O que é DNS Reverso?
Reverse DNS (rDNS) is the process of resolving an IP address back to a hostname. Unlike forward DNS which maps names to IPs, reverse DNS uses PTR (Pointer) records to map IPs to names. It's commonly used for email authentication, security logging, and network troubleshooting.
Como Funciona
Reverse DNS uses a special domain: in-addr.arpa for IPv4 and ip6.arpa for IPv6. The IP address is reversed and appended to this domain. For example, the reverse lookup for 1.2.3.4 queries 4.3.2.1.in-addr.arpa for a PTR record that returns the associated hostname.
Por Que Importa
Many mail servers reject or flag emails from IPs without valid reverse DNS. Security tools use rDNS to identify hosts in logs. Missing or mismatched PTR records can cause email delivery failures and indicate poorly configured infrastructure.
Problemas Comuns
- Missing PTR record causing email rejection
- PTR record not matching the HELO hostname
- ISP not delegating rDNS to the server operator
- Stale PTR records pointing to old hostnames