Network Configuration with NetworkManager: Managing Network Connectivity

NetworkManager is the standard network management service on modern Linux distributions, providing unified management of network interfaces, connections, and connectivity. Understanding how to configure networks using NetworkManager's command-line interface (nmcli) is essential for Linux system administrators. This article explores NetworkManager, nmcli, and network configuration techniques.

Understanding NetworkManager

NetworkManager is a daemon that manages network connectivity and configuration. It provides:

Unified Interface: Single tool for all network configuration
Automatic Management: Handles network detection and connection
Multiple Interfaces: Supports Ethernet, Wi-Fi, VPN, and more
Connection Profiles: Persistent network configurations
Command-Line and GUI: Both nmcli and graphical tools available

NetworkManager Command-Line Interface: `nmcli`

nmcli is the command-line tool for managing NetworkManager.

Basic `nmcli` Syntax

General Format: nmcli [options] <object> <command> [arguments]

Common Options:

-t: Terse output (machine-readable)
-p: Pretty output (human-readable)
-f: Specify fields to display
-g: Get specific field values
-m: Monitor mode
-h: Help

Managing Connections

Viewing Connections

List All Connections:

nmcli connection show

# Brief format
nmcli connection

# Show specific connection
nmcli connection show "Wired connection 1"

Active Connections:

nmcli connection show --active

Creating Connections

Create Ethernet Connection:

# Create static IP connection
nmcli connection add type ethernet con-name "MyConnection" \
  ifname eth0 ipv4.addresses 192.168.1.100/24 \
  ipv4.gateway 192.168.1.1 ipv4.dns "8.8.8.8" \
  ipv4.method manual

# Create DHCP connection
nmcli connection add type ethernet con-name "DHCP-Connection" \
  ifname eth0 ipv4.method auto

Create Wi-Fi Connection:

# Connect to open Wi-Fi
nmcli device wifi connect "NetworkName"

# Connect to secured Wi-Fi
nmcli device wifi connect "NetworkName" password "password"

# Create connection profile
nmcli connection add type wifi con-name "MyWiFi" \
  ifname wlan0 ssid "NetworkName" \
  wifi-sec.key-mgmt wpa-psk wifi-sec.psk "password"

Modifying Connections

nmcli connection modify: Modify connection settings

Common Modifications:

# Change IP address
nmcli connection modify "MyConnection" ipv4.addresses 192.168.1.200/24

# Change gateway
nmcli connection modify "MyConnection" ipv4.gateway 192.168.1.1

# Change DNS
nmcli connection modify "MyConnection" ipv4.dns "8.8.8.8 8.8.4.4"

# Change to DHCP
nmcli connection modify "MyConnection" ipv4.method auto

# Change to static
nmcli connection modify "MyConnection" ipv4.method manual

# Add additional IP address
nmcli connection modify "MyConnection" +ipv4.addresses 10.0.0.10/24

# Remove IP address
nmcli connection modify "MyConnection" -ipv4.addresses 10.0.0.10/24

Activating and Deactivating Connections

Activate Connection:

# Activate by name
nmcli connection up "MyConnection"

# Activate by UUID
nmcli connection up uuid <uuid>

Deactivate Connection:

nmcli connection down "MyConnection"

Delete Connection:

nmcli connection delete "MyConnection"

Managing Devices

Viewing Devices

List All Devices:

nmcli device status

# Detailed information
nmcli device show

# Show specific device
nmcli device show eth0

Device States:

connected: Device is connected and active
disconnected: Device is available but not connected
unavailable: Device is not available
unmanaged: Device is not managed by NetworkManager

Device Operations

Connect Device:

# Connect using existing connection
nmcli device connect eth0

Disconnect Device:

nmcli device disconnect eth0

Wi-Fi Operations:

# List available Wi-Fi networks
nmcli device wifi list

# Connect to Wi-Fi
nmcli device wifi connect "NetworkName" password "password"

# Rescan for networks
nmcli device wifi rescan

General NetworkManager Information

General Status

Show General Status:

nmcli general status

Show Hostname:

nmcli general hostname

# Set hostname
sudo nmcli general hostname newhostname

Show Permissions:

nmcli general permissions

Networking Control

Enable/Disable Networking

Disable Networking:

nmcli networking off

Enable Networking:

nmcli networking on

Check Connectivity:

nmcli networking connectivity check

# Show connectivity status
nmcli networking connectivity

Radio Management

Wi-Fi Radio Control

Turn Wi-Fi On/Off:

# Turn Wi-Fi on
nmcli radio wifi on

# Turn Wi-Fi off
nmcli radio wifi off

# Show Wi-Fi status
nmcli radio wifi

Turn All Radios On/Off:

nmcli radio all on
nmcli radio all off

Monitoring NetworkManager

Monitor Mode

Monitor NetworkManager Events:

# Monitor all events
nmcli monitor

# Monitor connectivity
nmcli monitor connectivity

NetworkManager Text User Interface: `nmtui`

nmtui provides a text-based graphical interface for NetworkManager.

Using nmtui

Launch nmtui:

sudo nmtui

Menu Options:

Edit a connection
Activate a connection
Set system hostname
Quit

Navigation:

Use arrow keys to navigate
Tab to move between fields
Enter to select
Esc to go back

IP Command (Alternative/Complementary)

The ip command is a powerful alternative for network configuration.

Basic `ip` Commands

Show Interfaces:

# Show all interfaces
ip link show

# Show specific interface
ip link show eth0

# Show IP addresses
ip addr show
ip a

Configure Interface:

# Bring interface up
sudo ip link set eth0 up

# Bring interface down
sudo ip link set eth0 down

# Set IP address
sudo ip addr add 192.168.1.100/24 dev eth0

# Remove IP address
sudo ip addr del 192.168.1.100/24 dev eth0

Routing:

# Show routing table
ip route show
ip r

# Add route
sudo ip route add 192.168.2.0/24 via 192.168.1.1

# Delete route
sudo ip route del 192.168.2.0/24

Network Configuration Files

Traditional Configuration (ifcfg files)

Location: /etc/sysconfig/network-scripts/ (RHEL/CentOS)

Example ifcfg-eth0:

TYPE=Ethernet
BOOTPROTO=static
NAME=eth0
DEVICE=eth0
ONBOOT=yes
IPADDR=192.168.1.100
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=8.8.8.8
DNS2=8.8.4.4

NetworkManager Configuration Files

Location: /etc/NetworkManager/system-connections/

Format: INI-style configuration files

Note: Generally managed through nmcli or nmtui, not edited directly

Common Network Configuration Tasks

Static IP Configuration

Using nmcli:

# Create static connection
nmcli connection add type ethernet con-name "Static-Connection" \
  ifname eth0 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

# Activate connection
nmcli connection up "Static-Connection"

DHCP Configuration

Using nmcli:

# Create DHCP connection
nmcli connection add type ethernet con-name "DHCP-Connection" \
  ifname eth0 ipv4.method auto

# Or modify existing
nmcli connection modify "MyConnection" ipv4.method auto

Multiple IP Addresses

Add Secondary IP:

nmcli connection modify "MyConnection" +ipv4.addresses 10.0.0.10/24
nmcli connection down "MyConnection"
nmcli connection up "MyConnection"

Bonding (NIC Teaming)

Create Bond Interface:

# Load bonding module
sudo modprobe bonding

# Create bond connection
nmcli connection add type bond con-name bond0 ifname bond0 \
  mode active-backup

# Add slaves
nmcli connection add type ethernet con-name bond0-slave1 \
  ifname eth0 master bond0 slave-type bond
nmcli connection add type ethernet con-name bond0-slave2 \
  ifname eth1 master bond0 slave-type bond

Troubleshooting Network Issues

Diagnostic Commands

Check Connection Status:

nmcli connection show --active
nmcli device status

Check Interface Configuration:

nmcli device show eth0
ip addr show eth0

Test Connectivity:

# Ping test
ping -c 4 8.8.8.8

# DNS test
nslookup google.com
dig google.com

View NetworkManager Logs:

journalctl -u NetworkManager
journalctl -u NetworkManager -f  # Follow logs

Common Issues

Connection Not Activating:

Check device status: nmcli device status
Verify connection exists: nmcli connection show
Check logs: journalctl -u NetworkManager

IP Address Not Applied:

Verify connection is active: nmcli connection show --active
Check for conflicts: ip addr show
Restart NetworkManager: sudo systemctl restart NetworkManager

DNS Not Working:

Check DNS configuration: nmcli connection show "MyConnection" | grep dns
Test DNS: nslookup google.com
Check /etc/resolv.conf

Best Practices

Connection Management

Use Descriptive Names: Name connections clearly
Document Configurations: Keep records of network settings
Test Changes: Test network changes before production
Backup Configurations: Backup /etc/NetworkManager/system-connections/

Security

Secure Wi-Fi: Use WPA2/WPA3 for wireless
Limit Access: Use firewall rules appropriately
Monitor Connections: Regularly review active connections
Update Regularly: Keep NetworkManager updated

Conclusion

NetworkManager and nmcli provide powerful tools for managing network connectivity on Linux systems. From basic IP configuration to advanced bonding and Wi-Fi management, NetworkManager offers a unified interface for all network operations. Understanding nmcli commands and NetworkManager concepts is essential for modern Linux administration.

By mastering NetworkManager, you can efficiently configure static and dynamic IP addresses, manage Wi-Fi connections, create network bonds, and troubleshoot connectivity issues. Whether you're working on servers or desktops, NetworkManager provides the tools needed for reliable network management.

In the next article, we'll explore package management, covering RPM, YUM, DNF, and APT for installing and managing software on Linux systems. Stay tuned!