How come DNS names resolve in this case?

CodeBlox · February 2012

I'm working on 70-640 and am finding it really cool to learn how some of this stuff is actually done. I'm on a helpdesk currently and we use AD a lot. Anyway, here is the scenario: I have a domain controller on my home network and it uses itself as the domain controller. Currently in the IPv4 settings, it points to 127.0.0.1. I joined another computer to the domain and pointed it to this domain controller as its DNS server. These devices have a valid default gateway configured with a connection to the internet. My question is, why am I able to still connect to websites using hostname instead of IP addresses? Neither computer points to my router as its DNS server nor do they point to any other DNS server. Are the computers somehow dynamically searching the network for a DNS server?

halaakajan · February 2012

In order to have a DC in an environment the DC itself should be a DNS server. When you install ADDS it asks you to install DNS, so you have DNS server because as you mentioned you directed the DNS of the 2nd Machine to the DC and the DC itself has the 127.0.0.1(localhost) directed. That is what I know.

atorven · February 2012

The DC doesn't have to have the DNS role installed in order to function, in your case, I assume you when you installed you ADDS role you may have installed the DNS role in which case the server will use the preconfigured root hints in order to resolve any external names.

Good luck on your 70-640 studies, lots of cool and some boring stuff ahead!

CodeBlox · February 2012

I installed the DNS Role on the first domain controller as well as the second. Seems like it resolves any hostname I throw at it. I was just expecting to get something like "ping request could not find host...". At work, I was always wondering why that sometimes happened and I think I see why now.

ptilsen · February 2012

As atorven indicated, your DNS server will forward to root hints out of the box. If you remove all forwarders and purge the DNS cache from your DC/DNS server and workstation, you will know longer resolve web addresses as you are expecting.

CodeBlox · February 2012

This is good to know. Did some googling and the file that stores this root hints information is at %systemroot%\system32\dns\cache.dns There are several mappings between DNS servers and IP addresses in the file. Very nice!!!

MentholMoose · February 2012

Your DC has a DNS server installed so it can receive DNS queries from clients, determine the answer to the query ("resolve" it), and provide the answer back to the client. Windows DNS server can resolve queries directly (i.e. use the root hints for queries it cannot answer itself), or it can be configured as forwarder in which case it would not resolve most queries itself and instead would forward to another DNS server (which would resolve the query directly, or forward to yet another DNS server), which is probably what your router does (it likely forwards queries to your ISP's DNS servers).

Wikipedia has a nice article on DNS (Domain Name System - Wikipedia, the free encyclopedia)... especially check out the "Address resolution mechanism" to help understand how it works. Also, if you have a study guide for 70-640 it should have a section on DNS. One handy way to really "see" how it works is to do a packet capture on the DC and look at the packets with Wireshark.

How come DNS names resolve in this case?

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