OUTPUT – filter packets that are going out from your server.īefore we begin this guide, make sure you have SSH root or sudo access to your machine that runs on Ubuntu 16.04 or up.

FORWARD – filters incoming packets that will be forwarded somewhere else.

INPUT – controls incoming packets to the server.

In this iptables tutorial, we are going to work with one of the default tables, called filter.

RETURN – stops the packet from traversing through a chain and tell it to go back to the previous chain.

DROP – will not let the packet pass through.

ACCEPT – will allow the packet to pass through.

When a packet matches a rule, it is given a target, which can be another chain or one of these special values:

These tables contain sets of rules, called chains, that will filter incoming and outgoing data packets. It will monitor traffic from and to your server using tables. Simply put, iptables is a firewall program for Linux. How to Install and Use Iptables Linux Firewall.

What is Iptables, and How Does It Work?.

Centos iptables