ffff:192.168.0.1", "9", 0, &ra);

//  err = getaddrinfo("2001:DB8::1", "9", 0, &ra);
//  err = getaddrinfo("::ffff:127.0.0.1", "9", 0, &ra);

    err = connect(fd, (struct sockaddr *)ra->ai_addr, sizeof(struct sockaddr_in6));
}

(I've removed error testing from the pasted code)

2001:DB8::2 and 192.168.0.2 are local addresses (both on the same interface).
2001:DB8::1 and 192.168.0.1 are the remote addresses (both on the same interface).

I change the remote address for the connect call and get the following:

• connect to ::ffff:127.0.0.1 success (localhost)
• connect to 2001:DB8::1 success (remote IPv6 address)
• connect to ::ffff:192.168.0.2 success (local IPv4 address)
• connect to ::ffff:192.168.0.1 failure (22 Invalid argument - remote IPv4)

If I change to doing IPv4 connects then the connects also work.

I think there must be an issue with routing somewhere but I'm at a loss to work out what I need to change. Firstly should I in theory be able to do this?
Any ideas what is going wrong?

Answer 1

• See the function "getaddrinfo()" as

    ~$ man getaddrinfo 

  .
• The ' hints ' paramter of the function has attribute ' ai_flags ', if you set it to ' AI_PASSIVE '. It can work for both IPv4 and IPv6 addressing modes.