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Install and Use Firewalld in CentOS / RHEL - Step by step process to implement it ?

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.


Block or Unblock Ping Request on Debian 10 - How to perform this task ?

This article covers how you can block/unblock ping requests to your Debian system. You will learn different ways for blocking/unblocking ping requests either temporarily or permanently.


The --query-icmp-block=<type> option can be used to determine if a type is confgured to allow or deny. 

The --add-icmp-block=<type> option can be used to block a certain type. 

The --remove-icmp-block=<type> option can be used to not block a certain type. 

After adding or removing a block, reload the firewall.


To block ping requests in Linux:

1. Edit /etc/sysctl.conf. Add the following line to your /etc/sysctl.conf : net.ipv4.icmp_echo_ignore_all=1. Then: sysctl -p.

2. Using iptables: iptables -I INPUT -p icmp --icmp-type echo-request -j DROP.

3. With cron. Run crontab -e as root, then add the following line: @reboot echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all.


To block ping in iptables:

1. Add a rule that tells the iptables firewall to block ping in and out of a server by controlling the ICMP requests.

2. Remove the rule that tells the iptables firewall to allow ping in and out of a server by controlling the ICMP requests.


To enable ping on Linux server?

# iptables -D INPUT -p icmp --icmp-type echo-request -j REJECT D : 

This command switch is used to delete the rule. Once the ping enabled, the server should now respond to ping requests


How to use Linux command to delete the PREROUTING rule in iptables ?

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.


Perform SSH Installation And Configuration in CentOS

This article will guide you on the steps to install openssh server (sshd) and clients on CentOS Linux using the yum command. The #ssh #command provides a secure encrypted connection between two hosts over an insecure #network. This connection can also be used for #terminal access, file transfers, and for tunneling other applications. Graphical X11 applications can also be run securely over SSH from a remote location.


How to Set Up OpenVPN Server on Debian 10 ?

This article will guide you on how to set up an OpenVPN server on Debian Linux 10 server.


How to set up OpenVPN Server on CentOS 8 Server ?

In this article, you will learn how to set up an OpenVPN server on CentOS 8 Linux server.


Easy method to install and configure Squid Proxy on CentOS 7 Server

In this article, you will learn how to install Squid and steps to configure the Squid Proxy port and adjusting the access control list.


Learn how to set up NFS Server of CentOS 8 and RHEL 8

This article will show you how to install and configure an NFS Server on CentOS 8 Machine, Our Server Experts will take you through the steps to create files on both the NFS Server and Client and enable you share files efficiently between two or more systems.


Steps to configure Caching Dns Server on CentOS 8 Machine

Here is a complete guide on how to configure the DNS caching-only server on CentOS 8.