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Firewall & Security

Firewalls are a critical component of network security. They act as a barrier between a trusted internal network and untrusted external networks, such as the internet.

firewalld Zones​

firewalld is a firewall management tool for Linux. It uses the concept of zones to manage traffic. A zone is a set of rules that determines what traffic is allowed or denied.

Some of the predefined zones in firewalld include:

  • public: For use in public areas. You do not trust the other computers on networks to not harm your computer.
  • trusted: All network connections are accepted.
  • home: For use in home areas. You mostly trust the other computers on networks to not harm your computer.
  • internal: For use on internal networks. You mostly trust the other computers on the networks to not harm your computer.
  • dmz: For computers in your demilitarized zone that are publicly-accessible with limited access to your internal network.

Common Rules (ssh, http, https)​

You can use the firewall-cmd command to manage firewalld rules.

  • Allow SSH traffic:

    sudo firewall-cmd --zone=public --add-service=ssh --permanent

  • Allow HTTP and HTTPS traffic:

    sudo firewall-cmd --zone=public --add-service=http --permanent
    sudo firewall-cmd --zone=public --add-service=https --permanent

  • Reload the firewall to apply the changes:

    sudo firewall-cmd --reload

How to Check Open Ports and Services​

  • List all open ports and services:

    sudo firewall-cmd --list-all

  • Check if a specific port is open:

    sudo firewall-cmd --zone=public --query-port=80/tcp

  • Check if a specific service is enabled:

    sudo firewall-cmd --zone=public --query-service=ssh