I've used xinetd to set up a test nameserver on port 1024. Here's the Net::DNS Perl I'm using to say (falsely) that news.yahoo.com resolves to 10.1.2.3 with a TTL of 1 day: 

$res = Net::DNS::Packet->new(); 
$rr = Net::DNS::RR->new("news.yahoo.com. 86400 A 10.1.2.3"); 
$res->push(answer => $rr); 
print $res->data;

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According to Net::DNS, here's the prettyprint version of the packet I create: 

;; HEADER SECTION
;; id = 26432
;; qr = 0    opcode = QUERY    aa = 0    tc = 0    rd = 1
;; ra = 0    ad = 0    cd = 0    rcode  = NOERROR
;; qdcount = 1  ancount = 1  nscount = 0  arcount = 0

;; QUESTION SECTION (1 record)
;; .    IN      A

;; ANSWER SECTION (1 record)
news.yahoo.com. 86400   IN      A       10.1.2.3

;; AUTHORITY SECTION (0 records)

;; ADDITIONAL SECTION (0 records)

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It's ugly and minimal, but is it a valid DNS answer? Does the question section actually have to contain the question asked or is that optional?

When I try using dig to test, I get this error: 

> dig -p 1024 @localhost news.yahoo.com

; <<>> DiG 9.3.1 <<>> -p 1024 @localhost news.yahoo.com
; (1 server found)
;; global options:  printcmd
;; connection timed out; no servers could be reached

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My debug logs show that my test nameserver is called thrice (dig tries 3 times by default?) with this packet (prettyprinted below): 

;; HEADER SECTION
;; id = 41909
;; qr = 0    opcode = QUERY    aa = 0    tc = 0    rd = 1
;; ra = 0    ad = 0    cd = 0    rcode  = NOERROR
;; qdcount = 1  ancount = 0  nscount = 0  arcount = 0

;; QUESTION SECTION (1 record)
;; news.yahoo.com.      IN      A

;; ANSWER SECTION (0 records)

;; AUTHORITY SECTION (0 records)

;; ADDITIONAL SECTION (0 records)

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I did notice the packet dig sends has id=41909 and my response has id=26432-- is that a problem?

I'm pretty sure the problem isn't with xinetd and that dig is getting my response packet-- it just doesn't seem to like it for some reason.

20061220 Janitored by Corion: Added formatting, code tags, as per Writeup Formatting Tips

In reply to Minimal DNS answer using Net::DNS by kelly.terry.jones

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