Hi,

We have an ugly message looping scenario where a SIP request message received at Kamailio is forwarded to the switch/router and back to Kamailio in a loop until the Max-forwards header value becomes 0 or the transaction times out.

After receiving an incoming INVITE request from a local user, Kamailio forwards the INVITE request to another proxy located in a different network. The call is established successfully.

During the call setup the external proxy sends an OPTIONS request to Kamailio (actually to the external public IP address from where it received INVITE request from Kamailio). The OPTIONS request arrives at Kamailio. But the request uri contains the mapped public address instead of the local ip address where Kamailio is listening. So Kamailio forwards the request to the public IP address (i.e. the switch) which again sends it back to Kamailio again and it keeps looping.

Here is the message flow. 192.168.1.3 is the local user registered to Kamailio which is running at 192.168.1.5. IP address of the external proxy server is 10.139.90.161 and 10.139.90.137 is the public IP address of the switch/router. NAT isn’t enabled at Kamailio.

Internet Protocol Version 4, Src: 192.168.1.3 (192.168.1.3), Dst: 192.168.1.5 (192.168.1.5)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: INVITE sip:1002@video-conf SIP/2.0

Message Header

Via: SIP/2.0/UDP 192.168.1.3:5060;rport;branch=z9hG4bK1941685709

From: "xxxx" <sip:1001@192.168.1.5>;tag=256977615

To: <sip:1002@video-conf>

Call-ID: 1110783207

CSeq: 20 INVITE

Contact: <sip:1001@192.168.1.3>

Content-Type: application/sdp

Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO

Max-Forwards: 70

User-Agent: Linphone/3.5.2 (eXosip2/3.6.0)

Subject: Phone call

Content-Length: 510

Message Body

Internet Protocol Version 4, Src: 192.168.1.5 (192.168.1.5), Dst: 192.168.1.3 (192.168.1.3)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Status-Line: SIP/2.0 100 trying -- your call is important to us

Message Header

Via: SIP/2.0/UDP 192.168.1.3:5060;rport=5060;branch=z9hG4bK1941685709

From: "xxxx" <sip:1001@192.168.1.5>;tag=256977615

To: <sip:1002@video-conf>

Call-ID: 1110783207

CSeq: 20 INVITE

Server: kamailio (3.3.3 (i386/linux))

Content-Length: 0

Internet Protocol Version 4, Src: 192.168.1.5 (192.168.1.5), Dst: 10.139.90.161 (10.139.90.161)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: INVITE sip:1002@vc-vcs-control.air2gnd.net SIP/2.0

Message Header

Record-Route: <sip:192.168.1.5;lr=on>

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bKd6e1.f7985e64.0

Via: SIP/2.0/UDP 192.168.1.3:5060;rport=5060;branch=z9hG4bK1941685709

From: "xxxx" <sip:1001@192.168.1.5>;tag=256977615

To: <sip:1002@video-conf>

Call-ID: 1110783207

CSeq: 20 INVITE

Contact: <sip:1001@192.168.1.3>

Content-Type: application/sdp

Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO

Max-Forwards: 69

User-Agent: Linphone/3.5.2 (eXosip2/3.6.0)

Subject: Phone call

Content-Length: 510

Message Body

Internet Protocol Version 4, Src: 10.139.90.161 (10.139.90.161), Dst: 192.168.1.5 (192.168.1.5)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Status-Line: SIP/2.0 100 Trying

Message Header

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bKd6e1.f7985e64.0;received=10.139.90.137

Via: SIP/2.0/UDP 192.168.1.3:5060;rport=5060;branch=z9hG4bK1941685709

From: "xxxx" <sip:1001@192.168.1.5>;tag=256977615

To: <sip:1002@video-conf>

Call-ID: 1110783207

CSeq: 20 INVITE

Content-Length: 0

Internet Protocol Version 4, Src: 10.139.90.161 (10.139.90.161), Dst: 192.168.1.5 (192.168.1.5)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Status-Line: SIP/2.0 101 Dialog Establishement

Message Header

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bKd6e1.f7985e64.0;received=10.139.90.137

Via: SIP/2.0/UDP 192.168.1.3:5060;rport=5060;branch=z9hG4bK1941685709

Record-Route: <sip:192.168.1.5;lr=on>

From: "xxxx” <sip:1001@192.168.1.5>;tag=256977615

To: <sip:1002@ video-conf>;tag=689763673

Call-ID: 1110783207

CSeq: 20 INVITE

Contact: <sip:1002@10.139.90.161:5060>

Content-Length: 0

Internet Protocol Version 4, Src: 192.168.1.5 (192.168.1.5), Dst: 192.168.1.3 (192.168.1.3)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Status-Line: SIP/2.0 101 Dialog Establishement

Message Header

Via: SIP/2.0/UDP 192.168.1.3:5060;rport=5060;branch=z9hG4bK1941685709

Record-Route: <sip:192.168.1.5;lr=on>

From: "xxxx" <sip:1001@192.168.1.5>;tag=256977615

To: <sip:1002@video-conf>;tag=689763673

Call-ID: 1110783207

CSeq: 20 INVITE

Contact: sip:1002@10.139.90.161:5060

Content-Length: 0

P-Received: 10.139.90.137

Internet Protocol Version 4, Src: 10.139.90.161 (10.139.90.161), Dst: 192.168.1.5 (192.168.1.5)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: OPTIONS sip:10.139.90.137:5060 SIP/2.0

Message Header

Via: SIP/2.0/UDP 10.139.90.161:5060;rport;branch=z9hG4bK231479102

From: "yyyy" <sip:1002@10.139.90.161>;tag=537974226

To: <sip:1001@192.168.1.5>

Call-ID: 1856507851

CSeq: 20 OPTIONS

Accept: application/sdp

Max-Forwards: 70

Content-Length: 0

Internet Protocol Version 4, Src: 192.168.1.5 (192.168.1.5), Dst: 10.139.90.137 (10.139.90.137)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: OPTIONS sip:10.139.90.137:5060 SIP/2.0

Message Header

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bK8ba7.fa94bab7.0

Via: SIP/2.0/UDP 10.139.90.161:5060;rport=5060;branch=z9hG4bK231479102

From: "yyyy" <sip:1002@10.139.90.100>;tag=537974226

To: <sip:1001@192.168.1.5>

Call-ID: 1856507851

CSeq: 20 OPTIONS

Accept: application/sdp

Max-Forwards: 69

Content-Length: 0

Internet Protocol Version 4, Src: 10.139.90.137 (10.139.90.137), Dst: 192.168.1.5 (192.168.1.5)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: OPTIONS sip:10.139.90.137:5060 SIP/2.0

Message Header

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bK8ba7.fa94bab7.0

Via: SIP/2.0/UDP 10.139.90.161:5060;rport=5060;branch=z9hG4bK231479102

From: "uuuu" <sip:1002@10.139.90.100>;tag=537974226

To: <sip:1001@192.168.1.5>

Call-ID: 1856507851

CSeq: 20 OPTIONS

Accept: application/sdp

Max-Forwards: 69

Content-Length: 0

Internet Protocol Version 4, Src: 192.168.1.5 (192.168.1.5), Dst: 10.139.90.137 (10.139.90.137)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: OPTIONS sip:10.139.90.137:5060 SIP/2.0

Message Header

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bK8ba7.0b94bab7.0

Via: SIP/2.0/UDP 192.168.1.5;received=10.139.90.137;branch=z9hG4bK8ba7.fa94bab7.0

Via: SIP/2.0/UDP 10.139.90.161:5060;rport=5060;branch=z9hG4bK231479102

From: "yyyy" <sip:1002@10.139.90.100>;tag=537974226

To: <sip:1001@192.168.1.5>

Call-ID: 1856507851

CSeq: 20 OPTIONS

Accept: application/sdp

Max-Forwards: 68

Content-Length: 0

Internet Protocol Version 4, Src: 10.139.90.137 (10.139.90.137), Dst: 192.168.1.5 (192.168.1.5)

User Datagram Protocol, Src Port: sip (5060), Dst Port: sip (5060)

Session Initiation Protocol

Request-Line: OPTIONS sip:10.139.90.137:5060 SIP/2.0

Message Header

Via: SIP/2.0/UDP 192.168.1.5;branch=z9hG4bK8ba7.0b94bab7.0

Via: SIP/2.0/UDP 192.168.1.5;received=10.139.90.137;branch=z9hG4bK8ba7.fa94bab7.0

Via: SIP/2.0/UDP 10.139.90.161:5060;rport=5060;branch=z9hG4bK231479102

From: "yyyy" <sip:1002@10.139.90.100>;tag=537974226

To: <sip:1001@192.168.1.5>

Call-ID: 1856507851

CSeq: 20 OPTIONS

Accept: application/sdp

Max-Forwards: 68

Content-Length: 0

This message forwarding goes on for a long time in a loop, each time with an extra Via header and Max-Forwards value decremented by one. After sometime it eventually times out and Kamailio starts sending 408 response for the OPTIONS request which again keeps looping.

Probably adding an alias for the public IP address i.e., 10.139.90.137 in the Kamailio config file would solve the problem. But this IP address is not fixed and may change and I guess there is no way Kamailio can learn the public IP address on its own.

Any help or reference to previous posts if it is already discussed and solved will be much helpful.

Regards,

Ajay