What Is Reverse DNS?

What Is Reverse DNS?

Reverse DNS (rDNS) is the process of resolving an IP address to a domain name, opposite of forward DNS which resolves domain names to IP addresses. Reverse DNS uses PTR (Pointer) records in DNS to map IP addresses to domain names.

Reverse DNS is important for email delivery - many mail servers check reverse DNS and may reject emails from servers without proper reverse DNS configuration. Reverse DNS helps verify server identity, improves email deliverability, and provides server identification.

Reverse DNS lookup queries PTR records in reverse DNS zones (in-addr.arpa for IPv4, ip6.arpa for IPv6) to find domain names associated with IP addresses. Use our domain health check to verify reverse DNS configuration.

Reverse DNS Purpose

1. Server Identification

Reverse DNS identifies servers by providing domain names for IP addresses, enabling server identification and verification.

2. Email Delivery

Reverse DNS is important for email delivery - many mail servers require reverse DNS and may reject emails from servers without proper configuration.

3. Security

Reverse DNS helps verify server identity, providing additional security layer for network communication.

4. Logging and Monitoring

Reverse DNS enables readable domain names in logs and monitoring tools instead of IP addresses.

5. Troubleshooting

Reverse DNS helps troubleshoot network issues by providing domain names for IP addresses in network diagnostics.

How Reverse DNS Works

1. Reverse DNS Zones

Reverse DNS uses special DNS zones: in-addr.arpa for IPv4 (e.g., 2.0.192.in-addr.arpa for 192.0.2.1) and ip6.arpa for IPv6.

2. PTR Records

PTR (Pointer) records in reverse DNS zones map IP addresses to domain names, opposite of A/AAAA records in forward DNS.

3. IP Address Reversal

IP addresses are reversed for reverse DNS lookup: IPv4 addresses are reversed octet-by-octet (192.0.2.1 → 1.2.0.192.in-addr.arpa), IPv6 addresses are reversed nibble-by-nibble.

4. Query Process

Reverse DNS lookup queries PTR records in reverse DNS zones, starting from IP address owner and following DNS hierarchy.

5. Result

Reverse DNS lookup returns domain name associated with IP address, or no result if PTR record doesn't exist.

PTR Records

What Are PTR Records?

PTR (Pointer) records are DNS records used for reverse DNS, mapping IP addresses to domain names.

PTR Record Format

PTR records in reverse DNS zones point to domain names: 1.2.0.192.in-addr.arpa. PTR mail.example.com.

PTR Record Requirements

PTR records must be configured by IP address owner (ISP or hosting provider), not domain owner. PTR records should match forward DNS (A/AAAA records).

PTR Record Configuration

Configure PTR records through IP address owner (ISP or hosting provider), requesting PTR record pointing to your domain name.

PTR Record Verification

Verify PTR records using reverse DNS lookup tools, ensuring PTR records exist and point to correct domain names.

Reverse DNS for Email

Email Delivery Requirements

Many mail servers require reverse DNS for email delivery - servers without reverse DNS may have emails rejected or marked as spam.

Reverse DNS Checks

Mail servers check reverse DNS by: performing reverse DNS lookup on sending server IP address, verifying PTR record exists, and checking PTR record matches forward DNS.

Email Deliverability

Proper reverse DNS configuration improves email deliverability by meeting mail server requirements and reducing spam filtering.

Best Practices

Best practices for reverse DNS: configure PTR records for mail server IPs, ensure PTR records match forward DNS, and verify reverse DNS is working correctly.

Configuration

Configure reverse DNS through IP address owner (ISP or hosting provider), requesting PTR records for mail server IP addresses.