RDNS is the abbreviation of Reverse Domain Name System. Working principle of RDNS is just opposite to that of normal DNS, Domain Name System. The RDNS is a pointer(PTR) record entry which helps to find out the host-name associated with the IP address. This is one of the way to show the genuinity of the server to public network. You had better to set the RDNS properly to avoid receiving emails from your server to Spam folder of the recipient. We can simply find-out the RDNS entry of an IP address using different command from command-line. Here is some common example are illustrated with the commands dig, host, nslookup.
The reverse DNS database of the Internet is routed in the Address and Routing Parameter Area (arpa) top-level domain of the Internet. IPv4 uses the in-addr.arpa domain and the ip6.arpa domain is delegated for IPv6. The process of reverse resolving an IP address uses the pointer DNS record type (PTR record).
Different methods to find out the RDNS entry are:
You can use the following commands to find out the RDNS entry of a server. Please see the details:
host 184.108.40.206 220.127.116.11.in-addr.arpa domain name pointer lax02s20-in-f22.1e100.net.
nslookup 18.104.22.168 22.214.171.124.in-addr.arpa name = lax02s20-in-f22.1e100.net.
dig -x IP.Address
dig -x 126.96.36.199 +short lax02s20-in-f22.1e100.net.
Uses of RDNS
The most common uses of the reverse DNS include:
1. The original use of the rDNS: network troubleshooting via tools such as traceroute, ping, and the “Received:” trace header field for SMTP e-mail, web sites tracking users (especially on Internet forums), etc.
2. One e-mail anti-spam technique: checking the domain names in the rDNS to see if they are likely from dialup users, dynamically assigned addresses, or other inexpensive internet services.
3. A forward-confirmed reverse DNS (FCrDNS) verification can create a form of authentication showing a valid relationship between the owner of a domain name and the owner of the server that has been given an IP address.