PTR Record Checks: Detecting Fake Bots with Reverse DNS in BotBlocker

One of the most effective ways to distinguish between real search engine crawlers and imposters is by checking PTR (reverse DNS) records. Many bots try to disguise themselves by using legitimate User-Agent strings like Googlebot or Bingbot. However, they almost never have the correct PTR records that true search engine bots maintain.

What Is a PTR (Reverse DNS) Record?

A PTR record maps an IP address to a domain name. In the context of web security, this is known as a reverse DNS lookup. While a normal DNS record translates a domain name (like google.com) into an IP address, a PTR record does the opposite: it tells you which domain is associated with a specific IP.

Example:

• Forward DNS: googlebot.com → 66.249.66.1
• PTR (reverse DNS): 66.249.66.1 → crawl-66-249-66-1.googlebot.com

How BotBlocker Uses PTR for Bot Detection

BotBlocker automatically performs a PTR check whenever a visitor claims to be a major search engine crawler. The plugin verifies:

• The IP address in the request matches the User-Agent (e.g., claims to be Googlebot)
• The reverse DNS (PTR) record for that IP points to the official domain (e.g., *.googlebot.com)
• Optionally, a forward DNS check ensures the hostname points back to the same IP for extra reliability

If any of these checks fail, the visitor is identified as a fake bot and is blocked or challenged.

Why PTR Checking Matters

Fake bots often spoof their User-Agent to crawl or attack your site without being detected by simple rules. Only official search engines own the required IP ranges and maintain valid PTR records. This makes PTR-based filtering one of the most reliable methods to stop:

• Content scrapers
• Spam bots pretending to be search engines
• Bots that try to avoid standard security filters

How PTR Checks Protect Your Site

• Prevents unauthorized access to valuable content meant for search engines
• Reduces the risk of SEO poisoning and fake indexing
• Blocks attackers who try to use search engine identity as camouflage

Limitations and Best Practices

• PTR checks are only relevant for bots that claim to be search engines (like Googlebot, Bingbot, etc.)
• Not used for ordinary users or generic bots
• Reverse DNS lookups may introduce a minor delay, but only for specific User-Agents, not for every visitor

FAQ

Can a real Googlebot be blocked accidentally?
Almost never. Google and other real bots maintain perfect PTR and forward DNS records.

Is PTR checking enabled for all visitors?
No, it’s only triggered for requests with suspicious User-Agent strings imitating search engine crawlers.

Does this affect site speed?
No, because reverse DNS checks are rare and optimized in BotBlocker.

PTR Anomalies