Network Working Group D. Crocker
Internet-Draft Brandenburg InternetWorking
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draft-crocker-dns-attrleaf-00
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
Historically, any DNS RR may occur for any name. Recent additions
have defined DNS leaf nodes that contain a reserved node name,
beginning with an underscore. With the underscore construct, the
choice of valid RRs is limited to a defined set. The underscore
construct is a basic paradigm modification to the DNS, because it
defines a scope-constrained attribute space for the containing domain
name. This note defines the nature of this DNS usage and defines the
procedures for registering new "underscore names" with IANA.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
4. Informative . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Appendix A. IANA Registration Procedures . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Introduction
Historically, any DNS RR may occur for any name. Recent additions
have defined DNS leaf nodes that contain a reserved node name,
beginning with an underscore. With the underscore construct, the
choice of valid RRs is limited to a defined set. The underscore
construct is a basic paradigm modification to the DNS, because it
defines a scope-constrained attribute space for the containing domain
name.
The DNS technical specification defines no semantics to domain names
and no constraints upon which resource records may be associated with
a particular name. This freedom in the basic technology has
permitted a wide range of administrative and semantic policies to be
used -- in parallel -- with the DNS. In the DNS specifications, data
semantics have been limited to the specifications for precise
resource records, on the expectation that new ones would be added as
needed. Although there remains an expectation that this method of
enhancement is to be preferred, alternative approaches have been
explored.
One uses a special class of DNS node name uses a leading underscore
character to define special contexts for specific resource records.
An established example is the SRV record, which generalizes concepts
long-used for email routing, with the MX record.[3][2] The use of
special DNS names has significant benefits and detriments. Some of
these are explored in [1].
One that has perhaps not been noticed is that the use of the
underscore construct substantially changes possible concerns for
scaling effects, when there are different uses for the same RR,
notably the free-form TXT record. Within the scope of a defined
underscore leaf, the specific uses of specific resource records is
formally constrained.
The purpose of this note is to attempt to provide an explicit
definition of this type of DNS naming, and to establish an IANA
registry for the reserved names beginning with underscore.
NOTE:
Apologies for the incomplete state of this note. It will be
revised, shortly, to provide more detail. Given the DNS-related
activities in the DKIM working group, I thought it worth marking
the established nature and the significant meaning of the
underscore construct.
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2. Security Considerations
This memo raises no security issues
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3. IANA Considerations
Domain node names that begin with an underscore MUST be registered
with IANA.
The procedures will be specified in a later version of this note.
4. Informative
[1] "IAB Discussion about alternative methods of adding information
to the DNS".
[2] "Definition of MX record".
[3] "Definition of SRV record".
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Appendix A. IANA Registration Procedures
TBD
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Author's Address
Dave Crocker
Brandenburg InternetWorking
675 Spruce Dr.
Sunnyvale, CA 94086
US
Phone: +1.408.246.8253
Email: dcrocker@bbiw.net
URI: http://bbiw.net/
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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