[OpenSIPS-Users] reply_to_via and topmost Via addressing

[John Quick]

Using v2.4.4 OpenSIPS server in a rather complex NAT'd network environment
using containers. Using sngrep to capture the SIP packets on the host
server.

I'm puzzled by what is observed:
An INVITE arrives from a peer via a NAT router and the topmost Via has the
true address of that peer (10.42.4.12) and does not have rport defined.
The source address of the request appears to be 10.2.102.194 because there
is a NAT router/interface between the peer and the OpenSIPS Proxy.

INVITE sip:221222 at 192.168.5.90:2048;line=4yh07htg SIP/2.0
Record-Route: <sip:10.42.4.12;lr;ftag=KN32XDQyXv16D;mydg=cb6.db4ef483>
Via: SIP/2.0/UDP 10.42.4.12:5060;branch=z9hG4bKfa55.ce70bde1.0
Via: SIP/2.0/UDP
10.2.69.161;received=10.42.7.0;rport=1024;branch=z9hG4bKpm809p8y95m4N

The opensips.cfg script does not call the force_rport() or
fix_nated_contact() functions.

...and yet the "100 Giving a try" response is *not* sent to 10.42.4.12, but
instead is sent to the apparent source address of the INVITE request.

I found a setting in the documentation called "reply_to_via" (CoreParameters
section 2.55) which looked like it might alter this behaviour.
However, when a line is added to opensips.cfg "reply_to_via=1" it causes
syntax error on line and OpenSIPS will not start.

Any help would be much appreciated.

John Quick
Smartvox Limited