Hi, I am dealing with an Asterisk server behind NAT that is not set properly, with its external IP I am asking them to fix it on there side but I am curious to know if there is a way to deal with this implemented in FS Freeswitch --> Internet --> NAT --> Asterisk In the "200 OK" returned by Asterisk as the private IP in the "Contact" header FS is returning ACK to the private IP. INVITE ---> <--- 200 OK ---> ACK <--- 200 OK ---> ACK <--- 200 OK ---> ACK .... It seems <param name="apply-nat-acl" value="rfc1918"/><param name="aggressive-nat-detection" value="true"/> does It seems sip-force-contact could patch the problem caused by the remote gateway Is there a way to us sip-force-contact with gateway instead of an entry in the directory ?