How to restrict access to the local network, but at the same time keep access to the Internet?

Question

Computer networks

There is a task and I need to understand whether it can be done. It is necessary to restrict access to the local network, but at the same time retain access to the Internet connection (with the possibility of further resetting to the initial settings). It is necessary to do this without using third-party software through console commands.
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Update: This task needs to be done on OS X. And it is done for VPN. Therefore, solutions with a router are not suitable.

Answer 1

Restrict the hypothetical firewall built into your hypothetical operating system through the hypothetical commands of your command processor to introduce rules blocking traffic to an unknown range of your local network.

Answer 2

The simplest solution is to have a different subnet on the router.

Answer 3

Is the server on macos vpn? Or should this computer be limited?

Answer 4

VLAN is a more elegant solution for network separation.
You can use firewall rules, but imagine that your park is expanding, will you write rules for everyone?
Static routing is possible, but this is a crutch rather than a solution.