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This article covers the best-rated and most reviewed Open Source firewall software for Linux. Open Source Firewall is best known for protecting the network from a threat by filtering the inbound and outbound traffic and ensure network security.



This article covers how to set up UFW on Ubuntu 18.04 system. It advised to deny all the incoming connections except necessary ports. Uncomplicated Firewall or UFW is an interface to iptables that is designed to simplify the process of configuring a firewall. While iptables is a firm and flexible tool, it can be sometimes tricky for beginners to learn how to use it to properly configure a firewall. If a user is looking to get started securing his or her network, UFW may be the appropriate solution.


UFW is installed on Ubuntu by default. If it has been uninstalled for some reason, we can install it with the following command:

$ sudo apt install ufw

By default, UFW denies all incoming connections and allows all outgoing connections. It means that a client trying to reach our server would not be able to connect. When an application from our server tries to connect any other server outside, it will be allowed. The following commands serve the purpose:

$ sudo ufw default deny incoming
$ sudo ufw default allow outgoing



This article covers how to stop and disable FirewallD on your CentOS 7 system. Firewalld is a complete firewall solution that has been made available by default on all CentOS 7 servers. It is highly recommended that you have another firewall protecting your network or server before, or immediately after, disabling firewalld.


How to manage Firewalld ?

1. To disable firewalld, run the following command as root:

$ systemctl disable firewalld

2. To Stop Firewalld, execute the following command as root:

$ systemctl stop firewalld

3. To check the status of firewalld, run the following command as root:

$ systemctl status firewalld



This article covers how to disable FirewallD and install and iptables on CentOS 7 server. The iptables service stores configuration in /etc/sysconfig/iptables and /etc/sysconfig/ip6tables , while firewalld stores it in various XML files in /usr/lib/firewalld/ and /etc/firewalld/ . 

Note that the /etc/sysconfig/iptables file does not exist as firewalld is installed by default on Red Hat Enterprise Linux.

FirewallD is a complete firewall solution that can be controlled with a command-line utility called firewall-cmd. If you are more comfortable with the Iptables command line syntax, then you can disable FirewallD and go back to the classic iptables setup.


To Install and Use Iptables Linux Firewall:

1. Connect to your server via SSH.

2. Execute the following command one by one: 

$ sudo apt-get update 
$ sudo apt-get install iptables

3. Check the status of your current iptables configuration by running:

$ sudo iptables -L -v


Location of iptables rules on CentOS ?

CentOS 7 uses FirewallD by default. If you would like to manage iptables/ip6tables rules directly without using FirewallD, you may use the old good iptables-services service which will load the iptables/ip6tables rules saved in /etc/sysconfig/iptables and /etc/sysconfig/ip6tables when it is started during boot time.



This article covers how to configure and manage the FirewallD service on your CentOS system. A Linux firewall used to protect your workstation or server from unwanted traffic. You can set up rules to either block traffic or allow through. You can add or delete or update firewall rules without restarting the firewall daemon or service. The firewall-cmd act as a frontend for the nftables. In CentOS 8 nftables replaces iptables as the default Linux network packet filtering framework. 


To Start and enable firewalld, run the commands:

$ sudo systemctl start firewalld
$ sudo systemctl enable firewalld

To Stop and disable firewalld, run the commands:

$ sudo systemctl stop firewalld
$ sudo systemctl disable firewalld

To Check the firewalld status, run the command:

$ sudo firewall-cmd --state

To Command to reload a firewalld configuration when you make change to rules, run the command:

$ sudo firewall-cmd --reload

To Get the status of the firewalld service, run the command:

$ sudo systemctl status firewalld



This article covers how to secure Red Hat Enterprise Linux 8 with UFW. UFW may not be intended to provide complete firewall functionality, but it does provide an easy way to create and manage simple firewall rules.

A firewall is a way to protect machines from any unwanted traffic from outside. 

It enables users to control incoming network traffic on host machines by defining a set of firewall rules. 

These rules are used to sort the incoming traffic and either block it or allow through.

Note that firewalld with nftables backend does not support passing custom nftables rules to firewalld, using the --direct option.


How to start, stop, restart firewalld service on an RHEL 8?

By now you know about firewalld zones, services, and how to view the defaults. It is time to activate and configure our firewall.

1. Start and enable firewalld

$ sudo systemctl start firewalld
$ sudo systemctl enable firewalld

2. Stop and disable firewalld

$ sudo systemctl stop firewalld
$ sudo systemctl disable firewalld

3. Check the firewalld status

$ sudo firewall-cmd --state

4. Command to reload a firewalld configuration when you make change to rules

$ sudo firewall-cmd --reload

5. Get the status of the firewalld service

$ sudo systemctl status firewalld


When to use firewalld, nftables, or iptables:

1. firewalld: Use the firewalld utility for simple firewall use cases. The utility is easy to use and covers the typical use cases for these scenarios.

2. nftables: Use the nftables utility to set up complex and performance critical firewalls, such as for a whole network.

3. iptables: The iptables utility on Red Hat Enterprise Linux 8 uses the nf_tables kernel API instead of the legacy back end. 

The nf_tables API provides backward compatibility so that scripts that use iptables commands still work on Red Hat Enterprise Linux 8. For new firewall scripts, Red Hat recommends to use nftables.



This article covers method to Install and Use Firewalld in CentOS in order to increase the security of your Linux system. Note that the host-based firewall like firewalld is recommended by compliances like PCI DSS. 

FirewallD is a complete firewall solution that manages the system's iptables rules and provides a D-Bus interface for operating on them. Starting with CentOS 7, FirewallD replaces iptables as the default firewall management tool.

Firewalld services are predefined rules that apply within a zone and define the necessary settings to allow incoming traffic for a specific service.


How to install Firewalld on CentOS?

Firewalld is installed by default on CentOS 7, but if it is not installed on your system, you can install the package by running the command:

$ sudo yum install firewalld

Firewalld service is disabled by default. You can check the firewall status with:

$ sudo firewall-cmd --state

If you just installed or never activated before, the command will print not running. Otherwise, you will see running.

To start the FirewallD service and enable it on boot type:

$ sudo systemctl start firewalld
$ sudo systemctl enable firewalld


To open HTTP and HTTPS ports add permanent service rules to the dmz zone:

$ sudo firewall-cmd --permanent --zone=dmz --add-service=http
$ sudo firewall-cmd --permanent --zone=dmz --add-service=https

Make the changes effective immediately by reloading the firewall:

$ sudo firewall-cmd --reload

Zones provided by FirewallD:

1. drop: All incoming connections are dropped without any notification. Only outgoing connections are allowed.

2. block: All incoming connections are rejected with an icmp-host-prohibited message for IPv4 and icmp6-adm-prohibited for IPv6n. Only outgoing connections are allowed.

3. public: For use in untrusted public areas. You do not trust other computers on the network, but you can allow selected incoming connections.

4. external: For use on external networks with NAT masquerading enabled when your system acts as a gateway or router. Only selected incoming connections are allowed.

5. internal: For use on internal networks when your system acts as a gateway or router. Other systems on the network are generally trusted. Only selected incoming connections are allowed.

6. dmz: Used for computers located in your demilitarized zone that have limited access to the rest of your network. Only selected incoming connections are allowed.

7. work: Used for work machines. Other computers on the network are generally trusted. Only selected incoming connections are allowed.

8. home: Used for home machines. Other computers on the network are generally trusted. Only selected incoming connections are allowed.

9. trusted: All network connections are accepted. Trust all of the computers in the network.



This article will guide you on steps to block or unblock #ping requests on #Ubuntu Server 20.04 LTS. Also you will learn how to unblock the ping requests in case you need to use ping for system administration and troubleshooting.

To block #ping requests in #Linux:

You can implement blocking ICMP messages in your Linux system by adding the below #kernel variable that will drop all ping packets. In order to make the above rule permanent, append following line to /etc/sysctl. conf file and, subsequently, apply the rule with sysctl command.



This article will guide you on how to list and remove/delete iptables pretrouting chain nat rules on your #Linux based system. The -D or --delete option delete one or more rules from the selected chain. There are two versions of this #command, the rule can be specified as a number in the chain or a rule to match. One of the ways to delete #iptables #rules is by rule specification. To do so, you can run the iptables command with the -D option followed by the rule specification.




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