FCrDNS
Forward-confirmed reverse DNS: resolve the requesting IP to a hostname, then resolve that hostname back and check it returns the same IP.
What FCrDNS does not show
It is the verification method for crawlers that publish no IP list, and it is the only honest way to test a Googlebot claim.
Related terms in Crawlers and access
Who is fetching, whether they are who they claim, and what your rules actually permit.
visitor resolve · published crawler ranges · operator origin · signed agent · agent arrival · agent conduct record · agent traffic index · user-triggered fetch exemption · retrieval crawler · user-triggered fetch · verified crawler · forged crawler identity · unverifiable · robots.txt · user-agent group · AI opt-out · Content-Signal · crawl budget · cloaking · challenge page at 200 · uniform refusal · nonexistent-path control · blocked render resource · off-host redirect · homepage refused · Crawler trap · Conditional request · ASN blocking · operator feed · residential proxy · Google-Extended · Google-Agent · GPTBot vs OAI-SearchBot · ClaudeBot vs Claude-User · PerplexityBot vs Perplexity-User · CCBot · Bytespider · agentic traffic · crawler classification · user agent · datacenter IP · vantage point · rate limit · delivery comparison · honeypot
Questions about FCrDNS
What is FCrDNS?
Forward-confirmed reverse DNS: resolve the requesting IP to a hostname, then resolve that hostname back and check it returns the same IP.
What does FCrDNS not show or guarantee?
It is the verification method for crawlers that publish no IP list, and it is the only honest way to test a Googlebot claim.
Which area of the glossary does FCrDNS belong to?
Crawlers and access: Who is fetching, whether they are who they claim, and what your rules actually permit.
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See it in the full glossary · 772 terms across 19 areas.
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