Chapter 20: The firewall

Control which network traffic reaches a machine with firewalld, change rules so they survive a reload and a reboot, limit services to chosen hosts, and find out why a connection fails.

What you will learn

• Read the active zone and allow services and ports in it.
• Keep the runtime and permanent rules apart, and make changes persistent.
• Limit access to one host, define a service, forward a port and write a rich rule.
• Diagnose a failed connection layer by layer from the symptom the client sees.

Sections

1. Zones and services
2. Exercise: Publish a web server through the firewall
3. Runtime and permanent rules
4. Exercise: Runtime, permanent and temporary rules
5. Sources, forwarding and special rules
6. Exercise: One trusted host, a custom port and a forward
7. Diagnosing connection problems
8. Exercise: Find four faults
9. Exercise: Firewall review
10. firewalld quiz
11. firewalld cheat sheet