Chapter 15. Configuring NetworkManager to ignore certain devices

By default, NetworkManager manages all devices. To ignore certain devices, you can configure NetworkManager by setting as unmanaged.

15.1. Configuring the loopback interface by using nmcli

By default, NetworkManager does not manage the loopback (lo) interface. After creating a connection profile for the lo interface, you can configure this device by using NetworkManager. Some of the examples are as follows:

  • Assign additional IP addresses to the lo interface
  • Define DNS addresses
  • Change the Maximum Transmission Unit (MTU) size of the lo interface

Procedure

  1. Create a new connection of type loopback: 

    # nmcli connection add con-name example-loopback type loopback

  2. Configure custom connection settings, for example:

    1. To assign an additional IP address to the interface, enter: 

      # nmcli connection modify example-loopback +ipv4.addresses 192.0.2.1/24
      Note

      NetworkManager manages the lo interface by always assigning the IP addresses 127.0.0.1 and ::1 that are persistent across the reboots. You can not override 127.0.0.1 and ::1. However, you can assign additional IP addresses to the interface.

    2. To set a custom Maximum Transmission Unit (MTU), enter: 

      # nmcli con mod example-loopback loopback.mtu 16384

    3. To set an IP address to your DNS server, enter: 

      # nmcli connection modify example-loopback ipv4.dns 192.0.2.0

      If you set a DNS server in the loopback connection profile, this entry is always available in the /etc/resolv.conf file. The DNS server entry remains independent of whether or not the host roams between different networks.

  3. Activate the connection: 

    # nmcli connection up example-loopback

Verification

  1. Display the settings of the lo interface: 

    # ip address show lo

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16384 qdisc noqueue state UNKNOWN group default qlen 1000

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet 192.0.2.1/24 brd 192.0.2.255 scope global lo valid_lft forever preferred_lft forever

inet6 ::1/128 scope host
valid_lft forever preferred_lft forever

  2. Verify the DNS address: 

    # cat /etc/resolv.conf

...
nameserver 192.0.2.0
...

15.2. Permanently configuring a device as unmanaged in NetworkManager

You can permanently configure devices as unmanaged based on several criteria, such as the interface name, MAC address, or device type.

To temporarily configure network devices as unmanaged, see Temporarily configuring a device as unmanaged in NetworkManager.

Procedure

  1. Optional: Display the list of devices to identify the device or MAC address you want to set as unmanaged: 

    # ip link show
...
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:74:79:56 brd ff:ff:ff:ff:ff:ff
...

  2. Create the /etc/NetworkManager/conf.d/99-unmanaged-devices.conf file with the following content:

    • To configure a specific interface as unmanaged, add: 

      [keyfile]
unmanaged-devices=interface-name:enp1s0

    • To configure a device with a specific MAC address as unmanaged, add: 

      [keyfile]
unmanaged-devices=mac:52:54:00:74:79:56

    • To configure all devices of a specific type as unmanaged, add: 

      [keyfile]
unmanaged-devices=type:ethernet

    • To set multiple devices as unmanaged, separate the entries in the unmanaged-devices parameter with a semicolon, for example: 

      [keyfile]
unmanaged-devices=interface-name:enp1s0;interface-name:enp7s0

  3. Reload the NetworkManager service: 

    # systemctl reload NetworkManager

Verification

  • Display the list of devices: 

    # nmcli device status
DEVICE  TYPE      STATE      CONNECTION
enp1s0  ethernet  unmanaged  --
...

    The unmanaged state next to the enp1s0 device indicates that NetworkManager does not manage this device.

Troubleshooting

  • If the device is not shown as unmanaged, display the NetworkManager configuration: 

    # NetworkManager --print-config
...
[keyfile]
unmanaged-devices=interface-name:enp1s0
...

    If the output does not match the settings that you configured, ensure that no configuration file with a higher priority overrides your settings. For details about how NetworkManager merges multiple configuration files, see the NetworkManager.conf(5) man page.

15.3. Temporarily configuring a device as unmanaged in NetworkManager

You can temporarily configure devices as unmanaged.

Use this method, for example, for testing purposes. To permanently configure network devices as unmanaged, see Permanently configuring a device as unmanaged in NetworkManager.

Procedure

  1. Optional: Display the list of devices to identify the device you want to set as unmanaged: 

    # nmcli device status
DEVICE  TYPE      STATE         CONNECTION
enp1s0  ethernet  disconnected  --
...

  2. Set the enp1s0 device to the unmanaged state: 

    # nmcli device set enp1s0 managed no

Verification

  • Display the list of devices: 

    # nmcli device status
DEVICE  TYPE      STATE      CONNECTION
enp1s0  ethernet  unmanaged  --
...

    The unmanaged state next to the enp1s0 device indicates that NetworkManager does not manage this device.

Additional resources

  • NetworkManager.conf(5) man page