route{


        # initial sanity checks -- messages with
        # max_forwards==0, or excessively long requests
        if (!mf_process_maxfwd_header("10")) {
                sl_send_reply("483","Too Many Hops");
                break;
        };
        if (msg:len >= max_len ) {
                sl_send_reply("513", "Message too big");
                break;
        };


        # !! Nathelper
        # Special handling for NATed clients; first, NAT test is
        # executed: it looks for via!=received and RFC1918 addresses
        # in Contact (may fail if line-folding is used); also,
        # the received test should, if completed, should check all
        # vias for rpesence of received
        if (nat_uac_test("3")) {
                # Allow RR-ed requests, as these may indicate that
                # a NAT-enabled proxy takes care of it; unless it is
                # a REGISTER
                if (method == "REGISTER" || ! search("^Record-Route:")) {
                    log("LOG: Someone trying to register from private IP, rewriting\n");


                    # This will work only for user agents that support symmetric
                    # communication. We tested quite many of them and majority is
                    # smart enough to be symmetric. In some phones it takes a configuration
                    # option. With Cisco 7960, it is called NAT_Enable=Yes, with kphone it is
                    # called "symmetric media" and "symmetric signalling".


                    fix_nated_contact(); # Rewrite contact with source IP of signalling
                    if (method == "INVITE") {
                        fix_nated_sdp("1"); # Add direction=active to SDP
                    };
                    force_rport(); # Add rport parameter to topmost Via
                    setflag(6);    # Mark as NATed
                };
        };


        # we record-route all messages -- to make sure that
        # subsequent messages will go through our proxy; that's
        # particularly good if upstream and downstream entities
        # use different transport protocol
        if (!method=="REGISTER") record_route();


        # subsequent messages withing a dialog should take the
        # path determined by record-routing
        if (loose_route()) {
                # mark routing logic in request
                append_hf("P-hint: rr-enforced\r\n");
                route(1);
                break;
        };
if (!uri==myself) {
                # mark routing logic in request
                append_hf("P-hint: outbound\r\n");
                route(1);
                break;
        };


        # if the request is for other domain use UsrLoc
        # (in case, it does not work, use the following command
        # with proper names and addresses in it)
        if (uri==myself) {


                if (method=="REGISTER") {


# Uncomment this if you want to use digest authentication
#                       if (!www_authorize("iptel.org", "subscriber")) {
#                               www_challenge("iptel.org", "0");
#                               break;
#                       };


                        save("location");
                        break;
                };


                lookup("aliases");
                if (!uri==myself) {
                        append_hf("P-hint: outbound alias\r\n");
                        route(1);
                        break;
                };
                # native SIP destinations are handled using our USRLOC DB
                if (!lookup("location")) {
                        sl_send_reply("404", "Not Found");
                        break;
                };
        };
        append_hf("P-hint: usrloc applied\r\n");
        route(1);
}


route[1]
{
        # !! Nathelper
        #if (uri=~"[@:](192\.168\.|10\.|172\.(1[6-9]|2[0-9]|3[0-1])\.)" && !search("^Route:")){
        #    sl_send_reply("479", "We don't forward to private IP addresses");
        #    break;
        #};


        # if client or server know to be behind a NAT, enable relay
        if (isflagset(6)) {
            force_rtp_proxy();
        };


        # NAT processing of replies; apply to all transactions (for example,
        # re-INVITEs from public to private UA are hard to identify as
        # NATed at the moment of request processing); look at replies
        t_on_reply("1");


        # send it out now; use stateful forwarding as it works reliably
        # even for UDP2TCP
        if (!t_relay()) {
                sl_reply_error();
        };
}


# !! Nathelper
onreply_route[1] {
    # NATed transaction ?
    if (isflagset(6) && status =~ "(183)|2[0-9][0-9]") {
        fix_nated_contact();
        force_rtp_proxy();
    # otherwise, is it a transaction behind a NAT and we did not
    # know at time of request processing ? (RFC1918 contacts)
    } else if (nat_uac_test("1")) {
        fix_nated_contact();
    };
}