Glossary
DNS RECORDS

NAPTR Record

Naming Authority Pointer — used with SRV for complex service discovery, especially SIP and ENUM.

NAPTR (Naming Authority Pointer, RFC 3403) is used in conjunction with SRV records for complex service-discovery scenarios. The typical use case is telephone-number-to-URI mapping (ENUM) and SIP service resolution.

Record Format

example.com.  NAPTR  100 10 "u" "E2U+sip" "!^.*$!sip:[email protected]!" .

Fields

  • order — evaluate NAPTRs in ascending order
  • preference — within same order, prefer the lower
  • flags — how to handle the result (u = terminal URI, s = SRV lookup, a = A/AAAA lookup)
  • services — the protocol identifier
  • regexp — a Perl-style substitution applied to the query
  • replacement — used instead of regexp when the regexp is empty

Where NAPTR Is Used

  • ENUM — mapping a phone number +14155551234 to a SIP URI
  • SIP service discovery — finding the SIP proxy for a domain (superseded by SRV in most modern deployments)

Modern Relevance

Outside of telecom, NAPTR sees little use. Modern service discovery has moved to SRV + well-known URIs (RFC 8615). Include it in glossary for completeness — you’ll encounter it in SIP/VoIP infrastructure.

Check the SRV record glossary entry, the MX record entry, and browse every major DNS record type.

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