draft-ietf-dhc-v4-threat-analysis-02.txt   draft-ietf-dhc-v4-threat-analysis-03.txt 
Network Working Group R. Hibbs Network Working Group R. Hibbs
Internet-Draft Richard Barr Hibbs, P.E. INTERNET-DRAFT Richard Barr Hibbs, P.E.
Expires: October 29, 2004 C. Smith Category: Informational C. Smith
C & C Catering Expires: December 15, 2006 C & C Catering
B. Volz B. Volz
Cisco Systems, Inc. Cisco Systems, Inc.
M. Zohar M. Zohar
IBM T. J. Watson Research Center IBM T. J. Watson Research Center
April 30, 2004 June 13, 2006
Dynamic Host Configuration Protocol for IPv4 (DHCPv4) Threat Analysis Dynamic Host Configuration Protocol for IPv4 (DHCPv4)
draft-ietf-dhc-v4-threat-analysis-02 Threat Analysis
Status of this Memo <draft-ietf-dhc-v4-threat-analysis-03.txt>
Saved: Tuesday, June 13, 2006, 12:56:25
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RFC 3668. applicable patent or other IPR claims of which he or she is aware
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Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2006).
Abstract Abstract
DHCPv4 (RFC 2131) is a stable, widely used protocol for configuration DHCPv4 (RFC 2131) is a stable, widely used protocol for
of host systems in a TCP/IPv4 network. It did not provide for configuration of host systems in a TCP/IPv4 network. It did not
authentication of clients and servers, nor did it provide for data provide for authentication of clients and servers, nor did it
confidentiality. This is reflected in the original "Security provide for data confidentiality. This is reflected in the original
Considerations" section of RFC 2131, which identifies a few threats "Security Considerations" section of RFC 2131, which identifies a
and leaves development of any defenses against those threats to few threats and leaves development of any defenses against those
future work. Beginning in about 1995 DHCP security began to attract threats to future work. In about 1995, DHCP security began to
attention from the Internet community, eventually resulting in the attract attention from the Internet community, eventually resulting
publication of RFC 3118 in 2001. Although RFC 3118 was a mandatory in the publication of RFC 3118 in 2001. Although RFC 3118 was a
prerequisite for the DHCPv4 Reconfigure Extension, RFC 3203, it has mandatory prerequisite for the DHCPv4 Reconfigure Extension, RFC
had no known usage by any commercial or private implementation since 3203, it has had no known usage by any commercial or private
its adoption. The DHC Working Group has adopted a work item for 2003 implementation since its adoption. The DHC Working Group adopted a
to review and modify or replace RFC 3118 to afford a workable, easily work item for 2003 to review and modify or replace RFC 3118 to
deployed security mechanism for DHCPv4. This memo provides a afford a workable, easily deployed security mechanism for DHCPv4.
comprehensive threat analysis of the Dynamic Host Configuration This memo provides a threat analysis of the Dynamic Host
Protocol for use both as RFC 2131 advances from Draft Standard to Configuration Protocol for Ipv4 (DHCPv4) for use both as RFC 2131
Full Standard and to support our chartered work improving the advances from Draft Standard to Full Standard and to support our
acceptance and deployment of RFC 3118. chartered work improving the acceptance and deployment of RFC 3118.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1 Introduction................................................4
1.1 Issues for Consideration . . . . . . . . . . . . . . . . . 4 1.1 Issues for Consideration...............................4
1.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Exclusions.............................................4
1.3 Scope of this Memo . . . . . . . . . . . . . . . . . . . . 4 2 Use of Key Words............................................5
1.4 Use of Key Words . . . . . . . . . . . . . . . . . . . . . 5 3 Applicability...............................................5
2. General Threats to DHCPv4 . . . . . . . . . . . . . . . . . . 5 3.1 Assumptions............................................5
2.1 Denial-of-Service Attacks . . . . . . . . . . . . . . . . 5 3.2 Scope of this Memo.....................................5
2.1.1 Refusal to Configure Clients . . . . . . . . . . . . . 5 4 General threats to DHCPv4...................................5
2.1.2 Impersonating Clients . . . . . . . . . . . . . . . . 5 4.1 Denial-of-Service Attacks..............................5
2.1.3 Flooding . . . . . . . . . . . . . . . . . . . . . . . 6 4.1.1 Refusal to Configure Clients.....,...............5
2.2 Client Misconfiguration . . . . . . . . . . . . . . . . . 6 4.1.2 Impersonating Clients.............,..............5
2.3 Theft of Network Service . . . . . . . . . . . . . . . . . 6 4.1.3 Flooding...........................,.............6
2.4 Packet Insertion, Deletion, or Modification . . . . . . . 7 4.2 Client Misconfiguration................................6
3. Weaknesses of RFC 3118 . . . . . . . . . . . . . . . . . . . . 7 4.3 Theft of Network Service...............................6
3.1 Key Exposure . . . . . . . . . . . . . . . . . . . . . . . 7 4.4 Packet Insertion, Deletion, or Modification............7
3.2 Key Distribution . . . . . . . . . . . . . . . . . . . . . 7 5 Weaknesses of RFC 3118......................................7
3.3 Replay attacks . . . . . . . . . . . . . . . . . . . . . . 8 5.1 Key Exposure...........................................7
3.4 Protocol Agreement Difficulties . . . . . . . . . . . . . 8 5.2 Key Distribution.......................................7
4. DHCPv4 Security Requirements . . . . . . . . . . . . . . . . . 8 5.3 Replay attacks.........................................8
4.1 Environments . . . . . . . . . . . . . . . . . . . . . . . 8 5.4 Protocol Agreement Difficulties........................8
4.2 Capabilities . . . . . . . . . . . . . . . . . . . . . . . 8 5.5 DHCPv4 Relay Agents Excluded...........................8
4.3 Musings on the Key Distribution Problem . . . . . . . . . 9 5.6 Unanticipated Infrastructure Changes...................8
4.4 Data Confidentiality . . . . . . . . . . . . . . . . . . . 10 6 DHCPv4 Security Requirements................................9
4.4.1 "Public" Data in DHCP Packets . . . . . . . . . . . . 10 6.1 Environments...........................................9
4.4.2 Protecting Data in DHCP Options . . . . . . . . . . . 11 6.2 Capabilities..........................................10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6.3 Musings on the Key Distribution Problem...............10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6.4 Data Confidentiality..................................11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 6.4.1 "Public" Data in DHCP Packets...................12
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.4.2 Protecting Data in DHCP Options.................12
8.1 01 Draft . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.5 Host versus User Authentication.......................12
8.2 02 Draft . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.5.1 Why do we make this distinction?................13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.5.2 Is one mechanism sufficient?....................13
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 12 7 IANA Considerations........................................14
9.2 Informative References . . . . . . . . . . . . . . . . . . . 13 8 Security Considerations....................................14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14 9 Acknowledgements...........................................14
Intellectual Property and Copyright Statements . . . . . . . . 15 10 References................................................14
10.1 Normative References.................................14
1. Introduction 10.2 Informative References...............................15
1 Introduction
DHCPv4 as defined in RFC 1541 [RFC1541] and RFC 2131 [RFC2131] does DHCPv4 as defined in [RFC1541] and [RFC2131] does not provide any
not provide any form of communication security, confidentiality, data form of communication security, confidentiality, data integrity, or
integrity, or peer entity authentication. peer entity authentication.
A design team was formed at IETF-55 in Atlanta in November 2002 to A design team was formed at IETF-55 in Atlanta in November 2002 to
look at DHCPv4 and RFC 3118 [RFC3118] to document security look at DHCPv4 and [RFC3118] to document security requirements for
requirements for DHCPv4. RFC 3118 defines the current security DHCPv4. [RFC3118] defines the current security mechanisms for
mechanisms for DHCPv4. DHCPv4.
Unfortunately, RFC 3118 has neither been implemented nor deployed to Unfortunately, RFC 3118 has neither been implemented nor deployed to
date. There is widespread feeling that its current restriction to date. There is widespread feeling that its current restriction to
manual keying of clients limits its deployment. The DHC Working Group manual keying of clients limits its deployment. The DHC Working
seeks to rectify this situation by defining security mechanisms for Group seeks to rectify this situation by defining security
DHCPv4 that have better deployment properties. mechanisms for DHCPv4 that have better deployment properties.
1.1 Issues for Consideration 1.1 Issues for Consideration
Specific issues to be considered include: Specific issues to be considered include:
o Improved key management and scalability.
o Security for messages passed between relay agents and servers. O Improved key management and scalability.
o The increased usage of DHCPv4 on insecure (e.g., wireless) and
O Security for messages passed between relay agents and servers.
O The increased usage of DHCPv4 on insecure (e.g., wireless) and
public LANs. public LANs.
o The need for clients to be able to authenticate servers, without
O The need for clients to be able to authenticate servers, without
simultaneously requiring client authentication by the server. simultaneously requiring client authentication by the server.
1.2 Assumptions O Does use of the Relay Agent Information Option imply the need
for authenticated messages between DHCP servers and relay
agents?
This document assumes that the reader is familiar with both the base 1.2 Exclusions
DHCPv4 protocol as defined in RFC 2131 and the DHCPv4 authentication
extension as defined in RFC 3118, and does not attempt to provide a
tutorial on either.
1.3 Scope of this Memo Excluded from our analysis are:
This document confines its analysis to DHCPv4, as defined in RFC 2131 O Securing messages between relay agents and servers: work is
and RFC 2132 [RFC2132] and DHCP Authentication, as defined in RFC already underway on this, see [RFC4030] and [relay-ipsec].
3118.
Excluded from our analysis are: O DHCP Reconfigure Extension (FORCERENEW) [RFC3203]: the authors
o Securing messages between relay agents and servers: work is believe it is appropriate to put the onus to provide the
already underway on this, see [auth-subopt] and [relay-ipsec].
o DHCP Reconfigure Extension (FORCERENEW), RFC 3203 [RFC3203]: the
authors believe it is appropriate to put the onus to provide the
analysis on those who are interested in moving that work forward. analysis on those who are interested in moving that work forward.
o DHCP Failover Protocol, as defined in [failover]: the [Editor's note: despite repeated calls on the DHC Working Group
server-to-server protocol used differs significantly from DHCP. mailing list to identify even a single implementation of
FORCERENEW, we are unable to put forward an example of its use.]
o DHCP-DNS Interaction, as defined in [fqdn]: securing communication O DHCP Failover Protocol, as defined in [failover]: the server-
between DHCP servers and DNS servers is a DNS update security to-server protocol used differs significantly from DHCP, and
issue and therefore out of scope for the DHC working group. there has been no recent work on the [failover] draft.
o DHCPv6, as defined in RFC 3315 [RFC3315]: while we believe that
authentication techniques developed for DHCPv4 would generally be O DHCP-DNS Interaction, as defined in [fqdn]: securing
applicable to DHCPv6, there are fundamental differences between communication between DHCP servers and DNS servers is a DNS
the two protocols and RFC 3118 specifies DHCPv4-style message and update security issue and therefore out of scope for the DHC
options formats, so we have chosen to concentrate on DHCPv4. working group.
o DHCP Lease Query, as defined in [leasequery]: because of lack of
O DHCPv6, as defined in [RFC3315]: while we believe that
authentication techniques developed for DHCPv4 would generally
be applicable to DHCPv6, there are fundamental differences
between the two protocols and RFC 3118 specifies DHCPv4-style
message and options formats, so we have chosen to concentrate on
DHCPv4.
O DHCP Lease Query, as defined in [RFC4388]: because of lack of
maturity. maturity.
1.4 Use of Key Words 2 Use of Key Words
The key words "MUST," "MUST NOT," "REQUIRED," "SHALL," "SHALL NOT," The key words "MUST," "MUST NOT," "REQUIRED," "SHALL," "SHALL NOT,"
"SHOULD," "SHOULD NOT," "RECOMMENDED," "MAY," and "OPTIONAL" in this "SHOULD," "SHOULD NOT," "RECOMMENDED," "MAY," and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in [RFC2119].
2. General Threats to DHCPv4 3 Applicability
These are the classes of threats to the base DHCPv4 protocol. Not all 3.1 Assumptions
of these are DHCP-specific, nor can all the concerns listed be
This document assumes that the reader is familiar with both the base
DHCPv4 protocol as defined in [RFC2131] and the DHCPv4
authentication extension as defined in [RFC3118], and does not
attempt to provide a tutorial on either.
3.2 Scope of this Memo
This document confines its analysis to DHCPv4, as defined in
[RFC2131] and [RFC2132] and DHCP Authentication, as defined in
[RFC3118].
4 General threats to DHCPv4
These are the classes of threats to the base DHCPv4 protocol. Not
all of these are DHCP-specific, nor can all the concerns listed be
addressed by DHCP authentication. addressed by DHCP authentication.
2.1 Denial-of-Service Attacks 4.1 Denial-of-Service Attacks
2.1.1 Refusal to Configure Clients 4.1.1 Refusal to Configure Clients
A rogue DHCP server can refuse to configure clients by responding A rogue DHCP server can refuse to configure clients by responding
with either partial information (i.e., missing the IP address, yet with either partial information (i.e., missing the IP address, yet
containing other information) or a non-routable (or otherwise bad) IP containing other information), or a non-routable (or otherwise bad)
address. Or, the server may respond to DHCPDISCOVER messages (with IP address, or the server may respond to DHCPDISCOVER messages (with
DHCPOFFER messages) but then ignore the subsequent client DHCPREQUEST DHCPOFFER messages) but then ignore the subsequent client
messages. This may cause a client to repeatedly fail to be DHCPREQUEST messages. This may cause a client to repeatedly fail to
configured, though clients could take steps to ensure that they be configured, though clients could take steps to ensure that they
subsequently ignore such servers for a period of time. subsequently ignore such servers for some time.
2.1.2 Impersonating Clients 4.1.2 Impersonating Clients
A rogue client can impersonate a client or many clients, by using A rogue client can impersonate a client or many clients, by using
another client's client identifer (client identifier option) and/or another client's client identifier (client identifier option) and/or
hardware address (chaddr) or by generating these identifiers. This hardware address (chaddr) or by generating these identifiers. This
may be done to: may be done to:
o Obtain addresses when hardware address or client identifier
restrictions (lists) are configured into the site's server through
some mechanism not described in RFC 2131. Some sites may use such
a mechanism to restrict the clients that are allowed addresses. A
rogue client listens to DHCPv4 traffic and captures a few chaddrs
or client identifiers and starts using them.
o Simulate many clients to consume all available addresses. The O Obtain addresses when hardware address or client identifier
restrictions (lists) are configured into the site's server
through some mechanism not described in RFC 2131. Some sites
may use such a mechanism to restrict the clients that are
allowed addresses. A rogue client listens to DHCPv4 traffic and
captures a few chaddrs or client identifiers and starts using
them.
O Simulate many clients to consume all available addresses. The
rogue client may either hold on to these addresses (until the rogue client may either hold on to these addresses (until the
leases expire) or decline the addresses (by sending a DHCPDECLINE) leases expire) or decline the addresses (by sending a
in the hopes that the server will remove the declined address from DHCPDECLINE) in the hopes that the server will remove the
use for a longer period of time. declined address from use for a longer period.
o Create havoc on the subnet by injecting fake messages on behalf of
other clients that prematurely release (DHCPRELEASE) or decline
(DHCPDECLINE) their addresses. A rogue client listens to DHCPv4
traffic and gleans client identity and address information and
uses this information to inject fake messages.
2.1.3 Flooding O Create havoc on the subnet by injecting fake messages on behalf
of other clients, prematurely releasing (DHCPRELEASE) or
declining (DHCPDECLINE) their addresses. A rogue client listens
to DHCPv4 traffic and gleams client identity and address
information and uses this information to inject fake messages.
4.1.3 Flooding
A rogue client can flood the network with (near-) continuous DHCPv4 A rogue client can flood the network with (near-) continuous DHCPv4
request messages thereby consuming processing resources and network request messages thereby consuming processing resources and network
bandwidth. bandwidth.
We mention this attack only for completeness, as there is little or We mention this attack only for completeness, as there is little or
nothing that a DHCP server can do to prevent such an attack and the nothing that a DHCP server can do to prevent such an attack and the
client could just as well send messages of other protocols; and we client could just as well send messages of other protocols, so we
will not discuss it further. will not discuss it further.
2.2 Client Misconfiguration 4.2 Client Misconfiguration
Rogue servers may give out bad configuration information (such as Rogue servers may give out bad configuration information (such as
fake gateways or DNS servers), or relay agents or other network fake gateways or DNS servers), or relay agents or other network
elements may alter packets between a client and server, to cause the elements may alter packets between a client and server, to cause the
client to be misconfigured, or to enable future man-in-the-middle client to be misconfigured, or potentially worse cause future man-
attacks. This category is usually part of another attack, be it theft in-the-middle attacks. This category is usually part of another
of service, business espionage, or business interruption including attack, be it theft of service, business espionage, or business
denial of service. interruption including denial of service.
2.3 Theft of Network Service 4.3 Theft of Network Service
By "theft of network service" we mean the taking of an unused address By "theft of network service", we mean the taking of an unused
for network access or the use of an assigned address not belonging to address for network access or the use of an assigned address not
the client, in contrast with "client masquerading" (Section 2.1.2) belonging to the client, in contrast with "client masquerading"
which refers specifically to the use of a legitimate client's chaddr (Section 2.1.2) which refers specifically to the use of a legitimate
or client identifier. client's chaddr or client identifier.
Instantiation of an unauthorized client for purposes of using network Instantiation of an unauthorized client for purposes of using
resources or services is only partially preventable using network resources or services is only partially preventable using
client-server authentication techniques. We mention this attack only client-server authentication techniques. We mention this attack
for completeness, as there is little or nothing that a DHCP server, only for completeness, as there is little or nothing a DHCP server
itself, can do to prevent such an attack. Additional host and itself can do to prevent such an attack. Additional host and
application security is required to prevent theft of service, and application security is required to prevent theft of service, and
such layer 5 and higher functions are declared out of scope for this such layer 5 and higher functions are declared out of scope for this
analysis. analysis.
2.4 Packet Insertion, Deletion, or Modification 4.4 Packet Insertion, Deletion, or Modification
If a client (or server or relay agent) is known to crash or shut down If a client (or server or relay agent) is known to crash or shut
when invalid packets of some type are sent, this could be simply down when invalid packets of some type are sent, this could be
another type of denial of service attack. Likewise, simply deleting simply another type of denial of service attack. Likewise, simply
certain packet types (DHCPREQUEST to renew or rebind a lease) would deleting certain packet types (DHCPREQUEST to renew or rebind a
eventually result in client lease expiration, a denial of service lease) would eventually result in client lease expiration, a denial
attack. A rogue relay agent or other host would typically use packet of service attack. A rogue relay agent or other host would
insertion and deletion to interrupt service. In a different vein, the typically use packet insertion and deletion to interrupt service.
modification of packets in the DHCP exchange may be used to In a different vein, the modification of packets in the DHCP
facilitate many different types of attacks on either client or exchange may be used to facilitate many different types of attacks
server. For example, a DHCPACK could be modified to a DHCPNAK, on either client or server. For example, a DHCPACK could be
thereby denying the client a lease. modified to a DHCPNAK, thereby denying the client a lease.
3. Weaknesses of RFC 3118 5 Weaknesses of RFC 3118
An authentication mechanism for DHCPv4 protocol messages was An authentication mechanism for DHCPv4 protocol messages was
developed in RFC 3118, proposing two basic authentication mechanisms developed in RFC 3118, proposing two basic authentication mechanisms
and the means for extending the repertoire of methods as needed. The and the means for extending the repertoire of methods as needed.
configuration token method (protocol 0) relies on exchanging The configuration token method (protocol 0) relies on exchanging
clear-text authentication tokens between as yet unconfigured DHCPv4 clear-text authentication tokens between unconfigured DHCPv4 clients
clients and DHCPv4 servers. It is also vulnerable to message and DHCPv4 servers. It is also vulnerable to message interception.
interception. Delayed authentication (protocol 1) focuses on solving Delayed authentication (protocol 1) focuses on solving the
the intradomain authentication problem where the out-of-band exchange intradomain authentication problem where the out-of-band exchange of
of a shared secret is feasible. a shared secret is feasible.
3.1 Key Exposure 5.1 Key Exposure
The configuration token protocol, protocol 0, utilizes clear-text The configuration token protocol, protocol 0, utilizes clear-text
authentication tokens (i.e., passwords), providing only weak entity authentication tokens (i.e., passwords), providing only weak entity
authentication and no message authentication. This protocol is authentication and no message authentication. This protocol is
vulnerable to interception and provides only the most rudimentary vulnerable to interception and provides only the most rudimentary
protection against inadvertently instantiated DHCP servers. It also protection against inadvertently instantiated DHCP servers. It also
leaks the key before knowing whether the server supports protocol 0. leaks the key before knowing whether the server supports protocol 0.
3.2 Key Distribution 5.2 Key Distribution
Both protocols 0 and 1 suffer from the lack of a means to easily, Both protocols 0 and 1 suffer from the lack of a means to easily,
quickly, and reliably distribute authentication tokens used in the quickly, and reliably distribute authentication tokens used in the
protocols. In many environments, some existing key distribution protocols. In many environments, some existing key distribution
mechanism is presumed to be trusted and reliable, with strong mechanism is presumed to be trusted and reliable, with strong
administrative procedures and a security-conscious user population in administrative procedures and a security-conscious user population
place, leaving only the selection and specification of an appropriate in place, leaving only the selection and specification of an
cryptographic algorithm as a concern of the protocol designer. appropriate cryptographic algorithm as a concern of the protocol
designer.
Relying on such out-of-band methods to distribute and manage tens or Relying on such out-of-band methods to distribute and manage tens or
hundreds of thousands of tokens is a significant barrier to the hundreds of thousands of tokens is a significant barrier to the
widespread implementation of either protocol 0 or 1. widespread implementation of either protocol 0 or 1.
Key distribution presents a significant system management challenge Key distribution presents a significant system management challenge
that is in marked contrast with DHCP itself, a protocol that has been that is in marked contrast with DHCP itself, a protocol that has
successfully deployed in environments that make few demands or been successfully deployed in environments that make few demands or
assumptions. If we are to hope for similarly successful deployment of assumptions. If we are to hope for similarly successful deployment
authentication for DHCP, a means for mitigating (if not eliminating) of authentication for DHCP, a means for mitigating (if not
these difficulties must be offered. eliminating) these difficulties must be offered.
3.3 Replay attacks 5.3 Replay attacks
Since the configuration token protocol, protocol 0, passes a Since the configuration token protocol, protocol 0, passes a clear-
clear-text authentication token, the token would be visible to any text authentication token, the token would be visible to any host on
host on the same subnet. Delayed authentication, protocol 1, is not the same subnet. Delayed authentication, protocol 1, is not
susceptible to replay attacks since it contains a nonce value susceptible to replay attacks since it contains a nonce value
generated by the source and a message authentication code (MAC) which generated by the source and a message authentication code (MAC)
provides both message and entity authentication. which provides both message and entity authentication.
3.4 Protocol Agreement Difficulties 5.4 Protocol Agreement Difficulties
An a priori agreement is presumed to have taken place between client An a priori agreement is presumed to have taken place between client
and server on the authentication protocol to use. No mechanism is and server on the authentication protocol to use. No mechanism is
provided to allow for the discovery of supported protocols, nor is provided to allow for the discovery of supported protocols, nor is
there a facility for negotiation. The only way to express non-support there a facility for negotiation. The only way to express non-
of a protocol is by failing to respond. support of a protocol is by failing to respond.
4. DHCPv4 Security Requirements 5.5 DHCPv4 Relay Agents Excluded
[RFC3118] is defined exclusively for client-server communication.
The role of relay agents has expanded somewhat from their earliest
definition to include a DHCP option carrying relay agent information
via sub-options [RFC3046]. An authentication sub-option for the
relay agent information option has been defined by [RFC4030], though
it only defines a single protocol, symmetrical shared-secret keys,
to protect the contents of the messages between DHCP relay agents
and servers. Work-in-progress to protect the interaction between
relay agents and servers using IPSEC [relay-ipsec] seems to have
halted, with no recent work.
5.6 Unanticipated Infrastructure Changes
Rapid commit, defined by [RFC4039], specifies how a two-message
exchange between client and server can dramatically decrease the
elapsed time for address assignment, a feature becoming significant
as more and more highly mobile devices desire an abbreviated address
assignment phase for short duration communications.
While a two-message exchange by itself does not affect the overall
security of the communications, it has two side effects. First, the
delayed authentication protocol simply cannot be used as the
DHCPOFFER message required to return a nonce value to the client is
not present. Second, as noted by the authors of [RFC4039], without
authentication it is considerably more likely to consume addresses,
increasing the risk of one type of denial of service attack.
CableLabs client configuration [RFC3495] adds another two-tier
option to the DHCPv4 options list, defining an initial set of sub-
options for passing configuration information specific to CableLabs
VoIP and possible future services. Although several of the sub-
options contain potentially sensitive information regarding Kerberos
tickets to be used by cable modems and media terminal adapters. The
option specification does not require used of DHCP authentication,
although it would seem to be necessary. The authors of this memo do
not wish to go so far as to recommend that DHCP authentication be a
requirement for any or all DHCP options, but the CableLabs client
configuration option will likely not be the last option that could
benefit from a robust, workable authentication implementation.
Passive duplicate address detection [p-dad] is a relatively new
proposal to replace the use of ICMPECHO and ARP messages by DHCP
clients and servers to improve the duplicate address detection
process by passively listening to message traffic and developing a
table of matches between chaddr, DHCP client identifier, and IP
address that would be periodically transmitted to interested DHCP
servers. The presence of an entry for a particular IP address would
signify that it is known to be in use, so a DHCP server could
exclude the address from its pool of addresses available for
assignment.
The address usage collector (AUC) defined by [p-dad] does not use
the DHCP client-server protocol, nor does it function by actively
handling DHCP messages, so its implementation would not affect
authenticated DHCP messages. However, DHC Working Group discussion
of the [p-dad] draft raised the point that the AUC must capture the
client identifiers used in DHCP message exchanges. If DHCP
authentication were enabled, an AUC of necessity would be required
to have the same authentication configuration data (protocol,
algorithm, and key) as the clients and servers, certainly a
consideration for scalability and risk assessment.
6 DHCPv4 Security Requirements
DHCPv4 was developed in an era when computers were primarily used in DHCPv4 was developed in an era when computers were primarily used in
business and university environments. Security was either not a business and university environments. Security was either not a
concern or was addressed by controlling physical access stemming from concern or was addressed by controlling physical access stemming
the belief that intrusion into critical systems was most likely to from the belief that intrusion into critical systems was most likely
come from an external source. Now, with wireless access points and to come from an external source. Now, with wireless access points
ubiquitous networking, physical access control mechanisms are no and ubiquitous networking, physical access control mechanisms are no
longer sufficient, and security and privacy issues are a major longer sufficient, and security and privacy issues are a major
concern. concern.
4.1 Environments 6.1 Environments
The following environments can be expected for DHCPv4 The following environments can be expected for DHCPv4
implementations: implementations:
o Network size from a few hosts to hundreds of thousands of hosts.
o Network topology from a single subnet to Class-A networks.
o Network location from a single room to international dispersion.
o Wired, broadcast wireless, and directional wireless media.
o Movement between different media and networks.
4.2 Capabilities O Network size, from a few hosts to hundreds of thousands of hosts.
O Network topology, from a single subnet to Class-A networks.
O Network location, from a single room to international dispersion.
O Wired, broadcast wireless, and directional wireless media.
O Movement between different media and networks.
6.2 Capabilities
The following are essential elements of DHCPv4 security: The following are essential elements of DHCPv4 security:
o Clients MUST be able to authenticate servers (to prevent 1. Clients MUST be able to authenticate servers (to prevent
misconfigured clients and assure that the correct servers are misconfigured clients and assure that the correct servers are
being contacted). being contacted).
o Servers MUST be able to authenticate clients (use of hardware
addresses and client-IDs provides no real security but is all that 2. Servers MUST be able to authenticate clients (use of hardware
is easily possible today). Better mechanisms are needed for addresses and client-IDs provides no real security but is all
servers to identify clients to which they will offer service (to that is easily possible today). Better mechanisms are needed
prevent IP address pool depletion, for example). for servers to identify clients to whom they will offer service
o Administrators MUST be able to choose between four authentication (to prevent IP address pool depletion, for example).
paradigms:
* No authentication required. 3. Administrators MUST be able to choose between four
* Mutual authentication required. authentication paradigms:
* Client authenticates server.
* Server authenticates client. a. No authentication required.
o Integrity of DHCP packet exchanges MUST be assured.
b. Mutual authentication required.
c. Client authenticates server.
d. Server authenticates client.
4. Integrity of DHCP packet exchanges MUST be assured.
Not all capabilities may be needed or desired in all situations. Not all capabilities may be needed or desired in all situations.
4.3 Musings on the Key Distribution Problem 6.3 Musings on the Key Distribution Problem
The authors believe that only by addressing scalability issues with The authors believe that only by addressing scalability issues with
key distribution can RFC 3118 achieve wide deployment. While it is key distribution can RFC 3118 achieve wide deployment. While it is
not our intention to describe solutions in this document, we admit not our intention to describe solutions in this document, we admit
that we find the model used today by browsers and secure web servers that we find several models used today by browsers and secure web
attractive: trusted root certificates are distributed with the client servers as well as token-based user authentication schemes such as
implementation (web browser); users have the ability to extend the the RSA SecureID token to be attractive. Trusted root certificates
certificates that they will accept, install their own certificates are distributed with the client implementation (web browser); users
(should client identification be required), and choose which have the ability to extend the certificates that they will accept,
certificate to present to servers requesting the client's identity. install their own certificates (should client identification be
required), and choose which certificate to present to servers
requesting the client's identity. Security tokens that combine a
secure seed value with the current time of day using a cryptographic
algorithm to produce effectively a random one-time pad are
relatively inexpensive and widely available.
Analogously, DHCPv4 servers could make use of certificates just as Analogously, DHCPv4 servers could make use of certificates just as
web servers do, while DHCPv4 clients could be distributed with web servers do, while DHCPv4 clients could be distributed with
appropriate certificate authority certificates (trust anchors). appropriate certificate authority certificates (trust anchors).
Self-signed certificates are, of course, a possibility, should an Self-signed certificates are, of course, a possibility should an
organization wish full control over its domain of trust. organization wish full control over its domain of trust.
Should this path be pursued, we believe that certificate revocation Should this path be pursued, we believe that certificate revocation
will be a major problem to confront, just as it is in the browser/ will be a major problem to confront, just as it is in the
web server environment today. Revocation of client certificates browser/web server environment today. Revocation of client
(which we believe would occur, on the whole, much more frequently certificates (which we believe would occur, on the whole, much more
than revocation of server certificates), would require only ordinary frequently than revocation of server certificates) would require
care in certificate validation by the DHCP server. only ordinary care in certificate validation by the DHCP server.
Revocation of server certificates is more complex because of the Revocation of server certificates is more complex because of the
difficulty updating client configurations, as well as the inability difficulty updating client configurations, as well as the inability
of clients to rely on certificate revocation lists while in the of clients to rely on certificate revocation lists while in the
process of performing IP address and configuration management. process of performing IP address and configuration management.
4.4 Data Confidentiality Using a security token device today is mostly to identify a person
requesting access to a private resource. Key fobs, USB dongles, or
wallet cards are in the possession of a user, and in conjunction
with a user name, password, and possibly other information confirms
two of the three classic dimensions of provable identity (something
you know--user name and password, something you have--the security
token, and something you are--biometrics typically satisfy this
dimension.)
We envision a security token becoming part of the host system's
hardware complement in the near future, such that the token then
becomes not a user identity validator, but a host system validator.
It is common today to have a system service tag or serial number
that is machine-readable. Some hardware configurations include
processors with readable serial numbers as well. What we lack is a
secure means to generate a cryptographically random key that cannot
be easily defeated by software or component swapping.
Either of these approaches offers a simple way to avoid the classic
key distribution problem, though neither is totally without cost.
Somehow, somewhere, a token's identifiers (seed and algorithm) must
be recorded by the DHCP and other interested servers, or the
certificate infrastructure must be in place. We see no way to
eliminate administrative issues associated with security, but we can
see an end to passwords written on a sticky note.
An interesting Internet-Draft by Alper Yegin et al. [eap-auth]
proposed the use of EAP for DHCP authentication using the delayed
method. Their draft required modifications to several components of
an AAA solution, but illustrated how delayed authentication could be
"bootstrapped" using tools at our disposal.
That idea is also suggested by [RFC4014] Ralph Droms and John
Schnizlein, who define a DHCP option code for RADIUS information
provided by an NAS, similar to the mechanism in [eap-auth]. These
two documents taken together may provide a third solution to the key
distribution problem.
6.4 Data Confidentiality
Data Confidentiality was not provided for in the original DHCP Data Confidentiality was not provided for in the original DHCP
protocol as defined in RFC 2131 or any of the subsequent RFCs. protocol as defined in RFC 2131 or any of the subsequent RFCs.
Historically, DHCP was mainly used to assign IP addresses and return Historically, DHCP was mainly used to assign IP addresses and return
configuration options such as the local gateway and DNS information. configuration options such as the local gateway and DNS information.
Over time the DHCP protocol has evolved, deployments are extending Over time the DHCP protocol has evolved, deployments are extending
beyond physically secure intranets to public networks in hotspots, beyond physically secure intranets to public networks in hotspots,
cafes, airports, and at home over broadband. And we are seeing an cafes, airports, and at home over broadband. We are seeing an
accompanying proliferation of new configuration options. accompanying proliferation of new configuration options.
DHCP has, in fact, become so successful that it is now used to DHCP has, in fact, become so successful that it is now used to
transport a great deal of configuration data that could be obtained transport a great deal of configuration data that could be obtained
in a variety of other ways. It is certainly possible that a client or in a variety of other ways. It is certainly possible that a client
server might wish to reveal some of these data only to a or server will wish to reveal some of these data only to a properly
properly-authenticated peer. authenticated peer.
4.4.1 "Public" Data in DHCP Packets 6.4.1 "Public" Data in DHCP Packets
We assume that any information that may be gleaned directly from the We assume that any information that may be gleaned directly from the
network using, for example, Ethernet promiscuous mode is not network using, for example, Ethernet promiscuous mode is not
confidential. It could be argued that over time more and more confidential. It could be argued that over time more and more
communication will be switched, encrypted, or secured at the physical communication will be switched, encrypted, or secured at the
layer, so that less information could easily be gleaned from the physical layer, so that less information could easily be gleaned
network traffic. from the network traffic.
Taking encryption into consideration, the IP packet payload might be Taking encryption into consideration, the IP packet payload might be
encrypted, but not the IP header itself since it is required for encrypted, but not the IP header itself since it is required for
packet routing. As a result none of the IP header fields are packet routing. As a result, none of the IP header fields are
confidential. IP addresses included in the header are therefore not confidential. IP addresses included in the header are therefore not
confidential. Similarly, the hardware addresses are also not confidential. Similarly, the hardware addresses are also not
confidential. confidential.
Although the IP packet payload (which would include the UDP or TCP Although the IP packet payload (which would include the UDP or TCP
header) might normally be encrypted, some protocols have made header) might normally be encrypted, some protocols have made
explicit decisions not to encrypt their exchanges, declaring their explicit decisions not to encrypt their exchanges, declaring their
data public. DNS is such a protocol [dns-threats]. Thus we may also data public. DNS is such a protocol [dns-threats]. Thus, we may
treat DNS domain and server information as public. also treat DNS domain and server information as public.
Commonly-used routing protocols such as BGP (RFC 1771) [RFC1771], RIP
(RFC 1721) [RFC1721], and router discovery (RFC 1256) [RFC1256] also
normally send advertisements in the clear and we therefore extend our
definition of public DHCP data to include routing information
options.
4.4.2 Protecting Data in DHCP Options Commonly used routing protocols such as BGP [RFC1771], RIP [RFC1721],
and router discovery [RFC1256] also normally send advertisements in
the clear and we therefore extend our treatment of public DHCP data
to routing information.
Some DHCP options (e.g., relay agent options, RFC 3046 [RFC3046]) or 6.4.2 Protecting Data in DHCP Options
option families (site or vendor options) admit no analysis because
the data carried by them may be of unknown sensitivity. Analysis of
their confidentiality requirements must be done by their users.
Other DHCPv4 options contain opaque data, not subject to Some DHCP options (e.g., relay agent options, [RFC3046]) or option
interpretation by a DHCPv4 server. With no RFC-based definition of families (site or vendor options) admit no analysis because the data
the data content of these options, we can offer no opinion of the carried by them may be of unknown sensitivity. Users must do their
sensitivity of the data, and leave any confidentiality treatment to own analysis of confidentiality.
other work.
Should some data require confidentiality, it may be possible to Should some data require confidentiality, it may be possible to
exploit the "public" data above to allow a two-step configuration exploit the "public" data above to allow a two-step configuration
process in which sufficient client configuration is first obtained by process in which sufficient client configuration is first obtained
the normal DHCPDISCOVER/OFFER/REQUEST/ACK exchange, and private data by the normal DHCPDISCOVER/OFFER/REQUEST/ACK exchange, and private
subsequently transmitted over a secure communications channel (such data subsequently transmitted over a secure communications channel
as IPsec) using DHCPINFORM. (such as IPsec) using DHCPINFORM.
5. IANA Considerations 6.5 Host versus User Authentication
None known. [RFC3118] is concerned specifically with DHCP clients and servers
authenticating themselves to each other if required by an
administrative domain. This is not the same thing as authenticating
users for establishing their Identity, access rights, permissions,
or other matters relating to what they can view or do once connected
to the network.
6. Security Considerations 6.5.1 Why do we make this distinction?
This entire memo presents a threat analysis of the DHCPv4 protocol. Host authentication provides only assurance that the hosts
connecting to a network are recognized. This may be for several
reasons, including:
7. Acknowledgements O Requirement to restrict network access from "foreign" hosts to
ensure consistent technical support or meet other regulatory
requirements such as double-insulation or non-sparking.
This document is the result of work undertaken the by DHCP working O Requirement to restrict network access from "unsecured" (for
group, beginning at 55th IETF meeting in Atlanta. The authors would instance, non-TEMPEST compliant) hosts in a high security
also like to acknowledge contributions from others not directly network.
involved in writing this memo, including John Beatty and Vipul Gupta
of Sun Microsystems, and Ralph Droms of Cisco Systems. And Bernard
Aboba and Mark Stapp for their careful reviews and suggestions.
8. Change Log O Requirement to restrict network access from unknown hosts whose
identity has not been recorded by existing administrative
procedures, saving troubleshooting and administrative effort.
This section summaries the changes made to this Internet-Draft as it User authentication focuses on the individual users of a host system,
has evolved. seeking to uniquely identify someone to establish their rights to
view, print, add, alter, delete, edit, modify, copy, or manipulate
any data maintained by an organization, run software programs, or
affect changes in the environment. This may be for such reasons as:
8.1 01 Draft O Requirement to be compliant with regulations such as HIPAA, SOX,
and GLBA designed to safeguard and protect confidentiality and
various reporting requirements.
No significant changes were made: O Requirement to maintain reasonable controls over access to
o Updated author information. certain critical systems such as utility power grids, water and
o Converted to using xml2rfc to generate the draft. sewage treatment plants, the network infrastructure itself, and
life safety systems of all sorts.
o Removed unused references. O Requirement to maintain administrative controls over certain
o Added the Change Log section. sensitive information such as trade secrets and personnel data
8.2 02 Draft 6.5.2 Is one mechanism sufficient?
The following changes were made: Full discussion of this question is beyond the scope of this memo,
o Updated author information. but the simple answer is, "probably not." This has a significant
o Added text to 1.3 to exclude security for messages passed between implication for the claims of certain techniques such as
relay agents and servers as there are two Internet-Drafts on this "sandboxing" of unverified users, restricting their network access
subject. to a user registration web site until their identity has been
o Reworded several sections, particularily in section 2. established. Simply put, limiting network access is not DHCP
o Revised and renamed section 2.1.2; now includes more attacks. authentication, although it does represent a very workable approach
o Revised section 2.1.3. to user authentication in many cases.
o Minor revisions to section 3, 3.2, and 3.2.
o Added more to section 4.4.2.
o Other minor insertions, deletions, and modifications based on
comments from Bernard Aboba and Mark Stapp and to otherwise
improve the document.
9. References Recall that a user can be identified by "something they know,"
"something they have," and "something they are." While the same
could be said to be true of host systems, the authors point out that
while we do not pretend to understand all of the ways that future
developers might imbue hosts with the tools to independently create
attacks on our infrastructure, we will assert that users will be the
greatest risk for some time still.
9.1 Normative References DHCP Authentication addresses only host authentication from the
belief that other, existing mechanisms such as IPSEC, SSL, and VPN
can protect the content of communications, with Identity Management
and other technologies can protect applications and data.
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256, A properly authenticated host could still launch a denial of service
attack, corrupt sensitive data, or wreak other havoc, which
underscores our point that host and user authentication are
different.
A well-secured network needs both.
7 IANA Considerations
None known.
8 Security Considerations
This entire memo presents a threat analysis of the DHCPv4 protocol.
9 Acknowledgements
This document is the result of work undertaken the by DHCP working
group, beginning at the 55th IETF meeting in Atlanta. The authors
would also like to acknowledge contributions from others not
directly involved in writing this memo, including John Beatty and
Vipul Gupta of Sun Microsystems, Ralph Droms of Cisco Systems,
Bernard Aboba of Microsoft, and Mark Stapp of Cisco Systems for
their careful reviews and helpful suggestions.
10 References
10.1 Normative References
[RFC1256] Deering, S., "ICMP Router Discovery Messages," RFC 1256,
September 1991. September 1991.
[RFC1541] Droms, R., "Dynamic Host Configuration Protocol", RFC [RFC1541] Droms, R., "Dynamic Host Configuration Protocol," RFC 1541,
1541, October 1993. October 1993.
[RFC1721] Malkin, G., "RIP Version 2 Protocol Analysis", RFC 1721, [RFC1721] Malkin, G., "RIP Version 2 Protocol Analysis," RFC 1721,
November 1994. November 1994.
[RFC1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 [RFC1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-
(BGP-4)", RFC 1771, March 1995. 4)," RFC 1771, March 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC [RFC2131] Droms, R., "Dynamic Host Configuration Protocol," RFC 2131,
2131, March 1997. March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. Extensions", RFC 2132, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC [RFC3046] Patrick, M., "DHCP Relay Agent Information Option," RFC
3046, January 2001. 3046, January 2001.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001. Messages," RFC 3118, June 2001.
9.2 Informative References [RFC4014] Droms, R. and J. Schnizlein, " Remote Authentication Dial-
In User Service (RADIUS) Attributes Suboption for the Dynamic
Host Configuration Protocol (DHCP) Relay Agent Information
Option," RFC 4014, February 2005.
[RFC3203] T'Joens, Y., Hublet, C. and P. De Schrijver, "DHCP 10.2 Informative References
reconfigure extension", RFC 3203, December 2001.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3," RFC 2026, BCP 9, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3203] T'Joens, Y., C. Hublet and P. De Schrijver, "DHCP
Reconfigure Extension," RFC 3203, December 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
M. Carney, "Dynamic Host Configuration Protocol for IPv6 M. Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003. (DHCPv6)," RFC 3315, July 2003.
[auth-subopt] [RFC3495] Beser, B. and P. Duffy, "Dynamic Host Configuration
Stapp, M. and T. Lemon, "The Authentication Suboption for Protocol (DHCP) Option for CableLabs Client Configuration," RFC
the DHCP Relay Agent Option", 3495, March 2003.
draft-ietf-dhc-auth-suboption-03 (work in progress),
February 2004.
[dns-threats] [RFC3594] Duffy, P., PacketCable Security Ticket Control Sub-Option
Atkins, D. and R. Austein, "Threat Analysis Of The Domain for the DHCP CableLabs Client Configuration (CCC) Option"," RFC
Name System", draft-ietf-dnsext-dns-threats-06 (work in 3594, September 2003.
progress), February 2004.
[failover] [RFC3978] Bradner, S., "IETF Rights in Contributions," RFC 3978, BCP
Droms, R. and K. Kinnear, "DHCP Failover Protocol", 78, March 2005.
draft-ietf-dhc-failover-12 (work in progress), December
2003.
[fqdn] Stapp, M. and Y. Rekhter, "The DHCP Client FQDN Option", [RFC3979] Bradner, S., "Intellectual Property Rights in IETF
draft-ietf-dhc-fqdn-option-06 (work in progress), October Technology," RFC 3979, BCP 79, March 2005.
2003.
[leasequery] [RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for
Woundy, R., "DHCP Lease Query", the DHCP Relay Agent Option," draft-ietf-dhc-auth-suboption-03),
draft-ietf-dhc-leasequery-07 (work in progress), March RFC 4030, March 2005.
2004.
[relay-ipsec] [RFC4039] Park, S., P. Kim and B. Volz, "Rapid Commit Option for the
Droms, R., "Authentication of DHCP Relay Agent Options Dynamic Host Configuration Protocol version 4 (DHCPv4)," RFC
Using IPsec", draft-ietf-dhc-relay-agent-ipsec-01 (work in 4039, March 2005.
progress), November 2003.
[RFC4388] Woundy, R., and Kinnear, K., "Dynamic Host Configuration
Protocol (DHCP) Leasequery," February 2006.
[dns-threats] Atkins, D. and R. Austein, "Threat Analysis Of The
Domain Name System," draft-ietf-dnsext-dns-threats-07 (work in
progress), April 2004.
[draft2223bis] Reynolds, J. and R. Braden, "Instructions to Request
for Comments (RFC) Authors," draft-rfc-editor-rfc2223bis-08.txt
(work in progress), August 2004.
[eap-auth] Yegin, A., H. Tschofenig and D. Forsberg, "Bootstrapping
RFC3118 Delayed DHCP Authentication Using EAP-based Network
Access Authentication," draft-yegin-eap-boot-rfc3118-02, (work
in progress), March 2006.
[failover] Droms, R. and K. Kinnear, "DHCP Failover Protocol,"
draft-ietf-dhc-failover-12 (work in progress), December 2003.
[Editor's note: at the time of publication of this memo, the
Failover Internet-Draft has expired.]
[fqdn] Stapp, M., Volz, B., and Y. Rekhter, "The DHCP Client FQDN
Option," draft-ietf-dhc-fqdn-option-13 (work in progress), March
2006.
[p-dad] Forte, A., S. Shin and H. Schulzrinne, "Passive Duplicate
Address Detection for Dynamic Host Configuration Protocol
(DHCP)," draft-forte-dhc-passive-dad-02 (work-in-progress), June
2006.
[relay-ipsec] Droms, R., "Authentication of DHCP Relay Agent Options
Using Ipsec," draft-ietf-dhc-relay-agent-ipsec-02 (work in
progress), May 2005. [Editor's note: at the time of
publication of this memo, the Relay IPSEC Internet-Draft has
expired.]
Authors' Addresses Authors' Addresses
Richard Barr Hibbs Richard Barr Hibbs
Richard Barr Hibbs, P.E. Richard Barr Hibbs, P.E.
952 Sanchez Street 952 Sanchez Street
San Francisco, California 94114-3362 San Francisco, California 94114-3362
USA USA
Phone: +1 415 648 3920 Phone: +1 415 648 3920
Fax: +1 415 648 9017 Fax: +1 415 648 9017
EMail: rbhibbs@pacbell.net E-Mail: rbhibbs@pacbell.net
Carl Smith Carl Smith
C & C Catering C & C Catering
1121 Holly St 1121 Holly Street
Alameda, California 94502 Alameda, California 94502
USA USA
EMail: islandia@alumni.ucsd.edu E-Mail: islandia@alumni.ucsd.edu
Bernard Volz Bernard Volz
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Avenue
Boxborough, MA 01719 Boxborough, Massachusetts 01719
USA USA
Phone: +1 978 936 0382 Phone: +1 978 936 0382
EMail: volz@cisco.com E-Mail: volz@cisco.com
Mimi Zohar Mimi Zohar
IBM T. J. Watson Research Center IBM T. J. Watson Research Center
19 Skyline Drive 19 Skyline Drive
Hawthorne, New York 10532-2134 Hawthorne, New York 10532-2134
USA USA
Phone: +1 914 784 7606 Phone: +1 914 784 7606
EMail: zohar@us.ibm.com E-Mail: zohar@us.ibm.com
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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.
Copyright Statement APPENDIX: NOTES
Copyright (C) The Internet Society (2004). This document is subject This appendix will be removed in its entirety before the memo goes
to the rights, licenses and restrictions contained in BCP 78, and to Working Group Last Call.
except as set forth therein, the authors retain all their rights.
Acknowledgment ISSUES LIST
Funding for the RFC Editor function is currently provided by the This section summarizes issues raised in this memo that require
Internet Society. resolution by the DHC Working Group.
1. Because of the specific exception for inclusion of the Relay
Agent Information Option [RFC3046] in cases where it does not
fit in the main payload portion of a DHCP response packet,
should the use of DHCP Authentication be mandated in place of
the Relay Agent Authentication suboption?
2. Does the CableLabs Client Configuration option [RFC3495] require
the use of DHCP Authentication to protect sensitive information
about Kerberos domains and keys?
3. Should the DHC Working Group promote the development of a new
authentication protocol based on the use of certificates?
4. Should the DHC Working Group solicit an update from the authors
of the EAP-based authentication protocol [eap-auth] and develop
it as a new authentication protocol?
5. Should the DHC Working Group promote the development of a new
authentication protocol based on hardware security tokens?
CHANGE LOG
This section summarizes the changes made to this memo as it has
evolved.
"-01" Draft
No significant changes were made from initial ("-0") version:
O Updated author information.
O Removed unused references.
O Added the Change Log section.
"-02" Draft
The following changes were made:
O Updated author information.
O Added text to 1.3 to exclude security for messages passed
between relay agents and servers, as there are two Internet-
Drafts on this subject.
O Reworded several sections in section 2.
O Revised and renamed section 2.1.2. Now includes more attacks.
O Revised section 2.1.3.
O Minor revisions to section 3, 3.2, and 3.2.
O Other minor insertions, deletions, and modifications based on
comments from Bernard Aboba and Mark Stapp and to otherwise
improve the document.
"-03" Draft
The draft was updated, correcting minor spelling, grammatical, and
typographical errors, and modified in the following ways:
O Removed Section 8, "Change Log," to APPENDIX and added an issues
list section.
O Replaced all Internet-Draft boilerplate with the most current
versions.
O Renumbered document sections.
O Updated author information.
O Updated references for I-Ds advanced to RFCs.
O Added normative and informative references.
O Added discussion of Relay Agents (section 3.5.)
O Added section 3.6, discussing the side effects of infrastruture
changes from the Rapid Commit and CableLabs configuration
options, and the newly proposed Address Usage Collector (AUC)
for passive duplicate address detection.
O Expanded section 4.3, "Musings on the Key Distribution Problem"
to include description of hardware-based key generation tokens.
O Added section 4.5, "Host versus User Authentication," to help
clarify the problem [RFC3118] is intended to address.
O Added discussion of the RADIUS-based authentication proposal
described in [RFC4014].
O Added discussion of the EAP-based authentication protocol
proposed by A. Yegin et al.
O Inserted Intellectual Property Rights statement on first page.
O Performed general spelling, grammar, and typography update of
entire memo text.
O Reviewed all drafts used as references, updated as necessary.
 End of changes. 126 change blocks. 
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