• How Prestaged Clients Are Located
  
  
• When Prestaged Clients Are Joined to a Domain
  
  
• Diagram of Prestaging Clients
  
  

When a client computer attempts to boot from the network, limited data is transferred from the client to the server as part of the Pre-Boot Execution Environment (PXE) protocol. Windows Deployment Services can locate prestaged clients by using either of the following:

• GUID (recommended). A computer's GUID is a unique 32-character hexadecimal value supplied by the manufacturer of the computer that is stored within the system BIOS. The GUID format occurs in two formats:
  
  
  • String format (also known as wire format). Example: 0123456789ABCDEF0123456789ABCDEF
    
    
  • Display format. Example (using the same GUID as the first bullet): {67452301-AB89-EFCD-0123-456789ABCDEF}
    
    
  The management tools enable you to specify the GUID in either format. For details, see How to Perform Common Tasks (http://go.microsoft.com/fwlink/?LinkId=115268).
  
  
• MAC address. The MAC address is a 128-bit hardware address that uniquely identifies each node of a network. The first part of the address is unique to the company that produced the device and is a sequence of digits that are unique to a device manufactured by that company.
  
  

The following is the Lightweight Directory Access Protocol (LDAP) search filter used by Windows Deployment Services: (&(objectCategory=<DN of Computer Schema object>)(|(netbootGUID=<GUID>)(netbootGUID=MAC))). This filter ensures that a device will be found if it is prestaged using either a computer GUID or a MAC address. The netbootGUID attribute on a prestaged client is used to store the value of the physical computer’s GUID or the MAC address. You can use the Ldp GUI tool to view this value.

When a PXE request is submitted, it contains both of these values in the DHCPREQUEST packet. The computer's GUID is in the Dynamic Host Control Protocol (DHCP) options (tag 97 in DHCP options), and the MAC address is in the Ethernet Source Address part of the packet. The PXE server forwards the PXE request to the Windows Deployment Services server. The server extracts both pieces of information, binds against an AD DS server, and searches for a match on either value. If a match is found, the client is considered known. If no match is found, the client is considered unknown.

The following are three scenarios in which the booting device will not be uniquely identified and the server will return an error:

• Two computers are found in AD DS with the same computer GUID.
  
  
• Two computers are found in AD DS with the same MAC address. For example, if you prestage the MAC address of Server1, then you build and prestage Server2 by using the network adapter from Server1. Now you have two prestaged devices in AD DS with the same MAC address.
  
  
• Two devices in AD DS represent a single physical computer — one device prestaged with a computer GUID, and the other one prestaged with a MAC address.
  
  

If a client computer is prestaged in AD DS, the client will be joined to the domain as the prestaged device. You can override this by running the /JoinDomain:No command on the command line (for example, WDSUTIL /Set-Device /Device:Computer2 /User:Domain\user /JoinRights:JoinOnly /JoinDomain:No). If a client computer is not prestaged, the per-server policy settings dictate the domain join behavior (for example, the computer name and location in AD DS). In all cases where Windows Deployment Services creates a computer object to facilitate the domain join process, the account that is created will contain either the client's GUID or MAC address (as stored in the netbootGUID attribute). This automatic prestaging is beneficial because if you rebuild a computer (for example, from a failed hard disk drive), the computer will be joined to the same domain using the same computer name.

For instructions on setting these options, see the “Prestage Computers” section in How to Manage Client Computers (http://go.microsoft.com/fwlink/?LinkID=115265).

The following flowchart shows the connections that the Windows Deployment Services PXE provider (BINLSVC) will make to locate a prestaged device and read its attributes.

Examples