Connecting within the local WiFi
Within the local WiFi, the client finds the connection to the server automatically via Bonjour.
If you do not want to access the server from outside the local WiFi or invite friends to connect to the server, you can stop reading.
Router adress and port
The public TCP/IP address of the router can be found within the local WiFi by selecting our remote address service .
In addition, some routers (like the Fritz!Box) can be setup to send a notification mail if the public TCP/IP address has been changed.
Another solution could be to use a dynamic DNS service to connect to the server by a hostname.
Router port forwarding
The server uses two ports for the connection:
the port number entered in the server window (e.g. 1400)
and a second port (port number plus 1, e.g. 1401).
Thus you must setup port forwarding (to the computer running the server) for two ports using the TCP/IP protocol - e.g. from port 1400 to port 1400 and from port 1401 to port 1401.
Even if router port forwarding must be setup for IPv6 as well, the connecting to the server is established by the static IPv6 address of the computer (and not the router). Thus our remote address service (as well as other services) returns not the router but the computer address.
Automatically there are 2 IPv6 addresses for the computer: a static address and a temporary address. And because the router port forwarding uses the static address (and not the temporary address), the IPv6 address of the computer must be configured manually (System Settings -> Network Settings -> Advanced -> TCP/IP) to setup only one address.
In other words: the IPv6 address of the router port forwarding, the result of our remote address service and the computer address must be the same.