PXE boot process is a very important concept in Operating System Deployment specially during setting up an OSD environment and during troubleshooting. I will explain you the entire process in detail.
What is PXE
PXE stands for Preboot Execution Environment is a feature that allows you to boot a PC from the network instead of the normal local drive. Generally you have an option in BIOS by which you can enable PXE boot
But you can also select a temporary boot device by pressing F12 during BIOS start up and select to boot from Network.
PXE was evolved generally for enterprise network Clients for downloading software images and configuration parameter.
What is TFTP
TFTP (Trivial File Transfer Protocol) is a basic lightweight version of FTP (File Transfer Protocol). TFTP is a dated, exceedingly small, stateless protocol which was chosen for its security or its performance. Once the client receives boot file details, TFTP plays an important role in downloading the file to Client TFTP stack.
Step Description
The System BIOS boots up using PXE
PXE Client broadcasts DHCP Discover to UDP port 67
DHCP sends DHCP offer that contains an IP address to Client 68
The client sends a DHCP request to DHCP server for the boot file name
The boot server sends back DHCP Acknowledgement that contains Network Bootstrap Program File Name (WDSNBP)
The client requests the NBP file from the boot server
The Client is directed to download WDSNBP.com using TFTP
WDSNBP.com validates the DHCP/PXE response packet and proceeds to download PXEboot.com
PXEBoot.co downloads Bootmgr.exe and BCD store
Bootmgr.exe reads the BCD operating system entries and downloads boot.sdi and Win PE Image
Bootmgr.exe begins booting Win PE by calling Winload.exe within Windows PE image
Windows PE queries for a Management Point and determines if any task sequences are advertised for the Client.
Once the task sequence is selected, Client contacts the DP and image is installed using the parameters defined in the task sequence.
What is PXE
PXE stands for Preboot Execution Environment is a feature that allows you to boot a PC from the network instead of the normal local drive. Generally you have an option in BIOS by which you can enable PXE boot
But you can also select a temporary boot device by pressing F12 during BIOS start up and select to boot from Network.
PXE was evolved generally for enterprise network Clients for downloading software images and configuration parameter.
What is TFTP
TFTP (Trivial File Transfer Protocol) is a basic lightweight version of FTP (File Transfer Protocol). TFTP is a dated, exceedingly small, stateless protocol which was chosen for its security or its performance. Once the client receives boot file details, TFTP plays an important role in downloading the file to Client TFTP stack.
Step Description
The System BIOS boots up using PXE
PXE Client broadcasts DHCP Discover to UDP port 67
DHCP sends DHCP offer that contains an IP address to Client 68
The client sends a DHCP request to DHCP server for the boot file name
The boot server sends back DHCP Acknowledgement that contains Network Bootstrap Program File Name (WDSNBP)
The client requests the NBP file from the boot server
The Client is directed to download WDSNBP.com using TFTP
WDSNBP.com validates the DHCP/PXE response packet and proceeds to download PXEboot.com
PXEBoot.co downloads Bootmgr.exe and BCD store
Bootmgr.exe reads the BCD operating system entries and downloads boot.sdi and Win PE Image
Bootmgr.exe begins booting Win PE by calling Winload.exe within Windows PE image
Windows PE queries for a Management Point and determines if any task sequences are advertised for the Client.
Once the task sequence is selected, Client contacts the DP and image is installed using the parameters defined in the task sequence.
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