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.

Note: Network booting with legacy BIOS firmware is possible only over IPv4. Network booting with UEFI BIOS firmware is possible over IPv4 or IPv6.

Overview of the Network Boot Installation Process

You can boot an ESXi host from a network interface. The network boot process varies depending on whether the target host is using legacy BIOS or UEFI firmware, and whether the boot process uses PXE TFTP, iPXE HTTP, or UEFI HTTP.

When you boot a target host, it interacts with the different servers in the environment to get a network adapter, boot loader, kernel, IP address for the kernel, and finally an installation script. When all components are in place, installation starts, as shown in the following illustration.

Figure 1. Overview of PXE Boot Installation Process
Flow of interactions between the ESXi host, the DHCP server, the TFTP server, the Web server, and the scripts depot.

The interaction between the ESXi host and other servers proceeds as follows:

  1. The user boots the target ESXi host.
  2. The target ESXi host makes a DHCP request.
  3. The DHCP server responds with the IP information, the location of the TFTP or HTTP server, and the filename or URL of the initial network boot loader.
  4. The ESXi host contacts the TFTP or HTTP server and requests the filename or URL that the DHCP server specified.
  5. The TFTP or HTTP server sends the network boot loader, and the ESXi host runs it. The initial boot loader might load additional boot loader components from the server.
  6. The boot loader searches for a configuration file on the TFTP or HTTP server, downloads the kernel and other ESXi components as specified in the configuration file, and boots the kernel on the ESXi host.
  7. The installer runs interactively or using a kickstart script, as specified in the configuration file.

Network Boot Background Information

Understanding the network boot process can help you during troubleshooting.

TFTP Server

Trivial File Transfer Protocol (TFTP) is similar to the FTP service, and is typically used only for network booting systems or loading firmware on network devices such as routers. TFTP is available on Linux and Windows.
  • Most Linux distributions include a copy of the tftp-hpa server. If you require a supported solution, purchase a supported TFTP server from your vendor of choice. You can also acquire a TFTP server from one of the packaged appliances on the VMware Marketplace.

  • If your TFTP server runs on a Microsoft Windows host, use tftpd32 version 2.11 or later. See http://tftpd32.jounin.net/.

SYSLINUX and PXELINUX

If you are using PXE in a legacy BIOS environment, you must understand the different boot environments.
  • SYSLINUX is an open-source boot environment for machines that run legacy BIOS firmware. The ESXi boot loader for BIOS systems, mboot.c32, runs as a SYSLINUX plugin. You can configure SYSLINUX to boot from several types of media, including disk, ISO image, and network. You can find the SYSLINUX package at http://www.kernel.org/pub/linux/utils/boot/syslinux/.
  • PXELINUX is a SYSXLINUX configuration for booting from a TFTP server according to the PXE standard. If you use PXELINUX to boot the ESXi installer, the pxelinux.0 binary file, mboot.c32, the configuration file, the kernel, and other files are transferred by TFTP.
Note: VMware builds the mboot.c32 plugin to work with SYSLINUX version 3.86 and tests PXE booting only with that version. Other versions might be incompatible. The Open Source Disclosure Package for VMware vSphere Hypervisor includes bug fixes for SYSLINUX version 3.86.

iPXE

iPXE is open-source software that provides an implementation of HTTP. You can use the software to perform an initial boot. For more information, see https://ipxe.org/.

VMware includes a build of iPXE as part of Auto Deploy. The source tree for this build is available in The Open Source Disclosure Package for VMware vCenter Server.

UEFI PXE and UEFI HTTP

Most UEFI firmware natively includes PXE support that allows booting from a TFTP server. The firmware can directly load the ESXi boot loader for UEFI systems, mboot.efi. Additional software such as PXELINUX is not required.

Some UEFI firmware support native UEFI HTTP boot. The feature is introduced in version 2.5 of the UEFI specification. The firmware can load the ESXi boot loader from an HTTP server, without additional software, such as iPXE.

Note: Apple Macintosh products do not include PXE boot support. They include support for network booting through an Apple-specific protocol instead.

Alternative Approaches to Network Booting

Alternative approaches to network booting different software on different hosts are also possible, for example:
  • Configuring the DHCP server to provide different initial boot loader filenames to different hosts depending on MAC address or other criteria. See your DCHP server's documentation.
  • Approaches using iPXE as the initial bootloader with an iPXE configuration file that selects the next bootloader based on the MAC address or other criteria.

PXELINUX Configuration Files

You need a PXELINUX configuration file to boot the ESXi installer on a legacy BIOS system. The configuration file defines the menu displayed to the target ESXi host as it starts.

This section gives general information about PXELINUX configuration files.

For syntax details, see the SYSLINUX website at http://www.syslinux.org/.

Required Files

In the PXE configuration file, you must include paths to the following files:

  • mboot.c32 is the boot loader.
  • boot.cfg is the boot loader configuration file.

See About the boot.cfg File

Filename for the PXE Configuration File

For the filename of the PXE configuration file, select one of the following options:

  • 01-mac_address_of_target_ESXi_host. For example, 01-23-45-67-89-0a-bc
  • The target ESXi host IP address in a hexadecimal notation.
  • default
The initial boot file pxelinux.0 tries to load a PXE configuration file in the following order:
  1. It tries with the MAC address of the target ESXi host, prefixed with its ARP type code, which is 01 for Ethernet.
  2. If that attempt fails, it tries with the hexadecimal notation of target ESXi system IP address.
  3. Ultimately, it tries to load a file named default.

File Location for the PXE Configuration File

Save the file in /tftpboot/pxelinux.cfg/ on the TFTP server.

For example, you might save the file on the TFTP server at /tftpboot/pxelinux.cfg/01-00-21-5a-ce-40-f6. The MAC address of the network adapter on the target ESXi host is 00-21-5a-ce-40-f6.