+static int
+dns_send_packet(int fd, struct iovec *iov, int iov_len)
+{
+ static size_t cmsg_data[( CMSG_SPACE(sizeof(struct in_pktinfo)) / sizeof(size_t)) + 1];
+ static struct sockaddr_in a = {
+ .sin_family = AF_INET,
+ .sin_port = htons(MCAST_PORT),
+ };
+ static struct msghdr m = {
+ .msg_name = (struct sockaddr *) &a,
+ .msg_namelen = sizeof(a),
+ .msg_control = cmsg_data,
+ .msg_controllen = CMSG_LEN(sizeof(struct in_pktinfo)),
+ };
+ struct in_pktinfo *pkti;
+ struct cmsghdr *cmsg;
+
+ m.msg_iov = iov;
+ m.msg_iovlen = iov_len;
+
+ memset(cmsg_data, 0, sizeof(cmsg_data));
+ cmsg = CMSG_FIRSTHDR(&m);
+ cmsg->cmsg_len = m.msg_controllen;
+ cmsg->cmsg_level = IPPROTO_IP;
+ cmsg->cmsg_type = IP_PKTINFO;
+
+ pkti = (struct in_pktinfo*) CMSG_DATA(cmsg);
+ pkti->ipi_ifindex = iface_index;
+
+ a.sin_addr.s_addr = inet_addr(MCAST_ADDR);
+
+ return sendmsg(fd, &m, 0);
+}
+