Expanding the IPv6 Documentation Space
Reserves 3fff::/20 as a second, much larger IPv6 block for documentation examples.
Huston, G. and N. Buraglio, "Expanding the IPv6 Documentation Space", RFC 9637, DOI 10.17487/RFC9637, August 2024, <https://www.rfc-editor.org/info/rfc9637>.
@misc{rfc9637,
series = {Request for Comments},
number = 9637,
howpublished = {RFC 9637},
publisher = {RFC Editor},
doi = {10.17487/RFC9637},
url = {https://www.rfc-editor.org/info/rfc9637},
author = {G. Huston and N. Buraglio},
title = {{Expanding the IPv6 Documentation Space}},
pagetotal = 5,
year = 2024,
month = aug,
} RFC text
Contents
Internet Engineering Task Force (IETF) G. Huston
Request for Comments: 9637 APNIC
Updates: 3849 N. Buraglio
Category: Informational Energy Sciences Network
ISSN: 2070-1721 August 2024
Expanding the IPv6 Documentation Space
Abstract
The document describes the reservation of an additional IPv6 address
prefix for use in documentation. This update to RFC 3849 expands on
the existing 2001:db8::/32 address block with the reservation of an
additional, larger prefix. The addition of a /20 prefix allows
documented examples to more closely reflect a broader range of
realistic, current deployment scenarios and more closely aligns with
contemporary allocation models for large networks.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9637.
Copyright Notice
Copyright (c) 2024 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
(https://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 Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Requirements Language
3. Current Assignment and Allocation Data
4. Filtering and Appropriate Use
5. Security Considerations
6. IANA Considerations
7. References
7.1. Normative References
7.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
[RFC3849] introduced the IPv6 address prefix 2001:db8::/32 as a
reserved prefix for use in documentation. The rationale for this
reservation was to reduce the likelihood of conflict and confusion
when relating documented examples to deployed systems.
As the global deployment of IPv6 expands and evolves, individual IPv6
network deployment scenarios have also increased in size and
diversity, and there is a requirement for documentation to reflect
this increased diversity and scope. The original 2001:db8::/32
reservation is inadequate to describe many realistic, current
deployment scenarios.
Without this additional address allocation, documentation prefixes
are drawn from address blocks already allocated or assigned to
existing organizations or well-known ISPs, or they are drawn from the
currently unallocated address pool. Such use conflicts with existing
or future allocations or assignments of IPv6 address space. The
reservation of a /20 IPv6 address prefix from the Global Unicast
Address pool [RFC4291] for documentation purposes allows such
conflicts to be avoided.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Current Assignment and Allocation Data
According to the allocation and assignment data published by the
Regional Internet Registries (RIRs) (see [NROStatsReport]), in August
2023, 25.9% of the 62,770 recorded IPv6 unicast allocations and
assignments were larger than a /32 in size. The most common
allocation or assignment size was a /29, used in 24.8% of cases.
The four largest assignments made to end users have been /19s, but
these allocations were made before the RIRs moved away from the use
of a fixed /48 site address prefix in IPv6 address assignment
policies, and in the foreseeable future, it is unlikely that
individual networks will require more than a /20. It is believed
that reservation of a /20 will cover the documentation needs as they
relate to the broad range of realistic network deployments.
4. Filtering and Appropriate Use
Documentation prefixes are for the use of relaying configuration and
documentation examples, and as such, they MUST NOT be used for actual
traffic, MUST NOT be globally advertised, and SHOULD NOT be used
internally for routed production traffic or other connectivity.
Documentation prefixes should be considered bogon [BOGON] and
filtered in routing advertisements as appropriate.
5. Security Considerations
This special-use prefix should be marked as and considered bogon
[BOGON]. As is appropriate with bogon prefixes, packets whose source
or destination belongs to this prefix should be dropped and
disallowed over the public Internet.
6. IANA Considerations
IANA has registered the following in the "IANA IPv6 Special-Purpose
Address Registry" [IANA-IPv6-SPAR].
Address Block: 3fff::/20
Name: Documentation
RFC: RFC 9637
Allocation Date 2024-07
Termination Date: N/A
Source: False
Destination: False
Forwardable: False
Globally Reachable : False
Reserved-by-Protocol: False
7. References
7.1. Normative References
[IANA-IPv6-SPAR]
IANA, "IANA IPv6 Special-Purpose Address Registry",
<https://www.iana.org/assignments/iana-ipv6-special-
registry>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[BOGON] Team Cymru, "Unravelling the Mystery of Bogons: A senior
stakeholder and IT professional guide", July 2023,
<https://www.team-cymru.com/post/unravelling-the-mystery-
of-bogons-a-senior-stakeholder-and-it-professional-guide>.
[NROStatsReport]
"NRO Stats Reports",
<https://ftp.ripe.net/pub/stats/ripencc/nro-stats>.
[RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849,
DOI 10.17487/RFC3849, July 2004,
<https://www.rfc-editor.org/info/rfc3849>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
Acknowledgments
The authors would like to acknowledge the valuable input from XiPeng
Xiao, Chris Cummings, Russ White, Kevin Myers, Ed Horley, Tom
Coffeen, and Scott Hogg.
Authors' Addresses
Geoff Huston
APNIC
Email: gih@apnic.net
Nick Buraglio
Energy Sciences Network
Email: buraglio@forwardingplane.net
AI ELI5
On this page
§1Why a Bigger Documentation Prefix
RFC 3849 reserved 2001:db8::/32 for documentation, to reduce the chance of conflict and confusion between examples and deployed systems. IPv6 networks have since grown in size and diversity, and the RFC says the original block is inadequate for many realistic scenarios.
Without more space, documentation prefixes are drawn from blocks already allocated to organizations or well-known ISPs, or from the unallocated pool. That conflicts with existing or future allocations. Reserving a /20 from the Global Unicast Address pool avoids this.
If the pretend-address box is too small, writers grab real addresses by mistake. A bigger box stops that.
§2Why a /20
Using Regional Internet Registry data from August 2023, the RFC notes that 25.9% of the 62,770 recorded IPv6 unicast allocations and assignments were larger than a /32. The most common size was a /29, at 24.8%.
The four largest end-user assignments have been /19s, but they predate the RIRs moving away from a fixed /48 site prefix. It is unlikely that individual networks will need more than a /20 in the foreseeable future, so a /20 is believed to cover documentation needs.
The authors looked at how big real networks are and picked a block big enough for nearly all of them.
§3Filtering and Appropriate Use
Documentation prefixes are for configuration and documentation examples. They MUST NOT be used for actual traffic, MUST NOT be globally advertised, and SHOULD NOT be used internally for routed production traffic or other connectivity.
They should be treated as bogons and filtered in routing advertisements as appropriate.
These are pretend addresses. Never send real mail to them, and tell nobody they are real.
§4Security and the IANA Entry
The prefix should be considered bogon, and packets whose source or destination belongs to it should be dropped and disallowed over the public Internet.
IANA registered address block 3fff::/20, named Documentation, in the IPv6 Special-Purpose Address Registry, with an allocation date of 2024-07 and Source, Destination, Forwardable, Globally Reachable and Reserved-by-Protocol all set to False.
Routers should throw away anything using these pretend addresses, and the official list now records the new block.