When browsing the Internet, you may have come across a web page URL in which the domain name is expressed as an IP address. Your curiosity grows and you wonder whether it is possible to see its actual domain name. Reverse DNS is the process that allows this to happen. Reverse DNS can therefore be defined as the process that determines what host is associated with a given IP address. In other words, reverse DNS uses an IP address to find a domain name. It is the opposite of forward DNS (commonly referred to as WhoIs) which uses an Internet domain name to find an IP address.
How can I do a Reverse DNS?
In order to do a Reverse DNS lookup, you need to use the nslookup (name server lookup) command on Windows or UNIX. The nslookup command can be used to find various details relating to a particular DNS (Domain Name System) such as IP address, MX records etc
You can look for a reverse DNS testing tool to do a sample look up by merely entering the IP address you want to look up. The tool will do a reverse DNS lookup of the IP address by searching the domain name registry and registrar tables. IP addresses contain four numbers in the range of 0 to 255 separated by periods. Note that the DNS is a public service meaning any Internet user is freely able to query the DNS system for forward or reverse translations.
Reverse DNS files use the implementation and structure specified in RFC 1035. The Internet will use a special domain (ARPA) to cater for reverse-name lookup queries. This domain beginning at IN-ADDR.ARPA performs address-to-host mapping. The domain names in the IN-ADDR-ARPA zone have up to four labels, each representing an Internet address. This fixed naming allows for querying up to two servers. When a reverse DNS is done, the servers dedicated to the private segment of the reverse IN-ADDR.ARPA will dominate and then provide information on any additional servers for that particular sub zone in the private Internet address portion of the IN-ADDR.ARPA. For example, if you have an address which is 180.10.0.0, then the Reverse Lookup file for this network would be 10.180.IN-ADDR.ARPA.
Why would I want to do a Reverse DNS?
· Reverse DNS can help you identify the domain name of a spammer sending you spam e-mail.
· Reverse DNS can help you identify the domain name of a computer trying to break into your firewall or someone trying to hack into your system.
· Reverse DNS can help you know the name of the internet service provider assigned to a particular IP address.
Can reverse DNS lookup fail?
Yes it can. Occasionally, you may get an “Unable to Resolve IP Address” result.
This may happen if the IP address you are looking for is unlisted. For example, an Internet Service Provider may be assigned a block of IP addresses and it may not give names to all those addresses.
For more information on Reverse DNS read What is reverse DNS
