What Is Reverse DNS Lookup?

Overview of Reverse DNS Lookup

A Reverse DNS (rDNS) lookup allows an organization that owns IP addresses to give names to them. Unlike the standard DNS lookup, which maps domain names to IP addresses, rDNS works in reverse of the usual domain-to-IP DNS lookups and allows users to register IP-to-domain mapping, instead typically via PTR (pointer) records.

• Forward DNS maps a domain name to an IP address.
• Reverse DNS does the opposite: it finds the domain name (if any) associated with a specific IP address.
  Administrators create PTR records under special reverse DNS zones (in-addr.arpa for IPv4 and ip6.arpa for IPv6).

What's Important About Reverse DNS Lookup

Reverse DNS lookups allow organizations to assign names to IP addresses. These names often contain hints about the function of the host (e.g. is it a mail server, a web server, or a router) and its location (typically an airport code). Many platforms convert IPs to hostnames for more readable logs, aiding troubleshooting and security analysis. Mail services often check if a sending IP has a matching PTR record. If it doesn’t, messages are more likely to be flagged as spam. PTR records aren’t required for every IP. Consumer or dynamically assigned IPs often lack PTR entries, and that’s usually fine for everyday web use. However, they’re crucial in contexts like: email servers, network infrastructure, logging and security.

How You Can Use Reverse DNS Lookup at IPinfo

IPinfo’s Reverse DNS IP lookup API makes it easy to determine the hostname associated with an IP address making tasks like mail server verification, log analysis, and network management easier.

Links to Related Documentation and Tooling

• Reverse DNS Lookup