What is PTR Record?
Also known as: Pointer Record
A PTR record maps an IP address to a hostname in the reverse DNS tree, used for reverse lookups under in-addr.arpa (IPv4) or ip6.arpa (IPv6).
A pointer record (PTR record) is a type of DNS resource record that maps an IP address to a domain name, performing the reverse operation of an A or AAAA record. Where an A record answers the question 'what IP does this name have?', a PTR record answers 'what name does this IP belong to?'. PTR records are the foundation of reverse DNS (rDNS).
The record lives in a special DNS namespace. For IPv4, the IP address is reversed and appended with '.in-addr.arpa'. For example, the PTR record for 192.0.2.45 is stored under 45.2.0.192.in-addr.arpa. For IPv6, the nibbles (hex digits) of the address are reversed and appended with '.ip6.arpa'. A PTR record contains a single owner name (the reversed IP) and a single RDATA field: the fully qualified domain name (FQDN) of the host. The TTL class is typically IN (Internet).
PTR records are not automatically created when an A or AAAA record is added. They must be configured separately, usually by the entity that controls the reverse zone (often the ISP or cloud provider). Many services rely on PTR records: mail servers check the PTR of a connecting SMTP client to reduce spam, SSH servers can log hostnames from IPs, and traceroute uses reverse lookups to display human-readable hop names. Without a PTR record, a reverse lookup returns a non-existent domain (NXDOMAIN) or no data, which can cause deliverability problems for email.
Key facts
- PTR records are defined in RFC 1035 for DNS and RFC 3596 for IPv6 reverse mapping.
- IPv4 PTRs live under in-addr.arpa; IPv6 PTRs live under ip6.arpa.
- A single IP can have only one PTR record per class and zone origin.
- PTR records are optional but widely required by email servers for anti-spam validation.
- Reverse DNS zones are typically delegated by the IP address registrant, not the domain owner.
How it works in practice
Related terms
References
More in DNS
A Record
A DNS resource record that maps a hostname to a 32-bit IPv4 address. It is the most fundamental record type for translating domain names to numeric addresses on the Internet.
AAAA Record
A DNS resource record that maps a hostname to a 128-bit IPv6 address, analogous to the A record for IPv4.
Authoritative DNS
An authoritative DNS server holds the definitive resource records for a specific domain and responds to queries with the final answer for that zone, not a cached copy.
CAA Record
A CAA (Certification Authority Authorization) DNS record lets domain owners specify which certificate authorities are permitted to issue SSL/TLS certificates for their domain.
CNAME Record
A DNS record that maps an alias hostname to the true or canonical hostname, allowing multiple names to resolve to the same IP address without duplicating A or AAAA records.
DNS
The Domain Name System (DNS) is a hierarchical, distributed naming system that translates human-readable domain names (like example.com) into IP addresses and other resource records used by internet protocols.
DNS Anycast
DNS Anycast uses one IP address served from multiple geographically distributed nameservers; queries are routed to the nearest or healthiest node, improving resilience and reducing latency.
DNS Caching
DNS caching stores resolved domain name query results for the specified TTL duration to avoid repeated queries to upstream authoritative servers.
DNS Hijacking
DNS hijacking is an attack or misconfiguration that returns forged DNS responses, causing users to connect to attacker-controlled hosts instead of the intended server.
DNSSEC
DNSSEC (DNS Security Extensions) add cryptographic digital signatures to DNS records, enabling resolvers to verify that responses have not been tampered with or spoofed.