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A Beginner’s Guide to Iptables for Network Routing

20 October 2025bpd · ubuntu

Mastering the Basics of Linux Firewalls

The ‘Ubuntu System Administration Guide’ provides a practical introduction to `iptables`, the command-line utility used to configure the Linux kernel firewall. The guide focuses on the essential rules needed to make your Ubuntu server act as a network router.

Key Iptables Chains

`iptables` uses a set of ‘chains’ to process network traffic. For a basic router, you’ll work with three main chains:

  • INPUT: Controls traffic destined for the firewall server itself.
  • OUTPUT: Controls traffic originating from the firewall server.
  • FORWARD: This is the most important chain for a router, as it controls traffic passing *through* the server from one network to another (e.g., from your private network to the internet).

Essential Forwarding Rules

The book provides example rules that allow traffic from your private network to go out to the internet and permit the return traffic for those established connections, while blocking unsolicited traffic from the internet. This is the foundation of a secure network firewall.

This post is based from content of the book Ubuntu System adminstration guide. And the book can be found here https://www.amazon.com/stores/Mattias-Hemmingsson/author/B0FF5CQX13