freeswitch/conf/sip_profiles/nat.xml

<!-- http://wiki.freeswitch.org/wiki/Sofia_Configuration_Files -->
<profile name="nat">
  <gateways>
    <X-PRE-PROCESS cmd="include" data="nat/*.xml"/>
  </gateways>

  <settings>
    <param name="debug" value="0"/>
    <param name="sip-trace" value="no"/>
    <param name="rfc2833-pt" value="101"/>
    <param name="sip-port" value="5070"/>
    <param name="dialplan" value="XML"/>
    <param name="context" value="public"/>
    <param name="dtmf-duration" value="100"/>
    <param name="codec-prefs" value="$${global_codec_prefs}"/>
    <param name="use-rtp-timer" value="true"/>
    <param name="hold-music" value="$${moh_uri}"/>
    <param name="rtp-timer-name" value="soft"/>
    <param name="manage-presence" value="true"/>
    <param name="inbound-codec-negotiation" value="generous"/>
    <param name="nonce-ttl" value="60"/>
    <param name="auth-calls" value="false"/>
    <param name="rtp-timeout-sec" value="1800"/>
    <param name="rtp-ip" value="$${local_ip_v4}"/>
    <param name="sip-ip" value="$${local_ip_v4}"/>
    <param name="ext-rtp-ip" value="$${external_rtp_ip}"/>
    <param name="ext-sip-ip" value="$${external_sip_ip}"/>
  </settings>
</profile>