[OpenSIPS-Users] nat_traversal: register keepalive not engaging

[Gremaud Odin]

Hello everyone,

I began using the nat_traversal module to create a NAT traversal 
dedicated box, but I'm now stuck on something probably pretty stupid. 
Here is the design I'm working with:

Public network  ||  Private network
                 ||
     U1 -------> P1 -------> P2
                 ||
                 ||

U1 being the NATed UAC, P1 the NAT box and P2 an OpenSIPS Proxy/Registrar.

The registration process is OK, and I can even call another UA using U1. 
When checking the proper functioning of my script, I noticed that I 
could not call U1 from any other UA: indeed, the register keepalive did 
not trigger properly (no keepalive engaged for REGISTER, even if it pass 
on the function). The keepalive mechanism is working fine with INVITE 
(did not try with SUBSCRIBE), I traced OPTION messages going to U1 
(which replies with a "404 Not Found", is this normal?). I 
double-checked using the module statistics, and there was no register 
keepalive, but during an dialog, it effectively shows that U1 is 
keepalived. I traced the registration process for a possible error, but 
the request is correctly transfered to P2, which responds with a 200 OK 
that P1 receives correctly. I have no more ideas about what I'm missing 
here...

If it can help, here is the NAT and registrar process I use:

### NAT DETECTION ###
force_rport();

# Avoid NAT detection if source IP is local
if ( client_nat_test("8") && $si!~"^10\.0\.0\.[0-9]{1,3}$") {
     fix_contact();
     append_hf("NAT-Scope: nat-relay\r\n");

     # For initial invites and all subscribe
     if ((is_method("INVITE") && !has_totag()) || is_method("SUBSCRIBE")) {
         nat_keepalive();

     # For registers
     } else if (is_method("REGISTER")) {
         nat_keepalive();
         append_hf("NAT-Received: $source_uri\r\n");
     }

     setflag(5);
}

### REGISTRAR ###
if (is_domain_local("$fd") && is_method("REGISTER")) {
     append_hf("Supported: Path\r\n");
     add_path_received();
     force_send_socket(10.0.0.1:5060);
     t_relay("10.0.0.2:5060");
     exit;
}

### RELAYING ###
# The request was processed by the proxy/registrar
if ($hdr(NAT-Scope)=="nat-relay" && !isflagset(5)) {
     #$du = $hdr(NAT-Received);
     $fs = $keepalive.socket($du);
# Not a subsequent message (REGISTER, SUBSCRIBE or initial INVITE), 
avoid looping on P2
} else if (!has_totag() && $si != "10.0.0.2") {
     $du = "sip:10.0.0.2:5060";
     $fs = "10.0.0.1:5060";
}

if (!t_relay("0x03")) {
     sl_reply_error();
}

Any advice or idea is welcome :)

Odin