Freeswitch under NAT

If your M2 box is under NAT, you should edit /usr/local/freeswitch/conf/sip_profiles/external.xml file (find these lines in file):

<param name="ext-rtp-ip" value="auto-nat"/>
<param name="ext-sip-ip" value="auto-nat"/>

And change 'auto-nat' to your real external IP, for example, if your external IP is 1.2.3.4, these lines should look like this:

<param name="ext-rtp-ip" value="1.2.3.4"/>
<param name="ext-sip-ip" value="1.2.3.4"/>

Forward SIP and RTP ports (UDP 5060, 10000-50000) on your firewall to this Freeswitch machine.

Restart Freeswitch:

service freeswitch restart