Expanding the IPv6 Documentation Space

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Table of Contents

1. Introduction

[RFC3849] introduced 2001:DB8::/32, describing the use of 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 is 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 address prefixes are drawn from address blocks already allocated or assigned to existing organizations or to well known ISPs, or 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 further /20 IPv6 address prefix from the Global Unicast Address pool [RFC4291] for documentation purposes avoids such conflicts.¶

2. Current Assignment and Allocation Data

According to the allocation and assignment data published by the Regional Internet Registries, [NROStatsReport], in August 2023 some 25.9% of all 62,770 recorded IPv6 unicast allocations and assignments are larger than a /32 in size. The most common allocation or assignment size is 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' address allocation policies moved away from the use of a fixed /48 site address prefix IPv6 address assignment policies, and in the foreseeable future its unlikely that individual networks require more than a /20. It is believed that a reservation of a /20 would cover the documentation needs as they relate the broad range of realistic network deployments.¶

3. Filtering and appropriate use

Documentation prefixes are for the use or relaying configuration and documentation examples and as such 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 and filtered in routing advertisements as appropriate.¶

4. Conventions and Definitions

None.¶

5. Security Considerations

This special use prefix should be marked as and considered [BOGON]. As is appropriate with bogon prefixes, packets whose src/dst belongs to this prefix should be dropped and disallowed over the public Internet.¶

6. IANA Considerations

IANA is to record the reservation of TBD::/20 in the IANA IPv6 Special-Purpose Address Registry; [IANAIPv6SPAR]. The Source, Destination, Forwardable, Globally Reachable and Reserved-by-Protocol fields should be recorded as False. There is no Termination Date for this entry. The name of the reservation is “Documentation".¶

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