How to Configure DHCP Option 119 in Windows DHCP Server and Cisco Switch

This post is to document the process to configure DHCP option 119 in Windows DHCP Server and Cisco Switch.

Environment

Windows Server 2022 Domain Controller with DHCP roles configured

Windows 10 devices on the end user side

Multiple Domains with two-way trust configured

DNS Suffix needs to be configure for both domains: ICTFella.com and DomainAA.com

Windows 10 devices has DHCP Option 119 supported since 2018

Configure DHCP Predefine Options

Go to your DHCP server, expand it out and right click on “IPv4” – “Set Predefined Options

Click on the “Add” button and use below values for “Option Type”, give it a Name and Description as well.

1. Data Type: Byte
2. Array: Ticked
3. Code: 119
dhcp-option-predefined-options-and-values-add-domain-search-list-byte-array-119

Click “OK’ for now, we will configure the Array soon

Window DHCP Option 119 – Value/Array Configuration

The URL below is a brilliant GitHub online page for encoding DHCP Option for different devices, I personally haven’t test the PowerShell yet, as I prefer do it manually. Obversely you can use

https://jjjordan.github.io/dhcp119/

Prepare a simply table as below as we need to configure the array from the bottom.

ObjectHex ValueDHCP Array Value
Number of characters for the next string080x8
I690x69
C630x63
T740x74
F660x66
e650x65
l6c0x6c
l6c0x6c
a610x61
Number of characters for the next string030x3
c63 0x63
o6f0x6f
m6d0x6d
Space – End of the first domain000x0
Number of characters for the next string070x7
D640x64
o6f0x6f
m6d0x6d
a610x61
i690x69
n6E0x6e
a610x61
Number of characters for the next string030x3
c630x63
o6f0x6f
m6d0x6d
Space – End of the first domain000x0

Now you can click “Edit Array” and add the Hex Value one by one:

On Cisco Devices

ip dhcp pool POOL_NAME
    option 119 hex 0869.6374.6665.6C6C.6103.636F.6D00.0764.6F6D.6169.6E61.0363.6f6d.00

Useful Links

https://docs.microsoft.com/en-us/windows-server/networking/technologies/dhcp/what-s-new-in-dhcp

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