Expanding the IPv6 Documentation Space

04/07/2024

Expanding the IPv6 Documentation Space

By Alejandro Acosta

Introduction and a bit of history

First, let’s talk a bit about the IP prefixes reserved for documentation. The goal of these prefixes is for them to be exclusively used in books, texts, examples, tutorials, and so on, and they are not routed on the Internet. However, their success has created greater needs, reminding me of a very wise saying: today’s problems are a result of yesterday’s solutions.

Second, something very interesting is happening within the IETF, specifically within the v6ops working group. Exactly 10 years ago, a group of professionals (myself included) attempted to expand the IPv6 documentation space[1]. Unfortunately, this attempt was unsuccessful.

Finally, today an Internet Draft (ID) is under discussion which we believe will become an RFC. Its name is “Expanding the IPv6 Documentation Space”, and it is a document we support and believe is necessary and important for the community. We also believe that it was better to revisit and revive the draft from 10 years ago, a perfectly valid mechanism within the IETF.

Are documentation prefixes necessary? Don’t private addresses serve the same purpose?

These are two different concepts, each addressing distinct problems. While they may sometimes be confused, each approach seeks to solve different issues.

Additional reading:

Private addresses in IPv4 and Unique Local Address (ULA) in IPv6 are designed for use in internal networks. In other words, these IP addresses are assigned to the network and configured on our devices (i.e., computers, servers, printers, mobile phones, and others). In fact, it’s very likely that the computer you are using to read this article has a private address right now.

On the other hand, documentation IP addresses or prefixes are specifically intended for use in documents, magazines, online examples, labs, and other similar applications. These prefixes are crucial for ensuring clarity and consistency in topological documentation, without affecting network operation. For example, in the world of IPv6, any addressing you see in a document, video, or magazine is very likely part of the 2001:db8::/32 prefix.

Finally, neither private nor documentation prefixes should be routed on the Internet, nor should they be accepted, for example, on routers using BGP to connect to Internet providers.

For the remainder of this article, we will focus on documentation IP addresses, which is precisely the change that is coming to the world of IPv6.

About the current draft titled “Expanding the IPv6 Documentation Space”

This document was authored by Geoff Huston and Nick Buraglio. The first version was introduced in 2021 and it is currently on version 03, which will expire this 30 November. However, it is already in Last Call and is broadly supported by most of the community. We anticipate that it will soon become an Informational RFC.

How has the document progressed within the IETF?

What is the goal of the draft?

This document proposes reserving an additional IPv6 prefix for documentation purposes. Currently, address block 2001:db8::/32 is reserved for this use, but the draft suggests expanding this with a larger prefix, specifically a /20.

Reasons

This expansion will allow the documented examples to more accurately reflect a broader range of realistic deployment scenarios and better align with contemporary allocation models for large networks. For those of us who have taught courses on IPv6, this change will address the limitations we often face when creating IPv6 topologies and addressing plans adapted to multiple companies and needs.

Arguments

It is argued that with the expansion of global IPv6 deployment, individual IPv6 network deployment scenarios have increased in size and diversity, making the original 2001:db8::/32 prefix insufficient for describing many realistic current deployment scenarios. Reserving a further /20 prefix will address these limitations and even open new possibilities beyond our imagination.

Supporting information

According to data released by the Regional Internet Registries in August 2023, approximately 25.9% of all registered IPv6 assignments are larger than a /32. The majority of assignments are /29. It is believed that reserving a /20 would cover the documentation needs for a broad range of realistic deployments. For reference, there are 4096 /32s in a /20. In our region, this would allow creating an IPv6 addressing plan for a multinational company that wishes to have a /32 in each country in Latin America (and globally) without any problem.

Important

Please note that documentation prefixes should not be used for real traffic, should not be advertised globally, and should not be used internally for production traffic or connectivity. It is important to filter out documentation prefixes in routing prefix publications as appropriate.

Conclusions

We expect that this document will advance within the IETF in the coming months, and that we will soon have a /20 documentation prefix that will effectively cover almost all imaginable network needs. This will benefit the Internet ecosystem and contribute to promote the IPv6 protocol.

References

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