Hi all,
I have a scenario where it’s not clear to me what the best approach should be (Kamailio 3.2.0 on Squeeze, although I think it’s a matter of routing logic only).
I have a client behind NAT that sends an initial REGISTER request with a Contact containing private ip:port (e.g.
Contact: “GV” <sip:12345@192.168.1.2:54321;transport=tcp>
)
However, after it’s challenged for authentication with a 401, it sends the following REGISTER request with Authorization header and with a Contact containing ip:port equal to the ‘received’ SIP URI (with a combination of ‘rport’ and ‘received’ parameters (e.g.
Contact: “GV” <sip:12345@[receivedIP]:[rport];transport=tcp>
)
In this case kamailio’s routing logic is not marking the REGISTER as natted (no Received field in location and no NAT flags set).
You can imagine I have a fairly standard NAT handling:
route[NATDETECT] {
force_rport();
if (nat_uac_test("19")) {
if (is_method("REGISTER")) {
fix_nated_register();
} else {
fix_nated_contact();
}
setflag(FLT_NATS);
}
return;
}
FLT_NATS won’t be set, and so it won’t FLB_NATB in the following processing.
This client receives a call: Kamailio relays the INVITE to it using the stored Contact. The INVITE is correctly received by the client, because the stored Contact refers to the connected socket ([received]:rport).
The trouble starts when then the client replies with a 200 OK containing the private ip:port in the Contact header field (again 192.168.1.2:54321).
The ACK will then have that private ip:port in the R-URI, and its relaying will fail.
One of the solutions I’ve found is using always add_contact_alias() in onreply_route when handling the 200 OK, and then use handle_ruri_alias() when defining the destination for the ACK.
I know that without traces and the full .cfg this is quite a broad question, but I wonder if you have already had to deal with this kind of client behaviour and can provide advice on the best practices.
This is in particular useful for the re-use of TCP-based connections.
Thanks in advance,
Giacomo
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