If you are using AIRShip to ship or synchronise data direct between two computers, at least one of them must be able to accept an inbound connection on port 4115. If you are unable to adjust your firewall/router to enable this, you will need to make use of a Transit Hub.
We explain all about firewalls, ports and port-forwarding in the video above.
Those using Windows may need to configure - or simply turn off - their Windows firewall, which is often enabled when the operating system is installed (only consider turning it off if another firewall sits in front of your computer).
Our Ports, Firewalls and Transit Hubs guide (link below) provides you with a checklist to determine if you will need to use a Transit Hub.