All things related to multicast

[Alan Crosswell <>]

Stig,

This "just works."  Thanks.
/a

Stig Venaas wrote:
> 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;
> }