How to restrict an app from the internet but allow it on local?

[The-Maize]

Hello, I have a server & program that works together, i would like to completely restrict the access to the net on both programs, as in no connection at all to the internet, but allow the connections from (0.0.0.0:1234 /127.0.0.1:1234) for the server and the same for the software that connects to it (only on single port). I am building a server + program but i want to learn how to use firejail to provide these functionalities for my working environment. but i dont want any other connections to it.
i need the server to be able to send and receive locally on about 10 different ports.

is this possible?

[kmk3]

Duplicate of:

• Support for --net=local #108