According to the official website of firewalld, “Firewalld provides a dynamically managed firewall with support for network/firewall zones that define the trust level of network connections or interfaces. It has support for IPv4, IPv6 firewall settings, ethernet bridges, and IP sets. There is a separation of runtime and permanent configuration options. It also provides an interface for services or applications to add firewall rules directly.”.

So it’s a tool for managing firewall on Fedora/CentOS/RHEL/Debian/Ubuntu and many other famous Linux operating systems along with iptables. You can find more about firewalld at firewalld.org.

Let’s see how to use firewalld.

Installing firewalld on CentOS/RHEL/Fedora:

The firewalld program should install on CentOS/RHEL/Fedora systems by default.

Installing firewalld on Ubuntu/Debian

By default, firewalld program is not installed on Debian/Ubuntu based systems. But you can easily install it by running the following commands.

surendra@linuxnix$ sudo apt-get update
surendra@linuxnix$ sudo apt-get install firewalld

The architecture of firewalld Program:

The firewalld program has two parts.

  1. The daemon that runs in the background.
  2. The firewall-cmd command to add, modify, remove firewall rules.

How firewalld works:

The firewalld defines several zones, and each zone has its own interfaces and own rules. The firewall-cmd command can be used to add, modify, remove zones, interfaces from the zones, allow or deny ports for zones.

Benefits of firewalld:

The most significant advantage of firewalld is that firewalld daemon doesn’t have to restart when the configuration is changed. The changes are immediate and can be made at runtime.

View the current firewall settings:

To view the current settings of firewalld, you can use the ‘firewall-cmd’ command as follows.

surendra@linuxnix$ sudo firewall-cmd --list-all
public (default, active)
  interfaces: eno16777760
  sources: 
  services: dhcpv6-client ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules:

You can see from the output that, the current active zone is called ‘public.’ The ‘public’ zone is activated on the interface ‘eno16777760’. The services enabled on the ‘public’ zone are ‘dhcpv6-client’ and ‘ssh’. You can see that; there are no open ports in ‘public’ zone right now. It has other information as well. But it’s not something we are interested in right now.

Opening a TCP port using firewall-cmd

You can quickly open a TCP port using the firewall-cmd command. For example, if you want to open the TCP port 53, which is the port for domain name service (DNS), run the following command.

surendra@linuxnix$ sudo firewall-cmd --add-port=53/tcp
success

The TCP port 53 should be added. You can verify it using the following command.

surendra@linuxnix$ sudo firewall-cmd --list-all
public (default, active)
  interfaces: eno16777760
  sources: 
  services: dhcpv6-client ssh
  ports: 53/tcp
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules:

You can see from the output of the ‘firewall-cmd’ command that the TCP port 53 has been opened. Have a look at important ports in Linux.

Opening a UDP port using firewall-cmd

You can quickly open a UDP port using the firewall-cmd command. For example, if you want to open the UDP port 53, which is the port for domain name service (DNS), run the following command.

surendra@linuxnix$ sudo firewall-cmd --add-port=53/udp
success

The UDP port 53 should be added. You can verify it using the following command.

surendra@linuxnix$ sudo firewall-cmd --list-all
public (default, active)
  interfaces: eno16777760
  sources: 
  services: dhcpv6-client ssh
  ports: 53/udp 53/tcp
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules:

You can see from the output of the ‘firewall-cmd’ command that the UDP port 53 has been opened.

Removing a TCP port using firewall-cmd

You can remove a TCP port using firewall-cmd. For example, if you want to remove the TCP port 53 added earlier, run the following command.

surendra@linuxnix$ sudo firewall-cmd --remove-port=53/tcp
success

 

Removing a UDP port using firewall-cmd

You can remove a TCP port using firewall-cmd. For example, if you want to remove the UDP port 53 added earlier, run the following command.

surendra@linuxnix$ sudo firewall-cmd --remove-port=53/udp
success

Adding a Service using firewall-cmd

There are predefined services on firewalld. For example, if you want to enable the default HTTP port 80, you can run the following command.

surendra@linuxnix$ sudo firewall-cmd --add-service=http
success

The HTTP service should be enabled. You can verify it with the following command.

surendra@linuxnix$ sudo firewall-cmd --list-all
public (default, active)
  interfaces: eno16777760
  sources: 
  services: dhcpv6-client http ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules:

You can see that, HTTP service is enabled.

Removing a Service using firewall-cmd

You can remove a service using the firewall-cmd command. For example, if you want to remove the HTTP service added earlier, run the following command.

surendra@linuxnix$ sudo ffirewall-cmd --remove-service=http
success

The HTTP service should be removed. You can verify it with the following command.

surendra@linuxnix$ sudo firewall-cmd --list-all
public (default, active)
  interfaces: eno16777760
  sources: 
  services: dhcpv6-client ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules:

You can see that, HTTP service is removed.

Blocking a specific IP address using firewall-cmd

If you want to prevent a particular IP address using firewalld, you can do so with rich rules. Rich rules are advanced rules for firewalld. Not everything can be done with firewall-cmd command. So rich controls fill the gap.

You can block the ip address 192.168.17.12 with the following command.

surendra@linuxnix$ sudo firewall-cmd --add-rich-rule='rule family=ipv4 source address=192.168.17.112 reject'
success

Now the host with the IP address 192.168.17.12 can not connect to this machine anymore.

Unblocking a blocked IP address using firewall-cmd

You can unblock an already blocked IP address using the firewall-cmd command. For example, if you want to unblock the IP address 192.168.17.12, you can do so with the following command.

surendra@linuxnix$ sudo firewall-cmd --remove-rich-rule='rule family=ipv4 source address=192.168.17.112 reject'
success

Now you should be able to ping from the host 192.168.17.12.

Adding rules permanently to firewalld

The rules you add using firewall-cmd is temporary. That is, once you restart your computer, the rules will disappear. This is good for the testing purpose. But if you want to make the rules permanent, then you should append ‘–permanent’ parameter to the firewall-cmd command and restart the firewalld daemon.

For example, if you want to enable the HTTPS service permanently, run the following command.

surendra@linuxnix$ sudo firewall-cmd --add-service=https --permanent
success

Now to reload the firewalld configuration, run the following command.

surendra@linuxnix$ sudo firewall-cmd --reload
success

You can verify the change by running the following command.

surendra@linuxnix$ sudo firewall-cmd --list-all
public (default, active)
  interfaces: eno16777760
  sources: 
  services: dhcpv6-client https ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules:

You can see that the HTTPS service is active.

That’s the basics of firewalld. It’s an excellent tool for managing firewalls on Linux. You may go to the official website of firewalld to learn more about the firewalld program.

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Surendra Anne

Mr Surendra Anne is from Vijayawada, Andhra Pradesh, India. He is a Linux/Open source supporter who believes in Hard work, A down to earth person, Likes to share knowledge with others, Loves dogs, Likes photography. He works as Devops Engineer with Taggle systems, an IOT automatic water metering company, Sydney . You can contact him at surendra (@) linuxnix dot com.