The Domain Name Servers make Internet Protocol (IP) addresses into human-readable format such as “http://xyz.com”. The DNS have a huge repository of all domains, linking them to their characteristic IP address. Thus, when we type in an address in the URL (Universal Resource Locator) bar of any browser, we are actually asking the DNS to link to the IP address of the website and accordingly the browser performs the functions required and links to the website with the networking layer.
Reverse DNS is the exact reverse of this process in which an IP address is converted to its human-readable format. It is an important tool in searching to the roots of a certain IP address that has your interest – that is it could be the IP address of a spammer who comments/emails you absolute junk and you want to block him and want to know who he is. It is also necessitated by the fact that some hackers and crackers also leave vital IP’s behind that can lead to their apprehension. Reverse DNS is also required in networks that use SMTP servers, express management systems and other tools of networking.
DNS lookup tools are free to use by any internet user and have always been so, since the right to information is what the internet is all about. A simple command that is used in both DOS and Bash is the “nslookup” command. Simply type nslookup followed by the IP address whose reverse DNS is needed and the output will be the desired web page’s name.
Forward DNS works on A-records or “Address” records, while Reverse DNS works on PTR or “Pointer” records. Usually the ISP’s do their own reverse DNS engineering before serving it to the consumers, but if the case may arise that some reverse DNS is needed by the computer network user he or she may use some freely available software to program the DNS servers to their choosing.
Reverse DNS engineering is as important as forward DNS engineering. The method of backward calls to IP addresses from many networking software require reverse DNS lookups which may fail or give invalid results if the reverse DNS is not properly configured. Although forward DNS is all that is necessary for internet web browsing, enterprise networks need a thorough backbone of reverse DNS for them to work properly. As troubleshooting reverse DNS problems are a headache, it pays to configure it properly the first time.