How do I restrict network access to websites using a monitoring system?

Question

I am making a Java Project a LAB MONITORING SYSTEM for my University practical exams. Where a teacher or admin can monitor some selected computers and can give permissions to what the user at that computer can do.

One application is deployed at the admin computer and one application is deployed at the client computer (which is being monitored).

The client application is responsible for making permission in effect. Permission likes.
-Whether the USB Port should be enabled for disabled ( as they should be disabled during examination).
-Disable or enable task manager. etc.

Since the client application is responsible for making the permission in effect and it is running as a service that can be configurable by the administrator only.

I want that the admin can block some sites or can enable only selected websites that the client can browse. And if the user tries to access a restricted website, then a message should be displayed that "This website is Restricted by the ADMIN".

This software model is only for LAN networks. How can I accomplish the above task? Please help
I will be very grateful to you.

Answer 1

One possible solution to this problem is changing the /etc/hosts file (or equivalent) on the target system to point to a webserver running on the local intranet displaying your message of choice.

Example on Unix-like (Unix, Linux, BSD, Mac) systems:

# Static table lookup for hostnames.
# See hosts(5) for details

127.0.0.1       localhost
::1             localhost

your_webserver_ip blockedsite.com

A simpler approach (without the webserver) is doing this:

# Static table lookup for hostnames.
# See hosts(5) for details.

<snip>

172.0.0.1       blockedsite.com    

The Windows equivalent to this file is C:\Windows\System32\drivers\etc.

Do note for all these examples you will have to have root/admin privs.