DHC R. Droms
Internet-Draft Cisco Systems, Inc.
Expires: February 27, 2004 August 29, 2003
Authentication of DHCP Relay Agent Options Using IPsec
<draft-ietf-dhc-relay-agent-ipsec-00.txt>
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The DHCP Relay Agent Information Option (RFC 3046) conveys
information between a DHCP relay agent and a DHCP server. This
specification defines a mechanism for securing the messages
exchanged between a relay agent and a server using IPsec (RFC 2401).
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Table of Contents
1. Requirements Terminology . . . . . . . . . . . . . . . . . . . . 3
2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Use of IPsec to secure DHCP messages . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IPsec Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
Normative references . . . . . . . . . . . . . . . . . . . . . . 5
Informative References . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . 7
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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. DHCP Terminology
This document uses the terms "DHCP server" (or "server") and "DHCP
client" (or "client") as defined in RFC 2131. The term "DHCP relay
agent" refers to a "BOOTP relay agent" as defined in RFC 2131.
3. Introduction
DHCP (RFC 2131 [5]) provides IP addresses and configuration
information for DHCP clients. It includes a relay agent capability
(RFC 951 [6], RFC 1542 [7]), in which processes within the network
infrastructure receive broadcast messages from clients and forward
them to 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
[2]. The kind of information that a relay agent adds is often used in
the server's decision making about the addresses and configuration
parameters that the client should receive. The way that the relay
agent data is used in server decision-making tends to make that data
very important, and highlights the importance of the trust
relationship between the relay agent and the server.
The existing DHCP Authentication specification (RFC 3118) [8] only
secures communication between the DHCP client and server. Because
relay agent information is added after the client has signed its
message, the DHCP Authentication specification explictly excludes
relay agent data from that authentication.
The goals of this specification is to define a method that a relay
agent can use to:
1. protect the integrity of the data that the relay adds
2. provide replay protection for that data
3. leverage the existing IPsec mechanism
4. Use of IPsec to secure DHCP messages
Relay agents and servers that exchange messages securely can use
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IPsec mechanisms [3] as described in this section. If a client
message is relayed through multiple relay agents, each of the relay
agents must have established independent, pairwise trust
relationships. That is, if messages from client C will be relayed by
relay agent A to relay agent B and then to the server, relay agents A
and B must be configured to use IPSec for the messages they exchange,
and relay agent B and the server must be configured to use IPSec for
the messages they exchange.
Relay agents and servers that support secure relay agent to server or
relay agent to relay agent communication use IPsec under the
following conditions:
Selectors: Relay agents are manually configured with the
addresses of the relay agent or server to which DHCP messages are
to be forwarded. Each relay agent and server that will be using
IPsec for securing DHCP messages must also be configured with a
list of the relay agents to which messages will be returned. The
selectors for the relay agents and servers will be the pairs of
addresses defining relay agents and servers that exchange DHCP
messages on the DHCP UDP ports 67 and 68.
Mode: Relay agents and servers use transport mode and ESP [4]. The
information in DHCP messages is not generally considered
confidential, so encryption need not be used (i.e., NULL
encryption can be used).
Key management: Because the relay agents and servers are used within
an organization, public key schemes are not necessary. Because
the relay agents and servers must be manually configured, manually
configured key management may suffice, but does not provide
defense against replayed messages. Accordingly, IKE with
preshared secrets SHOULD be supported. IKE with public keys MAY be
supported.
Security policy: DHCP messages between relay agents and servers
should only be accepted from DHCP peers as identified in the local
configuration.
Authentication: Shared keys, indexed to the source IP address of the
received DHCP message, are adequate in this application.
Availability: Appropriate IPsec implementations are likely to be
available for servers and for relay agents in more featureful
devices used in enterprise and core ISP networks. IPsec is less
likely to be available for relay agents in low end devices
primarily used in the home or small office markets.
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5. IANA Considerations
There are no IANA considerations for the authentication mechanisms
described in this document.
6. Security Considerations
This specification describes a mechanism that can be used to provide
authentication and message integrity protection to the messages
between DHCP relay agents and DHCP servers.
The authentication sub-option protocol requires configuration of
relay agents and servers with shared secret keys.
7. IPsec Considerations
The use of IPsec for securing relay agent options in DHCP messages
requires the existence of an IPsec implementation available to the
relay agents and DHCP servers. It also requires manual configuration
of the participants, including manual distribution of keys.
8. Acknowledgments
The need for this specification was made clear by comments made by
Thomas Narten and John Schnizlein at IETF 53.
Normative references
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001.
[3] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[4] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
Informative References
[5] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[6] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
September 1985.
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[7] Wimer, W., "Clarifications and Extensions for the Bootstrap
Protocol", RFC 1542, October 1993.
[8] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001.
Author's Address
Ralph Droms
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Phone: +1 978.936.1674
EMail: rdroms@cisco.com
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