[SR-Users] Very strange reinvite behaviour

[Alex Balashov]

Hi,

We have a scenario like this:

   ITSP -----> Kamailio -----> Endpoint
        (UDP)            (TLS)

So, TLS is only being used on the last hop, and the upstream interaction
with the ITSP is plain-old UDP.

Kamailio has the following listeners:

   listen=udp:1.1.1.1:5060
   listen=udp:1.1.1.2:5060
   listen=tcp:10.0.0.1:5060
   listen=tls:1.1.1.1:5061

At some point, 'Endpoint' sends a reinvite which has the following RURI:

   INVITE sip:1.1.1.1:5061 SIP/2.0

This is clearly improper, and caused a loop that led to the rtpengine
SDP loop issue I previously reported in another thread.

So, in an effort to stop this, I added the following:

   if(has_totag()) {
      if(loose_route()) {
         ...

         if(is_method("INVITE")) {
	    xlog("L_INFO", "[R-MAIN:$ci] Re-INVITE received from $si:$sp to RURI $ru\n");
	    xlog("L_INFO", "[R-MAIN:$ci] Reinvite body: $mb\n");

	 if(!is_method("ACK") && uri == myself) { 
	    sl_send_reply("400", "Bad Request");
	    exit;
	 }
      }
   }

But it doesn't work. It appears that the '400 Bad Request' rejection
never happens, presumably because the this domain doesn't match
'myself'.

Another perplexing mystery: the log message containing the reinvite's
'$ru' does not show a RURI of 'sip:1.1.1.1:5061', but rather the remote
target in the initial inbound INVITE, which we also logged:

   Contact: "Anonymous" <sip:Restricted at 3.3.3.3:5060>

The log message says:

   [R-MAIN:...] Re-INVITE received from 4.4.4.4:5060 to RURI sip:Restricted at 3.3.3.3:5060;lr.

Note a subtle detail here: the ';lr' parameter is present, which is an
attribute of the Record-Route inserted by the sending ITSP (3.3.3.3).
It's at the bottom of the Route set, of course, below Kamailio's two RRs
(inserted for the ingress UDP interface and the egress TLS interface):

   Route: <sip:Restricted at 3.3.3.3:5060;lr>

This leads to two questions whose causes seem to be related:

1. Why does Kamailio think the request URI of this re-invite is
something other than what $mb reveals it to be?

2. Is that, presumably, why it does not match 'myself'?

3. Why would Kamailio think it is actually set to the far-end
Record-Route URI?

This is version: kamailio 4.4.5 (x86_64/linux) d48094.

Thanks,

-- Alex

-- 
Alex Balashov | Principal | Evariste Systems LLC

Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) 
Web: http://www.evaristesys.com/, http://www.csrpswitch.com/