Linux Firewall Configuration

Linux Firewall Configuration Guide

Complete beginner-friendly guide to firewalls on Linux, covering Arch Linux, CachyOS, and other distributions including UFW, firewalld, and iptables configuration.

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Table of Contents

1. Understanding Firewalls
2. UFW Setup
3. firewalld Setup
4. iptables Basics
5. Troubleshooting

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Understanding Firewalls

What is a Firewall?

Firewall controls network traffic to/from your system.

Types:

• Packet filter: Blocks/allows packets
• Stateful: Tracks connections
• Application: Controls by application

Why use a firewall:

• Security: Block unauthorized access
• Privacy: Control outgoing traffic
• Protection: Prevent attacks

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UFW Setup

Install UFW

Arch/CachyOS:

# Install UFW
sudo pacman -S ufw

# Enable service
sudo systemctl enable --now ufw

Debian/Ubuntu:

sudo apt install ufw
sudo ufw enable

Fedora:

sudo dnf install ufw

Configure UFW

Basic setup:

# Default deny incoming
sudo ufw default deny incoming

# Default allow outgoing
sudo ufw default allow outgoing

# Enable firewall
sudo ufw enable

Allow Services

Allow specific ports:

# Allow SSH
sudo ufw allow 22/tcp

# Allow HTTP
sudo ufw allow 80/tcp

# Allow HTTPS
sudo ufw allow 443/tcp

# Allow by service name
sudo ufw allow ssh

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firewalld Setup

Install firewalld

Arch/CachyOS:

# Install firewalld
sudo pacman -S firewalld

# Enable service
sudo systemctl enable --now firewalld

Fedora:

sudo dnf install firewalld
sudo systemctl enable firewalld

Configure firewalld

Using firewall-cmd:

# Check status
sudo firewall-cmd --state

# List zones
sudo firewall-cmd --list-all-zones

# Add service
sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --reload

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iptables Basics

Understanding iptables

iptables is low-level firewall tool.

Chains:

• INPUT: Incoming traffic
• OUTPUT: Outgoing traffic
• FORWARD: Routed traffic

Basic Rules

Allow SSH:

# Allow SSH
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# Allow loopback
sudo iptables -A INPUT -i lo -j ACCEPT

# Default deny
sudo iptables -P INPUT DROP

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Troubleshooting

Firewall Blocking Connections

Check rules:

# UFW
sudo ufw status verbose

# firewalld
sudo firewall-cmd --list-all

# iptables
sudo iptables -L -v

Test Connection

Test ports:

# Test port
nc -zv hostname 22

# Or use telnet
telnet hostname 22

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Summary

This guide covered firewall configuration using UFW, firewalld, and iptables for Arch Linux, CachyOS, and other distributions.

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Next Steps

• Security Configuration - Security setup
• SSH Configuration - SSH setup
• ArchWiki Firewalls: https://wiki.archlinux.org/title/Firewalls

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This guide covers Arch Linux, CachyOS, and other Linux distributions. For distribution-specific details, refer to your distribution's documentation.