What is a reverse DNS lookup?

By Nik Andreev, Founder & SEO specialist · Last reviewed · Editorial policy

A reverse DNS lookup asks DNS which hostname belongs to an IP address. It reverses the address, adds in-addr.arpa (or ip6.arpa for IPv6), and reads the PTR record there. For bot verification it is step one: a real Googlebot IP resolves to a googlebot.com name. Because the IP owner sets that record, you must forward-confirm it before trusting it.

Full guide Reverse DNS lookup: how bot verification actually works PTR records, why plain reverse DNS is spoofable, a full FCrDNS walk-through, and what to do for crawlers that skip DNS. Read the guide →

At a glance

Record type
PTR (pointer), defined in RFC 1035
IPv4 zone
in-addr.arpa (66.249.66.1 becomes 1.66.249.66.in-addr.arpa)
IPv6 zone
ip6.arpa
Who sets it
Whoever controls the IP block, not the domain the name points to
Used to verify
Googlebot (googlebot.com, google.com) and Bingbot (search.msn.com)
Missing PTR means
No reverse name. Not proof of a bad actor.

How it works

  • Take the IP from your logs, from a request whose user agent claims a crawler.
  • Look up its PTR record with dig -x or host. The answer is a hostname such as crawl-66-249-66-1.googlebot.com.
  • Check the suffix exactly, then forward-confirm it. A name like googlebot.com.example.net fails, and so does one that does not resolve back to the same IP.
dig -x 66.249.66.1 +short
# crawl-66-249-66-1.googlebot.com.

Finish the check

FCrDNS Adds the forward lookup that makes reverse DNS trustworthy. Published IP ranges The alternative for operators, like OpenAI, that do not use reverse DNS.

Quick answers

Can reverse DNS be faked?

Yes. The IP owner controls the PTR record and can point it at googlebot.com. The forward lookup is the part they cannot fake.

Do AI crawlers have reverse DNS?

Many do not. OpenAI, for example, documents published IP ranges for its bots instead.

Sources