What Is Iptables?
Iptables is a firewall program for Linux. It monitors traffic to and from your server using tables. These tables contain sets of rules, referred to as chains, which filter incoming and outgoing data packets.
How Do Iptables Work?
Iptables is a firewall program for Linux. It monitors traffic to and from your server using tables. These tables contain sets of rules, referred to as chains, which filter incoming and outgoing data packets.
When a packet matches a rule, it is assigned a target, which can be either another chain or one of these special values:
- ACCEPT – allows the packet to pass through.
- DROP – prevents the packet from passing through.
- RETURN – halts the packet's traversal through a chain and directs it back to the previous chain.
In this iptables tutorial, we will work with one of the default tables called filter. It consists of three chains:
- INPUT – controls incoming packets to the server.
- FORWARD – filters incoming packets that will be forwarded elsewhere.
- OUTPUT – filters packets leaving your server.
Before we begin this guide, ensure you have SSH root or sudo access to your machine running Ubuntu 16.04 or later. You can establish the connection using PuTTY (Windows) or a terminal shell (Linux, macOS).
Important! iptables rules only apply to IPv4. If you wish to set up a firewall for the IPv6 protocol, you need to use ip6tables instead.
Click Here to Know How to Install and Use Iptables Linux Firewall.