Some of the details of the PXE boot process vary depending on whether the target host is using legacy BIOS or UEFI firmware, and whether the boot process uses TFTP only or TFTP plus HTTP.

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

Figure 1. Overview of PXE Boot Installation Process
The PXE boot ESXi installation process is shown as sequence of interactions between the ESXi host, the DHCP server, the TFTP server, the Web server, and the scripts depot. These interactions provide the ESXi host with IP address for the virtual network adapter, the network boot loader, the kernel, the IP address for the kernel, and the installation script.

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 and the location of the TFTP server.
  4. The ESXi host contacts the TFTP server and requests the file that the DHCP server specified.
  5. The TFTP server sends the network boot loader, and the ESXi host executes it. The initial boot loader might load additional boot loader components from the TFTP server.
  6. The boot loader searches for a configuration file on the TFTP server, downloads the kernel and other ESXi components from the HTTP server or the TFTP server and boots the kernel on the ESXi host.
  7. The installer runs interactively or using a kickstart script, as specified in the configuration file.