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POCreating socket compatible with IPv4 and IPv6
 

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  1. POCreating socket compatible with IPv4 and IPv6
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    <p>I am writing a program which can read the IP address that I have been assigned on a specific network interface (VLAN: eth0.32). I won't know if I have been assigned an IPv4 or a IPv6 address so I try to write it protocol family agnostic. </p> <p>The way it works is: with a for, I navigate through the list of available network interfaces and I stop at the point where I find my VLAN (eth0.32) to read the IP address. Anyways, at this point of development I just want that it works for IPv4 but leave it ready when I want to implement IPv6 support.</p> <p>The program works and reads the IPv4 address if I create the socket normally:</p> <pre><code>sd=socket(PF_INET, SOCK_DGRAM, 0); </code></pre> <p>But as I won't be able to read IPv6 addresses with this socket family (PF_INET=IPv4) I do it like this:</p> <pre><code>sd=socket(PF_INET6, SOCK_DGRAM, 0); setsockopt(sd, SOL_SOCKET, IPV6_V6ONLY, 0, sizeof(int)); </code></pre> <p>The problem is that with this IPv6 socket, it fails to accomplish the if condition to read the ip address:</p> <pre><code>if (ioctl(sd, SIOCGIFCONF, &amp;ifc) == 0) </code></pre> <p>For more information, this is my whole code:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;string.h&gt; #include &lt;sys/types.h&gt; #include &lt;sys/socket.h&gt; #include &lt;sys/ioctl.h&gt; #include &lt;netinet/in.h&gt; #include &lt;netdb.h&gt; #include &lt;net/if.h&gt; int main(int argc, char **argv) { struct ifconf ifc; struct ifreq ifr[MAX_NETWORK_INTERFACES]; int ifc_num, addr, i; static uint8 sd=0; sd=socket(PF_INET6, SOCK_DGRAM, 0); setsockopt(sd, SOL_SOCKET, IPV6_V6ONLY, 0, sizeof(int)); //I change the socket option IPV6_V6ONLY to false, so it should be compatible with IPv4 if (sd &gt; 0) { ifc.ifc_len = sizeof(ifr); ifc.ifc_ifcu.ifcu_buf = (caddr_t)ifr; //Buffer address if (ioctl(sd, SIOCGIFCONF, &amp;ifc) == 0) { ifc_num = ifc.ifc_len / sizeof(struct ifreq); //Number of network interfaces found for (i = 0; i &lt; ifc_num; i++) { if(ifr[i].ifr_addr.sa_family != AF_INET) //If it is not an IPv4 address, we do nothing { continue; } if (strcmp(ifr[i].ifr_ifrn.ifrn_name,"eth0.32")==0) { if (ioctl(sd, SIOCGIFADDR, &amp;ifr[i]) == 0) // HERE IS WHERE THE IPv6 SOCKET DOESN'T ENTER!!! { addr = ntohl(((struct sockaddr_in *)(&amp;ifr[i].ifr_addr))-&gt;sin_addr.s_addr); } fclose(fp); break; // end loop } } } } return addr; } </code></pre> <p>Thanks in advance for your help!</p>
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    1. COGetSocketForAddressForAdapter might help you - https://github.com/jselbie/stunserver/blob/master/networkutils/adapters.cpp#L111
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