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PXE boot instructions overview

PXE boot instructions, which are defined within a job or job template, can direct controlled devices to boot using a virtual floppy disk, to boot and run the Deployment Agent, or to boot and run the operating system image installed on the hard disk. Controlled devices are defined by their device record in the Controller database.

The PXE boot process

After a device completes the power-on self test (POST) 

power-on self test (POST)
A set of routines stored in read-only memory (ROM) that tests various system components such as RAM, the disk drives, and the keyboard, to see if they are properly connected and operating. If problems are found, these routines alert the user with a series of beeps or a message, often accompanied by a diagnostic numeric value. If the POST is successful, it passes control to the bootstrap loader.
and begins the Pre-Boot eXecution Environment (PXE) boot process, the device sends a DHCPDISCOVER message that is received by both the DHCP server and the ADS PXE service. The DHCP server offers the device an IP address, and the ADS PXE service either ignores or responds to the device using cached boot responses from the Controller.

If the ADS PXE service responds to the device, it sends the device a DHCPOFFER message with the IP address of the ADS PXE service so that the device can request the Startnbs network boot program from the TFTPD service. On the device, Startnbs requests boot instructions from the ADS PXE service, which relays the request to the Controller. The Controller sends the PXE boot instructions to the ADS PXE service, which relays them to the device, only if the Controller can match the device's SMBIOS GUID or MAC address to an existing device record, or if the Controller is configured to add a new device record if the device is not listed in the Controller database. For more information about the configuring the Controller, see Controller service properties.

The Controller service retrieves the PXE boot instructions, in the form of /pxe/boot commands, from the appropriate job or job template and sends them to the ADS PXE service, which relays the boot instructions to the device. The /pxe/boot commands instruct the device to boot using a virtual floppy disk, to boot and run the Deployment Agent, or to boot and run the operating system that is installed on the hard disk. If a connection to the Controller cannot be established, the ADS PXE service responds to the device using cached boot instructions. For more information about the commands, see /pxe/boot-vf, /pxe/boot-da, and /pxe/boot-hd. For more information about jobs and job templates, see Jobs and job templates.

The following diagrams illustrate the interaction between the device, the DHCP server, and the ADS services when booting to a virtual floppy disk, to the Deployment Agent, or to the device's hard disk during the PXE boot process.

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