Hi all,

I am using Kamailio (5.7.2, Debian 11, Python KEMI) in a mutli-homed environment with the topos module to hide the topology.

I have noticed that when I use `set_send_socket` or `$fsn` to force the socket it's sent from, it breaks topos and the ACK is not proxied to the other leg of the call. I am calling record_route() after forcing the socket.

If I disable TOPOS the ACK works as expected, and the signalling looks correct.
Or, with TOPOS enabled, if I comment out set_send_socket TOPOS works as expected.
If I disable enable_double_rr, TOPOS works as expected and the ACK is forwarded, but without the double RR subsequent in-dialog requests use the wrong socket.

One other observation, when I change the send socket I also see these warnings in the logs:

24(32) WARNING: PY3 {ACK}: dialog [dlg_handlers.c:1348]: dlg_onroute(): tight matching failed for ACK with callid='!!:MByLMlFAM.NfWxFAM.cAMxyfWjyLz.yAO.y6MxF1MxVZWG4ZMy**'/55, ftag='2023101714101800015'/19, ttag='2f55349a-2c59-4e37-bf58-fd84fb69ece9'/36 and direction=0
24(32) WARNING: PY3 {ACK}: dialog [dlg_handlers.c:1355]: dlg_onroute(): dialog identification elements are callid='2023101714101800015@2900-0601-0284-80'/37, caller tag='2023101714101800015'/19, callee tag='2f55349a-2c59-4e37-bf58-fd84fb69ece9'/36

Is anyone using TOPOS + forcing the socket, or could someone advise where I am going wrong?

Thanks in advance

Matthew