Delegation question

[Jean-Yves Avenard]

Hi there..

I'm trying to create a delegation to a sub-domain ; for some reasons
I'm getting no-where

I have a domain.com zone ; I'd like to delegate mel.domain.com to
another dns server (windows server DNS fwiw)
Here is my zone file:
$ORIGIN .
$TTL 7200       ; 2 hours
domain.com.             IN SOA  m.domain.com. domainmaster.domain.com. (
                                2011020405 ; serial
                                7200       ; refresh (2 hours)
                                1800       ; retry (30 minutes)
                                1209600    ; expire (2 weeks)
                                86400      ; minimum (1 day)
                                )
                        NS      m.domain.com.
                        MX      0 mail.domain.com.

$ORIGIN domain.com.
                        A       192.168.0.2
; glue record
m                       A       192.168.0.2
mel                  A      192.168.0.3
;                         NS ad.domain.com
ad                      A       192.168.0.3
---


when NS ad.domain.com line is commented out ; querying for
mel.domain.com is properly resolved:

bash-3.2# dig @192.168.0.2  mel.domain.com

; <<>> DiG 9.6.0-APPLE-P2 <<>> @192.168.0.2 mel.domain.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2718
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1

;; QUESTION SECTION:
;mel.domain.com.			IN	A

;; ANSWER SECTION:
mel.domain.com.		7200	IN	A	192.168.0.3

;; AUTHORITY SECTION:
domain.com.		7200	IN	NS	m.domain.com.

;; ADDITIONAL SECTION:
m.domain.com.		7200	IN	A	192.168.0.2

;; Query time: 0 msec
;; SERVER: 192.168.0.2#53(192.168.0.2)
;; WHEN: Fri Feb  4 21:45:55 2011
;; MSG SIZE  rcvd: 80

Now if I uncomment the NS ad.domain.com. mel.domain.com will not
resolve anymore:

bash-3.2# dig @192.168.0.2  mel.domain.com

; <<>> DiG 9.6.0-APPLE-P2 <<>> @192.168.0.2 mel.domain.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 5170
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;mel.domain.com.			IN	A

;; Query time: 30 msec
;; SERVER: 192.168.0.2#53(192.168.0.2)
;; WHEN: Fri Feb  4 21:48:54 2011
;; MSG SIZE  rcvd: 32

For what it's worth; ad.domain.com (the other dns server) properly
answer the query:
bash-3.2# dig @192.168.0.3  mel.domain.com

; <<>> DiG 9.6.0-APPLE-P2 <<>> @192.168.0.3 mel.domain.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36709
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;mel.domain.com.			IN	A

;; ANSWER SECTION:
mel.domain.com.		600	IN	A	192.168.0.3

;; Query time: 0 msec
;; SERVER: 192.168.0.3#53(192.168.0.3)
;; WHEN: Fri Feb  4 21:49:42 2011
;; MSG SIZE  rcvd: 48

Could someone explained to me what I'm doing wrong ?
I've read every documents I could find on this topic ; and they are
all doing a similar thing ...

Why can't I define NS for my mel.domain.com ?

Thank you