Applying the New IPv6 Documentation Space: A Practical Approach (3FFF::/20)

06/02/2025

Applying the New IPv6 Documentation Space: A Practical Approach (3FFF::/20)

By Alejandro Acosta, R&D Coordinator, and Julio Buiza, Registration Services Specialist, at LACNIC

Introduction

On 23 July 2024, the IANA reserved 3FFF::/20 as a new dedicated IPv6 address prefix for documentation purposes, thus adding a new block to the existing documentation block (2001:db8::/32). This request was included in IETF draft https://datatracker.ietf.org/doc/draft-ietf-v6ops-rfc3849-update/05/ as follows:

“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 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.”

Following this expansion, in this article we will discuss an IPv6 address plan as an example, using address block3FFF::/20.

Importance of an IP Address Plan

What is an IP (v4/v6) address plan?

An IP address plan is defined as the form, actions, and systematic model used for assigning IP addresses on a network [1].

Why you should develop an IP address plan

An IP address plan:

  • Helps to keep the network documentation in order,
  • Simplifies the implementation of assignment policies,
  • Supports the orderly growth of the network (future assignments/scaling),
  • Improves network performance efficiency (smaller routing tables),
  • Facilitates troubleshooting, and
  • Simplifies network management.

What should an IP address plan look like? What aspects should it consider?

  • An IP address plan must be scalable (anticipate the potential growth of the network over the next 2, 5, 10, and 15 years).
  • It must be flexible. For example, in the future, new services may be added or coverage may be extended to other cities.
  • It must be simple and comprehensible, in other words, it must not introduce unnecessary complexity.
  • It must follow best practices.
  • It must separate the infrastructure from customers (important).

Recommendations to begin your IPv6 address plan

1)    The most important piece of advice, and one of the most fundamental, is to manipulate the blocks by nibbles, in other words, considering each character of the IPv6 address.

What would the new 3FFF::/20 prefix look like?

As shown in the image below, because the prefix is ​​a /20, the first five nibbles are fixed and every “X” character can be modified:

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Where:

  • C1, C2, C3, C4, C5, C6, C7, C8 -> Represent groups of 16 bits

2)    Mapping the nibbles to a function

A common practice is to map a nibble or a group of nibbles to “something”, where this “something” might be a function, a country, a service, a type of customer, or something else.

This is illustrated in the following image:

The views expressed by the authors of this blog are their own and do not necessarily reflect the views of LACNIC.

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