[OpenSER-Users] OpenSER corrects the "Contact" field only one way.

[Höskuldur]

Hi

I have two user clients behind separate NAT networks. My OpenSER is directly
connected to the Internet and has it's own external IP address.

Both clients are using STUN to get their external IP address and correct
port for SIP messages.

They successfully register with Openser, which is using Nathelper module and
Mediaproxy.

In this case, since the client is behind NAT, it puts the wrong port in the
Contact field of a SIP message.

As a result, SOME SIP messages from OpenSER are never received by the
client.

But with the help of Nathelper, OpenSER should correct the port in Contact
field, by replacing the NAT port with the src port of a SIP message (UDP
pack).

The problem is, that it looks like OpenSER only corrects the port in Contact
field for client A (The one who initiates the call) but not Client B(The one
who's called).

For a better explaination, please check out my logs from ngrep.


CLIENT A to OPENSER

U 2008/05/26 16:53:26.285586 157.157.78.173:54182 -> 212.50.206.33:5060
INVITE sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33> SIP/2.0.
From: 1006<sip:1006 at 212.50.206.33 <sip%3A1006 at 212.50.206.33>
>;tag=10007500-26260f5b.
To: <sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33>>.
Via: SIP/2.0/UDP 157.157.78.173:62356
;branch=z9hG4bKc0a8150a10007e0026261023.
Contact: 1006<sip:1006 at 157.157.78.173:62356>. !!!NB!!! <-- This is the WRONG
reply port.

OPENSER RELAYS TO CLIENT B

U 2008/05/26 16:53:26.301864 212.50.206.33:5060 -> 130.208.183.251:49211
INVITE sip:1001 at 130.208.183.251:49208 SIP/2.0.
Record-Route: <sip:212.50.206.33;lr;ftag=10007500-26260f5b;nat=yes>.
From: 1006<sip:1006 at 212.50.206.33 <sip%3A1006 at 212.50.206.33>
>;tag=10007500-26260f5b.
To: <sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33>>.
Via: SIP/2.0/UDP 212.50.206.33;branch=z9hG4bK5db1.ce9aea2.0;rport.
Via: SIP/2.0/UDP 157.157.78.173:62356
;rport=54182;branch=z9hG4bKc0a8150a10007e0026261023.
Contact: 1006<sip:1006 at 157.157.78.173:54182>. !!!NB!!! <-- OpenSER detects
it and changes it to correct reply port. Works great.

CLIENT B ANSWERS TO OPENSER

U 2008/05/26 16:53:27.301368 130.208.183.251:49211 -> 212.50.206.33:5060
SIP/2.0 200 OK.
From: 1006<sip:1006 at 212.50.206.33 <sip%3A1006 at 212.50.206.33>
>;tag=10007500-26260f5b.
To: <sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33>
>;tag=10007900-26261046.
Via: SIP/2.0/UDP 212.50.206.33;branch=z9hG4bK5db1.ce9aea2.0.
Via: SIP/2.0/UDP 157.157.78.173:62356
;branch=z9hG4bKc0a8150a10007e0026261023.
Contact: 1001<sip:1001 at 130.208.183.251:49208>. !!!NB!!! <-- Now lets try
Client B. Wrong reply port.

OPENSER TO CLIENT A

U 2008/05/26 16:53:27.305241 212.50.206.33:5060 -> 157.157.78.173:54182
SIP/2.0 200 OK.
From: 1006<sip:1006 at 212.50.206.33 <sip%3A1006 at 212.50.206.33>
>;tag=10007500-26260f5b.
To: <sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33>
>;tag=10007900-26261046.
Via: SIP/2.0/UDP 157.157.78.173:62356
;branch=z9hG4bKc0a8150a10007e0026261023.
Contact: 1001<sip:1001 at 130.208.183.251:49208>. !!!NB!!! <-- OpenSER didn't
change the port like before, so now Client B never receives ACK from Client
A.

CLIENT A TO OPENSER

U 2008/05/26 16:53:27.518621 157.157.78.173:54182 -> 212.50.206.33:5060
ACK sip:1001 at 130.208.183.251:49208 SIP/2.0.
From: 1006<sip:1006 at 212.50.206.33 <sip%3A1006 at 212.50.206.33>
>;tag=10007500-26260f5b.
To: <sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33>
>;tag=10007900-26261046.
Via: SIP/2.0/UDP 157.157.78.173:62356
;branch=z9hG4bKc0a8150a10007e0026261505.
Contact: 1006<sip:1006 at 157.157.78.173:62356>.
Route: <sip:212.50.206.33;lr;ftag=10007500-26260f5b;nat=yes>.

OPENSER TO CLIENT B

U 2008/05/26 16:53:27.519192 212.50.206.33:5060 -> 130.208.183.251:49208
!!!NB!!! <-- OpenSER sends to the WRONG port!
ACK sip:1001 at 130.208.183.251:49208 SIP/2.0.
Record-Route: <sip:212.50.206.33;lr;ftag=10007500-26260f5b;nat=yes>.
From: 1006<sip:1006 at 212.50.206.33 <sip%3A1006 at 212.50.206.33>
>;tag=10007500-26260f5b.
To: <sip:1001 at 212.50.206.33 <sip%3A1001 at 212.50.206.33>
>;tag=10007900-26261046.
CSeq: 101 ACK.
Via: SIP/2.0/UDP 212.50.206.33;branch=z9hG4bK5db1.ce9aea2.2;rport.
Via: SIP/2.0/UDP 157.157.78.173:62356
;rport=54182;branch=z9hG4bKc0a8150a10007e0026261505.


This last ACK message is never received by Client B because the client isn't
listening on port 49208.
If I manually use rewriteport("49211") it works, because obviously this last
package is then forced to port 49211 which the client listening on.

Also, the first line in my main route is force_rport(); but that still
doesn't do it.

I've been struggling with this problem for a few weeks now so all comments
and suggestions are very welcome.

My OpenSER config file can be found here: http://hoski.public.is/openser.cfg

Best regards,
Höskuldur
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