Asterisk operating over a NAT

Hello guys,

I’m on a big trouble trying to make a SIP account works with Asterisk + AMD (Answer machine detection).

When Asterisk make a Call, it sends to the IP of sip acc, (that’s a cisco gateway) and then, the cisco communicates with the carrier platform (using IP like 177.53.16.(6,41,43)).

But, the RTP packets come from IP 43 and doesn’t come back to the same IP (NAT IP).

With this capture in Wireshark i can explain easily whats going on (attached):
Link here:

Btw, I tried to configure the option “localnet” with the NAT IP and Gateway Cisco IP, but i got the same results.

I’ll appreciate if u guys can help me.
Many thanks!