#include    <errno.h>

#include    <sys/socket.h>

#include    <net/if.h>

#include    <netinet/in.h>

int sockfd_to_family(int);

int mcast_set_loop(int sockfd, int onoff)

{

    switch (sockfd_to_family(sockfd)) {

        case AF_INET: {

            u_char    flag;

            flag = onoff;

            return(setsockopt(sockfd, IPPROTO_IP,

                   IP_MULTICAST_LOOP, &flag, sizeof(flag)));

        }

#ifdef    IPV6

        case AF_INET6: {

            u_int    flag;

            flag = onoff;

            return(setsockopt(sockfd, IPPROTO_IPV6,

                   IPV6_MULTICAST_LOOP, &flag, sizeof(flag)));

        }

#endif

        default: {

            errno = EAFNOSUPPORT;

            return(-);

        }

    }

}