What is "SERVFAIL" mean?

[HeePok Lee]

Hi all!!!

When I use nslookup with debug mode,
I got a below message.
But I don't know meaning of "SERVFAIL".
And I don't know what is difference between "SERVFAIL" and "NXDOMAIN"
Could you explain about it?
Thank you!!!



$ nslookup -debug 12.21.2.1
Server:  ns.dacom.co.kr
Address:  164.124.101.2
.
.
.
.
;; res_mkquery(0, 1.2.21.12.in-addr.arpa, 1, 12)
timeout (5 secs)
timeout (10 secs)
timeout (20 secs)
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 50951, rcode = SERVFAIL
        header flags:  response, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 0,  additional = 0

    QUESTIONS:
        1.2.21.12.in-addr.arpa, type = PTR, class = IN

------------
*** ns.dacom.co.kr can't find 12.21.2.1: Server failed    





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