How to set up & configure firewall using FirewallD for CentOS 8

2020-07-13 By Aaron 13307 Views linux centos firewall networking

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Firewall is an integral part of any system and can be used to protect a server against unauthenticated access from the outside world. It helps to prevent hackers from logging into servers on the network. Firewall can also be used to set up specific rules in-order to restrict access to specific ports of the system based on IP address.

The basic functionality of a firewall is to control the incoming and outgoing traffic and choose whether to block a particular connection or let it through based on the defined set of security rules.

Steps to set up FirewallD on CentOS 8

FirewallD uses concepts of services and zones instead of iptables rules and chains. Using that you can configure which traffic should be allowed or disallowed to and from the system. FirewallD is using the firewall-cmd utility to manage your firewall configuration.

In CentOS 8 FirewallD uses the concept of services and zones instead of iptables rules and chains and by using this you can configure which traffic is allowed or not in and out of the system. FirewallD uses the firewall-cmd utility to control the firewall configuration.

Run the below command to install FirewallD on CentOS 8. By default, it is available on CentOS 8.
```
# yum install firewalld
```

Now start and enable the FirewallD with the below commands.

# systemctl start firewalld

# systemctl enable firewalld

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Run the below command to check the FirewallD service state.
```
# firewall-cmd --state
```
Below are the predefined zones included in FirewallD:
1. drop – Dropped all incoming connections without any reply and only allowed outgoing connections.
2. block – It is the same as the zone drop, but all incoming connections are blocked with an icmp-host- prohibited or icmp6-adm-prohibited messages.
3. public – It represents unreliable public areas.
4. external – External networks in the event that the firewall uses as the gateway. Because it is configured for NAT masquerading and internal network will remain private but accessible.
5. internal – Only accepted the selected incoming connections and it’s for the internal network.
6. dmz – Demilitarized zone is publicly accessible to the internal network with limited access and accepted only selected incoming connections.
7. work – Using for work machines.
8. home - Using for home machines.
9. trusted - Accept all network connections.

Configuration of the firewall with FirewallD

By default, the public zone is the default zone after the firewall service is enabled.

The below command is used to get the list of the default zone.
```
# firewall-cmd --get-default-zone
```
Run the below command to get the list of all available zones.
```
# firewall-cmd --get-zones
```
Run the below command to see what zones are used by the network interface.
```
# firewall-cmd --get-active-zones
```
The below commands are used to change the default zone and verify.
```
# firewall-cmd --set-default-zone=home

# firewall-cmd --get-default-zone
```
NOTE: Replace the zone name with the original zone name that needs to be set as default.

Example of open HTTP port 80 and HTTPS port 443

Below commands are used to open temporarily.

# firewall-cmd --zone=public --add-service=http

# firewall-cmd --zone=public --add-service=https

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Below commands are used to open permanently.

# firewall-cmd --zone=public --permanent --add-service=http

# firewall-cmd --zone=public --permanent --add-service=https

OR

# firewall-cmd --zone=public --permanent --add-port 80/tcp

# firewall-cmd --zone=public --permanent --add-port 443/tcp

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Run the below to reload the service.
```
# firewall-cmd --reload
```
Check for open ports/services.
```
# firewall-cmd --list-all
```

Example of close HTTP port 80 and HTTPS port 443

Below commands are used to open permanently.

# firewall-cmd --zone=public --permanent --remove-service=http

# firewall-cmd --zone=public --permanent --remove-service=https

OR

# firewall-cmd --zone=public --permanent --remove-port 80/tcp

# firewall-cmd --zone=public --permanent --remove-port 443/tcp

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