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Network Working Group                        Internet Architecture BoardRequest for Comments: 2826                                      May 2000Category: InformationalIAB Technical Comment on the Unique DNS RootStatus 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 (2000).  All Rights Reserved.Summary   To remain a global network, the Internet requires the existence of a   globally unique public name space.  The DNS name space is a   hierarchical name space derived from a single, globally unique root.   This is a technical constraint inherent in the design of the DNS.   Therefore it is not technically feasible for there to be more than   one root in the public DNS.  That one root must be supported by a set   of coordinated root servers administered by a unique naming   authority.   Put simply, deploying multiple public DNS roots would raise a very   strong possibility that users of different ISPs who click on the same   link on a web page could end up at different destinations, against   the will of the web page designers.   This does not preclude private networks from operating their own   private name spaces, but if they wish to make use of names uniquely   defined for the global Internet, they have to fetch that information   from the global DNS naming hierarchy, and in particular from the   coordinated root servers of the global DNS naming hierarchy.1.  Detailed Explanation   There are several distinct reasons why the DNS requires a single root   in order to operate properly.1.1.  Maintenance of a Common Symbol Set   Effective communications between two parties requires two essential   preconditions:IAB                          Informational                      [Page 1]

RFC 2826      IAB Technical Comment on the Unique DNS Root      May 2000   -  The existence of a common symbol set, and   -  The existence of a common semantic interpretation of these      symbols.   Failure to meet the first condition implies a failure to communicate   at all, while failure to meet the second implies that the meaning of   the communication is lost.   In the case of a public communications system this condition of a   common symbol set with a common semantic interpretation must be   further strengthened to that of a unique symbol set with a unique   semantic interpretation.  This condition of uniqueness allows any   party to initiate a communication that can be received and understood   by any other party.  Such a condition rules out the ability to define   a symbol within some bounded context.  In such a case, once the   communication moves out of the context of interpretation in which it   was defined, the meaning of the symbol becomes lost.   Within public digital communications networks such as the Internet   this requirement for a uniquely defined symbol set with a uniquely   defined meaning exists at many levels, commencing with the binary   encoding scheme, extending to packet headers and payload formats and   the protocol that an application uses to interact.  In each case a   variation of the symbol set or a difference of interpretation of the   symbols being used within the interaction causes a protocol failure,   and the communication fails.  The property of uniqueness allows a   symbol to be used unambiguously in any context, allowing the symbol   to be passed on, referred to, and reused, while still preserving the   meaning of the original use.   The DNS fulfills an essential role within the Internet protocol   environment, allowing network locations to be referred to using a   label other than a protocol address.  As with any other such symbol   set, DNS names are designed to be globally unique, that is, for any   one DNS name at any one time there must be a single set of DNS   records uniquely describing protocol addresses, network resources and   services associated with that DNS name.  All of the applications   deployed on the Internet which use the DNS assume this, and Internet   users expect such behavior from DNS names.  Names are then constant   symbols, whose interpretation does not specifically require knowledge   of the context of any individual party.  A DNS name can be passed   from one party to another without altering the semantic intent of the   name.   Since the DNS is hierarchically structured into domains, the   uniqueness requirement for DNS names in their entirety implies that   each of the names (sub-domains) defined within a domain has a uniqueIAB                          Informational                      [Page 2]

RFC 2826      IAB Technical Comment on the Unique DNS Root      May 2000   meaning (i.e., set of DNS records) within that domain.  This is as   true for the root domain as for any other DNS domain.  The   requirement for uniqueness within a domain further implies that there   be some mechanism to prevent name conflicts within a domain.  In DNS   this is accomplished by assigning a single owner or maintainer to   every domain, including the root domain, who is responsible for   ensuring that each sub-domain of that domain has the proper records   associated with it.  This is a technical requirement, not a policy   choice.1.2.  Coordination of Updates   Both the design and implementations of the DNS protocol are heavily   based on the assumption that there is a single owner or maintainer   for every domain, and that any set of resources records associated   with a domain is modified in a single-copy serializable fashion.   That is, even assuming that a single domain could somehow be "shared"   by uncooperating parties, there is no means within the DNS protocol   by which a user or client could discover, and choose between,   conflicting definitions of a DNS name made by different parties.  The   client will simply return the first set of resource records that it   finds that matches the requested domain, and assume that these are   valid.  This protocol is embedded in the operating software of   hundreds of millions of computer systems, and is not easily updated   to support a shared domain scenario.   Moreover, even supposing that some other means of resolving   conflicting definitions could be provided in the future, it would   have to be based on objective rules established in advance.  For   example, zone A.B could declare that naming authority Y had been   delegated all subdomains of A.B with an odd number of characters, and   that naming authority Z had been delegated authority to define   subdomains of A.B with an even number of characters.  Thus, a single   set of rules would have to be agreed to prevent Y and Z from making   conflicting assignments, and with this train of actions a single   unique space has been created in any case.  Even this would not allow   multiple non-cooperating authorities to assign arbitrary sub-domains   within a single domain.   It seems that a degree of cooperation and agreed technical rules are   required in order to guarantee the uniqueness of names.  In the DNS,   these rules are established independently for each part of the naming   hierarchy, and the root domain is no exception.  Thus, there must be   a generally agreed single set of rules for the root.IAB                          Informational                      [Page 3]

RFC 2826      IAB Technical Comment on the Unique DNS Root      May 20001.3.  Difficulty of Relocating the Root Zone   There is one specific technical respect in which the root zone   differs from all other DNS zones: the addresses of the name servers   for the root zone come primarily from out-of-band information.  This   out-of-band information is often poorly maintained and, unlike all   other data in the DNS, the out-of-band information has no automatic   timeout mechanism.  It is not uncommon for this information to be   years out of date at many sites.   Like any other zone, the root zone contains a set of "name server"   resource records listing its servers, but a resolver with no valid   addresses for the current set of root servers will never be able to   obtain these records.  More insidiously, a resolver that has a mixed   set of partially valid and partially stale out-of-band configuration   information will not be able to tell which are the "real" root   servers if it gets back conflicting answers; thus, it is very   difficult to revoke the status of a malicious root server, or even to   route around a buggy root server.   In effect, every full-service resolver in the world "delegates" the   root of the public tree to the public root server(s) of its choice.   As a direct consequence, any change to the list of IP addresses that   specify the public root zone is significantly more difficult than   changing any other aspect of the DNS delegation chain.   Thus,   stability of the system calls for extremely conservative and cautious   management of the public root zone: the frequency of updates to the   root zone must be kept low, and the servers for the root zone must be   closely coordinated.   These problems can be ameliorated to some extent by the DNS Security   Extensions [DNSSEC], but a similar out-of-band configuration problem   exists for the cryptographic signature key to the root zone, so the   root zone still requires tight coupling and coordinated management   even in the presence of DNSSEC.2.  Conclusion   The DNS type of unique naming and name-mapping system may not be   ideal for a number of purposes for which it was never designed, such   a locating information when the user doesn't precisely know the   correct names.  As the Internet continues to expand, we would expect   directory systems to evolve which can assist the user in dealing with   vague or ambiguous references.  To preserve the many important   features of the DNS and its multiple record types -- including the   Internet's equivalent of telephone number portability -- we would   expect the result of directory lookups and identification of theIAB                          Informational                      [Page 4]

RFC 2826      IAB Technical Comment on the Unique DNS Root      May 2000   correct names for a particular purpose to be unique DNS names that   are then resolved normally, rather than having directory systems   "replace" the DNS.   There is no getting away from the unique root of the public DNS.3.  Security Considerations   This memo does not introduce any new security issues, but it does   attempt to identify some of the problems inherent in a family of   recurring technically naive proposals.4.  IANA Considerations   This memo is not intended to create any new issues for IANA.5.  References   [DNS-CONCEPTS]        Mockapetris, P., "Domain Names - Concepts and                         Facilities", STD 13,RFC 1034, November 1987.   [DNS-IMPLEMENTATION]  Mockapetris, P., "Domain Names - Implementation                         and Specification", STD 13,RFC 1035, November                         1987.   [DNSSEC]              Eastlake, D., "Domain Name System Security                         Extensions",RFC 2535, March 1999.6.  Author's Address   Internet Architecture Board   EMail: iab@iab.orgIAB                          Informational                      [Page 5]

RFC 2826      IAB Technical Comment on the Unique DNS Root      May 20007.  Full Copyright Statement   Copyright (C) The Internet Society (2000).  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.IAB                          Informational                      [Page 6]