I did:

=>dig -x 44.24.240.173 @a.ns.hamwan.net.

; <<>> DiG 9.2.4 <<>> -x 44.24.240.173 @a.ns.hamwan.net.
; (1 server found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55622
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;173.240.24.44.in-addr.arpa.    IN      PTR

;; ANSWER SECTION:
173.240.24.44.in-addr.arpa. 3600 IN     PTR     ae7q.hamwan.net.

;; Query time: 147 msec
;; SERVER: 44.24.244.2#53(44.24.244.2)
;; WHEN: Thu May 15 20:44:05 2014
;; MSG SIZE  rcvd: 73

=>dig ae7q.hamwan.net. @a.ns.hamwan.net.

; <<>> DiG 9.2.4 <<>> ae7q.hamwan.net. @a.ns.hamwan.net.
; (1 server found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46180
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;ae7q.hamwan.net.               IN      A

;; AUTHORITY SECTION:
ae7q.hamwan.net.        3600    IN      NS      ns1.ae7q.ampr.org.

;; Query time: 101 msec
;; SERVER: 44.24.244.2#53(44.24.244.2)
;; WHEN: Thu May 15 20:45:39 2014
;; MSG SIZE  rcvd: 64

=>dig ns1.ae7q.ampr.org. @ampr.org.

; <<>> DiG 9.2.4 <<>> ns1.ae7q.ampr.org. @ampr.org.
; (1 server found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27978
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 7, ADDITIONAL: 1

;; QUESTION SECTION:
;ns1.ae7q.ampr.org.             IN      A

;; ANSWER SECTION:
ns1.ae7q.ampr.org.      3600    IN      A       44.24.240.173

;; AUTHORITY SECTION:
ampr.org.               3600    IN      NS      ampr-dns.in-berlin.de.
ampr.org.               3600    IN      NS      ampr.org.
ampr.org.               3600    IN      NS      munnari.OZ.AU.
ampr.org.               3600    IN      NS      ns1.defaultroute.net.
ampr.org.               3600    IN      NS      ns2.threshinc.com.
ampr.org.               3600    IN      NS      ns0.comgw.net.
ampr.org.               3600    IN      NS      hamradio.ucsd.edu.

;; ADDITIONAL SECTION:
ampr.org.               3600    IN      A       44.0.0.1

;; Query time: 157 msec
;; SERVER: 44.0.0.1#53(44.0.0.1)
;; WHEN: Thu May 15 20:47:46 2014
;; MSG SIZE  rcvd: 263


Now, this is not correct.  While I appreciate the PTR record for 44.24.240.173, it needs to point to a hostname record ("A" or CNAME"), not a domainname record.  This is not the fault of the PTR record, but the record that it points to:  The NS record for ae7q.hamwan.net effectively declares ae7q.hamwan.net as a subdomain, with ns1.ae7q.ampr.org as its nameserver.  Now, ns1.ae7q.ampr.org has the IP address of 44.24.240.173, but that doesn't mean that the domain ae7q.hamwan.net is anywhere near 44.24.240.x.

The correct solution to this problem is to replace the NS record for ae7q.hamwan.net with a reference to a host;  eg:
  1. ae7q.hamwan.net.  3600  IN  A       44.24.240.173
  2. ae7q.hamwan.net.  3600  IN  CNAME   ns1.ae7q.ampr.org.
The administrative advantage of the CNAME is that if my IP address changes, you don''t have to change the forward record (you'll still have to update PTR records).  The administrative disadvantage is that the CNAME is dependent upon a different administrative organization.  However, neither solution above allows for ae7q.hamwan.net to be a subdomain.

If you want to allow ae7q.hamwan.net to be a subdomain, you need to lay the following foundation:

173.240.24.44.in-addr.arpa.  3600  IN  PTR  ns1.ae7q.hamwan.net.  ; (or ns1.ae7q.ampr.org.)
ae7q.hamwan.net.             3600  IN  NS   ns1.ae7q.hamwan.net.  ; (or ns1.ae7q.ampr.org.)
ns1.ae7q.hamwan.net.         3600  IN  A    44.24.240.173         ; (if
ns1.ae7q.ampr.org. is not used)

That by itself will not allow me to add subdomain records, but it lays the foundation.  I prefer creating ns1.ae7q.hamwan.net (all three records above), as it keeps the records independent of a different administrative organization.

If you want to get carried away, you could also add the following record:

www.ae7q.hamwan.net.  3600  IN  CNAME   ns1.ae7q.hamwan.net.  ; (or ns1.ae7q.ampr.org.)

-- Dean