Firewall and Network Management in Red Hat Linux

Welcome to Day 24 of the 30 Days of Linux Challenge!

Today’s focus is on securing and managing network access using firewalld, nmcli, and iptables — tools that are deeply integrated into Red Hat-based systems.

📚 Table of Contents

• Why Firewall & Network Management Matters
• Start and Enable firewalld
• Check Firewall Status and Rules
• Allow and Block Services
• Port-Based Rules with firewalld
• Use Zones for Granular Control
• Manage Network Connections with nmcli
• Inspect Rules with iptables
• Try It Yourself
• Why This Matters

Why Firewall & Network Management Matters

🔒 Firewalls protect your system from unauthorized access

🌐 Network tools ensure connectivity, DNS, IP config, and interface control

🚀 Red Hat provides enterprise-grade options to manage both with precision

Start and Enable firewalld

sudo systemctl enable --now firewalld
sudo systemctl status firewalld

Check Firewall Status and Rules

sudo firewall-cmd --state
sudo firewall-cmd --list-all

This shows:

• Active zone (usually public)
• Allowed services and ports

Allow and Block Services

Allow SSH (if it’s not already):

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

sudo firewall-cmd --reload

Block a service:

sudo firewall-cmd --remove-service=ftp --permanent
sudo firewall-cmd --reload

Port-Based Rules with firewalld

Open a custom port:

sudo firewall-cmd --add-port=8080/tcp --permanent
sudo firewall-cmd --reload

Check open ports:

sudo firewall-cmd --list-ports

Use Zones for Granular Control

List available zones:

sudo firewall-cmd --get-zones

Change zone for a specific interface:

sudo firewall-cmd --zone=internal --change-interface=eth0 --permanent

Manage Network Connections with nmcli

List connections:
nmcli connection show

View device status:
nmcli device status

Static IP configuration:

nmcli connection modify eth0 ipv4.addresses 192.168.1.100/24
nmcli connection modify eth0 ipv4.gateway 192.168.1.1
nmcli connection modify eth0 ipv4.dns 8.8.8.8
nmcli connection modify eth0 ipv4.method manual
nmcli connection up eth0

Inspect Rules with iptables

View raw firewall rules:
sudo iptables -L -n -v

Although firewalld is preferred, iptables is still useful for inspection and legacy troubleshooting.

Try It Yourself

🧪 Practice tasks:

• Start and enable firewalld
• Add and remove a service or port
• View current zone and active rules
• Use nmcli to set a static IP (test on a VM or safe machine)
• Run iptables -L to inspect low-level rules

Why This Matters

Firewall and network misconfigurations are one of the top causes of downtime.

By learning:

firewalld → fast, zone-based rule management

nmcli → flexible, scriptable network config

iptables → rule-level diagnostics

…you gain complete control over how and when your system communicates.