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DNS and Nslookup question Active Directory

Posted on 2010-11-30
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Last Modified: 2012-06-27
Hi,

I have just type nslookup 'AD domain name' and it returned a list of DC's
but also a strange IP of a subnet.

For example:

Name: gb.vo.local
Addresses: 192.168.21.4
192.168.21.0 (what is this?)
192.168.21.1  - this is DC1
192.168.21.2  - this is DC2

In DNS:

(same as parent folder) - 192.168.21.0

This is 192.168.21.0 the IP of a subnet (what is this?)

I am having the same problem but pointing to a different IP.

http://forums.techarena.in/active-directory/1205416.htm

Why this happens? Any ideas?
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Question by:llarava
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18 Comments
 
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Expert Comment

by:SteveeB
ID: 34241685
192.168.21.0 is not a valid IP address. It  is used in routing tables and by the Internet Protocol internally to identify the 192.168.21.x network as a whole
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Expert Comment

by:BDoellefeld
ID: 34241790
Are you using a 24 bit subnet? What is the subnet mask that is set?
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Expert Comment

by:SteveeB
ID: 34241795
Are you having any DNS problems on the LAN?

(same as parent folder) - 192.168.21.0 this is not good, it should be
(same as parent folder) - 192.168.21.x (x= IP that you want the root of the domain to point to)

so for example if all you have in your dns is (same as parent folder) - 192.168.21.0, and your DNS zone is company.com, if someone will try to ping company.com it will not work.

If you are hosting a website, typically you would point (same as parent folder) - 192.168.21.x to IP of your website so that users can browse the site using company.com
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Author Comment

by:llarava
ID: 34241894
Basically a third party app that was using AD authentication was failing to authenticate because sometimes the query was going to the subnet IP instead of the DC.

I don't know why the IP was registered there...how could you create (same as parent folder) record?

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Expert Comment

by:SteveeB
ID: 34241943
On the domain controller, go to the DNS MMC plugin, look at my screenshot

You can double click on that record and change the 0 to something else.

Is your subnet mask 255.255.255.0 ?
SampleDNS.JPG
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Expert Comment

by:SteveeB
ID: 34241961
It can be created by just creating new (A) record, input the IP in lower portion, leave top portion empty.
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Author Comment

by:llarava
ID: 34242006
You can double click on that record and change the 0 to something else.  --> What is this?

Is your subnet mask 255.255.255.0 ? yes
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Expert Comment

by:SteveeB
ID: 34242089
See the 3rd record from the top in screenshot, you can double click on it, on your DNS server and change the 192.168.21.0 to something else like 192.168.21.1
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Expert Comment

by:SteveeB
ID: 34242100
sorry 4th record from top in my screenshot
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Author Comment

by:llarava
ID: 34242122
Right, the problem is that the record was created there and I don't know why that happened.

My DC's are all good in DNS but somehow this record showed up there...

How do you create a new (same as parent folder) record.
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Expert Comment

by:SteveeB
ID: 34242147
to create a new one, just create a new (A) record, input the IP in lower portion, leave top portion empty.
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Author Comment

by:llarava
ID: 34242215
input the IP in lower portion, leave top portion empty - Can you please give an example of this?
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Expert Comment

by:SteveeB
ID: 34242266
You have access to the domain controller server? If so do you know how to get to the DNS console?
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Author Comment

by:llarava
ID: 34242286
Yes I am in the console. I just don't understand the "IP in lower portion, leave top portion empty"
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Expert Comment

by:SteveeB
ID: 34242335
right click and choose create new (A) record, in window that pop-s up, leave the Name field blank and just put in an IP address, click add host, this will create a new

(same as parent folder) record.
NewDNS.JPG
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Author Comment

by:llarava
ID: 34242475
The question is why would you create (same as parent folder) record?

Thank you!
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Accepted Solution

by:
SteveeB earned 500 total points
ID: 34242549
so that if a client device, lets say IE browser, if you type in url company.com unless there is a (same as parent folder) record it will not be able to resolve to IP address. now usually I know there is a www record but my point is what if you don't use www. in the URL, you need the root record.

Think of it like this as an example
ns1.company.com - 192.168.1.1
ns2.company.com - 192.168.1.2
www.company.com - 192.168.1.6
ftp.company.com - 192.168.1.7
mail.company.com 192.168.1.8
company.com ?

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Expert Comment

by:SteveeB
ID: 34242742
In active directory dns zone this record should point to ip of domain controller
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