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PXE architecture

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

PXE architecture

Remote Installation Services (RIS) uses the Dynamic Host Configuration Protocol (DHCP) that follows the Pre-Boot eXecution Environment (PXE) architecture to bootstrap a client computer.

When a new PXE remote boot-enabled client computer starts for the first time, it uses the DHCP to request an Internet Protocol (IP) address and the IP address of an active RIS server. As part of the initial request, the client computer sends out its globally unique identifier (GUID), which identifies the client computer within Active Directory.

After the client computer receives an IP address from the DHCP server, it then requests service from a RIS server. The request to the RIS server is a broadcast, which means all of the RIS servers on the network will receive the request. If the RIS server is allowed to answer, it queries its preferred domain controller for the client computer's GUID. If the server fails to find the GUID, it queries the global catalog for the forest. If the GUID is found in either location, the client computer is considered "known." If the GUID is not found, it is considered "unknown." In this case --that is, the query by the RIS server found no computer account object in Active Directory with this computer's GUID --only RIS servers that are configured to answer unknown clients will do so.

If the client is known, all the available RIS servers query the domain to determine whether the client computer account has been prestaged with settings that specify that the client computer is to be answered by a particular server. If so, only the designated server answers the service request. The other servers respond by telling the client which server will answer it. This is called a referral. If the client computer account settings do not require the client computer to be answered by a particular server, all RIS servers answer it if they are aware of this client and configured to answer it. Each RIS server then offers its own files to download.

For information on configuring how RIS servers respond to client computers, see Configure Remote Installation Services. For information on prestaging clients computers and configuring the setting that specifies whether the client computer is to be answered by a particular server, see Prestage client computers.

After the client computer receives a reply to its service request, it initiates a Trivial File Transfer Protocol (TFTP) download of the bootstrap program. The Remote Installation Services implementation of this program is called Startrom.com (located at \\RIS_server_name\REMINST\oschooser\i386\startrom.com).

After Startrom.com has been downloaded, the client computer runs it. The default version of Startrom.com then prompts the user to press F12 to initiate a network installation. If the user fails to press F12 within three seconds, the network boot is stopped, and the client computer attempts to start up from the next available boot device. When the user presses F12, the client computer uses TFTP to download the Client Installation Wizard. The wizard then requests the user to log on to the network. For more information about user choices available during remote installation, see Perform a network installation using RIS and Installation options available through RIS.

For information about security limitations related to the PXE standard, see PXE architecture, RIS, and security considerations.

Considerations for 64-bit client computers

For 64-bit client computers, Startrom.com is not required and the F12 prompt is not provided to the user. The 64-bit client computer simply downloads the Extensible Firmware Interface (EFI) version of the Client Installation Wizard (located at \\RIS_server_name\REMINST\oschooser\ia64\oschoice.efi) when the user selects a remote installation option during computer startup.

The 64-bit client computers can request service from RIS servers even if the servers are configured not to answer clients. These client computers can request service if they have received a referral from one of the other RIS servers in the same forest.

Note

  • This topic does not apply to Windows Server 2003, Web Edition.

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