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Versions: 00 01 02 03 04 05 06 RFC 4137

EAP Working Group                                          J. Vollbrecht
Internet-Draft                                 Vollbrecht Consulting LLC
Expires: August 16, 2004                                       P. Eronen
                                                                   Nokia
                                                              N. Petroni
                                                  University of Maryland
                                                                 Y. Ohba
                                                                    TAIS
                                                       February 16, 2004


             State Machines for EAP Peer and Authenticator
                     draft-ietf-eap-statemachine-02

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 other
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at 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 August 16, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   This document describes a set of state machines for EAP Peer, EAP
   Standalone Authenticator (non-pass-through), EAP Backend
   Authenticator (for use on AAA servers), and EAP Full Authenticator
   (for both local and pass-through). This set of state machines shows
   how EAP can be implemented to support deployment in either a Peer/AP
   or Peer/AP/AAA Server environment. The Peer and Standalone
   Authenticator machines are illustrative of how the EAP protocol



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   defined in [I-D.ietf-eap-rfc2284bis]  may be implemented.  The
   Backend and Full/Pass-Through Authenticators illustrate how EAP/
   RADIUS protocol support defined in [RFC3579] may be implemented.
   Where there are differences [I-D.ietf-eap-rfc2284bis]/[RFC3579] are
   authoritative.

   This document describes a state machine based on an EAP "Switch"
   model. This model includes  events and actions for the interaction
   between the EAP Switch and EAP methods. The State Machine and
   associated model are informative only. Implementations may achieve
   the same results using different methods.

   A brief description of the EAP "Switch" model is given in the
   Introduction section.

   The authors believe this document corresponds to the current state of
   revisions to the defining [I-D/ietf-eap-rfc2284bis]/[RFC3579]
   documents. The intent is for this document to synchronize with the
   defining documents when they are released, and if discrepancies are
   found the defining documents are authoritative.































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Table of Contents

   1.  Specification of Requirements  . . . . . . . . . . . . . . . .  4
   2.  The EAP Switch Model . . . . . . . . . . . . . . . . . . . . .  4
   3.  Notational conventions used in state diagrams  . . . . . . . .  5
   3.1 Notational specifics . . . . . . . . . . . . . . . . . . . . .  5
   3.2 State Machine Symbols  . . . . . . . . . . . . . . . . . . . .  8
   3.3 Document authority . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Peer State Machine . . . . . . . . . . . . . . . . . . . . . . 10
   4.1 Interface between peer state machine and lower layer . . . . . 10
   4.2 Interface between peer state machine and methods . . . . . . . 12
   4.3 Peer state machine local variables . . . . . . . . . . . . . . 13
   4.4 Peer state machine procedures  . . . . . . . . . . . . . . . . 15
   4.5 Peer state machine states  . . . . . . . . . . . . . . . . . . 15
   5.  Standalone Authenticator State Machine . . . . . . . . . . . . 17
   5.1 Interface between standalone authenticator state machine
       and lower layer  . . . . . . . . . . . . . . . . . . . . . . . 17
   5.2 Interface between standalone authenticator state machine
       and methods  . . . . . . . . . . . . . . . . . . . . . . . . . 19
   5.3 Standalone authenticator state machine local variables . . . . 20
   5.4 EAP standalone authenticator procedures  . . . . . . . . . . . 22
   5.5 EAP standalone authenticator states  . . . . . . . . . . . . . 23
   6.  EAP Backend Authenticator  . . . . . . . . . . . . . . . . . . 25
   6.1 Interface between backend authenticator state machine and
       lower layer  . . . . . . . . . . . . . . . . . . . . . . . . . 25
   6.2 Interface between backend authenticator state machine and
       methods  . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
   6.3 Backend authenticator state machine local variables  . . . . . 28
   6.4 EAP backend authenticator procedures . . . . . . . . . . . . . 28
   6.5 EAP backend authenticator states . . . . . . . . . . . . . . . 28
   7.  EAP Full Authenticator . . . . . . . . . . . . . . . . . . . . 28
   7.1 Interface between full authenticator state machine and
       lower layers . . . . . . . . . . . . . . . . . . . . . . . . . 29
   7.2 Interface between full authenticator state machine and
       methods  . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
   7.3 Full authenticator state machine local variables . . . . . . . 31
   7.4 EAP full authenticator procedures  . . . . . . . . . . . . . . 31
   7.5 EAP full authenticator states  . . . . . . . . . . . . . . . . 31
   8.  Implementation Considerations  . . . . . . . . . . . . . . . . 33
   8.1 Robustness . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   8.2 Method/Method and Method/Lower-Layer Interfaces  . . . . . . . 34
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 34
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 34
       Normative References . . . . . . . . . . . . . . . . . . . . . 34
       Informative References . . . . . . . . . . . . . . . . . . . . 35
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 35
       Intellectual Property and Copyright Statements . . . . . . . . 37




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1. Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  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 [RFC2119].

2. The EAP Switch Model

   This document offers a proposed state machine for RFCs
   [I-D.ietf-eap-rfc2284bis] and [RFC3579]  . There are state machines
   for the peer, the standalone authenticator, a backend authenticator
   and a full/pass-through authenticator.  Accompanying each state
   machine diagram is a description of the variables, the functions and
   the states in the diagram. Whenever possible, the same notation has
   been used in each of the state machines.

   An EAP authentication consists of one or more EAP methods in sequence
   followed by an EAP Success or EAP Failure sent from the Authenticator
   to the peer.  The EAP Switches control negotiation of EAP methods and
   sequences of methods.

         Peer             Peer  |  Authenticator       Auth
         Method                 |                      Method
                \               |                   /
                  \             |                 /
                   Peer         |             Auth
                   EAP    <-----|---------->  EAP
                   Switch       |             Switch

                       Figure 1: EAP Switch Model

   At both the peer and authenticator one or more EAP methods exist.
   The EAP switches select which methods each is willing to use, and
   negotiate between themselves to pick a method or sequence of methods.

   Note that the methods may also have state machines. The details of
   these are out of scope for this paper.












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                 Peer  |  Authenticator              | Backend
                       |               /  Local      |
                       |             /    Method     |
                 Peer  |        Auth                 |        Backend
                 EAP --|----->  EAP                  |      -> EAP
                Switch |       Switch                |   /    Server
                       |             \               |/
                       |               \ pass-through|
                       |                             |


                    Figure 2: EAP Pass-Through Model

   The Full/Pass-Through state machine allows a NAS or Edge Device to
   pass EAP Response messages to a Backend Server where the
   Authentication Method resides.  This paper includes a state machine
   for the EAP authenticator that supports both local and pass-through
   methods as well as a state machine for the backend authenticator
   existing at the AAA server. A simple "Standalone" authenticator is
   also provided to show a basic, non-pass-through authenticator's
   behavior.

   This document describes a set of State Machines that can manage EAP
   authentication from the peer to an EAP method on the Authenticator or
   from the Peer through the Authenticator pass-through method to the
   EAP method on the Backend EAP server.

   Some environments where EAP is used, such as PPP, may support
   peer-to-peer operation. That is, both parties act as peers and
   authenticators at the same time, in two simultaneous and independent
   EAP conversations. In this case, the implementation at each node has
   to perform demultiplexing of incoming EAP packets. EAP packets with
   Code set to Response are delivered to the Authenticator state
   machine, and all other EAP packets are delivered to the Peer state
   machine.

   The state diagrams presented in this document have been coordinated
   with the diagrams in [IEEE-802-1X-REV].  The format of the diagrams
   is adapted from the format therein.  The interface between the state
   machines defined here and the IEEE-802-1X-REV state machines is also
   explained in Appendix F of [IEEE-802-1X-REV].

3. Notational conventions used in state diagrams

3.1 Notational specifics

   The following state diagrams have been completed based on the
   conventions specified in [IEEE-802-1X-REV], section 8.2.1. The



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   complete text is reproduced here:

      State diagrams are used to represent the operation of the protocol
      by a number of cooperating state machines each comprising a group
      of connected,mutually exclusive states. Only one state of each
      machine can be active at any given time.

      Each state is represented in the state diagram as a rectangular
      box, divided into two parts by a horizontal line. The upper part
      contains the state identifier, written in upper case letters. The
      lower part contains any procedures that are executed on entry to
      the state.

      All permissible transitions between states are represented by
      arrows, the arrowhead denoting the direction of the possible
      transition. Labels attached to arrows denote the condition(s) that
      must be met in order for the transition to take place. All
      conditions are expressions that evaluate to TRUE or FALSE; if a
      condition evaluates to TRUE, then the condition is met. The label
      UCT denotes an unconditional transition (i.e., UCT always
      evaluates to TRUE). A transition that is global in nature (i.e., a
      transition that occurs from any of the possible states if the
      condition attached to the arrow is met) is denoted by an open
      arrow; i.e., no specific state is identified as the origin of the
      transition. When the condition associated with a global transition
      is met, it supersedes all other exit conditions including UCT. The
      special global condition BEGIN supersedes all other global
      conditions, and once asserted remains asserted until all state
      blocks have executed to the point that variable assignments and
      other consequences of their execution remain unchanged.

      On entry to a state, the procedures defined for the state (if any)
      are executed exactly once, in the order that they appear on the
      page. Each action is deemed to be atomic; i.e., execution of a
      procedure completes before the next sequential procedure starts to
      execute. No procedures execute outside of a state block. The
      procedures in only one state block execute at a time, even if the
      conditions for execution of state blocks in different state
      machines are satisfied, and all procedures in an executing state
      block complete execution before the transition to and execution of
      any other state block occurs, i.e., the execution of any state
      block appears to be atomic with respect to the execution of any
      other state block and the transition condition to that state from
      the previous state is TRUE when execution commences. The order of
      execution of state blocks in different state machines is undefined
      except as constrained by their transition conditions.A variable
      that is set to a particular value in a state block retains this
      value until a subsequent state block executes a procedure that



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      modifies the value.

      On completion of all of the procedures within a state, all exit
      conditions for the state (including all conditions associated with
      global transitions) are evaluated continuously until one of the
      conditions is met. The label ELSE denotes a transition that occurs
      if none of the other conditions for transitions from the state are
      met (i.e., ELSE evaluates to TRUE if all other possible exit
      conditions from the state evaluate to FALSE). Where two or more
      exit conditions with the same level of precedence become TRUE
      simultaneously, the choice as to which exit condition causes the
      state transition to take place is arbitrary.

      Where it is necessary to split a state machine description across
      more than one diagram, a transition between two states that appear
      on different diagrams is represented by an exit arrow drawn with
      dashed lines, plus a reference to the diagram that contains the
      destination state. Similarly, dashed arrows and a dashed state box
      are used on the destination diagram to show the transition to the
      destination state. In a state machine that has been split in this
      way, any global transitions that can cause entry to states defined
      in one of the diagrams are deemed to be potential exit conditions
      for all of the states of the state machine, regardless of which
      diagram the state boxes appear in.

      Should a conflict exist between the interpretation of a state
      diagram and either the corresponding global transition tables or
      the textual description associated with the state machine, the
      state diagram takes precedence. The interpretation of the special
      symbols and operators used in the state diagrams is as defined in
      Section 3.2; these symbols and operators are derived from the
      notation of the  C++  programming language, ISO/IEC 14882. If a
      boolean variable is described in this clause as being set it has
      or is assigned the value TRUE, if reset or clear the value FALSE.

   In addition to the above notation, there are a couple of
   clarifications specific to this document. First, all boolean
   variables are initialized to FALSE before the state machine execution
   begins. Second, the following notational shorthand is specific to
   this document:

   <variable> = <expression1> | <expression2> | ...

      Execution of a statement of this form will result in <variable>
      having a value of exactly one of the expressions. The logic for
      which of those expressions gets executed is outside of the state
      machine and could be environmental, configurable, or based on
      another state machine such as that of the Method.



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3.2 State Machine Symbols

   ( )

      Used to force the precedence of operators in Boolean expressions
      and to delimit the argument(s) of actions within state boxes.

   ;

      Used as a terminating delimiter for actions within state boxes.
      Where a state box contains multiple actions, the order of
      execution follows the normal English language conventions for
      reading text.

   =

      Assignment action. The value of the expression to the right of the
      operator is assigned to the variable to the left of the operator.
      Where this operator is used to define multiple assignments, e.g.,
      a = b = X the action causes the value of the expression following
      the right-most assignment operator to be assigned to all of the
      variables that appear to the left of the right-most assignment
      operator.

   !

      Logical NOT operator.

   &&

      Logical AND operator.

   ||

      Logical OR operator.

   if...then...

      Conditional action. If the Boolean expression following the if
      evaluates to TRUE, then the action following the then is executed.

   { statement 1, ... statement N }

      Compound statement. Braces are used to group statements that are
      executed together as if they were a single statement.






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   !=

      Inequality. Evaluates to TRUE if the expression to the left of the
      operator is not equal in value to the expression to the right.

   ==

      Equality. Evaluates to TRUE if the expression to the left of the
      operator is equal in value to the expression to the right.

   <

      Less than. Evaluates to TRUE if the value of the expression to the
      left of the operator is less than the value of the expression to
      the right.

   >

      Greater than. Evaluates to TRUE if the value of the expression to
      the left of the operator is greater than the value of the
      expression to the right.

   >=

      Greater than or equal to. Evaluates to TRUE if the value of the
      expression to the left of the operator is either greater than or
      equal to the value of the expression to the right.

   +

      Arithmetic addition operator.

   -

      Arithmetic subtraction operator.


3.3 Document authority

   Should a  conflict  exist  between  the  interpretation  of  a  state
   diagram and  either  the  corresponding  global transition  tables
   or the  textual  description  associated  with  the  state  machine,
   the state  diagram  takes precedence. When a discrepancy occurs
   between any part of this document (text or diagram) and any of the
   related documents ([I-D.ietf-eap-rfc2284bis], [RFC3579], etc.) the
   latter (the other document) is considered authoritative and takes
   precedence.




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4. Peer State Machine

   The following is a diagram of the EAP Peer state machine. Also
   included is an explanation of the primitives and procedures
   referenced in the diagram, as well as a clarification of notation.

                    Figure 3: EAP Peer State Machine

   (see draft-ietf-eap-statemachine-02.pdf for missing diagram if
   reading [.txt] version)

4.1 Interface between peer state machine and lower layer

   The lower layer presents messages to the EAP peer state machine by
   storing the packet in eapReqData and setting the eapReq signal to
   TRUE. Note that despite the name of the signal, the lower layer does
   not actually inspect the contents of the EAP packet (it could be a
   Success or Failure message instead of a Request).

   When the EAP peer state machine has finished processing the message
   it sets either eapResp or eapNoResp.  If it sets eapResp, the
   corresponding response packet is stored in eapRespData. The lower
   layer is responsible for actually transmitting this message. When the
   EAP peer state machine authentication is complete it will set
   eapSuccess or eapFailure to indicate to the lower layer that the
   authentication has succeeded or failed.

4.1.1 Variables (lower layer to peer)

   eapReq (boolean)

      set to TRUE in lower layer, FALSE in peer state machine. Indicates
      there is a request available in the lower layer.

   eapReqData (EAP packet)

      set in lower layer when eapReq is set to TRUE. The contents of the
      available request.

   portEnabled (boolean)

      Indicates that the EAP peer state machine should be ready for
      communication. This is set to TRUE when the EAP conversation is
      started by the lower layer. If at any point the communication port
      or session is not available, portEnabled is set to FALSE and the
      state machine transitions to DISABLED.





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   idleWhile (integer)

      outside timer used to indicate how long the peer has waited for a
      new (valid) request.

   altAccept (boolean)

      alternate indication of success, as described in
      [I-D.ietf-eap-rfc2284bis].

   altReject (boolean)

      alternate indication of failure, as described in
      [I-D.ietf-eap-rfc2284bis].


4.1.2 Variables (peer to lower layer)

   eapResp (boolean)

      Set to TRUE in peer state machine, FALSE in lower layer. Indicates
      there is a response to be sent.

   eapNoResp (boolean)

      Set to TRUE in peer state machine, FALSE in lower layer. Indicates
      the request has been processed, but there is no response to send.

   eapSuccess (boolean)

      Set to TRUE in peer state machine, FALSE in lower layer. Indicates
      the Peer has reached the SUCCESS state.

   eapFail (boolean)

      Set to TRUE in peer state machine, FALSE in lower layer. Indicates
      the Peer has reached the FAILURE state.

   eapRespData (EAP Packet)

      Set in peer state machine when eapResp is set to TRUE. The EAP
      packet which is the response to send.

   eapKeyData (EAP Key)

      Set in peer state machine when keying material becomes available.
      Set during the METHOD state. Note that this document does not yet
      define the structure of the type "EAP Key". We expect it to be



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      defined in [I-D.ietf-eap-keying].

   eapKeyAvailable (boolean)

      Set to TRUE in the SUCCESS state if keying material is available.
      The actual key is stored in eapKeyData.


4.1.3 Constants

   ClientTimeout (integer)

      Configurable amount of time to wait for a valid request before
      aborting, initialized by implementation-specific means (e.g. a
      configuration setting).


4.2 Interface between peer state machine and methods

   IN: eapReqData (includes reqId)

   OUT: ignore, eapRespData, allowNotifications, decision

   IN/OUT: methodState, (method-specific state)

   If methodState==INIT, the method starts by initializing its own
   method-specific state.

   Next, the method must decide whether to process the packet or
   silently discard it. If the packet looks like it wasn't sent by the
   legitimate authenticator (for instance, it has invalid MIC, this case
   should never occur, and the method treats MIC failures as non-fatal),
   the method can set ignore=FALSE. In this case, the method should not
   modify any other variables.

   If the method decides to process the packet, it behaves as follows.

   o  Updates its own method-specific state.

   o  If the method has derived keying material it wants to export,
      stores the keying material to eapKeyData.

   o  Creates a response packet (with the same identifier as the
      request), and stores it to eapRespData.

   o  Sets ignore=TRUE.

   Next, the method must update methodState and decision according to



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   the following rules.

   methodState=CONT: The method always continues at this point (and the
      peer wants to continue it). The decision variable is always set to
      FAIL.

   methodState=MAY_CONT: At this point, the authenticator can decide
      either to continue the method or end the conversation. The
      decision variable tells us what to do in the case the conversation
      ends. If the current situation does not satisfy the peer's
      security policy (that is, if the authenticator now decides to
      allow access, the peer will not use it), set decision=FAIL.
      Otherwise, set decision=COND_SUCC.

   methodState=DONE: The method never continues at this point, (or the
      peer sees no point in continuing it).

      If either (a) the authenticator has informed us that it will not
      allow access, or (b) we're not willing to talk to this
      authenticator (e.g. our security policy is not satisfied), set
      decision=FAIL. (Note that this state can occur even if the method
      still has additional messages left, if continuing it can't change
      the peer's decision to success).

      If both (a) the server has informed us that it will allow access
      and the next packet will be EAP Success, and (b) we're willing to
      use this access, set decision=UNCOND_SUCC.

      Otherwise, we don't know what the server's decision is, but are
      willing to use the access if the server allows.  In this case, set
      decision=COND_SUCC.

   Finally, the method must set the allowNotifications variable. If the
   new methodState is either CONT or MAY_CONT, and the method
   specification does not forbid the use of Notification messages, set
   allowNotifications=TRUE.  Otherwise, set allowNotifications=FALSE.

4.3 Peer state machine local variables

4.3.1 Long-term (maintained between packets)

   selectMethod (EAP Type)

      Set in GET_METHOD state. The method the peer believes to be
      currently "in progress"






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   methodState (enumeration)

      As described above.

   lastId (integer)

      Set in SEND_RESPONSE state. The EAP identifier value of the last
      request.

   lastRespData (EAP packet)

      Set in SEND_RESPONSE state. The EAP packet last sent from the
      peer.

   decision (enumeration)

      As described above

   NOTE: EAP type can be normal type (0..253,255), or an extended type
   consisting of type 254, Vendor-Id, and Vendor-Type.

4.3.2 Short-term (not maintained between packets)

   rxReq (boolean)

      Set in RECEIVED state. Indicates the current received packet is an
      EAP request.

   rxSuccess (boolean)

      Set in RECEIVED state. Indicates the current received packet is an
      EAP Success.

   rxFailure (boolean)

      Set in RECEIVED state. Indicates the current received packet is an
      EAP Failure.

   reqId (integer)

      Set in RECEIVED state. The identifier value associated with the
      current EAP request.

   reqMethod (EAP type)

      Set in RECEIVED state. The method type of the current EAP request





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   ignore (boolean)

      Set in METHOD state. Indicates whether the method has decided to
      accept the current packet.


4.4 Peer state machine procedures

   parseEapReq()

      Determine the code, identifier value, and type of the current
      request. Also checks that the length field is not longer than the
      received packet.

   processNotify()

      Process the contents of Notification Request (for instance,
      display it to the user or log it).

   buildNotify()

      Create the appropriate notification response.

   processIdentity()

      Process the contents of Identity Request.

   buildIdentity()

      Create the appropriate identity response.

   m.integrityCheck()

      Method-specific procedure to test for the validity of a message.

   m.process()

      Method procedure to parse and process a request for that method.

   m.getKey()

      Method procedure to obtain key material for use by EAP or lower
      layers.


4.5 Peer state machine states





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   DISABLED

      This state is reached anytime service from the lower layer is
      interrupted or unavailable. Immediate transition to INITIALIZE
      occurs when the port becomes enabled.

   INITIALIZE

      Initializes variables when the state machine is activated.

   IDLE

      The state machine spends most of its time here, waiting for
      something to happen.

   RECEIVED

      This state is entered when an EAP packet is received: the packet
      header is parsed here.

   GET_METHOD

      This state is entered when a request for a new type comes in:
      either the correct method is started, or a Nak response is built.

   METHOD

      The method processing happens here: the request from the
      authenticator is processed, and an appropriate response packet is
      built.

   SEND_RESPONSE

      This state signals the lower layer that a response packet is ready
      to be sent.

   DISCARD

      This state signals the lower layer that the request was discarded,
      and no response packet will be sent at this time.

   IDENTITY:

      Handles requests for Identity method, and builds a response.

   NOTIFICATION





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      Handles requests for Notification method, and builds a response.

   RETRANSMIT

      Retransmits the previous response packet.

   SUCCESS

      A final state indicating success.

   FAILURE

      A final state indicating failure.


5. Standalone Authenticator State Machine

   The following is a diagram of the "Standalone" EAP Authenticator
   state machine. This diagram should be used for those interested in a
   self-contained, or non-pass-through, authenticator. Included is an
   explanation of the primitives and procedures referenced in the
   diagram, as well as a clarification of notation.

          Figure 4: EAP Standalone Authenticator State Machine

   (see draft-ietf-eap-statemachine-02.pdf for missing diagram if
   reading [.txt] version)

5.1 Interface between standalone authenticator state machine and lower
    layer

   The lower layer presents messages to the EAP authenticator state
   machine by storing the packet in eapRespData and setting the eapResp
   signal to TRUE.

   When the EAP authenticator state machine has finished processing the
   message, it sets one of the signals eapReq, eapNoReq, eapSuccess, and
   eapFail.  If it sets eapReq, eapSuccess, or eapFail, the
   corresponding request (or success/failure) packet is stored in
   eapReqData. The lower layer is responsible for actually transmitting
   this message.

5.1.1 Variables (lower layer to standalone authenticator)

   eapResp (boolean)






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      Set to TRUE in lower layer, FALSE in authenticator state machine.
      Indicates an EAP response is available for processing.

   eapRespData (EAP packet)

      Set in lower layer when eapResp is set to TRUE. The EAP packet to
      be processed.

   portEnabled (boolean)

      Indicates that the EAP authenticator state machine should be ready
      for communication.  This is set to TRUE when the EAP conversation
      is started by the lower layer. If at any point the communication
      port or session is not available, portEnabled is set to FALSE and
      the state machine transitions to DISABLED.

   retransWhile (integer)

      Outside timer used to indicate how long the authenticator has
      waited for a new (valid) response.

   eapRestart (boolean)

      Indicates the lower layer would like to restart authentication

   eapSRTT (integer)

      Smoothed round-trip time. (see [I-D.ietf-eap-rfc2284bis], Section
      4.3)

   eapRTTVAR (integer)

      Round-trip time variation. (see [I-D.ietf-eap-rfc2284bis], Section
      4.3)


5.1.2 Variables (standalone authenticator to lower layer)

   eapReq (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates a new EAP request is ready to be sent.

   eapNoReq (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates the most recent response has been processed, but there
      is no new request to send.



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   eapSuccess (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates the state machine has reached the SUCCESS state.

   eapFail (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates the state machine has reached the FAILURE state.

   eapReqData (EAP packet)

      Set in authenticator state machine when eapReq, eapSuccess, or
      eapFail is set to TRUE. The actual EAP request to be sent (or
      success/failure).

   eapKeyData (EAP Key)

      Set in authenticator state machine when keying material becomes
      available. Set during the METHOD state. Note that this document
      does not yet define the structure of the type "EAP Key". We expect
      it to be defined in [I-D.ietf-eap-keying].

   eapKeyAvailable (boolean)

      Set to TRUE in the SUCCESS state if keying material is available.
      The actual key is stored in eapKeyData.


5.1.3 Constants

   MaxRetrans (integer)

      Configurable maximum for how many retransmissions should be
      attempted before aborting.


5.2 Interface between standalone authenticator state machine and methods

   IN: eapRespData, methodState

   IN/OUT: currentId, (method-specific state), (policy)

   OUT: ignore, eapReqData

   m.init (in: -, out: -)

   When the method is first started, it must initialize its own



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   method-specific state, possibly using some information from Policy
   (e.g. identity).

   m.buildReq (in: integer, out: EAP packet)

   Next, the method creates a new EAP Request packet, with the given
   identifier value, and updates its method-specific state accordingly.

   m.getTimeout (in: -, out: integer or NONE)

   The method can also provide a hint for retransmission timeout with
   m.getTimeout.

   m.check (in: EAP packet, out: boolean)

   When a new EAP Response is received, the method must first decide
   whether to process the packet or silently discard it. If the packet
   looks like it wasn't sent by the legitimate peer (e.g. it has invalid
   MIC, and this case should never occur), the method can indicate this
   by returning FALSE. In this case, the method should not modify its
   own method-specific state.

   m.process (in: EAP packet, out: -)

   m.isDone (in: -, out: boolean)

   m.getKey (in: -, out: EAP key or NONE)

   Next, the method processes the EAP Response and updates its own
   method-specific state. Now the options are to continue the
   conversation (send another request) or end this method.

   If the method wants to end the conversation, it

   o  Tells Policy about the outcome of the method, and possibly other
      information.

   o  If the method has derived keying material it wants to export,
      returns it from m.getKey().

   o  Indicates that the method wants to end by returning TRUE from
      m.isDone().

   Otherwise, the method continues by sending another request, as
   described earlier.

5.3 Standalone authenticator state machine local variables




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5.3.1 Long-term (maintained between packets)

   currentMethod (EAP Type)

      EAP type, IDENTITY, or NOTIFICATION.

   currentId (integer)

      0-255 or NONE.  Usually updated in PROPOSE_METHOD state. Indicates
      the identifier value of the currently outstanding EAP request.

   methodState (enumeration)

      As described above.

   retransCount (integer)

      Reset in SEND_REQUEST state and updated in RETRANSMIT state.
      Current number of retransmissions.

   lastReqData (EAP packet)

      Set in SEND_REQUEST state. EAP packet containing the last sent
      request.

   methodTimeout (integer)

      Method-provided hint for suitable retransmission timeout, or NONE.


5.3.2 Short-term (not maintained between packets)

   rxResp (boolean)

      Set in RECEIVED state. Indicates the current received packet is an
      EAP response.

   respId (integer)

      Set in RECEIVED state. The identifier from the current EAP
      response.

   respMethod (EAP Type)

      Set in RECEIVED state. The method type of the current EAP
      response.





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   ignore (boolean)

      Set in METHOD state. Indicates whether the method has decided to
      accept the current packet.

   decision (enumeration)

      Set in SELECT_ACTION state. Temporarily store the policy decision
      to succeed, fail, or continue.


5.4 EAP standalone authenticator procedures

   calculateTimeout()

      Calculates the retransmission timeout, taking into account the
      retransmission count, round-trip time measurements, and
      method-specific timeout hint (see [I-D.ietf-eap-rfc2284bis],
      Section 4.3).

   parseEapResp()

      Determine the code, identifier value, and type of the current
      response. Also checks that the length field is not longer than the
      Received EAP packet

   buildSuccess()

      Create an EAP Success Packet.

   buildFailure()

      Create an EAP Failure Packet.

   nextId()

      Determine the next identifier value to use, based on the previous
      one.

   Policy.update()

      Update all variables related to internal policy state.

   Policy.getNextMethod()

      Determine the method that should be used at this point in the
      conversation based on pre-defined policy.




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   Policy.getDecision()

      Determine if the policy will allow SUCCESS, FAIL, or is yet to
      determine (CONTINUE).

   m.check()

      Method-specific procedure to test for the validity of a message.

   m.process()

      Method procedure to parse and process a response for that method.

   m.init()

      Method procedure to initialize state just before use.

   m.reset()

      Method procedure to indicate the method is ending in the middle or
      before completion.

   m.isDone()

      Method procedure to check for method completion.

   m.getTimeout()

      Method procedure to determine an appropriate timeout hint for that
      method.

   m.getKey()

      Method procedure to obtain key material for use by EAP or lower
      layers.

   m.buildReq()

      Method procedure to produce the next request.


5.5 EAP standalone authenticator states

   DISABLED

      The authenticator is disabled until the port is enabled by the
      lower layer.




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   INITIALIZE

      Initializes variables when the state machine is activated.

   IDLE

      The state machine spends most of its time here, waiting for
      something to happen.

   RECEIVED

      This state is entered when an EAP packet is received: the packet
      header is parsed here.

   INTEGRITY_CHECK

      A method state in which the integrity of the incoming packet from
      the peer is verified by the method.

   METHOD_RESPONSE

      A method state in which the incoming packet is processed.

   METHOD_REQUEST

      A method state in which a new request is formulated if necessary.

   PROPOSE_METHOD

      A state in which the authenticator decides which method to try
      next in the authentication.

   SELECT_ACTION

      In between methods, the state machine re-evaluates whether or not
      its policy is satisfied and succeeds, fails, or remains undecided.

   SEND_REQUEST

      This state signals the lower layer that a request packet is ready
      to be sent.

   DISCARD

      This state signals the lower layer that the response was
      discarded, and no new request packet will be sent at this time.





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   NAK

      This state processes Nak responses from the peer.

   RETRANSMIT

      Retransmits the previous request packet.

   SUCCESS

      A final state indicating success.

   FAILURE

      A final state indicating failure.

   TIMEOUT_FAILURE

      A final state indicating failure with no EAP Failure packet sent.


6. EAP Backend Authenticator

   When operating in pass-through mode, there are conceptually two parts
   to the authenticator- the part that passes packets through and the
   backend that actually implements the EAP method. The following
   diagram shows a state machine for the backend part of this model when
   using a AAA server. Note that this diagram is identical to Figure 4
   except no retransmit is included in the IDLE state because with
   RADIUS retransmit is handled by the NAS, and  a PICK_UP_METHOD state
   and variable in INITIALIZE state are added to allow the Method to
   "pickup" a method started in a NAS. Included is an explanation of the
   primitives and procedures referenced in the diagram, many of which
   are the same as above. It should be noted that the "lower layer" in
   this case is some AAA protocol (e.g. RADIUS).

           Figure 5: EAP Backend Authenticator State Machine

   (see draft-ietf-eap-statemachine-02.pdf for missing diagram if
   reading [.txt] version)

6.1 Interface between backend authenticator state machine and lower
    layer

   The lower layer presents messages to the EAP backend authenticator
   state machine by storing the packet in aaaEapRespData and setting the
   aaaEapResp signal to TRUE.




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   When the EAP backend authenticator state machine has finished
   processing the message, it sets one of the signals aaaEapReq,
   aaaEapNoReq, aaaSuccess, and aaaFail.  If it sets eapReq, eapSuccess,
   or eapFail, the corresponding request (or success/failure) packet is
   stored in aaaEapReqData. The lower layer is responsible for actually
   transmitting this message.

6.1.1 Variables (AAA interface to backend authenticator)

   aaaEapResp (boolean)

      Set to TRUE in lower layer, FALSE in authenticator state machine.
      Indicates an EAP response is available for processing.

   aaaEapRespData (EAP packet)

      Set in lower layer when eapResp is set to TRUE. The EAP packet to
      be processed.

   backendEnabled (boolean)

      Indicates that there is a valid link to use for the communication.
      If at any point the port is not available, backendEnabled is set
      to FALSE and the state machine transitions to DISABLED.


6.1.2 Variables (backend authenticator to AAA interface)

   aaaEapReq (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates a new EAP request is ready to be sent.

   aaaEapNoReq (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates the most recent response has been processed, but there
      is no new request to send.

   aaaSuccess (boolean)

      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates the state machine has reached the SUCCESS state.

   aaaFail (boolean)






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      Set to TRUE in authenticator state machine, FALSE in lower layer.
      Indicates the state machine has reached the FAILURE state.

   aaaEapReqData (EAP packet)

      Set in authenticator state machine when aaaEapReq, aaaSuccess, or
      aaaFail is set to TRUE. The actual EAP request to be sent (or
      success/failure).

   aaaEapKeyData (EAP Key)

      Set in authenticator state machine when keying material becomes
      available. Set during the METHOD_RESPONSE state. Note that this
      document does not yet define the structure of the type "EAP Key".
      We expect it to be defined in [I-D.ietf-eap-keying].

   aaaEapKeyAvailable (boolean)

      Set to TRUE in the SUCCESS state if keying material is available.
      The actual key is stored in aaaEapKeyData.

   aaaMethodTimeout (integer)

      Method-provided hint for suitable retransmission timeout, or NONE
      (note that this hint is for the EAP retransmissions done by the
      pass-through authenticator, not retransmissions of AAA packets).


6.2 Interface between backend authenticator state machine and methods

   The backend method interface is almost the same as in standalone
   authenticator described in Section 5.2. The only difference is that
   some methods on the backend may support "picking up" a conversation
   started by the pass-through. That is, the EAP Request packet was sent
   by the pass-through, but the backend must process the corresponding
   EAP Response. Usually only the Identity method supports this, but
   others are possible.

   When "picking up" a conversation, m.initPickUp() is called instead of
   m.init(). Next, m.process() must examine eapRespData and update its
   own method-specific state to match what it would have been if it had
   actually sent the corresponding request. (Obviously, this only works
   for methods that can determine what the initial request contained;
   Identity and EAP-TLS are good examples.)

   After this, the processing continues as described in Section 5.2





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6.3 Backend authenticator state machine local variables

   For definitions of the variables used in the Backend Authenticator,
   see Section 5.3.

6.4 EAP backend authenticator procedures

   Most of the procedures of the backend authenticator have already been
   defined in Section 5.4. This section contains definitions for those
   not existent in the standalone version, as well as those which are
   defined differently.

   Policy.doPickUp()

      Notify the policy that an already-chosen method is being picked up
      and will be completed.

   m.initPickUp()

      Method procedure to initialize state when continuing from an
      already-started method.


6.5 EAP backend authenticator states

   Most of the states of the backend authenticator have already been
   defined in Section 5.5. This section contains definitions for those
   not existent in the standalone version, as well as those which are
   defined differently.

   PICK_UP_METHOD

      Set an initial state for a method that is being continued and was
      started elsewhere.


7. EAP Full Authenticator

   The following two diagrams show the state machine for a complete
   authenticator. The first diagram is identical to the Standalone State
   Machine, shown in Figure 4, with the exception that the SELECT_ACTION
   state has an added transition to PASSTHROUGH.  The second diagram
   also keeps most of the logic except the four method states, and shows
   how the state machine works once it goes to Pass-Through Mode.

   The first diagram is largely a reproduction of that found above, with
   the added hooks for a transition to PASSTHROUGH mode.




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        Figure 6: EAP Full Authenticator State Machine (Part 1)

   (see draft-ietf-eap-statemachine-02.pdf for missing diagram if
   reading [.txt] version)

   The second diagram describes the functionality necessary for an
   authenticator operating in pass-through mode. This section of the
   diagram is the counterpart of the backend diagram above.

        Figure 7: EAP Full Authenticator State Machine (Part 2)

   (see draft-ietf-eap-statemachine-02.pdf for missing diagram if
   reading [.txt] version)

7.1 Interface between full authenticator state machine and lower layers

   The full authenticator is unique in that it interfaces to multiple
   lower layers in order to support pass-through mode. The interface to
   the primary EAP transport layer is the same as described in Section
   5. The following describes the interface to the second lower layer,
   which represents an interface to AAA. It should be noted that there
   is not necessarily a direct interaction between the EAP layer and the
   AAA layer, as in the case of [IEEE-802-1X-REV].

7.1.1 Variables (AAA interface to full authenticator)

   aaaEapReq (boolean)

      Set to TRUE in lower layer,  FALSE in authenticator state machine.
      Indicates a new EAP request is available from the AAA server.

   aaaEapNoReq (boolean)

      Set to TRUE in lower layer, FALSE in authenticator state machine.
      Indicates the most recent response has been processed, but there
      is no new request to send.

   aaaSuccess (boolean)

      Set to TRUE in lower layer. Indicates the AAA backend
      authenticator has reached the SUCCESS state.

   aaaFail (boolean)

      Set to TRUE in lower layer. Indicates the AAA backend
      authenticator has reached the FAILURE state.





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   aaaEapReqData (EAP packet)

      Set in the lower layer when aaaEapReq, aaaSuccess, or aaaFail is
      set to TRUE. The actual EAP request to be sent (or success/
      failure).

   aaaEapKeyData (EAP Key)

      Set in lower layer when keying material becomes available from the
      AAA server.  Note that this document does not yet define the
      structure of the type "EAP Key". We expect it to be defined in
      [I-D.ietf-eap-keying].

   aaaEapKeyAvailable (boolean)

      Set to TRUE in the lower layer if keying material is available.
      The actual key is stored in aaaEapKeyData.

   aaaMethodTimeout (integer)

      Method-provided hint for suitable retransmission timeout, or NONE
      (note that this hint is for the EAP retransmissions done by the
      pass-through authenticator, not retransmissions of AAA packets).


7.1.2 Variables (full authenticator to AAA interface)

   aaaEapResp (boolean)

      Set to TRUE in authenticator state machine, FALSE in the lower
      layer. Indicates an EAP response is available for processing by
      the AAA server.

   aaaEapRespData (EAP packet)

      Set in authenticator state machine when eapResp is set to TRUE.
      The EAP packet to be processed.

   aaaIdentity (EAP packet)

      Set in authenticator state machine when an IDENTITY response is
      received. Makes that identity available to AAA lower layer.

   aaaTimeout (boolean)

      Set in AAA_IDLE if after a configurable amount of time there is no
      response from the AAA layer. The AAA layer in the NAS is itself
      alive and OK, but for some reason it hasn't received a valid



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      Access-Accept/Reject indication from the backend


7.1.3 Constants

   Same as Section 5.

7.2 Interface between full authenticator state machine and methods

   Same as standalone authenticator (Section 5.2)

7.3 Full authenticator state machine local variables

   Many of the variables of the full authenticator have already been
   defined in Section 5. This section contains definitions for those not
   existent in the standalone version, as well as those which are
   defined differently.

7.3.1 Short-term (not maintained between packets)

   decision (enumeration)

      Set in SELECT_ACTION state. Temporarily store the policy decision
      to succeed, fail, continue with a local method, or continue in
      pass-through mode.


7.4 EAP full authenticator procedures

   All of the procedures defined in Section 5 exist in the full version.
   In addition, the following procedures are defined.

   getId()

      Determine the identifier value chosen by the AAA server for the
      current EAP request.


7.5 EAP full authenticator states

   All of the states defined in Section 5 exist in the full version. In
   addition, the following states are defined.

   INITIALIZE_PASSTHROUGH

      Initializes variables when the pass-through portion of the state
      machine is activated.




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   IDLE2

      The state machine waits for a response from the primary lower
      layer, which transports EAP traffic from the peer.

   IDLE

      The state machine spends most of its time here, waiting for
      something to happen.

   RECEIVED2

      This state is entered when an EAP packet is received and the
      authenticator is in PASSTHROUGH mode: the packet header is parsed
      here.

   AAA_REQUEST

      The incoming EAP packet is parsed for sending to the AAA server.

   AAA_IDLE

      Idle state which tells the AAA layer it has a response and then
      waits for a new request, a no-request signal, or success/failure.

   AAA_RESPONSE

      State in which the request from the AAA interface is processed
      into an EAP request.

   SEND_REQUEST2

      This state signals the lower layer that a request packet is ready
      to be sent.

   DISCARD2

      This state signals the lower layer that the response was
      discarded, and no new request packet will be sent at this time.

   RETRANSMIT2

      Retransmits the previous request packet.

   SUCCESS2






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      A final state indicating success.

   FAILURE2

      A final state indicating failure.

   TIMEOUT_FAILURE2

      A final state indicating failure with no EAP Failure packet sent.


8. Implementation Considerations

8.1 Robustness

   In order to deal with erroneous cases that are not directly related
   to the protocol behavior, implementations may need additional
   considerations to provide robustness against errors.

   For example, an implementation of a state machine may spend a
   significant amount of time in a particular state for performing the
   procedure defined for the state without returning a response.  If
   such an implementation is made on a multithreading system, the
   procedure may be performed in a separate thread so that the
   implementation can perform appropriate action to deal with the case
   without blocking on the state for a long time (or forever if the
   procedure never completes due to, e.g., a non-responding user or a
   bug in an application callback function.)

   The following states are identified as the possible places of
   blocking:

   o  IDENTITY state in the peer state machine.  It may take some time
      to process Identity request when a user input is needed for
      obtaining an identity from the user.  The user may never input an
      identity. An implementation may define an additional state
      transition from IDENTITY state to FAILURE state so that
      authentication can fail if no identity is obtained from the user
      before ClientTimeout timer expires.

   o  METHOD state in the peer state machine and in METHOD_RESPONSE
      state in the authenticator state machines.  It may take some time
      to perform method-specific procedures in these states.  An
      implementation may define an additional state transition from
      METHOD state and METHOD_RESPONSE state to FAILURE or
      TIMEOUT_FAILURE state so that authentication can fail if no method
      processing result is obtained from the method before methodTimeout
      timer expires.



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8.2 Method/Method and Method/Lower-Layer Interfaces

   Implementations may define additional interfaces to pass
   method-specific information between methods and lower layers. These
   interfaces are beyond the scope of this document.

9. Security Considerations

   This document's intent is to describe the EAP state machine fully. To
   this end, any security concerns with this document are likely a
   reflection of security concerns with EAP itself.

10. Acknowledgments

   The work in this document was done as part of the EAP Design Team.
   It was done primarily by Nick Petroni, John Vollbrecht, Pasi Eronen
   and Yoshihiro Ohba.  Nick started this work with Bryan Payne and Chuk
   Seng at the University of Maryland.  John Vollbrecht, of Vollbrecht
   Consulting, started independently with help from Dave Spence at
   Interlink Networks.  John and Nick combined to create a common draft,
   and then were joined by Pasi Eronen of Nokia who has made major
   contributions in creating coherent state machines, and Yoshihiro Ohba
   of Toshiba who insisted on including Pass-Through documentation and
   provided significant support for understanding implementation issues.

   In addition significant response and conversation has come from the
   design team, especially including Jari Arkko of Ericsson and Bernard
   Aboba of Microsoft as well as the rest of the team.  It has also been
   passed through the 802.1aa group, and has had input from Jim Burns of
   Meetinghouse and Paul Congdon of Hewlett Packard.

Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2284]  Blunk, L. and J. Vollbrecht, "PPP Extensible
              Authentication Protocol (EAP)", RFC 2284, March 1998.

   [RFC3579]  Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
              Dial In User Service) Support For Extensible
              Authentication Protocol (EAP)", RFC 3579, September 2003.

   [I-D.ietf-eap-rfc2284bis]
              Blunk, L., "Extensible Authentication Protocol (EAP)",
              draft-ietf-eap-rfc2284bis-07 (work in progress), December
              2003.




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Informative References

   [I-D.ietf-eap-keying]
              Aboba, B., "EAP Key Management Framework",
              draft-ietf-eap-keying-01 (work in progress), October 2003.

   [IEEE-802-1X-REV]
              Institute of Electrical and Electronics Engineers, "DRAFT
              Standard for Local and Metropolitan Area Networks:
              Port-Based Network Access Control (Revision)", IEEE
              802-1X-REV/D9, January 2004.


Authors' Addresses

   John R. Vollbrecht
   Vollbrecht Consulting LLC
   9682 Alice Hill Drive
   Dexter, MI  48130
   USA

   EMail: jrv@umich.edu


   Pasi Eronen
   Nokia Research Center
   P.O. Box 407
   FIN-00045 Nokia Group,
   Finland

   EMail: pasi.eronen@nokia.com


   Nick L. Petroni, Jr.
   University of Maryland, College Park
   A.V. Williams Building
   College Park, MD  20742
   USA

   EMail: npetroni@cs.umd.edu











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   Yoshihiro Ohba
   Toshiba America Information Systems, Inc.
   9740 Irvine Blvd.
   Irvine, CA  92619-1697
   USA

   EMail: yohba@tari.toshiba.com












































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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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