Simple Firewall with ufw or firewalld
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Olatunde salami

Olatunde salami @salamilinux

About: Cloud Engineer | DevOps| Linux | Automation

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Simple Firewall with ufw or firewalld

Publish Date: May 21
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Welcome to Day 16 of our Linux Security Basics series! After securing file permissions on topic 5, it’s time to add a layer of network security with a firewall. A firewall controls incoming and outgoing traffic, protecting your system from unauthorized access. Today, we’ll explore two user friendly tools: ufw (Uncomplicated Firewall) and firewalld. Let’s set up a simple firewall to fortify your Linux system!

Index

Why Use a Firewall?

A firewall acts as a gatekeeper, allowing only trusted traffic while blocking potential threats. Without one, your system is vulnerable to attacks like port scanning or unauthorized remote logins. Both ufw and firewalld simplify firewall management, making them ideal for beginners and experienced users alike.

Choosing Between ufw and firewalld

  • ufw: Lightweight and easy to use, pre installed on Ubuntu and Debian-based systems. Best for simple setups.
  • firewalld: More dynamic, with support for runtime changes and zones. Common on Red Hat-based systems (e.g., CentOS, Fedora).

Check which tool is available:

  • For ufw: sudo ufw version
  • For firewalld: sudo firewall-cmd --version

If both are installed, you can use either let’s cover both!

Setting Up a Firewall with ufw

1. Check Status

Ensure ufw is active:

sudo ufw status
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If it says "inactive," proceed to enable it.

2. Enable ufw

Enable the firewall (this may disrupt existing connections, so plan ahead):

sudo ufw enable
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3. Allow Essential Services

Allow traffic for services you need (e.g., SSH on port 22):

sudo ufw allow 22/tcp
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Or use service names (if configured):

sudo ufw allow ssh
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4. Deny Unwanted Traffic

Block specific ports (e.g., deny port 23, used for telnet):

sudo ufw deny 23
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5. Set Default Policies

Restrict all incoming traffic by default, allowing only specified ports:

sudo ufw default deny incoming
sudo ufw default allow outgoing
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6. Verify and Apply

Check the rules:

sudo ufw status
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Apply changes (usually automatic with enable).

Setting Up a Firewall with firewalld

1. Check Status

See if firewalld is running:

sudo firewall-cmd --state
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If it returns "not running," start it:

sudo systemctl start firewalld
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2. Enable firewalld

Ensure it starts on boot:

sudo systemctl enable firewalld
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3. Allow Services

Allow SSH (port 22):

sudo firewall-cmd --add-service=ssh --permanent
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4. Add Custom Ports

Allow a custom port (e.g., 8080 for a web server):

sudo firewall-cmd --add-port=8080/tcp --permanent
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5. Reload Rules

Apply changes:

sudo firewall-cmd --reload
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6. Check Rules

View active rules:

sudo firewall-cmd --list-all
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Best Practices

  • Allow Only Necessary Ports: Minimize open ports to reduce attack surfaces.
  • Test After Changes: Ensure services (e.g., SSH) still work after enabling rules.
  • Backup Rules: Save ufw rules with sudo ufw show raw or firewalld with sudo firewall-cmd --runtime-to-permanent.
  • Monitor Logs: Check /var/log/ufw.log (ufw) or firewalld logs for issues.

Troubleshooting

  • Locked Out?: If you block SSH, use the console or a rescue method to regain access.
  • Conflicting Rules?: Reset with sudo ufw reset or sudo firewall-cmd --reload.

What’s Next?

You’ve now added a firewall to protect your network traffic! On our next topic, we’ll explore Monitoring Users and Login Activity with commands like last, w, and who. Stay tuned!

I would love to hear your thoughts, experiences, or tips about Linux!
Feel free to share in the comments and join the conversation.
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