Freebox Revolution port forwarding

We have a Freebox Revolution at home and I have been wanting to run a Yunohost server from behind it because...it's more fun that way. However, when I went to do the port forwarding on the Freebox I discovered that I can only choose a port above 49152 which makes the whole effort a waste of time.

It turns out that Free issues shared IPv4 address's and then gives a range of ports allowed to be used by each partner. So somewhere out there is someone with the same IP address as me but they can only use ports under 49152, or from 20000 to 49152, or something like that.

You can change this by logging into Free.fr the Ma Freebox and then choosing "Demander une adresse IP fixe V4 full-stack". There will be a couple of popups saying that this is for advanced users who want to host a server behind their router and then a final one saying if you reboot your router in half and hour then you will be assigned a new IPv4 address. This time with the entire range of ports available.