How to configure DHCP to work with LANDESK PXE boot

Version 7

    Disclaimer

     


    Related: About LANDESK Management Suite PXE


    Description

     

    When PXE booting using LANDESK PXE boot, a DHCP server is necessary to provide an IP Address. However, there are 4 scope options in DHCP that are related to PXE. This article summarizes them and their settings.


    DHCP Scope Options

     

    There are 4 DHCP Scope options related to PXE that can work in 2 sets of 2:

     

    • 43 and 60
    • 66 and 67

     

    OptionNameDescription
    43Vendor SpecificVendor specific information
    60Class IDClass Identifier
    66Server-NameTFTP Server Name
    67Bootfile-NameBoot File Name

     

     

    When a PXE client boots, it sends out a DHCP request. This DHCP request contains option 60 to identify it as coming from a PXE client and not an OS.

     

    A normal (Microsoft) DHCP server will reply with a DHCP provided IP address but, when neither option 60 nor option 43 is set in the DHCP Scope options, the PXE clients will still have no clue where the PXE server is and will therefore wait until a PXE server contacts them. In this way, the PXE server must listen to DHCP discovery packets containing option 60 sent by PXE clients and answer at the same time as the DHCP server does. This is the default method and also the reason why you might need to add IP Helper addresses of the IP of your PXE Representative to your VLAN configuration in the same way you would for a DHCP server when the clients and your DHCP/PXE are in seperate VLANS.

     

    However, a DHCP Server that also has the PXE representative installed will send out only 1 reply, so we need option 60 set in DHCP. When option 60 is set to 'PXEClient', it means that the DHCP server knows where the PXE server is. If option 43 is not set, it means the PXE server is on the same computer as the DHCP server (same IP address). If option 43 is set, PXE clients must decode option 43 to know how to reach the PXE server.

     

    Option 60 is not normally available in DHCP, but can be created and set automatically by running the following commands:

    netsh dhcp server add optiondef 60 PXEClient String 0 comment=PXE support

    netsh dhcp server set optionvalue 60 STRING PXEClient

    After the client receives the PXE answer it needs to go to the next step, which is to download a boot environment. This is where DHCP options 66 and 67 come in. Option 66 tells the PXE booted client what the Bootserver is and option 67 the Bootfile that needs to be loaded.

     

    These 2 options (66 and 67) don't work with LANDESK PXE representatives and should always be left unconfigured.

     

    The LANDESK PXE makes use of an extra layer in the bootprocess, the LANDESK PXE menu, which includes options for Local Boot, WinPE menu, WinPE Provisioning etc. Configuring the DHCP option 66 and 67 means a PXE Boot will equal a boot to a boot environment like WinPE, which presents no flexibility.

     

    Summary:

     

    • Set Option 60 if the PXE representative is installed on a DHCP Server, leave option 43 unconfigured.
    • Set Option 60 in combination with option 43 if the PXE representative is not on the DHCP server, but also not in the broadcast range of the client
    • Options 66 and 67 should NOT be set.