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I'm trying to work out why I cannot create a bridge (asked separately Unable to create bridge using NetworkManager ).

I think something is interferring with NetworkManager but I cannot tell what it is.

I want to disconnect the ethernet device and bring the interface down.

Running nmcli dev disconnect enp42s0 or nmcli con down enp42s0 then nmcli c

Shows the ethernet device is disconnected.

DEVICE            TYPE      STATE                   CONNECTION  
enp42s0           ethernet  disconnected            --          

but then the output of ip a shows the device is UP, althoguh without an ip address assigned.

3: enp42s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
    link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff

My question here is: is this normal behaviour?

I have systemd-networkd disabled and stopped.

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  • That is normal behavior.
    – larsks
    Mar 16 at 10:54

1 Answer 1

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"disconnected" for NetworkManager means that the interface is logically not connected. That is, it has no profile activated. It may also be subject to autoconnect, if you had a suitable profile.

That is different from the link state (UP) or the carrier state (LOWER_UP) of the interface, as you see it in ip link.

When NetworkManager manages an interface, it always sets the interface UP (ip link set up). It does so, because it is interested in getting the carrier state (LOWER_UP), which kernel only determines if the interface is up.

Btw, if the interface would not have carrier, then the logical device state in NetworkManager would be "unavailable", instead of "disconnected".

This seems all normal, and behaves as expected. If you want to keep the interface down, then configure it as unmanaged in NetworkManager. For example nmcli device set enp42s0 managed no && ip link set enp42s0 down.

In general, look at nmcli device and nmcli connection to see what devices/profiles are activated. Activate/Deactivate the desired profiles with nmcli connection up|down and nmcli device up|down.

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