Thanks for the reply, however I have check that and it is enabled. Is there anything else I can look at?? They showed me the sip head and it clearly shows my local ip address.. Thanks for the input.

I have a RB750G running 4.x RouterOS. I'm having a problem with my sip trunk provider seeing my local ip address on there end so I get one way audio. How can I, or can I have the router NAT the Sip header?

Thanks in advance.