08 - Network Configuration¶

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1. Executive Summary¶

Topic Scope: Network interface configuration, static IP assignment, hostname management, and network troubleshooting in RHEL 9

RHCSA Relevance: Essential system administration skill - network configuration is fundamental for server management

Exam Weight: Medium-High - Network tasks appear frequently in exam scenarios

Prerequisites: Basic understanding of TCP/IP networking and Linux command line operations

Related Topics: System Installation, SSH Configuration, Firewall

2. Conceptual Foundation¶

Core Theory¶

RHEL 9 uses NetworkManager as the primary network management service:

NetworkManager: Modern network configuration service replacing traditional networking scripts
Connection profiles: Persistent network configurations stored by NetworkManager
Device vs Connection: Devices are physical/virtual interfaces; connections are configurations applied to devices
Static vs DHCP: Manual IP assignment versus automatic configuration
Network namespaces: Isolated network environments (advanced topic)

Real-World Applications¶

Server deployment: Configuring static IPs for production servers
Network troubleshooting: Diagnosing connectivity issues in enterprise environments
Remote management: Ensuring SSH access through proper network configuration
Service hosting: Setting up networks for web servers, databases, and applications
Network isolation: Separating different types of traffic for security

Common Misconceptions¶

NetworkManager vs network scripts: RHEL 9 uses NetworkManager, not legacy scripts
Interface naming: Modern systems use predictable names (ens3, enp0s3) not eth0
Connection vs device state: A device can be up but connection down
DNS configuration: Managed by NetworkManager, not directly in /etc/resolv.conf
Gateway terminology: Default route and default gateway are the same concept

Key Terminology¶

Interface: Physical or virtual network device (ens3, enp0s3, virbr0)
Connection: NetworkManager configuration profile applied to interface
Profile: Persistent network configuration including IP, DNS, gateway
DHCP: Dynamic Host Configuration Protocol for automatic IP assignment
Static IP: Manually configured IP address that doesn't change
Gateway: Router that connects local network to other networks
DNS: Domain Name System for resolving hostnames to IP addresses
MTU: Maximum Transmission Unit - largest packet size for interface

3. Command Mastery¶

NetworkManager Commands (nmcli)¶

# Connection management
nmcli connection show                    # List all connections
nmcli connection show --active           # Show active connections
nmcli connection show "connection-name"  # Show specific connection details
nmcli connection up "connection-name"    # Activate connection
nmcli connection down "connection-name"  # Deactivate connection
nmcli connection delete "connection-name" # Delete connection
nmcli connection reload                  # Reload connection files

# Device information
nmcli device status                      # Show device status
nmcli device show                        # Show all device details
nmcli device show ens3                   # Show specific device details
nmcli device connect ens3                # Connect device to auto connection
nmcli device disconnect ens3             # Disconnect device

# Creating connections
nmcli connection add type ethernet con-name "static-ens3" ifname ens3 \
  ipv4.addresses 192.168.1.100/24 \
  ipv4.gateway 192.168.1.1 \
  ipv4.dns "8.8.8.8 8.8.4.4" \
  ipv4.method manual

nmcli connection add type ethernet con-name "dhcp-ens3" ifname ens3 \
  ipv4.method auto

# Modifying connections
nmcli connection modify "static-ens3" ipv4.addresses 192.168.1.150/24
nmcli connection modify "static-ens3" ipv4.dns "8.8.8.8,1.1.1.1"
nmcli connection modify "static-ens3" connection.autoconnect yes

Traditional Network Commands¶

# Interface information
ip addr show                    # Show all interface addresses
ip addr show ens3               # Show specific interface
ip link show                    # Show link layer information
ip route show                   # Show routing table
ip route show default           # Show default route only

# Legacy commands (still useful for information)
ifconfig                        # Show interface configuration (if installed)
route -n                        # Show routing table (if installed)
netstat -rn                     # Show routing table
ss -tuln                        # Show listening sockets (replaces netstat)

Network Testing Commands¶

# Connectivity testing
ping -c 4 8.8.8.8              # Test internet connectivity
ping -c 4 192.168.1.1          # Test gateway connectivity
traceroute google.com          # Trace route to destination
tracepath google.com           # Alternative to traceroute

# DNS testing
nslookup google.com            # Basic DNS lookup
dig google.com                 # Detailed DNS query
host google.com                # Simple DNS lookup

# Port and service testing
telnet host 80                 # Test TCP port connectivity
nc -zv host 80                 # Test port with netcat
ss -tuln | grep :80            # Check if service listening on port

Hostname Management¶

# Hostname commands
hostnamectl                     # Show hostname information
hostnamectl set-hostname server1.example.com  # Set hostname
hostnamectl status             # Detailed hostname status

# Legacy hostname commands
hostname                       # Show current hostname
hostname server1               # Set hostname (temporary)

Network Configuration Files¶

# NetworkManager connection files
ls /etc/NetworkManager/system-connections/  # Connection profiles
cat /etc/NetworkManager/NetworkManager.conf # NetworkManager config

# System network files
cat /etc/hosts                 # Local hostname resolution
cat /etc/resolv.conf           # DNS configuration (managed by NetworkManager)
cat /etc/nsswitch.conf         # Name resolution order

Command Reference Table¶

Command	Purpose	Key Options	Example
`nmcli con show`	List connections	`--active`	`nmcli con show --active`
`nmcli con add`	Create connection	`type`, `con-name`, `ifname`	`nmcli con add type ethernet con-name static ifname ens3`
`nmcli con modify`	Modify connection	`ipv4.addresses`, `ipv4.method`	`nmcli con modify static ipv4.addresses 192.168.1.100/24`
`ip addr show`	Show IP addresses	`dev`	`ip addr show dev ens3`
`ping`	Test connectivity	`-c`	`ping -c 4 8.8.8.8`
`hostnamectl`	Manage hostname	`set-hostname`	`hostnamectl set-hostname server1`

4. Procedural Workflows¶

Standard Procedure: Configure Static IP Address¶

Identify available interface bash nmcli device status ip link show
Create static connection bash nmcli connection add type ethernet \ con-name "static-connection" \ ifname ens3 \ ipv4.addresses 192.168.1.100/24 \ ipv4.gateway 192.168.1.1 \ ipv4.dns "8.8.8.8 8.8.4.4" \ ipv4.method manual \ connection.autoconnect yes
Activate connection bash nmcli connection up "static-connection"
Verify configuration bash ip addr show ens3 ip route show cat /etc/resolv.conf ping -c 2 8.8.8.8

Standard Procedure: Switch from DHCP to Static¶

Check current configuration bash nmcli connection show --active nmcli device show ens3
Modify existing connection ```bash # Get current connection name CON_NAME=$(nmcli -t -f NAME connection show --active | head -1)

# Modify to static nmcli connection modify "$CON_NAME" \ ipv4.method manual \ ipv4.addresses 192.168.1.100/24 \ ipv4.gateway 192.168.1.1 \ ipv4.dns "8.8.8.8,8.8.4.4" ```

Apply changes bash nmcli connection down "$CON_NAME" nmcli connection up "$CON_NAME"
Verify changes bash ip addr show ping -c 2 google.com

Decision Tree: Network Configuration Strategy¶

Network Configuration Need
├── New system setup?
│   ├── DHCP available? → Use auto method
│   └── Static required? → Configure manual method
├── Change existing config?
│   ├── Modify current connection → nmcli con modify
│   └── Create new connection → nmcli con add
├── Troubleshooting?
│   ├── Check device status → nmcli device status
│   ├── Check connection status → nmcli con show --active
│   └── Test connectivity → ping, traceroute
└── Advanced needs?
    ├── Multiple IPs? → Add secondary addresses
    ├── VLANs? → Create VLAN connections
    └── Bonding? → Create bond connections

Standard Procedure: Network Troubleshooting¶

Check physical connectivity bash nmcli device status ip link show # Look for "connected" state and "UP" flags
Check IP configuration bash ip addr show nmcli connection show --active
Test network layers ```bash # Layer 3 - IP connectivity ping -c 2 127.0.0.1 # Loopback ping -c 2 $(ip route | grep default | awk '{print $3}') # Gateway ping -c 2 8.8.8.8 # External IP

# Layer 7 - DNS resolution nslookup google.com ping -c 2 google.com ```

Check services and ports bash ss -tuln # Listening services systemctl status NetworkManager

5. Configuration Deep Dive¶

NetworkManager Connection Files¶

Static IP Connection¶

# /etc/NetworkManager/system-connections/static-ens3.nmconnection
[connection]
id=static-ens3
uuid=12345678-1234-1234-1234-123456789012
type=ethernet
interface-name=ens3
autoconnect=true

[ethernet]

[ipv4]
address1=192.168.1.100/24,192.168.1.1
dns=8.8.8.8;8.8.4.4;
method=manual

[ipv6]
addr-gen-mode=eui64
method=auto

[proxy]

DHCP Connection¶

# /etc/NetworkManager/system-connections/dhcp-ens3.nmconnection
[connection]
id=dhcp-ens3
uuid=87654321-4321-4321-4321-210987654321
type=ethernet
interface-name=ens3
autoconnect=true

[ethernet]

[ipv4]
method=auto

[ipv6]
addr-gen-mode=eui64
method=auto

[proxy]

Advanced Network Configuration¶

Multiple IP Addresses¶

# Add secondary IP to existing connection
nmcli connection modify "static-ens3" \
  +ipv4.addresses 192.168.1.101/24

# Or specify multiple IPs during creation
nmcli connection add type ethernet con-name "multi-ip" ifname ens3 \
  ipv4.addresses "192.168.1.100/24,192.168.1.101/24" \
  ipv4.gateway 192.168.1.1 \
  ipv4.method manual

DNS Configuration¶

# Set specific DNS servers
nmcli connection modify "connection-name" \
  ipv4.dns "8.8.8.8,8.8.4.4,1.1.1.1"

# Set DNS search domains
nmcli connection modify "connection-name" \
  ipv4.dns-search "example.com,lab.local"

# Ignore auto DNS (use manual only)
nmcli connection modify "connection-name" \
  ipv4.ignore-auto-dns yes

Network Interface Naming¶

Predictable Network Interface Names¶

# Modern naming scheme (RHEL 9):
# ens3    - Ethernet slot 3
# enp0s3  - Ethernet PCI bus 0, slot 3  
# enp1s0f0 - Ethernet PCI bus 1, slot 0, function 0
# wls1    - Wireless LAN slot 1

# View interface naming details
udevadm info /sys/class/net/ens3

6. Hands-On Labs¶

Lab 6.1: Basic Network Configuration (Asghar Ghori Style)¶

Objective: Configure static IP address and test connectivity

Steps: 1. Explore current network configuration ```bash # Check current interfaces and connections nmcli device status nmcli connection show

# Show detailed interface information ip addr show ip route show

# Check current connectivity ping -c 2 8.8.8.8 ```

Create static IP configuration ```bash # Create new static connection (adjust IP range for your environment) nmcli connection add type ethernet \ con-name "lab-static" \ ifname ens3 \ ipv4.addresses 192.168.1.150/24 \ ipv4.gateway 192.168.1.1 \ ipv4.dns "8.8.8.8 8.8.4.4" \ ipv4.method manual \ connection.autoconnect yes

# Activate the new connection nmcli connection up "lab-static" ```

Verify static configuration ```bash # Check new IP configuration ip addr show ens3 ip route show cat /etc/resolv.conf

# Test connectivity ping -c 3 192.168.1.1 # Gateway ping -c 3 8.8.8.8 # External IP ping -c 3 google.com # DNS resolution ```

Test connection management ```bash # Bring connection down and up nmcli connection down "lab-static" ip addr show ens3 # Should show no IP

nmcli connection up "lab-static" ip addr show ens3 # Should show static IP

# Show connection details nmcli connection show "lab-static" ```

Verification:

# Complete verification
nmcli connection show --active | grep lab-static
ping -c 2 google.com
nslookup google.com
ip route show | grep default

Lab 6.2: Advanced Network Management (Sander van Vugt Style)¶

Objective: Modify existing connections and manage multiple network configurations

Steps: 1. Analyze existing network setup bash # Document current configuration nmcli connection show > /tmp/original-connections.txt nmcli device show > /tmp/original-devices.txt ip addr show > /tmp/original-ips.txt

Create DHCP backup connection ```bash # Create DHCP connection for same interface nmcli connection add type ethernet \ con-name "lab-dhcp-backup" \ ifname ens3 \ ipv4.method auto \ connection.autoconnect no

# Test switching between static and DHCP nmcli connection down "lab-static" nmcli connection up "lab-dhcp-backup"

# Check what IP was assigned by DHCP ip addr show ens3 ```

Modify connection properties ```bash # Switch back to static and modify it nmcli connection down "lab-dhcp-backup" nmcli connection up "lab-static"

# Add secondary IP address nmcli connection modify "lab-static" \ +ipv4.addresses 192.168.1.151/24

# Change DNS servers nmcli connection modify "lab-static" \ ipv4.dns "1.1.1.1,8.8.8.8"

# Apply changes nmcli connection down "lab-static" nmcli connection up "lab-static" ```

Verify multiple IPs and DNS changes ```bash # Check multiple IP addresses ip addr show ens3 | grep inet

# Verify DNS changes cat /etc/resolv.conf

# Test connectivity from both IPs ping -c 2 -I 192.168.1.150 google.com ping -c 2 -I 192.168.1.151 google.com ```

Verification:

# Document final configuration
nmcli connection show "lab-static"
ip addr show ens3
nslookup google.com

Lab 6.3: Network Troubleshooting Scenario (Synthesis Challenge)¶

Objective: Diagnose and resolve complex network connectivity issues

Scenario: A server has lost network connectivity and needs systematic troubleshooting

Requirements: - Systematically diagnose network issues - Test connectivity at multiple network layers - Document findings and resolution steps - Restore full network functionality

Solution Steps: 1. Create a "broken" network scenario ```bash # Simulate network problems (choose one or more):

# Problem 1: Wrong gateway nmcli connection modify "lab-static" ipv4.gateway 192.168.1.99

# Problem 2: Wrong DNS nmcli connection modify "lab-static" ipv4.dns "192.168.1.99"

# Problem 3: Wrong IP range nmcli connection modify "lab-static" ipv4.addresses 10.0.0.100/24

# Apply one of these problematic configs nmcli connection down "lab-static" nmcli connection up "lab-static"

# Verify the problem exists ping -c 2 google.com # This should fail ```

Systematic network troubleshooting ```bash # Step 1: Check physical and link layer echo "=== LAYER 1 & 2 DIAGNOSTICS ===" nmcli device status ip link show ens3

# Step 2: Check network layer (IP configuration) echo "=== LAYER 3 DIAGNOSTICS ===" ip addr show ens3 ip route show

# Step 3: Test connectivity at each level echo "=== CONNECTIVITY TESTS ==="

# Test loopback ping -c 1 127.0.0.1 && echo "Loopback: OK" || echo "Loopback: FAIL"

# Test local IP LOCAL_IP=$(ip addr show ens3 | grep 'inet ' | awk '{print $2}' | cut -d'/' -f1) ping -c 1 $LOCAL_IP && echo "Local IP: OK" || echo "Local IP: FAIL"

# Test gateway GATEWAY=$(ip route show default | awk '{print $3}') ping -c 1 $GATEWAY && echo "Gateway: OK" || echo "Gateway: FAIL"

# Test external IP ping -c 1 8.8.8.8 && echo "External IP: OK" || echo "External IP: FAIL"

# Test DNS resolution nslookup google.com > /dev/null 2>&1 && echo "DNS Resolution: OK" || echo "DNS Resolution: FAIL" ```

Diagnose and fix the specific problem ```bash # Based on the test results, fix the issue:

# If gateway test failed: echo "Fixing gateway configuration..." nmcli connection modify "lab-static" ipv4.gateway 192.168.1.1

# If DNS resolution failed but external IP worked: echo "Fixing DNS configuration..." nmcli connection modify "lab-static" ipv4.dns "8.8.8.8,8.8.4.4"

# If external IP failed but gateway worked (wrong IP range): echo "Fixing IP address configuration..." nmcli connection modify "lab-static" ipv4.addresses 192.168.1.150/24

# Apply the fix nmcli connection down "lab-static" nmcli connection up "lab-static" ```

Verify resolution and document ```bash # Re-run connectivity tests echo "=== POST-FIX VERIFICATION ===" ping -c 2 127.0.0.1 # Loopback ping -c 2 192.168.1.1 # Gateway ping -c 2 8.8.8.8 # External IP ping -c 2 google.com # DNS resolution

# Create troubleshooting report cat > /tmp/network-troubleshooting-report.txt << EOF Network Troubleshooting Report Date: $(date)

Problem Description: - Network connectivity was lost - Systematic diagnostics performed

Diagnostics Performed: 1. Physical layer check: nmcli device status 2. IP configuration check: ip addr show, ip route show 3. Connectivity tests: loopback, gateway, external IP, DNS

Issue Found: $(if ping -c 1 google.com > /dev/null 2>&1; then echo "Issue resolved successfully"; else echo "Issue still present"; fi)

Resolution Applied: - Modified connection: lab-static - Updated configuration parameters - Reactivated network connection

Final Configuration: $(nmcli connection show "lab-static" | grep ipv4)

Post-Fix Tests: - Gateway connectivity: $(ping -c 1 192.168.1.1 > /dev/null 2>&1 && echo "PASS" || echo "FAIL") - External connectivity: $(ping -c 1 8.8.8.8 > /dev/null 2>&1 && echo "PASS" || echo "FAIL") - DNS resolution: $(ping -c 1 google.com > /dev/null 2>&1 && echo "PASS" || echo "FAIL") EOF

# Display the report cat /tmp/network-troubleshooting-report.txt ```

Verification:

# Final comprehensive verification
echo "=== FINAL NETWORK STATUS ==="
nmcli connection show --active
ip addr show ens3
ip route show | grep default
ping -c 2 google.com
nslookup google.com
cat /tmp/network-troubleshooting-report.txt

7. Troubleshooting Playbook¶

Common Issues¶

Issue 1: No Network Connectivity After Configuration¶

Symptoms: - Cannot ping gateway or external hosts - New IP configuration not applied - Connection shows as activated but no connectivity

Diagnosis:

# Check connection and device status
nmcli connection show --active
nmcli device status

# Verify IP configuration applied
ip addr show interface-name
ip route show

# Check NetworkManager logs
journalctl -u NetworkManager --since "10 minutes ago"

Resolution:

# Restart NetworkManager service
systemctl restart NetworkManager

# Reload connection configuration
nmcli connection reload

# Manually bring connection down and up
nmcli connection down "connection-name"
nmcli connection up "connection-name"

# Check for conflicting connections
nmcli connection show | grep interface-name

Prevention: Always verify configuration before applying, test in stages

Issue 2: DNS Resolution Not Working¶

Symptoms: - Can ping IP addresses but not hostnames - /etc/resolv.conf has wrong or no DNS servers - nslookup/dig commands fail

Diagnosis:

# Check DNS configuration
cat /etc/resolv.conf
nmcli connection show active-connection | grep dns

# Test DNS directly
nslookup google.com 8.8.8.8
dig @8.8.8.8 google.com

# Check DNS service
systemctl status systemd-resolved  # If using resolved

Resolution:

# Fix DNS in connection configuration
nmcli connection modify "connection-name" \
  ipv4.dns "8.8.8.8,8.8.4.4"

# Ignore auto-assigned DNS if needed
nmcli connection modify "connection-name" \
  ipv4.ignore-auto-dns yes

# Restart connection
nmcli connection down "connection-name"
nmcli connection up "connection-name"

Issue 3: Interface Name Changes After Reboot¶

Symptoms: - Network interface has different name after reboot - Connection tied to specific interface fails - Previous interface name no longer exists

Diagnosis:

# Check current interfaces
nmcli device status
ip link show

# Check for renamed interfaces
dmesg | grep -i "renamed network interface"
journalctl -b | grep "renamed network interface"

Resolution:

# Update connection to use correct interface
nmcli connection modify "connection-name" \
  connection.interface-name new-interface-name

# Or create new connection with correct interface
nmcli connection clone "old-connection" "new-connection"
nmcli connection modify "new-connection" \
  connection.interface-name new-interface-name

Diagnostic Command Sequence¶

# Network troubleshooting workflow
nmcli device status              # Check device status
nmcli connection show --active   # Check active connections  
ip addr show                     # Check IP assignments
ip route show                    # Check routing table
ping -c 2 gateway-ip            # Test gateway connectivity
ping -c 2 8.8.8.8              # Test external connectivity
nslookup google.com             # Test DNS resolution

Log File Analysis¶

journalctl -u NetworkManager: NetworkManager service logs
/var/log/messages: General system messages including network events
dmesg: Kernel messages about network interfaces
journalctl -f: Real-time log monitoring during troubleshooting

8. Quick Reference Card¶

Essential Commands At-a-Glance¶

# Connection management
nmcli con show                   # List connections
nmcli con up "name"             # Activate connection
nmcli con down "name"           # Deactivate connection

# Static IP setup
nmcli con add type ethernet con-name "static" ifname ens3 \
  ipv4.addresses 192.168.1.100/24 \
  ipv4.gateway 192.168.1.1 \
  ipv4.dns "8.8.8.8" \
  ipv4.method manual

# Network information
ip addr show                    # Show IP addresses
ip route show                   # Show routing table
ping -c 2 host                  # Test connectivity

NetworkManager Configuration Structure¶

# Connection properties:
connection.id                   # Connection name
connection.interface-name       # Interface to use
connection.autoconnect         # Auto-connect on boot

# IPv4 properties:
ipv4.method                    # auto (DHCP) or manual (static)
ipv4.addresses                 # IP address/netmask
ipv4.gateway                   # Default gateway
ipv4.dns                       # DNS servers

Common Network Ranges¶

Private Class A: 10.0.0.0/8 (10.0.0.0 - 10.255.255.255)
Private Class B: 172.16.0.0/12 (172.16.0.0 - 172.31.255.255)
Private Class C: 192.168.0.0/16 (192.168.0.0 - 192.168.255.255)
Loopback: 127.0.0.0/8 (127.0.0.1 is localhost)

DNS Servers¶

Google: 8.8.8.8, 8.8.4.4
Cloudflare: 1.1.1.1, 1.0.0.1
Quad9: 9.9.9.9, 149.112.112.112

9. Knowledge Check¶

Conceptual Questions¶

Question: What's the difference between a network device and a network connection in NetworkManager? Answer: A device is a physical or virtual network interface (like ens3), while a connection is a configuration profile that can be applied to a device. One device can have multiple connection profiles, but only one can be active at a time.
Question: Why might /etc/resolv.conf show different DNS servers than what you configured? Answer: NetworkManager dynamically manages /etc/resolv.conf. If you have multiple connections or DHCP is providing DNS servers, NetworkManager combines them. Use nmcli connection show to see the actual DNS configuration for each connection.
Question: What happens when you set ipv4.method to "auto" versus "manual"? Answer: "auto" uses DHCP to automatically obtain IP address, gateway, and DNS servers from a DHCP server. "manual" requires you to explicitly specify all network parameters and creates a static configuration.

Practical Scenarios¶

Scenario: Server needs to be accessible from multiple subnets but only has one interface. Solution: Add multiple IP addresses to the same connection: bash nmcli con modify "connection" ipv4.addresses "192.168.1.100/24,10.0.1.100/24"
Scenario: Need to quickly switch between office and home network configurations. Solution: Create two connection profiles for the same interface and switch between them: bash nmcli con add type ethernet con-name "office" ifname ens3 ipv4.method manual ... nmcli con add type ethernet con-name "home" ifname ens3 ipv4.method auto # Switch: nmcli con up "office" or nmcli con up "home"

Command Challenges¶

Challenge: Create a connection that gets IP via DHCP but uses custom DNS servers. Answer: bash nmcli con add type ethernet con-name "dhcp-custom-dns" ifname ens3 \ ipv4.method auto \ ipv4.dns "8.8.8.8,8.8.4.4" \ ipv4.ignore-auto-dns yes
Challenge: Find all interfaces that are up but don't have an IP address. Answer: ip link show | grep "state UP" -A1 | grep -B1 "NO-CARRIER\|state UP" | grep "^[0-9]" | cut -d: -f2

10. Exam Strategy¶

Topic-Specific Tips¶

Always use nmcli for configuration - it's the modern RHEL 9 way
Verify configuration with both nmcli and ip commands
Remember that connections must be activated after creation
Test connectivity at multiple levels (gateway, external, DNS)

Common Exam Scenarios¶

Scenario: Configure static IP address on server Approach: Use nmcli con add with manual method, specify all required parameters
Scenario: Fix server that lost network connectivity Approach: Check device status, connection status, IP configuration, test connectivity systematically
Scenario: Change hostname of server Approach: Use hostnamectl set-hostname and verify with hostnamectl status

Time Management¶

Static IP configuration: 5-7 minutes including verification
Network troubleshooting: 8-10 minutes for systematic diagnosis
Hostname changes: 2-3 minutes
Always verify: Test connectivity after any network changes

Pitfalls to Avoid¶

Don't forget to activate connections after creating them
Remember that interface names may not be eth0 (use nmcli device status to find correct names)
Always test both IP connectivity and DNS resolution
Don't modify /etc/resolv.conf directly - use NetworkManager
Verify changes persist after reboot if required

Summary¶

Key Takeaways¶

NetworkManager is the standard in RHEL 9 - master nmcli commands
Connections are profiles applied to devices - understand this relationship
Systematic troubleshooting saves time - test connectivity at each network layer
Always verify configuration with multiple commands and connectivity tests

Critical Commands to Remember¶

nmcli con add type ethernet con-name "static" ifname ens3 \
  ipv4.addresses 192.168.1.100/24 \
  ipv4.gateway 192.168.1.1 \
  ipv4.dns "8.8.8.8" \
  ipv4.method manual               # Create static IP connection

nmcli con show --active            # Show active connections
ip addr show                       # Show interface IP addresses
ping -c 2 gateway-ip              # Test connectivity
hostnamectl set-hostname name      # Set system hostname

Next Steps¶

Continue to Module 09: SELinux Management
Practice network configuration in the Vagrant environment
Review related topics: Firewall Configuration, SSH Setup

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