[asterisk-users] x-ast-orig-host - How is this IP taken ?

[Administrator]

Hi list,

We have a strange behavior: a customer Snom300 behind a public FW has 
contact like

contact              : 
sip:user at x.y.39.147:2048;x-ast-orig-host=169.254.252.1:2048

The phone can place calls but not receive any. Also, qualify give 
unreachable which seems correct when looking the x-ast-orig-host IP. 
Problem is that the local IP of this phone is 192.168.1.75

Question: how asterisk sets this IP ? It looks for us like a FW issue as 
we have other customers with approaching local network organisation and 
which are not facing this problem.

Thanks for any hint.

-- 
Daniel