Unable to set socket options IPV6 multicast : No such device error - c

Question

I am working on linux Ubuntu 14.04 and trying to multicast using IPv6. I have a link local address of fe80::9a90:96ff:fe98:a985. Running the following code :
int main (int argc, char *argv[]) {
int sd;
struct in6_addr localInterface;
/* Create a datagram socket on which to send/receive. */
sd = socket(AF_INET6, SOCK_DGRAM, 0);
if(sd < 0) {
perror("Opening datagram socket error");
exit(1);
}
else {
printf("Opening the datagram socket...OK.\n");
}
/* Set local interface for outbound multicast datagrams. */
/* The IP address specified must be associated with a local, */
/* multicast capable interface. */
inet_pton (AF_INET6, "fe80::9a90:96ff:fe98:a985", &(localInterface.s6_addr));
if(setsockopt(sd, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char *)&localInterface, sizeof(localInterface)) < 0)
{
perror("Setting local interface error");
printf ("%d\n", errno);
exit(1);
}
else {
printf("Setting the local interface...OK\n");
}
}
gives the error : Setting local interface error : No such device
I have tested multicast to work with IPv4 and also successfully tested that IPv6 works by pinging a local node using ping6 command.

Answer 1

With a few adjustments I was able to modify your program to get it to send multicast packets (that show up in WireShark) on my Mac (running OS/X 10.10.5). I haven't tried it under other OS's, but it should more or less work on other OS's as well.
Note that the program has hard-coded the interface number to 4, since that is what en0 is on my computer; the interface number will likely be different on your computer, and for a generally useful program you'd want to discover the correct interface number dynamically (using getifaddrs() or GetAdaptersAddresses() or similar); it's only hard-coded here for simplicity.
Modified program follows:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>
int main (int argc, char *argv[])
{
int sd = socket(AF_INET6, SOCK_DGRAM, 0);
if(sd < 0)
{
perror("Opening datagram socket error");
exit(1);
}
else printf("Opening the datagram socket...OK.\n");
// 4 is the interface ID (scope_id) of interface en0 on my Mac,
// as printed by ifconfig; the appropriate interface index
// value on your computer will likely be different --jaf
int my_network_devices_scope_id = 4;
if(setsockopt(sd, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char *)&my_network_devices_scope_id, sizeof(my_network_devices_scope_id)) < 0)
{
perror("Setting local interface error");
printf ("%d\n", errno);
exit(1);
}
else printf("Setting the local interface...OK\n");
struct sockaddr_in6 multicastIP;
multicastIP.sin6_family = AF_INET6;
multicastIP.sin6_scope_id = my_network_devices_scope_id;
multicastIP.sin6_port = htons(9999); // destination port chosen at random
inet_pton(AF_INET6, "ff12::bead:cede:deed:feed", &multicastIP.sin6_addr.s6_addr); // a multicast address I chose at random
while(1)
{
char buf[] = "hello";
if (sendto(sd, buf, sizeof(buf), 0, (const struct sockaddr *) &multicastIP, sizeof(multicastIP)) == sizeof(buf))
{
printf("Sent a %i-byte multicast packet!\n", (int) sizeof(buf));
}
else perror("sendto");
sleep(1);
}
return 0;
}