RFC 4580

Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent Subscriber-ID Option

📅 published June 2006, from ietf

Network Working Group Request for Comments 4580 💖

Written by: Bernard Volz, Cisco Systems, Inc. Category: Standards Track 🎀 Date: June 2006 🌸

Bestie, this one is all about a brand-new Relay Agent Subscriber-ID option for DHCPv6 (the protocol that hands IPv6 addresses and config to clients) ✨

Status of This Memo 🧚

This document is an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements. For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited 💅

Copyright Notice 🌈

Abstract 🦋

This memo defines a new Relay Agent Subscriber-ID option for DHCPv6. The option lets a DHCPv6 relay agent attach a stable "Subscriber-ID" to client messages, and it's independent of both the client and the physical network infrastructure underneath. It's giving stable and independent, iykyk 🫶

Table of Contents 📋

1. Introduction ....................................................2
2. The Relay Agent Subscriber-ID Option ............................2
3. DHCPv6 Relay Agent Behavior .....................................3
4. DHCPv6 Server Behavior ..........................................3
5. Security Considerations .........................................4
6. IANA Considerations .............................................4
7. Acknowledgements ................................................4
8. References ......................................................4
   8.1. Normative References .......................................4
   8.2. Informative References .....................................4

1. Introduction 🌸

Okay so DHCPv6 [1] gives IP addresses and config info to IPv6 clients 🧚 It has a relay agent capability, where processes inside the network infrastructure catch multicast messages from clients and relay them over to DHCPv6 servers. In some network environments, it's really useful for the relay agent to add info to the DHCPv6 message before it gets relayed. Main character energy for the relay agent 👑

The info relay agents supply can also help the server decide which addresses, delegated prefixes [2], and config parameters the client gets. Slay 💅

In a lot of service-provider environments, people think it's a good idea to attach some provider-specific info to a client's DHCPv6 messages. That info should be independent of the physical network setup, and the relay agent learned it some other way, which is outside the scope of this memo 🦋

2. The Relay Agent Subscriber-ID Option 💖

In complex service-provider environments, there's a real need to connect a customer's DHCPv6 config with the customer's administrative info. The Relay Agent Subscriber-ID option carries a value that can be independent of the physical network the subscriber connects through 🫶 This value complements the network-based info, and it might totally be used alongside it ✨ The "subscriber-id" the provider assigns is meant to stay stable as customers connect through different paths and as the network changes 🔥

The subscriber-id lets the service provider switch on subscriber-specific actions. Think assigning specific IP addresses, prefixes, or DNS config, triggering accounting, and so on 🎀 Because this option is decoupled from the access network's physical structure, a subscriber who moves from one access point to another, for example, wouldn't need reconfiguration at the provider's DHCPv6 servers. Literally seamless 🧚

The subscriber-id info is only meant for use within a single administrative domain, and it's only exchanged between the relay agents and DHCPv6 servers in that domain 🔒 So the format and encoding of the data in the option is not standardized, and this spec doesn't set any semantic requirements on the data. This spec only defines the option for carrying this info from relay agents to DHCPv6 servers 💜

Now here's the plot twist. The DHCPv4 Subscriber-ID suboption [3] specifies that its data is encoded in Network Virtual Terminal (NVT) American Standard Code for Information Interchange (ASCII) [4]. So in environments where both DHCPv4 [5] and DHCPv6 are in use, it may be beneficial to use that same encoding 🌈

The format of the DHCPv6 Relay Agent Subscriber-ID option looks like this:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     OPTION_SUBSCRIBER_ID      |         option-len            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.                                                               .
.                         subscriber-id                         .
.                                                               .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Here's what each field means 🍓

option-code: OPTION_SUBSCRIBER_ID (38)
option-len: the length, in octets, of the subscriber-id field. The minimum length is 1 octet.
subscriber-id: the subscriber's identity.

3. DHCPv6 Relay Agent Behavior 🦋

DHCPv6 relay agents may be configured to include a Subscriber-ID option in relayed (RELAY-FORW) DHCPv6 messages. How the subscriber-id gets assigned, and the mechanisms used to configure it, are outside the scope of this memo 🫶

4. DHCPv6 Server Behavior 🔥

This option gives the DHCPv6 server extra info 👑 The server can use it, if it's available, alongside other relay agent option data, other options in the DHCPv6 client messages, and physical network topology info. It can use all of that to assign IP addresses, delegate prefixes, and/or set other config parameters for the client. There's no special extra processing for this option 💅

There's no requirement that a server return this option and its data in a RELAY-REPLY message 🙈

5. Security Considerations 🔒

Since the subscriber-id option is only exchanged between relay agents and DHCPv6 servers, [1], Section 21.1, explains how to secure DHCPv6 messages sent between servers and relay agents. [1], Section 23, covers general DHCPv6 security considerations. Read both, no skipping 💀

6. IANA Considerations 📋

IANA has assigned DHCPv6 option code 38 to the Relay Agent Subscriber-ID Option ✨

7. Acknowledgements 🫶

Thank you to Richard Johnson, Theyn Palaniappan, and Mark Stapp, since this document is essentially an edited version of their memo [3] 💖

8. References 📚

8.1. Normative References

[1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.

8.2. Informative References

[2] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003.

[3] Johnson, R., Palaniappan, T., and M. Stapp, "Subscriber-ID Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option", RFC 3993, March 2005.

[4] Postel, J. and J. Reynolds, "Telnet Protocol Specification", STD 8, RFC 854, May 1983.

[5] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.

Author's Address 🎀

Bernard Volz
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA  01719
USA

Phone: +1 978 936 0382
EMail: volz@cisco.com

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📦 where this page comes from

ietf: rfc4580 2006-06
💖 girlified by claude-haiku-5-5 on 2026-10-16: a language model's rewrite of the original, under its terms