If you don’t have a static IP and don’t use a DDNS, how can you access to your EX2 from outside ? No glue :o
So I’m using a Dynamic DNS via No-IP: https://www.noip.com/
DUC is the software provided by No-IP to automatically update your hostname when your IP is changing.
EX2 has integrated this service in “Settings / Network / Dynamic DNS”.
Mouarrff, very funny thing. To make these pictures, I switched my EX2 to english. And you know what ? The No-Ip update is suddenly working. Nice bug !!!
So problem fixed just by switching the language of the EX2 to english 
