while you are working on Linux systems, you might have come across firewalls. but what is a firewall anyway?

Iptables is one such popular and powerful tool in the Linux operating system, designed to enable users to configure, maintain, and examine the tables of IP packet filter rules within the Linux kernel.

By configuring iptables we can allow or deny network traffic based on a set of configurable rules like

source ip
destination port
network interface

so without further ado let's dig in.

for this post, I have already created an instance in AWS with ubuntu os.

I provisioned an ec2 instance with ubuntu latest image which has iptables pre-installed

we can use iptables -L to list all rules setup

for this example, I will install nginx webserver and then add http (port 80) block rule for demonstration.

for that, I installed nginx using the below commands

sudo apt update
sudo apt install nginx

after the above step, we can see nginx default page when we visit the instance public ip

now let's add an iptables firewall rule to block all incoming http (port 80) connections.

sudo iptables -A INPUT -p tcp --dport 80 -j DROP

above command will DROP all incoming requests to port 80.

now if we try to access nginx it will not load.

now to unblock port 80 we can remove the previously added rule.

for that first, we need to list all rules with line numbers

sudo iptables -L --line-numbers

then run sudo iptables -D INPUT 1 which indicates that remove rule 1 in input rules which corresponds to what we created earlier.

after removing iptables block rule we can access nginx default webpage.

And there you have it.