06_Basic_Networking

06: Basic Networking (RHEL 9)

This section covers the configuration of network interfaces, hostname resolution, and basic traffic filtering using the system firewall.

🎯 Exam Objectives (RHEL 9)

• IPv4 and IPv6 Configuration: Manually configure addresses, gateways, and DNS.
• Hostname Management: Set and verify the persistent system hostname.
• Network Services: Ensure networking starts automatically at boot.
• Firewall Management: Use firewall-cmd to allow or restrict services and ports.
• Name Resolution: Configure /etc/hosts for local resolution.

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🛠️ Key Command Reference

1. Networking with nmcli

Task	Command
List Connections	nmcli con show
Set Static IP	nmcli con mod "eth0" ipv4.addresses 192.168.1.10/24 ipv4.gateway 192.168.1.1 ipv4.method manual
Set DNS	nmcli con mod "eth0" ipv4.dns "8.8.8.8 8.8.4.4"
Apply Changes	nmcli con down "eth0" && nmcli con up "eth0"

2. Hostname Configuration

• Set Hostname: hostnamectl set-hostname server1.example.com
• Check Status: hostnamectl status

3. Firewall (Firewalld)

• List All Rules: firewall-cmd --list-all
• Allow a Service: firewall-cmd --permanent --add-service=http
• Allow a Port: firewall-cmd --permanent --add-port=8080/tcp
• Reload (Required): firewall-cmd --reload

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🚀 Lab Exercises to Practice

1. The Static Challenge: Change your VM from DHCP to a static IP address using only nmcli. Verify you can still ping your gateway.
2. The Name Resolver: Add an entry to /etc/hosts so that the name lab-server points to your own IP address. Test it with ping lab-server.
3. The Firewall Shield: Enable the firewall, allow ssh and http, but block all other incoming traffic. Verify using firewall-cmd --list-all.

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📝 The "Double-Check" List

• Persistence: Use nmcli con show to ensure autoconnect is set to yes.
• Testing: Always use ip addr and ip route to verify your manual settings took effect.
• Firewall: Remember that without --permanent, your firewall rules will disappear after a reboot!