[unkmail]

How to send multicast datagram via non-default network interface?
I try this:

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <err.h>
#include <fcntl.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define IFACE_ADDR      "192.168.2.1"
#define MCAST_ADDR      "239.1.2.3"
#define MCAST_PORT      1234

int main(void)
{
        struct sockaddr_in      ifaddr, mcaddr;
        int                     sock, on;
        char                    msg[] = "test test test";

        if ((sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
                err(1, "socket");

        on = 1;
        if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &on, sizeof on) == -1)
                err(1, "setsockopt(SO_REUSEADDR)");

        ifaddr.sin_addr.s_addr = inet_addr(IFACE_ADDR);
        if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF,
            &ifaddr.sin_addr.s_addr, sizeof(ifaddr.sin_addr.s_addr)) == -1)
                err(1, "setsockopt(IP_MULTICAST_IF)");

        memset(&mcaddr, 0, sizeof mcaddr);
        mcaddr.sin_family = AF_INET;
        mcaddr.sin_addr.s_addr = inet_addr(MCAST_ADDR);
        mcaddr.sin_port = (unsigned short)htons(MCAST_PORT);

        if (sendto(sock, msg, sizeof msg, 0,
            (struct sockaddr *)&mcaddr, sizeof mcaddr) == -1)
                err(1, "sendto");
        close(sock);
        return (0);
}

but allways get "sendto: No route to host".