On Monday, 16 October 2023 10:15:03 BST Tsukasa Mcp_Reznor wrote:
> Well, you're probably gonna have to spam us some more info.
> 
> On the working knoppix boot, spam lspci showing what driver is loaded.  then
> spam it on ubuntu to verify if it's loaded there as well.
> 
> dmesg for the relevant parts on both would also help.
> 
> I'd make sure ubuntu has linux-firmware installed, could simply be failing
> if it's missing.
> 
> ifconfig could show if it is loaded and just doesn't have an ip assigned, if
> the mac address says 00:00:00:00:00 that'd be a different problem.
[snip ...]

From what I recall Ubuntu has been chopping & changing its network scripts on 
a regular basis.  So in the first instance check what you're running on this 
system:

systemctl status systemd-networkd

or 

systemctl status NetworkManager 

I think the server version does not have NetworkManager and as your thread 
says, netplan is now (since early 2023?) used to configure the network 
connections:

netplan status

If netplan is running with renderer networkd, check the contents of your /etc/
netplan/01-netcfg.yaml, which you list your ethernet NIC and include "dhcp4: 
yes", then run:

sudo netplan generate
sudo netplan apply

You may have to also restart networkd service:

sudo systemctl restart systemd-networkd

If the above does not work, you'll need to fish for error messages in dmesg 
and by running journalctl.