[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 4072

Network Working Group                                     P. Eronen, Ed.
Internet-Draft                                                     Nokia
Expires: April 23, 2004                                        T. Hiller
                                                     Lucent Technologies
                                                                 G. Zorn
                                                           Cisco Systems
                                                        October 24, 2003


     Diameter Extensible Authentication Protocol (EAP) Application
                      draft-ietf-aaa-eap-03.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 other
   groups may also distribute working documents as Internet-Drafts.

   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 April 23, 2004.

Copyright Notice

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

Abstract

   The Extensible Authentication Protocol (EAP) provides a standard
   mechanism for support of various authentication methods.  This
   document defines the Command-Codes and AVPs necessary to carry EAP
   packets between a Network Access Server (NAS) and a back-end
   authentication server.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",



Eronen, et al.           Expires April 23, 2004                 [Page 1]

Internet-Draft          Diameter EAP Application            October 2003


   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.    Extensible Authentication Protocol Support in Diameter . . .  4
   2.1   Advertising application support  . . . . . . . . . . . . . .  4
   2.2   Protocol Overview  . . . . . . . . . . . . . . . . . . . . .  5
   2.3   Sessions and NASREQ interaction  . . . . . . . . . . . . . .  7
   2.3.1 Scenario 1: Direct connection  . . . . . . . . . . . . . . .  8
   2.3.2 Scenario 2: Direct connection with redirects . . . . . . . .  9
   2.3.3 Scenario 3: Direct EAP, authorization via agents . . . . . . 10
   2.3.4 Scenario 4: Proxy agents . . . . . . . . . . . . . . . . . . 12
   2.4   Invalid packets  . . . . . . . . . . . . . . . . . . . . . . 12
   2.5   Retransmission . . . . . . . . . . . . . . . . . . . . . . . 13
   2.6   Fragmentation  . . . . . . . . . . . . . . . . . . . . . . . 14
   2.7   Accounting . . . . . . . . . . . . . . . . . . . . . . . . . 14
   2.8   Usage guidelines . . . . . . . . . . . . . . . . . . . . . . 14
   2.8.1 User-Name AVP  . . . . . . . . . . . . . . . . . . . . . . . 14
   2.8.2 Conflicting AVPs . . . . . . . . . . . . . . . . . . . . . . 15
   2.8.3 Displayable messages . . . . . . . . . . . . . . . . . . . . 15
   2.8.4 Role reversal  . . . . . . . . . . . . . . . . . . . . . . . 15
   2.8.5 Alternative Uses . . . . . . . . . . . . . . . . . . . . . . 15
   3.    Command-Codes  . . . . . . . . . . . . . . . . . . . . . . . 16
   3.1   Diameter-EAP-Request (DER) Command . . . . . . . . . . . . . 16
   3.2   Diameter-EAP-Answer (DEA) Command  . . . . . . . . . . . . . 17
   4.    Attribute-Value Pairs  . . . . . . . . . . . . . . . . . . . 19
   4.1   New AVPs . . . . . . . . . . . . . . . . . . . . . . . . . . 19
   4.1.1 EAP-Payload AVP  . . . . . . . . . . . . . . . . . . . . . . 19
   4.1.2 EAP-Reissued-Payload AVP . . . . . . . . . . . . . . . . . . 19
   4.1.3 EAP-Master-Session-Key AVP . . . . . . . . . . . . . . . . . 20
   4.1.4 Accounting-EAP-Auth-Method AVP . . . . . . . . . . . . . . . 20
   5.    AVP Occurrence Tables  . . . . . . . . . . . . . . . . . . . 20
   5.1   EAP Command AVP Table  . . . . . . . . . . . . . . . . . . . 20
   5.2   Accounting AVP Table . . . . . . . . . . . . . . . . . . . . 22
   6.    RADIUS/Diameter interactions . . . . . . . . . . . . . . . . 22
   6.1   RADIUS Request forwarded as Diameter Request . . . . . . . . 22
   6.2   Diameter Request forwarded as RADIUS Request . . . . . . . . 23
   6.3   Accounting Requests  . . . . . . . . . . . . . . . . . . . . 24
   7.    IANA Considerations  . . . . . . . . . . . . . . . . . . . . 24
   8.    Security Considerations  . . . . . . . . . . . . . . . . . . 25
   8.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 25
   8.2   AVP editing  . . . . . . . . . . . . . . . . . . . . . . . . 26
   8.3   Negotiation attacks  . . . . . . . . . . . . . . . . . . . . 27
   8.4   Session key distribution . . . . . . . . . . . . . . . . . . 28
   8.5   Privacy issues . . . . . . . . . . . . . . . . . . . . . . . 28
   8.6   Note about EAP and impersonation . . . . . . . . . . . . . . 29



Eronen, et al.           Expires April 23, 2004                 [Page 2]

Internet-Draft          Diameter EAP Application            October 2003


   9.    Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
         Normative References . . . . . . . . . . . . . . . . . . . . 30
         Informative References . . . . . . . . . . . . . . . . . . . 30
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 31
   A.    Changelog  . . . . . . . . . . . . . . . . . . . . . . . . . 32
         Intellectual Property and Copyright Statements . . . . . . . 35













































Eronen, et al.           Expires April 23, 2004                 [Page 3]

Internet-Draft          Diameter EAP Application            October 2003


1. Introduction

   The Extensible Authentication Protocol (EAP), defined in
   [RFC2284bis], is an authentication framework which supports multiple
   authentication mechanisms.  EAP may be used on dedicated links as
   well as switched circuits, and wired as well as wireless links.

   To date, EAP has been implemented with hosts and routers that connect
   via switched circuits or dial-up lines using PPP [RFC1661], IEEE 802
   wired switches [IEEE-802.1X], and IEEE 802.11 wireless access points
   [IEEE-802.11i].  EAP has also been adopted for IPsec remote access in
   IKEv2 [IKEv2].

   This document specifies the Diameter EAP application that carries EAP
   packets between a Network Access Server (NAS) working as an EAP
   Authenticator and a back-end authentication server.  The Diameter EAP
   application is based on NASREQ and is intended for similar
   environments as NASREQ.

   In Diameter EAP application, authentication occurs between the EAP
   client and its home Diameter server.  This end-to-end authentication
   reduces the possibility for fraudulent authentication, such as replay
   and man-in-the-middle attacks.  End-to-end authentication also
   provides a possibility for mutual authentication, which is not
   possible with PAP and CHAP in a roaming PPP environment.

   Diameter EAP application relies heavily on [NASREQ], and in earlier
   drafts was part of the Diameter NASREQ application.  It can also be
   used in conjunction with NASREQ, selecting the application based on
   the used authentication mechanism (EAP or PAP/CHAP).  Diameter EAP
   application defines new Command-Codes and new AVPs, and can work
   together with RADIUS EAP support [RFC3579].

2. Extensible Authentication Protocol Support in Diameter

2.1 Advertising application support

   Diameter nodes conforming to this specification MAY advertise support
   by including the value of TBD in the Auth-Application-Id AVP of the
   Capabilities-Exchange-Request and Capabilities-Exchange-Answer
   command [BASE].

   If the NAS receives a response with the Result-Code set to
   DIAMETER_APPLICATION_UNSUPPORTED [BASE], it is an indication that the
   Diameter server in the home realm does not support EAP.  If possible,
   the access device MAY attempt to negotiate another authentication
   protocol, such as PAP or CHAP.  An access device SHOULD be cautious
   when determining whether a less secure authentication protocol will



Eronen, et al.           Expires April 23, 2004                 [Page 4]

Internet-Draft          Diameter EAP Application            October 2003


   be used, since this could be a result of a bidding down attack (see
   Section 8.3).

2.2 Protocol Overview

   The EAP conversation between the authenticating peer and the access
   device begins with the initiation of EAP within a link layer, such as
   PPP [RFC1661] or IEEE 802.1X [IEEE-802.1X].  Once EAP has been
   initiated, the access device will typically send to the Diameter
   server a Diameter-EAP-Request message with an empty EAP-Payload AVP,
   signifying an EAP-Start.

   If the Diameter home server is willing to do EAP authentication, it
   respons with a Diameter-EAP-Answer message containing an EAP-Payload
   AVP that includes an encapsulated EAP packet.  The Result-Code AVP
   set to DIAMETER_MULTI_ROUND_AUTH, signifying that a subsequent
   request is expected.  The EAP payload is forwarded by the access
   device to the EAP client.  This is illustrated in the diagram below.

   User                             NAS                           Server
    |                                |                                |
    |        (initiate EAP)          |                                |
    |<------------------------------>|                                |
    |                                | Diameter-EAP-Request           |
    |                                | EAP-Payload(EAP Start)         |
    |                                |------------------------------->|
    |                                |                                |
    |                                |            Diameter-EAP-Answer |
    |                           Result-Code=DIAMETER_MULTI_ROUND_AUTH |
    |                                |    EAP-Payload(EAP Request #1) |
    |                                |<-------------------------------|
    |                 EAP Request #1 |                                |
    |<-------------------------------|                                |
    :                                :                                :
    :                        ...continues...                          :

   The initial Diameter-EAP-Answer in a multi-round exchange normally
   includes an EAP-Request/Identity, requesting the EAP client to
   identify itself.  Upon receipt of the EAP client's EAP-Response, the
   access device will then issue a second Diameter-EAP-Request message,
   with the client's EAP payload encapsulated within the EAP-Payload
   AVP.

   A preferred approach is for the access device to issue the
   EAP-Request/Identity message to the EAP client, and forward the
   EAP-Response/Identity packet, encapsulated within the EAP-Payload
   AVP, as a Diameter-EAP-Request to the Diameter server (see the
   diagram below).  This alternative reduces the number of Diameter



Eronen, et al.           Expires April 23, 2004                 [Page 5]

Internet-Draft          Diameter EAP Application            October 2003


   message round trips.  When the EAP-Request/Identity message is issued
   by the access device, it SHOULD interpret the EAP-Response/Identity
   packet returned by the authenticating peer, and copy its value to a
   User-Name AVP in Diameter-EAP-Request.  This is useful in roaming
   environments, since the Destination-Realm is needed for routing
   purposes.  Note that this alternative cannot be universally employed,
   as there are circumstances where a user's identity is not needed
   (such as when authorization occurs based on a calling or called phone
   number).

   User                             NAS                           Server
    |                                |                                |
    |        (initiate EAP)          |                                |
    |<------------------------------>|                                |
    |                                |                                |
    |          EAP Request(Identity) |                                |
    |<-------------------------------|                                |
    |                                |                                |
    | EAP Response(Identity)         |                                |
    |------------------------------->|                                |
    |                                | Diameter-EAP-Request           |
    |                                | EAP-Payload(EAP Response)      |
    |                                |------------------------------->|
    :                                :                                :
    :                        ...continues...                          :

   The conversation continues until the Diameter server sends a
   Diameter-EAP-Answer with a Result-Code AVP indicating success or
   failure, and an optional EAP-Payload.  The Result-Code AVP is used by
   the access device to determine whether service is to be provided to
   the EAP client.  The access device MUST NOT rely on the contents of
   the optional EAP-Payload to determine whether service is to be
   provided.


















Eronen, et al.           Expires April 23, 2004                 [Page 6]

Internet-Draft          Diameter EAP Application            October 2003


    :                        ...continued...                          :
    :                                :                                :
    | EAP Response #N                |                                |
    |------------------------------->|                                |
    |                                | Diameter-EAP-Request           |
    |                                | EAP-Payload(EAP Response #N)   |
    |                                |------------------------------->|
    |                                |                                |
    |                                |            Diameter-EAP-Answer |
    |                                |   Result-Code=DIAMETER_SUCCESS |
    |                                |       EAP-Payload(EAP Success) |
    |                                |       [EAP-Master-Session-Key] |
    |                                |           (authorization AVPs) |
    |                                |<-------------------------------|
    |                                |                                |
    |                    EAP Success |                                |
    |<-------------------------------|                                |

   If authorization was requested, a Diameter-EAP-Answer with
   Result-Code set to DIAMETER_SUCCESS MUST also include the appropriate
   authorization AVPs required for the service requested (see Section 5
   and [NASREQ]).  If the Result-Code DIAMETER_LIMITED_SUCCESS is
   returned, this means that the NAS has to get additional authorization
   AVPs using a separate NASREQ request.  This case is described in
   Section TBD below.  Diameter-EAP-Answer messages whose Result-Code
   AVP is set to DIAMETER_MULTI_ROUND_AUTH MAY include authorization
   AVPs.

   A Diameter-EAP-Answer with succesful Result-Code MAY also include an
   EAP-Master-Session-Key AVP that contains keying material for
   protecting the communication between the user and the NAS.  Exactly
   how this keying material is used depends on the link layer in
   question, is beyond the scope of this document.

   A home Diameter server MAY request EAP re-authentication by issuing
   the Re-Auth-Request [BASE] message to the Diameter client.

   Should an EAP authentication session be interrupted due to a home
   server failure, the session MAY be directed to an alternate server,
   but the authentication session will have to be restarted from the
   beginning.

2.3 Sessions and NASREQ interaction

   (NOTE: This section has not received sufficient WG discussion yet,
   and is likely to be changed in the future.)

   The previous section introduced the basic protocol between the NAS



Eronen, et al.           Expires April 23, 2004                 [Page 7]

Internet-Draft          Diameter EAP Application            October 2003


   and the home server.  Since the Diameter-EAP-Answer message may
   include a Master Session Key (MSK) for protecting the communication
   between the user and the NAS, care must be taken to ensure that this
   key does not fall into wrong hands.

   Basic Diameter security mechanisms (IPsec and TLS) protect Diameter
   messages hop-by-hop.  Since there are currently no end-to-end
   (NAS-to-home server) security mechanisms defined for Diameter, this
   section describes some possible scenarios how the messages could be
   transported protected using these hop-by-hop mechanisms.

   The list of scenarios is not intended to be exhaustive, and it is
   possible to combine them.  For instance, the first proxy agent after
   the NAS could use redirects as in scenario 2 to bypass any additional
   proxy agents.

2.3.1 Scenario 1: Direct connection

   The simplest case is when the NAS contacts the home server directly.
   All the authorization AVPs are delivered by the home server, as is
   EAP keying material.

   NAS                                                       home server
    |                                                                 |
    | Diameter-EAP-Request                                            |
    | Auth-Request-Type=AUTHORIZE_AUTHENTICATE                        |
    | EAP-Payload(EAP Start)                                          |
    |---------------------------------------------------------------->|
    |                                                                 |
    |                                             Diameter-EAP-Answer |
    |                           Result-Code=DIAMETER_MULTI_ROUND_AUTH |
    |                                        EAP-Payload(EAP Request) |
    |<----------------------------------------------------------------|
    |                                                                 |
    :              ...more EAP Request/Response pairs...              :
    |                                                                 |
    | Diameter-EAP-Request                                            |
    | EAP-Payload(EAP Response)                                       |
    |---------------------------------------------------------------->|
    |                                                                 |
    |                                             Diameter-EAP-Answer |
    |                                    Result-Code=DIAMETER_SUCCESS |
    |                                        EAP-Payload(EAP Success) |
    |                                          EAP-Master-Session-Key |
    |                                            (authorization AVPs) |
    |<----------------------------------------------------------------|

   This scenario is the most likely to be used in small networks, or in



Eronen, et al.           Expires April 23, 2004                 [Page 8]

Internet-Draft          Diameter EAP Application            October 2003


   cases where Diameter agents are not needed to provide routing or
   additional authorization AVPs.

2.3.2 Scenario 2: Direct connection with redirects

   In this scenario the NAS uses a redirect agent to locate the home
   server, and the rest of the session proceeds as before.

   NAS                      Local redirect agent             Home server
    |                                |                                |
    | Diameter-EAP-Request           |                                |
    | Auth-Request-Type=AUTHORIZE_AUTHENTICATE                        |
    | EAP-Payload(EAP Start)         |                                |
    |------------------------------->|                                |
    |                                |                                |
    |                       Diameter-EAP-Answer                       |
    |      Redirect-Host=homeserver.example.com                       |
    | Redirect-Host-Usage=REALM_AND_APPLICATION                       |
    |<-------------------------------|                                |
    |                                :                                |
    | Diameter-EAP-Request          :                                 |
    | Auth-Request-Type=AUTHORIZE_AUTHENTICATE                        |
    | EAP-Payload(EAP Start)        :                                 |
    |---------------------------------------------------------------->|
    |                                :                                |
    :      ...rest of the session continues as in first case...       :
    :                                :                                :

   The advantage of this scenario is that knowledge of realms and home
   servers is centralized to a redirect agent, and it is not necessary
   to modify the NAS configuration when, e.g., a new roaming agreement
   is done.



















Eronen, et al.           Expires April 23, 2004                 [Page 9]

Internet-Draft          Diameter EAP Application            October 2003


2.3.3 Scenario 3: Direct EAP, authorization via agents

   In this scenario the EAP authentication is done directly with the
   home server (with Auth-Request-Type set to AUTHENTICATE_ONLY), and
   the authorization AVPs are retrieved from the local proxy agents.
   This scenario is intended for environments where the home server
   cannot provide all the necessary authorization AVPs to the NAS.

   NAS                       Local proxy agent               Home server
    |                                :                                |
    | Diameter-EAP-Request           :                                |
    | Auth-Request-Type=AUTHENTICATE_ONLY                             |
    | EAP-Payload(EAP Start)         :                                |
    |---------------------------------------------------------------->|
    |                                :                                |
    |                                :            Diameter-EAP-Answer |
    |                           Result-Code=DIAMETER_MULTI_ROUND_AUTH |
    |                                :       EAP-Payload(EAP Request) |
    |<----------------------------------------------------------------|
    |                                :                                |
    :              ...more EAP Request/Response pairs...              :
    |                                :                                |
    | Diameter-EAP-Request           :                                |
    | EAP-Payload(EAP Response)      :                                |
    |---------------------------------------------------------------->|
    |                                :                                |
    |                                :            Diameter-EAP-Answer |
    |                                :   Result-Code=DIAMETER_SUCCESS |
    |                                :       EAP-Payload(EAP Success) |
    |                                :         EAP-Master-Session-Key |
    |                                :           (authorization AVPs) |
    |<----------------------------------------------------------------|
    |                                |                                |
    | AA-Request                     |                                |
    | Auth-Request-Type=AUTHORIZE_ONLY                                |
    | (some AVPs from first session) |                                |
    |------------------------------->|                                |
    |                                |                                |
    |                      AA-Answer |                                |
    |   Result-Code=DIAMETER_SUCCESS |                                |
    |           (authorization AVPs) |                                |
    |<-------------------------------|                                |

   The NASREQ application is used here for authorization because the
   realm-specific routing table does support routing based on
   application, but not more...TO BE CLARIFIED.

   A second possibility is that the home server signals the NAS to



Eronen, et al.           Expires April 23, 2004                [Page 10]

Internet-Draft          Diameter EAP Application            October 2003


   perform a separate authorization step.  In this case, the NAS begins
   the Diameter EAP session with
   Auth-Request-Type=AUTHORIZE_AUTHENTICATE.  The last
   Diameter-EAP-Answer from the home server contains
   Result-Code=DIAMETER_LIMITED_SUCCESS, so the NAS does additional
   AUTHORIZE_ONLY NASREQ step.

   NAS                       Local proxy agent               Home server
    |                                :                                |
    | Diameter-EAP-Request           :                                |
    | Auth-Request-Type=AUTHORIZE_AUTHENTICATE                        |
    | EAP-Payload(EAP Start)         :                                |
    |---------------------------------------------------------------->|
    |                                :                                |
    |                                :            Diameter-EAP-Answer |
    |                           Result-Code=DIAMETER_MULTI_ROUND_AUTH |
    |                                :       EAP-Payload(EAP Request) |
    |<----------------------------------------------------------------|
    |                                :                                |
    :              ...more EAP Request/Response pairs...              :
    |                                :                                |
    | Diameter-EAP-Request           :                                |
    | EAP-Payload(EAP Response)      :                                |
    |---------------------------------------------------------------->|
    |                                :                                |
    |                                :            Diameter-EAP-Answer |
    |                            Result-Code=DIAMETER_LIMITED_SUCCESS |
    |                                :       EAP-Payload(EAP Success) |
    |                                :         EAP-Master-Session-Key |
    |                                :           (authorization AVPs) |
    |<----------------------------------------------------------------|
    |                                |                                |
    | AA-Request                     |                                |
    | Auth-Request-Type=AUTHORIZE_ONLY                                |
    | (some AVPs from first session) |                                |
    |------------------------------->|                                |
    |                                |                                |
    |                      AA-Answer |                                |
    |   Result-Code=DIAMETER_SUCCESS |                                |
    |           (authorization AVPs) |                                |
    |<-------------------------------|                                |










Eronen, et al.           Expires April 23, 2004                [Page 11]

Internet-Draft          Diameter EAP Application            October 2003


2.3.4 Scenario 4: Proxy agents

   Same as scenario 1, but through proxies.  Note that in this case the
   proxies can see the EAP session keys, so this is not suitable for
   environments where proxies can't be trusted for this.

   NAS                    Local proxy/relay agent            Home server
    |                                |                                |
    |  Diameter-EAP-Request          |                                |
    |  Auth-Request-Type=AUTHORIZE_AUTHENTICATE                       |
    |  EAP-Payload(EAP Start)        |                                |
    |------------------------------->|------------------------------->|
    |                                |                                |
    |                                |           Diameter-EAP-Answer  |
    |                          Result-Code=DIAMETER_MULTI_ROUND_AUTH  |
    |                                |      EAP-Payload(EAP Request)  |
    |<-------------------------------|<-------------------------------|
    |                                :                                |
    :              ...more EAP Request/Response pairs...              :
    |                                :                                |
    |  Diameter-EAP-Request          |                                |
    |  EAP-Payload(EAP Response)     |                                |
    |------------------------------->|------------------------------->|
    |                                |                                |
    |                                |           Diameter-EAP-Answer  |
    |                                |  Result-Code=DIAMETER_SUCCESS  |
    |                                |      EAP-Payload(EAP Success)  |
    |                                |        EAP-Master-Session-Key  |
    |                                |          (authorization AVPs)  |
    |<-------------------------------|<-------------------------------|


2.4 Invalid packets

   While acting as a pass-through, the NAS MUST validate the EAP header
   fields (Code, Identifier, Length) prior to forwarding an EAP packet
   to or from the Diameter server.  On receiving an EAP packet from the
   peer, the NAS checks the Code (2) and Length fields, and matches the
   Identifier value against the current Identifier, supplied by the
   Diameter server in the most recently validated EAP Request.  On
   receiving an EAP packet from the Diameter server (encapsulated within
   a Diameter-EAP-Answer), the NAS checks the Code (1) and Length
   fields, then updates the current Identifier value.  Pending EAP
   Responses that do not match the current Identifier value are silently
   discarded by the NAS.

   Since EAP method fields (Type, Type-Data) are typically not validated
   by a NAS operating as a pass-through, despite these checks it is



Eronen, et al.           Expires April 23, 2004                [Page 12]

Internet-Draft          Diameter EAP Application            October 2003


   possible for a NAS to forward an invalid EAP packet to or from the
   Diameter server.

   A Diameter server receiving an EAP-Payload AVP it does not understand
   SHOULD make the determination of whether the error is fatal or
   non-fatal based on the EAP Type.  A Diameter server determining that
   a fatal error has occurred MUST send an a Diameter-EAP-Answer with a
   failure Result-Code and an EAP-Payload AVP encapsulating an EAP
   Failure packet.  A Diameter server determining that a non-fatal error
   has occurred MUST send a Diameter-EAP-Answer with
   DIAMETER_MULTI_ROUND_AUTH Result-Code, but no EAP-Payload AVP.  To
   simplify RADIUS translation, this message MUST also include an
   EAP-Reissued-Payload AVP encapsulating the previous EAP Request sent
   by the server.

   When receiving a Diameter-EAP-Answer without an EAP-Payload AVP (and
   DIAMETER_MULTI_ROUND_AUTH Result-Code), the NAS SHOULD discard the
   EAP-Response packet most recently transmitted to the Diameter server
   and check whether additional EAP Response packets have been received
   matching the current Identifier value.  If so, a new EAP Response
   packet, if available, MUST be sent to the Diameter server within an
   Diameter-EAP-Request.  If no EAP Response packet is available, then
   the previous EAP Request is resent to the peer, and the
   retransmission timer is reset.

   In order to provide protection against Denial of Service (DoS)
   attacks, it is advisable for the NAS to allocate a finite buffer for
   EAP packets received from the peer, and to discard packets according
   to an appropriate policy once that buffer has been exceeded.  Also,
   the Diameter server is advised to permit only a modest number of
   invalid EAP packets within a single session, prior to terminating the
   session with TBD.  By default a value of 5 invalid EAP packets is
   recommended.

2.5 Retransmission

   As noted in [RFC2284bis], if an EAP packet is lost in transit between
   the authenticating peer and the NAS (or vice versa), the NAS will
   retransmit.

   It may be necessary to adjust retransmission strategies and
   authentication timeouts in certain cases.  For example, when a token
   card is used, additional time may be required to allow the user to
   find the card and enter the token.  Since the NAS will typically not
   have knowledge of the required parameters, these need to be provided
   by the Diameter server.

   If a Multi-Round-Time-Out AVP [BASE] is present in an



Eronen, et al.           Expires April 23, 2004                [Page 13]

Internet-Draft          Diameter EAP Application            October 2003


   Diameter-EAP-Answer message that also contains an EAP-Payload AVP,
   that value is used to set the EAP retransmission timer for that EAP
   Request, and that Request alone.

2.6 Fragmentation

   Using the EAP-Payload AVP, it is possible for the Diameter server to
   encapsulate an EAP packet that is larger than the MTU on the link
   between the NAS and the peer.  Since it is not possible for the
   Diameter server to use MTU discovery to ascertain the link MTU, a
   Framed-MTU AVP may be included in a Diameter-EAP-Request message so
   as to provide the Diameter server with this information.

   A Diameter server having received a Framed-MTU AVP in a
   Diameter-EAP-Request message MUST NOT send any subsequent packet in
   this EAP conversation containing EAP-Payload AVP whose length exceeds
   the length specified by the Framed-MTU value, taking the link type
   (specified by the NAS-Port-Type AVP) into account. For example, as
   noted in [RFC3580] Section 3.10, for a NAS-Port-Type value of IEEE
   802.11, the RADIUS server may send an EAP packet as large as
   Framed-MTU minus four (4) octets, taking into account the additional
   overhead for the IEEE 802.1X Version (1), Type (1) and Body Length
   (2) fields.

2.7 Accounting

   When a user is authenticated using EAP, the NAS MAY include an
   Accounting-Auth-Method AVP [NASREQ] with value 5 (EAP) in
   Accounting-Request messages. This document specifies one additional
   AVP for accounting messages: one or more Accounting-EAP-Auth-Method
   AVPs (see Section 4.1.4) MAY be included in Accounting-Request
   messages to indicate the EAP method(s) used to authenticate the user.

   If the NAS has authenticated the user with a locally implemented EAP
   method, it knows the method used and SHOULD include it in an
   Accounting-EAP-Auth-Method AVP.

   If the authentication was done using Diameter-EAP-Request/Answer
   messages, the Diameter server SHOULD include one more more
   Accounting-EAP-Auth-Method AVPs in Diameter-EAP-Answer packets with a
   successful result code.  In this case, the NAS SHOULD include these
   AVPs in Accounting-Request messages.

2.8 Usage guidelines

2.8.1 User-Name AVP

   Unless the access device interprets the EAP-Response/Identity packet



Eronen, et al.           Expires April 23, 2004                [Page 14]

Internet-Draft          Diameter EAP Application            October 2003


   returned by the authenticating peer, it will not have access to the
   user's identity.  Furthermore, some EAP methods support identity
   protection where the user's real identity is not included in
   EAP-Response/Identity.  Therefore, the Diameter Server SHOULD return
   the user's identity by inserting it in the User-Name AVP of
   subsequent Diameter-EAP-Answer packets.  Without the user's identity,
   the Session-Id AVP MAY be used for accounting and billing, however
   operationally this could be very difficult to manage.

2.8.2 Conflicting AVPs

   A Diameter-EAP-Answer message containing an EAP-Payload of type
   EAP-Success or EAP-Failure MUST NOT have the Result-Code AVP set to
   DIAMETER_MULTI_ROUND_AUTH.  Also, the Result-Code SHOULD match the
   contained EAP packet (successful Result-Code if EAP-Success, and a
   failure Result-Code for EAP-Failure).  TO BE WRITTEN: clarify this.

2.8.3 Displayable messages

   The Reply-Message AVP [NASREQ] contains text which may be displayed
   to the user.  Note that the NAS does not necessarily have any
   facility for actually sending these messages to the user.  In any
   case, the NAS MUST NOT manufacture any EAP packets (such as
   EAP-Request/Notification) from Reply-Message AVPs.

2.8.4 Role reversal

   Some environments where EAP is used, such as PPP, support
   peer-to-peer operation.  That is, both parties act as authenticators
   and authenticatees at the same time, in two simultaneous and
   independent EAP conversations.

   This specification is intended for communication between EAP
   (passthrough) authenticator and backend authentication server.  A
   Diameter client MUST NOT send a Diameter-EAP-Request encapsulating an
   EAP Request packet, and a Diameter server receiving such packet MUST
   respond with a failure Result-Code..

2.8.5 Alternative Uses

   Currently the conversation between the backend authentication server
   and the Diameter server is proprietary because of lack of
   standardization.  In order to increase standardization and provide
   interoperability between Diameter vendors and backend security
   vendors, it is recommended that Diameter-encapsulated EAP be used for
   this conversation.

   This has the advantage of allowing the Diameter server to support EAP



Eronen, et al.           Expires April 23, 2004                [Page 15]

Internet-Draft          Diameter EAP Application            October 2003


   without the need for authentication-specific code within the Diameter
   server.  Authentication-specific code can then reside on a back-end
   authentication server instead.

   In the case where Diameter-encapsulated EAP is used in a conversation
   between a Diameter server and a backend authentication server, the
   latter will typically return an Diameter-EAP-Answer/EAP-Payload/
   EAP-Success message without inclusion of the expected authorization
   AVPs required in a successful response.  This means that the Diameter
   server MUST add these attributes prior to sending an
   Diameter-EAP-Answer/EAP-Payload/EAP-Success message to the access
   device.

3. Command-Codes

   This section defines new Command-Code values that MUST be supported
   by all Diameter implementations conforming to this specification.
   The following Command Codes are defined in this section:

      Command-Name             Abbrev.    Code       Reference
      --------------------------------------------------------
      Diameter-EAP-Request      DER       268          3.1
      Diameter-EAP-Answer       DEA       268          3.2


3.1 Diameter-EAP-Request (DER) Command

   The Diameter-EAP-Request (DER) command, indicated by the Command-Code
   field set to 268 and the 'R' bit set in the Command Flags field, is
   sent by a Diameter client to a Diameter server and conveys an
   EAP-Response from the EAP client.  The Diameter-EAP-Request MUST
   contain one EAP-Payload AVP, which contains the actual EAP payload.
   An EAP-Payload AVP with no data MAY be sent to the Diameter server to
   initiate an EAP authentication session.

   The DER message MAY be the result of a multi-round authentication
   exchange, which occurs when the DEA is received with the Result-Code
   AVP set to DIAMETER_MULTI_ROUND_AUTH [BASE].  A subsequent DER
   message MUST include any State AVPs [NASREQ] that were present in the
   DEA.  For re-authentication, it is recommended that the Identity
   request be skipped in order to reduce the number of authentication
   round trips.  This is only possible when the user's identity is
   already known by the home Diameter server.

   Message format

      <Diameter-EAP-Request> ::= < Diameter Header: 268, REQ, PXY >
                                 < Session-Id >



Eronen, et al.           Expires April 23, 2004                [Page 16]

Internet-Draft          Diameter EAP Application            October 2003


                                 { Auth-Application-Id }
                                 { Origin-Host }
                                 { Origin-Realm }
                                 { Destination-Realm }
                                 { Auth-Request-Type }
                                 [ NAS-Port ]
                                 [ NAS-Port-Id ]
                                 [ Origin-State-Id ]
                                 [ Destination-Host ]
                                 [ NAS-Identifier ]
                                 [ NAS-IP-Address ]
                                 [ NAS-IPv6-Address ]
                                 [ NAS-Port-Type ]
                                 [ Port-Limit ]
                                 [ User-Name ]
                                 { EAP-Payload }
                                 [ Service-Type ]
                                 [ Idle-Timeout ]
                                 [ State ]
                                 [ Authorization-Lifetime ]
                                 [ Auth-Grace-Period ]
                                 [ Auth-Session-State ]
                                 [ Session-Timeout ]
                                 [ Callback-Number ]
                                 [ Called-Station-Id ]
                                 [ Calling-Station-Id ]
                               * [ Class ]
                                 [ Originating-Line-Info ]
                                 [ Connect-Info ]
                               * [ Framed-Compression ]
                                 [ Framed-Interface-Id ]
                                 [ Framed-IP-Address ]
                               * [ Framed-IPv6-Prefix ]
                                 [ Framed-IP-Netmask ]
                                 [ Framed-MTU ]
                                 [ Framed-Protocol ]
                               * [ Tunneling ]
                               * [ Proxy-Info ]
                               * [ Route-Record ]
                               * [ AVP ]


3.2 Diameter-EAP-Answer (DEA) Command

   The Diameter-EAP-Answer (DEA) message, indicated by the Command-Code
   field set to 268 and the 'R' bit cleared in the Command Flags field,
   is sent by the Diameter server to the client for one of the following
   reasons:



Eronen, et al.           Expires April 23, 2004                [Page 17]

Internet-Draft          Diameter EAP Application            October 2003


   1.  The message is part of a multi-round authentication exchange, and
       the server is expecting a subsequent Diameter-EAP-Request.  This
       is indicated by setting the Result-Code to
       DIAMETER_MULTI_ROUND_AUTH, and MAY include zero or more State
       AVPs.

   2.  the EAP client has been successfully authenticated and
       authorized, in which case the message MUST include the
       Result-Code AVP indicating success, and SHOULD include an
       EAP-Payload of type EAP-Success.  This event MUST cause the
       access device to provide service to the EAP client.

   3.  The EAP client has not been successfully authenticated and/or
       authorized, and the Result-Code AVP is set to indicate failure.
       This message SHOULD include an EAP-Payload, but this AVP is not
       used to determine whether service is to be provided.

   If the message from the Diameter client included a request for
   authorization, a successful response MUST include the authorization
   AVPs that are relevant to the service being provided.

   Message format


      <Diameter-EAP-Answer> ::= < Diameter Header: 268, PXY >
                                < Session-Id >
                                { Auth-Application-Id }
                                { Auth-Request-Type }
                                { Result-Code }
                                { Origin-Host }
                                { Origin-Realm }
                                [ User-Name ]
                                [ EAP-Payload ]
                                [ Multi-Round-Time-Out ]
                                [ Service-Type ]
                              * [ Class ]
                              * [ Configuration-Token ]
                                [ Acct-Interim-Interval ]
                                [ Error-Message ]
                                [ Error-Reporting-Host ]
                                [ Idle-Timeout ]
                                [ Authorization-Lifetime ]
                                [ Auth-Grace-Period ]
                                [ Auth-Session-State ]
                                [ Re-Auth-Request-Type ]
                                [ Session-Timeout ]
                                [ State ]
                              * [ Reply-Message ]



Eronen, et al.           Expires April 23, 2004                [Page 18]

Internet-Draft          Diameter EAP Application            October 2003


                                [ Origin-State-Id ]
                              * [ Filter-Id ]
                                [ Port-Limit ]
                                [ Callback-Id ]
                                [ Callback-Number ]
                                [ Framed-Appletalk-Link ]
                              * [ Framed-Appletalk-Network ]
                                [ Framed-Appletalk-Zone ]
                              * [ Framed-Compression ]
                                [ Framed-Interface-Id ]
                                [ Framed-IP-Address ]
                              * [ Framed-IPv6-Prefix ]
                                [ Framed-IPv6-Pool ]
                              * [ Framed-IPv6-Route ]
                                [ Framed-IP-Netmask ]
                              * [ Framed-Route ]
                                [ Framed-Pool ]
                                [ Framed-IPX-Network ]
                                [ Framed-MTU ]
                                [ Framed-Protocol ]
                                [ Framed-Routing ]
                              * [ NAS-Filter-Rule ]
                              * [ Tunneling ]
                              * [ Redirect-Host ]
                                [ Redirect-Host-Usage ]
                                [ Redirect-Max-Cache-Time ]
                              * [ Proxy-Info ]
                              * [ AVP ]


4. Attribute-Value Pairs

   This section both defines new AVPs, unique to the EAP Diameter
   application and describes the usage of AVPs defined elsewhere if that
   usage in the EAP application is noteworthy.

4.1 New AVPs

4.1.1 EAP-Payload AVP

   The EAP-Payload AVP (AVP Code TBD) is of type OctetString and is used
   to encapsulate the actual EAP packet that is being exchanged between
   the EAP client and the home Diameter server.

4.1.2 EAP-Reissued-Payload AVP

   The EAP-Reissued-Payload AVP (AVP Code TBD) is of type OctetString.
   The use of this AVP is described in Section 2.4.



Eronen, et al.           Expires April 23, 2004                [Page 19]

Internet-Draft          Diameter EAP Application            October 2003


4.1.3 EAP-Master-Session-Key AVP

   The EAP-Master-Session-Key AVP (AVP Code TBD) is of type OctetString.
   It is used by the Diameter server...TBD

4.1.4 Accounting-EAP-Auth-Method AVP

   The Accounting-EAP-Auth-Method AVP (AVP Code TBD) is of type
   Unsigned64.  In case of expanded types [RFC2284bis, Section 5.7], the
   least significant 32 bits contain the Vendor-Type field, and the next
   24 bits contain the Vendor-Id field.

   The use of this AVP is described in Section 2.7.

5. AVP Occurrence Tables

   The following tables use these symbols:

      0     The AVP MUST NOT be present in the message
      0+    Zero or more instances of the AVP MAY be present in the
            message
      0-1   Zero or one instance of the AVP MAY be present in the
            message
      1     One instance of the AVP MUST be present in the message

   Note that AVPs that can only be present within a Grouped AVP are not
   represented in these tables.

5.1 EAP Command AVP Table

   The following table lists the AVPs that may be present in the DER and
   DEA Commands, defined in this document; however, the AVPs listed are
   defined both here and in [NASREQ].

                                       +---------------+
                                       |  Command-Code |
                                       |-------+-------+
   Attribute Name                      |  DER  |  DEA  |
   ------------------------------------|-------+-------|
   Accounting-EAP-Auth-Method          |   0   |   0+  |
   Acct-Interim-Interval [BASE]        |   0   |  0-1  |
   Auth-Application-Id [BASE]          |   1   |   1   |
   Auth-Grace-Period [BASE]            |  0-1  |  0-1  |
   Auth-Request-Type [BASE]            |   1   |   1   |
   Auth-Session-State [BASE]           |  0-1  |  0-1  |
   Authorization-Lifetime [BASE]       |  0-1  |  0-1  |
   Callback-Id [NASREQ]                |   0   |  0-1  |
   Callback-Number [NASREQ]            |  0-1  |  0-1  |



Eronen, et al.           Expires April 23, 2004                [Page 20]

Internet-Draft          Diameter EAP Application            October 2003


   Called-Station-Id [NASREQ]          |  0-1  |   0   |
   Calling-Station-Id [NASREQ]         |  0-1  |   0   |
   Class [BASE]                        |   0+  |   0+  |
   Configuration-Token [NASREQ]        |   0   |   0+  |
   Connect-Info [NASREQ]               |  0-1  |   0   |
   Destination-Host [BASE]             |  0-1  |   0   |
   Destination-Realm [BASE]            |   1   |   0   |
   EAP-Payload                         |   1   |  0-1  |
   Error-Message [BASE]                |   0   |  0-1  |
   Error-Reporting-Host [BASE]         |   0   |  0-1  |
   Failed-AVP [BASE]                   |   0+  |   0+  |
   Filter-Id [NASREQ]                  |   0   |   0+  |
   Framed-Appletalk-Link [NASREQ]      |   0   |  0-1  |
   Framed-Appletalk-Network [NASREQ]   |   0   |   0+  |
   Framed-Appletalk-Zone [NASREQ]      |   0   |  0-1  |
   Framed-Compression [NASREQ]         |   0+  |   0+  |
   Framed-Interface-Id [NASREQ]        |  0-1  |  0-1  |
   Framed-IP-Address [NASREQ]          |  0-1  |  0-1  |
   Framed-IP-Netmask [NASREQ]          |  0-1  |  0-1  |
   Framed-IPv6-Prefix [NASREQ]         |   0+  |   0+  |
   Framed-IPv6-Pool [NASREQ]           |   0   |  0-1  |
   Framed-IPv6-Route [NASREQ]          |   0   |   0+  |
   Framed-IPX-Network [NASREQ]         |   0   |  0-1  |
   Framed-MTU [NASREQ]                 |  0-1  |  0-1  |
   Framed-Pool [NASREQ]                |   0   |  0-1  |
   Framed-Protocol [NASREQ]            |  0-1  |  0-1  |
   Framed-Route [NASREQ]               |   0   |   0+  |
   Framed-Routing [NASREQ]             |   0   |  0-1  |
   Idle-Timeout [NASREQ]               |  0-1  |  0-1  |
   Multi-Round-Time-Out [BASE]         |   0   |  0-1  |
   NAS-Filter-Rule [NASREQ]            |   0   |   0+  |
   NAS-Identifier [NASREQ]             |  0-1  |   0   |
   NAS-IP-Address [NASREQ]             |  0-1  |   0   |
   NAS-IPv6-Address [NASREQ]           |  0-1  |   0   |
   NAS-Port [NASREQ]                   |  0-1  |   0   |
   NAS-Port-Id [NASREQ]                |  0-1  |   0   |
   NAS-Port-Type [NASREQ]              |  0-1  |   0   |
   Originating-Line-Info [NASREQ]      |  0-1  |   0   |
   Origin-Host [BASE]                  |   1   |   1   |
   Origin-Realm [BASE]                 |   1   |   1   |
   Origin-State-Id [BASE]              |  0-1  |  0-1  |
   Port-Limit [NASREQ]                 |  0-1  |  0-1  |
   Proxy-Info [BASE]                   |   0+  |   0+  |
   Re-Auth-Request-Type [BASE]         |   0   |  0-1  |
   Redirect-Host [BASE]                |   0   |   0+  |
   Redirect-Host-Usage [BASE]          |   0   |  0-1  |
   Redirect-Max-Cache-Time [BASE]      |   0   |  0-1  |
   Reply-Message [NASREQ]              |   0   |   0+  |



Eronen, et al.           Expires April 23, 2004                [Page 21]

Internet-Draft          Diameter EAP Application            October 2003


   Result-Code [BASE]                  |   0   |   1   |
   Route-Record [BASE]                 |   0+  |   0+  |
   Service-Type [NASREQ]               |  0-1  |  0-1  |
   Session-Id [BASE]                   |   1   |   1   |
   Session-Timeout [BASE]              |  0-1  |  0-1  |
   State [NASREQ]                      |  0-1  |  0-1  |
   Tunneling [NASREQ]                  |   0+  |   0+  |
   User-Name [BASE]                    |  0-1  |  0-1  |


5.2 Accounting AVP Table

   The table in this section is used to represent which AVPs defined in
   this document are to be present in the Accounting messages, defined
   in [BASE].

                                          +-----------+
                                          |  Command  |
                                          |    Code   |
                                          |-----+-----+
   Attribute Name                         | ACR | ACA |
   ---------------------------------------|-----+-----+
   Accounting-EAP-Auth-Method             |  0+ |  0  |


6. RADIUS/Diameter interactions

   Section 9 of [NASREQ] describes basic guidelines that translation
   agents may follow when translating between RADIUS and Diameter
   protocols.  This section gives additional guidelines for the Diameter
   EAP application.  Note that this document does not restrict
   implementations from creating additional methods, as long as the
   translation function doesn't violate the RADIUS or the Diameter
   protocols.

6.1 RADIUS Request forwarded as Diameter Request

   RADIUS Access-Request to Diameter-EAP-Request:

   o  RADIUS EAP-Message attribute(s) are translated to a Diameter
      EAP-Payload AVP.  If multiple RADIUS EAP-Message attributes are
      present, they are concatenated and translated to a single Diameter
      EAP-Payload AVP.

   o  An empty RADIUS EAP-Message attribute (with length 2) signifies
      EAP-Start, and it is translated to an empty EAP-Payload AVP.





Eronen, et al.           Expires April 23, 2004                [Page 22]

Internet-Draft          Diameter EAP Application            October 2003


   Diameter-EAP-Answer to RADIUS Access-Accept/Reject/Challenge:

   o  Diameter EAP-Payload AVP is translated to RADIUS EAP-Message
      attribute(s).  If necessary, the value is split into multiple
      RADIUS EAP-Message attributes.

   o  Diameter EAP-Reissued-Payload AVP is translated to a message that
      contains RADIUS EAP-Message attribute(s), and a RADIUS Error-Cause
      attribute [RFC3576] with value 202 (decimal), "Invalid EAP Packet
      (Ignored)" [RFC3579].

   o  As described in [NASREQ], if the Result-Code AVP set to
      DIAMETER_MULTI_ROUND_AUTH and the Multi-Round-Time-Out AVP is
      present, it is translated to the RADIUS Session-Timeout attribute.

   o  Diameter EAP-Master-Session-Key AVP can be translated to the
      vendor-specific RADIUS MS-MPPE-Recv-Key and MS-MPPE-Send-Key
      attributes [RFC2548].  The first up to 32 octets of the key is
      stored into MS-MPPE-Recv-Key, and the next up to 32 octets (if
      present) are stored into MS-MPPE-Send-Key.

   o  Diameter Accounting-EAP-Auth-Method AVPs, if present, are
      discarded.


6.2 Diameter Request forwarded as RADIUS Request

   Diameter-EAP-Request to RADIUS Access-Request:

   o  The Diameter EAP-Payload AVP is translated to RADIUS EAP-Message
      attribute(s).

   o  An empty Diameter EAP-Payload AVP signifies EAP-Start, and it is
      translated to an empty RADIUS EAP-Message attribute.

   o  The type (or expanded type) field from the EAP-Payload AVP can be
      saved either in a local state table, or encoded in a RADIUS
      Proxy-State attribute.  This information is needed to construct an
      Accounting-EAP-Auth-Method AVP for the answer message (see below).

   RADIUS Access-Accept/Reject/Challenge to Diameter-EAP-Answer:

   o  If the RADIUS Access-Challenge message does not contain an
      Error-Cause attribute [RFC3576] with value 202 (decimal), "Invalid
      EAP Packet (Ignored)" [RFC3579], any RADIUS EAP-Message attributes
      are translated to a Diameter EAP-Payload AVP, concatenating them
      if multiple attributes are present.




Eronen, et al.           Expires April 23, 2004                [Page 23]

Internet-Draft          Diameter EAP Application            October 2003


   o  If the Error-Cause attribute with value 202 is present, any RADIUS
      EAP-Message attributes are translated to a Diameter
      EAP-Reissued-Payload AVP, concatenating them if multiple
      attributes are present.

   o  As described in [NASREQ], if the Session-Timeout attribute is
      present in a RADIUS Access-Challenge message, it is translated to
      the Diameter Multi-Round-Time-Out AVP.

   o  If the vendor-specific RADIUS MS-MPPE-Recv-Key and/or
      MS-MPPE-Send-Key attributes [RFC2548] are present, they can be
      translated to a Diameter EAP-Master-Session-Key AVP.  Their values
      are concatenated (MS-MPPE-Recv-Key first, MS-MPPE-Send-Key next),
      and the concatenated value is stored into a Diameter
      EAP-Master-Session-Key AVP.

   o  If the Diameter-EAP-Answer will have a successful result code, the
      saved state (see above) can be used to construct an
      Accounting-EAP-Auth-Method AVP.


6.3 Accounting Requests

   In Accounting-Requests, the vendor-specific RADIUS MS-Acct-EAP-Type
   attribute [RFC2548] can be translated to a Diameter
   Accounting-EAP-Auth-Method AVP, and vice versa.

   When translating from Diameter to RADIUS, note that the
   MS-Acct-EAP-Type attribute does not support expanded EAP types.  Type
   values greater than 255 should be translated to type 254.

7. IANA Considerations

   This document does not create any new namespaces to be maintained by
   IANA, but it requires new values in namespaces that have been defined
   in the Diameter Base protocol [BASE].

   o  IANA has assigned a Command Code value of TBD-BY-IANA (suggested
      value: 268) for the Diameter-EAP-Request/Diameter-EAP-Answer
      command (in the Command Code namespace defined in [BASE]).

   o  IANA has assigned the following AVP Code values for the new AVPs
      defined in this document (in the AVP Code namespace defined in
      [BASE]).

      AVP name                       Code
      -----------------------------------
      EAP-Payload                     TBD



Eronen, et al.           Expires April 23, 2004                [Page 24]

Internet-Draft          Diameter EAP Application            October 2003


      EAP-Reissued-Payload            TBD
      EAP-Master-Session-Key          TBD
      Accounting-EAP-Auth-Method      TBD

   o  IANA has assigned an Application Identifier value of TBD-BY-IANA
      for this specification (in the Application Identifier namespace
      defined in [BASE]).


8. Security Considerations

8.1 Overview

   Diameter peer-to-peer connections can be protected with IPsec or TLS.
   These mechanisms are believed to provide sufficient protection under
   the normal Internet threat model--that is, assuming the authorized
   nodes engaging in the protocol have not been compromised, but the
   attacker has complete control over the communication channels between
   them.  This includes eavesdropping, message modification, insertion,
   man-in-the-middle and replay attacks.  The details and related
   security considerations are discussed in [BASE].

   In addition to authentication provided by IPsec or TLS, authorization
   is also required.  Authorization here means the act of determining if
   a Diameter message received from an authenticated Diameter peer
   should be accepted (and not authorization of users requesting network
   access from a NAS).  In other words, when a Diameter server receives
   a Diameter-EAP-Request, it has to decide if the client is authorized
   to act as a NAS for the specific user, service type, and so on.
   Correspondingly, when a NAS contacts a server to send a
   Diameter-EAP-Request, it has to determine whether the server is
   authorized to act as home server for the realm in question.

   Authorization can involve local Access Control Lists (ACLs),
   information contained in certificates, or some other means.  See
   [BASE] for more discussion and related security considerations.

   The hop-by-hop security mechanisms (IPsec and TLS) combined with
   proper authorization provide good protection against "outside"
   attackers (denial-of-service is, of course, possible).  The remaining
   part of this section deals with attacks by nodes that have been
   properly authorized (to function as a NAS, Diameter agent, or
   Diameter server) but abuse their authorization or have been
   compromised.  In general, it is not possible to completely protect
   against attacks by compromised nodes, but this section offers some
   advice that can be used to limit the extent of the damage.

   Attacks involving eavesdropping or modification of EAP messages are



Eronen, et al.           Expires April 23, 2004                [Page 25]

Internet-Draft          Diameter EAP Application            October 2003


   beyond the scope of these document. See [RFC2284bis] for discussion
   of these security considerations (including method negotation,
   dictionary attacks, and privacy issues). While these attacks can be
   carried out by an attacker between the client and the NAS,
   compromised NASes and Diameter agents are naturally also in a good
   position to modify and eavesdrop the EAP messages.

   Similarly, attacks involving whatever link layer protocol is used
   between the client and the NAS, such as PPP or IEEE 802.11, are
   beyond the scope of this document.

8.2 AVP editing

   Diameter agents can modify, insert, and delete AVPs. Diameter agents
   are usually meant to modify AVPs, and the protocol in general cannot
   distinguish well-intentioned and malicious modifications (see
   [RFC2607] for more discussion). Similarly, a compromised NAS or
   server can naturally include different set of AVPs than expected.

   The question is thus "what can an attacker who compromises an
   authorized NAS, agent, or server do using Diameter EAP messages?"
   Some of the consequences are rather obvious--for instance, a Diameter
   agent can give access to unauthorized users by changing the
   Result-Code to DIAMETER_SUCCESS. Other consequences are less obvious,
   and are discussed below (authentication method negotiation attacks
   are discussed in the next section).

   By including suitable AVPs in an AA-Answer/Diameter-EAP-Answer
   messages an attacker (depending on implementation and configuration
   details) may be able to:

   o  Give unauthorized users access, or deny access to authorized users
      (Result-Code).

   o  Give attacker a login session to a host otherwise protected by
      firewalls, or redirect an authorized user's login session to a
      host controlled by the attacker (Login-Host).

   o  Route an authorized user's traffic through a host controlled by
      the attacker (various tunneling AVPs).

   o  Redirect an authorized user's DNS requests to a malicious DNS
      server (various vendor-specific AVPs).

   o  Modify routing tables at the NAS and thus redirect packets
      destined for someone else (Framed-Route, Framed-Routing).

   o  Remove packet filters and other restrictions for user (Filter,



Eronen, et al.           Expires April 23, 2004                [Page 26]

Internet-Draft          Diameter EAP Application            October 2003


      Callback, various vendor-specific AVPs).

   o  Cause the NAS to call some number, possibly expensive toll number
      controlled by the attacker (callback AVPs)

   o  Execute Command Line Interface (CLI) commands on the NAS (various
      vendor-specific attributes).

   By modifying an AA-Request/Diameter-EAP-Request, an attacker may be
   able to:

   o  Change NAS-Identifier/NAS-Port/Origin-Host (or something) so that
      a valid user appears to be accessing the network from a different
      NAS than in reality.

   o  Modify Calling-Station-ID (either to hide the true value, gain
      access, or frame someone else).

   o  Modify password change messages (some vendor-specific attributes)

   o  Modify usage information in accounting messages.

   o  Modify contents of Class and State AVPs.

   Some of these attacks can be prevented if the NAS or server can be
   configured not to accept some particular AVPs, or accepting them only
   from some nodes.

8.3 Negotiation attacks

   This section deals with attacks where the NAS, any Diameter agents,
   or Diameter server attempts to cause the authenticating user to
   choose some authentication method other than EAP, such as PAP or CHAP
   (negotiation attacks within EAP are discussed in [RFC2284bis],
   Section 7.8).

   The vulnerability can be mitigated via implementation of
   per-connection policy on the part of the authenticating peer, and
   per-peer policy on the part of the Diameter server.  For the
   authenticating peer, authentication policy should be set on a
   per-connection basis.

   With per-connection policy, an authenticating peer will only attempt
   to negotiate EAP for a session in which EAP support is expected.  As
   a result, there is a presumption that an authenticating peer
   selecting EAP requires that level of security. If it cannot be
   provided, it is likely that there is some kind of misconfiguration,
   or even that the authenticating peer is contacting the wrong server.



Eronen, et al.           Expires April 23, 2004                [Page 27]

Internet-Draft          Diameter EAP Application            October 2003


   In this case, the authenticating peer simply disconnects.

   Similarly, with a per-user policy, the home server will not accept
   authentication methods other than EAP for users for which EAP support
   is expected.

   For a NAS, it may not be possible to determine whether a peer is
   required to authenticate with EAP until the peer's identity is known.
   For example, for shared-uses NASes it is possible for one reseller to
   implement EAP while another does not.  Alternatively, some peer might
   be authenticated locally by the NAS while other peers are
   authenticated via Diameter.  In such cases, if any peers of the NAS
   MUST do EAP, then the NAS MUST attempt to negotiate EAP for every
   session.  This avoids forcing a peer to support more than one
   authentication type, which could weaken security.

8.4 Session key distribution

   Since there are currently no end-to-end (NAS-to-home server) security
   mechanisms specified for Diameter, any agents that process
   Diameter-EAP-Answer messages can see the contents of the
   EAP-Session-Key AVP.  For this reason, this specification strongly
   recommends avoiding Diameter agents when they cannot be trusted to
   keep the keys secret.

   In environments where agents are present, several factors should be
   considered when deciding whether the agents that are authorized (and
   considered "trustworthy enough") to grant access to users and specify
   various authorization and tunneling AVPs are also "trustworthy
   enough" to handle the session keys.  These factors include (but are
   not limited to) the type of access provided (e.g., public Internet or
   corporate internet), security level of the agents, and the
   possibilities for attacking user's traffic after it has been
   decrypted by the NAS.

   Note that the keys communicated in Diameter messages are usually
   short-term session keys (or short-term master keys that are used to
   derive session keys).  To actually cause any damage, those session
   keys must end with some malicious party; that party must be able to
   eavesdrop, modify, or insert traffic between the user and the NAS
   during the lifetime of those keys (e.g., in 802.11i the attacker must
   also eavesdrop the "four-way handshake"); and that eavesdropping or
   modification must cause some damage.

8.5 Privacy issues

   Diameter messages can contain AVPs that can be used to identify the
   user (e.g., User-Name) and approximate location of the user (e.g.



Eronen, et al.           Expires April 23, 2004                [Page 28]

Internet-Draft          Diameter EAP Application            October 2003


   Origin-Host for WLAN access points, Calling-Station-Id for fixed
   phone lines).  Thus, any Diameter nodes that process the messages may
   be able to determine the geographic location of users.

   Note that in many cases, the user identity is also sent in clear
   inside EAP-Payload AVPs, and it may be possible to eavesdrop this
   between the user and the NAS.

   This can mitigated somewhat by using EAP methods that provide
   identity protection (see [RFC2284bis], Section 7.3), and using
   Session-Id or pseudonyms for accounting.

8.6 Note about EAP and impersonation

   If the EAP method used does not provide mutual authentication,
   obviously anyone can impersonate as the network to the user.  Even
   when EAP mutual authentication is used, it occurs between the user
   and the Diameter home server. See [EAPKey] for an extensive
   discussion about the details and their implications.

   However, one issue is worth pointing out here. As described in
   [EAPKey], the current EAP architecture does not allow the home server
   to restrict what service parameters or identities (such as SSID or
   BSSID in 802.11 wireless LANs) are advertised by the NAS to the
   client. That is, a compromised NAS can change its BSSID or SSID, thus
   appearing to offer a different service than intended.  Even if these
   parameters are included in Diameter-EAP-Request messages, the NAS can
   tell different values to the client.

   Thus, the possession of the session keys by the NAS proves that the
   user is talking to *some* authorized NAS, but a compromised NAS can
   lie about its exact identity. See [EAPKey] for discussion how
   individual EAP methods can provide authentication of NAS service
   parameters and identities.

   Note that the usefulness of such authentication may be rather limited
   in many environments. For instance, in wireless LANs the user does
   not usually securely know the identity (such as BSSID) of the "right"
   access point--it's simply picked from a beacon message that has the
   correct SSID and good signal strength (something that's easy to
   spoof). Thus, simply authenticating the identity may not allow the
   user to distinguish the "right" access point from all other ones.

9. Acknowledgements

   This Diameter application relies heavily on earlier work on Diameter
   NASREQ application [NASREQ] and RADIUS EAP support [RFC3579].  Much
   of the material in this specification has been copied from these



Eronen, et al.           Expires April 23, 2004                [Page 29]

Internet-Draft          Diameter EAP Application            October 2003


   documents.

   The authors would also like to acknowledge the following people for
   their contributions to this document: Bernard Aboba, Jari Arkko, Pat
   Calhoun, Henry Haverinen, and John Loughney. (TBD: Who's missing from
   this list?)

Normative References

   [BASE]     Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [EAPKey]   Aboba, B., Simon, D., Arkko, J. and H. Levkowetz, "EAP Key
              Management Framework", draft-ietf-eap-keying-00 (work in
              progress), October 2003.

   [NASREQ]   Calhoun, P., Zorn, G., Spence, D. and D. Mitton, "Diameter
              Network Access Server Application",
              draft-ietf-aaa-diameter-nasreq-13 (work in progress),
              October 2003.

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

   [RFC2284bis]
              Blunk, L., Vollbrecht, J., Aboba, B., Carlson, J. and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)",
              draft-ietf-eap-rfc2284bis-06 (work in progress), September
              2003.

Informative References

   [Archie]   Walker, J. and R. Housley, "The EAP Archie Protocol",
              draft-jwalker-eap-archie-01 (work in progress), June 2003.

   [IEEE-802.1X]
              Institute of Electrical and Electronics Engineers, "Local
              and Metropolitan Area Networks: Port-Based Network Access
              Control", IEEE Standard 802.1X, September 2001.

   [IEEE-802.11i]
              Institute of Electrical and Electronics Engineers,
              "Unapproved Draft Supplement to Standard for
              Telecommunications and Information Exchange Between
              Systems - LAN/MAN Specific Requirements - Part 11:
              Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications: Specification for Enhanced
              Security", IEEE Draft 802.11i (work in progress), 2003.



Eronen, et al.           Expires April 23, 2004                [Page 30]

Internet-Draft          Diameter EAP Application            October 2003


   [IKEv2]    Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
              Protocol", draft-ietf-ipsec-ikev2-11 (work in progress),
              October 2003.

   [RFC1661]  Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
              RFC 1661, July 1994.

   [RFC2548]  Zorn, G., "Microsoft Vendor-specific RADIUS Attributes",
              RFC 2548, March 1999.

   [RFC2607]  Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
              Implementation in Roaming", RFC 2607, June 1999.

   [RFC3576]  Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B.
              Aboba, "Dynamic Authorization Extensions to Remote
              Authentication Dial In User Service (RADIUS)", RFC 3576,
              July 2003.

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

   [RFC3580]  Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese,
              "IEEE 802.1X Remote Authentication Dial In User Service
              (RADIUS) Usage Guidelines", RFC 3580, September 2003.


Authors' Addresses

   Pasi Eronen (editor)
   Nokia Research Center
   P.O. Box 407
   FIN-00045 Nokia Group
   Finland

   EMail: pasi.eronen@nokia.com


   Tom Hiller
   Lucent Technologies
   1960 Lucent Lane
   Naperville, IL  60566
   USA

   Phone: +1 630 979 7673
   EMail: tom.hiller@lucent.com





Eronen, et al.           Expires April 23, 2004                [Page 31]

Internet-Draft          Diameter EAP Application            October 2003


   Glen Zorn
   Cisco Systems
   500 108th Avenue N.E., Suite 500
   Bellevue, WA  98004
   USA

   Phone: +1 425 344 8113
   EMail: gwz@cisco.com

Appendix A. Changelog

   (This section will not appear in the final version submitted to RFC
   editor.)

   Changes from -02 to -03.a:

   o  Updated security considerations section.

   o  Removed the EAP-MTU attribute (use Framed-MTU instead).

   o  Clarified text about invalid packets and EAP-Reissued-Payload AVP.

   o  Added reference to Accounting-Auth-Method AVP to Section 2.7.

   o  Updated ABNFs and AVP occurrence tables to match NASREQ-13.

   o  Updated the IANA considerations to reflect the new AAA parameters
      registry. Changed EAP-Payload and Accounting-EAP-Auth-Method AVP
      codes to "TBD" since they collided with NASREQ codes (issue 429).

   o  Updated references: DynAuth to RFC3576, RFC2869bis to RFC3579,
      RADIUS1X to RFC3580, BASE TO RFC3588, NASREQ to -13, IKEv2 to -11,
      2284bis to -06.

   Version -02.e published as -02.

   Changes from -02.d to -02.e:

   o  Added a section on accounting, and changed how the
      Accounting-EAP-Auth-Method is determined.

   o  Updates to "authorization" and "impersonating as the network"
      security considerations.

   Changes from -02.c to -02.d:

   o  Some clarifications to Introduction section.




Eronen, et al.           Expires April 23, 2004                [Page 32]

Internet-Draft          Diameter EAP Application            October 2003


   o  Lots of clarifications and added diagrams in protocol overview
      section.  Moved non-EAP-supporting servers, User-Name AVP
      guidelines, and conflicting messages to separate sections.

   o  Added a new section about sessions and NASREQ interaction.

   o  Wrote a note about Reply-Message AVP, and added it back to ABNFs
      and occurance tables.

   o  Added EAP-Reissued-Payload AVP for signalling invalid packets, and
      RADIUS translation for this.

   o  Added EAP-Master-Session-Key AVP for keys, and suggestions for
      RADIUS translation.

   o  Attempted to clarify Framed-MTU RADIUS translation.

   o  Added a first attempt of security considerations section.

   o  Updated acknowledgements (please notify me if someone's missing).

   Changes from -02.b to -02.c:

   o  Rephrased abstract and introduction sections.

   o  A couple of minor changes in Sections 2.1 and 2.2.

   o  Added text about advertising application support and role
      reversal.

   o  Changed type of Accounting-EAP-Auth-Method AVP from Enumerated to
      Unsigned64, and explained how it is determined.

   o  Removed references to EAP-Master-Session-Key AVP added in -02.b.

   o  Added Diameter-RADIUS translation of accounting AVPs.

   o  Added IANA Considerations section.

   o  References section: Updated RFC2284bis, added IEEE-802.11i and
      IKEv2, deleted RFC1510 ad RFC1938.

   Changes from -02.a to -02.b:

   o  Added some text to Introduction section.

   o  Stole text from 2869bis about invalid packets, retransmissions,
      and fragmentation.



Eronen, et al.           Expires April 23, 2004                [Page 33]

Internet-Draft          Diameter EAP Application            October 2003


   o  In section 2.1, changed one "MAY" to "could" since it was not used
      to describe a requirement.

   o  Updated ABNF's and AVP occurance tables to match the current
      NASREQ-11 document.

   o  Added EAP-MTU and EAP-Master-Session-Key AVPs.

   o  Removed description of Configuration-Token, Nas-Port, Nas-Port-Id,
      and State AVPs (the text didn't add anything to their description
      in NASREQ).

   o  Added a first attempt of a section describing Diameter-RADIUS
      translation.

   o  Added references RFC2284bis, RFC2548, RFC2869bis, RADIUS1X, and
      DynAuth.

   Changes from -01 to -02.a:

   o  New editor.

   o  Added Changelog appendix.

   o  Converted source to XML format.  This will result in many small
      formatting changes in the ASCII version.

   o  Updated BASE and NASREQ references to current versions.























Eronen, et al.           Expires April 23, 2004                [Page 34]

Internet-Draft          Diameter EAP Application            October 2003


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.


Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



Eronen, et al.           Expires April 23, 2004                [Page 35]

Internet-Draft          Diameter EAP Application            October 2003


   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































Eronen, et al.           Expires April 23, 2004                [Page 36]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/