DHCP Server Options

[Bankesy]

Good afternoon all,

 

I have posted about this before, but now I am revisiting it and trying to achieve clarity on what I might break or the best way to not break anything.  The goal is to remove an old 2012 DC (Server 1) from the domain, and I was fairly sure that this DC was vital to DHCP, because the newer 2019 DC (Server 2) has the IP for itself and the 2012 DC (Server 1) in DHCP (in both the main 'Server Options' folder and some of the 'Scope Options' folders under the individual scopes).

 

However, looking at the 2012 DC (Server 1), it would appear that the DHCP role isn't even installed, so does this mean that the DHCP settings on the 2019 DC (Server 2) have never been correct, and in reality, clients have only ever received DHCP from the 2019 DC despite IP config showing both? I guess IP config just shows whatever you configure, regardless of whether or not it works when needed? Presumably, if Server 2 has never gone down, there has never been that reliance on Server 1, and we have never noticed it breaks.

 

There is a third DC (Server 3), which has the DHCP role installed but no scopes.  I was thinking I might be able to remove the 2012 DC (Server 1) from DHCP options on the 2019 DC (Server 2) and replace it with the IP for Server 3, but I basically just don't know if this will work or if it is correct given that Server 3 shows no scopes despite having the DHCP role installed.

 

All thoughts and suggestions welcome on this one.

 

Regards

[mavhc]

1. Which servers have the service DHCP Server running?

2. What does ipconfig /all show for a normal client? which server does it say it's using?

[Chris_Cook]

Is it a flat network, or multiple subnets?

 

I'd probably setup a second DHCP server on one of the other DCs and setup failover.

 

If you've got DHCP forwarding setup on your core switch, then that should point to all your DHCP servers. It might also point to an imaging server if you use PXE booting.

[Bankesy]

@mavhc @Chris_Cook

 

1. Server 1 (which I want to retire) has DHCP client service running, Server 3 (which I want to keep) has DHCP server and client service running, Server 2 (the one I want to use in place of Server 1) has DHCP server and client running

 

2. A normal client shows servers 3 and 2 but I guess that is because I have put those IP addresses in the scope options.

 

Thanks

Edited July 25, 2025 by Bankesy

[Davit2005]

On 25/07/2025 at 15:30, Bankesy said:

scope options

What scope options do you mean?

 

DHCP server role can sit on any server, switch or router at the end of the day as long as the clients can get to it whether it is on the same vlan/subnet or a helper address (i.e. on a core switch) if the client is on a different vlan/subnet. Are you on a flat network, do you use a layer 3 core switch for IntervLAN routing, is your firewall relaying DHCP??

 

Fresh out of the box I'm not aware of scopes replicating between windows servers.

Edited July 28, 2025 by Davit2005

[Bankesy]

@Davit2005

 

In DHCP on the 2019 DC that I want to keep, I see a whole list of scopes, and each scope has a 'Scope Options' folder.  This 'Scope Options' folder has an Option Name called DNS Servers, the values for which are the IP address of the 2019 DC itself and the 2012 DC, which I am trying to remove.

 

My simplistic thinking is that I will simply remove the IP address of the old 2012 DC from each scope option and replace it with the IP address of the other 2019 DC. However, I have doubts that this other 2019 DC is properly configured for DHCP, given that I do not see the DHCP scopes on it.

 

 

[Davit2005]

2 hours ago, Bankesy said:

My simplistic thinking is that I will simply remove the IP address of the old 2012 DC from each scope option and replace it with the IP address of the other 2019 DC. However, I have doubts that this other 2019 DC is properly configured for DHCP, given that I do not see the DHCP scopes on it.

 

 

As long as the new DC has DNS configured as all you are doing is giving clients a new DNS server. Nothing to do with DHCP been configured as long as when you do configure DHCP it has the correct DNS options set 🙂 

Edited July 29, 2025 by Davit2005

[mavhc]

In this context DHCP client doesn't matter, so it's just S2 and S3, so there's nothing about DHCP servers on S1, good.

 

DNS can replicate using AD, is that enabled?

 

Looks like you can just remove the IP of S1 from your DHCP options and the clients will pick up S2 and S3 for DNS as you wish

[Davit2005]

As @mavhc mentions Active Directory-Intergrated Zones can be used if DNS roles are installed on Domain Controllers and makes the setup far easier as well as secure.

 

https://learn.microsoft.com/en-us/windows-server/identity/ad-ds/plan/active-directory-integrated-dns-zones

 

Quote

Domain Name System (DNS) servers running on domain controllers can store their zones in Active Directory Domain Services (AD DS). In this way, it is not necessary to configure a separate DNS replication topology that uses ordinary DNS zone transfers because all zone data is replicated automatically by means of Active Directory replication. This simplifies the process of deploying DNS and provides the following advantages:

• Multiple masters are created for DNS replication. Therefore, any domain controller in the domain running the DNS Server service can write updates to the Active Directory-integrated DNS zones for the domain name for which they are authoritative. A separate DNS zone transfer topology is not needed.

• Secure dynamic updates are supported. Secure dynamic updates allow an administrator to control what computers update what names and prevent unauthorized computers from overwriting existing names in DNS.

 

 

[Bankesy]

@mavhc @Davit2005

 

Thanks for your responses, I will investigate whether or not DNS replication via AD is enabled or not.