When running nslookup on Windows, you might encounter the following output:
*** Can't find server name for address 172.27.0.12: Non-existent domain
*** Default servers are not available
Default Server: Unknown
This occurs when:

1. Your DNS server (172.27.0.12 in this case) doesn't have a PTR record for its own IP address

2. The reverse DNS lookup fails while nslookup tries to display a friendly server name
Despite the warning messages, your DNS queries succeed because:
> chj.dev.nls
Server:  UnKnown
Address:  172.27.0.12

Name:    chj.dev.nls
Address:  172.27.0.120
The DNS server is fully functional - it's just the reverse lookup that fails during nslookup's initialization.
When nslookup starts, it performs these steps:

1. Contacts the DNS server specified in your network configuration

2. Attempts a reverse DNS lookup (PTR record query) for that server's IP

3. If unsuccessful, displays the "Unknown" status
The debug output reveals:
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
Option 1: Add PTR record

On your DNS server (172.27.0.12):
dnscmd /recordadd 11.168.192.in-addr.arpa. 120 PTR yourservername.domain.com
Option 2: Specify server explicitly
nslookup
> server 172.27.0.12
Default Server:  [172.27.0.12]
Address:  172.27.0.12
Option 3: Check DNS configuration

Verify with:
ipconfig /all | find "DNS Servers"
nslookup -querytype=soa yourdomain.com
This is primarily a cosmetic issue unless:

- You see actual query failures

- Other DNS-dependent services malfunction

- The warning appears with multiple DNS servers
For more detailed analysis:
nslookup -d2 yourdomain.com > dnsdebug.log
netstat -ano | find "53"
dnscmd /info

When running nslookup on Windows, you might encounter the following output:
*** 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

The message indicates that while your DNS server (172.27.0.12 in this case) is responding to queries, nslookup cannot resolve its own hostname. This occurs because:

The DNS server doesn't have a PTR record for its IP address
Reverse DNS lookup is failing for the server's IP
The server is configured to respond to queries but not to identify itself

When nslookup starts, it attempts to:
1. Resolve the DNS server's IP to a hostname (reverse lookup)
2. Display the server's friendly name
3. If step 1 fails, it shows "UnKnown"
This doesn't affect functionality - queries still work as shown in your example:
> chj.dev.nls
Server:  UnKnown
Address:  172.27.0.12

Name:    chj.dev.nls
Address:  172.27.0.120
Check if your DNS server has a PTR record:
nslookup -type=ptr 172.27.0.12
For Windows DNS servers, ensure reverse lookup zone is configured:
dnscmd /enumzones | find "in-addr.arpa"
The "UnKnown" message is typically harmless if:

Forward lookups work correctly
You're not using features that require reverse DNS
The server is internal/private

Consider fixing it if:

You need proper server identification
Applications require reverse DNS
You're troubleshooting mail servers

For deeper investigation, use these commands:
nslookup -debug
nslookup -d2
dcdiag /test:dns /v
To check DNS server responsiveness:
Test-NetConnection -ComputerName 172.27.0.12 -Port 53
To add a PTR record in Windows DNS Manager:
1. Open DNS Manager
2. Expand Reverse Lookup Zones
3. Right-click → New Zone (if needed)
4. Add PTR record for your server's IP