DHCPv6 Remote-ID: Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent Remote-ID Option
How a DHCPv6 relay agent tells the server which remote user, port or circuit a request came from.
Volz, B., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent Remote-ID Option", RFC 4649, DOI 10.17487/RFC4649, August 2006, <https://www.rfc-editor.org/info/rfc4649>.
@misc{rfc4649,
series = {Request for Comments},
number = 4649,
howpublished = {RFC 4649},
publisher = {RFC Editor},
doi = {10.17487/RFC4649},
url = {https://www.rfc-editor.org/info/rfc4649},
author = {B. Volz},
title = {{Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent Remote-ID Option}},
pagetotal = 6,
year = 2006,
month = aug,
} RFC text
Contents
Network Working Group B. Volz
Request for Comments: 4649 Cisco Systems, Inc.
Category: Standards Track August 2006
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Relay Agent Remote-ID Option
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This memo defines a new Relay Agent Remote-ID option for the Dynamic
Host Configuration Protocol for IPv6 (DHCPv6). This option is the
DHCPv6 equivalent for the Dynamic Host Configuration Protocol for
IPv4 (DHCPv4) Relay Agent Option's Remote-ID suboption as specified
in RFC 3046.
Table of Contents
1. Introduction ....................................................2
2. Requirements Terminology ........................................2
3. The Relay Agent Remote-ID Option ................................2
4. DHCPv6 Relay Agent Behavior .....................................3
5. DHCPv6 Server Behavior ..........................................3
6. Security Considerations .........................................3
7. IANA Considerations .............................................4
8. Acknowledgements ................................................4
9. References ......................................................4
9.1. Normative References .......................................4
9.2. Informative References .....................................4
1. Introduction
DHCPv6 [1] provides IP addresses and configuration information for
IPv6 clients. It includes a relay agent capability, in which
processes within the network infrastructure receive multicast
messages from clients and relay them to DHCPv6 servers. In some
network environments, it will be useful for the relay agent to add
information to the DHCPv6 message before relaying it.
The information that relay agents supply can also be used in the
server's decision making about the addresses, delegated prefixes [4],
and configuration parameters that the client is to receive.
The memo specifies the DHCPv6 equivalent of the DHCPv4 Relay Agent
option's Remote-ID suboption as specified in [2]. The motivation and
usage scenarios are provided in [2].
2. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [3].
3. The Relay Agent Remote-ID Option
This option may be added by DHCPv6 relay agents that terminate
switched or permanent circuits and have mechanisms to identify the
remote host end of the circuit.
The format of the DHCPv6 Relay Agent Remote-ID option is shown below:
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_REMOTE_ID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. remote-id .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_REMOTE_ID (37)
option-len 4 + the length, in octets, of the remote-id
field. The minimum option-len is 5 octets.
enterprise-number The vendor's registered Enterprise Number as
registered with IANA [5].
remote-id The opaque value for the remote-id.
The definition of the remote-id carried in this option is vendor
specific. The vendor is indicated in the enterprise-number field.
The remote-id field may be used to encode, for instance:
o a "caller ID" telephone number for dial-up connection
o a "user name" prompted for by a Remote Access Server
o a remote caller ATM address
o a "modem ID" of a cable data modem
o the remote IP address of a point-to-point link
o a remote X.25 address for X.25 connections
o an interface or port identifier
Each vendor must ensure that the remote-id is unique for its
enterprise-number, as the octet sequence of enterprise-number
followed by remote-id must be globally unique. One way to achieve
uniqueness might be to include the relay agent's DHCP Unique
Identifier (DUID) [1] in the remote-id.
4. DHCPv6 Relay Agent Behavior
DHCPv6 relay agents may be configured to include a Remote-ID option
in relayed (RELAY-FORW) DHCPv6 messages.
5. DHCPv6 Server Behavior
This option provides additional information to the DHCPv6 server.
The DHCPv6 server, if it is configured to support this option, may
use this information to select parameters specific to particular
users, hosts, or subscriber modems. The combined enterprise-number
and remote-id SHOULD be considered an opaque value, with policies
based on exact string match only; that is, the remote-id field SHOULD
NOT be internally parsed by the server.
There is no requirement that a server return this option and its data
in a RELAY-REPLY message.
6. Security Considerations
See [1] section 21.1, on securing DHCPv6 messages sent between
servers and relay agents, and section 23, on general DHCPv6 security
considerations. [2] discusses how this information can be used to
enhance trust in some environments.
Note that even if the DHCP server trusts the relay agent not to
modify information provided in this option, the confidence in that
information is no higher than the confidence that the relay agent has
in the information it puts in the option. For example, in some
protocols it may be possible for a DHCP client to spoof or otherwise
choose port identifiers, caller ID information, or other information
carried in this option. Sites should consider such possible spoofing
and how likely it is in their environment when deciding what uses of
this option are appropriate.
7. IANA Considerations
IANA has assigned the DHCPv6 option code 37 for the Relay Agent
Remote-ID Option.
8. Acknowledgements
Thanks to Michael Patrick for [2], from which I've liberally borrowed
text.
9. References
9.1. 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.
[2] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[4] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633, December
2003.
[5] IANA, "Private Enterprise Numbers",
<http://www.iana.org/assignments/enterprise-numbers>.
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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AI ELI5
On this page
§1Why a Relay Adds Information
DHCPv6 (RFC 3315) gives IPv6 clients addresses and configuration. It includes a relay agent capability: processes in the network infrastructure receive multicast messages from clients and relay them to DHCPv6 servers. In some networks it is useful for the relay to add information to the message before passing it on.
A server can use that information when deciding which addresses, delegated prefixes and configuration parameters a client should get. This memo defines the DHCPv6 equivalent of the Remote-ID suboption of the DHCPv4 Relay Agent option from RFC 3046. The motivation and usage scenarios are described there, not repeated here.
Sometimes the helper in the middle knows something the address office would like to know. This note lets the helper pass it along.
§3The Remote-ID Option Format
The option has four parts: OPTION_REMOTE_ID (the option code), option-len, a 32-bit enterprise-number and a variable-length remote-id.
The option code is 37. The option-len is 4 plus the length, in octets, of the remote-id field, so the minimum option-len is 5 octets. The enterprise number is the vendor's registered Enterprise Number as registered with IANA. The remote-id is an opaque value.
The note has a label saying what kind of note it is, a length, the name of the company that made the helper, and then the actual identifying text.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
OPTION-CODE | OPTION_REMOTE_ID | 2 bytes | 37 | Option code, 37. |
OPTION-LEN | option-len | 2 bytes | 4 plus the length of remote-id in octets; minimum 5. | |
ENTERPRISE-NUMBER | enterprise-number | 4 bytes | The vendor's registered Enterprise Number from IANA. | |
REMOTE-ID | remote-id | 4 bytes | Opaque, vendor-specific value; variable length. |
§3.1What the Remote-ID Contains
What the remote-id means is vendor specific, and the enterprise-number field says which vendor. The RFC suggests it may encode, for instance, a caller ID telephone number for a dial-up connection, a user name prompted for by a Remote Access Server, a remote caller ATM address, a modem ID of a cable data modem, the remote IP address of a point-to-point link, a remote X.25 address, or an interface or port identifier.
The enterprise-number followed by the remote-id must be globally unique, so each vendor must ensure the remote-id is unique within its own enterprise number. One suggested way is to include the relay agent's DHCP Unique Identifier (DUID) in the remote-id. The option may be added by relay agents that terminate switched or permanent circuits and can identify the remote host end of the circuit.
The note can say things like a phone number or a port number. To make sure two notes are never confused, it starts with the name of the company that wrote it.
§4Relay and Server Behavior
A DHCPv6 relay agent may be configured to include a Remote-ID option in the relayed (RELAY-FORW) messages it sends.
A server that is configured to support the option may use it to select parameters specific to particular users, hosts or subscriber modems. The server SHOULD treat the combined enterprise-number and remote-id as one opaque value and base policies on exact string match only. It SHOULD NOT parse the remote-id field internally. There is no requirement that a server return the option and its data in a RELAY-REPLY message.
The helper may add the note. The address office reads it as one single label and only checks whether it matches exactly, without trying to understand the inside.
§6How Far the Information Can Be Trusted
The RFC points to RFC 3315 section 21.1 on securing messages between servers and relay agents, and section 23 on general DHCPv6 security. RFC 3046 discusses how this information can enhance trust in some environments.
Even if the server trusts the relay agent not to modify the option, its confidence in the data is no higher than the relay's own confidence in the information it put there. In some protocols a client may be able to spoof or choose port identifiers, caller ID information or other data carried in the option. Sites should weigh that risk when deciding what uses of the option are appropriate.
The note is only as honest as what the helper was told. If someone can fib to the helper, the note will carry the fib.
§7IANA Assignment
IANA has assigned DHCPv6 option code 37 for the Relay Agent Remote-ID Option. The enterprise-number field refers to the IANA registry of Private Enterprise Numbers.
The official number list now has the number 37 reserved for this kind of note.