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I'd like to solve a question with your kind help, about nslookup on Windows. Please see my CMD commands below(run on WinXP SP2).

C:\>ipconfig /all

Windows IP Configuration

        Host Name . . . . . . . . . . . . : vchjXPsp3MUI
        Primary Dns Suffix  . . . . . . . :
        Node Type . . . . . . . . . . . . : Hybrid
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter LAN1-hostvn1:

        Connection-specific DNS Suffix  . :
        Description . . . . . . . . . . . : VMware Accelerated AMD PCNet Adapter

        Physical Address. . . . . . . . . : 00-0C-29-E0-68-00
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.11.120
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.11.1
        DHCP Server . . . . . . . . . . . : 192.168.11.1
        DNS Servers . . . . . . . . . . . : 172.27.0.12
        Primary WINS Server . . . . . . . : 172.27.0.12
        Lease Obtained. . . . . . . . . . : Wednesday, August 03, 2011 8:58:19 AM
        Lease Expires . . . . . . . . . . : Thursday, August 02, 2012 8:58:19 AM

Ethernet adapter LAN2-bridged:

        Media State . . . . . . . . . . . : Media disconnected
        Description . . . . . . . . . . . : VMware Accelerated AMD PCNet Adapter

        Physical Address. . . . . . . . . : 00-0C-29-E0-68-0A

C:\>ipconfig /flushdns

Windows IP Configuration

Successfully flushed the DNS Resolver Cache.

C:\>nslookup
*** Can't find server name for address 172.27.0.12: Non-existent domain
*** Default servers are not available
Default Server:  UnKnown
Address:  172.27.0.12

> chj.dev.nls
Server:  UnKnown
Address:  172.27.0.12

Name:    chj.dev.nls
Address:  172.27.0.120

>

You can see that I have assigned a DNS server in my IP configuration, but WHY does nslookup spouts

*** Can't find server name for address 172.27.0.12: Non-existent domain
*** Default servers are not available
Default Server: Unknown

What does it mean by saying "not available" and Unknown".?

The DNS server(172.27.0.12) is working correctly because it answers query of chj.dev.nls as expected. The DNS server is a Win2003 SP2.

Some detail info:

> set debug
> chj.dev.nls
Server:  UnKnown
Address:  172.27.0.12

------------
Got answer:
    HEADER:
        opcode = QUERY, id = 4, rcode = NOERROR
        header flags:  response, auth. answer, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        chj.dev.nls, type = A, class = IN
    AUTHORITY RECORDS:
    ->  dev.nls
        ttl = 3600 (1 hour)
        primary name server = nlserver.dev.nls
        responsible mail addr = hostmaster.dev.nls
        serial  = 14716
        refresh = 900 (15 mins)
        retry   = 600 (10 mins)
        expire  = 86400 (1 day)
        default TTL = 3600 (1 hour)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 5, rcode = NOERROR
        header flags:  response, auth. answer, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        chj.dev.nls, type = A, class = IN
    AUTHORITY RECORDS:
    ->  dev.nls
        ttl = 3600 (1 hour)
        primary name server = nlserver.dev.nls
        responsible mail addr = hostmaster.dev.nls
        serial  = 14716
        refresh = 900 (15 mins)
        retry   = 600 (10 mins)
        expire  = 86400 (1 day)
        default TTL = 3600 (1 hour)

------------
Name:    chj.dev.nls

>

Any idea? Thank you.

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3 Answers 3

up vote 10 down vote accepted

Nslookup will try to resolve the name for the ip address of the DNS server configured as the primary DNS server on the client by performing a reverse lookup of the ip address. If you don't have a rDNS zone set up for your network/subnet you'll get the "server unknown" message as nslookup will be unable to resolve the name for the ip address.

It's not an error condition and won't cause any problems for normal AD and DNS operations.

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Your server isn't returning a reverse lookup for its name. That's why you're seeing "Unknown" there. You'll need to create the appropriate reverse lookup zone to allow your server to reverse-resolve its own IP address back to its name.

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Well, after adding reverse lookup to my internal DNS server, Default Server now show the domain name of my DNS server.

Sample output:

C:\>nslookup
Default Server:  nlserver.dev.nls
Address:  172.27.0.12

NOTE: If there are multiple names mapping to 172.27.0.12 , Default Server will randomly display one of the names.

enter image description here

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