That's what I would think as well, but instead I see the IP of the FS and not the IP of the Aavay_CM.
2017-11-27 14:13:16.271429 [WARNING] sofia_reg.c:1792 SIP auth challenge (INVITE) on sofia profile 'internal' for [18005551212@10.172.210.190] from ip 10.172.193.151
Is there anyway to force it?