When attempting to connect to a computer with Screens, the gateway device (router or modem) on the destination network must pass Screens traffic through to the computer you're connecting to. Screens Connect can work with supported routers to configure these settings automatically or you can configure them manually.
Step-by-step instructions vary from model to model, but portforward.com offers a large database of instructions for specific models. By way of example, the screenshot above depicts a D-Link router admin interface. Note the IP address/hostname and port numbers.
The process is essentially as follows:
Log into the router's administrative interface.
Navigate to the Port Mapping or Port Forwarding configuration area.
Configure settings to instruct the router to forward TCP traffic to port 5900 (the default for VNC) and/or port 22 (the default for SSH, if you want to encrypt connections to the destination computer).