How to send multicast data over UDP - IPv6 using global address - c++

Question

I want to send and receive data over UDP using IPv6 multicast address(ff02::1). I am able to send data to multicast address but it's using link local address(fe80: instead of unicast(global) address. How can I send data to link local address instead of unicast(global) address?
Moreover, if program is bind to any addressgroupSock.sin6_addr = in6addr_any; bind(sd, (sockaddr*)&groupSock, sizeof groupSock)); it receives the same data that's being transmitted(loop back). Is there any way to avoid reception of data that's transmitted by host itself.
Any help/support in this regard would be highly appreciated.
using namespace std;
int main(int argc, char const *argv[]) {
struct sockaddr_in6 groupSock;
int sd = -1;
char databuf[10];
int datalen = sizeof databuf;
/* Create a datagram socket on which to send/receive. */
if((sd = socket(AF_INET6, SOCK_DGRAM, 0)) < 0) {
perror("Opening datagram socket error");
return 1;
} else {
cout << "Opening the datagram socket...OK." << endl;;
}
/* Enable SO_REUSEADDR to allow multiple instances of this */
/* application to receive copies of the multicast datagrams. */
int reuse = 1;
if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof reuse) < 0) {
perror("Setting SO_REUSEADDR error");
close(sd);
return 1;
} else {
cout << "Setting SO_REUSEADDR...OK." << endl;
}
/* Initialize the group sockaddr structure with a */
memset((char *) &groupSock, 0, sizeof groupSock);
groupSock.sin6_family = AF_INET6;
// address of the group
inet_pton(AF_INET6, "ff02::01", &groupSock.sin6_addr);
groupSock.sin6_port = htons(13400);
/* Set local interface for outbound multicast datagrams. */
/* The IP address specified must be associated with a local, */
/* multicast capable interface. */
int ifindex = if_nametoindex ("vx0");
cout << "ifindex is " << ifindex << endl;
if(setsockopt(sd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &ifindex, sizeof ifindex)) {
perror("Setting local interface error");
return 1;
} else {
cout << "Setting the local interface...OK" << endl;
}
struct ifreq ifr;
if_indextoname(ifindex , ifr.ifr_name);
if(setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof(ifr))){
perror("Setting SO_BINDTODEVICE interface error");
return 1;
} else {
cout << "Setting the SO_BINDTODEVICE interface...OK" << endl;
}
// choice is 0 for sending and 1 for receiving
int choice;
if (argc < 2) {
cout << "missing argv[1]" << endl;
return 1;
}
sscanf (argv[1], "%d", &choice);
// if sending
if (choice == 0) {
memset(databuf, 'a', datalen);
databuf[sizeof databuf - 1] = '\0';
if (sendto(sd, databuf, datalen, 0, (sockaddr*)&groupSock, sizeof groupSock) < 0) {
cout << "Error in send" << endl;
} else {
cout << "Send okay!" << endl;
}
}
// if receiving
else if (choice == 1) {
groupSock.sin6_addr = in6addr_any;
if(bind(sd, (sockaddr*)&groupSock, sizeof groupSock)) {
perror("Binding datagram socket error");
close(sd);
return 1;
} else {
cout << "Binding datagram socket...OK." << endl;
}
/* Join the multicast group ff0e::/16 on the local */
/* interface. Note that this IP_ADD_MEMBERSHIP option must be */
/* called for each local interface over which the multicast */
/* datagrams are to be received. */
struct ipv6_mreq group;
inet_pton (AF_INET6, "ff02::01", &group.ipv6mr_multiaddr.s6_addr);
group.ipv6mr_interface = ifindex;
if(setsockopt(sd, IPPROTO_IPV6, IPV6_JOIN_GROUP, (char *)&group, sizeof group) < 0) {
perror("Adding multicast group error");
close(sd);
return 1;
} else {
cout << "Adding multicast group...OK." << endl;
}
if (read(sd, databuf, datalen) < 0) {
perror("Error in read");
} else {
databuf[sizeof databuf - 1] = '\0';// just for safety
cout << "Read Okay" << endl;
cout << "Message is : " << databuf << endl;
}
}
return 0;
}