Board index Linux DNS

Moderator: chandranjoy


Postby chandranjoy » Wed Mar 17, 2010 5:34 pm

RDNS(Reverse DNS):

Reverse DNS lookup (also known as rDNS) is a process to determine the hostname associated with a given IP address.

Typically, the DNS is used to determine what IP address is associated with a given hostname; so to reverse resolve a known IP address is to lookup what the associated hostname for it. A reverse lookup is often referred to simply as reverse resolving, or more specifically reverse DNS lookups.

The most common uses of the reverse DNS are:
=> Anti-spam
=> Network troubleshooting
=> Avoid spammers and phishers using a forward confirmed reverse DNS etc

You can use standard UNIX / Linux utilities such as nslookup, dig or hosts to find out reverse DNS of a given IP address.

Task: Find Reverse DNS for IP under Linux/UNIX
$ host

Output: domain name pointer

IP is reverse mapped to
Task: Find Reverse DNS for IP under Linux/UNIX/Windows


dig -x IP

nslookup works under Windows and UNIX like OS's:

;; Got recursion not available from, trying next server

Non-authoritative answer: name =

Authoritative answers can be found from: nameserver = nameserver = internet address = internet address =

How can I setup RDNS in Linux?

#vi /etc/named.conf

Add the following entries,

zone "" IN {
type master;
file "/var/named/66.90.111.db";
allow-update { none; };

Then you will need to create a new zone file something like this.
#vi /var/named/

add the following lines,

$TTL 86400
@ IN SOA (
2005021601 ; serial
28800 ; refresh
14400 ; retry
3600000 ; expire
86400 ; ttl
50 IN PTR WhatEverYouWant.Com.
51 IN PTR WhatEverYouWant.Com.
52 IN PTR WhatEverYouWant.Com.
53 IN PTR WhatEverYouWant.Com.
54 IN PTR WhatEverYouWant.Com.
55 IN PTR WhatEverYouWant.Com.

rndc reload
/etc/init.d/named restart
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