What Is Reverse DNS? PTR Records Explained

Q: What is a PTR record?

A PTR record maps an IP address back to a hostname, which is the reverse of what an A record does. It lives in a special reverse DNS zone such as in-addr.arpa for IPv4 or ip6.arpa for IPv6. Reverse DNS lookups read this record to find the name associated with an address.

Q: Who controls reverse DNS for an IP address?

The owner of the IP block controls reverse DNS, not the domain owner. Authority is delegated by a Regional Internet Registry to the holder of the address range, which is usually an ISP or hosting provider. To set a custom PTR record you normally request it from that provider.

Q: What is the difference between a PTR record and an A record?

An A record maps a hostname to an IP address, while a PTR record maps an IP address back to a hostname. They point in opposite directions and are configured independently. One does not automatically create or update the other.

Q: What is forward-confirmed reverse DNS?

Forward-confirmed reverse DNS, or FCrDNS, checks that an IP PTR record points to a hostname and that the hostname forward record points back to the same IP. When both directions match, the result is treated as more trustworthy. It is used as a lightweight legitimacy check because matching both directions requires control of both records.

Q: Why does my IP have a generic reverse DNS name or none at all?

Residential and default cloud IP addresses often get a generic auto-generated PTR record or no PTR at all, because the provider that controls the reverse zone assigns them in bulk. This is normal for consumer and uncustomized cloud addresses. It does not by itself mean anything is wrong with your connection.

~/sheets/what-is-reverse-dns-ptr.md

Reverse DNS answers the opposite question from normal DNS: instead of what IP a hostname points to, it asks what hostname an IP belongs to. It does this through a special record type called a PTR record. This page explains how reverse DNS works, who controls it, and why mail servers care about it so much. You can look up the PTR record for any address with our reverse DNS tool.
Forward DNS vs Reverse DNS
Normal forward DNS uses an A record (or AAAA for IPv6) to map a hostname to an IP address. Reverse DNS uses a PTR record to map an IP address back to a hostname, the opposite direction. The two are independent: a forward record and a reverse record are configured separately and do not automatically mirror each other. For how name resolution works in general, see what is a DNS resolver, and try a forward lookup with the DNS lookup tool.
The in-addr.arpa and ip6.arpa Zones
Reverse lookups live in dedicated DNS zones. For IPv4, PTR records are stored under in-addr.arpa, with the IP address octets reversed, because DNS reads from most specific to least specific. For IPv6, reverse records live under ip6.arpa, expanded nibble by nibble. When you do a reverse lookup, the resolver queries one of these zones to find the PTR record for the address.
Who Controls a PTR Record
This is the part that surprises people: the domain owner does not control reverse DNS for an IP, the owner of the IP block does. Authority over an IP range is delegated by a Regional Internet Registry (RIR) to whoever holds that block, typically an ISP or hosting provider. So to set a custom PTR record for your address, you generally have to ask your ISP or cloud provider, not your domain registrar. You can check who holds an IP block with the WHOIS tool, and learn about block ownership in what is an ASN.
Forward-Confirmed Reverse DNS (FCrDNS)
Forward-confirmed reverse DNS is a verification step where a system checks that an IP PTR record points to a hostname, and that the hostname forward record points back to the same IP. When both directions agree, the result is considered more trustworthy. FCrDNS is a common, lightweight legitimacy signal because matching both directions requires control of both the forward and reverse records.
Why Mail Servers Check Reverse DNS
Mail servers commonly use reverse DNS as an anti-spam signal. A sending mail server that has a valid PTR record, and ideally passes FCrDNS, looks more like a legitimately operated server and less like a compromised home machine sending spam. Many receiving servers treat a missing or generic PTR record as a reason for extra suspicion, which is why mail operators are careful to set proper reverse DNS for their sending IPs. Residential and many cloud addresses have a generic provider-assigned PTR or none at all, which is normal and not a problem by itself.
Frequently Asked Questions
What is a PTR record?
A PTR record maps an IP address back to a hostname, which is the reverse of what an A record does. It lives in a special reverse DNS zone such as in-addr.arpa for IPv4 or ip6.arpa for IPv6. Reverse DNS lookups read this record to find the name associated with an address.
Who controls reverse DNS for an IP address?
The owner of the IP block controls reverse DNS, not the domain owner. Authority is delegated by a Regional Internet Registry to the holder of the address range, which is usually an ISP or hosting provider. To set a custom PTR record you normally request it from that provider.
What is the difference between a PTR record and an A record?
An A record maps a hostname to an IP address, while a PTR record maps an IP address back to a hostname. They point in opposite directions and are configured independently. One does not automatically create or update the other.
What is forward-confirmed reverse DNS?
Forward-confirmed reverse DNS, or FCrDNS, checks that an IP PTR record points to a hostname and that the hostname forward record points back to the same IP. When both directions match, the result is treated as more trustworthy. It is used as a lightweight legitimacy check because matching both directions requires control of both records.
Why does my IP have a generic reverse DNS name or none at all?
Residential and default cloud IP addresses often get a generic auto-generated PTR record or no PTR at all, because the provider that controls the reverse zone assigns them in bulk. This is normal for consumer and uncustomized cloud addresses. It does not by itself mean anything is wrong with your connection.
Last updated: April 2026