Introduction
Setting up a good firewall is an essential step to take in securing any modern operating system. Most Linux distributions ship with a few different firewall tools that we can use to configure our firewalls. In this guide, we’ll be covering the iptables firewall.
Iptables is a standard firewall included in most Linux distributions by default (a modern variant called nftables will begin to replace it). It is actually a front end to the kernel-level netfilter hooks that can manipulate the Linux network stack. It works by matching each packet that crosses the networking interface against a set of rules to decide what to do.
In the previous guide, we learned how iptables rules work to block unwanted traffic. In this guide, we’ll move on to a practical example to demonstrate how to create a basic rule set for an Ubuntu 14.04 server. The resulting firewall will allow SSH and HTTP traffic.
Note: This tutorial covers IPv4 security. In Linux, IPv6 security is maintained separately from IPv4. For example, “iptables” only maintains firewall rules for IPv4 addresses but it has an IPv6 counterpart called “ip6tables”, which can be used to maintain firewall rules for IPv6 network addresses.
If your VPS is configured for IPv6, please remember to secure both your IPv4 and IPv6 network interfaces with the appropriate tools. For more information about IPv6 tools, refer to this guide: How To Configure Tools to Use IPv6 on a Linux VPS