RFC 4727
Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers
Experimental Values in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers ✨
📜 RFC 4727 🎀 was written by B. Fenner of AT&T Labs - Research and dated November 2006. It's a Standards Track document, so it's meant to be a real protocol spec, not just an FYI. The title block doesn't list any RFCs it obsoletes or updates, so it doesn't replace or amend anything else. 💅
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 🫶. For where this protocol stands in standardization, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2006).
Abstract
okay so when you're experimenting with or extending protocols, you usually need some protocol number or constant to actually test your new stuff, even if you're only testing in a closed environment 🧪. This document sets aside some ranges of numbers for experimentation in specific protocols where that need was identified, and it lists the numbers that other documents have already reserved. ✨
1. Introduction 🌸
[RFC3692] recommends assigning option numbers for experiments and testing. This document records several of those assignments for the number spaces whose IANA considerations are covered in [RFC2780], and it generally follows the form of [RFC2780].
When you use these values, carefully consider the advice in Sections 1 and 1.1 of [RFC3692]. It is not appropriate to simply select one of these values and hard code it into a system. 🙈
Note: while [RFC3692] 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 [RFC0791] has a few fields that carry values assigned by 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. Iconic and consistent 💅.
2.2. IPv4 Type of Service Field
[RFC2474] 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 [RFC3168] has no free code points to assign. Lowkey no room here 😭.
2.3. IPv4 Protocol Field
[RFC3692] 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 [RFC1918] may be useful. It is not appropriate to use other special-purpose IPv4 addresses [RFC3330] 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. 🌈
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 [RFC2365] 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 [RFC2460] has fields that carry values assigned from IANA-managed name spaces: Version, Traffic Class, Next Header, Source and Destination Address. The IPv6 Hop-by-Hop Options and Destination Options extension headers also include an Option Type field with values from an IANA-managed name space. The IPv6 Routing Header has a Type field, but there isn't currently an explicit IANA assignment policy for it. Complicated, bestie 🫠.
3.1. IP Version Field in the IPv6 Header
The Version field in IPv6 packets is always 6. 👑
3.2. IPv6 Traffic Class Field
[RFC2474] 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 [RFC3168] has no free code points to assign. Same story as IPv4, no cap 💀.
3.3. IPv6 Next Header Field
[RFC3692] allocates two experimental code points (253 and 254) for the IPv6 Next Header field. 🌸
3.4. IPv6 Source and Destination Addresses
3.4.1. IPv6 Unicast Addresses
[RFC2928] 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 RFC3692-style experimental IPv6 addresses assigned. [HUSTON05] creates an IANA registry that may in the future contain such assignments. For certain experiments, Unique Local Addresses [RFC4193] may be useful. It is not appropriate to use addresses in the documentation prefix [RFC3849] 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 especially useful for experimentation, since they are defined not to leak out of a given 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 [RFC4291] 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. 🧚
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 🌈
[RFC4443] 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 [RFC2461] has 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. Nothing to see here, bestie 💅.
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. 🌸
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. Sadly, no room to play 😭.
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 RFC3692-style Experiment (*)
IPv4 Multicast Addresses (multicast-addresses relative addresses
section) (Section 2.4.2)
Relative Description
-------- ----------------------------
254 RFC3692-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
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 RFC3692-style Experiment 1 (*)
254 RFC3692-style Experiment 2 (*)
IPv6 Routing Header Routing Types (ipv6-parameters Section 5.c.)
(Section 3.6)
Type Description
---- ------------------------------
253 RFC3692-style Experiment 1 (*)
254 RFC3692-style Experiment 2 (*)
ICMPv4 Type Numbers (icmp-parameters) (Section 4)
Type Name
---- ------------------------------
253 RFC3692-style Experiment 1 (*)
254 RFC3692-style Experiment 2 (*)
System Port Numbers (port-numbers) (Sections 6 and 7.1)
Keyword Decimal Description
------- -------- ------------------------------
exp1 1021/udp RFC3692-style Experiment 1 (*)
exp1 1021/tcp RFC3692-style Experiment 1 (*)
exp2 1022/udp RFC3692-style Experiment 2 (*)
exp2 1022/tcp RFC3692-style Experiment 2 (*)
TCP Option Numbers (tcp-parameters) (Section 7.3)
Kind Length Meaning
---- ------ ------------------------------
253 N RFC3692-style Experiment 1 (*)
254 N RFC3692-style Experiment 2 (*)Each of these registrations comes with 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.🚨 Heads up: these values are only for explicitly configured experiments. They MUST NOT be shipped as defaults in implementations, so please don't let your code sneak them in 🙅♀️💖.
9. Security Considerations ✨
okay bestie, this part is SERIOUS 😭 production networks don't always support experimental code points in IP headers 💀 so before you deploy an experiment across big networks like the public Internet, you need to check what the network scope actually supports 🧐 using unsupported experimental values can literally mess up the stable operation of the network hosting your experiment, and that is a huge deal when you're planning this stuff 🚨
security analyzers like firewalls and network intrusion detection monitors kinda rely on fields being read in one clear way 🔍 as new values get assigned, analyzers that don't know the new values might fail. that can mean losing connectivity if the analyzer drops the unrecognized traffic, or losing security if it forwards the traffic and the new values are used in an attack 🙈 assigning known values for experiments can help, since analyzers can then take a known action on explicitly experimental traffic 🎀
the experimental IPv4 options from Section 2.5 are not included in the IPsec AH [RFC4302] calculations 🥺 so you can't authenticate their use. experimenters ought to keep that in mind when designing their experiments 💅 the experimental IPv6 options from Section 3.5 are different: users can choose whether the option is included in the AH calculations by picking the value of the "chg" field ✨
when experimental code points are deployed inside an administratively self-contained network domain, the network administrators should make sure each code point is used consistently so experiments don't interfere with each other 🫶 when they're used in traffic that crosses multiple administrative domains, experimenters should assume the same code points might be used at the same time by other experiments, which means the experiments could interfere 😬 pay special attention to any security threats that this kind of interference could create 🚨
10. References 🧚
10.1. Normative References 💜
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, July 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC2474] 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.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, March 2000.
[RFC2928] Hinden, R., Deering, S., Fink, R., and T. Hain, "Initial
IPv6 Sub-TLA ID Assignments", RFC 2928, September 2000.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", RFC
3168, September 2001.
[RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, September
2002.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849, July 2004.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[RFC4443] 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.comFull Copyright Statement 💖
Copyright (C) The IETF Trust (2006).
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contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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Acknowledgement 🫶
funding for the RFC Editor function is currently provided by the Internet Society 💜
📦 where this page comes from
- ietf: rfc4727 2006-11
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms