Reverse DNS Lookup

reversedns.xyz

Reverse DNS for {{ lastLookupIp }}

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Nothing found
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What is Reverse DNS?

In a nutshell, reverse DNS translates an IP address (ie, 1.1.1.1) into a hostname (ie, one.one.one.one). This is done through the use of PTR type DNS records, and is essentially the opposite of regular 'forward' DNS queries which translate a given domain name into a computer-friendly IP address.

RFC 1912 (Section 2.1) recommends that all internet-reachable hosts should have a "name". In practice, there are plenty of servers on the internet with no/misconfigured reverse DNS settings. One would most likely worry about reverse DNS configuration when setting up and managing a mail server, as they are often referenced when checking whether email is spammy, or coming from a reliable source.

The reverse DNS database of the Internet is rooted in the .arpa top-level domain. This is a special 'TLD' domain used for mapping an IP address back to its hostname. All IPv4 addresses are referenced under the in-addr.arpa subdomain, and IPv6 addresses under ip6.arpa.

In order to query the PTR record of an IPv4 address, we take the original IP in reverse notation, and place it under the special in-addr.arpa domain. Using the IP address 1.2.3.4 as an example, this would look like 4.3.2.1.in-addr.arpa.

The .arpa domain of an IPv6 address is formed in a similar manner. This time, taking 2001:db8::567:89ab as an example, the IPv6 address is expanded to its full notation, reversed, then placed under ip6.arpa. becoming b.a.9.8.7.6.5.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.

An IP address is said to be forward-confirmed if the A record it's PTR record resolves to matches the original IP address.