Technical Tip: How to configure DHCP option 119 (multiple search domains) for different domains

[aabukhshim]

Description

This article describes the steps to configure DHCP option 119 on FortiGate.

Scope

FortiOS.

Solution

Configuration Example Requirements:

• FortiGate’s DHCP server must be configured to use DHCP option 119 for the below domains:
  • test1.local
  • test2.net
  • test3.org

Preparing for the configuration:

•  Break each domain and convert it to Hex, and find the length of each string.
  • test1.local
    • test1 = 7465737431
    • local = 6c6f63616c   
  • test2.net
    • test2 = 7465737432
    • net = 6e6574
  • test3.net
    • test3 = 7465737433
    • org = 6f7267
  • Find the length of each string:
    • test1.local
      • test1 = 05
      • local = 05   
    • test2.net
      • test2 = 05
      • net = 03
    • test3.net
      • test3 = 05
      • org = 03
    • Prepare and append each domain in Hex (string length then string in HEX)
      • test1.local
        •  057465737431056c6f63616c   
      • test2.net
        • 057465737432036e6574
      • test3.net
        • 057465737433036f7267
      • Prepare the HEX for all domains and add 00 in between and 00 at the end
        • test1.local00test2.net00test3.net00
          • 057465737431056c6f63616c00057465737432036e657400057465737433036f726700

FortiGate’s Configuration:

• CLI Configuration:

config system dhcp server

edit 1

config options

edit 1

set code 119

set value "057465737431056c6f63616c00057465737432036e657400057465737433036f726700"

next

end

next

end

• GUI Configuration

Network -> Interface -> select an interface -> DHCP server -> Advanced -> Additional DHCP option -> Create New.

Verification: