Summary

  • RIPE NCC’s Database Working Group heard a commitment in August 2025 to add e164.arpa support to RDAP and document the extension.
  • Two live queries on 1 November 2026 returned HTTP 501. The endpoint says ENUM support is not implemented and points to Whois at port 43.

An RDAP client asking RIPE NCC about e164.arpa gets a tidy answer: 501, “Not Implemented.” The same response appears for the zone apex and for 6.4.e164.arpa, a branch beneath it. The service even supplies its fallback: whois.ripe.net on port 43. The error is explicit. The feature is still absent.

That status sits beside a public commitment made nearly fifteen months earlier. In a Database Working Group thread in August 2025, RIPE NCC staff said the team would proceed with RDAP support for e164.arpa and document the change in an RFC. The discussion had started with a report that RDAP returned 500 for child ENUM domains and 400 for e164.arpa itself. RIPE NCC replied that RFC 9082 did not include this zone in the RIR query format and raised two design questions: how clients would find the right service, and whether other RIRs should redirect requests to RIPE NCC. The team then said it would implement the support and aim for feature parity with Whois. The original Database Working Group thread

RIPE NCC also supplied one operational figure: a few hundred daily Whois queries for e164.arpa domains. That is a count of requests, not users, completed calls or RDAP clients. It cannot size a protocol migration; it identifies the old interface as the only published query counter in the discussion.

The object itself belongs to a different path from an RDAP response. IANA lists e164.arpa as the namespace used to map E.164 numbers to Internet URIs. ENUM performs that mapping through DNS. RDAP is a separate HTTPS interface for registration data. RIPE NCC’s documentation lists domain as a supported object type and demonstrates reverse-DNS queries such as in-addr.arpa; the current API response shows where the support stops. The 501 describes RIPE NCC’s registration-data interface; an ENUM lookup follows the DNS path. IANA’s .ARPA list · RIPE Database RDAP documentation

At RIPE 93 on 29 October 2026, the database team reported progress on e164.arpa support, then asked the community whether to proceed. The team was ready to implement if the community agreed. The transcript names no release, draft number or target date. On 1 November, both tested paths still answered 501. The response code changed from the 2025 report’s 400 and 500; support remained absent. RIPE 93 Database Working Group transcript

The design has more than one desk. RIPE NCC operates the zone; the 2025 thread raised standardisation and redirection by other RIRs; the IAB and ITU-T appear in the operating instructions because e164.arpa sits at the meeting point of Internet architecture and telephone numbering. That coordination can explain why a small-looking endpoint change needs a documented path. It cannot tell a client when the new path will work.

For now, a tool that needs ENUM registration data must keep the old Whois route available. RIPE NCC’s endpoint makes the reason machine-readable, which is better than an unexplained failure. It also leaves the implementation promise without a visible receipt. A release number or public draft would settle when the work is due; a published RDAP query count would show how many clients are waiting at the 501.

Sources: RIPE NCC Database Working Group thread, RIPE 93 transcript, RIPE Database RDAP documentation, live apex response, live branch response, IANA .ARPA list.