Troubleshooting › DHCP Server Does Not Provide Boot Server Information

DHCP Server Does Not Provide Boot Server Information

Symptom:

The DHCP server is not providing the boot server information.

Solution:

This happens if your boot server is not located on the DHCP server.

With PXE 2.x clients, you can assign a different boot server using the DHCP option 43 (encapsulated vendor-specific options). The DHCP server must be configured to provide additional boot server information in the DHCP offer using option 60 and option 43:

• Option 60: vendor-class-identifier
• Option 43: with the suboptions 6,8,9,10,71

After the PXE client has received an IP address from the DHCP server, the PXE client must send a DHCP Request to the specified boot server (in option 43:Suboption 8: PXE boot servers) to get the boot image file name.

Example: DHCP Offer

    Option 53: DHCP Message Type = DHCP Offer 
    Option 54: Server Identifier = 192.168.111.131 
    Option 60: Vendor class identifier = "PXEClient" 
    Option 97: UUID/GUID-based Client Identifier (17 bytes) 
    Option 43: Vendor-Specific Information (PXEClient) 
        Suboption 6: PXE discovery control = 2 
        Suboption 8: PXE boot servers (7 bytes) 
        Suboption 9: PXE boot menu (38 bytes) 
        Suboption 10: PXE menu prompt (24 bytes) 
        Suboption 71: PXE boot item (4 bytes) 
        End PXEClient option 
    End Option 
    option 43 in detail: 
    2b 55 06 01 02 08 07 00 07 01 c0 a8 6f 83 09   +U..........o.. 
    26 00 07 23 43 41 2d 55 6e 69 63 65 6e 74 65 72  &..#CA-Unicenter 
    20 4d 61 6e 61 67 65 64 50 43 20 42 6f 6f 74 20   ManagedPC Boot 
    53 65 72 76 65 72 00 0a 18 00 50 72 65 73 73 20  Server....Press 
    46 38 20 74 6f 20 76 69 65 77 20 6d 65 6e 75 00  F8 to view menu. 
    2e 47 04 00 08 00 00 ff                          .G...... 

In the above example, c0 a8 6f 83 is the IP address of the OSIM boot server.

Notes:

• The detail of option 43 above shows the complete hex string of the option.
• When defining the value for option 43, do not include the first 2 bytes (2b 55) as these are added by the DHCP server. (2b is the descriptor for option 43 and 55 is the length).
• Ensure that the DHCP offer should not contain option 67: boot file name
• Option 60 is not a standard option and must be manually added using netsh.exe

To add DHCP option 60 to DHCP server (Windows 2000 or later)

1. Open the command prompt.
2. Type netsh.
3. Type dhcp.
4. Type server \\servername or server ip_address

   A command prompt with the title dhcp server appears.

5. Type the following commands for PXE support:

   add optiondef 60 PXEClient STRING 0 comment=option added
   

   optionvalue 60 STRING PXEClient 
   

6. Type the following command to confirm that everything has been set correctly:

   show optionvalue all