Reverse DNS zone not working publicly

Question

I set up a dns server to run publicly and everything is running ok, except for the reverse zone, which locally is successful but doing the query in any other dns gives the following error:

root@ns1:/# nslookup
> server
Default server: 168.121.42.16
Address: 168.121.42.16#53
> labtech.inf.br
Server:     168.121.42.16
Address:    168.121.42.16#53

Name:   labtech.inf.br
Address: 168.121.42.16
> 168.121.42.16
Server:     168.121.42.16
Address:    168.121.42.16#53

16.42.121.168.in-addr.arpa  name = ns1.labtech.inf.br.
> server 8.8.8.8
Default server: 8.8.8.8
Address: 8.8.8.8#53
> labtech.inf.br
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
Name:   labtech.inf.br
Address: 168.121.42.16
> 168.121.42.16
Server:     8.8.8.8
Address:    8.8.8.8#53

** server can't find 16.42.121.168.in-addr.arpa: NXDOMAIN
> exit

My zones files:

 root@ns1:/# cat /etc/bind/zones/db.168.121.42 

$TTL    604800
@   IN  SOA labtech.inf.br. hostmaster.labtech.inf.br. (
        20160607        ; Serial
         604800     ; Refresh
          86400     ; Retry
        2419200     ; Expire
         604800 )   ; Negative Cache TTL
; Name servers
    IN  NS  ns1.labtech.inf.br.

; PTR records
16  IN  PTR ns1.labtech.inf.br.


root@ns1:/# cat /etc/bind/zones/db.labtech.inf.br 


$TTL    604800
@   IN  SOA ns1.labtech.inf.br. hostmaster.labtech.inf.br. (
         20160608       ; Serial
         604800     ; Refresh
          86400     ; Retry
        2419200     ; Expire
         604800 )   ; Negative Cache TTL

; Name servers
labtech.inf.br.     IN  NS  ns1.labtech.inf.br.
labtech.inf.br.     IN  A   168.121.42.16

; A records for name servers
ns1         IN  A   168.121.42.16

; MX records
@   3600        IN  MX  1   mail.labtech.inf.br.


; Other a records
www         IN  CNAME   labtech.inf.br.
mail            IN  A   184.107.51.101  

What could be the problem with this reverse zone?

Answer 1

Zones only become "public" once there's a delegation in the parent zone, and it seems that 168.IN-ADDR.ARPA. doesn't have anything like that right now.

For reverse DNS the delegation needs to be done by whoever owns the IP addresses – i.e. probably your ISP. LACNIC has an article about setting up rDNS.

(To clarify, this has absolutely nothing to do with labtech.inf.br. It's a separate delegation done by a different organization.)