RFC 3587

IPv6 Global Unicast Address Format

📅 published August 2003, from ietf

IPv6 Global Unicast Address Format 🦋

okay bestie, here's the title block tea ☕

  • RFC number: 3587
  • Authors: R. Hinden (Nokia), S. Deering (Cisco), E. Nordmark (Sun)
  • Category: Informational 🌸
  • Date: August 2003
  • Obsoletes: RFC 2374 💅
  • Updates: nothing listed

Status of This Memo ✨

This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract 🧚

So this doc obsoletes RFC 2374, "An IPv6 Aggregatable Global Unicast Address Format" 💅. RFC 2374 defined an IPv6 address allocation structure with a Top Level Aggregator (TLA) and a Next Level Aggregator (NLA). This document makes RFC 2374 and the TLA/NLA structure historic. Bye bye, TLA/NLA 👋💜

1. Introduction 🍓

RFC 2374, "An IPv6 Aggregatable Global Unicast Address Format", defined an IPv6 address allocation structure with TLA and NLA. This document replaces RFC 2374 and makes RFC 2374 and the TLA/NLA structure historic. It's giving "fresh start" energy 🌈

2. TLA/NLA Made Historic 👑

Okay so the TLA/NLA scheme got replaced by a coordinated allocation policy from the Regional Internet Registries (RIRs) [IPV6RIR]. iykyk 🙈

Part of the reason for retiring TLA/NLA is technical. There's concern that TLA/NLA isn't the technically best approach at this stage of IPv6 deployment. It's also about policy 📋. IPv6 address allocation ties into the stewardship of the IP address space and routing table size, which the RIRs have been managing for IPv4. The RIRs' policy will probably keep evolving as IPv6 deployment goes on ✨

The IETF gave technical input to the RIRs (for example, [RFC3177]), and the RIRs took it into account when they defined their address allocation policy. Teamwork makes the dream work 🫶

RFC 2374 defined addresses for Format Prefix 001 (2000::/3), and this document formally makes that historic too. Even though only 2000::/3 is currently being delegated by the IANA, implementations should not make any assumptions about 2000::/3 being special. In the future, the IANA might be directed to delegate currently unassigned portions of the IPv6 address space for Global Unicast as well. Plot twist, but also not a surprise 😭

The Subnet Local Aggregator (SLA) field from RFC 2374 is still doing its job, just with a new name in [ARCH]. The new name is "subnet ID" 🦋

3. Address Format 🧚‍♀️

The general format for IPv6 global unicast addresses, as defined in "IP Version 6 Addressing Architecture" [ARCH], looks like this:

 |         n bits          |   m bits  |       128-n-m bits         |
 +-------------------------+-----------+----------------------------+
 | global routing prefix   | subnet ID |       interface ID         |
 +-------------------------+-----------+----------------------------+

Here's the breakdown. The global routing prefix is a value (typically hierarchically structured) assigned to a site, which is a cluster of subnets/links. The subnet ID identifies a subnet within that site. The interface ID is as defined in section 2.5.1 of [ARCH]. The global routing prefix is designed to be structured hierarchically by the RIRs and ISPs, and the subnet field is designed to be structured hierarchically by site administrators. Structure goals, the tea is hot 🍵

[ARCH] also says that all unicast addresses, except those starting with the binary value 000, have 64-bit Interface IDs built in Modified EUI-64 format. In that case, the global unicast address looks like this:

 |         n bits          | 64-n bits |       64 bits              |
 +-------------------------+-----------+----------------------------+
 | global routing prefix   | subnet ID |       interface ID         |
 +-------------------------+-----------+----------------------------+

The routing prefix identifies a site (a cluster of subnets/links), the subnet ID identifies a subnet within the site, and the interface ID is a Modified EUI-64 format as defined in [ARCH]. Simple and iconic 💅

Here's an example of the resulting global unicast address format under the 2000::/3 prefix, which is currently being delegated by the IANA and is consistent with the recommendations in RFC 3177:

 | 3 |     45 bits         |  16 bits  |       64 bits              |
 +---+---------------------+-----------+----------------------------+
 |001|global routing prefix| subnet ID |       interface ID         |
 +---+---------------------+-----------+----------------------------+

4. Acknowledgments 🫶

The authors want to thank Alain Durand, Brian Carpenter, Fred Templin, Julian Sellers, Jun-ichiro Itojun Hagino, Margaret Wasserman, Michel Py, Pekka Savola, Tatuya Jinmei, and Thomas Narten for their review and constructive comments. Main character reviewers, every one of them 👑

5. References 📚

5.1. Normative References

  • [ARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 3513, April 2003.
  • [IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.

5.2. Informative References

6. Security Considerations 💀

Okay, serious moment 🙈 IPv6 addressing documents do not have any direct impact on Internet infrastructure security. Nothing in here touches your security, so no panic 🫶

7. Authors' Addresses 💌

Robert M. Hinden Nokia 313 Fairchild Drive Mountain View, CA USA

EMail: bob.hinden@nokia.com

Stephen E. Deering Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA

Erik Nordmark Sun Microsystems Laboratories 180, avenue de l'Europe 38334 SAINT ISMIER Cedex France

EMail: erik.nordmark@sun.com

Copyright (C) The Internet Society (2003). All Rights Reserved.

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Acknowledgement 🌈

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