How to fix NSLOOKUP Default Server: UnKnown?

Issue : "Default Server:  UnKnown" error on NSLOOKUP from Windows Server DNS Server.

This issue is not a critical one. Even under this error your DNS resolution can work smoothly. But it's embarrassing when there are issues like this. Right?. Yes I know! me too. :D

The reason for this is your DNS server does not posses a record for the server itself. Or simply it does not know what is it's own name. By creating a PTR static entry we can fix this and let DNS server know it's own name.


1. Open the DNS management console in the Server
        Start > Administrative Tools > DNS

2. Go to the your Reverse Lookup Zone icon and right click on it and select "New Pointer(PTR)".

3. In the New PTR window enter the  IP address of DNS server and enter(or select) the host name of the server.

4. Now click OK and restart the DNS server service.

Now check to see if it is working.

How to fix NSLOOKUP *** UnKnown can't find : Non-existent domain?

Issue : " *** UnKnown can't find : Non-existent domain" on NSLOOKUP from Windows Server 2008 DNS server

The reason for this error is there is there is no any Reverse Lookup Zone configured on the server. Or the Reverse zone is crashed. To fix this issue you need to create or reconfigure the reverse lookup zone.

Here is the way to do it.1. Open the DNS management console in the Server 2008
        Start > Administrative Tools > DNS

2. Go to the Reverse Zone Lookup folder icon, Right click on it and Select New Zone

3. New Zone Wizard will open up and click Next.

4. Select Primary Zone as the Zone Type and click Next.

5. Here you can select the Zone Replication Scope as you like. If you are not sure select    servers in the domain and click Next.

6. Select the address type based on your requirement (Here I use IPV4) and Next.

7. Type the first three octets of your network IPV4 address range like 192.168.1 and click Next.

8. Select Secure Update and click Next.

9. Click Finish and Restart the DNS Server service.

Now it will take some time based on the network utilization to learn the addresses and when it is finished your nslookup will work fine.

How to Allow Multiple RDP Sessions in Windows 10

Like in previous client versions of Microsoft operation systems, Windows 10 Pro and Enterprise users can connect to their computers remotely using Remote Desktop service (RDP). There is a restriction on the number of simultaneous RDP sessions: only one remote user can work at a time. When you try to open a second RDP session, the session of the first user is prompted to be closed.

Another user is signed in. If you continue, they’ll be disconnected. Do you want to sign in anyway?

Actually, the number of simultaneous rdp connections is limited rather by the license, which does not allow to create an RDP server based on the workstation for use by several users, than by any technical aspect.

Tip. In Windows 10 Home editions, the incoming remote desktop connections are forbidden at all. The problem, however, can be solved using RDP Wrapper Library.

Let’s consider two ways how to eliminate the restriction of simultaneous RDP connections to Windows 10:

• The Modification of termsrv.dll
• RDP Wrapper Library

Note. System modifications described in the article will be probably treated as a violation of Microsoft License Agreement with all the consequences that come with it.

The Modification of termsrv.dll

The restriction on the number of RDP connections can be eliminated using termsrv.dll file (a library file used by Remote Desktop Services) modification. The file is located in C:\Windows\System32) directory.

Before termsrv.dll file modification, create its backup (if necessary, you can use the original version of the file):

copy c:\Windows\System32\termsrv.dll termsrv.dll_backup

Before termsrv.dll file editing, you have to become its owner and give the Administrators group the full rights to it (all steps are similar to those described in the article “Enable Multiple Concurrent RDP Sessions in Windows 8”). After that, stop Remote Desktop service (TermService) in services.msc console or from the command prompt:

Net stop TermService

For Windows 10 x64 RTM edition (termsrv.dll file version is 10.0.10240.16384):

Open termsrv.dll file using any HEX editor (for example, Tiny Hexer)

Find the line:

39 81 3C 06 00 00 0F 84 73 42 02 00

Replace it with:

B8 00 01 00 00 89 81 38 06 00 00 90

Save the file and run TermService.

The ready patched termsrv.dll file for Windows 10 Pro x64 can be downloaded here: termsrv_for_windows_10_x64_10240.zip

RDP Wrapper Library

The alternative to termsrv.dll file modification is the use of RDP Wrapper Library project. This software serves as a layer between SCM (Service Control Manager) and Terminal Services and allows not only to enable the support of several simultaneous RDP sessions but also to enable the support of RDP Host on Windows 10 Home editions. RDP Wrapper does not make any changes to termsrv.dll file, it just load termsrv with the changed parameters.

Thus, this solution will work even in case of termsrv.dll file update. It allows not to be afraid of Windows updates.

RDP Wrapper can be downloaded from GitHub repository: https://github.com/binarymaster/rdpwrap/releases (the last version available is RDP Wrapper Library v1.6)

Tip. By the way, RDP Wrapper Library source code is also available. It means that if required, you can compile executables by yourself.

RDPWrap-v1.6.zip archive contains some files:

• RDPWinst.exe — an RDP Wrapper Library install/uninstall program
• RDPConf.exe — an RDP Wrapper configuration utility
• RDPCheck.exe — Local RDP Checker — an RDP check utility
• install.bat, uninstall.bat, update.bat — batch files for installation, uninstallation and update of RDP Wrapper

To install the utility, run install.bat with the Administrator privileges.

When the installation is over, run RDPConfig.exe. Make sure that all elements in Diagnostics section are green.

Try to open the second RDP session. It worked out well! Now, our Windows 10 allows two users to start RDP sessions simultaneously.