RFC 4076

RFC 4076: Renumbering Requirements for Stateless DHCPv6 🎀

okay bestie, look at this header 💅 This is RFC 4076, and it's called Renumbering Requirements for Stateless Dynamic Host Configuration Protocol for IPv6 (DHCPv6). It came out of the Network Working Group in May 2005, and its category is Informational, so it's giving "here's some good info" rather than "this is a standard, do it." 🌸

The authors are T. Chown from the University of Southampton, S. Venaas from UNINETT, and A. Vijayabhaskar from Cisco Systems (India) Private Limited 🧚 The title block doesn't list anything it obsoletes or updates, so it's standing on its own, no cap. ✨

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Status of This Memo 📚

This memo is here to give info to the Internet community 🦋 It does not specify an Internet standard of any kind. Distribution of this memo is unlimited, so share it with everyone you know 💜

Copyright Notice ©️

Copyright (C) The Internet Society (2005). 🎀

Abstract ✨

Okay so IPv6 hosts that use Stateless Address Autoconfiguration can set up their IPv6 address and default router settings all by themselves 🙌 But that's where the magic stops. If these hosts want their DNS, NTP, or other specific settings to be configured automatically, they can use the stateless version of the Dynamic Host Configuration Protocol for IPv6 (DHCPv6), and this combo could be used pretty commonly in IPv6 networks 💅

The catch is that hosts using this combo currently have no way to find out when stateless DHCPv6 option settings change. Think a new NTP server address, a change to DNS search paths, or full site renumbering 😭 This document is a problem statement, and the idea is that a solution gets proposed in a later document. We're setting the stage, bestie 🌈

Table of Contents 🗂️

   1.  Introduction ...................................................2
   2.  Problem Statement ..............................................3
   3.  Renumbering Scenarios ..........................................3
       3.1.  Site Renumbering .........................................4
       3.2.  Changes to a DHCPv6-assigned Setting .....................4
   4.  Renumbering Requirements .......................................4
   5.  Considerations in Choosing a Solution ..........................4
   6.  Solution Space .................................................5
   7.  Summary ........................................................5
   8.  Security Considerations ........................................6
   9.  Acknowledgements ...............................................6
   10. References .....................................................6
       10.1. Normative References .....................................6
       10.2. Informative References ...................................6

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1. Introduction 🦋

Okay so IPv6 hosts using Stateless Address Autoconfiguration [2] are able to set their own IPv6 address and default router settings automatically, which is iconic 👑 But Stateless Address Autoconfiguration doesn't give them a way to automatically configure any of the other non-IP-address settings 🙈

Then there's the full version of the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [3], which does both jobs: it does stateful address assignment for IPv6 hosts AND handles extra (non-IP-address) config like DNS, NTP, and other specific settings 🧚 A full stateful DHCPv6 server hands out the addresses and keeps track of each client's bindings so it knows who has what lease 📋

If hosts using Stateless Address Autoconfiguration want their DNS, NTP, or other specific settings handled automatically, they can use the stateless variant [4] of DHCPv6 🌸 This version is way more lightweight. It doesn't do address assignment. Instead, it only hands out extra config parameters, like DNS resolver addresses ✨ It also doesn't keep dynamic state about what it gave each client, so the server doesn't need to store any per-client state. Low maintenance, high slay 💅

Put Stateless Address Autoconfiguration and stateless DHCPv6 together and you get a combo that could be used quite commonly in IPv6 networks 🎀

2. Problem Statement 😭

Here's the problem: clients using this combo might not be able to find out about changes to DHCPv6-assigned settings, or they might not be able to figure them out either 💀

A full DHCPv6 server can unicast Reconfigure messages to individual clients. That tells them to start an Information-request/reply configuration exchange so they can update their settings 🫶 The stateless variant can't use the Reconfigure mechanism, though, because it doesn't keep a list of IP addresses (leases) to send those unicast messages to. And in DHCPv6, Reconfigure messages must be unicast. Multicast is not allowed 🙅‍♀️

So these events can't be handled right now:

• Full site renumbering
• DNS server change of address
• NTP server change of address
• A change in DNS search paths

It would be highly desirable for a host using the Stateless Address Autoconfiguration plus stateless DHCPv6 combo to handle a renumbering or reconfiguration event, whether the network admin planned it or not 🔥

Also, the problem could go beyond stateless DHCPv6 🤔 Only IP address options have a lifetime, which means not even full DHCPv6 has a mechanism that "expires" old information or otherwise forces a client to recheck that new or updated info is available. The one bit of luck is that with full DHCPv6, a node can learn about updates to non-address options when it renews its address lease 🍓

3. Renumbering Scenarios 🗺️

There are two main scenarios where DHCPv6-assigned settings change and the client has to start an Information-request/reply exchange to update its config 💖

3.1. Site Renumbering 🌍

One of the core principles of IPv6 is that sites get their IPv6 address allocations from an ISP, using provider-assigned (PA) address space 🎀 Right now there's no provider-independent (PI) address space in IPv6. So if a site changes its ISP, it has to renumber its network 😬 Any site renumbering like this means hosts need to reconfigure both their own address and default router settings, plus their stateless DHCPv6-assigned settings 🔄

3.2. Changes to a DHCPv6-assigned Setting ⚙️

An admin might need to change one or more stateless DHCPv6-assigned settings, like an NTP server, a DNS server, or the DNS search path 🧚 This might happen if a new, extra DNS server comes online and gets moved to a new network (prefix), or if an existing server gets decommissioned or is known to be unavailable 💔

4. Renumbering Requirements 📝

Ideally, hosts on the network should handle any of the scenarios above automatically 🦋 To make that happen, there needs to be a method that tells hosts they should request new stateless DHCPv6-assigned setting information.

How you solve this might depend on whether the renumbering or config change was planned or unplanned, from the network admin's point of view 🤓 There's already work underway to understand planned renumbering [5] for IPv6 networks. The catch is that stateless DHCPv6 doesn't have any mechanism for handling planned renumbering events yet 🙃

That's the first half, bestie! 🌈💖 More is coming in part 2, so stay tuned 🫶

10.2. Informative References ✨

Okay, last stop on the reading list! These are the informative references, which means they're good background reads but nothing in the spec depends on them. 📚

• [5] Baker, F., Lear, E. and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", Work in Progress, July 2004.
• [6] Choi, J., "Goals of Detecting Network Attachment (DNA) in IPv6", Work in Progress, October 2004.

Authors' Addresses 💖

Meet the people who wrote this thing! 🫶

Tim Chown
University of Southampton
School of Electronics and Computer Science
Southampton, Hampshire  SO17 1BJ
United Kingdom

EMail: tjc@ecs.soton.ac.uk

Stig Venaas
UNINETT
Trondheim  NO 7465
Norway

EMail: venaas@uninett.no

Vijayabhaskar A Kalusivalingam
Cisco Systems (India) Private Limited
9, Brunton Road
Bangalore  560025
India

EMail: vibhaska@cisco.com

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Full Copyright Statement 🎀

Copyright (C) The Internet Society (2005).

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That's the whole thing, bestie! 👑🫶