NAPTR Lookup
Naming Authority Pointer records (ENUM/SIP).
Enter a value above to run NAPTR Lookup
e.g. example.com
Quick answer
A NAPTR lookup returns Naming Authority Pointer records, which map a name to a service using rules and rewrite patterns. They are mainly used in ENUM (turning phone numbers into SIP addresses) and to discover VoIP and SIP services for a domain.
The NAPTR Lookup tool queries the Naming Authority Pointer (NAPTR) records published in DNS for a domain or an ENUM number. NAPTR records map an input string to a service and a rewrite rule, which is how a SIP proxy discovers where to route a call, or how an ENUM lookup turns a phone number into a SIP URI. If you run a VoIP platform, a SIP trunk, or any service that relies on dynamic delegation (via the DDDS algorithm), this lets you confirm the records resolve exactly as your telephony gear expects.
How it works
You enter a name and the tool asks the authoritative DNS for its NAPTR records (type 35). Each answer has six fields: order, preference, flags, service, regexp, and replacement. Clients sort by order first, then preference, then apply the flags and the regular-expression rewrite to produce the next lookup target. For ENUM, a number like +1 555 234 is reversed digit by digit into 4.3.2.5.5.5.1.e164.arpa before the query is sent.
How to read the results
Lower order and preference values win, so 10 is tried before 20. The flags field tells the resolver what comes next: "S" means the replacement is a domain to look up with SRV, "A" points to an address record, "U" means the regexp produces a final URI, and an empty flag means another NAPTR round follows. The service field names the protocol, such as "SIP+D2U" for SIP over UDP or "E2U+sip" for ENUM-to-SIP.
Common problems & fixes
If nothing returns, most likely no NAPTR is published; not every domain needs one, and many SIP setups use SRV records directly. A regexp that never matches the input string quietly breaks call routing, so check the delimiters and back-reference syntax. Also confirm the replacement is a fully qualified name ending in a dot, and that any SRV or A record the flag points to actually exists downstream.
Frequently asked questions
- What is the difference between NAPTR and SRV records?
- NAPTR sits one level above SRV. It selects a service and protocol, then usually hands off to an SRV lookup that provides the actual host and port. SRV alone gives you "where", while NAPTR adds "which service and by what rewrite rule". VoIP discovery often chains NAPTR to SRV to A records in sequence.
- Why is NAPTR used for ENUM phone numbers?
- ENUM maps E.164 telephone numbers to internet services. The number is reversed into an e164.arpa domain, and its NAPTR records carry regexp rules that rewrite the number into a SIP, mailto, or web URI. This lets a dialed number resolve to a VoIP endpoint through public DNS instead of a traditional carrier route.
- My domain returns no NAPTR record. Is that a problem?
- Usually not. NAPTR is only required when you use ENUM or advertise services through the DDDS algorithm. Plenty of working SIP deployments skip NAPTR and rely on SRV or static configuration. An empty result simply means clients should fall back to whatever discovery method your platform documents.