| Internet-Draft | Private use top-level domain | February 2025 |
| Davies, et al. | Expires 6 August 2025 | [Page] |
This document describes the "internal" top-level domain for use in private applications.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 6 August 2025.¶
Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.¶
There are certain circumstances in which private network operators may wish to use their own domain naming scheme that is not intended to be used or accessible by the global domain name system (DNS), such as within closed corporate or home networks.¶
The "internal" top-level domain provides this purpose in the DNS. Such domains will not resolve in the global DNS, but can be configured within closed networks as the network operator sees fit. It fulfils a similar purpose as private-use IP address ranges that are set aside (e.g. [RFC1918]).¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [BCP14] when, and only when, they appear in all capitals, as shown here.¶
This document assumes familiarity with DNS terms; please see [BCP219].¶
Network operators have been using different names for private-use DNS for many years. This usage has been uncoordinated and can result in incompatibilities or harm to Internet users. For example, an organization might choose to use a name for this purpose that has not been assigned to them, that would later appear in the global DNS thereby causing name collisions and undefined behavior for users.¶
If an organization determines that it requires a private-use DNS namespace, it should either use sub-domains of a global DNS name that is under its organizational and operational control, or use the "internal" top-level domain. This document does not offer guidance on when a network operators should choose the "internal" top-level domain instead of a sub-domain of a global DNS name. This decision will depend on multiple factors such as network design or organizational needs, and is outside the scope of this publication.¶
DNSSEC validating resolvers will always fail to resolve names ending in "internal". An organization wanting to use such names inside of their organization MAY want to sign and validate names ending in "internal" within their organization. The details of such configuration are outside the scope of this document.¶
Other namespaces are reserved for similar purposes, which superficially may seem to serve the same purpose as the "internal" domain, but are intended for different use cases.¶
The "local" namespace [RFC6762] is reserved for use with the multicast DNS protocol. This protocol allows for resolution between devices on a local network. This namespace does not use typical DNS zones for name allocation, and instead uses the multicast DNS protocol to negotiate names and resolve conflicts. It is expected "internal" will be used for applications where names are specified in locally-configured zones.¶
The "alt" namespace [RFC9476] is reserved for contexts where identifiers are used that may look like domain names, but do not use the DNS protocol for resolution. This is in contrast to the "internal" domain which is to be used with the DNS protocol, but in limited private-use network scope.¶
The "home.arpa" namespace [RFC8375] is reserved for use within residential networks, including the Home Networking Control Protocol [RFC7788].¶
The document requires no IANA actions. For the reasons stated above, as the "internal" top-level domain is reserved from being used in the global DNS it MUST NOT appear in the DNS root zone except to the minimum extent necessary to enable it to function for its intended purpose.¶
(Editor note (WK): It not yet decided if .internal should be added to the list of special-use domain names at https://www.iana.org/assignments/special-use-domain-names/.¶
Below are potential answers for the "Seven Questions" from [RFC6761], to help drive this discussion.¶
These answers were lifted from other documents which made similar reservations, because “Good artists copy; great artists steal.” -- Pablo Picasso)¶
Answer 1: copied from [RFC6762]. Additional sentence added to make it more explicit.¶
Answer 2: copied from [RFC6761], Sec 6.5. "Domain Name Reservation Considerations for Example Domains". Additional text about potential special handling for cookies.¶
Answers 3 and 4: copied from [RFC6761], Sec 6.5. "Domain Name Reservation Considerations for Example Domains".¶
Answers 5 and 6: copied from [RFC6761], Sec 6.1 "Domain Name Reservation Considerations for Private Addresses".¶
Answer 7: copied from [RFC6762].¶
Users SHOULD understand that .internal names are not expected to be globally unique, and may resolve to different addresses and services on different networks. Since there is no central authority responsible for assigning .internal names, users SHOULD be aware of this and SHOULD exercise appropriate caution. In an untrusted or unfamiliar network environment, users SHOULD be aware that using a name like "www.internal" may not actually connect them to the web site they expected, and could easily connect them to a different web page, or even a fake or spoof of their intended web site, designed to trick them into revealing confidential information. As always with networking, end-to-end cryptographic security can be a useful tool. For example, when connecting with ssh, the ssh host key verification process will inform the user if it detects that the identity of the entity they are communicating with has changed since the last time they connected to that name.¶
Application software, in general, SHOULD NOT recognize .internal names as special and SHOULD use .internal names as they would other domain names. An exception to this may be web browsers (and similar) which may wish to institute special handling for cookies, such as invalidation when a network change is detected.¶
Name resolution APIs and libraries SHOULD NOT recognize .internal names as special and SHOULD NOT treat them differently. Name resolution APIs SHOULD send queries for .internal names to their configured caching DNS server(s).¶
Caching DNS servers SHOULD NOT recognize .internal names as special and SHOULD resolve them normally.¶
Authoritative DNS servers SHOULD recognize these names as special and SHOULD, by default, generate immediate negative responses for all such queries, unless explicitly configured by the administrator to give positive answers for names within the .internal zone.¶
DNS server operators SHOULD, if they are using .internal names, configure their authoritative DNS servers to act as authoritative for these names.¶
DNS Registries/Registrars MUST NOT grant requests to register any of these names in the normal way to any person or entity. These names are reserved for use in private networks, and fall outside the set of names available for allocation by registries/ registrars. Attempting to allocate one of these names as if it were a normal DNS domain name will probably not work as desired, for reasons 4, 5 and 6 above.¶
While the namespace is designated for private use, there is no guarantee that the names utilized in this namespace will not leak into the broader Internet. Since usage may appear in log files, email headers, and the like; users should not rely on the confidentiality of the "internal" namespace.¶
Users should not expect that names in the "internal" namespace are globally unique; it is assumed that many of the same names will be used for entirely different purposes on different networks. This is similar to the use of the "local" namespace in the multicast DNS protocol - just as there are many different devices named "printer.local", there may be many different servers named "accounting.internal". Users should be aware of this when performing operations requiring authenticity, such as entering credentials.¶
Users should also not assume the appearance of such names is indicative of the true source of transmissions. When diagnosing network issues, the appearance of such addresses must be interpreted with the associated context to ascertain the private network with which the name is being used. A private-use name can never be used by itself to identify the origin of a communication.¶
The lack of global uniqueness also has implications for HTTP cookies; a cookie set for "accounting.internal" on one network may be sent to a different "accounting.internal" if the user changes their local network. This may be mitigated by adding the Secure flag to the cookie. It is expected that Certificate Authorities will not issue certificates for the "internal" namspace as it does not resolve in the global DNS. If an organization wants to use HTTP over TLS with names in the "internal" namespace, they will also need an internal, private CA. The details of this are outside the scope of this document.¶
This reservation is the result of a community deliberation on this topic over many years, most notably [SAC113]. The SAC113 advisory recommended the establishment of a single top-level domain for private-use applications. This top-level domain would not be delegated in the DNS root zone to ensure it is not resolvable in contexts outside of a private network.¶
A selection process [IANA-Assessment] determined "internal" was the best suited string given the requirement that a single string be selected for this purpose, and subsequently reserved for this purpose in July 2024. [ICANN-Board-Resolution]¶
It is currently assumed this domain should NOT be designated as a special-use domain name at¶
https://www.iana.org/assignments/special-use-domain-names/.¶
I-D source is maintained at: https://github.com/kjd/draft-davies-internal-tld¶