Ultimate nmcli Cheat Sheet for Linux Network Management

Introduction to the nmcli Command

The nmcli command is a powerful command-line tool in Red Hat Enterprise Linux (RHEL) used to manage network connections through the NetworkManager service.

It provides a comprehensive interface for configuring, monitoring, and troubleshooting various network aspects, from basic Ethernet connections to advanced features like bonding, VLAN tagging, and more.

Key Capabilities of nmcli:

• Device Management: nmcli lets you view the status of network devices, including their type, state, and connection information. It allows you to temporarily disable NetworkManager’s control over a device, enabling manual configuration if required.
• Connection Profile Management: A central concept in NetworkManager is the connection profile, which stores all settings for a network connection. nmcli enables you to:
  • List all existing connection profiles.
  • Show details of a specific profile, including IP configuration, DNS settings, gateway, and more.
  • Create new connection profiles for various connection types (Ethernet, Wi-Fi, bonds, VLANs, etc.).
  • Modify existing profiles to change settings like IP addresses, DNS servers, or gateway.
  • Activate and deactivate profiles, bringing connections online and offline.
  • Rename and delete connection profiles.
• Advanced Configuration: nmcli extends beyond basic connectivity to configure advanced networking features:
  • Bonding: Create and manage bonded interfaces, including setting the bonding mode and adding slave interfaces.
  • VLAN Tagging: Create and configure VLAN interfaces, specifying the parent interface and VLAN ID.
  • Static Routes: Add static routes to specific connection profiles, controlling network traffic flow.
  • Ethtool Settings: Fine-tune network interface card (NIC) parameters like offload features, interrupt coalescing settings (for optimizing performance), and ring buffer sizes.
• Offline Mode: nmcli can operate in offline mode, allowing you to create and modify connection profiles even when the NetworkManager service is not running. This is valuable for pre-configuring network settings or working in environments where NetworkManager is unavailable.

Why Use nmcli?

• Command-Line Control: nmcli offers a non-graphical way to manage network settings, making it ideal for headless servers or remote administration.
• Scripting and Automation: The command-line nature of nmcli makes it well-suited for scripting and automation, enabling you to manage network configurations programmatically.
• Detailed Information: nmcli commands often provide more detailed information than graphical tools, which can be essential for troubleshooting.

Alternatives to nmcli:

• Graphical Tools: RHEL provides graphical applications like nm-connection-editor and nmtui for network management. These tools offer a more user-friendly interface but may not expose all the configuration options available through nmcli.
• Network RHEL System Role (Ansible): This Ansible role provides a way to manage network settings in an automated and repeatable manner.
• nmstate API: This declarative API offers a programmatic way to manage network configuration, ensuring consistency and providing rollback capabilities.

The choice of tool depends on your specific needs and preferences. nmcli provides a balance of power, flexibility, and scripting capabilities for managing network connections in RHEL.

Here’s a comprehensive nmcli cheat sheet based on the sources you’ve provided. It’s organized by key functionalities within NetworkManager to give you a structured overview of common operations:

General Network Management

• List Network Interfaces:

  # nmcli device status

  This command shows you the status of all network devices recognized by NetworkManager, including their type, current state, and associated connection.

• List Connection Profiles:

  # nmcli connection show

  This command lists all configured network connection profiles, providing details like the profile name, UUID, type (e.g., Ethernet, Wi-Fi), and the associated device.

• Show Details of a Connection Profile:

  # nmcli connection show <connection_name>

  Replace <connection_name> with the actual name of the profile (e.g., ‘Wired connection 1’). This command provides a detailed view of the connection profile settings, including IP configuration, DNS, gateway, and more.

• Activate a Connection:

  # nmcli connection up <connection_name>

  This command activates the specified connection profile.

• Deactivate a Connection:

  # nmcli connection down <connection_name>

  This command deactivates the specified connection profile.

• Modify a Connection Profile:

  # nmcli connection modify <connection_name> <property> <value>

  This is a versatile command to modify settings within a connection profile. Replace <property> with the setting you want to change (e.g., ipv4.method, ipv4.addresses, ipv6.gateway) and <value> with the new value.

• Delete a Connection Profile:

  # nmcli connection delete <connection_name>

  Use this command to remove a connection profile.

• Rename a Connection Profile:

  # nmcli connection modify "<old_name>" connection.id "<new_name>"

  This command renames a connection profile from <old_name> to <new_name>. Use quotes around names that contain spaces.

Ethernet Connections

• Add an Ethernet Connection (DHCP):

  # nmcli connection add con-name <connection_name> ifname <device_name> type ethernet

  This creates a new Ethernet connection profile with a default DHCP configuration.

• Add an Ethernet Connection (Static IP):

  # nmcli connection add con-name <connection_name> ifname <device_name> type ethernet \
      ipv4.method manual ipv4.addresses <IP_address>/<subnet_mask> ipv4.gateway <gateway_IP> \
      ipv4.dns <DNS_server_IP>

• Temporarily Disable NetworkManager Management for a Device:

  # nmcli device set <device_name> managed no

  This command tells NetworkManager to stop managing the specified device, allowing you to configure it manually if needed.

Network Bonding

• Create a Bond Interface:

  # nmcli connection add type bond con-name <bond_name> ifname <bond_name>

  This command creates a bond interface named <bond_name>.

• Set the Bonding Mode:

  # nmcli connection modify <bond_name> bond.mode <mode>

  Replace <mode> with the desired bonding mode (e.g., active-backup, balance-rr, 802.3ad). Refer to the bonding modes section of this cheat sheet for explanations of the different modes.

• Add Slave Interfaces to the Bond:

  # nmcli connection add type ethernet port-type bond con-name <bond_name>-port<number> ifname <interface_name> controller <bond_name>

  Repeat this command for each interface you want to add to the bond, incrementing the <number> and replacing <interface_name> with the actual interface name.

VLAN Tagging

• Create a VLAN Interface:

  # nmcli connection add type vlan con-name <vlan_name> dev <parent_interface> id <VLAN_ID>

  Replace <vlan_name> with the desired VLAN interface name, <parent_interface> with the physical interface on which the VLAN is based, and <VLAN_ID> with the VLAN identifier.

Static Routes

• Add a Static IPv4 Route:

  # nmcli connection modify <connection_name> +ipv4.routes "<destination_network>/<subnet_mask> <gateway_IP>"

  This command adds a static route to the specified connection profile.

• Add a Static IPv6 Route:

  # nmcli connection modify <connection_name> +ipv6.routes "<destination_network>/<prefix_length> <gateway_IP>"

Advanced Network Configuration

• Ethtool Settings (Offload Features):

  # nmcli con modify <connection_name> ethtool.feature-<feature> on|off

  Replace <feature> with the specific offload feature you want to enable or disable (e.g., rx, tx, sg). This command allows you to manage offload features on the network interface.

• Ethtool Settings (Coalesce Settings):

  # nmcli connection modify <connection_name> ethtool.coalesce-<parameter> <value>

  Replace <parameter> with a coalesce setting like rx-frames, tx-frames, rx-usecs, and <value> with the desired numerical value. This allows you to control interrupt coalescing behavior.

• Ethtool Settings (Ring Buffer Size):

  # nmcli connection modify <connection_name> ethtool.ring-<parameter> <value>

  Replace <parameter> with either rx or tx to adjust the receive or transmit ring buffer sizes. Increasing the buffer size can potentially reduce packet drops.

nmcli Interactive Mode

• Enter Interactive Mode:

  # nmcli connection edit <connection_name>

  This enters an interactive shell for the specified connection, allowing for step-by-step configuration.

• Set a Property:

  nmcli> set <property> <value>

• Print Current Settings:

  nmcli> print

• Save Changes:

  nmcli> save persistent

  Persists the changes to the connection profile.

• Activate Connection:

  nmcli> activate

• Exit Interactive Mode:

  nmcli> quit

This cheat sheet covers a wide range of commonly used nmcli commands for network management in RHEL. You can refer to the man pages for more detailed information and options for each command.