All things related to multicast

[Stig Venaas <>]

I didn't look much at your code. Here's my variant of openSSM() that I
just wrote. I believe it works with both IPv4 and IPv6 on recent Linux
kernels. I tested with 2.6.7. Some more error checking should be done
and the reporting improved. Attached is the complete source I used.

I tested the program by running it with strace and while it sleeps
doing "cat /proc/net/mcfilter" and "netstat -a". In my case I then
see:

Idx Device        MCA        SRC    INC    EXC
  4   ath0 0xe0010203 0x9e263fc8      1      0

udp        0      0 224.1.2.3:5001          *:*

So I think it works.

Note that I have interface ath0 while you probably have eth0. In the
attached source it's eth0. In 2.6.9 I think perhaps you can leave
interface unspecified. It also includes more header files than is
needed.

Let me know if there are any problems.

Stig
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <errno.h>
#include <netdb.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef MCAST_JOIN_SOURCE_GROUP
struct group_source_req {
    uint32_t                gsr_interface; /* interface index */
    struct sockaddr_storage gsr_group;     /* group address */
    struct sockaddr_storage gsr_source;    /* source address */
};
#define MCAST_JOIN_SOURCE_GROUP         46
#define MCAST_LEAVE_SOURCE_GROUP        47
#endif

int openSSM(source, group, port)
     char *source;
     char *group;
     char *port;
{
    int e, s, slevel;
    struct addrinfo hints, *res;
    struct group_source_req gsreq;

    /* Should be possible to use "0" for interface or take interface
       name as argument */
    gsreq.gsr_interface = if_nametoindex("eth0");

    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;
    
    if ((e = getaddrinfo(source, NULL, &hints, &res))) {
        fprintf(stderr, "getaddrinfo failed: %s\n", gai_strerror(e));
        return -1;
    }

    /* We only use first value, a name might resolve to multiple */
    if ((s = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) < 0)
        return -1;

    memcpy(&gsreq.gsr_source, res->ai_addr, res->ai_addrlen);
    freeaddrinfo(res);

    if ((e = getaddrinfo(group, port, &hints, &res))) {
        fprintf(stderr, "getaddrinfo failed: %s\n", gai_strerror(e));
        return -1;
    }
    /* We only use first value, a name might resolve to multiple */
    slevel = res->ai_family == AF_INET ? IPPROTO_IP : IPPROTO_IPV6;
    memcpy(&gsreq.gsr_group, res->ai_addr, res->ai_addrlen);
    freeaddrinfo(res);

    if (bind(s, res->ai_addr, res->ai_addrlen) < 0)
        return -1;
    
    if (setsockopt(s, slevel, MCAST_JOIN_SOURCE_GROUP,
                   (char *)&gsreq, sizeof(gsreq)) == -1)
        return -1;
    return 0;
}

int main() {
    int i;
    
    i = openSSM("158.38.63.200", "224.1.2.3", "5001");
    sleep(30);
    return i;
}