Network Control: Block Domains and Show a Custom Message with dnsmasq

You can create a local HTML server that serves a "This page is blocked" message and use dnsmasq to redirect blocked domains to this local server. Here's how to do it:

Step 1: Create a Simple HTML Page

First, create a simple HTML page that shows the "This page is blocked" message.

Create a directory to hold the HTML files:
```
mkdir -p /var/www/blocked
```

Create an index.html file inside the directory with the blocked message:

sudo nano /var/www/blocked/index.html

Add the following content:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Blocked</title>
    <style>
        body {
            text-align: center;
            font-family: Arial, sans-serif;
            margin-top: 50px;
        }
        h1 {
            color: red;
        }
    </style>
</head>
<body>
    <h1>This Page is Blocked!</h1>
    <p>The site you are trying to access has been blocked by your administrator.</p>
</body>
</html>

Step 2: Set Up a Simple Local Web Server

To serve the HTML page, you can use a lightweight web server such as Python's HTTP server or NGINX/Apache. Here, I'll use Python’s built-in HTTP server for simplicity:

Navigate to the directory where your HTML file is located:
```
cd /var/www/blocked
```
Run the Python HTTP server on a specific port (for example, port 8080):
```
python3 -m http.server 8080
```
This will start a local HTTP server serving the index.html file. Now, if you go to http://localhost:8080 or http://<your-server-ip>:8080 in your browser, you should see the "This Page is Blocked" message.

Step 3: Configure dnsmasq to Redirect Blocked Domains

Next, configure dnsmasq to redirect blocked domains to your local HTML server.

Open the dnsmasq configuration file:
```
sudo nano /etc/dnsmasq.conf
```

Add entries for the domains you want to block and redirect them to your local server (replace 192.168.1.100 with your server's IP address):

# Redirect blocked domains to local web server running on 192.168.1.100:8080
address=/example.com/192.168.1.100
address=/ads.example.com/192.168.1.100

Restart dnsmasq to apply the changes:
```
sudo systemctl restart dnsmasq
```

Step 4: Verify the Setup

To test if the setup is working:

Try to access a blocked domain (e.g., example.com) from a browser on a client machine in your network.
You should see the custom "This Page is Blocked" message served from your local HTML server.

This approach gives you a simple and effective way to show a blocked page for specific domains using dnsmasq!