It is difficult to envisage a RHEL 9 system that does not have at least one network connection and harder still to imagine how such an isolated system could be of much practical use. The simple fact is that RHEL 9 is designed to provide enterprise-level services over network and internet connections. Therefore, a crucial part of learning how to administer a RHEL 9 system involves learning how to configure and manage the network interfaces installed on the system.
This chapter provides an overview of network management on RHEL 9, including the NetworkManager service and tools and some other useful utilities.
An Introduction to NetworkManager
NetworkManager is a service and set of tools designed specifically to make it easier to manage the networking configuration on Linux systems and is the default network management service on RHEL 9.
In addition to a service that runs in the background, NetworkManager also includes the following tools:
- nmcli – A tool for working with NetworkManager via the command line. This tool is useful when access to a graphical environment is unavailable and can also be used within scripts to make network configuration changes.
- nmtui – A basic text-based user interface for managing NetworkManager. This tool can be run within any terminal window and allows changes to be made by making menu selections and entering data. While helpful in performing basic tasks, nmtui lacks many of the features provided by the nmcli tool.
- nm-connection-editor – A complete graphical management tool providing access to most NetworkManager configuration options.
- GNOME Settings – The Network screen of the GNOME desktop Settings application allows basic network management tasks to be performed.
- Cockpit Network Settings – The Network screen of the Cockpit web interface allows a range of network management tasks to be performed.
Although there are several ways to manage the network environment on a RHEL 9 system, this chapter will focus on the nmcli command. While the graphical tools are certainly helpful when you have access to a desktop environment, or Cockpit has been enabled, understanding the command line interface is essential for situations where a command prompt is all that is available. Also, the graphical tools (Cockpit included) only include some of the capabilities of the nmcli tool. Finally, once you are familiar with NetworkManager and nmcli, those skills will translate easily when using the more intuitive tool options. The same cannot be said of the graphical tool options. It is harder to use nmcli if, for example, you have only ever used nm-connection-editor.
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Installing and Enabling NetworkManager
NetworkManager should be installed by default for most RHEL 9 installations. Use the rpm command to find out if it needs to be installed:
# rpm -q NetworkManager NetworkManager-1.14.0-14.el8.x86_64
If necessary, install the package as follows:
# dnf install NetworkManager
Once the package is installed, the NetworkManager daemon will need to be enabled so that it starts each time the system boots:
# systemctl enable NetworkManager
Finally, start the service running and check the status to verify that the launch was successful:
# systemctl start NetworkManager
# systemctl status NetworkManager
● NetworkManager.service - Network Manager
Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; enabled; vendor >
Drop-In: /usr/lib/systemd/system/NetworkManager.service.d
└─NetworkManager-ovs.conf
Active: active (running) since Tue 2019-04-09 10:07:22 EDT; 2h 48min ago
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.Basic nmcli Commands
The nmcli tool will have been installed as part of the NetworkManager package and can be executed from the command line using the following syntax:
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# nmcli [Options] Object {Command | help}In the above syntax, Object will be one of general, networking, radio, connection, monitor, device, or agent, which can be abbreviated to a few letters of the word (for example, con, or even just the letter c, for connection). For example, all of the following commands will output help information relating to the device object:
# nmcli device help # nmcli dev help # nmcli d help
To check the overall status of NetworkManager on the system, use the following command:
# nmcli general status STATE CONNECTIVITY WIFI-HW WIFI WWAN-HW WWAN connected full enabled enabled enabled enabled
To check the status of the devices installed on a system, the following command can be used:
# nmcli dev status DEVICE TYPE STATE CONNECTION eno1 ethernet connected eno1 wlp0s26u1u2 wifi connected zoneone virbr0 bridge connected virbr0 lo loopback unmanaged -- virbr0-nic tun unmanaged --
The output may also be modified by using the -p (pretty) option to make the output more human-friendly:
# nmcli -p dev status ===================== Status of devices ===================== DEVICE TYPE STATE CONNECTION ------------------------------------------------------------------- eno1 ethernet connected eno1 wlp0s26u1u2 wifi connected zoneone virbr0 bridge connected virbr0 lo loopback unmanaged -- virbr0-nic tun unmanaged --
Conversely, the -t option may be used to make the output more terse and suitable for automated processing:
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# nmcli -t dev status eno1:ethernet:connected:eno1 wlp0s26u1u2:wifi:connected:emilyzone virbr0:bridge:connected:virbr0 lo:loopback:unmanaged: virbr0-nic:tun:unmanaged:
The status output shows that the system has two physical devices installed, one Ethernet and the other a WiFi device.
The bridge (virbr) entries are virtual devices used to provide networking for virtual machines (the topic of virtualization will be covered starting with the chapter entitled An Overview of RHEL 9 Virtualization Techniques). Finally, the loopback interface is a special virtual device that allows the system to communicate with itself and is typically used to perform network diagnostics.
When working with NetworkManager, it is important to understand the difference between a device and a connection. As described above, a device is either a physical or virtual network device, while a connection is a network configuration that the device connects to.
The following command displays information about the connections configured on the system:
# nmcli con show NAME UUID TYPE DEVICE zoneone 2abecafa-4ea2-47f6-b20f-4fb0c0fd5e94 wifi wlp0s26u1u2 eno1 99d40009-6bb1-4182-baad-a103941c90ff ethernet eno1 zonetwo f940a2d1-8c18-4a9e-bf29-817702429b8a wifi -- zonethree fd65c5e5-3e92-4e9e-b924-1b0b07b70032 wifi --
The above output shows that the WiFi device (wlp0s26u1u2) is connected to a wireless network named zoneone while the Ethernet device (eno1) is connected to a connection named eno1. In addition to zoneone, NetworkManager has also listed two other WiFi connections named zonetwo and zonethree, neither of which currently has a device connected.
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To find out the IP address allocated to a connection, the ip tool can be used with the address option:
# ip address
The above command can also be abbreviated:
# ip a
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3: wlp0s26u1u2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
link/ether 74:da:38:ee:be:50 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.121/24 brd 192.168.1.255 scope global dynamic noprefixroute wlp0s26u1u2
valid_lft 57584sec preferred_lft 57584sec
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.The ip command will output information for all the devices detected on the system. For example, the above output shows that the WiFi device has been assigned an IP address of 192.168.1.121. If we only wanted to list active connections, the nmcli command could have been used with the -a option:
# nmcli con show -a NAME UUID TYPE DEVICE zoneone 2abecafa-4ea2-47f6-b20f-4fb0c0fd5e94 wifi wlp0s26u1u2 eno1 99d40009-6bb1-4182-baad-a103941c90ff ethernet eno1 virbr0 e13e9552-1765-42d1-b739-ff981668fbee bridge virbr0
To switch the WiFi device connection from zoneone to zonetwo, we can run the following command:
# nmcli device wifi connect zonetwo -ask Password:
The -ask flag causes nmcli to prompt the user to enter the password for the WiFi network. To include the WiFi password on the command line (particularly useful if the command is being executed in a script), use the password option:
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# nmcli device wifi connect zonetwo password <password here>
The nmcli tool may also be used to scan for available WiFi networks as follows:
# nmcli device wifi list
IN-USE SSID MODE CHAN RATE SIGNAL BARS SECURITY
zoneone Infra 6 195 Mbit/s 80 WPA2
* zonetwo Infra 11 130 Mbit/s 74 WPA1 WPA2A currently active connection can be deactivated as follows:
# nmcli con down <connection name>
Similarly, an inactive connection can be brought back up at any time:
# nmcli con up <connection name>
When a connection is brought down, NetworkManager automatically searches for another connection, activates it, and assigns it to the device to which the previous connection was established. To prevent a connection from being used in this situation, disable the autoconnect option as follows:
# nmcli con mod <connection name> connection.autoconnect no
The following command may be used to obtain additional information about a specific connection. This includes the current values for all the connection properties:
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# nmcli con show eno1 connection.id: eno1 connection.uuid: 99d40009-6bb1-4182-baad-a103941c90ff connection.stable-id: -- connection.type: 802-3-ethernet connection.interface-name: eno1 connection.autoconnect: yes connection.autoconnect-priority: 0 connection.autoconnect-retries: -1 (default) connection.multi-connect: 0 (default) connection.auth-retries: -1 connection.timestamp: 1554833695 connection.read-only: no connection.permissions: -- connection.zone: -- connection.master: -- connection.slave-type: -- connection.autoconnect-slaves: -1 (default) . .
All of these properties can be modified using nmcli with the modify option using the following syntax:
# nmcli con mod <connection name> connection.<property name> <setting>
Working with Connection Profiles
So far, we have explored using connections without explaining how a connection is configured. The configuration of a connection is referred to as a connection profile and is stored in a file located in the /etc/NetworkManager/system-connections directory, the contents of which might read as follows:
# ls /etc/NetworkManager/system-connections zoneone.nmconnection eno1.nmconnection zonethree.nmconnection zonetwo.nmconnection Consider, for example, the contents of the eno1.nmconnection file: id=eno1 uuid=efc69a99-17a3-3636-b68f-bfcc56a73844 type=ethernet autoconnect-priority=-999 interface-name=eno1 timestamp=1679678184 [ethernet] [ipv4] method=auto [ipv6] addr-gen-mode=eui64 method=auto [proxy]
The file contains basic information about the connection, including the type (Ethernet) of the device to which it is currently assigned (eno1) and the fact that the connection is to be automatically activated on system boot with an IP address obtained using DHCP (auto). Changes to the connection profile can be implemented by modifying this file and instructing nmcli to reload the connection configuration files:
# nmcli con reload
New connection profiles can also be created manually or generated automatically by nmcli. For example, assume a new network device has been installed on the system. When this happens, the NetworkManager service will detect the new hardware and create a device for it. In the example below, the new device has been assigned the name eno2:
# nmcli dev status DEVICE TYPE STATE CONNECTION en01 ethernet connected eno1 eno2 ethernet connected Wired connection 1
NetworkManager automatically detected the device, activated it, and assigned it to a connection named “Wired connection 1”. This is a default connection over which we have no configuration control because there is no interface configuration file for it in /etc/NetworkManager/systemconnections. Therefore, the next steps are to delete the “Wired connection 1” connection and use nmcli to create a new connection and assign it to the device. The command to delete a connection is as follows:
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# nmcli con delete "Wired connection 1"
Next, nmcli can be used to create a new connection profile configured either with a static IP address or a dynamic IP address obtained from a DHCP server. To create a dynamic connection profile named dyn_ip, the following command would be used:
# nmcli connection add type ethernet con-name dyn_ip ifname eno2 Connection 'dyn_ip' (160d9e10-bbc8-439a-9c47-a2ec52990472) successfully added.
To create a new connection profile without locking it to a specific device, omit the ifname option in the command:
# nmcli connection add type ethernet con-name dyn_ip
After creating the connection, a file named dyn_ip.nmconnection will be added to the /etc/ NetworkManager/system-connections directory.
Alternatively, to create a connection named static_ip assigned a static IP address (in this case 192.168.1.200) the following command would be used:
# nmcli con add type ethernet con-name static_ip ifname eno0 ip4 192.168.1.200/24 gw4 192.168.1.1 Connection 'static_ip' (3fccafb3-e761-4271-b310-ad0f28ee8606) successfully added.
The corresponding static_ip.nmconnection file will read as follows:
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[connection] id=static_ip uuid=41eca181-381c-4d12-b6c9-30446d4e29d1 type=ethernet interface-name=eno0 [ethernet] [ipv4] address1=192.168.1.200/24,192.168.1.1 method=manual [ipv6] addr-gen-mode=default method=auto [proxy]
The command to add a new connection may be altered slightly to assign both IPv4 and IPv6 static addresses:
# nmcli con add type ethernet con-name static_ip ifname eno0 ip4 192.168.1.200/24 gw4 192.168.1.1 gw4 192.168.1.1 ip6 cabf::4532 gw6 2010:dfa::1
Interactive Editing
In addition to using nmcli with command-line options, the tool also includes an interactive mode that can be used to create and modify connection profiles. The following transcript, for example, shows interactive mode being used to create a new Ethernet connection named demo_con:
The following transcript, on the other hand, modifies the previously created static_ip connection profile to use a different static IP address than the one originally specified:
# nmcli con edit static_ip ===| nmcli interactive connection editor |=== Editing existing '802-3-ethernet' connection: 'static_ip' Type 'help' or '?' for available commands. Type 'print' to show all the connection properties. Type 'describe [<setting>.<prop>]' for detailed property description. You may edit the following settings: connection, 802-3-ethernet (ethernet), 802-1x, dcb, sriov, ethtool, match, ipv4, ipv6, tc, proxy nmcli> print ipv4.addresses ipv4.addresses: 192.168.1.200/24 nmcli> set ipv4.addresses 192.168.1.201/24 nmcli> save Connection 'static_ip' (3fccafb3-e761-4271-b310-ad0f28ee8606) successfully updated. nmcli> quit
After modifying an existing connection, remember to instruct NetworkManager to reload the configuration profiles:
# nmcli con reload
When using interactive mode, it is useful to know that an extensive built-in help system is available to learn how to use the tool. The help topics can be accessed by typing help or ? at the nmcli > prompt:
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nmcli> ? ------------------------------------------------------------------------------ ---[ Main menu ]--- goto [<setting> | <prop>] :: go to a setting or property remove <setting>[.<prop>] | <prop> :: remove setting or reset property value set [<setting>.<prop> <value>] :: set property value describe [<setting>.<prop>] :: describe property print [all | <setting>[.<prop>]] :: print the connection verify [all | fix] :: verify the connection save [persistent|temporary] :: save the connection activate [<ifname>] [/<ap>|<nsp>] :: activate the connection back :: go one level up (back) help/? [<command>] :: print this help nmcli <conf-option> <value> :: nmcli configuration quit :: exit nmcli ------------------------------------------------------------------------------
Configuring NetworkManager Permissions
In addition to making it easier to manage networks on RHEL 9, NetworkManager also allows permissions to be specified for connections. The following command, for example, restricts a connection profile to root and user accounts named john and caitlyn:
# nmcli con mod static_ip connection.permissions user:root,john,caitlyn
Once NetworkManager has reloaded the connection profiles, the static_ip connection will only be active and accessible to other users when at least one designated user is logged in to an active session on the system. As soon as the last of these users logs out, the connection will go down and remain inactive until one of the users signs back in. In addition, only users with permission can change the connection status or configuration.
Summary
The NetworkManager service handles network management on RHEL 9. NetworkManager views a network as consisting of network interface devices and connections. A network device can be a physical Ethernet or WiFi device or a virtual device used by a virtual machine guest. Connections represent the network to which the devices connect and are configured by connection profiles. A configuration profile will, among other settings, define whether the connection has a static or dynamic IP address, the IP address of any gateway used by the network, and whether or not the connection should be established automatically each time the system starts up.
NetworkManager can be administered using several tools, including the nmcli and nmtui command-line tools, the nm-connection-editor graphical tool, and the network settings section of the Cockpit web interface. In general, the nmcli command-line tool provides the most features and flexibility.