Reverse DNS Lookup
Perform a reverse DNS (PTR) lookup to find the hostname associated with an IP address.
About Reverse DNS Lookup
Reverse DNS (rDNS) resolves an IP address back to a hostname, using PTR (pointer) records stored in special zones under in-addr.arpa (IPv4) or ip6.arpa (IPv6). Forward DNS maps names to addresses; reverse DNS maps addresses back to names.
How reverse DNS works
For an IPv4 address like 192.0.2.1, the PTR record is looked up at 1.2.0.192.in-addr.arpa — the octets are reversed and .in-addr.arpa is appended. The PTR record at that address returns the canonical hostname. This zone is administered by the organisation that owns the IP block, typically the ISP or hosting provider — not the domain owner.
Why reverse DNS matters
- Email deliverability — Many spam filters reject or score down email from IP addresses that have no PTR record, or whose PTR record doesn't match the sending hostname (forward-confirmed rDNS). Mail servers should have a PTR record matching their SMTP hostname.
- Network troubleshooting — Tools like
tracerouteandpingdisplay hostnames alongside IPs to help identify network hops. - Security logging — Enriching IP addresses in logs with hostnames for easier analysis and attribution.
Forward-confirmed rDNS (FCrDNS)
FCrDNS (also called full-circle rDNS) requires that the PTR record for an IP resolves to a hostname, and that hostname's A record resolves back to the same IP. This mutual verification is used by many mail servers and security systems to confirm that an IP is legitimately associated with a hostname. This tool shows whether forward and reverse DNS match.