Boot time is when you Turn on the target device up to the point where it downloads the bootstrap file. The bootstrap file contains the BOOTSTRAP PROGRAM
But what is a BOOTSTRAP PROGRAM?
A target device initiates the boot process by first loading a bootstrap program. A bootstrap program is a small program that runs before the operating system is loaded. Provisioning Services uses a special bootstrap program that initializes the streaming session between the target device and the Provisioning Server. After this session starts, the operating system begins to be streamed and loaded from the vDisk that was initiated.
- Over the network, via Preboot eXecution Environment (PXE)
- From a boot device stored on attached media
- From a BIOS Embedded bootstrap (OEM versions only)
Source: Citrix DOCS – BootStrap Program
BOOT TIME COMPONENTS
TFTP Service is a basic TFTP you can see anywhere else – Just sits there with the boot strap file, waits for someone/somebody to request it . When somebody (usually a target device) requests it, it uses the TFTP protocol to deliver the bootstrap file
Now, in order to get the bootstrap file when you perform a PXE booting, you need two pieces of information
- The IP Address of the Server or [Server name]
- The name of the bootstrap file [filename of the bootstrap file
So in order to do a Network boot via PXE, those two pieces of information have to be provided for, to accomplish that
There a couple ways of doing that:
- Using Option 66/67 in your DHCP server. So when you use option 66/67:
- a target with PXE enabled, boots up
- It will send out a DHCP discover packet
- DHCP will respond to that discover packet with the offer that can contain all the normal DHCP information (IP, subnet mask, gateway, DNS, domain, but in addition to that information, it will also provide the IP address and the filename for the boot strap. It will then, with that information in hand go to the TFTP server and download the bootstrap file
- Using PXE
Q. So, do you know what PXE service is used for?
A. It replaces Option 66 and 67
So, in a environment where you don’t want to use Option 66 and 67, you can enable the PXE Service in all your PVS servers. What happens here is the target boots up, and does a DHCP discovery (It will send out a DHCP discovery packet)
PXE services listens on port 67 which is the same port that DHCP listens on. So that discovery goes out and hits the DHCP server and will hit all PXE Services. DHCP will respond with the basic DHCP information (IP, subnet mask, gateway, DNS, domain). It will NOT have in this case (since it was not configured) the option 66 and 67. However, all the PXE servers will respond with the IP of themselves and the boot strap file name. So when you use PXE services you use both PXE service and TFTP on the same server. The way this works i: if you have multiple PXE services, the first one that gets received by the target devices is the one being used; it will contact the TFTP server and download the bootstrap
More to come: