I configured FS to use the STUN server to find the public IP address used by the NAT. FS sends the request to STUN and receives the reply from the STUN Server , But it does not uses this info ( IP and port obtained from STUN) neither while negotiation ( in SDP) nor in the RTP. My testbed: ----------- < FreeSwitch > ---- < NAT > ---+----<NAT>--- < SIP Phone Client > | | [ STUN Server] File conf/sip_profiles/internal.xml has below configuration. <param name="ext-rtp-ip" value="stun:120.120.120.120"/> ; This is the local STUN server. <param name="ext-sip-ip" value="stun:120.120.120.120"/> <param name="stun-auto-disable" value="false"/> <param name="rtp-ip" value="auto"/> Thanks Prakash