What is Reverse DNS?
Reverse DNS (rDNS) is the process of resolving an IP address to its associated domain name. While regular DNS translates domain names to IP addresses, reverse DNS does the opposite. This is accomplished using PTR (pointer) records in the DNS system.
Reverse DNS is configured by the owner of the IP address block, typically the ISP or hosting provider. Not all IP addresses have reverse DNS configured, and having a PTR record is not mandatory for most internet services.
Common Uses of Reverse DNS
- Email Verification: Many mail servers check reverse DNS to verify sender legitimacy
- Network Diagnostics: Identifying servers and network equipment by hostname
- Security Logging: Converting IP addresses to hostnames in log files
- Access Control: Some services use reverse DNS for authentication
- Spam Prevention: Email servers often reject mail from IPs without PTR records
How Reverse DNS Works
Reverse DNS uses a special domain called in-addr.arpa for IPv4 addresses and ip6.arpa for IPv6 addresses. The IP address is reversed and appended to this domain. For example:
- IP: 8.8.8.8 becomes 8.8.8.8.in-addr.arpa
- A DNS query for this special domain returns the PTR record containing the hostname
Setting Up Reverse DNS
To configure reverse DNS for your IP address:
- Contact your ISP or hosting provider (they control PTR records)
- Provide the IP address and desired hostname
- Ensure forward DNS (A/AAAA record) also points to the same IP
- Wait for DNS propagation (usually 24-48 hours)
Note: Most residential internet connections don't allow custom reverse DNS configuration. This is typically available only for business connections and dedicated servers.