lwip UDP problem

vRunNTPServer (void* pvParameters)
{
    if ((sock = lwip_socket(AF_INET, SOCK_DGRAM, 0)) == -1)
        perrorx("Socket");

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(webNTP_PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    memset(&(server_addr.sin_zero),0, 8);

    if (lwip_bind(sock, (struct sockaddr*) &server_addr, sizeof(struct sockaddr)) == -1)
        perrorx("Bind");

    addr_len = sizeof(struct sockaddr);

    while (1)
    {
        bytes_read = lwip_recvfrom(sock,recv_data, TCP_MSS, 0, (struct sockaddr*) &client_addr, &addr_len);

        if (bytes_read == (signed int) sizeof(sntp_message_t))
        {
            sntp_message_t reply;
            memset(&reply, 0, sizeof(reply));

            // Fill reply struct...

            if (lwip_sendto(socket, &reply, sizeof(reply), 0, (struct sockaddr*) receiver, recvlen) < 0)
            {
                // print send error
            }
        }
        else
        {
            // print receive size mismatch error
        }
    } // while
}