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:
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- 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
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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.
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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
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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
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7. 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
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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
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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