Viewing the iptables rules configured on our Linux system

Collection of basic Linux Firewall iptables rules

The purpose of this guide is to show some of the most common iptables commands for Linux systems. iptables is the firewall built into all Linux distributions. Even distros like Ubuntu, which utilizes ufw (uncomplicated firewall), and Red Hat, which utilizes firewalld still pass their commands to iptables and use it in the background.

Mastering iptables, or at least becoming familiar with some of the most basic commands, is essential for Linux administrators. Even casual Linux users can benefit from understanding the basics of the iptables firewall, since they may be required to apply some minor configurations to it at some point. Use some of the examples below to familiarize yourself with the iptables syntax and get an idea for how it works to protect your system.

WARNING
You should not apply iptables rules to a production system until you are somewhat familiar with how they work. Also be careful when applying rules to remote systems (a computer that you have established an SSH session with) because you can accidentally lock yourself out if you enter the wrong rule.

In this tutorial you will learn:

  • Collection of basic Linux firewall iptables rules
Viewing the iptables rules configured on our Linux system

Viewing the iptables rules configured on our Linux system

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Checking for open ports on Ubuntu Linux with the ss command

How to show/check for open ports on Ubuntu Linux

Some Linux software works by listening for incoming connections. A simple example would be a web server, which handles user requests whenever someone navigates to a website. As a Linux administrator or user, it’s important to always know which ports of your system are open to the internet. Otherwise, you could be unaware of outside connections being made to your computer, which consumes bandwidth and resources, along with being a potential security hole.

In this guide, we’ll see how to check for open ports on Ubuntu Linux. This can be done with several different command line utilities, which we’ll go over in detail. We’ll also see how to use Ubuntu’s ufw firewall to make sure ports are secure. So, do you know which ports of your system are open? Let’s find out.

In this tutorial you will learn:

  • How to check for open ports with ss command
  • How to check for open ports with Nmap utility
  • How to check for and add allowed ports in ufw firewall
Checking for open ports on Ubuntu Linux with the ss command

Checking for open ports on Ubuntu Linux with the ss command

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How to disable or enable the firewall on AlmaLinux

How to disable/enable firewall on AlmaLinux

firewalld is the firewall manager that comes pre-installed on AlmaLinux, whether you’ve freshly installed AlmaLinux or migrated from CentOS to AlmaLinux. By default, the firewall is turned on, meaning that a very limited number of services are able to receive incoming traffic.

This is a nice security feature, but it means that the user must be knowledgeable enough to configure the firewall whenever they install a new service on the system, like HTTPD or SSH for example. Otherwise, connections from the internet can’t reach these services.

In this guide, we’ll see how to disable or enable the firewall in AlmaLinux, along with checking the status of the firewall. These are good troubleshooting options when trying to determine if a firewall rule is blocking traffic to or from a particular service.

DID YOU KNOW?
firewalld is simply a front end for the system’s nftables (formerly iptables) firewall. This makes the firewall easier to interact with, but essentially firewalld just translates all our commands into corresponding nft commands.

In this tutorial you will learn:

  • How to check the firewall status on AlmaLinux
  • How to stop firewall on AlmaLinux
  • How to start firewall on AlmaLinux
  • How to permanently disable firewall on AlmaLinux
  • How to enable firewall to start after reboot
How to disable or enable the firewall on AlmaLinux

How to disable or enable the firewall on AlmaLinux

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ss command on Linux

Using ss command on Linux

The ss command is the successor to the netstat command on Linux systems. The command is used by system administrators to see information about network connections. It allows you to check things like the status, origin, and destination of connections. In addition, ss displays route tables, interface statistics, masquerade connections, and multicast memberships.

In this guide, you’ll learn how to use the ss command through examples and explanations. We’ll show you its most common uses and everything you need to know in order to use it effectively.

In this tutorial you will learn:

  • How to use ss command

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firewalld on CentOS

Install firewalld on CentOS Linux system

firewalld is a front-end for the built in netfilter firewall on Linux systems. The main advantage of firewalld over using raw nftables/iptables commands is that it’s easier to use, especially for more complex firewall features like timed rules. In this regard, it’s similar to the uncomplicated firewall (ufw) that comes installed by default on Ubuntu systems.

On CentOS, firewalld is the default firewall interface and should already be installed on your system. In this guide, we’ll take you through the installation of firewalld on CentOS, which includes some basic usage commands so you can get started managing the firewall.

In this tutorial you will learn:

  • How to install and update firewalld
  • firewalld basic usage commands

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Tips & Tricks with Netcat command on Linux

Tips & Tricks with Netcat command on Linux

Netcat is a versatile networking utility which can be used for reading from and writing to TCP and UDP connections on arbitrary ports (as with other utilities used on Linux, ports below 1024 require root/sudo privileges). By default netcat uses TCP connections, but UDP can be specified with the -u flag. Netcat can be used as both a server and a client. When used as a server the -l flag is used to listen for a connection. Similar to the cat command, netcat can receive information from stdin and write to stdout making it great for workflows involving pipes and redirects. The nc command is typically used to evoke netcat for ease of use.

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Settings menu for enabling and disabling the system firewall in Manjaro Linux

Enable/Disable Firewall on Manjaro Linux

There are a few reasons why you may need to enable or disable the firewall on your system. Managing the firewall on Manjaro Linux can be done either via GUI or the command line. In this guide, we’ll show you methods for both.

In this tutorial you will learn:

  • How to add enable or disable firewall from GUI (XFCE)
  • How to enable or disable firewall from command line

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How to deny all incoming ports except HTTP port 80 and HTTPS port 443 on Ubuntu 18.04 Bionic Beaver Linux

Objective

The objective is to enable UFW firewall, deny all incoming ports however only allow HTTP port 80 and HTTPS port 443 on Ubuntu 18.04 Bionic Beaver Linux

Operating System and Software Versions

  • Operating System: – Ubuntu 18.04 Bionic Beaver

Requirements

Privileged access to your Ubuntu 18.04 Bionic Beaver will be required.

Conventions

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