freeswitch/conf/autoload_configs/opal.conf.xml

<configuration name="opal.conf" description="Opal Endpoints">
  <settings>
    <param name="trace-level" value="4"/>
    <param name="context" value="default"/>
    <param name="dialplan" value="XML"/>
    <param name="codec-prefs" value="PCMU"/>
    <param name="gk-address" value=""/>    <!-- empty to disable, "*" to search LAN -->
    <param name="gk-identifer" value=""/>  <!-- optional name of gk -->
    <param name="gk-interface" value=""/>  <!-- optional listener interface name -->
  </settings>
  <listeners>
    <listener name="default">
      <param name="h323-ip" value="$${local_ip_v4}"/>
      <param name="h323-port" value="1720"/>
    </listener>
  </listeners>
</configuration>