NetworkManager duplicates a connection after restart of NetworkManager service.

Environment

• Red Hat Enterprise Linux 7
• Red Hat Enterprise Linux 8

Issue

• Performing a change in ifcfg files and restarting NetworkManager results in duplicate connection.

Resolution

• Do not restart NetworkManager when the configuration on the device differs from the configuration of the profile on disk. In order to apply the changes you need to reactivate the connection as the changes do not automatically apply on the device.

This can be achieved by either

$ nmcli connection up $PROFILE

Or

$ nmcli device reapply $DEV

Root Cause

• This is an expected behaviour.
• When NetworkManager is restarted, devices are left up. After the restart, NetworkManager tries to take over previously configured devices, however, if the connection on disk does not match the configuration on the device, NetworkManager will leave the existing device configuration and create an in-memory connection that reflects what is configured on the device.

Diagnostic Steps

$ nmcli connection show 
NAME             UUID                                  TYPE            DEVICE 
bond-slave-eth1  fae338aa-9d39-476a-b838-03f2db87f877  802-3-ethernet  eth1   
bond-slave-eth2  26815d39-f7a6-4921-9135-6376c8cceece  802-3-ethernet  eth2   
bond0            3c170ef9-32f2-4bde-9c56-d7ff2017f8a4  bond            bond0  
eth0             ce21b538-7c07-45f6-b00f-2eed0f731b67  802-3-ethernet  eth0   
virbr0           20a4ebb0-a91b-4fb9-9040-27c8e528ad50  bridge          virbr0 
$ vi /etc/sysconfig/network-scripts/ifcfg-eth0
$ systemctl restart NetworkManager
$ nmcli connection show 
NAME             UUID                                  TYPE            DEVICE 
bond-slave-eth1  fae338aa-9d39-476a-b838-03f2db87f877  802-3-ethernet  eth1   
bond-slave-eth2  26815d39-f7a6-4921-9135-6376c8cceece  802-3-ethernet  eth2   
bond0            3c170ef9-32f2-4bde-9c56-d7ff2017f8a4  bond            bond0  
eth0             494ee46d-6882-49cf-b661-79b81cf3a760  802-3-ethernet  eth0   
virbr0           c5a8817d-cda7-4ce2-a901-679a82542376  bridge          virbr0 
eth0             ce21b538-7c07-45f6-b00f-2eed0f731b67  802-3-ethernet  --   
$ vi /etc/sysconfig/network-scripts/ifcfg-eth0
$ nmcli device reapply eth0 
Connection successfully reapplied to device 'eth0'.
$ nmcli connection show 
NAME             UUID                                  TYPE            DEVICE 
bond-slave-eth1  fae338aa-9d39-476a-b838-03f2db87f877  802-3-ethernet  eth1   
bond-slave-eth2  26815d39-f7a6-4921-9135-6376c8cceece  802-3-ethernet  eth2   
bond0            3c170ef9-32f2-4bde-9c56-d7ff2017f8a4  bond            bond0  
eth0             ce21b538-7c07-45f6-b00f-2eed0f731b67  802-3-ethernet  eth0   
virbr0           c5a8817d-cda7-4ce2-a901-679a82542376  bridge          virbr0 

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.