Simple guide of Iptables

How to add and delete rules to your Firewall using Iptables directly

Attention:

All the operations will be accomplished considering that you’re logged as “root”, or that you’re running the commands with sudo, therefore, be careful

Show the Rules:

First, you’ll need to verify all the rules that you already have. To list all the rules,use the following command:

iptables -L

If you want to see the lines of the rules (this will be important later), you can simply type the following command:

iptables -L --line-numbers

You can see that the output will show all the rules, of all the chains, but,in this tutorial, I will use only the input chain, never the less the commands should work in all the other chains.

The chains are a list of rules processed in order. That’s why it is so important to verify all the other rules in the chain, to see where you’ll have to put new rules that you’re creating, or which one to delete.

Persist the changes (And backup,of course)

Install the package iptables-persistent, so you can save the alterations

apt install iptables-persistent

After the installation, the configuration will be saved in two places: one for the IPV4 rules, and the other one to IPV6 rules.

/etc/iptables/rules.v4
/etc/iptables/rules.v6

Now you can change whatever you desire on Iptables. Here,we’ll open a port as an example.

Adding a Rule

To open a port, execute the following command, where your_port is the port that you want:

iptables -m comment --comment "New Port" -A INPUT -p tcp --dport your_port -j ACCEPT

This will append the rule in the end of the chain (in this case, INPUT chain)

Important !

The rules inserted on Iptables are verified one by one on a sequence, therefore, if needed, use the following command to insert a new rule before any other rule that you want to add:

iptables -m comment --comment "New Port" -I INPUT line_number -p tcp --dport your_port -j ACCEPT

Delete

The simplest way to delete one rule is by the line number. You can simply specify which line of the chain to delete:

iptables -D INPUT number_of_the_line

After that, you’ll execute the following commands to save the configuration that you’ve done.

To save the IPV4 rules:

iptables-save > /etc/iptables/rules.v4

And to save the IPV6 rules:

iptables-save> /etc/iptables/rules.v6

Now, all your configurations will remain after the reboot. And that’s it !!!

A huge thanks to Mylena Rossato for helping me translate this guide !!!.