In theory, network booting with UEFI is fairly straightforward. Unlike the earlier BIOS based network booting, UEFI defines network booting in the standard itself (although it's not required). In practice, vendors of x86 servers have found any number of creative ways to put stumbling blocks in your way in their firmware (aka 'BIOS'). Here's an incomplete list of reasons that your server might not be willing to do a UEFI network boot the way you expect it.

• The firmware might not even be in UEFI mode, in which case at best it's trying to do BIOS PXE boot, which requires a different set of support infrastructure on your boot server that may not be there ( cf , also ).

• There's no UEFI network booting option (or options) in the server's UEFI boot order.
• The UEFI network boot option is trying to boot from the wrong interface (on a server with multiple interfaces).
• The firmware only supports UEFI network booting using the built-in 1G network interfaces, not with your 10G-T add-in PCIe card that is actually connected to your network.

• UEFI network booting is enabled in the boot order, but your firmware settings have disabled network booting for all network devices that the firmware will try. Depending on the firmware, this might be a master option that applies to all onboard network interfaces or it might be a per-interface setting.

  (In some firmware this isn't even in the regular 'BIOS' setup screens, but is instead in a completely separate top level configuration system for (some) network devices.)

• Your firmware settings have the network devices in 'legacy' network boot mode (ie, PXE booting) despite your firmware being in UEFI mode, so the firmware won't touch them for UEFI network booting. Sometimes the firmware's setup screens will vaguely describe this as the device firmware being in 'legacy' or 'UEFI' modes, and not specifically mention network booting.

  You might ask why vendors would allow this configuration mismatch. I have no answer, I just know that at least one vendor does have UEFI firmware that will let you do this.

If the server's firmware has a specific 'PXE/UEFI network boot' option that it offers to you on startup (along with things like 'enter setup' or a regular boot menu), this boot option may or may not provide any useful information if the firmware decides it has no valid UEFI network device to boot from. You may be in a situation where you pound on F12 (or whatever key is applicable) but nothing happens and you drop through to whatever 'boot failed' option the firmware has available.

(If the firmware is feeling especially hostile, it will drop you into the UEFI shell [PDF] , and see also the Arch wiki page .)

Similarly, if the server offers you a general one time boot menu, but when you pick it there's no UEFI network boot options, this could mean either that the general UEFI boot ordering in the firmware doesn't have network booting included or that the firmware thinks there's no valid UEFI network devices.

There are typically at least two ways to disable (UEFI) network booting on servers: you can take it out of the boot order, or you can tell the often built in network devices to not do network booting. If you've historically disabled network booting on your servers because you don't use it and typically all it did was add extra time to server boots as the firmware poked at network devices, you may have done either or both of these and now need to reverse either or both.

(In non-UEFI, BIOS MBR boot mode, network device firmware has historically fiddled around with PXE stuff even if the BIOS boot sequence wasn't going to wind up trying PXE booting. Or at least it did on some of our servers, so we often turned that off.)

All of this can leave you hunting all over your server firmware's setup screens in order to find whatever magic bit that's making the system not boot from the network the way you want it to. Good luck, but start by checking UEFI boot order and (network) device settings.