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rfc:rfc4072

Network Working Group P. Eronen, Ed. Request for Comments: 4072 Nokia Category: Standards Track T. Hiller

                                                   Lucent Technologies
                                                               G. Zorn
                                                         Cisco Systems
                                                           August 2005
   Diameter Extensible Authentication Protocol (EAP) Application

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

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.

Table of Contents

 1.  Introduction ...................................................2
     1.1.  Conventions Used in This Document ........................3
 2.  Extensible Authentication Protocol Support in Diameter .........3
     2.1.  Advertising Application Support ..........................3
     2.2.  Protocol Overview ........................................4
     2.3.  Sessions and NASREQ Interaction ..........................6
           2.3.1. Scenario 1: Direct Connection .....................7
           2.3.2. Scenario 2: Direct Connection with Redirects ......8
           2.3.3. Scenario 3: Direct EAP, Authorization via Agents ..9
           2.3.4. Scenario 4: Proxy Agents .........................10
     2.4.  Invalid Packets .........................................10
     2.5.  Retransmission ..........................................11
     2.6.  Fragmentation ...........................................12
     2.7.  Accounting ..............................................12
     2.8.  Usage Guidelines ........................................13

Eronen, et al. Standards Track [Page 1] RFC 4072 Diameter EAP Application August 2005

           2.8.1. User-Name AVP ....................................13
           2.8.2. Conflicting AVPs .................................13
           2.8.3. Displayable Messages .............................14
           2.8.4. Role Reversal ....................................14
           2.8.5. Identifier Space .................................14
 3.  Command-Codes .................................................14
     3.1.  Diameter-EAP-Request (DER) Command ......................15
     3.2.  Diameter-EAP-Answer (DEA) Command .......................16
 4.  Attribute-Value Pairs .........................................18
     4.1.  New AVPs ................................................18
           4.1.1. EAP-Payload AVP ..................................18
           4.1.2. EAP-Reissued-Payload AVP .........................18
           4.1.3. EAP-Master-Session-Key AVP .......................19
           4.1.4. EAP-Key-Name AVP .................................19
           4.1.5. Accounting-EAP-Auth-Method AVP ...................19
 5.  AVP Occurrence Tables .........................................19
     5.1.  EAP Command AVP Table ...................................20
     5.2.  Accounting AVP Table ....................................21
 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 .......................................24
     8.1.  Overview ................................................24
     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
 9.  Acknowledgements ..............................................29
 10. References ....................................................30
     10.1. Normative References ....................................30
     10.2. Informative References ..................................30

1. Introduction

 The Extensible Authentication Protocol (EAP), defined in [EAP], is an
 authentication framework which supports multiple authentication
 mechanisms.  EAP may be used on dedicated links, 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].

Eronen, et al. Standards Track [Page 2] RFC 4072 Diameter EAP Application August 2005

 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 the Diameter Network Access Server
 Application [NASREQ] and is intended for environments similar to
 NASREQ.
 In the 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.
 The Diameter EAP application relies heavily on [NASREQ], and in
 earlier versions was part of the Diameter NASREQ application.  It can
 also be used in conjunction with NASREQ, selecting the application
 based on the user authentication mechanism (EAP or PAP/CHAP).  The
 Diameter EAP application defines new Command-Codes and Attribute-
 Value Pairs (AVPs), and can work together with RADIUS EAP support
 [RFC3579].

1.1. Conventions Used in This Document

 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. Extensible Authentication Protocol Support in Diameter

2.1. Advertising Application Support

 Diameter nodes conforming to this specification MUST advertise
 support by including the Diameter EAP Application ID value of 5 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 indicates 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
 be used, since this could result from a downgrade attack (see
 Section 8.3).

Eronen, et al. Standards Track [Page 3] RFC 4072 Diameter EAP Application August 2005

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 802.11i [IEEE-802.11i].  Once EAP has been
 initiated, the access device will typically send a Diameter-EAP-
 Request message with an empty EAP-Payload AVP to the Diameter server,
 signifying an EAP-Start.
 If the Diameter home server is willing to do EAP authentication, it
 responds with a Diameter-EAP-Answer message containing an EAP-Payload
 AVP that includes an encapsulated EAP packet.  The Result-Code AVP in
 the message will be 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
 message round trips.  When the EAP-Request/Identity message is issued
 by the access device, it SHOULD interpret the EAP-Response/Identity

Eronen, et al. Standards Track [Page 4] RFC 4072 Diameter EAP Application August 2005

 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 in which 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. Standards Track [Page 5] RFC 4072 Diameter EAP Application August 2005

  :                        ...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 SHOULD also include the
 appropriate authorization AVPs required for the service requested
 (see Section 5 and [NASREQ]).  In some cases, the home server may not
 be able to provide all necessary authorization AVPs; in this case, a
 separate authorization step MAY be used as described in
 Section 2.3.3.  Diameter-EAP-Answer messages whose Result-Code AVP is
 set to DIAMETER_MULTI_ROUND_AUTH MAY include authorization AVPs.
 A Diameter-EAP-Answer with successful 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, and 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

 The previous section introduced the basic protocol between the NAS
 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, one must ensure that this key does not
 fall into wrong hands.

Eronen, et al. Standards Track [Page 6] RFC 4072 Diameter EAP Application August 2005

 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 possible scenarios on how the messages could be
 transport protected using these hop-by-hop mechanisms.
 This 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 authorization AVPs and EAP keying material are delivered by the
 home server.
 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
 cases where Diameter agents are not needed to provide routing or
 additional authorization AVPs.

Eronen, et al. Standards Track [Page 7] RFC 4072 Diameter EAP Application August 2005

2.3.2. Scenario 2: Direct Connection with Redirects

 In this scenario the NAS uses a redirect agent to locate the home
 server.  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, for example, a new roaming
 agreement is made.

Eronen, et al. Standards Track [Page 8] RFC 4072 Diameter EAP Application August 2005

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
 authorization AVPs are retrieved from local proxy agents.  This
 scenario is intended for environments in which 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 supports routing based on application,
 not on Diameter commands.

Eronen, et al. Standards Track [Page 9] RFC 4072 Diameter EAP Application August 2005

2.3.4. Scenario 4: Proxy Agents

 This scenario is the same as Scenario 1, but the NAS contacts the
 home server through proxies.  Note that the proxies can see the EAP
 session keys, thus it is not suitable for environments where proxies
 cannot be trusted.
 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 (Code 2=Response) 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
 (Code 1=Request) 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.

Eronen, et al. Standards Track [Page 10] RFC 4072 Diameter EAP Application August 2005

 Since EAP method fields (Type, Type-Data) are typically not validated
 by a NAS operating as a pass-through, despite these checks it is
 possible for a NAS to forward an invalid EAP packet to or from the
 Diameter server.
 A Diameter server receiving an EAP-Payload AVP that it does not
 understand SHOULD determine 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 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 that match the
 current Identifier value have been received.  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 DIAMETER_AUTHENTICATION_REJECTED Result-Code.  By
 default, a value of 5 invalid EAP packets is recommended.

2.5. Retransmission

 As noted in [EAP], 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 time-outs 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.

Eronen, et al. Standards Track [Page 11] RFC 4072 Diameter EAP Application August 2005

 If a Multi-Round-Time-Out AVP [BASE] is present in a 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 in
 order 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
 that 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 octet), Type (1 octet) and
 Body Length (2 octets) 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 4.1.5) 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 or 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.

Eronen, et al. Standards Track [Page 12] RFC 4072 Diameter EAP Application August 2005

2.8. Usage Guidelines

2.8.1. User-Name AVP

 Unless the access device interprets the EAP-Response/Identity packet
 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 a User-Name AVP to
 Diameter-EAP-Answer messages that have a Result-Code of
 DIAMETER_SUCCESS.  A separate billing identifier or pseudonym MAY be
 used for privacy reasons (see Section 8.5).  If the user's identity
 is not available to the NAS, 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.
 Some lower layers assume that the authorization decision is made by
 the EAP server, and thus the peer considers EAP Success as an
 indication that access was granted.  In this case, the Result-Code
 SHOULD match the contained EAP packet: a successful Result-Code for
 EAP-Success, and a failure Result-Code for EAP-Failure.  If the
 encapsulated EAP packet does not match the result implied by the
 Result-Code AVP, the combination is likely to cause confusion,
 because the NAS and peer will conclude the outcome of the
 authentication differently.  For example, if the NAS receives a
 failure Result-Code with an encapsulated EAP Success, it will not
 grant access to the peer.  However, on receiving the EAP Success, the
 peer will be led to believe that access was granted.
 This situation can be difficult to avoid when Diameter proxy agents
 make authorization decisions (that is, proxies can change the
 Result-Code AVP sent by the home server).  Because it is the
 responsibility of the Diameter server to avoid conflicts, the NAS
 MUST NOT "manufacture" EAP result packets in order to correct the
 contradictory messages that it receives.  This behavior, originally
 mandated within [IEEE-802.1X], is now deprecated.

Eronen, et al. Standards Track [Page 13] RFC 4072 Diameter EAP Application August 2005

2.8.3. Displayable Messages

 The Reply-Message AVP [NASREQ] MUST NOT be included in any Diameter
 message containing an EAP-Payload AVP.

2.8.4. Role Reversal

 Some environments in which EAP is used, such as PPP, support
 peer-to-peer operation.  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 a packet
 MUST respond with a failure Result-Code.

2.8.5. Identifier Space

 In EAP, each session has its own unique Identifier space.  Diameter
 server implementations MUST be able to distinguish between EAP
 packets with the same Identifier existing within distinct EAP
 sessions and originating on the same NAS.  This is done by using the
 Session-Id AVP.
 If a Diameter NAS is in the middle of a multi-round authentication
 exchange, and it detects that the EAP session between the client and
 the NAS has been terminated, it MUST select a new Diameter Session-Id
 for any subsequent EAP sessions.  This is necessary in order to
 distinguish a restarted EAP authentication process from the
 continuation of an ongoing process (by the same user on the same NAS
 and port).
 In RADIUS, the same functionality can be achieved through the
 inclusion or omission of the State attribute.  Translation rules in
 [NASREQ] ensure that an Access-Request without the State attribute
 maps to a new Diameter Session-Id AVP value.  Furthermore, a
 translation agent will always include a State attribute in
 Access-Challenge messages, making sure that the State attribute is
 available for a RADIUS NAS.

3. Command-Codes

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

Eronen, et al. Standards Track [Page 14] RFC 4072 Diameter EAP Application August 2005

    Command-Name             Abbrev.    Code       Reference
    --------------------------------------------------------
    Diameter-EAP-Request      DER       268          3.1
    Diameter-EAP-Answer       DEA       268          3.2
 When the NASREQ AA-Request (AAR) or AA-Answer (AAA) commands are used
 for AUTHORIZE_ONLY messages in conjunction with EAP (see
 Section 2.3.3), an Application Identifier value of 1 (NASREQ) is
 used, and the commands follow the rules and ABNF defined in [NASREQ].
 When the Re-Auth-Request (RAR), Re-Auth-Answer (RAA),
 Session-Termination-Request (STR), Session-Termination-Answer (STA),
 Abort-Session-Request (ASR), Abort-Session-Answer (ASA),
 Accounting-Request (ACR), and Accounting-Answer (ACA) commands are
 used together with the Diameter EAP application, they follow the
 rules in [NASREQ] and [BASE].  The accounting commands use
 Application Identifier value of 3 (Diameter Base Accounting); the
 others use 0 (Diameter Common Messages).

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 containing 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 that 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 >
                               { Auth-Application-Id }
                               { Origin-Host }
                               { Origin-Realm }
                               { Destination-Realm }
                               { Auth-Request-Type }
                               [ Destination-Host ]

Eronen, et al. Standards Track [Page 15] RFC 4072 Diameter EAP Application August 2005

                               [ NAS-Identifier ]
                               [ NAS-IP-Address ]
                               [ NAS-IPv6-Address ]
                               [ NAS-Port ]
                               [ NAS-Port-Id ]
                               [ NAS-Port-Type ]
                               [ Origin-State-Id ]
                               [ Port-Limit ]
                               [ User-Name ]
                               { EAP-Payload }
                               [ EAP-Key-Name ]
                               [ Service-Type ]
                               [ State ]
                               [ Authorization-Lifetime ]
                               [ Auth-Grace-Period ]
                               [ Auth-Session-State ]
                               [ Callback-Number ]
                               [ Called-Station-Id ]
                               [ Calling-Station-Id ]
                               [ 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:
 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.

Eronen, et al. Standards Track [Page 16] RFC 4072 Diameter EAP Application August 2005

 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 ]
                              [ EAP-Reissued-Payload ]
                              [ EAP-Master-Session-Key ]
                              [ EAP-Key-Name ]
                              [ Multi-Round-Time-Out ]
                              [ Accounting-EAP-Auth-Method ]
                              [ Service-Type ]
                            * [ Class ]
                            * [ Configuration-Token ]
                              [ Acct-Interim-Interval ]
                              [ Error-Message ]
                              [ Error-Reporting-Host ]
                            * [ Failed-AVP ]
                              [ Idle-Timeout ]
                              [ Authorization-Lifetime ]
                              [ Auth-Grace-Period ]
                              [ Auth-Session-State ]
                              [ Re-Auth-Request-Type ]
                              [ Session-Timeout ]
                              [ State ]
                            * [ Reply-Message ]
                              [ Origin-State-Id ]
                            * [ Filter-Id ]

Eronen, et al. Standards Track [Page 17] RFC 4072 Diameter EAP Application August 2005

                              [ 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 ]
                            * [ QoS-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 462) 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 463) is of type OctetString.
 The use of this AVP is described in Section 2.4.

Eronen, et al. Standards Track [Page 18] RFC 4072 Diameter EAP Application August 2005

4.1.3. EAP-Master-Session-Key AVP

 The EAP-Master-Session-Key AVP (AVP Code 464) is of type OctetString.
 It contains keying material for protecting the communications between
 the user and the NAS.  Exactly how this keying material is used
 depends on the link layer in question, and is beyond the scope of
 this document.

4.1.4. EAP-Key-Name AVP

 The EAP-Key-Name AVP (Radius Attribute Type 102) is of type
 OctetString.  It contains an opaque key identifier (name) generated
 by the EAP method.  Exactly how this name is used depends on the link
 layer in question, and is beyond the scope of this document (see
 [EAPKey] for more discussion).
 Note that not all link layers use this name, and currently most EAP
 methods do not generate it.  Since the NAS operates in pass-through
 mode, it cannot know the Key-Name before receiving it from the AAA
 server.  As a result, a Key-Name AVP sent in a Diameter-EAP-Request
 MUST NOT contain any data.  A home Diameter server receiving a
 Diameter-EAP-Request with a Key-Name AVP with non-empty data MUST
 silently discard the AVP.  In addition, the home Diameter server
 SHOULD include this AVP in Diameter-EAP-Response only if an empty
 EAP-Key-Name AVP was present in Diameter-EAP-Request.

4.1.5. Accounting-EAP-Auth-Method AVP

 The Accounting-EAP-Auth-Method AVP (AVP Code 465) is of type
 Unsigned64.  In case of expanded types [EAP, Section 5.7], this AVP
 contains the value ((Vendor-Id * 2^32) + Vendor-Type).
 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.

Eronen, et al. Standards Track [Page 19] RFC 4072 Diameter EAP Application August 2005

5.1. EAP Command AVP Table

 The following table lists the AVPs that may be present in the DER and
 DEA Commands, as defined in this document; 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  |
 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-Master-Session-Key              |   0   |  0-1  |
 EAP-Key-Name                        |  0-1  |  0-1  |
 EAP-Payload                         |   1   |  0-1  |
 EAP-Reissued-Payload                |   0   |  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  |

Eronen, et al. Standards Track [Page 20] RFC 4072 Diameter EAP Application August 2005

 Framed-Protocol [NASREQ]            |  0-1  |  0-1  |
 Framed-Route [NASREQ]               |   0   |   0+  |
 Framed-Routing [NASREQ]             |   0   |  0-1  |
 Idle-Timeout [NASREQ]               |   0   |  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+  |
 QoS-Filter-Rule [NASREQ]            |   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+  |
 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   |  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, as
 defined in [BASE].
                                        +-----------+
                                        |  Command  |
                                        |    Code   |
                                        |-----+-----+
 Attribute Name                         | ACR | ACA |
 ---------------------------------------|-----+-----+
 Accounting-EAP-Auth-Method             |  0+ |  0  |

Eronen, et al. Standards Track [Page 21] RFC 4072 Diameter EAP Application August 2005

6. RADIUS/Diameter Interactions

 Section 9 of [NASREQ] describes basic guidelines for translation
 agents that translate between RADIUS and Diameter protocols.  These
 guidelines SHOULD be followed for Diameter EAP application as well,
 with some additional guidelines given in this section.  Note that
 this document does not restrict implementations from creating
 additional methods, as long as the translation function does not
 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.
 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.  The encryption of this
    attribute is described in [RFC2548].
 o  Diameter Accounting-EAP-Auth-Method AVPs, if present, are
    discarded.

Eronen, et al. Standards Track [Page 22] RFC 4072 Diameter EAP Application August 2005

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 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.
 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.  The
    attributes have to be decrypted before conversion, and the Salt,
    Key-Length and Padding sub-fields are discarded.  The Key
    sub-fields 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.

Eronen, et al. Standards Track [Page 23] RFC 4072 Diameter EAP Application August 2005

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 and RADIUS specifications.
 o  This document defines one new Diameter command (in Section 3)
    whose Command Code is allocated from the Command Code namespace
    defined in [BASE].  The Command Code for DER / DEA is 268.
 o  This document defines four new AVPs whose AVP Codes are allocated
    from the AVP Code namespace defined in [BASE] as follows:
       462 for EAP-Payload (defined in Section 4.1.1),
       463 for EAP-Reissued-Payload (defined in Section 4.1.2),
       464 for EAP-Master-Session-Key (defined in Section 4.1.3), and
       465 for Accounting-EAP-Auth-Method (defined in Section 4.1.5).
 o  This document defines one new AVP (attribute) whose AVP Code
    (Attribute Type) is to be allocated from the Attribute Type
    namespace defined in [RFC2865] and [RFC3575].  The Radius
    Attribute Type for EAP-Key-Name (defined in Section 4.1.4) is 102.
 o  This document defines one new Diameter application (in
    Section 2.1) whose Application ID is to be allocated from the
    Application Identifier namespace defined in [BASE].  The
    Application ID for Diameter EAP is 5.

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,

Eronen, et al. Standards Track [Page 24] RFC 4072 Diameter EAP Application August 2005

 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.  Here, authorization means 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.  Note
 that authorization issues are particularly relevant when Diameter
 redirects are used.  While redirection reduces the number of nodes
 which have access to the contents of Diameter messages, a compromised
 Diameter agent may not supply the right home server's address.  If
 the Diameter client is unable to tell whether this particular server
 is authorized to act as the home server for this particular user, the
 security of the communications rests on the redirect agent.
 The hop-by-hop security mechanisms (IPsec and TLS) combined with
 proper authorization provide good protection against "outside"
 attackers, except for denial-of-service attacks.  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 advice on limiting the
 extent of the damage.
 Attacks involving eavesdropping or modification of EAP messages are
 beyond the scope of these document.  See [EAP] for discussion of
 these security considerations (including method negotiation,
 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 on the EAP messages.
 Similarly, attacks involving the link layer protocol used between the
 client and the NAS, such as PPP or IEEE 802.11, are beyond the scope
 of this document.

Eronen, et al. Standards Track [Page 25] RFC 4072 Diameter EAP Application August 2005

8.2. AVP Editing

 Diameter agents can modify, insert, and delete AVPs.  Diameter agents
 are usually meant to modify AVPs, and the protocol cannot distinguish
 well-intentioned and malicious modifications (see [RFC2607] for more
 discussion).  Similarly, a compromised NAS or server can naturally
 include a different set of AVPs than expected.
 Therefore, the question is what an attacker who compromises an
 authorized NAS, agent, or server can 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 and authentication method negotiation attacks
 are discussed in the next section.
 By including suitable AVPs in an AA-Answer/Diameter-EAP-Answer
 messages, an attacker may be able (depending on implementation and
 configuration details) to:
 o  Give unauthorized users access, or deny access to authorized users
    (Result-Code).
 o  Give an 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,
    Callback, various vendor-specific AVPs).
 o  Cause the NAS to call some number, possibly an expensive toll
    number controlled by the attacker (callback AVPs).
 o  Execute Command Line Interface (CLI) commands on the NAS (various
    vendor-specific attributes).

Eronen, et al. Standards Track [Page 26] RFC 4072 Diameter EAP Application August 2005

 By modifying an AA-Request/Diameter-EAP-Request, an attacker may be
 able to:
 o  Change NAS-Identifier/NAS-Port/Origin-Host (or another attribute)
    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 is
 configured to not accept some particular AVPs, or accepts them only
 from some nodes.

8.3. Negotiation Attacks

 This section deals with attacks where the NAS, any Diameter agents,
 or Diameter server attempt 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 [EAP], Section 7.8).
 The vulnerability can be mitigated via implementation of a per-
 connection policy by the authenticating peer, and a per-user policy
 by the Diameter server.  For the authenticating peer, the
 authentication policy should be set on a per-connection basis.
 With a per-connection policy, an authenticating peer will only
 attempt to negotiate EAP for a session in which EAP support is
 expected.  As a result, it is presumed that an authenticating peer
 selecting EAP requires that level of security.  If it cannot be
 provided, there is likely a misconfiguration, or the authenticating
 peer may be contacting the wrong server.  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 one reseller may implement EAP
 while another does not.  Alternatively, some peer might be

Eronen, et al. Standards Track [Page 27] RFC 4072 Diameter EAP Application August 2005

 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-Master-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 up with some malicious party that must be able to
 eavesdrop, modify, or insert traffic between the user and the NAS
 during the lifetime of those keys (for example, in 802.11i the
 attacker must also eavesdrop the "four-way handshake").

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

Eronen, et al. Standards Track [Page 28] RFC 4072 Diameter EAP Application August 2005

8.6. Note about EAP and Impersonation

 If the EAP method used does not provide mutual authentication,
 obviously anyone can impersonate 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.
 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, and thus appear
 to offer a different service than intended.  Even if these parameters
 are included in Diameter-EAP-Answer messages, the NAS can tell
 different values to the client.
 Therefore, the NAS's possession of the session keys proves that the
 user is talking to an authorized NAS, but a compromised NAS can lie
 about its exact identity.  See [EAPKey] for discussion on how
 individual EAP methods can provide authentication of NAS service
 parameters and identities.
 Note that the usefulness of this 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 is simply picked from a beacon message that has the
 correct SSID and good signal strength (something that is easy to
 spoof).  Thus, simply authenticating the identity may not allow the
 user to distinguish the "right" access point from all others.

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
 documents.
 The authors would also like to acknowledge the following people for
 their contributions to this document: Bernard Aboba, Jari Arkko,
 Julien Bournelle, Pat Calhoun, Henry Haverinen, John Loughney,
 Yoshihiro Ohba, and Joseph Salowey.

Eronen, et al. Standards Track [Page 29] RFC 4072 Diameter EAP Application August 2005

10. References

10.1. Normative References

 [BASE]         Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and
                J. Arkko, "Diameter Base Protocol", RFC 3588,
                September 2003.
 [EAP]          Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and
                H. Levkowetz, "Extensible Authentication Protocol
                (EAP)", RFC 3748, June 2004.
 [NASREQ]       Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
                "Diameter Network Access Server Application", RFC
                4005, August 2005.
 [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

10.2. Informative References

 [EAPKey]       Aboba, B., Simon, D., Arkko, J., Eronen, P., and H.
                Levkowetz, "Extensible Authentication Protocol (EAP)
                Key Management Framework", Work in Progress, July
                2004.
 [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,
                "IEEE Standard for Information technology -
                Telecommunications and information exchange between
                systems - Local and metropolitan area networks -
                Specific requirements - Part 11: Wireless Medium
                Access Control (MAC) and Physical Layer (PHY)
                Specifications: Amendment 6: Medium Access Control
                (MAC) Security Enhancements", IEEE Standard
                802.11i-2004, July 2004.
 [IKEv2]        Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
                Protocol", Work in Progress, June 2004.
 [RFC1661]      Simpson, W., "The Point-to-Point Protocol (PPP)",
                STD 51, RFC 1661, July 1994.

Eronen, et al. Standards Track [Page 30] RFC 4072 Diameter EAP Application August 2005

 [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.
 [RFC2865]      Rigney, C., Willens, S., Rubens, A., and W. Simpson,
                "Remote Authentication Dial In User Service (RADIUS)",
                RFC 2865, June 2000.
 [RFC3575]      Aboba, B., "IANA Considerations for RADIUS (Remote
                Authentication Dial In User Service)", RFC 3575,
                July 2003.
 [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.

Eronen, et al. Standards Track [Page 31] RFC 4072 Diameter EAP Application August 2005

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: tomhiller@lucent.com
 Glen Zorn
 Cisco Systems
 500 108th Avenue N.E., Suite 500
 Bellevue, WA  98004
 USA
 Phone: +1 425 344 8113
 EMail: gwz@cisco.com

Eronen, et al. Standards Track [Page 32] RFC 4072 Diameter EAP Application August 2005

Full Copyright Statement

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Eronen, et al. Standards Track [Page 33]

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