Configuring InfoBlox Appliance for PXE Forced Mode

Products

Deployment Solution

Issue/Introduction

An Infoblox DHCP appliance is being used to manage the distribution of DHCP addresses to client systems. However, when the Altiris PXE(version 7.1) boot process is introduced to the DHCP environment with options 60,66,67 and 43, the client systems never receive the PXE Boot menu and will fail to complete the PXE boot process. When using Symantec recommended DHCP options (For Infoblox appliances) as mentioned in article TECH40756 and TECH43159.

PXEpreZero: PXEPreXZero error invalid DHCP option format

Environment

Created Using InfoBlox Firmware 5.1r5-9-153574

Cause

The problem is two fold. First when a client machine boots with PXE booting it doesn’t actually look at option 60, 66 or 67. Instead, clients are actually looking at the value: “Boot File” and "Next Server IP address". If these entries are left blank or not defined, the client machine PXE booting will assume that the DHCP server is also acting as the TFTP server (DHCP server is not the same in our environment). It can be seen by network captures that the PXE process gets to the point where the client makes a TFTP read request to the Infoblox server (which it can’t respond to, since it is not acting as a TFTP server).

The other part of the problem is option 43. Infoblox will only accept HEX values in a specific format. The string provided in most KB article does not work as its not in true Hexadecimal format. The Infoblox required format does not like leading zeros except for “0A” which in hex is 8.

Please keep in mind Microsoft DHCP server takes the value in option 66 , and then sets it as value of "Next Server IP address". The problem is that not all DHCP servers automatically put the IP address of DHCP option 66 and replaces it with "Next Server IP address". Apparently, ISC's DHCP does not as well.

Resolution

Configure Infoblox appliance with Following BootP and DHCP options: (For individual subnet)

Go to “Data Management” tab once you are logged in.
Click “DHCP” tab
Click “Network” tab
Select the Network you want the PXE server settings implemented on
Click the “Edit” button to open up properties of the subnet (far right column)
Click “BootP” from the left column
Under BOOTP settings Enter, Boot File and Next server values. (Boot File(BStrap\X86pc\BStrap.0) is the image file residing on your PXE server and Next server is IP address (xxx.xxx.xxx.xxx)of the PXE server)
Click “DHCP” from the left column, scroll down till you see the “Custom DHCP Option”
Click + sign to add an option and pick option 43 Vendor-encapsulated-options
Copy and paste this value “6:1:B:8:7:AA:AA:1:0A:1E:81:CE” (Notice no leading zeros except in 0A)
1. (This HEX is an example only. The base Hex can be created using the “PXE Forced Mode Utility” in KB 180449
Click “Save & close”
Restart the services and test your client.

*Note: In at least one case of issues PXE booting with Infoblox DHCP, DHCP Snooping was required to be set to TRUST on the network ports for the PXE Sever. However, this may not be required for all PXE environments using Infoblox DHCP.

Symantec Support would like to thank Tanuja Shah and Giles Haney with Montgomery College in providing the information to make this article possible.