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Versions: (draft-stapp-dhc-vendor-suboption)
00 RFC 4243
DHC Working Group M. Stapp
Internet-Draft R. Johnson
Expires: February 7, 2005 T. Palaniappan
Cisco Systems, Inc.
August 9, 2004
Vendor-Specific Information Suboption for the DHCP Relay Agent Option
<draft-ietf-dhc-vendor-suboption-00.txt>
Status of this Memo
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This Internet-Draft will expire on February 7, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This memo defines a new Vendor-Specific Information suboption for the
Dynamic Host Configuration Protocol's (DHCP) relay agent information
option. The suboption allows a DHCP relay agent to include
vendor-specific information in DHCP messages it forwards, as
configured by its administrator.
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Table of Contents
1. Requirements Terminology . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The Vendor-Specific Suboption . . . . . . . . . . . . . . . . . 3
4. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . . . 4
5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Normative References . . . . . . . . . . . . . . . . . . . . . . 7
Informative References . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . 9
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1. 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 RFC 2119 [1].
2. Introduction
DHCP (RFC 2131 [2]) provides IP addresses and configuration
information for IPv4 clients. It includes a relay agent capability,
in which processes within the network infrastructure receive
broadcast messages from clients and forward them to DHCP servers as
unicast messages. In network environments like DOCSIS data-over-cable
and xDSL, for example, it has proven useful for the relay agent to
add information to the DHCP message before forwarding it, using the
relay agent information option (RFC 3046 [3]).
Servers that recognize the relay agent option echo it back in their
replies, and some of the information that relays add may be used to
help an edge device efficiently return replies to clients. The
information that relays supply can also be used in the server's
decision making about the addresses and configuration parameters that
the client should receive.
In many environments it's desirable to associate some vendor- or
provider-specific information with clients' DHCP messages. This is
often done using the relay agent information option. RFC 3046 defines
Remote-ID and Circuit-ID sub-options that are used to carry such
information. The values of those suboptions, however, are usually
based on some network resource, such as an IP address of a network
access device, an ATM Virtual Circuit identifier, or a DOCSIS
cable-modem identifier. As a result, the values carried in these
suboptions are dependent on the physical network configuration. The
Vendor-Specific suboption allows administrators to associate other
useful data with relayed DHCP messages.
3. The Vendor-Specific Suboption
This memo defines a new DHCP relay agent option suboption that
carries vendor-defined data. The suboption takes a form similar to
the Vendor-Identifying Vendor-Specific Option [8].
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Enterprise Number1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | DataLen1 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
\ Suboption Data1 \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Enterprise Number2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DataLen2 | Suboption Data2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Code for the suboption is <TBD> (to be assigned by IANA).
The one-byte Length field is the length of the data carried in the
suboption, in bytes. The length includes the length of the first
Enterprise Number; the minimum length is 4 bytes.
"Enterprise NumberN" is a vendor's Enterprise Number as registered
with IANA [4]. It is a four-byte integer value in network byte-order.
DataLenN is the length of the data associated with the Enterprise
Number.
The Suboption Data is an opaque sequence of bytes.
The Vendor-Specific suboption includes at least one Enterprise Number
and carries opaque data defined by the organization identified by the
Enterprise Number. A relay may include data associated with more than
one vendor's Enterprise Number within a single instance of the
Suboption.
The Vendor-Specific data are of course provider-specific. This
specification does not establish any requirements on the data in the
suboption. Vendors who make use of this suboption are encouraged to
document their usage in order to make interoperability possible.
4. Relay Agent Behavior
DHCP relay agents MAY be configured to include Vendor-Specific
suboptions if they include a relay agent information option in
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relayed DHCP messages. The suboptions' types and data are assigned
and configured through mechanisms that are outside the scope of this
memo.
Relay implementors are encouraged to offer their administrators some
means of configuring what data can be included in this suboption, and
to document what they are capable of.
5. DHCP Server Behavior
This suboption provides additional information to the DHCP server.
The DHCP server, if it is configured to support this suboption, may
use this information in addition to other relay agent option data and
other options included in the DHCP client messages in order to assign
an IP address and/or other configuration parameters to the client.
There is no special additional processing for this suboption.
DHCP server vendors are encouraged to offer their administrators some
means of configuring the use of data from incoming Vendor-Specific
suboptions in DHCP decision-making.
6. Security Considerations
Message authentication in DHCP for intradomain use where the
out-of-band exchange of a shared secret is feasible is defined in RFC
3118 [5]. Potential exposures to attack are discussed in section 7 of
the DHCP protocol specification in RFC 2131 [2].
The DHCP relay agent option depends on a trusted relationship between
the DHCP relay agent and the server, as described in section 5 of RFC
3046. Fraudulent relay agent option data could potentially lead to
theft-of-service or exhaustion of limited resources (like IP
addresses) by unauthorized clients. A host that tampered with relay
agent data associated with another host's DHCP messages could deny
service to that host, or interfere with its operation by leading the
DHCP server to assign it inappropriate configuration parameters.
While the introduction of fraudulent relay agent options can be
prevented by a perimeter defense that blocks these options unless the
relay agent is trusted, a deeper defense using authentication for
relay agent options via the Authentication Suboption [6] or IPSEC [7]
SHOULD be deployed as well.
There are several data in a DHCP message that convey information that
may identify an individual host on the network. These include the
chaddr, the client-id option, and the hostname and client-fqdn
options. Depending on the type of data included, the Vendor-Specific
suboption may also convey information that identifies a specific host
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or a specific user on the network. In practice, this information
isn't exposed outside the internal service-provider network, where
DHCP messages are usually confined. Administrators who configure data
that's going to be used in DHCP Vendor-Specific suboptions should be
careful to use data that are appropriate for the types of networks
they administer. If DHCP messages travel outside the
service-provider's own network, or if the suboption values may become
visible to other users, that may raise privacy concerns for the
access provider or service provider.
7. IANA Considerations
IANA is requested to assign a suboption number for the
Vendor-Specific Information Suboption from the DHCP Relay Agent
Information Option [3] suboption number space.
8. Acknowledgements
The authors are grateful to Andy Sudduth, Josh Littlefield, and Kim
Kinnear for their review and comments.
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[3] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001.
[4] IANA, "Private Enterprise Numbers (http://www.iana.org/
assignments/enterprise-numbers.html)".
Informative References
[5] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001.
[6] Stapp, M., "The Authentication Suboption for the DHCP Relay
Agent Option", draft-ietf-dhc-auth-suboption-04.txt (work in
progress), October 2003.
[7] Droms, R., "Authentication of Relay Agent Options Using IPsec",
draft-ietf-dhc-relay-agent-ipsec-01.txt (work in progress),
November 2003.
[8] Littlefield, J., "Vendor-Identifying Vendor Options for DHCPv4",
draft-ietf-dhc-vendor-03.txt (work in progress), June 2004.
Authors' Addresses
Mark Stapp
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Phone: 978.936.0000
EMail: mjs@cisco.com
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Richard Johnson
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
Phone: 408.526.4000
EMail: raj@cisco.com
Theyn Palaniappan
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
Phone: 408.526.4000
EMail: athenmoz@cisco.com
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