The Internet Assigned Number Authority (IANA) Application Configuration Access Protocol (ACAP) Vendor Subtrees Registry
A registry for company-specific namespace extensions in Internet protocols
Cridland, D., "The Internet Assigned Number Authority (IANA) Application Configuration Access Protocol (ACAP) Vendor Subtrees Registry", RFC 6075, DOI 10.17487/RFC6075, December 2010, <https://www.rfc-editor.org/info/rfc6075>.
@misc{rfc6075,
series = {Request for Comments},
number = 6075,
howpublished = {RFC 6075},
publisher = {RFC Editor},
doi = {10.17487/RFC6075},
url = {https://www.rfc-editor.org/info/rfc6075},
author = {D. Cridland},
title = {{The Internet Assigned Number Authority (IANA) Application Configuration Access Protocol (ACAP) Vendor Subtrees Registry}},
pagetotal = 7,
year = 2010,
month = dec,
} RFC text
Contents
Internet Engineering Task Force (IETF) D. Cridland
Request for Comments: 6075 Isode Limited
Updates: 2244 December 2010
Category: Standards Track
ISSN: 2070-1721
The Internet Assigned Number Authority (IANA) Application Configuration
Access Protocol (ACAP) Vendor Subtrees Registry
Abstract
The original Application Configuration Access Protocol (ACAP)
specification included a vendor registry now used in other protocols.
This document updates the description of this registry, removing the
need for a direct normative reference to ACAP and removing ambiguity.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6075.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . . 2
3. The Vendor Subtree Registry . . . . . . . . . . . . . . . . . . 3
3.1. Internationalization . . . . . . . . . . . . . . . . . . . 3
3.2. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.4. Changes from RFC 2244 . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Example Registration . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . . 7
1. Introduction
The [ACAP] specification includes the specification and creation of
the ACAP Vendor Registry, and this registry has subsequently been
reused by several specifications, including both [ANNOTATE] and
[METADATA], and is proving to be a useful mechanism for namespacing
various names to within a specific vendor's scope.
The use of textual rather than numeric identifiers for vendors
benefits engineers and operators who are diagnosing protocol problems
by allowing them some possibility of identifying the origin of a
vendor attribute without having to look it up in a registry (although
that remains a necessary fallback). As such, engineers and operators
already have to be familiar with international technical English to
diagnose textual protocol problems, the restriction to ASCII may help
and is not believed to harm that intended use. Exposure of vendor
attributes directly in end-user user interfaces was not an intended
use of the registry.
This document merely updates the registry to reduce ambiguity in the
original specification and dissociates it from the original document
in all but name, allowing easier referencing. It replaces Section
7.4 and portions of Section 4, particularly Section 4.3, of [ACAP].
2. Conventions Used in This Document
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 [KEYWORDS].
The formal syntax is to be considered normative and is specified
using [ABNF]. Where a formal syntax and the prose are in conflict,
the formal syntax takes precedence.
3. The Vendor Subtree Registry
A Vendor Token is a UTF-8 string that begins with "vendor." and that
is followed by the name of the company or product. This name MUST
NOT contain any slash character, period, or the percent and asterisk
characters typically used as wildcards.
Following this may be names, separated from the Vendor Token by a
period, which need not be registered, thus forming a complete Vendor
Name.
3.1. Internationalization
Vendor Tokens are able to contain any valid Unicode codepoint,
encoded as [UTF-8], except the special characters. Since the
publication of [ACAP], however, concerns have been raised on the
handling and comparison of full Unicode strings; therefore, this
specification restricts the current registrations to the ASCII subset
of UTF-8.
Furthermore, characters such as ASCII control characters, most
whitespace, and quotes are likely to be confusing and have been
similarly restricted.
Therefore, this document allows only ASCII letters, digits, the
hyphen, and space to be used in registrations (the <iana-vendor-tag>
ABNF production in Section 3.2).
At the time of publication of this document, no existing
registrations violate the new restricted syntax on characters allowed
in registrations. [ACAP] required all Vendor Tokens to be registered
with IANA, so the new restriction is not believed to introduce any
interoperability issue.
Finally, note that this document does not change the requirement on
processors to accept other non-ASCII Unicode codepoints in Vendor
Tokens (the <possible-vendor-tag> ABNF production in Section 3.2).
3.2. Formal Syntax
This syntax draws upon productions found within [ABNF] and [UTF-8].
Productions replace those in Section 4.3 of [ACAP].
vendor-name = vendor-token *("." name-component)
name-component = *(name-char / UTF8-2 / UTF8-3 / UTF8-4)
name-char = %x01-24 / %x26-29 / %x2B-2D / %x30-7F
;; ASCII-range characters not including ".",
;; "/", "%", or "*".
vendor-token = "vendor." vendor-tag
;; MUST be registered with IANA
vendor-tag = iana-vendor-tag / possible-vendor-tag
iana-vendor-tag = 1*(ALPHA / DIGIT / SP / "-")
;; This production represents
;; allowed forms for registrations
;; under the rules specified in this
;; document.
possible-vendor-tag = name-component
;; This production represents what
;; applications and specifications
;; MUST be able to accept.
3.3. Examples
A company Example, Ltd. might register the Subtree "vendor.example".
This means it may use "vendor.example", or any name at all beginning
"vendor.example.", such as "vendor.example.product".
These names might be used in several protocols, and are reserved in
all the relevant protocols, so "vendor.example" might be an ACAP
[ACAP] dataset class name, and "/vendor/vendor.example" might be a
tree of IMAP ANNOTATE entries [ANNOTATE].
Example, Ltd. is free to use either "vendor.example", and group
specific products under it using the relevant protocol's hierarchy --
perhaps "/shared/vendor/vendor.example/product" annotation
[ANNOTATE], or using more specific names, such as "/shared/vendor/
vendor.example.product" annotation.
Note that the solidus ("/") characters in the examples above are
protocol delimiters that are themselves not part of the Vendor Token.
3.4. Changes from RFC 2244
This non-normative section details changes from the original
specification of the registry in RFC 2244.
o Vendor Tokens are restricted to ASCII for registration purposes.
o Clarifications that "vendor.<company/product name>" means
"vendor.company name" or "vendor.product name" - "vendor.company/
product" is and always has been illegal.
o Made "vendor.company" a name in its own right - RFC 2244 only
refers to a prefix of "vendor.company.".
o Added example registration, in line with [EXAMPLES].
4. IANA Considerations
This specification updates the IANA registry named the ACAP "Vendor
Subtrees" registry. IANA has updated the registry to point at this
document.
Vendors may reserve a portion of the ACAP namespace, which is also
used as the namespace for several other protocols, for private use.
Vendor Names are reserved for use by that company or product,
wherever used, once registered. Registration is on a first come,
first served basis. Whenever possible, private attributes and
classes should be eschewed in favour of improving interoperable
protocols.
Vendors may only use names conforming to iana-vendor-tag at the
current time; future revisions of this specification may change this.
To: iana@iana.org
Subject: Registration of ACAP Vendor Subtree
Private Prefix: vendor.name
Person and email address to contact for further information:
(company names and addresses should be included where appropriate)
4.1. Example Registration
IANA is requested to add the following registration, for use by
specification authors in examples, similarly to the domains specified
in [EXAMPLES]:
To: iana@iana.org
Subject: Registration of ACAP Vendor Subtree
Private Prefix: vendor.example
Person and email address to contact for further information:
Dave Cridland <dave.cridland@isode.com>
5. Security Considerations
There are no known security issues with this registry. Individual
protocols using Vendor Subtree names may have security issues, and
the introduction of Unicode has, in itself, security implications --
the restriction of this is thought to mitigate these.
6. Acknowledgements
Thanks must go to Chris Newman, John Myers, and the other designers
of ACAP for the initial creation of the registry. Thanks also to
Alexey Melnikov for advice on this revision.
7. References
7.1. Normative References
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[ACAP] Newman, C. and J. Myers, "ACAP -- Application
Configuration Access Protocol", RFC 2244, November 1997.
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
7.2. Informative References
[ANNOTATE]
Daboo, C. and R. Gellens, "Internet Message Access
Protocol - ANNOTATE Extension", RFC 5257, June 2008.
[EXAMPLES]
Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[METADATA]
Daboo, C., "The IMAP METADATA Extension", RFC 5464,
February 2009.
Author's Address
Dave Cridland
Isode Limited
5 Castle Business Village
36, Station Road
Hampton, Middlesex TW12 2BX
GB
EMail: dave.cridland@isode.com
AI ELI5
On this page
§1The Vendor Registry Problem
The Application Configuration Access Protocol (ACAP) originally defined a registry for vendor-specific extensions. As described in the RFC, this vendor registry has proven useful and has been adopted by other protocols including IMAP ANNOTATE and IMAP METADATA, making it a general-purpose mechanism.
The registry allows companies and product vendors to reserve portions of a protocol's namespace for private use without needing IANA approval for each extension. This RFC updates the original specification to make the registry independent of ACAP while keeping its essential design.
When ACAP was invented, it created a system for companies to add their own features without stepping on each other's toes. Now other protocols want to use the same system, so this update makes it stand on its own.
§2Vendor Tokens and Names
A Vendor Token is a string that begins with the literal text vendor. followed by the name of a company or product. For example, vendor.example is a vendor token reserved by a fictional company.
Following the vendor token, additional names can be appended separated by periods, such as vendor.example.product. These extensions need not be registered; any name following the vendor token becomes part of that vendor's namespace.
The complete name is called a Vendor Name, and it is case-sensitive.
A vendor token is like a company's unique mailbox name. Companies register 'vendor.their-name' and then can make up their own sub-names inside it, like 'vendor.their-name.product-a'.
§3Character Restrictions and Format
To avoid confusion and security issues, the RFC restricts what characters can appear in registered vendor tokens. New registrations are limited to ASCII letters, digits, hyphens, and spaces. This restriction addresses concerns raised after ACAP was published about handling full Unicode strings safely.
The formal syntax, specified in ABNF, is:
vendor-token = "vendor." vendor-tag
Where vendor-tag uses only ALPHA / DIGIT / SP / "-". However, the RFC notes that implementations must still accept non-ASCII Unicode codepoints in vendor tokens for compatibility with future extensions.
Other special characters such as slashes, periods, percent signs, and asterisks are explicitly forbidden in vendor tokens to avoid conflicts with protocol delimiters.
Only simple characters (letters, numbers, hyphens, spaces) are allowed in the company name part. This keeps things simple and avoids confusion with special symbols used in protocols.
§4The Registration Process
Vendors reserve a vendor subtree by registering with IANA on a first come, first served basis. Once a vendor token such as vendor.example is registered, it is reserved for that vendor everywhere it appears in relevant protocols.
The RFC provides a template for registration requests. A vendor submits to iana@iana.org with the subject line 'Registration of ACAP Vendor Subtree' and specifies the desired vendor token (for example, vendor.companyname) along with contact information.
The RFC emphasizes that vendors should prefer improving interoperable standards over creating private attributes when possible. Once reserved, a vendor name applies consistently across all protocols that use this registry.
Companies contact IANA and say 'We want vendor.ourname', and IANA keeps a list. First to ask gets it. Once registered, nobody else can use that name in any protocol.
§5Updates from the Original RFC 2244
RFC 6075 makes several clarifications and updates to the original ACAP specification. The key changes include:
First, vendor tokens are now restricted to ASCII characters for registration purposes, addressing security and internationalization concerns.
Second, the RFC clarifies that 'vendor.company.product' means 'vendor.company' followed by '.product', not a structure like 'vendor.company/product' (which is illegal).
Third, the RFC changes the semantics so that 'vendor.company' is itself a valid vendor name that can be registered, not merely a prefix of longer names.
Finally, the RFC adds a concrete example registration for 'vendor.example' to match the example domain names in BCP 32.
At the time of publication, no existing registrations violated the new character restrictions, so backward compatibility was maintained.
The old rules were a bit vague about what you could do with vendor names. This update makes them clearer, restricts weird characters, and shows a real example of how to register one.