Network Working Group J. Littlefield

Network Working Group J. Littlefield
Request for Comments: 3925 Cisco Systems, Inc.
Category: Standards Track October 2004

Vendor-Identifying Vendor Options for
Dynamic Host Configuration Protocol version 4 (DHCPv4)

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 (2004).

Abstract

The Dynamic Host Configuration Protocol (DHCP) options for Vendor
Class and Vendor-Specific Information can be limiting or ambiguous
when a DHCP client represents multiple vendors. This document
defines two new options, modeled on the IPv6 options for vendor class
and vendor-specific information, that contain Enterprise Numbers to
remove ambiguity.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document. . . . . . . . . . . . 2
2. Supporting Multiple Vendor Instances . . . . . . . . . . . . . 3
3. Vendor-Identifying Vendor Class Option . . . . . . . . . . . . 3
4. Vendor-Identifying Vendor-Specific Information Option . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
8. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8
9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 9

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RFC 3925 Vendor-Identifying Vendor Options October 2004

1. Introduction

The DHCP protocol for IPv4, RFC 2131 [2], defines options that allow
a client to indicate its vendor type (option 60), and the DHCP client
and server to exchange vendor-specific information (option 43) [5].
Although there is no prohibition against passing multiple copies of
these options in a single packet, doing so would introduce ambiguity
of interpretation, particularly if conveying vendor-specific
information for multiple vendors. The vendor identified by option 60
defines the interpretation of option 43, which itself carries no
vendor identifier. Furthermore, the concatenation of multiple
instances of the same option, required by RFC 2131 and specified by
RFC 3396 [4], means that multiple copies of options 60 or 43 would
not remain independent.

In some circumstances, an implementation may need to support
multiple, independently defined forms of vendor-specific information.
For example, implementations that must conform to an industry-
standard use of DHCPv4, to allow interoperability in a particular
technology space, may be required to support the vendor-specific
options of that industry group. But the same implementation may also
require support for vendor-specific options defined by the
manufacturer. In particular, this is an issue for vendors of devices
supporting CableLabs [9] standards, such as DOCSIS, CableHome, and
PacketCable, as those standards define an industry-specific use for
options 60 and 43.

This document defines two new options, modeled on the IPv6 options
for vendor class and vendor-specific information defined in RFC 3315
[6], that contain IANA-assigned Enterprise Numbers [3] to remove
ambiguity about the interpretation of their contents. If desired,
these new options can be used in addition to the current vendor class
and vendor information options, whose definition is unaffected by
this document.

1.1. Conventions Used in This Document

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 BCP 14, RFC 2119 [1].

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RFC 3925 Vendor-Identifying Vendor Options October 2004

2. Supporting Multiple Vendor Instances

The options defined in this document may each contain data
corresponding to more than one vendor. The data portion of each
option defined here contains an enterprise number (assigned by IANA
[3]), followed by an internal data length, followed by vendor-
specific data. This sequence may be repeated multiple times within
each option. Because the aggregate of the vendor-specific data for
either option may exceed 255 octets, these options are hereby
declared to be "concatenation-requiring", as defined by RFC 3396 [4].
As such, for each of the two options defined here, the aggregate of
all instances of vendor-specific data is to be considered one long
option. These long options can be divided into smaller options for
packet encoding in conformance with RFC 3396, on whatever octet
boundaries are convenient to the implementation. Dividing on the
boundaries between vendor instances is not required but may be
convenient for encoding or packet tracing.

3. Vendor-Identifying Vendor Class Option

A DHCP client may use this option to unambiguously identify the
vendor that manufactured the hardware on which the client is running,
the software in use, or an industry consortium to which the vendor
belongs. The information contained in the per-vendor data area of
this option is contained in one or more opaque fields that may
identify details of the hardware configuration.

This option may be used wherever Vendor Class Identifier (option 60)
may be used, as described in RFC 2131 [2], except for DHCPNAK
messages, where other options are not permitted. It is most
meaningful in messages from DHCP client to DHCP server (DHCPDISCOVER,
DHCPREQUEST, DHCPINFORM).

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RFC 3925 Vendor-Identifying Vendor Options October 2004

The format of the V-I Vendor Class option is as follows:

1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number1 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data-len1 | |
+-+-+-+-+-+-+-+-+ |
/ vendor-class-data1 /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| enterprise-number2 | ^
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| data-len2 | | optional
+-+-+-+-+-+-+-+-+ | |
/ vendor-class-data2 / |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ ... ~ V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----

option-code OPTION_V-I_VENDOR_CLASS (124)

option-len total length of all following option data in
octets

enterprise-numberN The vendor's 32-bit Enterprise Number as
registered with IANA [3]

data-lenN Length of vendor-class-data field

vendor-class-dataN Details of the hardware configuration of the
host on which the client is running, or of
industry consortium compliance

This option contains information corresponding to one or more
Enterprise Numbers. Multiple instances of this option may be present
and MUST be concatenated in accordance with RFC 3396 [4]. An
Enterprise Number SHOULD only occur once among all instances of this
option. Behavior is undefined if an Enterprise Number occurs
multiple times. The information for each Enterprise Number is
treated independently, regardless or whether it occurs in an option
with other Enterprise Numbers or in a separate option.

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RFC 3925 Vendor-Identifying Vendor Options October 2004

The vendor-class-data comprises a series of separate items, each of
which describes some characteristic of the client's hardware
configuration or capabilities. Examples of vendor-class-data
instances might include the version of the operating system the
client is running or the amount of memory installed on the client.

Each instance of the vendor-class-data is formatted as follows:

1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data-len | |
+-+-+-+-+-+-+-+-+ opaque-data |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The data-len is one octet long and specifies the length of the opaque
vendor class data in network byte order.

4. Vendor-Identifying Vendor-Specific Information Option

DHCP clients and servers may use this option to exchange vendor-
specific information. Either party may send this option, as needed.
Although a typical case might be for a client to send the Vendor-
Identifying Vendor Class option, to elicit a useful Vendor-
Identifying Vendor-Specific Information Option, there is no
requirement for such a flow.

This option may be used in any packets where "other" options are
allowed by RFC 2131 [2], specifically DHCPDISCOVER, DHCPOFFER,
DHCPREQUEST, DHCPACK, and DHCPINFORM.

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RFC 3925 Vendor-Identifying Vendor Options October 2004

The format of the V-I Vendor-specific Information option is as
follows:

1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number1 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data-len1 | |
+-+-+-+-+-+-+-+-+ option-data1 |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| enterprise-number2 | ^
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| data-len2 | | optional
+-+-+-+-+-+-+-+-+ option-data2 | |
/ / |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ ... ~ V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----

option-code OPTION_V-I_VENDOR_OPTS (125)

option-len total length of all following option data in
octets

enterprise-numberN The vendor's registered 32-bit Enterprise Number
as registered with IANA [3]

data-lenN Length of option-data field

option-dataN Vendor-specific options, described below

The definition of the information carried in this option is vendor
specific. The vendor is indicated in the enterprise-number field.
This option contains information corresponding to one or more
Enterprise Numbers. Multiple instances of this option may be present
and MUST be concatenated in accordance with RFC 3396 [4].

An Enterprise Number SHOULD only occur once among all instances of
this option. Behavior is undefined if an Enterprise Number occurs
multiple times. The information for each Enterprise Number is
treated independently, regardless or whether it occurs in an option
with other Enterprise Numbers, or in a separate option.

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RFC 3925 Vendor-Identifying Vendor Options October 2004

Use of vendor-specific information allows enhanced operation,
utilizing additional features in a vendor's DHCP implementation.
Servers not equipped to interpret the vendor-specific information
sent by a client MUST ignore it. Clients that do not receive desired
vendor-specific information SHOULD make an attempt to operate without
it.

The encapsulated vendor-specific option-data field MUST be encoded as
a sequence of code/length/value fields of identical format to the
DHCP options field. The option codes are defined by the vendor
identified in the enterprise-number field and are not managed by
IANA. Option codes 0 and 255 have no pre-defined interpretation or
format. Each of the encapsulated options is formatted as follows:

1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-code | subopt-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ sub-option-data /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

subopt-code The code for the encapsulated option

subopt-len An unsigned integer giving the length of the
option-data field in this encapsulated option in
octets

sub-option-data Data area for the encapsulated option

5. IANA Considerations

The values for the OPTION_V-I_VENDOR_CLASS and OPTION_V-I_VENDOR_OPTS
option codes have been assigned from the numbering space defined for
public DHCP Options in RFC 2939 [7].

6. Security Considerations

This document in and by itself provides no security, nor does it
impact existing security. DHCP provides an authentication and
message integrity mechanism, as described in RFC 3118 [8], which may
be used if authenticity is required for data carried by the options
defined in this document.

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RFC 3925 Vendor-Identifying Vendor Options October 2004

7. References

7.1. Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

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

[3] IANA, "Private Enterprise Numbers",
<http://www.iana.org/assignments/enterprise-numbers>.

[4] Lemon, T. and S. Cheshire, "Encoding Long Options in the Dynamic
Host Configuration Protocol (DHCPv4)", RFC 3396, November 2002.

7.2. Informative References

[5] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.

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

[7] Droms, R., "Procedures and IANA Guidelines for Definition of New
DHCP Options and Message Types", BCP 43, RFC 2939, September
2000.

[8] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001.

URIs

[9] <http://www.cablelabs.com/>

8. Author's Address

Josh Littlefield
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
USA

Phone: +1 978-936-1379
EMail: [email protected]

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RFC 3925 Vendor-Identifying Vendor Options October 2004

9. Full Copyright Statement

Copyright (C) The Internet Society (2004).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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