Dear List

I upgraded from Kamailio v 3.3 to 4.0.1 and am now facing an issue for the below scenario:

PABX1 ==> Kamailio1 ==> Cisco PGW ==> Kamailio1 ==> PABX2

I understand that this is a hairpin scenario but was working normally on v 3.3.

Checking in the syslog i see:

ERROR: <core> [receive.c:230]: ERROR: receive_msg: no via found in reply

Checking the sip trace i see that when calling from PABX1 to PABX2. After PABX2 answers and the the 200 OK is eventually sent to PABX1 , PABX1 answers with ACK but seems like its not sent back to PABX2 as a result PABX resends a 200 OK and the cycle continues until PABX2 sends a BYE message. Please see below the ACK received from PABX1:

ACK sip:94294294@81.21.38.55 SIP/2.0
Via: SIP/2.0/UDP 192.168.10.189:5060;branch=z9hG4bK6bffe37c;rport
Route: <sip:81.21.38.34;lr=on;ftag=as1cd4f8f1;did=e36.c471>,<sip:94294294@81.21.38.5;pgw-call=call-26eb>,<sip:81.21.38.34;lr=on;ftag=as1cd4f8f1>
Max-Forwards: 70
From: "22498045" <sip:22498045@192.168.10.189>;tag=as1cd4f8f1
To: <sip:94294294@81.21.38.34>;tag=3d94f08-37261551-13c4-50022-1c1e67-87fe958-1c1e67
Contact: <sip:22498045@192.168.10.189:5060>
Call-ID: 03042a717e27a87e759f7f4879e70377@192.168.10.189:5060
CSeq: 102 ACK
User-Agent: FPBX-2.8.1(1.8.21.0)
Content-Length: 0

Is there an issue with the above ACK message? Is there any way to solve this issue quickly perhaps by disabling loose route?

I have observed that this issue occurs only when hairpinned.

Thanking you in advance!

Phillip