DNSEXT J. Reid
Internet-Draft Telnic Ltd
Expires: May 15, 2008 November 12, 2007
The Zone Status (ZS) DNS Resource Record
<draft-reid-dnsext-zs0-00.txt>
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Abstract
A Domain Name System (DNS) resource record which provides status
information about a zone is described in this document.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Justification For New RRtype . . . . . . . . . . . . . . . . . 6
5. ZS Resource Record . . . . . . . . . . . . . . . . . . . . . . 7
6. End User Considerations . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC2119 [7].
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2. Introduction
The DNS protocol is defined in RFC1034[1], RFC1035[2] and clarified
in RFC2181[3]. The DNS does not currently provide a well defined
mechanism for obtaining information about the status of a zone: what
it is being used for, the significance of the zone's contents, when
the zone was last updated and so on. This means a variety of ad-hoc
techniques are deployed whenever zone administrators choose to make
this information available. Typical strategies include descriptive
TXT records in the zone or embedding meta-information in the values
of existing RRtypes or subtypes such as the SOA record's serial
number and RNAME. These are confusing and impractical since an
arbitrary DNS client needs a priori knowledge of which of these
schemes, if any, has been used by a zone administrator.
This document advocates the introduction of a new resource record
specifically to provide this type of information.
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3. Rationale
Common examples where indicating the status of a zone would be useful
include: whenever the domain is in the process of a substantial
update; a domain undergoing a long-term migration; and changes to the
authoritative name servers for a zone. eg "Use of example.net was
deprecated on April 1st. Please visit example.com instead." It
would be convenient to store this type of meta information within the
zone in a way that makes it easily retrieved. This kind of status
information would be particularly helpful for systems such as ENUM
[8] which can be used for publishing real-time contact data for zone
owners.
These sorts of details are generally associated with the
administration of the zone rather than being tied to the rest of the
zone content. Clarifying this separation between information that
reflects the status of a zone from any text that a domain holder may
choose to publish via DNS is useful. It also avoids the current
subtyping issues that would affect processing of a TXT RRset if the
status information was embedded there. TXT records are too general
and would require imprecise RDATA parsing in order to extract any
relevant items of interest to a particular client.
The proposed RRtype will be of particular use for zones where contact
data are published in the DNS as NAPTR records [4]. For instance a
set of tel: and sip: URIs [5]. could be associated with the proposed
zone status RRtype. That could indicate these URIs are the ones
published by the zone owner when they are at work, or while
travelling or when at home. Client software could lookup the zone's
ZS records and display a meaningful message to the end user about the
NAPTR records that had been retrieved from an earlier lookup. A
description of which contact data the zone owner has published would
offer additional information to what might be inferred from the
actual NAPTR RRset or other zone data itself. The ZS RRtype could
express concepts like "the zone owner is asleep, so don't bother
trying voice-based communication" or "the zone owner is at work but
in a meeting".
Publishing and obtaining this information will become more
significant because of emerging applications and services which make
innovative use of the DNS such as the real-time manipulation of zone
content data. For example, updating NAPTR records (ie the zone
owner's contact data) whenever the zone owner switches between the
NAPTR RRset they publish while at work, at home, commuting or while
sleeping.
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4. Justification For New RRtype
TXT records are unsuitable for providing this sort of zone status
information because the semantics of TXT record RDATA are
unstructured. TXT records can and are used for all sorts of
purposes: version control strings, comments or reminders to zone
administrators, anti-spam information, references to ticketing
systems, contact details of the zone administrator and so on. It
would be impractical for an application to interpret the contents of
a response to a TXT query and guess which, if any, of the returned
TXT records contained meaningful data about the status of the zone.
One approach would be to adopt a convention that a "magic string" in
the RDATA for some TXT record identified zone status information.
This is not viable for two reasons. First, it may break backwards
compatibility with the installed base which might already be using
this "magic string" in TXT records. The second reason is this
proposal would introduce yet another example of subtyping which is
generally accepted as poor protocol design.
Likewise, it is not sensible to insert TXT records in some part of
the name space to be dedicated for this specific purpose. That would
be another instance of bad protocol design because a fundamental but
unstated principle of the Domain Name System is any RRtype can be
used in any zone irrespective of the name of the zone.
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5. ZS Resource Record
Apart from its type code, the wire and text formats for the proposed
ZS RRtype are identical to the definitions of the TXT record given in
RFC1035:
ZS RDATA format
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ ZS-DATA /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where: ZS-DATA One or more character-strings.
The ZS RRtype will hold descriptive text intended to contain
information reflecting the status of the zone in which it is held.
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6. End User Considerations
Users publishing ZS records SHOULD pay attention to the needs of
potential readers of these resource records, especially with respect
to character sets and language. Although arbitrary text can be used
in character-strings, publishers of ZS records should realise that
clients looking up these records may not be able to display them if
they are presented in unusual character sets. For example, a mobile
phone or other hand-held device may not have the font information or
rendering capabilities to display (say) Chinese or Arabic characters.
Similarly, publishers of ZS records should try to avoid displaying
information in multiple languages or assume that all readers of these
records understand the same language they have chosen to use.
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7. Security Considerations
Although this document does not appear to introduce any extra
security issues beyond those listed in the thorough analysis of the
threats to DNS in RFC3833 [9], there are some additional
considerations. These are described below.
It is unrealistic to assume that zone owners who publish ZS records
can be relied upon to ensure any ZS records contain accurate, timely
information. Similarly it cannot be assumed that ZS records contain
text that will be understandable by an arbitrary reader that looks
them up in the DNS. Therefore any data contained in a ZS record is
solely for informational purposes. The information contained in a ZS
record MUST NOT be relied upon for any location-based services. In
particular, emergency services MUST NOT not treat the contents of a
ZS record as definitive information about the location or disposition
of the domain name owner.
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8. IANA Considerations
IANA is requested to issue a new type code and mnemonic for the
proposed resource record. No other IANA services are required by
this document.
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9. Acknowledgements
The author would like to thank Ben Timms, John Cundall, John Tidmuss
and Lawrence Conroy for their constructive suggestions to this
document and for helping to identify potential uses for the proposed
record type.
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10. References
10.1. Normative References
[1] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",
RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[3] Elz, R. and R. Bush, "Clarifications to the DNS Specification",
RFC 2181, July 1997.
[4] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database", RFC 3403,
October 2002.
[5] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.
[6] Braden, R., "Requirements for Internet Hosts -- Application and
Support", RFC 1123, October 1989.
10.2. Informative References
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[8] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", RFC 3761, April 2004.
[9] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
[10] Bradner, S., "The Internet Standards Process -- Revision 3",
RFC 2026, BCP 9, October 1996.
[11] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3978,
March 2005.
[12] Bradner, S., "Intellectual Property Rights in IETF Technology",
BCP 79, RFC 3979, March 2005.
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Author's Address
Jim Reid
Telnic Ltd
Telnic Ltd.
6 Langside Court
Bothwell, SCOTLAND
United Kingdom
Phone: +44 20 7282 0000
Email: jim@telnic.org
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