I just bought an old IBM X3650 M2 and installed Ubuntu Server 20.04 LTS. My router (Netgear R7000) is not obeying the IP rules I set in the router setup (and so far, I've only noticed this for this "new" server, not for the other 67 devices where I have previously assigned IPs in the router DHCP).
In the IBM server configuration, I enabled the network (IPv4), and checked the "DHCP" option.
My router assigns a random IP (192.168.0.5). I then assign an IP address in the router config (192.168.0.99) and apply. Once the router finishes restarting the DHCP, the server is now at 192.168.0.2. Rebooting the server (even power cycling) or re-assigning the IP and re-applying doesn't change anything.
It seems the router is allowed to assign IP to the server, but the router won't obey its own rules. The rule is displayed loud and clear in the router config, it's not dissapearing (as I've seen other posts complain about).
I know (think?) I could just assign a static IP in the server config, but I'd rather have it done by the router, for various reasons. And the question "why is it doing this?" is also bugging me :)
EDIT: I tried setting a static IP in the BIOS setup of the server. First time it worked (my testing IP, 192.168.0.99), but when I tried changing it to the permanent IP I need to use (192.168.0.100), it reverted back to the router appointed (.2) address. What more is, I can no longer set it back to the "testing IP" (.99).
In the router, the change I made between being able to assign IP in BIOS setup and not, was to delete the entry for my old server (just an old NUC type computer, really), which was previously at 192.168.0.100.