Boot through LAN

This will greatly depedn upon the hardware and operating system. But most organisations that do this do it by having a Network Interface Card (NIC) that can be set to automatically Boot From Lan and then set the system BIOS of the motherboard to boot from LAN.

This way the motherboard looks to the LAN as the boot device and the NIC will have sufficient command codes to allow this operations. Most NICs can do this but many require a special chip with the relevant codes to be installed for this to work properly, some can come preinstalled.