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[ScreenOS] Configuring DHCP server with the PXE environment

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Article ID: KB22318 KB Last Updated: 10 Mar 2021Version: 4.0
Summary:
 

This article provides information about configuring the DHCP server on an NS or SSG device for a Pre-boot Execution Environment.

 

Symptoms:
 

Configuring DHCP server on a ScreenOS device with an option for Pre-boot Execution Environment

  • PXE means to boot computers using a network interface independently of data storage devices (such as HDD) or installed OS.

  • This method is mostly used for installing the OS on a computer, without using a CD/DVD drive. The image of the OS is stored on a TFTP server.

 

Solution:
 

Perform the following:

  1. Select DHCP from Network > DHCP:

  1. Select the interface on which you want to create the DHCP server and click Edit:

  1. From the available options, select DHCP Server. Type the relevant information in the required fields, such as Lease, Gateway, Netmask, DNS# 1, and so on. You can also add a domain name and more DNS servers in Advanced Options.

  1. Click Addresses to add an address range from which IPs will be assigned to hosts:

Add a range of addresses. Ensure that IPs assigned to the default gateway, firewall, TFTP server, and so on are not included in this range; else it might create conflict.

A normal DHCP server is now configured. To add options for PXE, proceed to step 5.

  1. Go to Custom Options:

Here you can add any number of options to be sent with DHCP. For details of each option, refer to RFC2132.

  1. Four commonly used options for PXE are:

    1. 43 – Vendor Specific Identifier: This option is a long hex value and has to be specifically calculated, as it is vendor specific, and then configured.

    2. 60 – Vendor Specific Information: This option is entered as a string:

  1. 66 – TFTP server IP: This is the IP address of the server hosting the OS image:

  1. 67 – Bootfile name: This is the name of the file (along with the path if the file is in a directory) on the TFTP server. When providing the path, ensure that you type double back-slash (“\\”), because a single back-slash is an escape character. "\\"will be interpreted as a single "\".

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  1. Return to the Edit interface of the DHCP list:

  1. Check if the Next Server IP option is set to From Option66:

  1. Click Apply and Exit.

Via the CLI:

set interface "ethernet0/4" dhcp server service
set interface "ethernet0/4" dhcp server config updatable
set interface "ethernet0/4" dhcp server option gateway 172.27.199.1
set interface "ethernet0/4" dhcp server option netmask 255.255.255.0
set interface "ethernet0/4" dhcp server option dns14.2.2.2
set interface "ethernet0/4" dhcp server option lease 1440000
set interface "ethernet0/4" dhcp server enable
set interface ethernet0/4 dhcp server ip 172.27.199.11 to 172.27.199.100
set interface ethernet0/4 dhcp server option custom60 String PXEClient
set interface ethernet0/4 dhcp server option custom66 IP 172.27.199.7
set interface ethernet0/4 dhcp server option custom67 String bstrap\\x86\\bstrap.0
set interface "ethernet0/4" dhcp server config next-server-ip option66
save

 

Modification History:
 

2021-03-10: Article checked for accuracy; article found to be valid and relevant

 

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