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Versions: 00 01 02 03 04 05 RFC 4030

DHC Working Group                                               M. Stapp
Internet-Draft                                       Cisco Systems, Inc.
Expires: April 23, 2004                                         T. Lemon
                                                           Nominum, Inc.
                                                        October 24, 2003


      The Authentication Suboption for the DHCP Relay Agent Option
                 <draft-ietf-dhc-auth-suboption-02.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 23, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   The DHCP Relay Agent Information Option (RFC 3046[1]) conveys
   information between a DHCP Relay Agent and a DHCP server. This
   specification defines a new authentication suboption for that option
   which supports source entity authentication and data integrity for
   relayed DHCP messages. The authentication suboption contains a
   cryptographic signature in a payload derived from the option used in
   DHCP Authentication (RFC 3118[9]).






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Table of Contents

   1.   Requirements Terminology . . . . . . . . . . . . . . . . . .   3
   2.   DHCP Terminology . . . . . . . . . . . . . . . . . . . . . .   3
   3.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.   Suboption Format . . . . . . . . . . . . . . . . . . . . . .   4
   5.   Replay Detection . . . . . . . . . . . . . . . . . . . . . .   5
   6.   The Relay Identifier Field . . . . . . . . . . . . . . . . .   5
   7.   Computing Authentication Information . . . . . . . . . . . .   6
   7.1  The HMAC-MD5 Algorithm . . . . . . . . . . . . . . . . . . .   6
   8.   Procedures for Sending Messages  . . . . . . . . . . . . . .   8
   8.1  Replay Detection . . . . . . . . . . . . . . . . . . . . . .   8
   8.2  Packet Preparation . . . . . . . . . . . . . . . . . . . . .   8
   8.3  Signature Computation  . . . . . . . . . . . . . . . . . . .   8
   8.4  Sending the Message  . . . . . . . . . . . . . . . . . . . .   8
   9.   Procedures for Processing Incoming Messages  . . . . . . . .   8
   9.1  Initial Examination  . . . . . . . . . . . . . . . . . . . .   8
   9.2  Replay Detection Check . . . . . . . . . . . . . . . . . . .   9
   9.3  Signature Check  . . . . . . . . . . . . . . . . . . . . . .   9
   10.  Relay Agent Behavior . . . . . . . . . . . . . . . . . . . .   9
   10.1 Receiving Messages from Other Relay Agents . . . . . . . . .  10
   10.2 Sending Messages to Servers  . . . . . . . . . . . . . . . .  10
   10.3 Receiving Messages from Servers  . . . . . . . . . . . . . .  10
   11.  DHCP Server Behavior . . . . . . . . . . . . . . . . . . . .  10
   11.1 Receiving Messages from Relay Agents . . . . . . . . . . . .  11
   11.2 Sending Reply Messages to Relay Agents . . . . . . . . . . .  11
   12.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  11
   13.  Security Considerations  . . . . . . . . . . . . . . . . . .  11
   13.1 Protocol Vulnerabilities . . . . . . . . . . . . . . . . . .  12
   14.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  12
        References . . . . . . . . . . . . . . . . . . . . . . . . .  12
        References . . . . . . . . . . . . . . . . . . . . . . . . .  12
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  13
        Full Copyright Statement . . . . . . . . . . . . . . . . . .  14

















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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[2].

2. DHCP Terminology

   This document uses the terms "DHCP server" (or "server") and "DHCP
   client" (or "client") as defined in (RFC 2131[6]. The term "DHCP
   relay agent" refers to a "BOOTP relay agent" as defined in RFC 2131.

3. Introduction

   DHCP (RFC 2131[6]) provides IP addresses and configuration
   information for IPv4 clients. It includes a relay-agent capability
   (RFC 951[7], RFC 1542[8]), 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[1]. The kind of information that relays add 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)[9] only
   covers 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 goal of this specification is to define methods 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 existing mechanisms such as DHCP Authentication

   In order to meet these goals, we specify a new relay-agent
   suboption, the Authentication suboption. The format of this
   suboption is very similar to the format of the DHCP Authentication
   option, and the specification of the cryptographic methods and
   signature computation for the suboption are also similar to that
   option's specification.

   The Authentication suboption is included by relay agents that wish


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   to ensure the integrity of the data they include in the Relay Agent
   option. These relay agents are configured with the parameters
   necessary to generate cryptographically strong signatures of the
   data in the DHCP messages which they forward to DHCP servers. A DHCP
   server configured to process the Authentication suboption uses the
   information in the suboption to validate the signature in the
   suboption, and continues processing the relay agent information
   option only if the signature is valid. If the DHCP server sends a
   response, it includes an Authentication suboption in its response
   message, signing the data in its message. Relay agents check the
   signatures in DHCP server responses and decide whether to forward
   the responses based on the signatures' validity.

4. Suboption Format


      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     |   Algorithm   |  MBZ  |  RDM  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Replay Detection (64 bits)                                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Replay Detection cont.                                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Relay Identifier                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                                                               |
      |                Authentication Information                     |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The code for the suboption is TBD. The length field includes the
   lengths of the algorithm, RDM, and all subsequent suboption fields
   in octets.

   The Algorithm field defines the algorithm used to generate the
   authentication information.

   Four bits are reserved for future use. These bits SHOULD be set to
   zero, and MUST be not be used when the suboption is processed.

   The Replay Detection Method (RDM) field defines the method used to
   generate the Replay Detection Data.

   The Replay Detection field contains a value used to detect replayed


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   messages, interpreted according to the RDM.

   The Relay Identifier field is used by relay agents that do not set
   giaddr, as described in RFC 3046[1], Section 2.1.

   The Authentication Information field contains the data required to
   communicate algorithm-specific parameters, as well as the signature.
   The signature is usually a digest of the data in the DHCP packet
   computed using the method specified by the Algorithm field.

5. Replay Detection

   The replay-detection mechanism is based on the notion that a
   receiver can determine whether or not a message has a valid replay
   token value. The default RDM, with value 1, specifies that the
   Replay Detection field contains an increasing counter value. The
   receiver associates a replay counter with each sender, and rejects
   any message containing an authentication suboption with a Replay
   Detection counter value less than or equal to the last valid value.
   DHCP servers MAY identify relay agents by giaddr value or by other
   data in the message (e.g. data in other relay agent suboptions).
   Relay agents identify DHCP servers by source IP address. If the
   message's replay detection value is valid, and the signature is also
   valid, the receiver updates its notion of the last valid replay
   counter value associated with the sender.

   All implementations MUST support the default RDM. Additional methods
   may be defined in the future, following the process described in
   Section 12.

   Receivers SHOULD perform the replay-detection check before
   validating the signature. The authentication hash calculation is
   likely to be much more expensive than the replay-detection value
   check.

      DISCUSSION:
      This places a burden on the receiver to maintain some run-time
      state (the most-recent valid counter value) for each sender, but
      the number of members in a DHCP agent-server system is unlikely
      to be unmanageably large.

6. The Relay Identifier Field

   The Relay Agent Information Option[1] specification permits a relay
   agent to add a relay agent option to relayed messages without
   setting the giaddr field. In this case, the eventual receiver of the
   message needs a stable identifier to use in order to associate
   per-sender state such as Key ID and replay-detection counters.



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   A relay agent that adds a relay agent information option and sets
   giaddr MUST NOT set the Relay ID field. A relay agent that does not
   set giaddr MAY be configured to place a value in the Relay ID field.
   If the relay agent is configured to use the Relay ID field, it MAY
   be configured with a value to use, or it MAY be configured to
   generate a value based on some other data, such its MAC or IP
   addresses. If a relay generates a Relay ID value it SHOULD select a
   value that it can regenerate reliably, e.g. across reboots.

   Servers that process an Authentication Suboption SHOULD use the
   giaddr value to identify the sender if the giaddr field is set.
   Servers MAY be configured to use some other data in the message to
   identify the signer. If giaddr is not set, the server SHOULD use the
   Relay ID field if it is non-zero. If neither the giaddr nor the
   Relay ID field is set, the server MAY be configured to use some
   other data in the message, or it MAY increment an error counter.

7. Computing Authentication Information

   The Authentication Information field contains a computed signature,
   generated by the sender. All algorithms are defined to process the
   data in the DHCP messages in the same way. The sender and receiver
   compute the signature across a buffer containing all of the bytes in
   the DHCP message, including the fixed DHCP message header, the DHCP
   options, and the relay agent suboptions, with the following
   exceptions. The value of the 'hops' field MUST be set to zero for
   the computation, because its value may be changed in transmission.
   The value of the 'giaddr' field MUST also be set to zero for the
   computation because it may be modified in networks where one relay
   agent adds the relay agent option but another relay agent sets
   'giaddr' (see RFC 3046, section 2.1). In addition, because the relay
   agent option itself is included in the computation, the 'signature'
   part of the 'authentication information' field in the Authentication
   suboption is set to all zeroes. The relay agent option length, the
   Authentication suboption length and other Authentication suboption
   fields are all included in the computation.

   All implementations MUST support Algorithm 1, the HMAC-MD5
   algorithm. Additional algorithms may be defined in the future,
   following the process described in Section 12.

7.1 The HMAC-MD5 Algorithm

   Algorithm 1 is assigned to the HMAC[3] protocol, using the MD5[4]
   hash function. This algorithm requires that a shared secret key be
   configured at the relay agent and the DHCP server. A 32-bit Key
   Identifier is associated with each shared key, and this identifier
   is carried in the first 4 bytes of the Authentication Information
   field of the Authentication suboption. The HMAC-MD5 computation


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   generates a 16-byte signature, which is placed in the Authentication
   Information field after the Key ID.

   The format of the Authentication suboption when Algorithm 1 is used
   is:


      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      |       34      |0 0 0 0 0 0 0 1|  MBZ  |  RDM  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Replay Detection (64 bits)                                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Replay Detection cont.                                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Relay Identifier                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Key ID (32 bits)                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                      HMAC-MD5 (128 bits)                      |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The suboption length is 34. The RDM and Replay Detection fields are
   as specified in Section 5. The Relay ID field is set as specified in
   Section 6. The Key ID is set by the sender to the ID of the key used
   in computing the signature, as an integer value in network
   byte-order. The HMAC signature follows the Key ID.

   The Key ID exists only to allow the sender and receiver to specify a
   shared secret in cases where more than one secret is in use among a
   network's relays and DHCP servers. The Key ID values are entirely a
   matter of local configuration; they only need to be locally unique.
   This specification does not define any semantics or impose any
   requirements on this algorithm's Key ID values.

      DISCUSSION:
      We specify a four-byte Key ID, following the example of the DHCP
      Authentication RFC. Other authentication protocols, like DNS
      TSIG[10], use a key name. A key name is more flexible and
      potentially more human-readable than a key id. DHCP servers may
      well be configured to use key names for DNS updates using TSIG,
      so it might simplify DHCP server configuration if some of the
      key-management for both protocols could be shared.
      On the other hand, it is crucial to minimize the size expansion


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      caused by the introduction of the relay agent information option.
      Named keys would require more physical space, and would entail
      more complex suboption encoding and parsing implementations.
      These considerations have led us to specify a fixed-length Key ID
      instead of a variable-length key name.

8. Procedures for Sending Messages

8.1 Replay Detection

   The sender obtains a replay-detection counter value to use, based on
   the RDM it is using. If the sender is using RDM 1, the default RDM,
   the value MUST be greater than any previously-sent value.

8.2 Packet Preparation

   The sender sets the 'giaddr' field and the 'hops' field to all
   zeroes. The sender appends the relay agent information option to the
   client's packet, including the Authentication suboption. The sender
   selects an appropriate Replay Detection value. The sender places its
   identifier into the Relay ID field, if necessary, or sets the field
   to all zeroes. The sender sets the suboption length, places the
   Replay Detection value into the Replay Detection field of the
   suboption, and sets the algorithm to the algorithm number that it is
   using. If the sender is using HMAC-MD5, it sets the Key ID field to
   the appropriate value. The sender sets the field which will contain
   the signature to all zeroes. Other algorithms may specify additional
   preparation steps.

8.3 Signature Computation

   The sender computes the signature across the entire DHCP message,
   using the algorithm it has selected. The sender places the result of
   the computation into the signature field of the Authentication
   suboption.

8.4 Sending the Message

   The sender restores the values of the 'hops' and 'giaddr' fields,
   and sends the message.

9. Procedures for Processing Incoming Messages

9.1 Initial Examination

   The receiver examines the message, the value of the giaddr field,
   and determines whether the packet includes the relay agent
   information option. The receiver uses its configuration to determine
   whether it should expect an Authentication suboption. The receiver


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   MUST support configuration that allows it to drop incoming messages
   that do not contain a valid relay agent information option and
   Authentication suboption.

   If the receiver determines that the Authentication suboption is
   present and that it should process the suboption, it uses the data
   in the message to determine which algorithm, key, and RDM to use in
   validating the message. If the receiver cannot determine which
   algorithm, key, and RDM to use, or if it does not support the value
   indicated in the message, it SHOULD drop the message. Because this
   situation could indicate a misconfiguration which could deny service
   to clients, receivers MAY attempt to notify their administrators or
   log an error message.

9.2 Replay Detection Check

   The receiver examines the RDM field.  Receivers MUST discard
   messages containing RDM values that they do not support. Because
   this may indicate a misconfiguration at the sender, an attempt
   SHOULD be made to indicate this condition to the administrator, by
   incrementing an error counter or writing a log message. If the
   receiver supports the RDM, it examines the value in the Replay
   Detection field using the procedures in the RDM and in Section 5. If
   the Replay value is not valid, the receiver MUST drop the message.

   Note that the receiver MUST NOT update its notion of the last valid
   Replay Detection value for the sender at this point. Until the
   signature has been checked, the Replay Detection field cannot be
   trusted. If the receiver trusts the Replay Detection value without
   checking the signature, a malicious host could send a replayed
   message with a Replay Detection value that was very high, tricking
   the receiver into rejecting legitimate values from the sender.

9.3 Signature Check

   The receiver prepares the packet in order to check the signature.
   The receiver sets the 'giaddr' and 'hops' fields to zero, and sets
   the signature field of the Authentication suboption to all zeroes.
   Using the algorithm and key associated with the sender, the receiver
   computes a hash of the message. The receiver compares the result of
   its computation with the value sent by the sender. If the signatures
   do not match, the receiver MUST drop the message. Otherwise, the
   receiver updates its notion of the last valid Replay Detection value
   associated with the sender, and processes the message.

10. Relay Agent Behavior

   DHCP Relay agents are typically configured with the addresses of one
   or more DHCP servers. A relay agent that implements this suboption


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   requires an algorithm number for each server, as well as appropriate
   credentials (i.e. keys) to use. Relay implementations SHOULD support
   configuration which indicates that all relayed messages should
   include the authentication suboption. Use of the authentication
   suboption SHOULD be disabled by default. Relay agents MAY support
   configuration that indicates that certain destination servers
   support the authentication suboption, while other servers do not.
   Relay agents MAY support configuration of a single algorithm number
   and key to be used with all DHCP servers, or they MAY support
   configuration of different algorithms and keys for each server.

10.1 Receiving Messages from Other Relay Agents

   There are network configurations in which one relay agent adds the
   relay agent option, and then forwards the DHCP message to another
   relay agent. For example, a layer-2 switch might be directly
   connected to a client, and it might forward messages to an
   aggregating router, which sets giaddr and then forwards the message
   to a DHCP server. When a DHCP relay which implements the
   Authentication suboption receives a message, it MAY use the
   procedures in Section 9 to verify the source of the message before
   forwarding it.

10.2 Sending Messages to Servers

   When the relay agent receives a broadcast packet from a client, it
   determines which DHCP servers (or other relay agents) should receive
   copies of the message. If the relay agent is configured to include
   the Authentication suboption, it determines which Algorithm and RDM
   to use, and then it performs the steps in Section 8.

10.3 Receiving Messages from Servers

   When the relay agent receives a message, it determines from its
   configuration whether it expects the message to contain a relay
   agent information option and an Authentication suboption. The relay
   agent MAY be configured to drop response messages that do not
   contain the Authentication suboption. The relay agent then follows
   the procedures in Section 9.

11. DHCP Server Behavior

   DHCP servers may interact with multiple relay agents. Server
   implementations MAY support configuration that associates the same
   algorithm and key with all relay agents. Servers MAY support
   configuration which specifies the algorithm and key to use with each
   relay agent individually.




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11.1 Receiving Messages from Relay Agents

   When a DHCP server which implements the Authentication suboption
   receives a message, it performs the steps in Section 9.

11.2 Sending Reply Messages to Relay Agents

   When the server has prepared a reply message, it uses the incoming
   request message and its configuration to determine whether it should
   include a relay agent information option and an Authentication
   suboption. If the server is configured to include the Authentication
   suboption, it determines which Algorithm and RDM to use, and then
   performs the steps in Section 8.

      DISCUSSION:
      This server behavior represents a slight variance from RFC
      3046[1], Section 2.2. The Authentication suboption is not echoed
      back from the server to the relay: the server generates its own
      suboption.

12. IANA Considerations

   Section 4 defines a new suboption for the DHCP relay agent option,
   called the Authentication Suboption. IANA is requested to allocate a
   new suboption code from the relay agent option suboption number
   space.

   This specification introduces two new number-spaces for the
   Authentication suboption's 'Algorithm' and 'Replay Detection Method'
   fields. These number spaces are to be created and maintained by IANA.

   The Algorithm identifier is a one-byte value. Algorithm value 0 is
   reserved. Algorithm value 1 is assigned to the HMAC-MD5 signature as
   defined in Section 7.1. Additional algorithm values will be
   allocated and assigned through IETF consensus, as defined in RFC
   2434[5].

   The RDM identifier is a four-bit value. RDM value 0 is reserved. RDM
   value 1 is assigned to the use of a monotonically increasing counter
   value as defined in Section 5. Additional RDM values will be
   allocated and assigned through IETF consensus, as defined in RFC
   2434[5].

13. Security Considerations

   This specification describes a protocol to add source authentication
   and message integrity protection to the messages between DHCP relay
   agents and DHCP servers.



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   The use of this protocol imposes a new computational burden on relay
   agents and servers, because they must perform cryptographic hash
   calculations when they send and receive messages. This burden may
   add latency to DHCP message exchanges. Because relay agents are
   involved when clients reboot, periods of very high reboot activity
   will result in the largest number of messages which have to be
   signed and verified. During a cable MSO head-end reboot event, for
   example, the time required for all clients to be served may increase.

13.1 Protocol Vulnerabilities

   Because DHCP is a UDP protocol, messages between relays and servers
   may be delivered in a different order than the order in which they
   were generated. The replay-detection mechanism will cause receivers
   to drop packets which are delivered 'late', leading to client
   retries. The retry mechanisms which most clients implement should
   not cause this to be an enormous issue, but it will cause senders to
   do computational work which will be wasted if their messages are
   re-ordered.

14. Acknowledgements

   The need for this specification was made clear by comments made by
   Thomas Narten and John Schnizlein, and the use of the DHCP
   Authentication option format was suggested by Josh Littlefield, at
   IETF 53.

Normative References

   [1]  Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
        January 2001.

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

   [3]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
        for Message Authentication", RFC 2104, February 1997.

   [4]  Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321, April
        1992.

   [5]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", RFC 2434, October 1998.

Informative References

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



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   [7]   Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
         September 1985.

   [8]   Wimer, W., "Clarifications and Extensions for the Bootstrap
         Protocol", RFC 1542, October 1993.

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

   [10]  Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
         "Secret Key Transaction Authentication for DNS (TSIG)", RFC
         2845, May 2000.


Authors' Addresses

   Mark Stapp
   Cisco Systems, Inc.
   1414 Massachusetts Ave.
   Boxborough, MA  01719
   USA

   Phone: 978.936.1535
   EMail: mjs@cisco.com


   Ted Lemon
   Nominum, Inc.
   950 Charter St.
   Redwood City, CA  94063
   USA

   EMail: mellon@nominum.com


















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Internet-Draft          Authentication Suboption            October 2003


Full Copyright Statement

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Acknowledgement

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