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This should be a simple question to answer, I'm just not that experienced yet.

I'm in the process of setting up an Active Directory domain in an existing office network. The network previously consisted of only a dozen Windows machines and a few VoIP phones, all handled using the router's DHCP. I've added to this a Windows Server 2019 machine, which we'll call Controller, that has been configured as the domain controller of a new domain, which we'll call mydomain.com.

So far so good. The problem comes when I try to join machines to the domain.

When attempting to join a Windows 10 Pro machine to the domain, I get the message:

An Active Directory Domain Controller for the domain "mydomain.com" could not be contacted.

I did some ping testing:

  • ping xxx.xxx.xxx.xxx (Controller's IP address) works.
  • ping Controller also works.
  • ping mydomain.com resolves to some public address, not the address of Controller.

So the problem is with DNS, it seems.

Since the network is governed by the router (DHCP and DNS), I'm assuming I need to configure the router to use Controller as a DNS server. I'd like some guidance on how to properly do that.

The router is an Arris TG1682G. This is what the current LAN configuration page looks like: current LAN configuration

The "?" icons provide some tool tips that might be useful:

  • DNS Override:
    DNS Override tool tip

  • DNS Relay:
    DNS Relay tool tip

Which settings do I need to change so that the router will try to resolve mydomain.com internally first, using Controller, before attempting to resolve it externally?

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To answer your question, you need conditional dns forwarding. When a query for mydomain.com (or any other dns domain you need to exclude from your dns to answer) is done, it'll be forwarded to another dns server. In this case, Controller.

But, if conditional dns forwarding is not supported in your router's dns server, you can use Controller as the 1st dns server for your clients. To be honest, in order for your AD domain to work properly, that should be the setup. Each time you join a pc in the domain, a computer account is made and also dns entries, both in forward and reverse zones. It'll be difficult, if not impossible, to achieve this on a third party dns server, especially in an embedded one in a router.

So I suggest you to use Controller as your main dns server, allow it to resolve to Internet also, in order for your clients to be able to browse the Internet. Another suggestion would be to name your domain mydomain.local to avoid conflicts with existing dns domain names in Internet.

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  • Thanks. I guess my only other confusion is which setting on the router I need to change in order to set Controller as the main DNS server. Should I use "DNS Override" or "DNS Relay"? I added the descriptions for both to the question so you can see an explanation of what they do. Hopefully you'll understand a bit better than me. – Keith Stein Jun 19 '20 at 21:04
  • You need to change nothing regarding dns on the router. You better not, so that it can still access the Internet. My oversight, if you are going to use controller as dns server, it's better to use it as dhcp server also. So disable dhcp on router, leave router's dns settings as is, and then on the dhcp settings of controller's dhcp server, set controller as dns server for the clients. – Krackout Jun 19 '20 at 21:16
  • So, if I install and configure the DHCP role on Controller and then disable DHCP on the router, will Controller automatically take over as the DHCP server for the network? Even for non-domain and non-Windows machines (like the IP phones)? – Keith Stein Jun 19 '20 at 21:35
  • Yes. A dhcp client, any client, broadcasts that it's trying to discover a dhcp server. The server responds, offering an IP. No need to be related to ad domain. So in your scenario, just leave one dhcp server, your DC, to do the job and co-operate with its dns and active directory services. – Krackout Jun 19 '20 at 21:47
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    Just to put the final nail in this question: Today we rechecked the DNS servers being used by the Windows 10 machine (using ipconfig) and it showed it was using the external DNS servers, not Controller. This made much more sense. I figured out I had to add Controller's IP address to the "DNS Servers" setting in the DHCP scope. This finally fixed the name resolution for the domain. – Keith Stein Jun 25 '20 at 23:59

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