Comments on: The Mysterious Microsoft DHCP Option ID 81

By: Carl Webster

Carl Webster — Thu, 02 Dec 2021 21:49:59 +0000

Remove-DhcpServerv4OptionValue -ComputerName -OptionId 81 will remove OptionID 81. I have no idea what the side effect is.

Get-DhcpServerv4OptionValue -ComputerName labdc1

OptionId Name Type Value VendorClass UserClass PolicyName
——– —- —- —– ———– ——— ———-
81 DWord {53}
15 DNS Domain Name String {LabADDomain.com}
3 Router IPv4Add… {192.168.1.1}
6 DNS Servers IPv4Add… {192.168.1.201, 1…

remove-DhcpServerv4OptionValue -ComputerName labdc1 -OptionId 81
Get-DhcpServerv4OptionValue -ComputerName labdc1

OptionId Name Type Value VendorClass UserClass PolicyName
——– —- —- —– ———– ——— ———-
15 DNS Domain Name String {LabADDomain.com}
3 Router IPv4Add… {192.168.1.1}
6 DNS Servers IPv4Add… {192.168.1.201, 1…

Thanks

Webster

By: Sebastian Gandini

Sebastian Gandini — Wed, 01 Dec 2021 21:42:24 +0000

I activated option 81 in every scope of a dhcp server. It works fine dealing with some issues but sometimes it has problems when you have a laptop that moves from one scope to another. In this situation you have two different IP leases active in two different scopes and dhcp first update DNS record with the new IP lease and a couple of minutes later it updates the record with the old one.
Is the a definitive way to disable Option 81 as you see in a newly created scope?

By: No One

No One — Thu, 01 Apr 2021 17:09:12 +0000

Option 81 manages the “”Always dynamically update DNS records” option of the scope…

I do not understand why the value can be different, though…

Best I can tell :
-Option 81 with a value of 7 is the same as “Enable DNS dynamic updates if requested by DHCP” and “Dynamically update DNS records for DCP clients that do not request updates (windows NT 4.0)”
-Option 81 with a value of 23 is the same as “Enable DNS dynamic updates, always dynamically update DNS records”