I have tried to tell netplan to let my ethernet device be managed by NetworkManager, so that I can then configure a pppoe connection on top of this device.
This fails with:
# nmcli c up netplan-wan
Error: Connection activation failed: No suitable device found for this connection (device lo not available because device is strictly unmanaged).
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I don't know why it mentions 'lo' in that message, but the wan interface is unmanaged (as are all devices on the system, but this one is supposed to be managed):
# nmcli d status | grep wan
wan ethernet unmanaged --
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After much searching, I've figured out that this comes from /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf:
keyfile]
unmanaged-devices=*,except:type:wifi,except:type:gsm,except:type:cdma
Even though I've told netplan to use the NM renderer for this device, the configuration emitted by netplan is insufficient to override this.
Using the workaround from https://askubuntu.com/questions/71159/network-manager-says-device-not-managed (sudo touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf) doesn't work, but if I set NetworkManager as the toplevel renderer in /etc/netplan, /run/NetworkManager/conf.d/10-globally-managed-devices.conf is emitted, which evidently DOES work. But I only have one device that I want rendered by NM, so I shouldn't have to declare NM at the top level of the yaml with a lot of duplication in order to get this result.
I would argue that the 10-globally-managed-devices.conf should not be there at all. But if it is going to be, then netplan needs to consistently override it whenever there is any use of the NetworkManager backend.
Yes, indeed. NetworkManager tries to control all interfaces that are available by default and netplan implemented some quirks in the past to avoid this. But we should review those quirks and rather implement a per-interface/