Network Working Group M. Mealling
Internet-Draft Network Solutions, Inc.
Expires: May 2, 2001 November 1, 2000
Assignment Procedures for URI Resolution Using DNS
draft-ietf-urn-net-procedures-06
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
RFCYYYY defines a how DNS is used as a DDDS database that contains
URI delegation rules (sometimes called resolution hints). That
document specifies that the first step in that algorithm is to
append 'URI.ARPA' to the URI scheme and retrieve the NAPTR record
for that domain-name. I.e., the first step in resolving
"http://foo.com/" would be to look up a NAPTR record for the domain
"http.URI.ARPA". URN resolution also follows a similar procedure but
uses the 'URN.ARPA' zone as its root. This document describes the
procedures for inserting a new rule into the 'URI.ARPA' and
'URN.ARPA' zones.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. URI Resolution vs URN Resolution . . . . . . . . . . . . . . 3
3. Registration Policies . . . . . . . . . . . . . . . . . . . 3
3.1 URI.ARPA Registration . . . . . . . . . . . . . . . . . . . 3
3.1.1 Only Schemes in the IETF Tree Allowed . . . . . . . . . . . 3
3.1.2 Scheme Registration Takes Precedence . . . . . . . . . . . . 3
3.1.3 NAPTR Registration May Accompany Scheme Registration . . . . 4
3.1.4 Registration or Changes after Scheme Registration . . . . . 4
3.2 URN.ARPA Registration . . . . . . . . . . . . . . . . . . . 4
3.2.1 NID Registration Takes Precedence . . . . . . . . . . . . . 4
3.2.2 NAPTR Registration May Accompany NID Registration . . . . . 4
3.2.3 Registration or Changes after Scheme Registration . . . . . 4
4. Requirements on hints . . . . . . . . . . . . . . . . . . . 5
5. Submission Procedure . . . . . . . . . . . . . . . . . . . . 6
6. Registration Template . . . . . . . . . . . . . . . . . . . 6
6.1 Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.2 Authority . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.3 Records . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Example Template . . . . . . . . . . . . . . . . . . . . . . 7
8. The URN Registration in the URI.ARPA zone . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . 8
Full Copyright Statement . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This document defines the policies and procedures for inserting
NAPTR records into the 'URI.ARPA' and 'URN.ARPA' zones for the
purpose of resolving URIs according to "URI Resolution using the
Dynamic Delegation Discovery System" (RFCXXXX)[7], which is an
Application that uses the DNS based DDDS Database defined in
RFCYYYY[6]. The algorithm expressed by these Rules is specified in
"Dynamic Delegation Discovery System (DDDS) (RFCZZZZ)[8].
2. URI Resolution vs URN Resolution
RFCXXXX[7] defines how both URI[2] resolution and URN[1] resolution
work when DNS is used as the delegation rule (or hint) database.
Specifically it says that the initial instructions ('hints') for
DNS-based resolution of URIs are stored as resource records in the
'URI.ARPA' DNS zone.
Since a URN is a kind of URI, a hint for resolution of the URI
prefix 'urn:' will also be stored in the 'URI.ARPA' zone. This rule
states that the namespace id[1] is extracted, 'URN.ARPA' is appended
to the end of the namespace id, and the result is used as the key
for retrieval of a subsequent NAPTR record[6].
3. Registration Policies
The creation of a given URI scheme or URN namespace id (NID) follows
the appropriate registration documents for those spaces. URI schemes
follow "Registration Procedures for URL Scheme Names" (RFC
2717)[5]. URN namespace ids follow "URN Namespace Definition
Mechanisms" (RFC 2611) (or updates thereto)[4].
3.1 URI.ARPA Registration
3.1.1 Only Schemes in the IETF Tree Allowed
In order to be inserted into the URI.ARPA zone, the subsequent URI
scheme MUST be registered under the IETF URI tree. The requirements
for this tree are specified in [5].
3.1.2 Scheme Registration Takes Precedence
The registration of a NAPTR record for a URI scheme MUST NOT precede
proper registration of that scheme and publication of a stable
specification in accordance with [5]. The IESG or its designated
expert will review the request for
1. correctness and technical soundness
2. consistency with the published URI specification, and
3. to ensure that the NAPTR record for a DNS-based URI does not
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delegate resolution of the URI to a party other than the holder
of the DNS name. This last rule is to insure that a given URI's
resolution hint doesn't hijack (inadvertently or otherwise)
network traffic for a given domain.
3.1.3 NAPTR Registration May Accompany Scheme Registration
A request for a URI.ARPA registration MAY accompany a request for a
URI scheme (in accordance with [5]), in which case both requests
will be reviewed simultaneously by IESG or its designated experts.
3.1.4 Registration or Changes after Scheme Registration
A request for a NAPTR record (or an request to change an existing
NAPTR record) MAY be submitted after the URI prefix has been
registered. If the specification for the URI prefix is controlled
by some other party than IETF, IESG will require approval from the
owner/maintainer of that specification before the registration will
be accepted. This is in addition to any technical review of the
NAPTR registration done by IESG or its designated experts.
3.2 URN.ARPA Registration
3.2.1 NID Registration Takes Precedence
The registration of a NAPTR record for a URN NID MUST NOT precede
proper registration of that NID and publication of a stable
specification in accordance with [4]. This is to prevent the
registration of a NAPTR record in URN.ARPA from circumventing the
NID registration process.
3.2.2 NAPTR Registration May Accompany NID Registration
A request for a URN.ARPA registration MAY accompany a request for a
NID (in accordance with [4]), in which case both requests will be
reviewed at the same time.
3.2.3 Registration or Changes after Scheme Registration
A request for a NAPTR record (or an request to change an existing
NAPTR record) MAY be submitted after the NID has been registered.
If the specification for the NID is controlled by some other party
than IETF, IESG will require approval from the owner/maintainer of
that specification before the registration will be accepted. This is
in addition to any technical review of the NAPTR registration done
by IESG or its designated experts.
Note that this applies to all NAPTR records for a particular NID,
even though a NAPTR record might affect only part of the URN space
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assigned to an NID
4. Requirements on hints
Delegation of a namespace can happen in two ways. In the case of
most URIs, the key being delegated to is hard-coded into the
identifier itself (e.g. a hostname in an HTTP URL). The syntax of
where this new key is located is predetermined by the syntax of the
scheme. In other cases, the new key can be part of the hint itself.
This is the functional equivalent of saying, "if this rule matches
then this is always the key."
In order to minimize the query load on the URI.ARPA and URN.ARPA
zones, it is anticipated that the resource records in those zones
will have extremely long "times to live" (TTLs), perhaps measured in
years.
Thus, for any URI prefix or URN namespace for which the resolution
hints are likely to change, the actual rule should be stored in some
other (less stable) DNS zone, and within URI.ARPA or URN.ARPA a
stable NAPTR record should be used to delegate queries to that less
stable zone.
For example, the 'foo' URN namespace has flexible rules for how
delegation takes place. Instead of putting those rules in the
URN.ARPA zone, the entry instead punts those rules off to a
nameserver that has a shorter time to live. The record in URN.ARPA
would look like this:
foo IN NAPTR 100 10 "" "" "" urn-resolver.foo.com.
Thus, when the client starts out in the resolution process, the
first step will be to query foo.URN.ARPA to find the above record,
the second step is to begin asking 'urn-resolver.foo.com' for the
NAPTR records that contain the resolution rules. The TTL at the root
is very long. The TTL at the 'urn-resolver.foo.com' is much shorter.
Conversely, the 'http' URL scheme adheres to a particular syntax
that specifies that the host to ask is specified in the URL in
question. Since this syntax does not change, that rule can be
specified in the URI.ARPA zone. The record would look like this:
http IN NAPTR 100 100 "" "" "/http:\\/\\/([^\\/:]+)/\\2/i" .
Thus, the second step of resolution is to use the domain-name found
in the URL as the next key in the cycle. If, for example, that NAPTR
was terminal and contains some hostname in the replacement field,
then the client could contact that host in order to ask questions
about this particular URI.
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5. Submission Procedure
Using the MIME Content-Type registration mechanism[3] as a model
for a successful registration mechanism, the 'URI.ARPA' and
'URN.ARPA' procedures consist of a request template submitted to an
open mailing list made up of interested parties. If no objections
are made within a two week period, a representative of the
registration authority considers the submission to be accepted and
enters that submission into the nameserver.
o Registrations for the 'URI.ARPA' zone are sent to
'register@URI.ARPA'.
o Registrations for the 'URN.ARPA' zone are sent to
'register@URN.ARPA'.
At this time the registration authority is expected to be the IANA.
Objections are restricted to those that point out impacts on the
zone itself or to DNS in general. Objections to the URL scheme or to
the URN namespace-id are not allowed, as these should be raised in
their respective forums. The logical conclusion of this is that ANY
sanctioned URL scheme or URN namespace MUST be allowed to be
registered if it meets the requirements specified in this document
as regards times to live and general impact to the DNS.
6. Registration Template
The template to be sent to the appropriate list MUST contain the
following values:
6.1 Key
This is the URN NID or URL scheme, which is used as the domain
portion of the DNS entry. It must be valid according to the
procedures specified in the URN namespace-id assignment document and
any future standards for registering new URL schemes.
6.2 Authority
This is the individual or organization (entity) which has authority
for registering the record. It must be an authority recognized as
either the IESG or any authority defined in the URN NID[4] or URL
scheme registration[5] documents.
6.3 Records
The actual DNS records representing the rule set for the key. The
required values are Preference, Order, Flags, Services, Regex, and
Replacement as defined by RFCYYYY[6].
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7. Example Template
To: register@URN.ARPA
From: joe@foo.com
Key: foo
Authority: Foo Technology, Inc as specified in RFCFOO
Record: foo IN NAPTR 100 100 "" "" "" urn.foo.com.
8. The URN Registration in the URI.ARPA zone
Since this document discusses the URI.ARPA and URN.ARPA zones and
the URN rule that exists in the URI.ARPA zone, it makes sense for
the registration template for the URN URI rule to be specified here:
To: register@URI.ARPA
From: The IETF URN Working Group
Key: urn
Authority: RFC2141
Record: urn IN NAPTR 0 0 "" "" "/urn:([^:]+)/\\2/i" .
9. IANA Considerations
This document describes a mechanism for registering representations
of protocol items that have already been registered with some IETF
sanctioned agency (probably the IANA as well). This means that the
IANA need not determine appropriateness of the underlying
namespaces, since that is determined by another process.
The only real impact on the IANA will be
o to create and maintain (or designate some other entity to
maintain) a primary nameserver for the URI.ARPA and URN.ARPA
zones. From time to time the IANA may delegate or change
delegation of operations at its discretion.
o to maintain the mailing lists "register@URI.ARPA" and
"register@URN.ARPA" as the forum for discussions of submissions;
and
o to act as the party that determines if all objections have been
noted and accommodated.
10. Acknowledgements
The author would like to thank Ron Daniel who was originally
co-author of these documents. Ron's original insite into the
intricate nature of delegation rules made these procedures and the
DDDS itself possible.
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References
[1] Moats, R., "URN Syntax", RFC 2141, November 1998.
[2] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[3] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", RFC
2048, November 1996.
[4] Faltstrom, P., Iannella, R., Daigle, L. and D. van Gulik, "URN
Namespace Definition Mechanisms", RFC 2611, October 1998.
[5] Petke, R. and I. King, "Registration Procedures for URL Scheme
Names", RFC 2717, January 1999.
[6] Mealling, M., "A DDDS Database Using The Domain Name System",
Internet-Draft draft-ietf-urn-dns-ddds-database-00.txt, May
2000.
[7] Mealling, M., "URI Resolution using the Dynamic Delegation
Discovery System", Internet-Draft
draft-ietf-urn-uri-res-ddds-00.txt, July 2000.
[8] Mealling, M., "Dynamic Delegation Discovery System (DDDS)",
Internet-Draft draft-ietf-urn-ddds-00.txt, May 2000.
Author's Address
Michael Mealling
Network Solutions, Inc.
505 Huntmar Park Drive
Herndon, VA 22070
US
Phone: (703) 742-0400
EMail: michaelm@netsol.com
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