CompTIA Network+ (N10-009)Network OperationsEasy
A user calls the help desk to report that reverse DNS lookups are failing for the company's mail server, causing outgoing email to be flagged as spam by some receivers. Which DNS record type must be correctly configured to allow a lookup from an IP address to a hostname?
- AMX
- BCNAME
- CPTR
- DSRV
Show answer & explanationAnswer & explanation
Correct answer: C. PTR
A PTR (pointer) record maps an IP address back to a hostname and is used for reverse DNS lookups, which is exactly what many mail servers check to reduce spam.
Why the other options are wrong
- A. MX identifies the mail server for a domain but does not support reverse lookups.
- B. CNAME maps one hostname to another hostname, not IP-to-name.
- D. SRV records locate specific services within a domain, unrelated to reverse resolution.
PTR Record
A DNS resource record used in the reverse lookup zone that resolves an IP address to a hostname.
- Stored in in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones
- Commonly checked by mail servers to combat spam
- Opposite function of an A/AAAA record
Memory trick: 'PTR = Pointing back' from IP to name.