Ubuntu 20.04 Network Management

It is difficult to envisage an Ubuntu 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 Ubuntu is designed to provide enterprise level services over network and internet connections. A key part of learning how to administer an Ubuntu system involves learning how to configure and manage the network interfaces installed on the system.

This chapter is intended to provide an overview of network management on Ubuntu including the NetworkManager service and tools together with some other useful utilities.

1.1  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 Ubuntu desktop installations.

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 not available 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 useful for performing basic tasks, nmtui lacks many of the features provided by the nmcli tool.
  • nm-connection-editor – A full graphical management tool providing access to most of the 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 a number of different ways to manage the network environment on an Ubuntu system, for the purposes of this chapter we will focus on the nmcli command. While the graphical tools are certainly useful 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) do not include all of the capabilities of the nmcli tool. Finally, once you have gained some familiarity 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.

1.2  Installing and Enabling NetworkManager

NetworkManager should be installed by default for most Ubuntu installations if the Desktop installation image was used. Use the apt command to find out if it needs to be installed:

# apt -qq list network-manager
network-manager/bionic-updates,now 1.22.10-1ubuntu1 amd64 [installed,automatic]

If necessary, install the package as follows:

# apt install network-manager

Once the package is installed, the NetworkManager daemon will need to be enabled so that it starts each time the system boots:

# systemctl status network-manager

Finally, start the service running and check the status to verify that the launch was successful:

# systemctl status network-manager
● NetworkManager.service - Network Manager
   Loaded: loaded (/lib/systemd/system/NetworkManager.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2020-04-08 14:31:58 EDT; 19h ago
     Docs: man:NetworkManager(8)
 Main PID: 704 (NetworkManager)
    Tasks: 4 (limit: 4915)
   CGroup: /system.slice/NetworkManager.service
           ├─704 /usr/sbin/NetworkManager --no-daemon
.
.

1.3  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:

# nmcli [Options] Object {Command | help}

In the above syntax, Object will be one of general, networking, radio, connection, monitor, device or agent, all of 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  Wired connection 1 
wlxc83a35cad517  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  Wired connection 1 
wlxc83a35cad517  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:

# nmcli -t dev status
eno1:ethernet:connected:Wired connection 1
wlxc83a35cad517:wifi:connected:EmilyZone
virbr0:bridge:connected:virbr0
lo:loopback:unmanaged:
virbr0-nic:tun:unmanaged:

From the status output, we can see 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 Virtualization Techniques”). 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            bbd6e294-5d0c-4eac-b3c2-4dfd44becc9c  wifi      wlxc83a35cad517 
Wired connection 1 56f32c14-a4d2-32c8-9391-f51967efa173  ethernet eno1            
virbr0             f2d3494f-6ea4-4c90-936c-5eda9ac96a85  bridge   virbr0          
zonetwo            f2a20df5-aa5e-4576-8379-579d154c3e0d  wifi      --              
zonethree          45beac50-8741-41a6-abff-415640e24071  wifi      --

From the above output, we can see that the WiFi device (wlxc83a35cad517) is connected to a wireless network named zoneone while the Ethernet device (eno1) is connected to a connection named Wired connection 1. In addition to zoneone, NetworkManager has also listed two other WiFi connections named zonetwo and zonethree, neither of which currently have a device connected.

To find out the IP address allocated to a connection, the ip tool can be used with the address option:

# ip address

This can also be abbreviated:

.
.
3: wlxc83a35cad517: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether c8:3a:35:ca:d5:17 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.121/24 brd 192.168.86.255 scope global dynamic noprefixroute wlxc83a35cad517
       valid_lft 86076sec preferred_lft 86076sec
.
.

The ip command will output information for all of the devices detected on the system. 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            bbd6e294-5d0c-4eac-b3c2-4dfd44becc9c  wifi      wlxc83a35cad517 
Wired connection 1 56f32c14-a4d2-32c8-9391-f51967efa173  ethernet eno1            
virbr0             f2d3494f-6ea4-4c90-936c-5eda9ac96a85  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:

# 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 WPA2

A 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:

# nmcli con show "Wired connection 1"
connection.id:                          Wired connection 1
connection.uuid:                        56f32c14-a4d2-32c8-9391-f51967efa173
connection.stable-id:                   --
connection.type:                        802-3-ethernet
connection.interface-name:              --
connection.autoconnect:                 yes
connection.autoconnect-priority:        -999
connection.autoconnect-retries:         -1 (default)
connection.auth-retries:                -1
connection.timestamp:                   1586442354
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>

1.4  Working with Connection Profiles

So far we have explored the use of 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   zonetwo.nmconnection  zonethree.nmconnection

Each of the files is an interface configuration file containing the connection profile for the corresponding connection.

Consider, for example, the contents of our hypothetical zoneone connection:

[connection]
id=zoneone
uuid=2842f180-1969-4dda-b473-6c641c25308d
type=wifi
permissions=
 
[wifi]
mac-address=C8:3A:35:CA:D5:17
mac-address-blacklist=
mode=infrastructure
ssid=zoneone
 
[wifi-security]
auth-alg=open
key-mgmt=wpa-psk
psk=MyPassword
 
[ipv4]
dns-search=
method=auto
 
[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto

The file contains basic information about the connection, including the type (wifi), and the SSID and WPA password key for the WiFi network. For both IPV4 and IPV6 the method property is set to auto (in other words the IP address for the connection will be obtained dynamically using DHCP). 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. As an example, assume that 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 enp0s8:

# nmcli dev status
DEVICE  TYPE      STATE      CONNECTION         
enp0s3  ethernet  connected  Wired connection 1 
enp0s8  ethernet  connected  Wired connection 2 

NetworkManager automatically detected the device, activated it and assigned it to a connection named “Wired connection 2”. 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. The next steps are to delete the “Wired connection 2” connection and use nmcli to create a new connection and assign it to the device. The command to delete a connection is as follows:

# nmcli con delete "Wired connection 2"

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 dd type ethernet con-name dyn_ip ifname enp0s8
Connection 'dyn_ip' (160d9e10-bbc8-439a-9c47-a2ec52990472) successfully added.

After the connection has been created, a file named dyn_ip will have been added to the /etc/ NetworkManager/system-connections directory and will read as follows:

[connection]
id=dyn_ip
uuid=3dc0bb6b-33dc-4cf8-b5da-5b9fd560342a
type=ethernet
interface-name=enp0s8
permissions=
 
[ethernet]
mac-address-blacklist=
 
[ipv4]
dns-search=
method=auto
 
[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto

Checking the device status should now verify that the enp0s8 device is now using the dyn_ip connection profile:

# nmcli dev status
DEVICE  TYPE      STATE      CONNECTION         
enp0s8  ethernet  connected  dyn_ip             
enp0s3  ethernet  connected  Wired connection 1 

At this point it is worth noting that the enp0s3 device is also using a default connection profile for which there is no interface file through which to modify the connection settings. The same steps used to create the dyn_ip profile can also be used for the enp0s3 device. For example, to create a connection named static_ip assigned a static IP address (in this case 192.168.1.200) assigned to the enp0s3 device, the following command would be used (keeping in mind that if you are connected remotely to the system via the Wired connection 1 interface you will lose the connection):

# nmcli con delete "Wired connection 1"
# nmcli con add type ethernet con-name static_ip ifname enp0s3 ip4 192.168.1.200/24 gw4 192.168.1.1
Connection 'static_ip' (3fccafb3-e761-4271-b310-ad0f28ee8606) successfully added.
# nmcli reload

The corresponding static_ip file will read as follows:

[connection]
id=static_ip
uuid=6e03666b-26a1-476e-b5b2-77c8eac6006c
type=ethernet
interface-name=enp0s3
permissions=
 
[ethernet]
mac-address-blacklist=
 
[ipv4]
address1=192.168.1.200/24,192.168.1.1
dns-search=
method=manual
 
[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto

The command to add a new connection may be altered slightly to also assign both IPv4 and IPv6 static addresses:

# nmcli con add type ethernet con-name static_ip ifname enp0s3 ip4 192.168.1.200/24 gw4 192.168.1.1  gw4 192.168.1.1 ip6 cabf::4532 gw6 2010:dfa::1

1.5  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:

# nmcli con edit
Valid connection types: 6lowpan, 802-11-olpc-mesh (olpc-mesh), 802-11-wireless (wifi), 802-3-ethernet (ethernet), adsl, bluetooth, bond, bridge, cdma, dummy, generic, gsm, infiniband, ip-tunnel, macsec, macvlan, ovs-bridge, ovs-interface, ovs-port, pppoe, team, tun, vlan, vpn, vxlan, wimax, wpan, bond-slave, bridge-slave, team-slave
Enter connection type: ethernet
 
===| nmcli interactive connection editor |===
 
Adding a new '802-3-ethernet' connection
 
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> set connection.id demo_con
nmcli> set connection.interface enp0s8
nmcli> set connection.autoconnect yes
nmcli> set ipv4.method auto 
nmcli> set 802-3-ethernet.mtu auto
nmcli> set ipv6.method auto
nmcli> save
Saving the connection with 'autoconnect=yes'. That might result in an immediate activation of the connection.
Do you still want to save? (yes/no) [yes] yes
Connection 'demo_con' (cb837408-6c6f-4572-9548-4932f88b9275) successfully saved.
nmcli> quit

The following transcript, on the other hand, modifies the previously created static_ip connection profile to use a different static IP address to 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 there is an extensive built-in help system available to learn how to use the tool. The help topics can be accessed by typing help or ? at the nmcli > prompt:

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
------------------------------------------------------------------------------

1.6  Configuring NetworkManager Permissions

In addition to making it easier to manage networks on Ubuntu, 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 the connection profiles have been reloaded by NetworkManager, the static_ip connection will only be active and accessible to other users when at least one of the designated users 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 are able to make changes to the connection status or configuration.

1.7  Summary

Network management on Ubuntu is handled by the NetworkManager service. 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 a number of different 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.