Overview
firewalld is a daemon that controls a system's network traffic, allowing different security levels to be applied based on network interfaces or source IP addresses through predefined zones. It provides a user-friendly interface instead of directly handling complex iptables rules.
Key Features
- Dynamic Rule Management: Rules can be changed without restarting the service
- Zone-based: Applies different security policies based on network interfaces or sources
- Service and Port Management: Easy to open/block specific services (SSH, HTTP, etc.) or ports
- Rich Rules: Allows for complex condition-based rule configuration
- IPv4 and IPv6 Support
Main Options
These are options used when running the firewalld daemon itself. Most firewall rule management is done through the firewall-cmd command.
Daemon Execution Options
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Description:
`firewalld` Executes the command.
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Usage Examples
The firewalld service is primarily managed via the systemctl command. Firewall rule configuration uses the firewall-cmd command.
Start firewalld Service
sudo systemctl start firewalldStarts the firewalld daemon.
Enable firewalld Service (Start on Boot)
sudo systemctl enable firewalldConfigures firewalld to start automatically on system boot.
Check firewalld Service Status
sudo systemctl status firewalldChecks the current status of the firewalld service.
Restart firewalld Service
sudo systemctl restart firewalldRestarts the firewalld service.
Reload firewalld Configuration (After Rule Changes)
sudo firewall-cmd --reloadReloads and applies firewall rules without stopping the service.
Installation
firewalld is included by default in many Red Hat-based Linux distributions such as CentOS, Fedora, and RHEL. It may need to be installed manually on Debian/Ubuntu-based systems.
CentOS/Fedora/RHEL
sudo dnf install firewalldInstalls firewalld using dnf (or yum).
Debian/Ubuntu
sudo apt install firewalldInstalls firewalld using apt.
Tips & Notes
Tips and notes for effectively using firewalld.
Utilizing firewall-cmd
All firewall rule configuration and management for firewalld is done through the 'firewall-cmd' command. For example, opening ports, adding services, and setting zones require using firewall-cmd.
- Check currently active zones: `firewall-cmd --get-active-zones`
- Open a specific port (e.g., HTTP 80/tcp): `sudo firewall-cmd --zone=public --add-port=80/tcp --permanent`
- Apply changes: `sudo firewall-cmd --reload`
Applying Permanent Rules
When adding rules with firewall-cmd, you must use the `--permanent` option for the rules to persist after a system reboot. After using the `--permanent` option, you must run `firewall-cmd --reload` to apply the changes.
Understanding Default Zones
firewalld defaults to the 'public' zone, but offers various other zones such as 'home', 'work', 'internal', 'external', 'trusted', 'drop', and 'block'. Each zone has a different security level.
Relationship with iptables
firewalld internally uses iptables (or nftables), but provides a more abstracted interface than directly using iptables commands. When using firewalld, it is advisable to avoid directly manipulating iptables commands.