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IETF RFC 4727
Experimental Values in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers
Last modified on Wednesday, November 29th, 2006
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Network Working Group B. Fenner
Request for Comments: 4727 AT&T Labs - Research
Category: Standards Track November 2006
Experimental Values
in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The IETF Trust (2006).
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. This document reserves some ranges of numbers
for experimentation purposes in specific protocols where the need to
support experimentation has been identified, and it describes the
numbers that have already been reserved by other documents.
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RFC 4727 Experimental Values in Headers November 2006
1. Introduction
[RFC 3692] recommends assigning option numbers for experiments and
testing. This document documents several such assignments for the
number spaces whose IANA considerations are documented in [RFC 2780].
This document generally follows the form of [RFC 2780].
When using these values, carefully consider the advice in Sections 1
and 1.1 of [RFC 3692]. It is not appropriate to simply select one of
these values and hard code it into a system.
Note: while [RFC 3692] says that it may not be necessary to allocate
values for UDP and TCP ports, Sections 6 and 7.1 explicitly reserve
ports for this purpose to avoid any possible conflict.
2. Fields in the IPv4 Header
The IPv4 header [RFC 791] contains the following fields that carry
values assigned by the IANA: Version, Type of Service, Protocol,
Source Address, Destination Address, and Option Type.
2.1. IP Version Field in the IPv4 Header
The Version field in IPv4 packets is always 4.
2.2. IPv4 Type of Service Field
[RFC 2474] defines Pool 2 (all code points xxxx11, where 'x' refers to
either '0' or '1') as Experimental/Local Use, so no additional code
points should be needed. The Explicit Congestion Notification (ECN)
field [RFC 3168] has no free code points to assign.
2.3. IPv4 Protocol Field
[RFC 3692] allocates two experimental code points (253 and 254) for
the IPv4 Protocol field.
2.4. IPv4 Source and Destination Addresses
2.4.1. IPv4 Unicast
No experimental IPv4 addresses are defined. For certain experiments,
the address ranges set aside for Private Internets in [RFC 1918] may
be useful. It is not appropriate to use other special-purpose IPv4
addresses [RFC 3330] for experimentation.
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At the time of this writing, some Internet Registries have policies
allowing experimental assignments from number spaces that they
control. Depending on the experiment, the registry, and their
policy, this may be an appropriate path to pursue.
2.4.2. IPv4 Multicast
The globally routable group 224.0.1.20 is set aside for
experimentation. For certain experiments, the administratively
scoped multicast groups defined in [RFC 2365] may be useful. This
document assigns a single link-local scoped group, 224.0.0.254, and a
single scope-relative group, 254.
2.5. IPv4 Option Type Field
This document assigns a single option number, with all defined values
of the "copy" and "class" fields, resulting in four distinct option
type codes. See Section 8 for the assigned values.
3. Fields in the IPv6 Header
The IPv6 header [RFC 2460] contains the following fields that carry
values assigned from IANA-managed name spaces: Version, Traffic
Class, Next Header, Source and Destination Address. In addition, the
IPv6 Hop-by-Hop Options and Destination Options extension headers
include an Option Type field with values assigned from an IANA-
managed name space. The IPv6 Routing Header contains a Type field
for which there is not currently an explicit IANA assignment policy.
3.1. IP Version Field in the IPv6 Header
The Version field in IPv6 packets is always 6.
3.2. IPv6 Traffic Class Field
[RFC 2474] defines Pool 2 (all code points xxxx11, where 'x' refers to
either '0' or '1') as Experimental/Local Use, so no additional code
points should be needed. The ECN field [RFC 3168] has no free code
points to assign.
3.3. IPv6 Next Header Field
[RFC 3692] allocates two experimental code points (253 and 254) for
the IPv6 Next Header field.
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3.4. IPv6 Source and Destination Addresses
3.4.1. IPv6 Unicast Addresses
[RFC 2928] defines a set of IPv6 addresses for testing and
experimental usage:
The block of Sub-TLA IDs assigned to the IANA (i.e.,
2001:0000::/29 - 2001:01F8::/29) is for assignment for testing and
experimental usage to support activities such as the 6bone, and
for new approaches like exchanges.
However, at this writing, there are no RFC 3692-style experimental
IPv6 addresses assigned. [HUSTON05] creates an IANA registry that
may in the future contain such assignments. For certain experiments,
Unique Local Addresses [RFC 4193] may be useful. It is not
appropriate to use addresses in the documentation prefix [RFC 3849]
for experimentation.
At the time of this writing, some Internet Registries have policies
allowing experimental assignments from number spaces that they
control. Depending on the experiment, the registry, and their
policy, this may be an appropriate path to pursue.
3.4.2. IPv6 Multicast Addresses
The group FF0X::114 is set aside for experimentation at all scope
levels. Smaller scopes may be particularly useful for
experimentation, since they are defined not to leak out of a given
defined boundary, which can be set to be the boundary of the
experiment. For certain experiments, other multicast addresses with
the T (non-permanently-assigned or "transient" address) bit [RFC 4291]
set may be useful.
3.5. IPv6 Hop-by-Hop and Destination Option Fields
This document assigns a single option type, with all possible values
of the "act" and "chg" fields, resulting in eight distinct option
type codes. See Section 8 for the assigned values.
3.6. IPv6 Routing Header Routing Type
This document assigns two values for the Routing Type field in the
IPv6 Routing Header, 253 and 254.
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RFC 4727 Experimental Values in Headers November 2006
4. Fields in the IPv4 ICMP Header
This document assigns two ICMPv4 type numbers, 253 and 254. ICMPv4
code values are allocated per type, so it's not feasible to assign
experimental values in this document.
5. Fields in the IPv6 ICMP Header
[RFC 4443] includes experimental ICMPv6 type values for Informational
(200, 201) and Error (100, 101) message types. ICMPv6 code values
are allocated per type, so it's not feasible to assign experimental
values in this document.
5.1. IPv6 Neighbor Discovery Fields
The IPv6 Neighbor Discovery header [RFC 2461] contains the following
fields that carry values assigned from IANA-managed name spaces:
Type, Code, and Option Type.
5.1.1. IPv6 Neighbor Discovery Type
The Neighbor Discovery Type field is the same as the ICMPv6 Type
field. See Section 5 for those code points.
5.1.2. IPv6 Neighbor Discovery Code
The ICMPv6 Code field is not used in IPv6 Neighbor Discovery, so no
experimental code points are necessary.
5.1.3. IPv6 Neighbor Discovery Option Type
This document assigns two IPv6 Neighbor Discovery Option Types, 253
and 254.
6. Fields in the UDP Header
Two system ports, 1021 and 1022, have been reserved for
experimentation for UDP and TCP.
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RFC 4727 Experimental Values in Headers November 2006
7. Fields in the TCP Header
7.1. TCP Source and Destination Port Fields
Two system ports, 1021 and 1022, have been reserved for
experimentation for UDP and TCP.
7.2. Reserved Bits in TCP Header
There are not enough reserved bits to allocate any for
experimentation.
7.3. TCP Option Kind Field
Two TCP options, 253 and 254, have been reserved for experimentation
with TCP Options.
8. IANA Considerations
The new assignments are summarized below.
IPv4 Multicast Addresses (multicast-addresses (224.0.0/24) Local
Network Control Block section) (Section 2.4.2)
Group Address Name
------------- ----------------------------
224.0.0.254 RFC 3692-style Experiment (*)
IPv4 Multicast Addresses (multicast-addresses relative addresses
section) (Section 2.4.2)
Relative Description
-------- ----------------------------
254 RFC 3692-style Experiment (*)
IPv4 Option Numbers (ip-parameters initial section) (Section 2.5)
Copy Class Number Value
---- ----- ------ -----
0 0 30 30
0 2 30 94
1 0 30 158
1 2 30 222
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IPv6 Option Types (ipv6-parameters Section 5.b.) (Section 3.5)
HEX act chg rest
---- --- --- -----
0x1e 00 0 11110
0x3e 00 1 11110
0x5e 01 0 11110
0x7e 01 1 11110
0x9e 10 0 11110
0xbe 10 1 11110
0xde 11 0 11110
0xfe 11 1 11110
IPv6 Neighbor Discovery Option Formats (icmpv6-parameters)
(Section 5.1.3)
Type Description
---- ------------------------------
253 RFC 3692-style Experiment 1 (*)
254 RFC 3692-style Experiment 2 (*)
IPv6 Routing Header Routing Types (ipv6-parameters Section 5.c.)
(Section 3.6)
Type Description
---- ------------------------------
253 RFC 3692-style Experiment 1 (*)
254 RFC 3692-style Experiment 2 (*)
ICMPv4 Type Numbers (icmp-parameters) (Section 4)
Type Name
---- ------------------------------
253 RFC 3692-style Experiment 1 (*)
254 RFC 3692-style Experiment 2 (*)
System Port Numbers (port-numbers) (Sections 6 and 7.1)
Keyword Decimal Description
------- -------- ------------------------------
exp1 1021/udp RFC 3692-style Experiment 1 (*)
exp1 1021/tcp RFC 3692-style Experiment 1 (*)
exp2 1022/udp RFC 3692-style Experiment 2 (*)
exp2 1022/tcp RFC 3692-style Experiment 2 (*)
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RFC 4727 Experimental Values in Headers November 2006
TCP Option Numbers (tcp-parameters) (Section 7.3)
Kind Length Meaning
---- ------ ------------------------------
253 N RFC 3692-style Experiment 1 (*)
254 N RFC 3692-style Experiment 2 (*)
Each of these registrations is accompanied by the following footnote:
(*) It is only appropriate to use these values in explicitly-
configured experiments; they MUST NOT be shipped as defaults in
implementations. See RFC 3692 for details.
9. Security Considerations
Production networks do not necessarily support the use of
experimental code points in IP headers. The network scope of support
for experimental values should carefully be evaluated before
deploying any experiment across extended network domains, such as the
public Internet. The potential to disrupt the stable operation of
the network hosting the experiment through the use of unsupported
experimental code points is a serious consideration when planning an
experiment using such code points.
Security analyzers such as firewalls and network intrusion detection
monitors often rely on unambiguous interpretations of the fields
described in this memo. As new values for the fields are assigned,
existing security analyzers that do not understand the new values may
fail, resulting in either loss of connectivity, if the analyzer
declines to forward the unrecognized traffic, or in loss of security
if it does forward the traffic and the new values are used as part of
an attack. Assigning known values for experiments can allow such
analyzers to take a known action for explicitly experimental traffic.
Because the experimental IPv4 options defined in Section 2.5 are not
included in the IPsec AH [RFC 4302] calculations, it is not possible
for one to authenticate their use. Experimenters ought to keep this
in mind when designing their experiments. Users of the experimental
IPv6 options defined in Section 3.5 can choose whether or not the
option is included in the AH calculations by choosing the value of
the "chg" field.
When experimental code points are deployed within an administratively
self-contained network domain, the network administrators should
ensure that each code point is used consistently to avoid
interference between experiments. When experimental code points are
used in traffic that crosses multiple administrative domains, the
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RFC 4727 Experimental Values in Headers November 2006
experimenters should assume that there is a risk that the same code
points will be used simultaneously by other experiments and thus that
there is a possibility that the experiments will interfere.
Particular attention should be given to security threats that such
interference might create.
10. References
10.1. Normative References
[RFC 791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC 1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC 2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, July 1998.
[RFC 2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC 2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC 2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
[RFC 2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, March 2000.
[RFC 2928] Hinden, R., Deering, S., Fink, R., and T. Hain, "Initial
IPv6 Sub-TLA ID Assignments", RFC 2928, September 2000.
[RFC 3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", RFC
3168, September 2001.
[RFC 3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, September
2002.
[RFC 3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
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RFC 4727 Experimental Values in Headers November 2006
[RFC 3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849, July 2004.
[RFC 4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC 4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC 4302] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[RFC 4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
10.2. Informative References
[HUSTON05] Huston, G., "Administration of the IANA Special Purpose
Address Block", Work in Progress, December 2005.
Author's Address
Bill Fenner
AT&T Labs - Research
75 Willow Rd
Menlo Park, CA 94025
USA
Phone: +1 650 330-7893
EMail: fenner@research.att.com
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RFC 4727 Experimental Values in Headers November 2006
Full Copyright Statement
Copyright © The IETF Trust (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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Experimental Values in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers
RFC TOTAL SIZE: 19745 bytes
PUBLICATION DATE: Wednesday, November 29th, 2006
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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