📦 DNS Firewall for Linux

An Automated Local DNS Filtering Firewall using Python & Systemd

✅ Project Overview

This project builds a lightweight DNS firewall for Linux machines. It runs as a systemd service, automatically intercepts all DNS queries, blocks unwanted domains based on a live blacklist (domain.txt), and forwards safe queries to real upstream DNS (default: Google DNS 8.8.8.8).

Ideal for:

• Home lab / Raspberry Pi network firewall
• Linux workstation DNS filter
• Educational research project
• Malware & phishing domain blocking

✅ Features

• Runs automatically at boot (systemd)
• Live blacklist reloading every 10 sec
• Logs all DNS requests (dns_firewall.log)
• Easy setup and uninstall scripts
• Supports any Linux distro (Debian, Ubuntu, Kali, Fedora, Arch etc.)

✅ Folder Structure

dnsfirewall/ │ ├── dns_firewall_linux.py → main Python firewall ├── domain.txt → list of blocked domains ├── setup_dns_firewall.sh → script to setup + start firewall ├── uninstall_dns_firewall.sh → script to uninstall + restore DNS └── /etc/systemd/system/ └── dns_firewall.service → systemd service file (manual step)

✅ Requirements

• Linux machine (physical or virtual)
• Python 3.6+
• Root (sudo) access

Install dependencies:

sudo apt update sudo apt install python3 python3-pip -y pip3 install dnslib

✅ Usage Guide

1️⃣ Place all files inside folder: dnsfirewall

2️⃣ Edit dns_firewall.service and Copy to the mentioned path

👉 Replace /home/YOUR_USERNAME with your actual full path.

Save as:

/etc/systemd/system/dns_firewall.service

3️⃣ Run setup script

cd ~/Linux_Proxy_Firewall_DNS

chmod +x setup_dns_firewall.sh

./setup_dns_firewall.sh

✅ Your DNS firewall is now active.

4️⃣ Test it

nslookup facebook.com 127.0.0.1 # Should be blocked (NXDOMAIN)

nslookup google.com 127.0.0.1 # Should be allowed

Logs:

tail -f ~/Linux_Proxy_Firewall_DNS/dns_firewall.log

✅ Example domain.txt

facebook.com

ads.google.com

malware-site.com

👉 Add any domain name (one per line) to block it. 👉 No restart needed. File reloads every 10 seconds.

✅ Uninstall (fully restore system)

cd ~/Linux_Proxy_Firewall_DNS

chmod +x uninstall_dns_firewall.sh

./uninstall_dns_firewall.sh

Restores:

• DNS resolver back to 8.8.8.8
• Removes firewall service
• Re-enables systemd-resolved

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✅ Safety Tip

To prevent automatic overwrite of /etc/resolv.conf:

sudo chattr +i /etc/resolv.conf

Remove lock:

sudo chattr -i /etc/resolv.conf

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🎉 Congratulations!

You now have a fully working Python DNS firewall service ready for lab use, research, or home network protection 🚀

✅ Credits

Developed with help of:

• Python 3
• dnslib library
• systemd

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