ssize_t UDPSendWithSourceIP(int fd, void * data, size_t len, const H323TransportAddress & toAddress)
{
    struct sockaddr_in6 dest;

    // set dest address
    PIPSocket::Address toIP;
    WORD toPort = 0;
    toAddress.GetIpAndPort(toIP, toPort);
    SetSockaddr(dest, toIP, toPort);

    // set source address
    PIPSocket::Address src = RasServer::Instance()->GetLocalAddress(toIP);

    struct msghdr msgh;
    struct cmsghdr *cmsg;
    struct iovec iov = { };
    char cbuf[256];
    memset(&cbuf, 0, sizeof(cbuf));

    // Set up iov and msgh structures
    memset(&msgh, 0, sizeof(struct msghdr));
    iov.iov_base = data;
    iov.iov_len = len;
    msgh.msg_iov = &iov;
    msgh.msg_iovlen = 1;
    msgh.msg_name = (struct sockaddr*)&dest;
    // must pass short len when sending to IPv4 address on Solaris 11, OpenBSD and NetBSD
    // sizeof(dest) is OK on Linux and FreeBSD
    size_t addr_len = sizeof(sockaddr_in);
    if (toIP.GetVersion() == 6)
        addr_len = sizeof(sockaddr_in6);
    msgh.msg_namelen = addr_len;

    if ((((struct sockaddr*)&dest)->sa_family == AF_INET6)) {
        struct in6_pktinfo *pkt;

        msgh.msg_control = cbuf;
        msgh.msg_controllen = CMSG_SPACE(sizeof(*pkt));

        cmsg = CMSG_FIRSTHDR(&msgh);
        cmsg->cmsg_level = IPPROTO_IPV6;
        cmsg->cmsg_type = IPV6_PKTINFO;
        cmsg->cmsg_len = CMSG_LEN(sizeof(*pkt));

        pkt = (struct in6_pktinfo *) CMSG_DATA(cmsg);
        memset(pkt, 0, sizeof(*pkt));
        pkt->ipi6_addr = src;
        msgh.msg_controllen = cmsg->cmsg_len;
    } else
    {
#if defined(IP_PKTINFO) && !defined(P_NETBSD) // Linux and Solaris 11 (NetBSD 7 only has incomplete IP_PKTINFO support)
        struct in_pktinfo *pkt;
        msgh.msg_control = cbuf;
        msgh.msg_controllen = CMSG_SPACE(sizeof(*pkt));

        cmsg = CMSG_FIRSTHDR(&msgh);
        cmsg->cmsg_level = IPPROTO_IP;
        cmsg->cmsg_type = IP_PKTINFO;
        cmsg->cmsg_len = CMSG_LEN(sizeof(*pkt));

        pkt = (struct in_pktinfo *) CMSG_DATA(cmsg);
        memset(pkt, 0, sizeof(*pkt));
        pkt->ipi_spec_dst = src;
#else
#ifdef IP_SENDSRCADDR   // FreeBSD
        struct in_addr *in;

        msgh.msg_control = cbuf;
        msgh.msg_controllen = CMSG_SPACE(sizeof(*in));

        cmsg = CMSG_FIRSTHDR(&msgh);
        cmsg->cmsg_level = IPPROTO_IP;
        cmsg->cmsg_type = IP_SENDSRCADDR;
        cmsg->cmsg_len = CMSG_LEN(sizeof(*in));

        in = (struct in_addr *) CMSG_DATA(cmsg);
        *in = src;
#endif  // IP_SENDSRCADDR
#endif  // IP_PKTINFO else
    }

    ssize_t bytesSent = sendmsg(fd, &msgh, 0);
    if (bytesSent < 0) {
        PTRACE(5, "RTPtSend error " << strerror(errno));
    }

    return bytesSent;
}