INTERNET-DRAFT Thomas Narten
IBM
<draft-iesg-iana-considerations-03.txt> Harald Tveit Alvestrand
UNINETT
March 13, 1998
Guidelines for Writing an IANA Considerations Section in RFCs
<draft-iesg-iana-considerations-03.txt>
Status of this Memo
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This Internet Draft expires September 13, 1998.
Abstract
Many protocols make use of identifiers consisting of constants and
other well-known values. Even after a protocol has been defined and
deployment has begun, new values may need to be assigned (e.g., for a
new option type in DHCP, or a new authentication algorithm). To
insure that such quantities have unique values, their assignment must
be administered by a central authority. In the Internet, that role is
provided by the Internet Assigned Numbers Authority (IANA).
In order for the IANA to manage a given numbering space prudently, it
needs guidelines describing the conditions under which new values can
be assigned. If the IANA is expected to play a role in the management
of a numbering space, the IANA must be given clear and concise
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instructions describing that role. This document discusses issues
that should be considered in formulating an identifier assignment
policy and provides guidelines to document authors on the specific
text that must be included in documents that place demands on the
IANA.
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Contents
Status of this Memo.......................................... 1
1. Introduction............................................. 3
2. Issues To Consider....................................... 4
3. Designated Experts....................................... 6
4. Registration maintenance................................. 7
5. What To Put In Documents................................. 7
6. Applicability to Past and Future RFCs.................... 8
7. Security Considerations.................................. 8
8. Acknowledgements......................................... 9
9. References............................................... 9
10. Authors' Addresses...................................... 10
1. Introduction
Many protocols make use of fields that contain constants and other
well-known values (e.g., the Protocol field in the IP header [IP] or
MIME types in mail messages [MIME-REG]). Even after a protocol has
been defined and deployment has begun, new values may need to be
assigned (e.g., a new option type in DHCP [DHCP] or a new
authentication algorithm for IPSec [IPSEC]). To insure that such
fields have unique values, their assignment must be administered by a
central authority. In the Internet, that role is provided by the
Internet Assigned Numbers Authority (IANA).
In order for the IANA to manage a given numbering space prudently, it
needs guidelines describing the conditions under which new values
should be assigned. This document provides guidelines to authors on
what sort of text should be added to their documents, and reviews
issues that should be considered in formulating an appropriate policy
for assigning identifiers.
Not all name spaces require centralized administration. In some
cases, it is possible to delegate a name space in such a way that
further assignments can be made independently and with no further
(central) coordination. In the Domain Name System, for example, the
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IANA only deals with assignments at the higher-levels, while
subdomains are administered by the organization to which the space
has been delegated. As another example, Object Identifiers (OIDs) as
defined by the ITU are also delegated [ASSIGNED]. When a name space
can be delegated, the IANA only deals with assignments at the top
level.
This document uses the terms 'MUST', 'SHOULD' and 'MAY', and their
negatives, in the way described in RFC 2119 [KEYWORDS]. In this case,
"the specification" as used by RFC 2119 refers to the processing of
protocols being submitted to the IETF standards process.
2. Issues To Consider
The primary issue to consider in managing a numbering space is its
size. If the space is small and limited in size, assignments must be
made carefully to insure that the space doesn't become exhausted. If
the space is essentially unlimited, on the other hand, it may be
perfectly reasonable to hand out new values to anyone that wants one.
Even when the space is essentially unlimited, however, it is usually
desirable to have a minimal review to prevent hoarding of the space.
For example, if the space consists of text strings, it may be
desirable to prevent organizations from obtaining large sets of
strings that correspond to the "best" names (e.g., existing company
names).
A second consideration is whether it makes sense to delegate the name
space in some manner. This route should be pursued when appropriate,
as it lessens the burden on the IANA for dealing with assignments.
In most cases, some review of prospective allocations is appropriate,
and the first question to consider is who should perform the review.
In some cases, reviewing requests is straightforward and requires no
subjective decision making. On those cases, it is reasonable for the
IANA to review prospective assignments, provided that the IANA is
given specific guidelines on what types of requests it should grant,
and what information must be provided before a request of an assigned
number will be considered. Note that the IANA will not define an
assignment policy; it should be given a set of guidelines that allow
it to make allocation decisions with little subjectivity. The
following are example policies, some of which are in use today:
Local Use - For local use only, with the type and purpose defined
by the local site. No attempt is made to prevent multiple
sites from using the same value in different (and
incompatible) ways. There is no need for IANA to review
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such assignments and assignments are not generally useful
for interoperability.
Examples: Site-specific options in DHCP [DHCP] have
significance only within a single site. XXX X-foo header
lines in email message (and mime types?)
Hierarchical allocation - Delegated managers can assign
identifiers provided they have been given control over that
part of the identifier space. IANA controls the higher
levels of the namespace according to one of the other
policies.
Examples: DNS names, Object Identifiers
First Come First Served - Anyone can obtain an identifier, so long
as they provide a point of contact and a brief description
of what the identifier would be used for. For numbers, the
exact value is generally assigned by the IANA, with names,
specific names are usually requested.
Examples: vnd. MIME types [MIME-REG], TCP and UDP port
numbers.
Specification Required - Values and their meaning must be
documented in an RFC or other permanent and readily
available reference, in sufficient detail so that
interoperability between independent implementations is
possible.
Examples: SCSP [SCSP]
IETF Consensus - New values are assigned through the IETF
consensus process. Specifically, new assignments are made
via RFCs approved by the IESG. Typically, the IESG will
seek input on prospective assignments from appropriate
persons (e.g., a relevant Working Group if one exists).
Examples: SMTP extensions [SMTP-EXT], BGP Subsequent
Address Family Identifiers [BGP4-EXT].
Standards Action - Identifiers are assigned only for Standards
Track RFCs approved by the IESG.
Examples: MIME top level types [MIME-REG]
It should be noted that it often makes sense to partition a number
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space into several categories, with assignments out of each category
handled differently. For example, the DHCP option space [DHCP] is
split into two parts. Option numbers in the range of 1-127 are
globally unique and assigned according to the Specification Required
policy described above, while options number 128-254 are "site
specific", i.e., Local Use. Dividing the number space up makes it
possible to allow some assignments to be made with minimal review,
while simultaneously reserving some part of the space for future use
via a more stringent review process.
3. Designated Experts
In many cases, it is be appropriate for the IANA to serve as a
point-of-contact for publishing information about numbers that have
been assigned, without actually having it evaluate and grant
requests. For example, it may be useful (and sometimes necessary) to
discuss proposed additions on a mailing list dedicated to the purpose
(e.g., the ietf-types@iana.org for media types) or on a more general
mailing list (e.g., that of a current or former IETF Working Group).
Such a mailing list provides a way for new registrations to be
publically reviewed prior to getting assigned, or to give advice for
persons who want help in understanding what a proper registration
should contain.
Since the IANA cannot participate in all of these mailing lists and
cannot determine if or when such discussion reaches a consensus, the
IANA in all cases relies on a "designated expert" to advise it in
assignment matters. That is, the IANA forwards the requests it
receives to a specific point-of-contact (one or a small number of
individuals) and acts upon the returned recommendation from the
designated expert. In all cases, it is the designated expert that the
IANA relies on for an authoritative response. In those cases where
wide review of a request is needed, it is the responsibility of the
designated expert to initiate such a review (e.g., by engaging the
relevant mailing lists). In no cases will the IANA allow general
mailing lists (e.g., that of a former or existing IETF Working Group)
to fill the role of the designated subject matter expert.
Designated experts serve at the pleasure of the IESG (e.g,, they are
appointed by the relevant Area Director) and are typically named at
the time a document that creates a new numbering space is published
as an RFC. Any decisions made by the designated expert can be
appealed using the normal IETF appeals process as outlined in Section
6.5 of [IETF-PROCESS].
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4. Registration maintenance
Registrations sometimes contain information that needs to be
maintained; in particular, point of contact information may need to
be changed, claims of freedom from security problems may need to be
modified, or new versions of a registration may need to be published.
A document must clearly state who is responsible for such
maintenance. It is appropriate to:
- Let the author update the registration, subject to the same
constraints and review as with new registrations
- Allow some mechanism to attach comments to the registration, for
cases where others have significant objections to claims in a
registration, but the author does not agree to change the
registration.
- Designate the IESG or another authority as having the right to
reassign ownership of a registration. This is mainly to get
around the problem when some registration owner cannot be
reached in order to make necessary updates.
In the absense of specific instructions, the designated expert will
assume such responsibilities.
5. What To Put In Documents
The previous sections presented some issues that should be considered
in formulating a policy for assigning well-known numbers and other
protocol constants. It is the Working Group and/or document author's
job to formulate an appropriate policy and specify it in the
appropriate document. In some cases, having an "IANA Considerations"
section may be appropriate. Specifically, documents that create an
identifier space (or modify the definition of an existing space) and
that expect the IANA to play a role in maintaining that space (e.g.,
serving as a repository for registered values) MUST document the
process through which future assignments are made. Such a section
should state clearly:
- whether or not an application for an assigned number should
first be reviewed by a designated expert. When a designated
expert is used, documents MUST NOT name the designated expert in
the document itself; instead, the name should be relayed to the
appropriate IESG Area Director at the time the document is sent
to the IESG for approval.
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- If the request should also be reviewed by a specific public
mailing list (such as the ietf-types@iana.org for media types),
that mailing address should be specified. Note, however, that a
designated subject matter expert must also be specified.
- if the IANA is expected to review requests itself, sufficient
guidance must be provided so that the requests can be evaluated
with minimal subjectivity.
Authors SHOULD attempt to provide guidelines that allow the IANA to
assign new values directly without requiring review by a designated
expert. This can be done easily in many cases by designating a range
of values for direct assignment by the IANA while simultaneously
reserving some of the identifier space for future use by requiring
that assignments from that space be made only after a more stringent
review.
Finally, it is quite acceptable to pick one of the example policies
cited above and refer to it by name. For example, a document could
say something like:
numbers in the range 0-127 are allocated as First Come First
Served as defined in [IANA-CONSIDERATIONS], numbers between
128-255 must be approved by the designated expert.
For examples of documents that provide good and detailed guidance to
the IANA on the issue of assigning identifiers, consult [MIME-REG,
MIME-LANG].
6. Applicability to Past and Future RFCs
All existing RFCs that either explicitely or implicitly rely on the
IANA to evaluate assignments without specifying a precise evaluation
policy, will have assignments evaluated by a designated expert, as
outlined in Section 3.
All future RFCs that either explicitely or implicitly rely on the
IANA to register or otherwise manage assignments MUST provide
guidelines for managing the identifier space.
7. Security Considerations
Information that creates or updates a registration needs to be
authenticated.
Information concerning possible security vulnerabilities of a
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protocol may change over time. Consequently, claims as to the
security properties of a registered protocol may change as well. As
new vulnerabilities are discovered, information about such
vulnerabilities may need to be attached to existing registrations, so
that users are not mislead as to the true security properties of a
registered protocol.
An analysis of security issues is required for all types registered
in the IETF Tree [MIME-REG]. A similar analysis for media types
registered in the vendor or personal trees is encouraged but not
required. However, regardless of what security analysis has or has
not been done, all descriptions of security issues must be as
accurate as possible regardless of registration tree. In particular,
a statement that there are "no security issues associated with this
type" must not be confused with "the security issues associated with
this type have not been assessed".
Delegations of a name space should only be assigned to someone with
adequate security.
8. Acknowledgements
Jon Postel and Joyce Reynolds provided a detailed explanation on what
the IANA needs in order to manage assignments efficiently. Brian
Carpenter provided helpful comments on earlier versions of the
document. One paragraph in the Security Considerations section was
borrowed from [MIME-REG].
9. References
[ASSIGNED] Reynolds, J., Postel, J., "Assigned Numbers", October
1994k, RFC 1700.
[BGP4-EXT] Bates. T., Chandra, R., Katz, D., Rekhter, Y.,
Multiprotocol Extensions for BGP-4, draft-ietf-idr-bgp4-
multiprotocol-02.txt, January, 1998
[DHCP-OPTIONS] S. Alexander, R. Droms, DHCP Options and BOOTP
Vendor Extensions, RFC 2132, March 1997.
[IANA-CONSIDERATIONS] Alvestrand, H., Narten, T., "Guidelines for
Writing an IANA Considerations Section in RFCs", draft-
iesg-iana-considerations-03.txt.
[IETF-PROCESS] Bradner, S., "The Internet Standards Process --
Revision 3", RFC 2026, October 1996.
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[IP] J. Postel, Internet Protocol, RFC 791, September 1, 1981.
[IPSEC] Atkinson, R., Security Architecture for the Internet
Protocol, RFC 1825, August 1995.
[KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[MIME-LANG] Freed, N., Moore, K., "MIME Parameter Value and Encoded
Word Extensions: Character Sets, Languages, and
Continuations", RFC 2184, August, 1997.
[MIME-REG] N. Freed, J. Klensin & J. Postel, Multipurpose Internet
Mail Extension (MIME) Part Four: Registration Procedures.
RFC 2048, November, 1996.
[SCSP] Luciani, J., Armitage, G, Halpern, J., "Server Cache
Synchronization Protocol (SCSP)" draft-ietf-ion-scsp-
02.txt.
[SMTP-EXT] Klensin, J., Freed, N., Rose, M., Stefferud, E.,
Crocker, D.. "SMTP Service Extensions", RFC 1869, November
1995.
10. Authors' Addresses
Thomas Narten
IBM Corporation
3039 Cornwallis Ave.
PO Box 12195 - BRQA/502
Research Triangle Park, NC 27709-2195
Phone: 919-254-7798
EMail: narten@raleigh.ibm.com
Harald Tveit Alvestrand
Maxware
Pirsenteret
N-7005 Trondheim
Norway
Phone: +47 73 54 57 97
Email: Harald@Alvestrand.no
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