Dynamic Delegation Discovery System (DDDS) Part Five: URI.ARPA
Status of this Memo
This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited.
Copyright © The Internet Society (2002). All Rights Reserved.
This document is fifth in a series that is completely specified in "Dynamic Delegation Discovery System (DDDS) Part One: The Comprehensive DDDS" (RFC 3401). It is very important to note that it is impossible to read and understand any document in this series without reading the others.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. URI Resolution vs URN Resolution . . . . . . . . . . . . . . 2 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 . . . . 3 3.1.4 Registration or Changes after Scheme Registration . . . . . 3 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 . . . . . . . . . . . . . . . . . . . 4 5. Submission Procedure . . . . . . . . . . . . . . . . . . . . 5 6. Registration Template . . . . . . . . . . . . . . . . . . . 6 6.1 Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.2 Authority . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.3 Records . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Example Template . . . . . . . . . . . . . . . . . . . . . . 6 8. The URN Registration in the URI.ARPA zone . . . . . . . . . 7 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7 10. Security Considerations . . . . . . . . . . . . . . . . . . 7 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 13. Author's Address . . . . . . . . . . . . . . . . . . . . . . 9 14. Full Copyright Statement . . . . . . . . . . . . . . . . . . 10
This document defines the policies and procedures for inserting Naming Authority Pointer (NAPTR) records into the 'URI.ARPA' and 'URN.ARPA' zones for the purpose of resolving Uniform Resource Identifiers (URIs) according to "Dynamic Delegation Discovery System (DDDS) Part Four: The URI Resolution Application" (RFC 3402) , which is an Application that uses the Domain Name System (DNS) based DDDS Database. All of these concepts are defined in RFC 3401 . It is very important to note that it is impossible to correctly understand this document without reading RFC 3401 and the documents it specifies.
RFC 3403 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.
2. URI Resolution vs URN Resolution
RFC 3402  defines how both URI  resolution and URN  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 URI scheme, 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  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 .
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) . URN namespace ids follow "URN Namespace Definition Mechanisms" (RFC 2611) (or updates thereto) .
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 .
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 . The IESG or its designated expert will review the request for
- correctness and technical soundness
- consistency with the published URI specification, and
- to ensure that the NAPTR record for a DNS-based URI does not 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 ), 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 . 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 ), 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 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 URI). 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' URI scheme adheres to a particular syntax that specifies that the host to ask is specified in the URI 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 URI 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.
5. Submission Procedure
Using the MIME Content-Type registration mechanism  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
o Registrations for the 'URN.ARPA' zone are sent to
The registration authority is the Internet Assigned Numbers Authority (IANA).
Objections are restricted to those that point out impacts on the zone itself or to DNS in general. Objections to the URI 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 URI 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:
This is the URN NID or URI 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 URI schemes.
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  or URI scheme registration  documents.
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 RFC 3404 .
7. Example Template
To: register@URN.ARPA From: firstname.lastname@example.org 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
The IANA has created the zones URN.ARPA and URI.ARPA. The hierarchical name structure, and the only names to be assigned within these zones, are the "keys" as described in Section 6.1 of this document. The administrative and operational management of these zones are to be undertaken by the IANA. The DNS records to be inserted in these zones are subject to the review process described in this document.
The IANA has also created two discussion lists, email@example.com and firstname.lastname@example.org, for the purposes described in this document. The IANA will manage these mailing lists.
10. Security Considerations
The 'uri.arpa' and 'urn.arpa' zones will be a common point of attack both for Denial of Service and for spoofing entries in order to redirect delegation paths. Any entity running nameservers that contain these zones should take appropriate action for securing an infrastructure level component of the Internet. When it becomes possible for a nameserver to reliably sign the records in its zone it should do so.
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.
 Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part One: The Comprehensive DDDS", RFC 3401, October 2002.  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Two: The Algorithm", RFC 3402, October 2002.  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database", RFC 3403, October 2002.  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Four: The Uniform Resource Identifiers (URI) Resolution Application", RFC 3404, October 2002.  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Five: URI.ARPA Assignment Procedures", RFC 3405, October 2002.  Moats, R., "URN Syntax", RFC 2141, November 1998.  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998.  Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", BCP 13, RFC 2048, November 1996.  Faltstrom, P., Iannella, R., Daigle, L. and D. van Gulik, "URN Namespace Definition Mechanisms", BCP 33, RFC 2611, October 1998.  Petke, R. and I. King, "Registration Procedures for URL Scheme Names", BCP 35, RFC 2717, January 1999.
13. Author's Address
Michael Mealling VeriSign 21345 Ridgetop Circle Sterling, VA 20166 US EMail: email@example.com URI: http://www.verisignlabs.com
14. Full Copyright Statement
Copyright © The Internet Society (2002). All Rights Reserved.
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