How do I manage the "lo" loopback interface using NetworkManager?
Environment
- Red Hat Enterprise Linux
- NetworkManager service
- Loopback network interface
lo
Issue
- How do I manage the
lo
loopback interface using NetworkManager? - The
lo
interface is shown as "unmanaged" innmcli
. - NetworkManager is not managing the loopback
Resolution
RHEL 9.2
Managing the loopback interface is possible in NetworkManager 1.41.6 and later in RHEL 9.2.
Remove any legacy configuration file:
mv /etc/sysconfig/network-scripts/ifcfg-lo /root
Reload configuration files:
nmcli con reload
Add a new loopback keyfile connection:
nmcli con add connection.id lo connection.type loopback connection.interface-name lo connection.autoconnect yes
Activate it:
nmcli con up lo
Any additional changes can be applied to the loopback:
nmcli con mod ...
nmcli con up lo
RHEL 9.1 and earlier
Depending on needs, there are multiple ways to configure the loopback interface or provide similar functionality:
- How to create a dummy interface via NetworkManager?
- How to write a systemd unit to manage the loopback interface?
- Add a secondary IP address to the
ifcfg-lo
file and bring the interface up using the network service initscript: How to add secondary IP address to loopback interface
Root Cause
NetworkManager traditionally did not manage the loopback interface by design.
Red Hat customer Requests For Enhancement resulted in upstream work to add it, which was done in NetworkManager 1.41.6 with:
This is a large feature and was deemed too risky to backport to RHEL 8's earlier NetworkManager code.
Diagnostic Steps
Check the device state using older NetworkManager:
# nmcli device show
DEVICE TYPE STATE CONNECTION
lo loopback unmanaged --
net0 ethernet connected net0
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