Brandenburg InternetWorking

675 Spruce Dr. Sunnyvale CA 94086 USA +1.408.246.8253 dcrocker@bbiw.net http://bbiw.net/

dnsop DNS Domain Name System> Formally, any DNS resource record may occur under any domain name. However some services use an operational convention for defining specific interpretations of an RRset, by locating the records in a DNS branch, under the parent domain to which the RRset actually applies. The top of this subordinate branch is defined by a naming convention that uses a reserved node name, which begins with an _underscore. The underscored naming construct defines a semantic scope for DNS record types that are associated with the parent domain, above the underscored branch. This specification explores the nature of this DNS usage and defines the "DNS Global Underscore Scoped Entry Registry" with IANA. The purpose of the Underscore registry is to avoid collisions resulting from the use of the same underscore-based name, for different services.

The core Domain Name System (DNS) technical specifications assign no semantics to domain names or their parts, and no constraints upon which resource record (RR) types are permitted to be stored under particular names , . Over time, some leaf node names, such as "www" and "ftp" have come to imply support for particular services, but this is a matter of operational convention, rather than defined protocol semantics. This freedom in the basic technology has permitted a wide range of administrative and semantic policies to be used -- in parallel. DNS data semantics have been limited to the specification of particular resource record types, on the expectation that new resource record types would be added as needed. Unfortunately, the addition of new resource record types has proven extremely challenging, over the life of the DNS, with significant adoption and use barriers.

As an alternative to defining a new RR type, some DNS service enhancements call for using an existing resource record type, but specify a restricted scope for its occurrence. Scope is meant as a static property, not one dependent on the nature of the query. It is an artifact of the DNS name. That scope is a leaf node, within which the uses of specific resource record sets can be formally defined and constrained. The leaf occurs in a branch having a distinguished naming convention: At the top of the branch -- beneath the parent domain name to which the scope applies -- one or more reserved DNS node names begin with an underscore ("_"). Because the DNS rules for a "host" (host name) do not allow use of the underscore character, this distinguishes the underscored name from all legal host names . Effectively, this convention for leaf node naming creates a space for the listing of "attributes" -- in the form of resource record types -- that are associated with the parent domain, above the underscored sub-branch. The scoping feature is particularly useful when generalized resource record types are used -- notably TXT, SRV, and URI , , , . It provides efficient separation of one use of them from others. Absent this separation, an undifferentiated mass of these RRsets is returned to the DNS client, which then must parse through the internals of the records in the hope of finding ones that are relevant. Worse, in some cases the results are ambiguous because a record type might not adequately self-identify its specific purpose. With underscore-based scoping, only the relevant RRsetss are returned. A simple example is DKIM , which uses "_domainkey" for defining a place to hold a TXT record containing signing information for the parent domain. This specification formally defines how underscored labels are used as "attribute" enhancements for their parent domain names. For example, domain name "_domainkey.example." acts as an attribute of the parent domain name "example." To avoid collisions resulting from the use of the same underscore-based labels for different applications using the same resource record type, this document establishes the DNS Underscore Global Scoped Entry IANA Registry. Use of such node names, which begin with underscore, are reserved when they are the underscored name closest to the DNS root; they are considered "global". Underscore-based names that are farther down the hierarchy are handled within the scope of the global underscore name. Discussion about this draft should be directed to the dnsop@ietf.org mailing list. Please remove "Discussion Venue" paragraph prior to publication. 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Some resource record types are used in a fashion that can create scaling problems, if an entire RRset associated with a domain name is aggregated in the leaf node for that name. An increasingly-popular approach, with excellent scaling properties, places the RRset under a specially named branch, which is in turn under the node name that would otherwise contain the RRset. The rules for naming that branch define the context for interpreting the RRset. That is, rather than:

domain-name.example / RRset

the arrangement is:

_branch.domain-name.example / RRset

A direct lookup to the subordinate leaf node produces only the desired record types, at no greater cost than a typical DNS lookup.

As defined in the DNS uses names organized in a tree-structured, or hierarchical fashion. A domain name might have multiple node names that begin with an _underscore. A "global" underscored node name is the one that is closest to the root of the DNS hierarchy, also called the highest-level or top-most. In the presentation convention described in Section 3.1 of this is the right-most name beginning with an underscore. In other presentation environments it might be positioned differently. To avoid concern for the presentation variations, the qualifier "global" is used here.

DNS wildcards interact poorly with underscored names in two ways. Since wildcards only are interpreted as leaf names, one cannot create the equivalent of a wildcard name for prefixed names. A name such as label.*.example.com is not a wildcard. Conversely, a wildcard such as *.example.com can match any name including an underscored name. So, a wildcard might match an underscored name, returning a record that is the type controlled by the underscored name but is not intended to be used in the underscored context and does not conform to its rules.

A registry for "global" DNS node names that begin with an underscore is defined here. The purpose of the Underscore Global Registry is to avoid collisions resulting from the use of the same underscore-based name, for different applications. If a public specification calls for use of an underscore-prefixed domain node name, the "global" underscored name -- the underscored name that is closest to the DNS root -- MUST be entered into this registry. An underscored name defines the scope of use for specific resource record types, which are associated with the domain name that is the "parent" to the branch defined by the underscored name. A given name defines a specific, constrained context for one or more RR types, where use of such record types conforms to the defined constraints. Within an underscore scoped leaf, other RRsets that are not specified as part of the scope MAY be used. Structurally, the registry is defined as a single, flat table of RR types, under node names beginning with underscore. In some cases, such as for use of an SRV record, the full scoping name might be multi-part, as a sequence of underscored names. Semantically, that sequence represents a hierarchical model and it is theoretically reasonable to allow re-use of a subordinate underscored name in a different, global underscored context; that is, a subordinate name is meaningful only within the scope of the global underscored name. Therefore they are ignored by this DNS Underscore Global Scoped Entry Registry. This registry is for the definition of highest-level -- ie, global -- underscored node name used. NAME _service1 _protoB._service2 _protoB._service3 _protoC._service3 _useX._protoD._service4 _protoE._region._authority Only global underscored names are registered in the IANA Underscore Global table. (From the example, that would mean registering _service1, _service2, _service3, _service 4, and _authority.) The use of underscored node names is specific to each RRTYPE that is being scoped. Each name defines a place, but does not define the rules for what appears underneath that place, either as additional underscored naming or as a leaf node with resource records. Details for those rules are provided by specifications for individual RRTYPEs. The sections below describe the way that existing underscore labels are used with the RRTYPEs that they name. Definition and registration of subordinate, underscore node names is the responsibility of the specification that creates the global registry entry. That is, if a scheme using a global underscore node name has one or more subordinate levels of underscore node naming, the namespaces from which names for those lower levels are chosen are controlled by the parent underscore node name. Each globally-registered underscore name owns a distinct, subordinate name space.

This section provides a basic template that can be used to register new entries in the IANA DNS Underscore Global Scoped Entry Registry, if the global underscored name above the RRTYPE is not already registered. The text can be added to specifications using RRTYPE/_Node-name combinations that have not already been registered. Per {RFC Attrleaf} please add the following entry to the DNS Underscore Global Scoped Entry Registry: Please replace the above "{RFC Attrleaf}" text with a reference to this document's RFC number. /d RR Type _NODE NAME REFERENCE {RRTYPE} _{DNS global node name} {citation for the document making the addition.}

Per , IANA is requested to establish the: DNS Underscore Global Scoped Entry Registry This section describes actions requested of IANA. The guidance in is used.

The DNS Global Underscore Scoped Entry Registry is any DNS node name that begin with the underscore character ("_", ASCII 0x5F) and is the underscored node name closest to the root; that is it defines the highest-level of a DNS branch, under a "parent" domain name. This registry is to operate under the IANA rules for "Expert Review" registration; see . The contents of each entry in the Global registry are defined in . Each entry in the registry MUST contain values for all of the fields specified in . Within the registry, the combination of RR Type and _Node Name MUST be unique. The table is to be maintained with entries sorted by the first column (RR Type) and, within that, the second column (_Node Name). The required Reference for an entry MUST have a stable resolution to the organization controlling that registry entry.

A registry entry contains: Lists an RR type that is defined for use within this scope Specifies a single, underscored name that defines a reserved name; this name is the "global" entry name for the scoped resource record types that are associated with that name; for characters in the name that have an upper-case form and a lower-case form, the character MUST be recorded as lower-case, to simplify name comparisons. Lists specification that defines a record type and its use under this Name. The organization producing the specification retains control over the registry entry for the _Node Name Each RR type that is to be used MUST have a separate registry entry.

Initial entries in the registry are: RR Type _NODE NAME REFERENCE NULL _ta-* {see note} OPENPGPKEY _openpgpkey PTR _tcp PTR _udp SMIMEA _smimecert SRV _dccp SRV _ipv6 SRV _sip SRV _sctp SRV _tcp SRV _udp SRV _xmpp TLSA _dane TLSA _sctp TLSA _tcp TLSA _udp TXT _mta-sts TXT _acme-challenge TXT _dmarc TXT _domainkey TXT _spf TXT _vouch URI _iax URI _acct URI _dccp URI _email URI _ems URI _fax URI _ft URI _h323 URI _ical-sched URI _ical-access URI _ifax URI _im URI _mms URI _pres URI _pstn URI _sctp URI _sip URI _sms URI _tcp URI _udp URI _unifmsg URI _vcard URI _videomsg URI _voice URI _voicemsg URI _vpim URI _web URI _xmpp Under the NULL RR, the entry "_ta-*" is meant to denote all node names beginning with the string "_ta-". It does NOT refer to a DNS wildcard specification.

This section provides guidance for expert review of registration requests in the DNS Underscore Global Scoped Entry Registry. This review is solely to determine adequacy of a requested entry in this Registry, and does not include review of other aspects of the document specifying that entry. For example such a document might also contain a definition of the resource record type that is referenced by the requested entry. Any required review of that definition is separate from the expert review required here. The review is for the purposes of ensuring that: The details for creating the registry entry are sufficiently clear, precise and complete The combination of the underscored name, under which the listed resource record type is used, and the resource record type, is unique in the table For the purposes of this Expert Review, other matters of the specification's technical quality, adequacy or the like are outside of scope.

This memo raises no security issues.

USC/ISI

4676 Admiralty Way Marina del Rey CA 90291 US +1 213 822 1511

USC/ISI

4676 Admiralty Way Marina del Rey CA 90291 US +1 213 822 1511

Harvard University

1350 Mass. Ave. Cambridge MA 02138 - +1 617 495 3864 sob@harvard.edu

General keyword In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. Authors who follow these guidelines should incorporate this phrase near the beginning of their document: The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. Note that the force of these words is modified by the requirement level of the document in which they are used. PTI Huawei Technologies IBM Corporation Troll Tech

Waldemar Thranes gate 98B Oslo N-0175 NO +47 22 806390 +47 22 806380 arnt@troll.no

Internet Software Consortium

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Microsoft Corporation

One Microsoft Way Redmond WA 98052 US levone@microsoft.com

This document describes a DNS RR which specifies the location of the server(s) for a specific protocol and domain. This memo describes extensions to and applications of the core features of the Extensible Messaging and Presence Protocol (XMPP) that provide the basic instant messaging (IM) and presence functionality defined in RFC 2779. [STANDARDS-TRACK] A Mobile IPv6 node requires a Home Agent address, a home address, and IPsec security associations with its Home Agent before it can start utilizing Mobile IPv6 service. RFC 3775 requires that some or all of these are statically configured. This document defines how a Mobile IPv6 node can bootstrap this information from non-topological information and security credentials pre-configured on the Mobile Node. The solution defined in this document solves the split scenario described in the Mobile IPv6 bootstrapping problem statement in RFC 4640. The split scenario refers to the case where the Mobile Node's mobility service is authorized by a different service provider than basic network access. The solution described in this document is also generically applicable to any bootstrapping case, since other scenarios are more specific realizations of the split scenario. [STANDARDS-TRACK] This document registers with IANA two new DNS SRV protocol labels for resolving Instant Messaging and Presence services with SIP. [STANDARDS TRACK] Domain Assurance Council Domain Assurance Council Alt-N Technologies This document revises all Enumservices that were IANA registered under the now obsolete specification of the Enumservice registry defined in RFC 3761. [STANDARDS-TRACK] This document registers an Enumservice for the Inter-Asterisk eXchange (IAX) protocol according to the guidelines given in RFC 6117. This document is not an Internet Standards Track specification; it is published for informational purposes. DomainKeys Identified Mail (DKIM) defines a domain-level authentication framework for email using public-key cryptography and key server technology to permit verification of the source and contents of messages by either Mail Transfer Agents (MTAs) or Mail User Agents (MUAs). The ultimate goal of this framework is to permit a signing domain to assert responsibility for a message, thus protecting message signer identity and the integrity of the messages they convey while retaining the functionality of Internet email as it is known today. Protection of email identity may assist in the global control of "spam" and "phishing". [STANDARDS TRACK] This document specifies how DNS resource records are named and structured to facilitate service discovery. Given a type of service that a client is looking for, and a domain in which the client is looking for that service, this mechanism allows clients to discover a list of named instances of that desired service, using standard DNS queries. This mechanism is referred to as DNS-based Service Discovery, or DNS-SD. Netnod ISOC This document registers an E.164 Number Mapping (ENUM) service for 'acct' URIs (Uniform Resource Identifiers). This document clarifies and updates the DNS-Based Authentication of Named Entities (DANE) TLSA specification (RFC 6698), based on subsequent implementation experience. It also contains guidance for implementers, operators, and protocol developers who want to use DANE records.

Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Martin Hoffmann, Paul Hoffman, Peter Koch, Olaf Kolkman, Murray Kucherawy, John Levine, and Andrew Sullivan for diligent review of the (much) earlier drafts. For the later enhancements, thanks to: Stephane Bortzmeyer, Alissa Cooper, Bob Harold, Benjamin Kaduk, Mirja Kühlewind, Warren Kumari, John Levine, Joel Jaeggli, Benno Overeinder, Eric Rescorla, Adam Roach, Petr Špaček, Ondřej Surý, Paul Vixie, Tim Wicinski, and Paul Wouters. Special thanks to Ray Bellis for his persistent encouragement to continue this effort, as well as the suggestion for an essential simplification to the registration model.