[OpenSIPS-Users] Port changes

[Schneur Rosenberg]

I have this interesting scenario, caller sends call to our OpenSIPS
who actsd as a loadbalancer which sends the call to a gateway for
termination and the gateway sets Session-Expires: 1800;refresher=uas,
the caller sends call the call through port 1090 and the rport in the
Via shows rport=1090 and so far everything is ok, but after 15 minutes
the gateway sends a reinvite,  OpenSIPS sends it to the client and the
client sends a OK and OpenSIPS properly sends the OK to the gateway,
the gateway sends a ACK to OpenSIPS, but here the problem starts
OpenSIPS sends the ACK to the port in the Contact header which is not
the same port as the rport, the clients router does not recognize the
packet and blocks it, the client sends multiple OK's to OpenSIPS who
ignores it because he has already moved on, as far as OpenSIPS is
concerned the ACK has already been sent to the next hop, and after
approx 30 seconds the client does not receive the ACK and sends a BYE
and the call terminates.

Why is OpenSIPS changing the port to the Contact port? and what can I
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