closed Name Collision IPv6 Research Study

Outcome

Based on the feedback received during the Public Comment proceeding and as a result of internal review, ICANN org has decided to not perform controlled interruption with IPv6 in the 2026 Round. Additional work is planned and ICANN will consider the topic again once the Internet Engineering Task Force (IETF) has developed a standardized solution.

What We Received Input On

ICANN org seeks input on the Controlled Interruption IPv6 Research Study Summary Report, which proposes the use of ::ffff:127.0.53.53 in the AAAA record for future controlled interruption activities. 

Background

Controlled interruption is a phase in the establishment of a new generic top-level domain (gTLD) that is designed to reduce the risk of name collision. During controlled interruption, certain DNS resource records, designed to interrupt resolution processes, are temporarily published at and below the gTLD name. The content of these DNS records is intended to minimize any harm that arises from such interruption.

Controlled Interruption uses ‘A’ resource records containing the IPv4 address 127.0.53.53. This address is within the 127.0.0.0/8 prefix, which is used for “loopback” interfaces (see RFC 1122, Section 3.2.1.2). The use of this prefix ensures that any application that uses the result of a DNS query that returns this IPv4 address will not initiate a network connection. 127.0.53.53 is used instead of 127.0.0.1 so that if a user or administrator performs a web search for this address, they are more likely to be shown links to the name collision resources on the ICANN website.

When the concept of controlled interruption was developed in 2014, no suitable equivalent address could be found for IPv6-enabled hosts. While this was noted as a limitation, at the time the impact was limited since fewer than 5% of internet hosts supported IPv6. In the intervening decade, IPv6 adoption has accelerated, and now more than 40% of all internet hosts have IPv6 connectivity. As a result, the lack of an IPv6 solution for controlled interruption has a greater impact.

A research study has been performed to identify one or more IPv6 candidate prefixes that may be suitable for use during controlled Interruption. This study involved a review of the IANA registries for IPv6 to produce a list of candidate addresses, followed by technical tests of multiple applications on popular end-user operating systems to determine whether or not DNS lookups that produce responses containing these addresses result in external network traffic. Two candidates were identified by the study, the preferred candidate is ::ffff:127.0.53.53

NOTE: The public comment description incorrectly listed ffff::127.0.53.53 and ffff:127.0.53.53 as the preferred candidate, rather than the correct value, ::ffff:127.0.53.53. These editorial errors were corrected on 3 November 2025. Formatting errors in the documents for input were corrected on 21 November 2025.