DNS Server : nslookup response "Default Server Unknown

Recently, I got a power Failure in my Data Center and face an Active Directory/DNS Crash as well. I configured Active Directory and DNS as well to support my users and organization and AD start replication but after a day I notice that on nslookup there was a message Default Server: Unknown. Ooops! I was really, really worried that what happens to it. Obviously, I start troubleshooting and the solution was much unexpected to me.

Solution 1:
You need to login your DNS Server and if you haven’t setup your reverse lookup zone, please do create it. If it’s already done than you need to create a PTR Record and point to Server (in my example). After creating PTR Record or configuring Reverse lookup zone, you will be able to see Server Name, as image below.

Solution 2:
In some cases, your DNS may behave differently like it shows exact Default Server Name but on giving any website name (google.com), it show error message like "request timed out. timeout was 2 seconds" etc. in this case you have to check your Firewall on DNS Server or any Firewall between your computer and DNS Server and you have to allow your DNS Server.
Solution 3:
You may notice that even disabling Firewall on DNS Server, Local Computer or even allowing DNS Server in middle Firewall doesn't help then you must check that your DNS Server have properly configured for Live DNS Server's. Please double check Live DNS IP Address in DNS Forwarders and hope these tips will help you, please show yourself in comments to improve the post.


  1. Thank you very much you post helped me resolve my issue - Reverse zone created and configured but the PTR records where missing.

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