Network Working Group Internet Architecture Board
Request for Comments: 2826 May 2000
Category: Informational

IAB Technical Comment on the Unique DNS Root

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 (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:

   -  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 unique

   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.

1.3. 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 the

   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.org

7. Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

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Acknowledgement

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