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Network Working Group                                         J. KlensinRequest for Comments: 3467                                 February 2003Category: InformationalRole of the Domain Name System (DNS)Status of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2003).  All Rights Reserved.Abstract   This document reviews the original function and purpose of the domain   name system (DNS).  It contrasts that history with some of the   purposes for which the DNS has recently been applied and some of the   newer demands being placed upon it or suggested for it.  A framework   for an alternative to placing these additional stresses on the DNS is   then outlined.  This document and that framework are not a proposed   solution, only a strong suggestion that the time has come to begin   thinking more broadly about the problems we are encountering and   possible approaches to solving them.Table of Contents1.  Introduction and History .....................................21.1 Context for DNS Development ...............................31.2 Review of the DNS and Its Role as Designed ................41.3 The Web and User-visible Domain Names .....................61.4 Internet Applications Protocols and Their Evolution .......72.  Signs of DNS Overloading .....................................83.  Searching, Directories, and the DNS ..........................123.1 Overview  .................................................123.2 Some Details and Comments .................................144.  Internationalization .........................................154.1 ASCII Isn't Just Because of English .......................164.2 The "ASCII Encoding" Approaches ...........................174.3 "Stringprep" and Its Complexities .........................174.4 The Unicode Stability Problem .............................194.5 Audiences, End Users, and the User Interface Problem ......20      4.6 Business Cards and Other Natural Uses of Natural Languages. 224.7 ASCII Encodings and the Roman Keyboard Assumption .........22Klensin                      Informational                      [Page 1]

RFC 3467          Role of the Domain Name System (DNS)     February 20034.8 Intra-DNS Approaches for "Multilingual Names" .............235.  Search-based Systems: The Key Controversies ..................236.  Security Considerations ......................................247.  References ...................................................257.1 Normative References ......................................257.2 Explanatory and Informative References ....................258.  Acknowledgements .............................................309.  Author's Address .............................................3010. Full Copyright Statement .....................................311. Introduction and History   The DNS was designed as a replacement for the older "host table"   system.  Both were intended to provide names for network resources at   a more abstract level than network (IP) addresses (see, e.g.,   [RFC625], [RFC811], [RFC819], [RFC830], [RFC882]).  In recent years,   the DNS has become a database of convenience for the Internet, with   many proposals to add new features.  Only some of these proposals   have been successful.  Often the main (or only) motivation for using   the DNS is because it exists and is widely deployed, not because its   existing structure, facilities, and content are appropriate for the   particular application of data involved.  This document reviews the   history of the DNS, including examination of some of those newer   applications.  It then argues that the overloading process is often   inappropriate.  Instead, it suggests that the DNS should be   supplemented by systems better matched to the intended applications   and outlines a framework and rationale for one such system.   Several of the comments that follow are somewhat revisionist.  Good   design and engineering often requires a level of intuition by the   designers about things that will be necessary in the future; the   reasons for some of these design decisions are not made explicit at   the time because no one is able to articulate them.  The discussion   below reconstructs some of the decisions about the Internet's primary   namespace (the "Class=IN" DNS) in the light of subsequent development   and experience.  In addition, the historical reasons for particular   decisions about the Internet were often severely underdocumented   contemporaneously and, not surprisingly, different participants have   different recollections about what happened and what was considered   important.  Consequently, the quasi-historical story below is just   one story.  There may be (indeed, almost certainly are) other stories   about how the DNS evolved to its present state, but those variants do   not invalidate the inferences and conclusions.   This document presumes a general understanding of the terminology ofRFC 1034 [RFC1034] or of any good DNS tutorial (see, e.g., [Albitz]).Klensin                      Informational                      [Page 2]

RFC 3467          Role of the Domain Name System (DNS)     February 20031.1  Context for DNS Development   During the entire post-startup-period life of the ARPANET and nearly   the first decade or so of operation of the Internet, the list of host   names and their mapping to and from addresses was maintained in a   frequently-updated "host table" [RFC625], [RFC811], [RFC952].  The   names themselves were restricted to a subset of ASCII [ASCII] chosen   to avoid ambiguities in printed form, to permit interoperation with   systems using other character codings (notably EBCDIC), and to avoid   the "national use" code positions of ISO 646 [IS646].  These   restrictions later became collectively known as the "LDH" rules for   "letter-digit-hyphen", the permitted characters.  The table was just   a list with a common format that was eventually agreed upon; sites   were expected to frequently obtain copies of, and install, new   versions.  The host tables themselves were introduced to:   o  Eliminate the requirement for people to remember host numbers      (addresses).  Despite apparent experience to the contrary in the      conventional telephone system, numeric numbering systems,      including the numeric host number strategy, did not (and do not)      work well for more than a (large) handful of hosts.   o  Provide stability when addresses changed.  Since addresses -- to      some degree in the ARPANET and more importantly in the      contemporary Internet -- are a function of network topology and      routing, they often had to be changed when connectivity or      topology changed.  The names could be kept stable even as      addresses changed.   o  Provide the capability to have multiple addresses associated with      a given host to reflect different types of connectivity and      topology.  Use of names, rather than explicit addresses, avoided      the requirement that would otherwise exist for users and other      hosts to track these multiple host numbers and addresses and the      topological considerations for selecting one over others.   After several years of using the host table approach, the community   concluded that model did not scale adequately and that it would not   adequately support new service variations.  A number of discussions   and meetings were held which drew several ideas and incomplete   proposals together.  The DNS was the result of that effort.  It   continued to evolve during the design and initial implementation   period, with a number of documents recording the changes (see   [RFC819], [RFC830], and [RFC1034]).Klensin                      Informational                      [Page 3]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   The goals for the DNS included:   o  Preservation of the capabilities of the host table arrangements      (especially unique, unambiguous, host names),   o  Provision for addition of additional services (e.g., the special      record types for electronic mail routing which quickly followed      introduction of the DNS), and   o  Creation of a robust, hierarchical, distributed, name lookup      system to accomplish the other goals.   The DNS design also permitted distribution of name administration,   rather than requiring that each host be entered into a single,   central, table by a central administration.1.2 Review of the DNS and Its Role as Designed   The DNS was designed to identify network resources.  Although there   was speculation about including, e.g., personal names and email   addresses, it was not designed primarily to identify people, brands,   etc.  At the same time, the system was designed with the flexibility   to accommodate new data types and structures, both through the   addition of new record types to the initial "INternet" class, and,   potentially, through the introduction of new classes.  Since the   appropriate identifiers and content of those future extensions could   not be anticipated, the design provided that these fields could   contain any (binary) information, not just the restricted text forms   of the host table.   However, the DNS, as it is actually used, is intimately tied to the   applications and application protocols that utilize it, often at a   fairly low level.   In particular, despite the ability of the protocols and data   structures themselves to accommodate any binary representation, DNS   names as used were historically not even unrestricted ASCII, but a   very restricted subset of it, a subset that derives from the original   host table naming rules.  Selection of that subset was driven in part   by human factors considerations, including a desire to eliminate   possible ambiguities in an international context.  Hence character   codes that had international variations in interpretation were   excluded, the underscore character and case distinctions were   eliminated as being confusing (in the underscore's case, with the   hyphen character) when written or read by people, and so on.  These   considerations appear to be very similar to those that resulted in   similarly restricted character sets being used as protocol elements   in many ITU and ISO protocols (cf. [X29]).Klensin                      Informational                      [Page 4]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   Another assumption was that there would be a high ratio of physical   hosts to second level domains and, more generally, that the system   would be deeply hierarchical, with most systems (and names) at the   third level or below and a very large percentage of the total names   representing physical hosts.  There are domains that follow this   model: many university and corporate domains use fairly deep   hierarchies, as do a few country-oriented top level domains   ("ccTLDs").  Historically, the "US." domain has been an excellent   example of the deeply hierarchical approach.  However, by 1998,   comparison of several efforts to survey the DNS showed a count of SOA   records that approached (and may have passed) the number of distinct   hosts.  Looked at differently, we appear to be moving toward a   situation in which the number of delegated domains on the Internet is   approaching or exceeding the number of hosts, or at least the number   of hosts able to provide services to others on the network.  This   presumably results from synonyms or aliases that map a great many   names onto a smaller number of hosts.  While experience up to this   time has shown that the DNS is robust enough -- given contemporary   machines as servers and current bandwidth norms -- to be able to   continue to operate reasonably well when those historical assumptions   are not met (e.g., with a flat, structure under ".COM" containing   well over ten million delegated subdomains [COMSIZE]), it is still   useful to remember that the system could have been designed to work   optimally with a flat structure (and very large zones) rather than a   deeply hierarchical one, and was not.   Similarly, despite some early speculation about entering people's   names and email addresses into the DNS directly (e.g., see   [RFC1034]), electronic mail addresses in the Internet have preserved   the original, pre-DNS, "user (or mailbox) at location" conceptual   format rather than a flatter or strictly dot-separated one.   Location, in that instance, is a reference to a host. The sole   exception, at least in the "IN" class, has been one field of the SOA   record.   Both the DNS architecture itself and the two-level (host name and   mailbox name) provisions for email and similar functions (e.g., see   the finger protocol [FINGER]), also anticipated a relatively high   ratio of users to actual hosts.  Despite the observation inRFC 1034   that the DNS was expected to grow to be proportional to the number of   users (section 2.3), it has never been clear that the DNS was   seriously designed for, or could, scale to the order of magnitude of   number of users (or, more recently, products or document objects),   rather than that of physical hosts.   Just as was the case for the host table before it, the DNS provided   critical uniqueness for names, and universal accessibility to them,   as part of overall "single internet" and "end to end" models (cf.Klensin                      Informational                      [Page 5]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   [RFC2826]).  However, there are many signs that, as new uses evolved   and original assumptions were abused (if not violated outright), the   system was being stretched to, or beyond, its practical limits.   The original design effort that led to the DNS included examination   of the directory technologies available at the time.  The design   group concluded that the DNS design, with its simplifying assumptions   and restricted capabilities, would be feasible to deploy and make   adequately robust, which the more comprehensive directory approaches   were not.  At the same time, some of the participants feared that the   limitations might cause future problems; this document essentially   takes the position that they were probably correct.  On the other   hand, directory technology and implementations have evolved   significantly in the ensuing years: it may be time to revisit the   assumptions, either in the context of the two- (or more) level   mechanism contemplated by the rest of this document or, even more   radically, as a path toward a DNS replacement.1.3 The Web and User-visible Domain Names   From the standpoint of the integrity of the domain name system -- and   scaling of the Internet, including optimal accessibility to content   -- the web design decision to use "A record" domain names directly in   URLs, rather than some system of indirection, has proven to be a   serious mistake in several respects.  Convenience of typing, and the   desire to make domain names out of easily-remembered product names,   has led to a flattening of the DNS, with many people now perceiving   that second-level names under COM (or in some countries, second- or   third-level names under the relevant ccTLD) are all that is   meaningful.  This perception has been reinforced by some domain name   registrars [REGISTRAR] who have been anxious to "sell" additional   names.  And, of course, the perception that one needed a second-level   (or even top-level) domain per product, rather than having names   associated with a (usually organizational) collection of network   resources, has led to a rapid acceleration in the number of names   being registered.  That acceleration has, in turn, clearly benefited   registrars charging on a per-name basis, "cybersquatters", and others   in the business of "selling" names, but it has not obviously   benefited the Internet as a whole.   This emphasis on second-level domain names has also created a problem   for the trademark community.  Since the Internet is international,   and names are being populated in a flat and unqualified space,   similarly-named entities are in conflict even if there would   ordinarily be no chance of confusing them in the marketplace.  The   problem appears to be unsolvable except by a choice between draconian   measures.  These might include significant changes to the legislation   and conventions that govern disputes over "names" and "marks".  OrKlensin                      Informational                      [Page 6]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   they might result in a situation in which the "rights" to a name are   typically not settled using the subtle and traditional product (or   industry) type and geopolitical scope rules of the trademark system.   Instead they have depended largely on political or economic power,   e.g., the organization with the greatest resources to invest in   defending (or attacking) names will ultimately win out.  The latter   raises not only important issues of equity, but also the risk of   backlash as the numerous small players are forced to relinquish names   they find attractive and to adopt less-desirable naming conventions.   Independent of these sociopolitical problems, content distribution   issues have made it clear that it should be possible for an   organization to have copies of data it wishes to make available   distributed around the network, with a user who asks for the   information by name getting the topologically-closest copy.  This is   not possible with simple, as-designed, use of the DNS: DNS names   identify target resources or, in the case of email "MX" records, a   preferentially-ordered list of resources "closest" to a target (not   to the source/user).  Several technologies (and, in some cases,   corresponding business models) have arisen to work around these   problems, including intercepting and altering DNS requests so as to   point to other locations.   Additional implications are still being discovered and evaluated.   Approaches that involve interception of DNS queries and rewriting of   DNS names (or otherwise altering the resolution process based on the   topological location of the user) seem, however, to risk disrupting   end-to-end applications in the general case and raise many of the   issues discussed by the IAB in [IAB-OPES].  These problems occur even   if the rewriting machinery is accompanied by additional workarounds   for particular applications.  For example, security associations and   applications that need to identify "the same host" often run into   problems if DNS names or other references are changed in the network   without participation of the applications that are trying to invoke   the associated services.1.4 Internet Applications Protocols and Their Evolution   At the applications level, few of the protocols in active,   widespread, use on the Internet reflect either contemporary knowledge   in computer science or human factors or experience accumulated   through deployment and use.  Instead, protocols tend to be deployed   at a just-past-prototype level, typically including the types of   expedient compromises typical with prototypes.  If they prove useful,   the nature of the network permits very rapid dissemination (i.e.,   they fill a vacuum, even if a vacuum that no one previously knew   existed).  But, once the vacuum is filled, the installed baseKlensin                      Informational                      [Page 7]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   provides its own inertia: unless the design is so seriously faulty as   to prevent effective use (or there is a widely-perceived sense of   impending disaster unless the protocol is replaced), future   developments must maintain backward compatibility and workarounds for   problematic characteristics rather than benefiting from redesign in   the light of experience.  Applications that are "almost good enough"   prevent development and deployment of high-quality replacements.   The DNS is both an illustration of, and an exception to, parts of   this pessimistic interpretation. It was a second-generation   development, with the host table system being seen as at the end of   its useful life.  There was a serious attempt made to reflect the   computing state of the art at the time.  However, deployment was much   slower than expected (and very painful for many sites) and some fixed   (although relaxed several times) deadlines from a central network   administration were necessary for deployment to occur at all.   Replacing it now, in order to add functionality, while it continues   to perform its core functions at least reasonably well, would   presumably be extremely difficult.   There are many, perhaps obvious, examples of this.  Despite many   known deficiencies and weaknesses of definition, the "finger" and   "whois" [WHOIS] protocols have not been replaced (despite many   efforts to update or replace the latter [WHOIS-UPDATE]).  The Telnet   protocol and its many options drove out the SUPDUP [RFC734] one,   which was arguably much better designed for a diverse collection of   network hosts.  A number of efforts to replace the email or file   transfer protocols with models which their advocates considered much   better have failed.  And, more recently and below the applications   level, there is some reason to believe that this resistance to change   has been one of the factors impeding IPv6 deployment.2. Signs of DNS Overloading   Parts of the historical discussion above identify areas in which the   DNS has become overloaded (semantically if not in the mechanical   ability to resolve names).  Despite this overloading, it appears that   DNS performance and reliability are still within an acceptable range:   there is little evidence of serious performance degradation.  Recent   proposals and mechanisms to better respond to overloading and scaling   issues have all focused on patching or working around limitations   that develop when the DNS is utilized for out-of-design functions,   rather than on dramatic rethinking of either DNS design or those   uses.  The number of these issues that have arisen at much the same   time may argue for just that type of rethinking, and not just for   adding complexity and attempting to incrementally alter the design   (see, for example, the discussion of simplicity insection 2 of   [RFC3439]).Klensin                      Informational                      [Page 8]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   For example:   o  While technical approaches such as larger and higher-powered      servers and more bandwidth, and legal/political mechanisms such as      dispute resolution policies, have arguably kept the problems from      becoming critical, the DNS has not proven adequately responsive to      business and individual needs to describe or identify things (such      as product names and names of individuals) other than strict      network resources.   o  While stacks have been modified to better handle multiple      addresses on a physical interface and some protocols have been      extended to include DNS names for determining context, the DNS      does not deal especially well with many names associated with a      given host (e.g., web hosting facilities with multiple domains on      a server).   o  Efforts to add names deriving from languages or character sets      based on other than simple ASCII and English-like names (see      below), or even to utilize complex company or product names      without the use of hierarchy, have created apparent requirements      for names (labels) that are over 63 octets long.  This requirement      will undoubtedly increase over time; while there are workarounds      to accommodate longer names, they impose their own restrictions      and cause their own problems.   o  Increasing commercialization of the Internet, and visibility of      domain names that are assumed to match names of companies or      products, has turned the DNS and DNS names into a trademark      battleground.  The traditional trademark system in (at least) most      countries makes careful distinctions about fields of      applicability.  When the space is flattened, without      differentiation by either geography or industry sector, not only      are there likely conflicts between "Joe's Pizza" (of Boston) and      "Joe's Pizza" (of San Francisco) but between both and "Joe's Auto      Repair" (of Los Angeles).  All three would like to control      "Joes.com" (and would prefer, if it were permitted by DNS naming      rules, to also spell it as "Joe's.com" and have both resolve the      same way) and may claim trademark rights to do so, even though      conflict or confusion would not occur with traditional trademark      principles.   o  Many organizations wish to have different web sites under the same      URL and domain name.  Sometimes this is to create local variations      -- the Widget Company might want to present different material to      a UK user relative to a US one -- and sometimes it is to provide      higher performance by supplying information from the server      topologically closest to the user.  If the name resolutionKlensin                      Informational                      [Page 9]

RFC 3467          Role of the Domain Name System (DNS)     February 2003      mechanism is expected to provide this functionality, there are      three possible models (which might be combined):      -  supply information about multiple sites (or locations or         references).  Those sites would, in turn, provide information         associated with the name and sufficient site-specific         attributes to permit the application to make a sensible choice         of destination, or      -  accept client-site attributes and utilize them in the search         process, or      -  return different answers based on the location or identity of         the requestor.   While there are some tricks that can provide partial simulations of   these types of function, DNS responses cannot be reliably conditioned   in this way.   These, and similar, issues of performance or content choices can, of   course, be thought of as not involving the DNS at all.  For example,   the commonly-cited alternate approach of coupling these issues to   HTTP content negotiation (cf. [RFC2295]), requires that an HTTP   connection first be opened to some "common" or "primary" host so that   preferences can be negotiated and then the client redirected or sent   alternate data.  At least from the standpoint of improving   performance by accessing a "closer" location, both initially and   thereafter, this approach sacrifices the desired result before the   client initiates any action.  It could even be argued that some of   the characteristics of common content negotiation approaches are   workarounds for the non-optimal use of the DNS in web URLs.   o  Many existing and proposed systems for "finding things on the      Internet" require a true search capability in which near matches      can be reported to the user (or to some user agent with an      appropriate rule-set) and to which queries may be ambiguous or      fuzzy.  The DNS, by contrast, can accommodate only one set of      (quite rigid) matching rules.  Proposals to permit different rules      in different localities (e.g., matching rules that are TLD- or      zone-specific) help to identify the problem.  But they cannot be      applied directly to the DNS without either abandoning the desired      level of flexibility or isolating different parts of the Internet      from each other (or both).  Fuzzy or ambiguous searches are      desirable for resolution of names that might have spelling      variations and for names that can be resolved into different sets      of glyphs depending on context.  Especially when      internationalization is considered, variant name problems go      beyond simple differences in representation of a character orKlensin                      Informational                     [Page 10]

RFC 3467          Role of the Domain Name System (DNS)     February 2003      ordering of a string.  Instead, avoiding user astonishment and      confusion requires consideration of relationships such as      languages that can be written with different alphabets, Kanji-      Hiragana relationships, Simplified and Traditional Chinese, etc.      See [Seng] for a discussion and suggestions for addressing a      subset of these issues in the context of characters based on      Chinese ones.  But that document essentially illustrates the      difficulty of providing the type of flexible matching that would      be anticipated by users; instead, it tries to protect against the      worst types of confusion (and opportunities for fraud).   o  The historical DNS, and applications that make assumptions about      how it works, impose significant risk (or forces technical kludges      and consequent odd restrictions), when one considers adding      mechanisms for use with various multi-character-set and      multilingual "internationalization" systems.  See the IAB's      discussion of some of these issues [RFC2825] for more information.   o  In order to provide proper functionality to the Internet, the DNS      must have a single unique root (the IAB provides more discussion      of this issue [RFC2826]).  There are many desires for local      treatment of names or character sets that cannot be accommodated      without either multiple roots (e.g., a separate root for      multilingual names, proposed at various times by MINC [MINC] and      others), or mechanisms that would have similar effects in terms of      Internet fragmentation and isolation.   o  For some purposes, it is desirable to be able to search not only      an index entry (labels or fully-qualified names in the DNS case),      but their values or targets (DNS data).  One might, for example,      want to locate all of the host (and virtual host) names which      cause mail to be directed to a given server via MX records.  The      DNS does not support this capability (see the discussion in      [IQUERY]) and it can be simulated only by extracting all of the      relevant records (perhaps by zone transfer if the source permits      doing so, but that permission is becoming less frequently      available) and then searching a file built from those records.   o  Finally, as additional types of personal or identifying      information are added to the DNS, issues arise with protection of      that information.  There are increasing calls to make different      information available based on the credentials and authorization      of the source of the inquiry.  As with information keyed to site      locations or proximity (as discussed above), the DNS protocols      make providing these differentiated services quite difficult if      not impossible.Klensin                      Informational                     [Page 11]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   In each of these cases, it is, or might be, possible to devise ways   to trick the DNS system into supporting mechanisms that were not   designed into it.  Several ingenious solutions have been proposed in   many of these areas already, and some have been deployed into the   marketplace with some success.  But the price of each of these   changes is added complexity and, with it, added risk of unexpected   and destabilizing problems.   Several of the above problems are addressed well by a good directory   system (supported by the LDAP protocol or some protocol more   precisely suited to these specific applications) or searching   environment (such as common web search engines) although not by the   DNS.  Given the difficulty of deploying new applications discussed   above, an important question is whether the tricks and kludges are   bad enough, or will become bad enough as usage grows, that new   solutions are needed and can be deployed.3. Searching, Directories, and the DNS3.1 Overview   The constraints of the DNS and the discussion above suggest the   introduction of an intermediate protocol mechanism, referred to below   as a "search layer" or "searchable system".  The terms "directory"   and "directory system" are used interchangeably with "searchable   system" in this document, although the latter is far more precise.   Search layer proposals would use a two (or more) stage lookup, not   unlike several of the proposals for internationalized names in the   DNS (seesection 4), but all operations but the final one would   involve searching other systems, rather than looking up identifiers   in the DNS itself.  As explained below, this would permit relaxation   of several constraints, leading to a more capable and comprehensive   overall system.   Ultimately, many of the issues with domain names arise as the result   of efforts to use the DNS as a directory.  While, at the time this   document was written, sufficient pressure or demand had not occurred   to justify a change, it was already quite clear that, as a directory   system, the DNS is a good deal less than ideal.  This document   suggests that there actually is a requirement for a directory system,   and that the right solution to a searchable system requirement is a   searchable system, not a series of DNS patches, kludges, or   workarounds.Klensin                      Informational                     [Page 12]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   The following points illustrate particular aspects of this   conclusion.   o  A directory system would not require imposition of particular      length limits on names.   o  A directory system could permit explicit association of      attributes, e.g., language and country, with a name, without      having to utilize trick encodings to incorporate that information      in DNS labels (or creating artificial hierarchy for doing so).   o  There is considerable experience (albeit not much of it very      successful) in doing fuzzy and "sonex" (similar-sounding) matching      in directory systems.  Moreover, it is plausible to think about      different matching rules for different areas and sets of names so      that these can be adapted to local cultural requirements.      Specifically, it might be possible to have a single form of a name      in a directory, but to have great flexibility about what queries      matched that name (and even have different variations in different      areas).  Of course, the more flexibility that a system provides,      the greater the possibility of real or imagined trademark      conflicts.  But the opportunity would exist to design a directory      structure that dealt with those issues in an intelligent way,      while DNS constraints almost certainly make a general and      equitable DNS-only solution impossible.   o  If a directory system is used to translate to DNS names, and then      DNS names are looked up in the normal fashion, it may be possible      to relax several of the constraints that have been traditional      (and perhaps necessary) with the DNS.  For example, reverse-      mapping of addresses to directory names may not be a requirement      even if mapping of addresses to DNS names continues to be, since      the DNS name(s) would (continue to) uniquely identify the host.   o  Solutions to multilingual transcription problems that are common      in "normal life" (e.g., two-sided business cards to be sure that      recipients trying to contact a person can access romanized      spellings and numbers if the original language is not      comprehensible to them) can be easily handled in a directory      system by inserting both sets of entries.   o  A directory system could be designed that would return, not a      single name, but a set of names paired with network-locational      information or other context-establishing attributes.  This type      of information might be of considerable use in resolving the      "nearest (or best) server for a particular named resource"Klensin                      Informational                     [Page 13]

RFC 3467          Role of the Domain Name System (DNS)     February 2003      problems that are a significant concern for organizations hosting      web and other sites that are accessed from a wide range of      locations and subnets.   o  Names bound to countries and languages might help to manage      trademark realities, while, as discussed insection 1.3 above, use      of the DNS in trademark-significant contexts tends to require      worldwide "flattening" of the trademark system.   Many of these issues are a consequence of another property of the   DNS:  names must be unique across the Internet.  The need to have a   system of unique identifiers is fairly obvious (see [RFC2826]).   However, if that requirement were to be eliminated in a search or   directory system that was visible to users instead of the DNS, many   difficult problems -- of both an engineering and a policy nature --   would be likely to vanish.3.2 Some Details and Comments   Almost any internationalization proposal for names that are in, or   map into, the DNS will require changing DNS resolver API calls   ("gethostbyname" or equivalent), or adding some pre-resolution   preparation mechanism, in almost all Internet applications -- whether   to cause the API to take a different character set (no matter how it   is then mapped into the bits used in the DNS or another system), to   accept or return more arguments with qualifying or identifying   information, or otherwise.  Once applications must be opened to make   such changes, it is a relatively small matter to switch from calling   into the DNS to calling a directory service and then the DNS (in many   situations, both actions could be accomplished in a single API call).   A directory approach can be consistent both with "flat" models and   multi-attribute ones.  The DNS requires strict hierarchies, limiting   its ability to differentiate among names by their properties.  By   contrast, modern directories can utilize independently-searched   attributes and other structured schema to provide flexibilities not   present in a strictly hierarchical system.   There is a strong historical argument for a single directory   structure (implying a need for mechanisms for registration,   delegation, etc.).  But a single structure is not a strict   requirement, especially if in-depth case analysis and design work   leads to the conclusion that reverse-mapping to directory names is   not a requirement (seesection 5).  If a single structure is not   needed, then, unlike the DNS, there would be no requirement for a   global organization to authorize or delegate operation of portions of   the structure.Klensin                      Informational                     [Page 14]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   The "no single structure" concept could be taken further by moving   away from simple "names" in favor of, e.g., multiattribute,   multihierarchical, faceted systems in which most of the facets use   restricted vocabularies.  (These terms are fairly standard in the   information retrieval and classification system literature, see,   e.g., [IS5127].)  Such systems could be designed to avoid the need   for procedures to ensure uniqueness across, or even within, providers   and databases of the faceted entities for which the search is to be   performed.  (See [DNS-Search] for further discussion.)   While the discussion above includes very general comments about   attributes, it appears that only a very small number of attributes   would be needed.  The list would almost certainly include country and   language for internationalization purposes.  It might require   "charset" if we cannot agree on a character set and encoding,   although there are strong arguments for simply using ISO 10646 (also   known as Unicode or "UCS" (for Universal Character Set) [UNICODE],   [IS10646] coding in interchange.  Trademark issues might motivate   "commercial" and "non-commercial" (or other) attributes if they would   be helpful in bypassing trademark problems.  And applications to   resource location, such as those contemplated for Uniform Resource   Identifiers (URIs) [RFC2396,RFC3305] or the Service Location   Protocol [RFC2608], might argue for a few other attributes (as   outlined above).4.  Internationalization   Much of the thinking underlying this document was driven by   considerations of internationalizing the DNS or, more specifically,   providing access to the functions of the DNS from languages and   naming systems that cannot be accurately expressed in the traditional   DNS subset of ASCII.  Much of the relevant work was done in the   IETF's "Internationalized Domain Names" Working Group (IDN-WG),   although this document also draws on extensive parallel discussions   in other forums.  This section contains an evaluation of what was   learned as an "internationalized DNS" or "multilingual DNS" was   explored and suggests future steps based on that evaluation.   When the IDN-WG was initiated, it was obvious to several of the   participants that its first important task was an undocumented one:   to increase the understanding of the complexities of the problem   sufficiently that naive solutions could be rejected and people could   go to work on the harder problems.  The IDN-WG clearly accomplished   that task. The beliefs that the problems were simple, and in the   corresponding simplistic approaches and their promises of quick and   painless deployment, effectively disappeared as the WG's efforts   matured.Klensin                      Informational                     [Page 15]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   Some of the lessons learned from increased understanding and the   dissipation of naive beliefs should be taken as cautions by the wider   community: the problems are not simple. Specifically, extracting   small elements for solution rather than looking at whole systems, may   result in obscuring the problems but not solving any problem that is   worth the trouble.4.1 ASCII Isn't Just Because of English   The hostname rules chosen in the mid-70s weren't just "ASCII because   English uses ASCII", although that was a starting point.  We have   discovered that almost every other script (and even ASCII if we   permit the rest of the characters specified in the ISO 646   International Reference Version) is more complex than hostname-   restricted-ASCII (the "LDH" form, seesection 1.1).  And ASCII isn't   sufficient to completely represent English -- there are several words   in the language that are correctly spelled only with characters or   diacritical marks that do not appear in ASCII.  With a broader   selection of scripts, in some examples, case mapping works from one   case to the other but is not reversible.  In others, there are   conventions about alternate ways to represent characters (in the   language, not [only] in character coding) that work most of the time,   but not always.  And there are issues in coding, with Unicode/10646   providing different ways to represent the same character   ("character", rather than "glyph", is used deliberately here).  And,   in still others, there are questions as to whether two glyphs   "match", which may be a distance-function question, not one with a   binary answer.  The IETF approach to these problems is to require   pre-matching canonicalization (see the "stringprep" discussion   below).   The IETF has resisted the temptations to either try to specify an   entirely new coded character set, or to pick and choose Unicode/10646   characters on a per-character basis rather than by using well-defined   blocks.  While it may appear that a character set designed to meet   Internet-specific needs would be very attractive, the IETF has never   had the expertise, resources, and representation from critically-   important communities to actually take on that job.  Perhaps more   important, a new effort might have chosen to make some of the many   complex tradeoffs differently than the Unicode committee did,   producing a code with somewhat different characteristics.  But there   is no evidence that doing so would produce a code with fewer problems   and side-effects.  It is much more likely that making tradeoffs   differently would simply result in a different set of problems, which   would be equally or more difficult.Klensin                      Informational                     [Page 16]

RFC 3467          Role of the Domain Name System (DNS)     February 20034.2 The "ASCII Encoding" Approaches   While the DNS can handle arbitrary binary strings without known   internal problems (see [RFC2181]), some restrictions are imposed by   the requirement that text be interpreted in a case-independent way   ([RFC1034], [RFC1035]).  More important, most internet applications   assume the hostname-restricted "LDH" syntax that is specified in the   host table RFCs and as "prudent" inRFC 1035.  If those assumptions   are not met, many conforming implementations of those applications   may exhibit behavior that would surprise implementors and users.  To   avoid these potential problems, IETF internationalization work has   focused on "ASCII-Compatible Encodings" (ACE).  These encodings   preserve the LDH conventions in the DNS itself.  Implementations of   applications that have not been upgraded utilize the encoded forms,   while newer ones can be written to recognize the special codings and   map them into non-ASCII characters. These approaches are, however,   not problem-free even if human interface issues are ignored.  Among   other issues, they rely on what is ultimately a heuristic to   determine whether a DNS label is to be considered as an   internationalized name (i.e., encoded Unicode) or interpreted as an   actual LDH name in its own right.  And, while all determinations of   whether a particular query matches a stored object are traditionally   made by DNS servers, the ACE systems, when combined with the   complexities of international scripts and names, require that much of   the matching work be separated into a separate, client-side,   canonicalization or "preparation" process before the DNS matching   mechanisms are invoked [STRINGPREP].4.3 "Stringprep" and Its Complexities   As outlined above, the model for avoiding problems associated with   putting non-ASCII names in the DNS and elsewhere evolved into the   principle that strings are to be placed into the DNS only after being   passed through a string preparation function that eliminates or   rejects spurious character codes, maps some characters onto others,   performs some sequence canonicalization, and generally creates forms   that can be accurately compared.  The impact of this process on   hostname-restricted ASCII (i.e., "LDH") strings is trivial and   essentially adds only overhead.  For other scripts, the impact is, of   necessity, quite significant.   Although the general notion underlying stringprep is simple, the many   details are quite subtle and the associated tradeoffs are complex. A   design team worked on it for months, with considerable effort placed   into clarifying and fine-tuning the protocol and tables.  Despite   general agreement that the IETF would avoid getting into the business   of defining character sets, character codings, and the associated   conventions, the group several times considered and rejected specialKlensin                      Informational                     [Page 17]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   treatment of code positions to more nearly match the distinctions   made by Unicode with user perceptions about similarities and   differences between characters.  But there were intense temptations   (and pressures) to incorporate language-specific or country-specific   rules.  Those temptations, even when resisted, were indicative of   parts of the ongoing controversy or of the basic unsuitability of the   DNS for fully internationalized names that are visible,   comprehensible, and predictable for end users.   There have also been controversies about how far one should go in   these processes of preparation and transformation and, ultimately,   about the validity of various analogies.  For example, each of the   following operations has been claimed to be similar to case-mapping   in ASCII:   o  stripping of vowels in Arabic or Hebrew   o  matching of "look-alike" characters such as upper-case Alpha in      Greek and upper-case A in Roman-based alphabets   o  matching of Traditional and Simplified Chinese characters that      represent the same words,   o  matching of Serbo-Croatian words whether written in Roman-derived      or Cyrillic characters   A decision to support any of these operations would have implications   for other scripts or languages and would increase the overall   complexity of the process.  For example, unless language-specific   information is somehow available, performing matching between   Traditional and Simplified Chinese has impacts on Japanese and Korean   uses of the same "traditional" characters (e.g., it would not be   appropriate to map Kanji into Simplified Chinese).   Even were the IDN-WG's other work to have been abandoned completely   or if it were to fail in the marketplace, the stringprep and nameprep   work will continue to be extremely useful, both in identifying issues   and problem code points and in providing a reasonable set of basic   rules.  Where problems remain, they are arguably not with nameprep,   but with the DNS-imposed requirement that its results, as with all   other parts of the matching and comparison process, yield a binary   "match or no match" answer, rather than, e.g., a value on a   similarity scale that can be evaluated by the user or by user-driven   heuristic functions.Klensin                      Informational                     [Page 18]

RFC 3467          Role of the Domain Name System (DNS)     February 20034.4 The Unicode Stability Problem   ISO 10646 basically defines only code points, and not rules for using   or comparing the characters.  This is part of a long-standing   tradition with the work of what is now ISO/IEC JTC1/SC2: they have   performed code point assignments and have typically treated the ways   in which characters are used as beyond their scope.  Consequently,   they have not dealt effectively with the broader range of   internationalization issues.  By contrast, the Unicode Technical   Committee (UTC) has defined, in annexes and technical reports (see,   e.g., [UTR15]), some additional rules for canonicalization and   comparison.  Many of those rules and conventions have been factored   into the "stringprep" and "nameprep" work, but it is not   straightforward to make or define them in a fashion that is   sufficiently precise and permanent to be relied on by the DNS.   Perhaps more important, the discussions leading to nameprep also   identified several areas in which the UTC definitions are inadequate,   at least without additional information, to make matching precise and   unambiguous.  In some of these cases, the Unicode Standard permits   several alternate approaches, none of which are an exact and obvious   match to DNS needs.  That has left these sensitive choices up to   IETF, which lacks sufficient in-depth expertise, much less any   mechanism for deciding to optimize one language at the expense of   another.   For example, it is tempting to define some rules on the basis of   membership in particular scripts, or for punctuation characters, but   there is no precise definition of what characters belong to which   script or which ones are, or are not, punctuation.  The existence of   these areas of vagueness raises two issues: whether trying to do   precise matching at the character set level is actually possible   (addressed below) and whether driving toward more precision could   create issues that cause instability in the implementation and   resolution models for the DNS.   The Unicode definition also evolves.  Version 3.2 appeared shortly   after work on this document was initiated.  It added some characters   and functionality and included a few minor incompatible code point   changes.  IETF has secured an agreement about constraints on future   changes, but it remains to be seen how that agreement will work out   in practice.  The prognosis actually appears poor at this stage,   since UTC chose to ballot a recent possible change which should have   been prohibited by the agreement (the outcome of the ballot is not   relevant, only that the ballot was issued rather than having the   result be a foregone conclusion).  However, some members of the   community consider some of the changes between Unicode 3.0 and 3.1   and between 3.1 and 3.2, as well as this recent ballot, to beKlensin                      Informational                     [Page 19]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   evidence of instability and that these instabilities are better   handled in a system that can be more flexible about handling of   characters, scripts, and ancillary information than the DNS.   In addition, because the systems implications of internationalization   are considered out of scope in SC2, ISO/IEC JTC1 has assigned some of   those issues to its SC22/WG20 (the Internationalization working group   within the subcommittee that deals with programming languages,   systems, and environments).  WG20 has historically dealt with   internationalization issues thoughtfully and in depth, but its status   has several times been in doubt in recent years.  However, assignment   of these matters to WG20 increases the risk of eventual ISO   internationalization standards that specify different behavior than   the UTC specifications.4.5 Audiences, End Users, and the User Interface Problem   Part of what has "caused" the DNS internationalization problem, as   well as the DNS trademark problem and several others, is that we have   stopped thinking about "identifiers for objects" -- which normal   people are not expected to see -- and started thinking about "names"   -- strings that are expected not only to be readable, but to have   linguistically-sensible and culturally-dependent meaning to non-   specialist users.   Within the IETF, the IDN-WG, and sometimes other groups, avoided   addressing the implications of that transition by taking "outside our   scope -- someone else's problem" approaches or by suggesting that   people will just become accustomed to whatever conventions are   adopted.  The realities of user and vendor behavior suggest that   these approaches will not serve the Internet community well in the   long term:   o  If we want to make it a problem in a different part of the user      interface structure, we need to figure out where it goes in order      to have proof of concept of our solution.  Unlike vendors whose      sole [business] model is the selling or registering of names, the      IETF must produce solutions that actually work, in the      applications context as seen by the end user.   o  The principle that "they will get used to our conventions and      adapt" is fine if we are writing rules for programming languages      or an API.  But the conventions under discussion are not part of a      semi-mathematical system, they are deeply ingrained in culture.      No matter how often an English-speaking American is told that the      Internet requires that the correct spelling of "colour" be used,      he or she isn't going to be convinced. Getting a French-speaker in      Lyon to use exactly the same lexical conventions as a French-Klensin                      Informational                     [Page 20]

RFC 3467          Role of the Domain Name System (DNS)     February 2003      speaker in Quebec in order to accommodate the decisions of the      IETF or of a registrar or registry is just not likely.  "Montreal"      is either a misspelling or an anglicization of a similar word with      an acute accent mark over the "e" (i.e., using the Unicode      character U+00E9 or one of its equivalents). But global agreement      on a rule that will determine whether the two forms should match      -- and that won't astonish end users and speakers of one language      or the other -- is as unlikely as agreement on whether      "misspelling" or "anglicization" is the greater travesty.   More generally, it is not clear that the outcome of any conceivable   nameprep-like process is going to be good enough for practical,   user-level, use.  In the use of human languages by humans, there are   many cases in which things that do not match are nonetheless   interpreted as matching.  The Norwegian/Danish character that appears   in U+00F8 (visually, a lower case 'o' overstruck with a forward   slash) and the "o-umlaut" German character that appears in U+00F6   (visually, a lower case 'o' with diaeresis (or umlaut)) are clearly   different and no matching program should yield an "equal" comparison.   But they are more similar to each other than either of them is to,   e.g., "e".  Humans are able to mentally make the correction in   context, and do so easily, and they can be surprised if computers   cannot do so.  Worse, there is a Swedish character whose appearance   is identical to the German o-umlaut, and which shares code point   U+00F6, but that, if the languages are known and the sounds of the   letters or meanings of words including the character are considered,   actually should match the Norwegian/Danish use of U+00F8.   This text uses examples in Roman scripts because it is being written   in English and those examples are relatively easy to render.  But one   of the important lessons of the discussions about domain name   internationalization in recent years is that problems similar to   those described above exist in almost every language and script.   Each one has its idiosyncrasies, and each set of idiosyncracies is   tied to common usage and cultural issues that are very familiar in   the relevant group, and often deeply held as cultural values.  As   long as a schoolchild in the US can get a bad grade on a spelling   test for using a perfectly valid British spelling, or one in France   or Germany can get a poor grade for leaving off a diacritical mark,   there are issues with the relevant language.  Similarly, if children   in Egypt or Israel are taught that it is acceptable to write a word   with or without vowels or stress marks, but that, if those marks are   included, they must be the correct ones, or a user in Korea is   potentially offended or astonished by out-of-order sequences of Jamo,   systems based on character-at-a-time processing and simplistic   matching, with no contextual information, are not going to satisfy   user needs.Klensin                      Informational                     [Page 21]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   Users are demanding solutions that deal with language and culture.   Systems of identifier symbol-strings that serve specialists or   computers are, at best, a solution to a rather different (and, at the   time this document was written, somewhat ill-defined), problem.  The   recent efforts have made it ever more clear that, if we ignore the   distinction between the user requirements and narrowly-defined   identifiers, we are solving an insufficient problem.  And,   conversely, the approaches that have been proposed to approximate   solutions to the user requirement may be far more complex than simple   identifiers require.4.6 Business Cards and Other Natural Uses of Natural Languages   Over the last few centuries, local conventions have been established   in various parts of the world for dealing with multilingual   situations.  It may be helpful to examine some of these.  For   example, if one visits a country where the language is different from   ones own, business cards are often printed on two sides, one side in   each language.  The conventions are not completely consistent and the   technique assumes that recipients will be tolerant. Translations of   names or places are attempted in some situations and transliterations   in others.  Since it is widely understood that exact translations or   transliterations are often not possible, people typically smile at   errors, appreciate the effort, and move on.   The DNS situation differs from these practices in at least two ways.   Since a global solution is required, the business card would need a   number of sides approximating the number of languages in the world,   which is probably impossible without violating laws of physics.  More   important, the opportunities for tolerance don't exist:  the DNS   requires a exact match or the lookup fails.4.7 ASCII Encodings and the Roman Keyboard Assumption   Part of the argument for ACE-based solutions is that they provide an   escape for multilingual environments when applications have not been   upgraded.  When an older application encounters an ACE-based name,   the assumption is that the (admittedly ugly) ASCII-coded string will   be displayed and can be typed in.  This argument is reasonable from   the standpoint of mixtures of Roman-based alphabets, but may not be   relevant if user-level systems and devices are involved that do not   support the entry of Roman-based characters or which cannot   conveniently render such characters.  Such systems are few in the   world today, but the number can reasonably be expected to rise as the   Internet is increasingly used by populations whose primary concern is   with local issues, local information, and local languages.  It is,Klensin                      Informational                     [Page 22]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   for example, fairly easy to imagine populations who use Arabic or   Thai scripts and who do not have routine access to scripts or input   devices based on Roman-derived alphabets.4.8 Intra-DNS Approaches for "Multilingual Names"   It appears, from the cases above and others, that none of the intra-   DNS-based solutions for "multilingual names" are workable.  They rest   on too many assumptions that do not appear to be feasible -- that   people will adapt deeply-entrenched language habits to conventions   laid down to make the lives of computers easy; that we can make   "freeze it now, no need for changes in these areas" decisions about   Unicode and nameprep; that ACE will smooth over applications   problems, even in environments without the ability to key or render   Roman-based glyphs (or where user experience is such that such glyphs   cannot easily be distinguished from each other); that the Unicode   Consortium will never decide to repair an error in a way that creates   a risk of DNS incompatibility; that we can either deploy EDNS   [RFC2671] or that long names are not really important; that Japanese   and Chinese computer users (and others) will either give up their   local or IS 2022-based character coding solutions (for which addition   of a large fraction of a million new code points to Unicode is almost   certainly a necessary, but probably not sufficient, condition) or   build leakproof and completely accurate boundary conversion   mechanisms; that out of band or contextual information will always be   sufficient for the "map glyph onto script" problem; and so on.  In   each case, it is likely that about 80% or 90% of cases will work   satisfactorily, but it is unlikely that such partial solutions will   be good enough.  For example, suppose someone can spell her name 90%   correctly, or a company name is matched correctly 80% of the time but   the other 20% of attempts identify a competitor: are either likely to   be considered adequate?5. Search-based Systems: The Key Controversies   For many years, a common response to requirements to locate people or   resources on the Internet has been to invoke the term "directory".   While an in-depth analysis of the reasons would require a separate   document, the history of failure of these invocations has given   "directory" efforts a bad reputation.  The effort proposed here is   different from those predecessors for several reasons, perhaps the   most important of which is that it focuses on a fairly-well-   understood set of problems and needs, rather than on finding uses for   a particular technology.   As suggested in some of the text above, it is an open question as to   whether the needs of the community would be best served by a single   (even if functionally, and perhaps administratively, distributed)Klensin                      Informational                     [Page 23]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   directory with universal applicability, a single directory that   supports locally-tailored search (and, most important, matching)   functions, or multiple, locally-determined, directories.  Each has   its attractions.  Any but the first would essentially prevent   reverse-mapping (determination of the user-visible name of the host   or resource from target information such as an address or DNS name).   But reverse mapping has become less useful over the years --at least   to users -- as more and more names have been associated with many   host addresses and as CIDR [CIDR] has proven problematic for mapping   smaller address blocks to meaningful names.   Locally-tailored searches and mappings would permit national   variations on interpretation of which strings matched which other   ones, an arrangement that is especially important when different   localities apply different rules to, e.g., matching of characters   with and without diacriticals.  But, of course, this implies that a   URL may evaluate properly or not depending on either settings on a   client machine or the network connectivity of the user.  That is not,   in general, a desirable situation, since it implies that users could   not, in the general case, share URLs (or other host references) and   that a particular user might not be able to carry references from one   host or location to another.   And, of course, completely separate directories would permit   translation and transliteration functions to be embedded in the   directory, giving much of the Internet a different appearance   depending on which directory was chosen.  The attractions of this are   obvious, but, unless things were very carefully designed to preserve   uniqueness and precise identities at the right points (which may or   may not be possible), such a system would have many of the   difficulties associated with multiple DNS roots.   Finally, a system of separate directories and databases, if coupled   with removal of the DNS-imposed requirement for unique names, would   largely eliminate the need for a single worldwide authority to manage   the top of the naming hierarchy.6.  Security Considerations   The set of proposals implied by this document suggests an interesting   set of security issues (i.e., nothing important is ever easy).  A   directory system used for locating network resources would presumably   need to be as carefully protected against unauthorized changes as the   DNS itself.  There also might be new opportunities for problems in an   arrangement involving two or more (sub)layers, especially if such a   system were designed without central authority or uniqueness of   names.  It is uncertain how much greater those risks would be as   compared to a DNS lookup sequence that involved looking up one name,Klensin                      Informational                     [Page 24]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   getting back information, and then doing additional lookups   potentially in different subtrees.  That multistage lookup will often   be the case with, e.g., NAPTR records [RFC 2915] unless additional   restrictions are imposed.  But additional steps, systems, and   databases almost certainly involve some additional risks of   compromise.7.  References7.1 Normative References   None7.2 Explanatory and Informative References   [Albitz]       Any of the editions of Albitz, P. and C. Liu, DNS and                  BIND, O'Reilly and Associates, 1992, 1997, 1998, 2001.   [ASCII]        American National Standards Institute (formerly United                  States of America Standards Institute), X3.4, 1968,                  "USA Code for Information Interchange". ANSI X3.4-1968                  has been replaced by newer versions with slight                  modifications, but the 1968 version remains definitive                  for the Internet.  Some time after ASCII was first                  formulated as a standard, ISO adopted international                  standard 646, which uses ASCII as a base.  IS 646                  actually contained two code tables: an "International                  Reference Version" (often referenced as ISO 646-IRV)                  which was essentially identical to the ASCII of the                  time, and a "Basic Version" (ISO 646-BV), which                  designates a number of character positions for                  national use.   [CIDR]         Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless                  Inter-Domain Routing (CIDR): an Address Assignment and                  Aggregation Strategy",RFC 1519, September 1993.                  Eidnes, H., de Groot, G. and P. Vixie, "Classless IN-                  ADDR.ARPA delegation",RFC 2317, March 1998.   [COM-SIZE]     Size information supplied by Verisign Global Registry                  Services (the zone administrator, or "registry                  operator", for COM, see [REGISTRAR], below) to ICANN,                  third quarter 2002.   [DNS-Search]   Klensin, J., "A Search-based access model for the                  DNS", Work in Progress.Klensin                      Informational                     [Page 25]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   [FINGER]       Zimmerman, D., "The Finger User Information Protocol",RFC 1288, December 1991.                  Harrenstien, K., "NAME/FINGER Protocol",RFC 742,                  December 1977.   [IAB-OPES]     Floyd, S. and L. Daigle, "IAB Architectural and Policy                  Considerations for Open Pluggable Edge Services",RFC3238, January 2002.   [IQUERY]       Lawrence, D., "Obsoleting IQUERY",RFC 3425, November                  2002.   [IS646]        ISO/IEC 646:1991 Information technology -- ISO 7-bit                  coded character set for information interchange   [IS10646]      ISO/IEC 10646-1:2000 Information technology --                  Universal Multiple-Octet Coded Character Set (UCS) --                  Part 1: Architecture and Basic Multilingual Plane and                  ISO/IEC 10646-2:2001 Information technology --                  Universal Multiple-Octet Coded Character Set (UCS) --                  Part 2: Supplementary Planes   [MINC]         The Multilingual Internet Names Consortium,http://www.minc.org/ has been an early advocate for                  the importance of expansion of DNS names to                  accommodate non-ASCII characters.  Some of their                  specific proposals, while helping people to understand                  the problems better, were not compatible with the                  design of the DNS.   [NAPTR]        Mealling, M. and R. Daniel, "The Naming Authority                  Pointer (NAPTR) DNS Resource Record",RFC 2915,                  September 2000.                  Mealling, M., "Dynamic Delegation Discovery System                  (DDDS) Part One: The Comprehensive DDDS",RFC 3401,                  October 2002.                  Mealling, M., "Dynamic Delegation Discovery System                  (DDDS) Part Two: The Algorithm",RFC 3402, October                  2002.                  Mealling, M., "Dynamic Delegation Discovery System                  (DDDS) Part Three: The Domain Name System (DNS)                  Database",RFC 3403, October 2002.Klensin                      Informational                     [Page 26]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   [REGISTRAR]    In an early stage of the process that created the                  Internet Corporation for Assigned Names and Numbers                  (ICANN), a "Green Paper" was released by the US                  Government.   That paper introduced new terminology                  and some concepts not needed by traditional DNS                  operations.  The term "registry" was applied to the                  actual operator and database holder of a domain                  (typically at the top level, since the Green Paper was                  little concerned with anything else), while                  organizations that marketed names and made them                  available to "registrants" were known as "registrars".                  In the classic DNS model, the function of "zone                  administrator" encompassed both registry and registrar                  roles, although that model did not anticipate a                  commercial market in names.   [RFC625]       Kudlick, M. and E. Feinler, "On-line hostnames                  service",RFC 625, March 1974.   [RFC734]       Crispin, M., "SUPDUP Protocol",RFC 734, October 1977.   [RFC811]       Harrenstien, K., White, V. and E. Feinler, "Hostnames                  Server",RFC 811, March 1982.   [RFC819]       Su, Z. and J. Postel, "Domain naming convention for                  Internet user applications",RFC 819, August 1982.   [RFC830]       Su, Z., "Distributed system for Internet name                  service",RFC 830, October 1982.   [RFC882]       Mockapetris, P., "Domain names: Concepts and                  facilities",RFC 882, November 1983.   [RFC883]       Mockapetris, P., "Domain names: Implementation                  specification",RFC 883, November 1983.   [RFC952]       Harrenstien, K, Stahl, M. and E. Feinler, "DoD                  Internet host table specification",RFC 952, October                  1985.   [RFC953]       Harrenstien, K., Stahl, M. and E. Feinler, "HOSTNAME                  SERVER",RFC 953, October 1985.   [RFC1034]      Mockapetris, P., "Domain names, Concepts and                  facilities", STD 13,RFC 1034, November 1987.Klensin                      Informational                     [Page 27]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   [RFC1035]      Mockapetris, P., "Domain names - implementation and                  specification", STD 13,RFC 1035, November 1987.   [RFC1591]      Postel, J., "Domain Name System Structure and                  Delegation",RFC 1591, March 1994.   [RFC2181]      Elz, R. and  R. Bush, "Clarifications to the DNS                  Specification",RFC 2181, July 1997.   [RFC2295]      Holtman, K. and A. Mutz, "Transparent Content                  Negotiation in HTTP",RFC 2295, March 1998   [RFC2396]      Berners-Lee, T., Fielding, R. and L. Masinter,                  "Uniform Resource Identifiers (URI): Generic Syntax",RFC 2396, August 1998.   [RFC2608]      Guttman, E., Perkins, C., Veizades, J. and M. Day,                  "Service Location Protocol, Version 2",RFC 2608, June                  1999.   [RFC2671]      Vixie, P., "Extension Mechanisms for DNS (EDNS0)",RFC2671, August 1999.   [RFC2825]      IAB, Daigle, L., Ed., "A Tangled Web: Issues of I18N,                  Domain Names, and the Other Internet protocols",RFC2825, May 2000.   [RFC2826]      IAB, "IAB Technical Comment on the Unique DNS Root",RFC 2826, May 2000.   [RFC2972]      Popp, N., Mealling, M., Masinter, L. and K. Sollins,                  "Context and Goals for Common Name Resolution",RFC2972, October 2000.   [RFC3305]      Mealling, M. and R. Denenberg, Eds., "Report from the                  Joint W3C/IETF URI Planning Interest Group: Uniform                  Resource Identifiers (URIs), URLs, and Uniform                  Resource Names (URNs):  Clarifications and                  Recommendations",RFC 3305, August 2002.   [RFC3439]      Bush, R. and D. Meyer, "Some Internet Architectural                  Guidelines and Philosophy",RFC 3439, December 2002.   [Seng]         Seng, J., et al., Eds., "Internationalized Domain                  Names:  Registration and Administration Guideline for                  Chinese, Japanese, and Korean", Work in Progress.Klensin                      Informational                     [Page 28]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   [STRINGPREP]   Hoffman, P. and M. Blanchet, "Preparation of                  Internationalized Strings (stringprep)",RFC 3454,                  December 2002.                  The particular profile used for placing                  internationalized strings in the DNS is called                  "nameprep", described in Hoffman, P. and M. Blanchet,                  "Nameprep: A Stringprep Profile for Internationalized                  Domain Names", Work in Progress.   [TELNET]       Postel, J. and J. Reynolds, "Telnet Protocol                  Specification", STD 8,RFC 854, May 1983.                  Postel, J. and J. Reynolds, "Telnet Option                  Specifications", STD 8,RFC 855, May 1983.   [UNICODE]      The Unicode Consortium, The Unicode Standard, Version                  3.0, Addison-Wesley: Reading, MA, 2000.  Update to                  version 3.1, 2001.  Update to version 3.2, 2002.   [UTR15]        Davis, M. and M. Duerst, "Unicode Standard Annex #15:                  Unicode Normalization Forms", Unicode Consortium,                  March 2002.  An integral part of The Unicode Standard,                  Version 3.1.1.  Available at                  (http://www.unicode.org/reports/tr15/tr15-21.html).   [WHOIS]        Harrenstien, K, Stahl, M. and E. Feinler,                  "NICNAME/WHOIS",RFC 954, October 1985.   [WHOIS-UPDATE] Gargano, J. and K. Weiss, "Whois and Network                  Information Lookup Service, Whois++",RFC 1834, August                  1995.                  Weider, C., Fullton, J. and S. Spero, "Architecture of                  the Whois++ Index Service",RFC 1913, February 1996.                  Williamson, S., Kosters, M., Blacka, D., Singh, J. and                  K. Zeilstra, "Referral Whois (RWhois) Protocol V1.5",RFC 2167, June 1997;                  Daigle, L. and P. Faltstrom, "The                  application/whoispp-query Content-Type",RFC 2957,                  October 2000.                  Daigle, L. and P. Falstrom, "The application/whoispp-                  response Content-type",RFC 2958, October 2000.Klensin                      Informational                     [Page 29]

RFC 3467          Role of the Domain Name System (DNS)     February 2003   [X29]          International Telecommuncations Union, "Recommendation                  X.29: Procedures for the exchange of control                  information and user data between a Packet                  Assembly/Disassembly (PAD) facility and a packet mode                  DTE or another PAD", December 1997.8. Acknowledgements   Many people have contributed to versions of this document or the   thinking that went into it.  The author would particularly like to   thank Harald Alvestrand, Rob Austein, Bob Braden, Vinton Cerf, Matt   Crawford, Leslie Daigle, Patrik Faltstrom, Eric A. Hall, Ted Hardie,   Paul Hoffman, Erik Nordmark, and Zita Wenzel for making specific   suggestions and/or challenging the assumptions and presentation of   earlier versions and suggesting ways to improve them.9. Author's Address   John C. Klensin   1770 Massachusetts Ave, #322   Cambridge, MA 02140   EMail: klensin+srch@jck.com   A mailing list has been initiated for discussion of the topics   discussed in this document, and closely-related issues, at   ietf-irnss@lists.elistx.com.  Seehttp://lists.elistx.com/archives/for subscription and archival information.Klensin                      Informational                     [Page 30]

RFC 3467          Role of the Domain Name System (DNS)     February 200310. Full Copyright Statement   Copyright (C) The Internet Society (2003).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Klensin                      Informational                     [Page 31]