Can somebody please explain whats going on here?

localuser@localhost:~$ host domain name pointer localhost.

What's up with the IP address being resolved backwards? : ( == ?
Also; what is the significance of this new appendage, accompanying it? : (.in-addr.arpa) ?

Thanks in advance, guys.

  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 12 '17 at 19:11

What you are seeing is the local forward and reverse entry for the ip address (localhost loopback)

in.addr.arpa is a reserved top-level domain for infrastructure purposes.

The reason you see the ip address in reverse format is due to the way DNS works. The notation is used to pass the Forward Confirmed reverse DNS process that is used for verification purposes (e.g. does a mail from the ipaddress really belongs to the domain example.com).

Long story short... in.addr.arpa is a reserved top-level domain for reverse lookups and the inverted format is used because it was specified back in the days. Reverse DNS is used for verifying that a certain ip address really belongs do a domain.

  • Thanks for contributing. Perhaps if you would like to expand your answer, I could mark it as the solution. :) – voices Oct 15 '15 at 6:37
  • I have added some details but will not go further since describing the whole reverse dns process is beyond the scope of the question. ;) – kaisero Oct 15 '15 at 15:42

The reverse order of the IP address on the query is because when you do some research for some IP, the order matters. You need to find a specific machine in some network, and not matching the network part and the host part. You need to go to from the host to the network on a recursive lookup, like it's said on this link.

This reversed ordering of the domains for each octet value is necessary because, unlike DNS names, when IP addresses are read from left to right, they are interpreted in the opposite manner. When an IP address is read from left to right, it is viewed from its most generalized information (an IP network address) in the first part of the address to the more specific information (an IP host address) that is contained in the last octets. For this reason, the order of IP address octets must be reversed when the in-addr.arpa domain tree is built. The IP addresses of the DNS in-addr.arpa tree can be delegated to organizations as they are assigned a specific or limited set of IP addresses within the Internet-defined address classes.


here's a little suitable example for setting up a local reverse zone, is simple in the file "db.127" we have the definition of reverse zone, and then in the following section we have the setting for the zone 127 for the file "named. conf "along with other areas.

db.127 - File Reverse Addres

; ; BIND reverse data file for local loopback interface ;

$TTL    604800

@           IN      SOA     localhost. root.localhost. (
            1    ; Serial
       604800    ; Refresh
        86400    ; Retry
      2419200    ; Expire
       604800 )  ; Negative Cache TTL

@           IN  NS      localhost.
1.0.0       IN  PTR     localhost.
1           IN  PTR     localhost.


- The defination of the reverse address on the named.conf file.

zone        "127.in-addr.arpa"
                  type master;
                file "db.127";

So simple that way ...

  • I'm not sure what I'm looking at.. – voices Oct 26 '15 at 20:37

Not the answer you're looking for? Browse other questions tagged or ask your own question.