You can use preboot execution environment (PXE) to boot an ESXi host from a network device, if your host uses legacy BIOS or UEFI. Alternatively, if your ESXi host supports native UEFI HTTP, you can use hypertext transfer protocol (HTTP) to boot the host from a network device.
ESXi is distributed in an ISO format that is used to install to flash memory or to a local hard drive. You can extract the files and boot them over a network interface.
PXE uses Dynamic Host Configuration Protocol (DHCP) and Trivial File Transfer Protocol (TFTP) to boot an operating system over a network.
PXE booting requires some network infrastructure and a machine with a PXE-capable network adapter. Most machines that can run ESXi have network adapters that can PXE boot.
Native UEFI HTTP uses DHCP and HTTP to boot over a network. UEFI HTTP boot requires a network infrastructure, UEFI firmware version on the ESXi host that includes HTTP boot feature, and a network adapter that supports UEFI networking.
Booting by using HTTP is faster and more reliable than using TFTP. This is due to the capabilities of the TCP protocol that underlies the HTTP, such as built-in streaming and lost packet recovery. If your ESXi hosts do not support native UEFI HTTP, you can use iPXE HTTP for the boot process.