DHCP Test Tool

I had to check my DHCP configuration for a Dell Wyse Thin Client. But when you configure specific options like 161 and 162 you don’t see that options in a Wireshark capture during a Windows DHCP request.

Luckily for us CyberShadow created a great tool to test some specific DHCP settings an he even make it open source: https://github.com/CyberShadow/dhcptest

This DHCP tool have 2 great features:

  1. You can do a request for specific DHCP option
  2. You can send a vendor class so in my case I can pretend to be a Wyse Thin client.

DHCP Request Option

This will only work when you have configured Global DHCP settings.

dhcptest.exe --query --request 161

DHCP Vendor Class

First I had to figure what the vendor class was. I checked this on the DHCP server:

Or on a Thin client itself:

Then run this command:

dhcptest.exe --query --option "60=wyse-1000"

And you will get Vendor Specific Information in Hex.

You can do different things to translate the Hex into readable data.

  1. Compile the open source yourself yourself and create a output in a string
  2. Use a (online) hex convertor
  3. Open wireshark during the capture. Wireshark will translate this for you 🙂

Compile the tool

  • Download the git repo
git clone https://github.com/CyberShadow/dhcptest.git
  • Edit the file (add these 2 lines)
161 : DHCPOptionSpec("File Server", OptionFormat.str),
162 : DHCPOptionSpec("Root Path to the File Server", OptionFormat.str),
dmd dhcptest.d

This will create a exe for you and will translate the Hex to readable format.

Happy sniffing!

Author: Thomas Faddegon

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