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

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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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English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

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Acknowledgement

Funding for the RFC Editor function is currently provided by the

Internet Society.

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