Network Working Group T. Narten
Request for Comments: 3692 IBM
BCP: 82 January 2004
Updates: 2434
Category: Best Current Practice
Assigning Experimental and Testing Numbers Considered Useful
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 Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
When experimenting with or extending protocols, it is often necessary
to use some sort of protocol number or constant in order to actually
test or experiment with the new function, even when testing in a
closed environment. For example, to test a new DHCP option, one
needs an option number to identify the new function. This document
recommends that when writing IANA Considerations sections, authors
should consider assigning a small range of numbers for
experimentation purposes that implementers can use when testing
protocol extensions or other new features. This document reserves
some ranges of numbers for experimentation purposes in specific
protocols where the need to support experimentation has been
identified.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Recommendation for Protocols . . . . . . . . . . . . . . 4
2. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 5
2.1. IP Protocol Field. . . . . . . . . . . . . . . . . . . . 5
2.2. Existing Name Spaces . . . . . . . . . . . . . . . . . . 5
3. Security Considerations. . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 6
6. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6
7. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
When experimenting with or extending protocols, it is often necessary
to have a protocol number as part of the implementation [RFC2434].
For example, to develop a protocol that runs directly above IP, one
needs an IP Protocol Number to place in the Protocol field of the IP
header [RFC791]. In some cases, obtaining a new number is
straightforward (e.g., a well-known TCP or UDP port) or not even
necessary (e.g., TCP and UDP port numbers for testing purposes). In
other cases, obtaining a number is more difficult. For example, the
number of available and unassigned values in a name space may be
small enough that there is concern that all available numbers will be
used up if assigned carelessly. Even in cases where numbers are
potentially plentiful, it may be undesirable to assign numbers unless
the proposed usage has been adequately reviewed by the broader
community. Consequently, some number spaces specify that IANA only
make assignments in cases where there is strong community support for
a proposed protocol. For example, values out of some name spaces are
only assigned through an "IETF Standards Action" [RFC2434], which
requires that the proposed use be in an IETF Standards Track RFC.
In order to experiment with a new protocol, an experimental value may
be needed that won't collide with an existing or future usage.
One approach is to allow IANA to make temporary assignments for such
purposes. The idea is that a protocol value can be assigned to allow
experimentation, but after the experiment ends, the number would be
returned to IANA. There are several drawbacks to this approach,
however. First, experience has shown that it can be difficult to
reclaim numbers once assigned. For example, contact information
becomes outdated and it can become difficult to find out what the
status of an experiment actually is. Second, should deployment with
the temporarily assigned number take place (e.g., it is included as
part of a product), it becomes very difficult to determine whether or
not reuse of that number would lead to adverse impact with regards to
deployed devices. Finally, it can be difficult to determine when an
experiment has ended and whether the number needs to be returned.
An alternate approach, and the one recommended in this document, is
to assign a range of numbers specifically earmarked for testing and
experimentation purposes. Mutually consenting devices could use
these numbers for whatever purposes they desire, but under the
understanding that they are reserved for generic testing purposes,
and other implementations may use the same numbers for different
experimental uses.
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RFC 3692 Assigning Experimental and Testing Numbers January 2004
Numbers in the experimentation range are similar to those called
"Private Use" in RFC 2434 [IANA-CONSIDERATIONS]. They are not
intended to be used in general deployments or be enabled by default
in products or other general releases. In those cases where a
product or release makes use of an experimental number, the end user
must be required to explicitly enable the experimental feature and
likewise have the ability to chose and assign which number from the
experimental range will be used for a specific purpose (i.e., so the
end user can ensure that use of a particular number doesn't conflict
with other on-going uses). Shipping a product with a specific value
pre-enabled would be inappropriate and can lead to interoperability
problems when the chosen value collides with a different usage, as it
someday surely will.
From the above, it follows that it would be inappropriate for a group
of vendors, a consortia, or another Standards Development
Organization to agree among themselves to use a particular value for
a specific purpose and then agree to deploy devices using those
values. By definition, experimental numbers are not guaranteed to be
unique in any environment other than one where the local system
administrator has chosen to use a particular number for a particular
purpose and can ensure that a particular value is not already in use
for some other purpose.
Once an extension has been tested and shown to be useful, a permanent
number could be obtained through the normal assignment procedures.
Most implementations will not do anything special with numbers
assigned for testing purposes. In particular, unless a packet or
other Protocol Data Unit (PDU) is specifically directed at a device,
that device will not even look at the field while processing the PDU.
For example, IP routers do not need to examine or understand the
Protocol Type field of IP datagrams in order to know how to correctly
forward them. In those cases where a packet or PDU is directed at a
device, and that device has not been configured to recognize the
extension, the device will either ignore the PDU, discard it, or
signal an error, depending on the protocol-specific rules that
indicate how to process unknown options or features. In those cases
where a protocol has different ways of handling unrecognized
extensions (e.g., silently discard vs. signal an error), that
protocol needs to reserve values for testing purposes from all the
appropriate ranges. Only those implementations specifically enabled
or configured to make use of an extension or feature that is being
experimented with would process the data further.
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RFC 3692 Assigning Experimental and Testing Numbers January 2004
1.1. Recommendation for Protocols
To make it possible to experiment with protocol extensions safely,
protocol documents should consider reserving a small set of protocol
numbers for experimentation. Such reservations can be made through
an explicit reservation in an IANA Considerations section.
The exact number of values to reserve for experimentation will depend
on the specific protocol and factors specific to that protocol. For
example, in cases where the values of a field are subdivided into
ranges that are treated differently (e.g., "silently ignore" vs.
"return an error" if the value is not understood), one or more values
from each sub-range may need to be reserved.
For protocols that return error codes, it may also be appropriate to
reserve a small number of experimental error values that can be used
in conjunction with possible experimental uses. For example, an
experimental message might result (even under normal conditions) in
an error, with a special error code (or sub-code) indicating the type
of error condition.
In many, if not most cases, reserving a single value for experimental
use will suffice. While it may be tempting to reserve more in order
to make it easy to test many things at once, reserving many may also
increase the temptation for someone using a particular value to
assume that a specific experimental value can be used for a given
purpose exclusively. Values reserved for experimental use are never
to be made permanent; permanent assignments should be obtained
through standard processes. As described above, experimental numbers
are intended for experimentation and testing and are not intended for
wide or general deployments.
When protocols that use experimental numbers are included in
products, the shipping versions of the products must disable
recognition of protocol experimental numbers by default -- that is,
the end user of the product must explicitly "turn on" the
experimental protocol functionality. In most cases, a product
implementation must require the end user to configure the value
explicitly prior to enabling its usage. Should a product not have a
user interface for such end user configuration, the product must
require explicit re-programming (e.g., a special firmware download,
or installation of a feature card) to configure the experimental
number(s) of the protocol(s) implicitly.
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RFC 3692 Assigning Experimental and Testing Numbers January 2004
2. IANA Considerations
2.1. IP Protocol Field
Assignment of new values for the IP Protocol field requires an IETF
Standards Action per [RFC2780]. For the purposes of experimentation
and testing, IANA has assigned the two values 253 and 254 for this
purpose. These values have been allocated from the upper end of the
available number space in order to make them easy to identify by
having them stand out relative to the existing assignments that have
been made.
2.2. Existing Name Spaces
Numerous name spaces exist for which no values have been reserved for
experimentation or testing purpose. Experimental values for such
protocols can of course be assigned through the normal process of
publishing an RFC that documents the details of such an allocation.
To simplify the process in those cases where the publication of a
documentation just for the purpose of assigning an experimental
allocation seems overkill, experimental values can be made through
IESG Approval [RFC2434].
3. Security Considerations
This document has no known security implications.
4. Acknowledgments
Improvements to this document came as a result of specific feedback
from Steve Bellovin, Scott Bradner, Randy Bush, Bill Fenner, Steve
Hanna, Paul Hoffman, Henrik Levkowetz, John Loughney, Allison Mankin,
and Richard Woundy.
5. References
5.1. Normative References
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, March 2000.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
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5.2. Informative References
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
6. Author's Address
Thomas Narten
IBM Corporation
P.O. Box 12195
Research Triangle Park, NC 27709-2195
USA
Phone: +1 919 254 7798
EMail: narten@us.ibm.com
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7. Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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