I built a new firewall under Debian 12. The machine has eight network ports, and during configuration I accidentally used the same name for a couple of the ports in the files under /etc/systemd/network/*.link. I ended up with two link files referencing two different MAC addresses but naming each of them as WAN0, and once systemd got that configuration it wouldn't let it go.

From what I could find online, normally I would just issue systemctl daemon-reload followed by a update-initramfs -u and after a reboot systemd should have had the updated information... but no dice this time. The way I finally discovered the problem was when I noticed under ifconfig that my wan0 port was pointing to the wrong MAC address (even though the link files had been corrected).

After several hours of fighting with it, I finally managed to get it to work by renumbering all of my link files, and now the information for each port matches up correctly. But my real question here is WHY did systemd refuse to read updated link files? Is there another step I should have taken which was mysteriously never mentioned in any of the dozens of web pages I looked at trying to fix this? I really need to understand the proper process for getting it to correctly use these files so I can maintain the machine in the future.

(God I miss the reliability of udev already)