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Network Working Group                                           B. AbobaRequest for Comments: 3579                                     MicrosoftUpdates:2869                                                 P. CalhounCategory: Informational                                        Airespace                                                          September 2003RADIUS (Remote Authentication Dial In User Service)Support For Extensible Authentication Protocol (EAP)Status of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2003).  All Rights Reserved.Abstract   This document defines Remote Authentication Dial In User Service   (RADIUS) support for the Extensible Authentication Protocol (EAP), an   authentication framework which supports multiple authentication   mechanisms.  In the proposed scheme, the Network Access Server (NAS)   forwards EAP packets to and from the RADIUS server, encapsulated   within EAP-Message attributes.  This has the advantage of allowing   the NAS to support any EAP authentication method, without the need   for method-specific code, which resides on the RADIUS server.  While   EAP was originally developed for use with PPP, it is now also in use   with IEEE 802.   This document updatesRFC 2869.Aboba & Calhoun              Informational                      [Page 1]

RFC 3579                      RADIUS & EAP                September 2003Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Specification of Requirements. . . . . . . . . . . . . .31.2.  Terminology. . . . . . . . . . . . . . . . . . . . . . .32.  RADIUS Support for EAP . . . . . . . . . . . . . . . . . . . .42.1.  Protocol Overview. . . . . . . . . . . . . . . . . . . .52.2.  Invalid Packets. . . . . . . . . . . . . . . . . . . . .92.3.  Retransmission . . . . . . . . . . . . . . . . . . . . .102.4.  Fragmentation. . . . . . . . . . . . . . . . . . . . . .102.5.  Alternative uses . . . . . . . . . . . . . . . . . . . .112.6.  Usage Guidelines . . . . . . . . . . . . . . . . . . . .113.  Attributes . . . . . . . . . . . . . . . . . . . . . . . . . .143.1.  EAP-Message. . . . . . . . . . . . . . . . . . . . . . .153.2.  Message-Authenticator. . . . . . . . . . . . . . . . . .163.3.  Table of Attributes. . . . . . . . . . . . . . . . . . .184.  Security Considerations. . . . . . . . . . . . . . . . . . . .194.1.  Security Requirements. . . . . . . . . . . . . . . . . .194.2.  Security Protocol. . . . . . . . . . . . . . . . . . . .204.3.  Security Issues. . . . . . . . . . . . . . . . . . . . .225.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .306.  References . . . . . . . . . . . . . . . . . . . . . . . . . .306.1.  Normative References . . . . . . . . . . . . . . . . . .306.2.  Informative References . . . . . . . . . . . . . . . . .32Appendix A - Examples. . . . . . . . . . . . . . . . . . . . . . .34Appendix B - Change Log. . . . . . . . . . . . . . . . . . . . . .43   Intellectual Property Statement. . . . . . . . . . . . . . . . . .44   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . .44   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .45   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . .461.  Introduction   The Remote Authentication Dial In User Service (RADIUS) is an   authentication, authorization and accounting protocol used to control   network access.  RADIUS authentication and authorization is specified   in [RFC2865], and RADIUS accounting is specified in [RFC2866]; RADIUS   over IPv6 is specified in [RFC3162].   The Extensible Authentication Protocol (EAP), defined in [RFC2284],   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].  It has   also been implemented with bridges supporting [IEEE802].  EAP   encapsulation on IEEE 802 wired media is described in [IEEE8021X].Aboba & Calhoun              Informational                      [Page 2]

RFC 3579                      RADIUS & EAP                September 2003   RADIUS attributes are comprised of variable length Type-Length-Value   3-tuples.  New attribute values can be added without disturbing   existing implementations of the protocol.  This specification   describes RADIUS attributes supporting the Extensible Authentication   Protocol (EAP): EAP-Message and Message-Authenticator.  These   attributes now have extensive field experience.  The purpose of this   document is to provide clarification and resolve interoperability   issues.   As noted in [RFC2865], a Network Access Server (NAS) that does not   implement a given service MUST NOT implement the RADIUS attributes   for that service.  This implies that a NAS that is unable to offer   EAP service MUST NOT implement the RADIUS attributes for EAP.  A NAS   MUST treat a RADIUS Access-Accept requesting an unavailable service   as an Access-Reject instead.1.1.  Specification of Requirements   In this document, several words are used to signify the requirements   of the specification.  These words are often capitalized.  The key   words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",   "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document   are to be interpreted as described in [RFC2119].1.2.  Terminology   This document frequently uses the following terms:   authenticator             The end of the link requiring the authentication.  Also             known as the Network Access Server (NAS) or RADIUS client.             Within IEEE 802.1X terminology, the term Authenticator is             used.   peer      The other end of the point-to-point link (PPP),             point-to-point LAN segment (IEEE 802.1X) or wireless link,             which is being authenticated by the authenticator.  In IEEE             802.1X, this end is known as the Supplicant.   authentication server             An authentication server is an entity that provides an             authentication service to an authenticator (NAS).  This             service verifies from the credentials provided by the peer,             the claim of identity made by the peer; it also may provide             credentials allowing the peer to verify the identity of the             authentication server.  Within this document it is assumed             that the NAS operates as a pass-through, forwarding EAP             packets between the RADIUS server and the EAP peer.Aboba & Calhoun              Informational                      [Page 3]

RFC 3579                      RADIUS & EAP                September 2003             Therefore the RADIUS server operates as an authentication             server.   silently discard             This means the implementation discards the packet without             further processing.  The implementation SHOULD provide the             capability of logging the error, including the contents of             the silently discarded packet, and SHOULD record the event             in a statistics counter.   displayable message             This is interpreted to be a human readable string of             characters, and MUST NOT affect operation of the protocol.             The message encoding MUST follow the UTF-8 transformation             format [RFC2279].   Network Access Server (NAS)             The device providing access to the network.  Also known as             the Authenticator (IEEE 802.1X or EAP terminology) or             RADIUS client.   service   The NAS provides a service to the user, such as IEEE 802 or             PPP.   session   Each service provided by the NAS to a peer constitutes a             session, with the beginning of the session defined as the             point where service is first provided and the end of the             session defined as the point where service is ended.  A             peer may have multiple sessions in parallel or series if             the NAS supports that, with each session generating a             separate start and stop accounting record.2.  RADIUS Support for EAP   The Extensible Authentication Protocol (EAP), described in [RFC2284],   provides a standard mechanism for support of additional   authentication methods without the NAS to be upgraded to support each   new method.  Through the use of EAP, support for a number of   authentication schemes may be added, including smart cards, Kerberos   [RFC1510], Public Key [RFC2716], One Time Passwords [RFC2284], and   others.   One of the advantages of the EAP architecture is its flexibility.   EAP is used to select a specific authentication mechanism.  Rather   than requiring the NAS to be updated to support each new   authentication method, EAP permits the use of an authentication   server implementing authentication methods, with the NAS acting as a   pass-through for some or all methods and peers.Aboba & Calhoun              Informational                      [Page 4]

RFC 3579                      RADIUS & EAP                September 2003   A NAS MAY authenticate local peers while at the same time acting as a   pass-through for non-local peers and authentication methods it does   not implement locally.  A NAS implementing this specification is not   required to use RADIUS to authenticate every peer.  However, once the   NAS begins acting as a pass-through for a particular session, it can   no longer perform local authentication for that session.   In order to support EAP within RADIUS, two new attributes,   EAP-Message and Message-Authenticator, are introduced in this   document.  This section describes how these new attributes may be   used for providing EAP support within RADIUS.2.1.  Protocol Overview   In RADIUS/EAP, RADIUS is used to shuttle RADIUS-encapsulated EAP   Packets between the NAS and an authentication server.   The authenticating peer and the NAS begin the EAP conversation by   negotiating use of EAP.  Once EAP has been negotiated, the NAS SHOULD   send an initial EAP-Request message to the authenticating peer.  This   will typically be an EAP-Request/Identity, although it could be an   EAP-Request for an authentication method (Types 4 and greater).  A   NAS MAY be configured to initiate with a default authentication   method.  This is useful in cases where the identity is determined by   another means (such as Called-Station-Id, Calling-Station-Id and/or   Originating-Line-Info); where a single authentication method is   required, which includes its own identity exchange; where identity   hiding is desired, so that the identity is not requested until after   a protected channel has been set up.   The peer replies with an EAP-Response.  The NAS MAY determine from   the Response that it should proceed with local authentication.   Alternatively, the NAS MAY act as a pass-through, encapsulating the   EAP-Response within EAP-Message attribute(s) sent to the RADIUS   server within a RADIUS Access-Request packet.  If the NAS sends an   EAP-Request/Identity message as the initial packet, the peer responds   with an EAP-Response/Identity.  The NAS may determine that the peer   is local and proceed with local authentication.  If no match is found   against the list of local users, the NAS encapsulates the   EAP-Response/Identity message within an EAP-Message attribute,   enclosed within an Access-Request packet.   On receiving a valid Access-Request packet containing EAP-Message   attribute(s), a RADIUS server compliant with this specification and   wishing to authenticate with EAP MUST respond with an   Access-Challenge packet containing EAP-Message attribute(s).  If the   RADIUS server does not support EAP or does not wish to authenticate   with EAP, it MUST respond with an Access-Reject.Aboba & Calhoun              Informational                      [Page 5]

RFC 3579                      RADIUS & EAP                September 2003   EAP-Message attribute(s) encapsulate a single EAP packet which the   NAS decapsulates and passes on to the authenticating peer.  The peer   then responds with an EAP-Response packet, which the NAS encapsulates   within an Access-Request containing EAP-Message attribute(s).  EAP is   a 'lock step' protocol, so that other than the initial Request, a new   Request cannot be sent prior to receiving a valid Response.   The conversation continues until either a RADIUS Access-Reject or   Access-Accept packet is received from the RADIUS server.  Reception   of a RADIUS Access-Reject packet MUST result in the NAS denying   access to the authenticating peer.  A RADIUS Access-Accept packet   successfully ends the authentication phase.  The NAS MUST NOT   "manufacture" a Success or Failure packet as the result of a timeout.   After a suitable number of timeouts have elapsed, the NAS SHOULD   instead end the EAP conversation.   Using RADIUS, the NAS can act as a pass-through for an EAP   conversation between the peer and authentication server, without   needing to implement the EAP method used between them.  Where the NAS   initiates the conversation by sending an EAP-Request for an   authentication method, it may not be required that the NAS fully   implement the EAP method reflected in the initial EAP-Request.   Depending on the initial method, it may be sufficient for the NAS to   be configured with the initial packet to be sent to the peer, and for   the NAS to act as a pass-through for subsequent messages.  Note that   since the NAS only encapsulates the EAP-Response in its initial   Access-Request, the initial EAP-Request within the authentication   method is not available to the RADIUS server.  For the RADIUS server   to be able to continue the conversation, either the initial   EAP-Request is vestigial, so that the RADIUS server need not be aware   of it, or the relevant information from the initial EAP-Request (such   as a nonce) is reflected in the initial EAP-Response, so that the   RADIUS server can obtain it without having received the initial   EAP-Request.   Where the initial EAP-Request sent by the NAS is for an   authentication Type (4 or greater), the peer MAY respond with a Nak   indicating that it would prefer another authentication method that is   not implemented locally.  In this case, the NAS SHOULD send   Access-Request encapsulating the received EAP-Response/Nak.  This   provides the RADIUS server with a hint about the authentication   method(s) preferred by the peer, although it does not provide   information on the Type of the original Request.  It also provides   the server with the Identifier used in the initial EAP-Request, so   that Identifier conflicts can be avoided.Aboba & Calhoun              Informational                      [Page 6]

RFC 3579                      RADIUS & EAP                September 2003   In order to evaluate whether the alternatives preferred by the   authenticating peer are allowed, the RADIUS server will typically   respond with an Access-Challenge containing EAP-Message attribute(s)   encapsulating an EAP-Request/Identity (Type 1).  This allows the   RADIUS server to determine the peer identity, so as to be able to   retrieve the associated authentication policy.  Alternatively, an   EAP-Request for an authentication method (Type 4 or greater) could be   sent.  Since the RADIUS server may not be aware of the Type of the   initial EAP-Request, it is possible for the RADIUS server to choose   an unacceptable method, and for the peer to respond with another Nak.   In order to permit non-EAP aware RADIUS proxies to forward the   Access-Request packet, if the NAS initially sends an   EAP-Request/Identity message to the peer, the NAS MUST copy the   contents of the Type-Data field of the EAP-Response/Identity received   from the peer into the User-Name attribute and MUST include the   Type-Data field of the EAP-Response/Identity in the User-Name   attribute in every subsequent Access-Request.  Since RADIUS proxies   are assumed to act as a pass-through, they cannot be expected to   parse an EAP-Response/Identity encapsulated within EAP-Message   attribute(s).  If the NAS initially sends an EAP-Request for an   authentication method, and the peer identity cannot be determined   from the EAP-Response, then the User-Name attribute SHOULD be   determined by another means.  As noted in[RFC2865] Section 5.6, it   is recommended that Access-Requests use the value of the   Calling-Station-Id as the value of the User-Name attribute.   Having the NAS send the initial EAP-Request packet has a number of   advantages:   [1]  It saves a round trip between the NAS and RADIUS server.   [2]  An Access-Request is only sent to the RADIUS server if the        authenticating peer sends an EAP-Response, confirming that it        supports EAP.  In situations where peers may be EAP unaware,        initiating a RADIUS Access-Request on a "carrier sense" or        "media up" indication may result in many authentication        exchanges that cannot complete successfully.  For example, on        wired networks [IEEE8021X] Supplicants typically do not initiate        the 802.1X conversation with an EAPOL-Start.  Therefore an IEEE        802.1X-enabled bridge may not be able to determine whether the        peer supports EAP until it receives a Response to the initial        EAP-Request.   [3]  It allows some peers to be authenticated locally.Aboba & Calhoun              Informational                      [Page 7]

RFC 3579                      RADIUS & EAP                September 2003   Although having the NAS send the initial EAP-Request packet has   substantial advantages, this technique cannot be universally   employed.  There are circumstances in which the peer identity is   already known (such as when authentication and accounting is handled   based on Called-Station-Id, Calling-Station-Id and/or   Originating-Line-Info), but where the appropriate EAP method may vary   based on that identity.   Rather than sending an initial EAP-Request packet to the   authenticating peer, on detecting the presence of the peer, the NAS   MAY send an Access-Request packet to the RADIUS server containing an   EAP-Message attribute signifying EAP-Start.  The RADIUS server will   typically respond with an Access-Challenge containing EAP-Message   attribute(s) encapsulating an EAP-Request/Identity (Type 1).   However, an EAP-Request for an authentication method (Type 4 or   greater) can also be sent by the server.   EAP-Start is indicated by sending an EAP-Message attribute with a   length of 2 (no data).  The Calling-Station-Id SHOULD be included in   the User-Name attribute.  This may result in a RADIUS Access-Request   being sent by the NAS to the RADIUS server without first confirming   that the peer supports EAP.  Since this technique can result in a   large number of uncompleted RADIUS conversations, in situations where   EAP unaware peers are common, or where peer support for EAP cannot be   determined on initial contact (e.g. [IEEE8021X] Supplicants not   initiating the conversation with an EAPOL-Start) it SHOULD NOT be   employed by default.   For proxied RADIUS requests, there are two methods of processing.  If   the domain is determined based on the Calling-Station-Id,   Called-Station-Id and/or Originating-Line-Info, the RADIUS server may   proxy the initial RADIUS Access-Request/EAP-Start.  If the realm is   determined based on the peer identity, the local RADIUS server MUST   respond with a RADIUS Access-Challenge including an EAP-Message   attribute encapsulating an EAP-Request/Identity packet.  The response   from the authenticating peer SHOULD be proxied to the final   authentication server.   If an Access-Request is sent to a RADIUS server which does not   support the EAP-Message attribute, then an Access-Reject MUST be sent   in response.  On receiving an Access-Reject, the NAS MUST deny access   to the authenticating peer.Aboba & Calhoun              Informational                      [Page 8]

RFC 3579                      RADIUS & EAP                September 20032.2.  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 RADIUS 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   RADIUS server in the most recently validated EAP-Request.  On   receiving an EAP packet from the RADIUS server (encapsulated within   an Access-Challenge), 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   possible for a NAS to forward an invalid EAP packet to or from the   RADIUS server.  A RADIUS server receiving EAP-Message attribute(s) it   does not understand SHOULD make the determination of whether the   error is fatal or non-fatal based on the EAP Type.  A RADIUS server   determining that a fatal error has occurred MUST send an   Access-Reject containing an EAP-Message attribute encapsulating   EAP-Failure.   A RADIUS server determining that a non-fatal error has occurred MAY   send an Access-Challenge to the NAS including EAP-Message   attribute(s) as well as an Error-Cause attribute [RFC3576] with value   202 (decimal), "Invalid EAP Packet (Ignored)".  The Access-Challenge   SHOULD encapsulate within EAP-Message attribute(s) the most recently   sent EAP-Request packet (including the same Identifier value).  On   receiving such an Access-Challenge, a NAS implementing previous   versions of this specification will decapsulate the EAP-Request and   send it to the peer, which will retransmit the EAP-Response.   A NAS compliant with this specification, on receiving an   Access-Challenge with an Error-Cause attribute of value 202 (decimal)   SHOULD discard the EAP-Response packet most recently transmitted to   the RADIUS 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 RADIUS   server within an Access-Request, and the EAP-Message attribute(s)   included within the Access-Challenge are silently discarded.  If no   EAP-Response packet is available, then the EAP-Request encapsulated   within the Access-Challenge is sent to the peer, and the   retransmission timer is reset.Aboba & Calhoun              Informational                      [Page 9]

RFC 3579                      RADIUS & EAP                September 2003   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 RADIUS server is advised to permit only a modest number of   invalid EAP packets within a single session, prior to terminating the   session with an Access-Reject.  By default a value of 5 invalid EAP   packets is recommended.2.3.  Retransmission   As noted in [RFC2284], 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 RADIUS server.  This can be accomplished by inclusion of   Session-Timeout attribute within the Access-Challenge packet.   If Session-Timeout is present in an Access-Challenge packet that also   contains an EAP-Message, the value of the Session-Timeout is used to   set the EAP retransmission timer for that EAP Request, and that   Request alone.  Once the EAP-Request has been sent, the NAS sets the   retransmission timer, and if it expires without having received an   EAP-Response corresponding to the Request, then the EAP-Request is   retransmitted.2.4.  Fragmentation   Using the EAP-Message attribute, it is possible for the RADIUS 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   RADIUS server to use MTU discovery to ascertain the link MTU, the   Framed-MTU attribute may be included in an Access-Request packet   containing an EAP-Message attribute so as to provide the RADIUS   server with this information.  A RADIUS server having received a   Framed-MTU attribute in an Access-Request packet MUST NOT send any   subsequent packet in this EAP conversation containing EAP-Message   attributes whose values, when concatenated, exceed the length   specified by the Framed-MTU value, taking the link type (specified by   the NAS-Port-Type attribute) into account.  For example, as noted in[RFC3580] Section 3.10, for a NAS-Port-Type value of IEEE 802.11, theAboba & Calhoun              Informational                     [Page 10]

RFC 3579                      RADIUS & EAP                September 2003   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.2.5.  Alternative Uses   Currently the conversation between security servers and the RADIUS   server is often proprietary because of lack of standardization.  In   order to increase standardization and provide interoperability   between RADIUS vendors and  security vendors, it is recommended that   RADIUS- encapsulated EAP be used for this conversation.   This has the advantage of allowing the RADIUS server to support EAP   without the need for authentication-specific code within the RADIUS   server.  Authentication-specific code can then reside on a security   server instead.   In the case where RADIUS-encapsulated EAP is used in a conversation   between a RADIUS server and a security server, the security server   will typically return an Access-Accept message without inclusion of   the expected attributes currently returned in an Access-Accept.  This   means that the RADIUS server MUST add these attributes prior to   sending an Access-Accept message to the NAS.2.6.  Usage Guidelines2.6.1.  Identifier Space   In EAP, each session has its own unique Identifier space.  RADIUS   server implementations MUST be able to distinguish between EAP   packets with the same Identifier existing within distinct sessions,   originating on the same NAS.  For this purpose, sessions can be   distinguished based on NAS and session identification attributes.   NAS identification attributes include NAS-Identifier,   NAS-IPv6-Address and NAS-IPv4-Address.  Session identification   attributes include User-Name, NAS-Port, NAS-Port-Type, NAS-Port-Id,   Called-Station-Id, Calling-Station-Id and Originating-Line-Info.2.6.2.  Role Reversal   Since EAP is a peer-to-peer protocol, an independent and simultaneous   authentication may take place in the reverse direction.  Both peers   may act as authenticators and authenticatees at the same time.   However, role reversal is not supported by this specification.  A   RADIUS server MUST respond to an Access-Request encapsulating an   EAP-Request with an Access-Reject.  In order to avoid retransmissionsAboba & Calhoun              Informational                     [Page 11]

RFC 3579                      RADIUS & EAP                September 2003   by the peer, the Access-Reject SHOULD include an EAP-Response/Nak   packet indicating no preferred method, encapsulated within   EAP-Message attribute(s).2.6.3.  Conflicting Messages   The NAS MUST make its access control decision based solely on the   RADIUS Packet Type (Access-Accept/Access-Reject).  The access control   decision MUST NOT be based on the contents of the EAP packet   encapsulated in one or more EAP-Message attributes, if present.   Access-Accept packets SHOULD have only one EAP-Message attribute in   them, containing EAP Success; similarly, Access-Reject packets SHOULD   have only one EAP-Message attribute in them, containing EAP Failure.   Where the encapsulated EAP packet does not match the result implied   by the RADIUS Packet Type, the combination is likely to cause   confusion, because the NAS and peer will arrive at different   conclusions as to the outcome of the authentication.   For example, if the NAS receives an Access-Reject with an   encapsulated EAP Success, it will not grant access to the peer.   However, on receiving the EAP Success, the peer will be lead to   believe that it authenticated successfully.   If the NAS receives an Access-Accept with an encapsulated EAP   Failure, it will grant access to the peer.  However, on receiving an   EAP Failure, the peer will be lead to believe that it failed   authentication.  If no EAP-Message attribute is included within an   Access-Accept or Access-Reject, then the peer may not be informed as   to the outcome of the authentication, while the NAS will take action   to allow or deny access.   As described in [RFC2284], the EAP Success and Failure packets are   not acknowledged, and these packets terminate the EAP conversation.   As a result, if these packets are encapsulated within an   Access-Challenge, no response will be received, and therefore the NAS   will send no further Access-Requests to the RADIUS server for the   session.  As a result, the RADIUS server will not indicate to the NAS   whether to allow or deny access, while the peer will be informed as   to the outcome of the authentication.Aboba & Calhoun              Informational                     [Page 12]

RFC 3579                      RADIUS & EAP                September 2003   To avoid these conflicts, the following combinations SHOULD NOT be   sent by a RADIUS server:      Access-Accept/EAP-Message/EAP Failure      Access-Accept/no EAP-Message attribute      Access-Accept/EAP-Start      Access-Reject/EAP-Message/EAP Success      Access-Reject/no EAP-Message attribute      Access-Reject/EAP-Start      Access-Challenge/EAP-Message/EAP Success      Access-Challenge/EAP-Message/EAP Failure      Access-Challenge/no EAP-Message attribute      Access-Challenge/EAP-Start   Since the responsibility for avoiding conflicts lies with the RADIUS   server, the NAS MUST NOT "manufacture" EAP packets in order to   correct contradictory messages that it receives.  This behavior,   originally mandated within [IEEE8021X], will be deprecated in the   future.2.6.4.  Priority   A RADIUS Access-Accept or Access-Reject packet may contain EAP-   Message attribute(s). In order to ensure the correct processing of   RADIUS packets, the NAS MUST first process the attributes, including   the EAP-Message attribute(s), prior to processing the Accept/Reject   indication.2.6.5.  Displayable Messages   The Reply-Message attribute, defined in[RFC2865], Section 5.18,   indicates text which may be displayed to the peer.  This is similar   in concept to EAP Notification, defined in [RFC2284].  When sending a   displayable message to a NAS during an EAP conversation, the RADIUS   server MUST encapsulate displayable messages within   EAP-Message/EAP-Request/Notification attribute(s).  Reply-Message   attribute(s) MUST NOT be included in any RADIUS message containing an   EAP-Message attribute.  An EAP-Message/EAP-Request/Notification   SHOULD NOT be included within an Access-Accept or Access-Reject   packet.   In some existing implementations, a NAS receiving Reply-Message   attribute(s) copies the Text field(s) into the Type-Data field of an   EAP-Request/Notification packet, fills in the Identifier field, and   sends this to the peer.  However, several issues arise from this:Aboba & Calhoun              Informational                     [Page 13]

RFC 3579                      RADIUS & EAP                September 2003   [1]  Unexpected Responses.  On receiving an EAP-Request/Notification,        the peer will send an EAP-Response/Notification, and the NAS        will pass this on to the RADIUS server, encapsulated within        EAP-Message attribute(s).  However, the RADIUS server may not be        expecting an Access-Request containing an        EAP-Message/EAP-Response/Notification attribute.        For example, consider what happens when a Reply-Message is        included within an Access-Accept or Access-Reject packet with no        EAP-Message attribute(s) present.  If the value of the        Reply-Message attribute is copied into the Type-Data of an        EAP-Request/Notification and sent to the peer, this will result        in an Access-Request containing an        EAP-Message/EAP-Response/Notification attribute being sent by        the NAS to the RADIUS server.  Since an Access-Accept or        Access-Reject packet terminates the RADIUS conversation, such an        Access-Request would not be expected, and could be interpreted        as the start of another conversation.   [2]  Identifier conflicts.  While the EAP-Request/Notification is an        EAP packet containing an Identifier field, the Reply-Message        attribute does not contain an Identifier field.  As a result, a        NAS receiving a Reply-Message attribute and wishing to translate        this to an EAP-Request/Notification will need to choose an        Identifier value.  It is possible that the chosen Identifier        value will conflict with a value chosen by the RADIUS server for        another packet within the EAP conversation, potentially causing        confusion between a new packet and a retransmission.   To avoid these problems, a NAS receiving a Reply-Message attribute   from the RADIUS server SHOULD silently discard the attribute, rather   than attempting to translate it to an EAP Notification Request.3.  Attributes   The NAS-Port or NAS-Port-Id attributes SHOULD be included by the NAS   in Access-Request packets, and either NAS-Identifier, NAS-IP-Address   or NAS-IPv6-Address attributes MUST be included.  In order to permit   forwarding of the Access-Reply by EAP-unaware proxies, if a User-Name   attribute was included in an Access-Request, the RADIUS server MUST   include the User-Name attribute in subsequent Access-Accept packets.   Without the User-Name attribute, accounting and billing becomes   difficult to manage.  The User-Name attribute within the Access-   Accept packet need not be the same as the User-Name attribute in the   Access-Request.Aboba & Calhoun              Informational                     [Page 14]

RFC 3579                      RADIUS & EAP                September 20033.1.  EAP-Message   Description      This attribute encapsulates EAP [RFC2284] packets so as to allow      the NAS to authenticate peers via EAP without having to understand      the EAP method it is passing through.      The NAS places EAP messages received from the authenticating peer      into one or more EAP-Message attributes and forwards them to the      RADIUS server within an Access-Request message.  If multiple      EAP-Message attributes are contained within an Access-Request or      Access-Challenge packet, they MUST be in order and they MUST be      consecutive attributes in the Access-Request or Access-Challenge      packet.  The RADIUS server can return EAP-Message attributes in      Access-Challenge, Access-Accept and Access-Reject packets.      When RADIUS is used to enable EAP authentication, Access-Request,      Access-Challenge, Access-Accept, and Access-Reject packets SHOULD      contain one or more EAP-Message attributes.  Where more than one      EAP-Message attribute is included, it is assumed that the      attributes are to be concatenated to form a single EAP packet.      Multiple EAP packets MUST NOT be encoded within EAP-Message      attributes contained within a single Access-Challenge,      Access-Accept, Access-Reject or Access-Request packet.      It is expected that EAP will be used to implement a variety of      authentication methods, including methods involving strong      cryptography.  In order to prevent attackers from subverting EAP      by attacking RADIUS/EAP, (for example, by modifying EAP Success or      EAP Failure packets) it is necessary that RADIUS provide      per-packet authentication and integrity protection.      Therefore the Message-Authenticator attribute MUST be used to      protect all Access-Request, Access-Challenge, Access-Accept, and      Access-Reject packets containing an EAP-Message attribute.      Access-Request packets including EAP-Message attribute(s) without      a Message-Authenticator attribute SHOULD be silently discarded by      the RADIUS server.  A RADIUS server supporting the EAP-Message      attribute MUST calculate the correct value of the      Message-Authenticator and MUST silently discard the packet if it      does not match the value sent.  A RADIUS server not supporting the      EAP-Message attribute MUST return an Access-Reject if it receives      an Access-Request containing an EAP-Message attribute.Aboba & Calhoun              Informational                     [Page 15]

RFC 3579                      RADIUS & EAP                September 2003      Access-Challenge, Access-Accept, or Access-Reject packets      including EAP-Message attribute(s) without a Message-Authenticator      attribute SHOULD be silently discarded by the NAS.  A NAS      supporting the EAP-Message attribute MUST calculate the correct      value of the Message-Authenticator and MUST silently discard the      packet if it does not match the value sent.      A summary of the EAP-Message attribute format is shown below.  The      fields are transmitted from left to right.       0                   1                   2       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |     Type      |    Length     |     String...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      79 for EAP-Message   Length      >= 3   String      The String field contains an EAP packet, as defined in [RFC2284].      If multiple EAP-Message attributes are present in a packet their      values should be concatenated; this allows EAP packets longer than      253 octets to be transported by RADIUS.3.2.  Message-Authenticator   Description      This attribute MAY be used to authenticate and integrity-protect      Access-Requests in order to prevent spoofing.  It MAY be used in      any Access-Request.  It MUST be used in any Access-Request,      Access-Accept, Access-Reject or Access-Challenge that includes an      EAP-Message attribute.      A RADIUS server receiving an Access-Request with a      Message-Authenticator attribute present MUST calculate the correct      value of the Message-Authenticator and silently discard the packet      if it does not match the value sent.Aboba & Calhoun              Informational                     [Page 16]

RFC 3579                      RADIUS & EAP                September 2003      A RADIUS client receiving an Access-Accept, Access-Reject or      Access-Challenge with a Message-Authenticator attribute present      MUST calculate the correct value of the Message-Authenticator and      silently discard the packet if it does not match the value sent.      This attribute is not required in Access-Requests which include      the User-Password attribute, but is useful for preventing attacks      on other types of authentication.  This attribute is intended to      thwart attempts by an attacker to setup a "rogue" NAS, and perform      online dictionary attacks against the RADIUS server.  It does not      afford protection against "offline" attacks where the attacker      intercepts packets containing (for example) CHAP challenge and      response, and performs a dictionary attack against those packets      offline.      A summary of the Message-Authenticator attribute format is shown      below.  The fields are transmitted from left to right.       0                   1                   2       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |     Type      |    Length     |     String...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      80 for Message-Authenticator   Length      18   String      When present in an Access-Request packet, Message-Authenticator is      an HMAC-MD5 [RFC2104] hash of the entire Access-Request packet,      including Type, ID, Length and Authenticator, using the shared      secret as the key, as follows.      Message-Authenticator = HMAC-MD5 (Type, Identifier, Length,      Request Authenticator, Attributes)      When the message integrity check is calculated the signature      string should be considered to be sixteen octets of zero.Aboba & Calhoun              Informational                     [Page 17]

RFC 3579                      RADIUS & EAP                September 2003      For Access-Challenge, Access-Accept, and Access-Reject packets,      the Message-Authenticator is calculated as follows, using the      Request-Authenticator from the Access-Request this packet is in      reply to:      Message-Authenticator = HMAC-MD5 (Type, Identifier, Length,      Request Authenticator, Attributes)      When the message integrity check is calculated the signature      string should be considered to be sixteen octets of zero.  The      shared secret is used as the key for the HMAC-MD5 message      integrity check.  The Message-Authenticator is calculated and      inserted in the packet before the Response Authenticator is      calculated.3.3.  Table of Attributes   The following table provides a guide to which attributes may be found   in packets including EAP-Message attribute(s), and in what quantity.   The EAP-Message and Message-Authenticator attributes specified in   this document MUST NOT be present in an Accounting-Request.  If a   table entry is omitted, the values found in [RFC2548], [RFC2865],   [RFC2868], [RFC2869] and [RFC3162] should be assumed.Request  Accept  Reject  Challenge   #    Attribute0-1      0-1     0       0            1   User-Name0        0     0       0            2   User-Password [Note 1]0        0     0       0            3   CHAP-Password [Note 1]0        0     0       0           18   Reply-Message0        0     0       0           60   CHAP-Challenge0        0     0       0           70   ARAP-Password [Note 1]0        0     0       0           75   Password-Retry1+       1+      1+      1+          79   EAP-Message [Note 1]1        1     1       1           80   Message-Authenticator [Note 1]0-1      0       0       0           94   Originating-Line-Info [Note 3]0        0     0-1     0-1        101   Error-Cause [Note 2]Request  Accept  Reject  Challenge   #    Attribute   [Note 1] An Access-Request that contains either a User-Password or   CHAP-Password or ARAP-Password or one or more EAP-Message attributes   MUST NOT contain more than one type of those four attributes.  If it   does not contain any of those four attributes, it SHOULD contain a   Message-Authenticator.  If any packet type contains an EAP-Message   attribute it MUST also contain a Message-Authenticator.  A RADIUS   server receiving an Access-Request not containing any of those four   attributes and also not containing a Message-Authenticator attribute   SHOULD silently discard it.Aboba & Calhoun              Informational                     [Page 18]

RFC 3579                      RADIUS & EAP                September 2003   [Note 2] The Error-Cause attribute is defined in [RFC3576].   [Note 3] The Originating-Line-Info attribute is defined in [NASREQ].   The following table defines the meaning of the above table entries.   0     This attribute MUST NOT be present.   0+    Zero or more instances of this attribute MAY be present.   0-1   Zero or one instance of this attribute MAY be present.   1     Exactly one instance of this attribute MUST be present.   1+    One or more of these attributes MUST be present.4.  Security Considerations4.1.  Security Requirements   RADIUS/EAP is used in order to provide authentication and   authorization for network access.  As a result, both the RADIUS and   EAP portions of the conversation are potential targets of an attack.   Threats are discussed in [RFC2607], [RFC2865], and [RFC3162].   Examples include:   [1]  An adversary may attempt to acquire confidential data and        identities by snooping RADIUS packets.   [2]  An adversary may attempt to modify packets containing RADIUS        messages.   [3]  An adversary may attempt to inject packets into a RADIUS        conversation.   [4]  An adversary may launch a dictionary attack against the RADIUS        shared secret.   [5]  An adversary may launch a known plaintext attack, hoping to        recover the key stream corresponding to a Request Authenticator.   [6]  An adversary may attempt to replay a RADIUS exchange.   [7]  An adversary may attempt to disrupt the EAP negotiation, in        order to weaken the authentication, or gain access to peer        passwords.   [8]  An authenticated NAS may attempt to forge NAS or session        identification attributes,   [9]  A rogue (unauthenticated) NAS may attempt to impersonate a        legitimate NAS.Aboba & Calhoun              Informational                     [Page 19]

RFC 3579                      RADIUS & EAP                September 2003   [10] An attacker may attempt to act as a man-in-the-middle.   To address these threats, it is necessary to support confidentiality,   data origin authentication, integrity, and replay protection on a   per-packet basis.  Bi-directional authentication between the RADIUS   client and server also needs to be provided.  There is no requirement   that the identities of RADIUS clients and servers be kept   confidential (e.g., from a passive eavesdropper).4.2.  Security Protocol   To address the security vulnerabilities of RADIUS/EAP,   implementations of this specification SHOULD support IPsec [RFC2401]   along with IKE [RFC2409] for key management.  IPsec ESP [RFC2406]   with non-null transform SHOULD be supported, and IPsec ESP with a   non-null encryption transform and authentication support SHOULD be   used to provide per-packet confidentiality, authentication, integrity   and replay protection.  IKE SHOULD be used for key management.   Within RADIUS [RFC2865], a shared secret is used for hiding of   attributes such as User-Password, as well as in computation of the   Response Authenticator.  In RADIUS accounting [RFC2866], the shared   secret is used in computation of both the Request Authenticator and   the Response Authenticator.   Since in RADIUS a shared secret is used to provide confidentiality as   well as integrity protection and authentication, only use of IPsec   ESP with a non-null transform can provide security services   sufficient to substitute for RADIUS application-layer security.   Therefore, where IPSEC AH or ESP null is used, it will typically   still be necessary to configure a RADIUS shared secret.   Where RADIUS is run over IPsec ESP with a non-null transform, the   secret shared between the NAS and the RADIUS server MAY NOT be   configured.  In this case, a shared secret of zero length MUST be   assumed.  However, a RADIUS server that cannot know whether incoming   traffic is IPsec-protected MUST be configured with a non-null RADIUS   shared secret.   When IPsec ESP is used with RADIUS, per-packet authentication,   integrity and replay protection MUST be used.  3DES-CBC MUST be   supported as an encryption transform and AES-CBC SHOULD be supported.   AES-CBC SHOULD be offered as a preferred encryption transform if   supported.  HMAC-SHA1-96 MUST be supported as an authentication   transform.  DES-CBC SHOULD NOT be used as the encryption transform.Aboba & Calhoun              Informational                     [Page 20]

RFC 3579                      RADIUS & EAP                September 2003   A typical IPsec policy for an IPsec-capable RADIUS client is   "Initiate IPsec, from me to any destination port UDP 1812".  This   causes an IPsec SA to be set up by the RADIUS client prior to sending   RADIUS traffic.  If some RADIUS servers contacted by the client do   not support IPsec, then a more granular policy will be required:   "Initiate IPsec, from me to IPsec-Capable-RADIUS-Server, destination   port UDP 1812".   For an IPsec-capable RADIUS server, a typical IPsec policy is "Accept   IPsec, from any to me, destination port 1812".  This causes the   RADIUS server to accept (but not require) use of IPsec.  It may not   be appropriate to require IPsec for all RADIUS clients connecting to   an IPsec-enabled RADIUS server, since some RADIUS clients may not   support IPsec.   Where IPsec is used for security, and no RADIUS shared secret is   configured, it is important that the RADIUS client and server perform   an authorization check.  Before enabling a host to act as a RADIUS   client, the RADIUS server SHOULD check whether the host is authorized   to provide network access.  Similarly, before enabling a host to act   as a RADIUS server, the RADIUS client SHOULD check whether the host   is authorized for that role.   RADIUS servers can be configured with the IP addresses (for IKE   Aggressive Mode with pre-shared keys) or FQDNs (for certificate   authentication) of RADIUS clients.  Alternatively, if a separate   Certification Authority (CA) exists for RADIUS clients, then the   RADIUS server can configure this CA as a trust anchor [RFC3280] for   use with IPsec.   Similarly, RADIUS clients can be configured with the IP addresses   (for IKE Aggressive Mode with pre-shared keys) or FQDNs (for   certificate authentication) of RADIUS servers.  Alternatively, if a   separate CA exists for RADIUS servers, then the RADIUS client can   configure this CA as a trust anchor for use with IPsec.   Since unlike SSL/TLS, IKE does not permit certificate policies to be   set on a per-port basis, certificate policies need to apply to all   uses of IPsec on RADIUS clients and servers.  In IPsec deployments   supporting only certificate authentication, a management station   initiating an IPsec-protected telnet session to the RADIUS server   would need to obtain a certificate chaining to the RADIUS client CA.   Issuing such a certificate might not be appropriate if the management   station was not authorized as a RADIUS client.   Where RADIUS clients may obtain their IP address dynamically (such as   an Access Point supporting DHCP), IKE Main Mode with pre-shared keys   [RFC2409] SHOULD NOT be used, since this requires use of a groupAboba & Calhoun              Informational                     [Page 21]

RFC 3579                      RADIUS & EAP                September 2003   pre-shared key; instead, Aggressive Mode SHOULD be used.  IKEv2, a   work in progress, may address this issue in the future.  Where RADIUS   client addresses are statically assigned, either Aggressive Mode or   Main Mode MAY be used.  With certificate authentication, Main Mode   SHOULD be used.   Care needs to be taken with IKE Phase 1 Identity Payload selection in   order to enable mapping of identities to pre-shared keys even with   Aggressive Mode.  Where the ID_IPV4_ADDR or ID_IPV6_ADDR Identity   Payloads are used and addresses are dynamically assigned, mapping of   identities to keys is not possible, so that group pre-shared keys are   still a practical necessity.  As a result, the ID_FQDN identity   payload SHOULD be employed in situations where Aggressive mode is   utilized along with pre-shared keys and IP addresses are dynamically   assigned.  This approach also has other advantages, since it allows   the RADIUS server and client to configure themselves based on the   fully qualified domain name of their peers.   Note that with IPsec, security services are negotiated at the   granularity of an IPsec SA, so that RADIUS exchanges requiring a set   of security services different from those negotiated with existing   IPsec SAs will need to negotiate a new IPsec SA.  Separate IPsec SAs   are also advisable where quality of service considerations dictate   different handling RADIUS conversations.  Attempting to apply   different quality of service to connections handled by the same IPsec   SA can result in reordering, and falling outside the replay window.   For a discussion of the issues, see [RFC2983].4.3.  Security Issues   This section provides more detail on the vulnerabilities identified   inSection 4.1., and how they may be mitigated.  Vulnerabilities   include:   Privacy issues   Spoofing and hijacking   Dictionary attacks   Known plaintext attacks   Replay attacks   Negotiation attacks   Impersonation   Man in the middle attacks   Separation of authenticator and authentication server   Multiple databasesAboba & Calhoun              Informational                     [Page 22]

RFC 3579                      RADIUS & EAP                September 20034.3.1.  Privacy Issues   Since RADIUS messages may contain the User-Name attribute as well as   NAS-IP-Address or NAS-Identifier attributes, an attacker snooping on   RADIUS traffic may be able to determine the geographic location of   peers in real time.  In wireless networks, it is often assumed that   RADIUS traffic is physically secure, since it typically travels over   the wired network and that this limits the release of location   information.   However, it is possible for an authenticated attacker to spoof ARP   packets [RFC826] so as to cause diversion of RADIUS traffic onto the   wireless network.  In this way an attacker may obtain RADIUS packets   from which it can glean peer location information, or which it can   subject to a known plaintext or offline dictionary attack.  To   address these vulnerabilities, implementations of this specification   SHOULD use IPsec ESP with non-null transform and per-packet   encryption, authentication, integrity and replay protection to   protect both RADIUS authentication [RFC2865] and accounting [RFC2866]   traffic, as described inSection 4.2.4.3.2.  Spoofing and Hijacking   Access-Request packets with a User-Password attribute establish the   identity of both the user and the NAS sending the Access-Request,   because of the way the shared secret between the NAS and RADIUS   server is used.  Access-Request packets with CHAP-Password or   EAP-Message attributes do not have a User-Password attribute.  As a   result, the Message-Authenticator attribute SHOULD be used in   Access-Request packets that do not have a User-Password attribute, in   order to establish the identity of the NAS sending the request.   An attacker may attempt to inject packets into the conversation   between the NAS and the RADIUS server, or between the RADIUS server   and the security server.  RADIUS [RFC2865] does not support   encryption other than attribute hiding.  As described in [RFC2865],   only Access-Reply and Access-Challenge packets are integrity   protected.  Moreover, the per-packet authentication and integrity   protection mechanism described in [RFC2865] has known weaknesses   [MD5Attack], making it a tempting target for attackers looking to   subvert RADIUS/EAP.   To provide stronger security, the Message-Authenticator attribute   MUST be used in all RADIUS packets containing an EAP-Message   attribute.  Implementations of this specification SHOULD use IPsec   ESP with non-null transform and per-packet encryption,   authentication, integrity and replay protection, as described inSection 4.2.Aboba & Calhoun              Informational                     [Page 23]

RFC 3579                      RADIUS & EAP                September 20034.3.3.  Dictionary Attacks   The RADIUS shared secret is vulnerable to offline dictionary attack,   based on capture of the Response Authenticator or   Message-Authenticator attribute.  In order to decrease the level of   vulnerability, [RFC2865] recommends:      The secret (password shared between the client and the RADIUS      server) SHOULD be at least as large and unguessable as a      well-chosen password.  It is preferred that the secret be at least      16 octets.   The risk of an offline dictionary attack can be further reduced by   employing IPsec ESP with non-null transform in order to encrypt the   RADIUS conversation, as described inSection 4.2.4.3.4.  Known Plaintext Attacks   Since EAP [RFC2284] does not support PAP, the RADIUS User-Password   attribute is not used to carry hidden user passwords within   RADIUS/EAP conversations.  The User-Password hiding mechanism,   defined in [RFC2865] utilizes MD5, defined in [RFC1321], in order to   generate a key stream based on the RADIUS shared secret and the   Request  Authenticator.  Where PAP is in use, it is possible to   collect key streams corresponding to a given Request Authenticator   value, by capturing RADIUS conversations corresponding to a PAP   authentication attempt, using a known password.  Since the   User-Password is known, the key stream corresponding to a given   Request Authenticator can be determined and stored.   Since the key stream may have been determined previously from a known   plaintext attack, if the Request Authenticator repeats, attributes   encrypted using the RADIUS attribute hiding mechanism should be   considered compromised.  In addition to the User-Password attribute,   which is not used with EAP, this includes attributes such as   Tunnel-Password [RFC2868,section 3.5] and MS-MPPE-Send-Key and   MS-MPPE-Recv-Key attributes [RFC2548,section 2.4], which include a   Salt field as part of the hiding algorithm.   To avoid this,[RFC2865], Section 3 advises:      Since it is expected that the same secret MAY be used to      authenticate with servers in disparate geographic regions, the      Request Authenticator field SHOULD exhibit global and temporal      uniqueness.Aboba & Calhoun              Informational                     [Page 24]

RFC 3579                      RADIUS & EAP                September 2003   Where the Request Authenticator repeats, the Salt field defined in[RFC2548], Section 2.4 does not provide protection against   compromise.  This is because MD5 [RFC1321], rather than HMAC-MD5   [RFC2104], is used to generate the key stream, which is calculated   from the 128-bit RADIUS shared secret (S), the  128-bit Request   Authenticator (R), and the Salt field (A), using the formula b(1) =   MD5(S + R + A).  Since the Salt field is placed at the end, if the   Request Authenticator were to repeat on a network where PAP is in   use, then the salted keystream could be calculated from the   User-Password keystream by continuing the MD5 calculation based on   the Salt field (A), which is sent in the clear.   Even though EAP does not support PAP authentication, a security   vulnerability can still exist where the same RADIUS shared secret is   used for hiding User-Password as well as other attributes.  This can   occur, for example, if the same RADIUS proxy handles authentication   requests for both EAP and PAP.   The threat can be mitigated by protecting RADIUS with IPsec ESP with   non-null transform, as described inSection 4.2.  Where RADIUS shared   secrets are configured, the RADIUS shared secret used by a NAS   supporting EAP MUST NOT be reused by a NAS utilizing the   User-Password attribute, since improper shared secret hygiene could   lead to compromise of hidden attributes.4.3.5.  Replay Attacks   The RADIUS protocol provides only limited support for replay   protection.  RADIUS Access-Requests include liveness via the 128-bit   Request Authenticator.  However, the Request Authenticator is not a   replay counter.  Since RADIUS servers may not maintain a cache of   previous Request Authenticators, the Request Authenticator does not   provide replay protection.   RADIUS accounting [RFC2866] does not support replay protection at the   protocol level.  Due to the need to support failover between RADIUS   accounting servers, protocol-based replay protection is not   sufficient to prevent duplicate accounting records.  However, once   accepted by the accounting server, duplicate accounting records can   be detected by use of the the Acct-Session-Id [RFC2866,section 5.5]   and Event-Timestamp [RFC2869,section 5.3] attributes.   Unlike RADIUS authentication, RADIUS accounting does not use the   Request Authenticator as a nonce.  Instead, the Request Authenticator   contains an MD5 hash calculated over the Code, Identifier, Length,   and request attributes of the Accounting Request packet, plus the   shared secret.  The Response Authenticator also contains an MD5 hash   calculated over the Code, Identifier and Length, the RequestAboba & Calhoun              Informational                     [Page 25]

RFC 3579                      RADIUS & EAP                September 2003   Authenticator field from the Accounting-Request packet being replied   to, the response attributes and the shared secret.   Since the Accounting Response Authenticator depends in part on the   Accounting Request Authenticator, it is not possible to replay an   Accounting-Response unless the Request Authenticator repeats.  While   it is possible to utilize EAP methods such as EAP TLS [RFC2716] which   include liveness checks on both sides, not all EAP messages will   include liveness so that this provides incomplete protection.   Strong replay protection for RADIUS authentication and accounting can   be provided by enabling IPsec replay protection with RADIUS, as   described inSection 4.2.4.3.6.  Negotiation Attacks   In a negotiation attack a rogue NAS, tunnel server, RADIUS proxy or   RADIUS server attempts to cause the authenticating peer to choose a   less secure authentication method.  For example, a session that would   normally be authenticated with EAP would instead be authenticated via   CHAP or PAP; alternatively, a connection that would normally be   authenticated via a more secure EAP method such as EAP-TLS [RFC2716]   might be made to occur via a less secure EAP method, such as   MD5-Challenge.  The threat posed by rogue devices, once thought to be   remote, has gained currency given compromises of telephone company   switching systems, such as those described in [Masters].   Protection against negotiation attacks requires the elimination of   downward negotiations.  The RADIUS exchange may be further protected   by use of IPsec, as described inSection 4.2.  Alternatively, where   IPsec is not used, 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 RADIUS   server.  For the authenticating peer, authentication policy should be   set on a per-connection basis.  Per-connection policy allows an   authenticating peer to negotiate a strong EAP method when connecting   to one service, while negotiating a weaker EAP method for another   service.   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.   Should the NAS not be able to negotiate EAP, or should the   EAP-Request sent by the NAS be of a different EAP type than what is   expected, the authenticating peer MUST disconnect.  An authenticatingAboba & Calhoun              Informational                     [Page 26]

RFC 3579                      RADIUS & EAP                September 2003   peer expecting EAP to be negotiated for a session MUST NOT negotiate   a weaker method, such as CHAP or PAP.  In wireless networks, the   service advertisement itself may be spoof-able, so that an attacker   could fool the peer into negotiating an authentication method   suitable for a less secure network.   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 RADIUS.  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.   If CHAP is negotiated, the NAS will pass the User-Name and   CHAP-Password attributes to the RADIUS server in an Access-Request   packet.  If the peer is not required to use EAP, then the RADIUS   server will respond with an Access-Accept or Access-Reject packet as   appropriate.  However, if CHAP has been negotiated but EAP is   required, the RADIUS server MUST respond with an Access-Reject,   rather than an Access-Challenge/EAP-Message/EAP-Request packet.  The   authenticating peer MUST refuse to renegotiate authentication, even   if the renegotiation is from CHAP to EAP.   If EAP is negotiated but is not supported by the RADIUS proxy or   server, then the server or proxy MUST respond with an Access-Reject.   In these cases, a PPP NAS MUST send an LCP-Terminate and disconnect   the peer.  This is the correct behavior since the authenticating peer   is expecting EAP to be negotiated, and that expectation cannot be   fulfilled.  An EAP-capable authenticating peer MUST refuse to   renegotiate the authentication protocol if EAP had initially been   negotiated.  Note that problems with a non-EAP capable RADIUS proxy   could prove difficult to diagnose, since a peer connecting from one   location (with an EAP-capable proxy) might be able to successfully   authenticate via EAP, while the same peer connecting at another   location (and encountering an EAP-incapable proxy) might be   consistently disconnected.4.3.7.  Impersonation   [RFC2865]Section 3 states:      A RADIUS server MUST use the source IP address of the RADIUS UDP      packet to decide which shared secret to use, so that RADIUS      requests can be proxied.Aboba & Calhoun              Informational                     [Page 27]

RFC 3579                      RADIUS & EAP                September 2003   When RADIUS requests are forwarded by a proxy, the NAS-IP-Address or   NAS-IPv6-Address attributes may not match the source address.  Since   the NAS-Identifier attribute need not contain an FQDN, this attribute   also may not correspond to the source address, even indirectly, with   or without a proxy present.   As a result, the authenticity check performed by a RADIUS server or   proxy does not verify the correctness of NAS identification   attributes.  This makes it possible for a rogue NAS to forge   NAS-IP-Address, NAS-IPv6-Address or NAS-Identifier attributes within   a RADIUS Access-Request in order to impersonate another NAS.  It is   also possible for a rogue NAS to forge session identification   attributes such as Called-Station-Id, Calling-Station-Id, and   Originating-Line-Info.   This could fool the RADIUS server into subsequently sending   Disconnect or CoA-Request messages [RFC3576] containing forged   session identification attributes to a NAS targeted by an attacker.   To address these vulnerabilities RADIUS proxies SHOULD check whether   NAS identification attributes (NAS-IP-Address, NAS-IPv6-Address,   NAS-Identifier) match the source address of packets originating from   the NAS.  Where a match is not found, an Access-Reject SHOULD be   sent, and an error SHOULD be logged.   However, such a check may not always be possible.  Since the   NAS-Identifier attribute need not correspond to an FQDN, it may not   be resolvable to an IP address to be matched against the source   address.  Also, where a NAT exists between the RADIUS client and   proxy, checking the NAS-IP-Address or NAS-IPv6-Address attributes may   not be feasible.   To allow verification of NAS and session identification parameters,   EAP methods can support the secure exchange of these parameters   between the EAP peer and EAP server.  NAS identification attributes   include NAS-IP-Address, NAS-IPv6-Address and Called-Station-Id;   session identification attributes include User-Name and   Calling-Station-Id.  The secure exchange of these parameters between   the EAP peer and server enables the RADIUS server to check whether   the attributes provided by the NAS match those provided by the peer;   similarly, the peer can check the parameters provided by the NAS   against those provided by the EAP server.  This enables detection of   a rogue NAS.Aboba & Calhoun              Informational                     [Page 28]

RFC 3579                      RADIUS & EAP                September 20034.3.8.  Man in the Middle Attacks   RADIUS only provides security on a hop-by-hop basis, even where IPsec   is used.  As a result, an attacker gaining control of a RADIUS proxy   could attempt to modify EAP packets in transit.  To protect against   this, EAP methods SHOULD incorporate their own per-packet integrity   protection and authentication mechanisms.4.3.9.  Separation of Authenticator and Authentication Server   As noted in [RFC2716], it is possible for the EAP peer and   authenticator to mutually authenticate, and derive a Master Session   Key (MSK) for a ciphersuite used to protect subsequent data traffic.   This does not present an issue on the peer, since the peer and EAP   client reside on the same machine; all that is required is for the   EAP client module to derive and pass a Transient Session Key (TSK) to   the ciphersuite module.   The situation is more complex when EAP is used with RADIUS, since the   authenticator and authentication server may not reside on the same   host.   In the case where the authenticator and authentication server reside   on different machines, there are several implications for security.   First, mutual authentication will occur between the peer and the   authentication server, not between the peer and the authenticator.   This means that it is not possible for the peer to validate the   identity of the NAS or tunnel server that it is speaking to, using   EAP alone.   As described inSection 4.2, when RADIUS/EAP is used to encapsulate   EAP packets, IPsec SHOULD be used to provide per-packet   authentication, integrity, replay protection and confidentiality.   The Message-Authenticator attribute is also required in RADIUS   Access-Requests containing an EAP-Message attribute sent from the NAS   or tunnel server to the RADIUS server.  Since the   Message-Authenticator attribute involves an HMAC-MD5 message   integrity check, it is possible for the RADIUS server to verify the   integrity of the Access-Request as well as the NAS or tunnel server's   identity, even where IPsec is not used.  Similarly, Access-Challenge   packets containing an EAP-Message attribute sent from the RADIUS   server to the NAS are also authenticated and integrity protected   using an HMAC-MD5 message integrity check, enabling the NAS or tunnel   server to determine the integrity of the packet and verify the   identity of the RADIUS server, even where IPsec is not used.   Moreover, EAP packets sent using methods that contain their own   integrity protection cannot be successfully modified by a rogue NAS   or tunnel server.Aboba & Calhoun              Informational                     [Page 29]

RFC 3579                      RADIUS & EAP                September 2003   The second issue that arises where the authenticator and   authentication server reside on separate hosts is that the EAP Master   Session Key (MSK) negotiated between the peer and authentication   server will need to be transmitted to the authenticator.  Therefore a   mechanism needs to be provided to transmit the MSK from the   authentication server to the NAS or tunnel server that needs it.  The   specification of the key transport and wrapping mechanism is outside   the scope of this document.  However, it is expected that the   wrapping mechanism will provide confidentiality, integrity and replay   protection, and data origin authentication.4.3.10.  Multiple Databases   In many cases a security server will be deployed along with a RADIUS   server in order to provide EAP services.  Unless the security server   also functions as a RADIUS server, two separate user databases will   exist, each containing information about the security requirements   for the user.  This represents a weakness, since security may be   compromised by a successful attack on either of the servers, or their   databases.  With multiple user databases, adding a new user may   require multiple operations, increasing the chances for error.  The   problems are further magnified in the case where user information is   also being kept in an LDAP server.  In this case, three stores of   user information may exist.   In order to address these threats, consolidation of databases is   recommended.  This can be achieved by having both the RADIUS server   and security server store information in the same database; by having   the security server provide a full RADIUS implementation; or by   consolidating both the  security server and the RADIUS server onto   the same machine.5.  IANA Considerations   This specification does not create any new registries, or define any   new RADIUS attributes or values.6.  References6.1.  Normative References   [RFC1321]      Rivest, R., "The MD5 Message-Digest Algorithm",RFC1321, April 1992.   [RFC2104]      Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:                  Keyed-Hashing for Message Authentication",RFC 2104,                  February 1997.Aboba & Calhoun              Informational                     [Page 30]

RFC 3579                      RADIUS & EAP                September 2003   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate                  Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2279]      Yergeau, F., "UTF-8, a transformation format of ISO                  10646",RFC 2279, January 1998.   [RFC2284]      Blunk, L. and J. Vollbrecht, "PPP Extensible                  Authentication Protocol (EAP)",RFC 2284, March 1998.   [RFC2401]      Atkinson, R. and S. Kent, "Security Architecture for                  the Internet Protocol",RFC 2401, November 1998.   [RFC2406]      Kent, S. and R. Atkinson, "IP Encapsulating Security                  Payload (ESP)",RFC 2406, November 1998.   [RFC2409]      Harkins, D. and D. Carrel, "The Internet Key Exchange                  (IKE)",RFC 2409, November 1998.   [RFC2486]      Aboba, B. and M. Beadles, "The Network Access                  Identifier",RFC 2486, January 1999.   [RFC2865]      Rigney, C., Willens, S., Rubens, A. and W. Simpson,                  "Remote Authentication Dial In User Service (RADIUS)",RFC 2865, June 2000.   [RFC2988]      Paxson, V. and M. Allman, "Computing TCP's                  Retransmission Timer",RFC 2988, November 2000.   [RFC3162]      Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IP6",RFC 3162, August 2001.   [RFC3280]      Housley, R., Polk, W., Ford, W. and D. Solo, "Internet                  X.509 Public Key Infrastructure Certificate and                  Certificate Revocation List (CRL) Profile",RFC 3280,                  April 2002.   [RFC3576]      Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B.                  Aboba, "Dynamic Authorization Extensions to Remote                  Authentication Dial In User Service (RADIUS)",RFC3576, July 2003.Aboba & Calhoun              Informational                     [Page 31]

RFC 3579                      RADIUS & EAP                September 20036.2.  Informative References   [RFC826]       Plummer, D., "An Ethernet Address Resolution                  Protocol", STD 37,RFC 826, November 1982.   [RFC1510]      Kohl, J. and C. Neuman, "The Kerberos Network                  Authentication Service (V5)",RFC 1510, September                  1993.   [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.   [RFC2716]      Aboba, B. and D. Simon,"PPP EAP TLS Authentication                  Protocol",RFC 2716, October 1999.   [RFC2866]      Rigney, C., "RADIUS Accounting",RFC 2866, June 2000.   [RFC2867]      Zorn, G., Aboba, B. and D. Mitton, "RADIUS Accounting                  Modifications for Tunnel Protocol Support",RFC 2867,                  June 2000.   [RFC2868]      Zorn, G., Leifer, D., Rubens, A., Shriver, J.,                  Holdrege, M. and I. Goyret, "RADIUS Attributes for                  Tunnel Protocol Support",RFC 2868, June 2000.   [RFC2869]      Rigney, C., Willats, W. and P. Calhoun, "RADIUS                  Extensions",RFC 2869, June 2000.   [RFC2983]      Black, D. "Differentiated Services and Tunnels",RFC2983, October 2000.   [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.   [IEEE802]      IEEE Standards for Local and Metropolitan Area                  Networks:  Overview and Architecture, ANSI/IEEE Std                  802, 1990.Aboba & Calhoun              Informational                     [Page 32]

RFC 3579                      RADIUS & EAP                September 2003   [IEEE8021X]    IEEE Standards for Local and Metropolitan Area                  Networks:  Port based Network Access Control, IEEE Std                  802.1X-2001, June 2001.   [MD5Attack]    Dobbertin, H., "The Status of MD5 After a Recent                  Attack", CryptoBytes Vol.2 No.2, Summer 1996.   [Masters]      Slatalla, M. and  J. Quittner, "Masters of Deception."                  HarperCollins, New York, 1995.   [NASREQ]       Calhoun, P., et al., "Diameter Network Access Server                  Application", Work in Progress.Aboba & Calhoun              Informational                     [Page 33]

RFC 3579                      RADIUS & EAP                September 2003Appendix A - Examples   The examples below illustrate conversations between an authenticating   peer, NAS, and RADIUS server.  The OTP and EAP-TLS protocols are used   only for illustrative purposes; other authentication protocols could   also have been used, although they might show somewhat different   behavior.   Where the NAS sends an EAP-Request/Identity as the initial packet,   the exchange appears as follows:Authenticating peer     NAS                    RADIUS server-------------------     ---                    -------------                        <- EAP-Request/                        IdentityEAP-Response/Identity (MyID) ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        (MyID) ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Request                                               OTP/OTP Challenge                        <- EAP-Request/                        OTP/OTP ChallengeEAP-Response/OTP, OTPpw ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        OTP, OTPpw ->                                                <- RADIUS                                                Access-Accept/                                                EAP-Message/EAP-Success                                                (other attributes)                        <- EAP-SuccessAboba & Calhoun              Informational                     [Page 34]

RFC 3579                      RADIUS & EAP                September 2003   In the case where the NAS initiates with an EAP-Request for EAP TLS   [RFC2716], and the identity is determined based on the contents of   the client certificate, the exchange will appear as follows:Authenticating peer     NAS                    RADIUS server-------------------     ---                    -------------                        <- EAP-Request/                        EAP-Type=EAP-TLS                        (TLS Start, S bit set)EAP-Response/EAP-Type=EAP-TLS(TLS client_hello)->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        EAP-Type=EAP-TLS->                                              <-RADIUS Access-Challenge/                                              EAP-Message/                                              EAP-Request/                                              EAP-Type=EAP-TLS                         <- EAP-Request/                         EAP-Type=EAP-TLS                         (TLS server_hello,                         TLS certificate,                   [TLS server_key_exchange,]                   [TLS certificate_request,]                       TLS server_hello_done)EAP-Response/EAP-Type=EAP-TLS(TLS certificate,TLS client_key_exchange,[TLS certificate_verify,]TLS change_cipher_spec,TLS finished)->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        EAP-Type=EAP-TLS->                                              <-RADIUS Access-Challenge/                                              EAP-Message/                                              EAP-Request/                                              EAP-Type=EAP-TLS                        <- EAP-Request/                        EAP-Type=EAP-TLS                        (TLS change_cipher_spec,                        TLS finished)Aboba & Calhoun              Informational                     [Page 35]

RFC 3579                      RADIUS & EAP                September 2003EAP-Response/EAP-Type=EAP-TLS ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        EAP-Type=EAP-TLS->                                              <-RADIUS Access-Accept/                                              EAP-Message/EAP-Success                                              (other attributes)                        <- EAP-Success   In the case where the NAS first sends an EAP-Start packet to the   RADIUS server,  the conversation would appear as follows:Authenticating peer     NAS                    RADIUS server-------------------     ---                    -------------                        RADIUS Access-Request/                        EAP-Message/Start ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Request/                                               Identity                        <- EAP-Request/                        IdentityEAP-Response/Identity (MyID) ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        Identity (MyID) ->                                                <- RADIUS                                                Access-Challenge/                                                EAP-Message/EAP-Request/                                                OTP/OTP Challenge                        <- EAP-Request/                        OTP/OTP ChallengeEAP-Response/OTP, OTPpw ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        OTP, OTPpw ->                                                <- RADIUS                                                Access-Accept/                                                EAP-Message/EAP-Success                                                (other attributes)                        <- EAP-SuccessAboba & Calhoun              Informational                     [Page 36]

RFC 3579                      RADIUS & EAP                September 2003   In the case where the NAS initiates with an EAP-Request for EAP TLS   [RFC2716], but the peer responds with a Nak, indicating that it would   prefer another method not implemented locally on the NAS, the   exchange will appear as follows:Authenticating peer     NAS                    RADIUS server-------------------     ---                    -------------                        <- EAP-Request/                        EAP-Type=EAP-TLS                        (TLS Start, S bit set)EAP-Response/EAP-Type=Nak(Alternative(s))->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        Nak ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Request/                                               Identity                        <- EAP-Request/                        IdentityEAP-Response/Identity (MyID) ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        (MyID) ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Request                                               OTP/OTP Challenge                        <- EAP-Request/                        OTP/OTP ChallengeEAP-Response/OTP, OTPpw ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        OTP, OTPpw ->                                                <- RADIUS                                                Access-Accept/                                                EAP-Message/EAP-Success                                                (other attributes)                        <- EAP-SuccessAboba & Calhoun              Informational                     [Page 37]

RFC 3579                      RADIUS & EAP                September 2003   In the case where the authenticating peer attempts to authenticate   the NAS, the conversation would appear as follows:Authenticating peer     NAS                    RADIUS Server-------------------     ---                    -------------EAP-Request/Challenge, MD5 ->                        RADIUS Access-Request/                        EAP-Message/EAP-Request/                        Challenge, MD5 ->                                                <- RADIUS                                                Access-Reject/                                                EAP-Message/                                                EAP-Response/                                                Nak (no alternative)                        <- EAP-Response/Nak                         (no alternative)EAP-Failure ->Aboba & Calhoun              Informational                     [Page 38]

RFC 3579                      RADIUS & EAP                September 2003   In the case where an invalid EAP Response is inserted by an attacker,   the conversation would appear as follows:Authenticating peer     NAS                    RADIUS server-------------------     ---                    -------------                        <- EAP-Request/                        EAP-Type=FooEAP-Response/EAP-Type=Foo ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        EAP-Type=Foo ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Request/                                               EAP-Type=Foo                        <- EAP-Request/                        EAP-Type=FooAttacker spoof:EAP-Response/EAP-Type=Bar ->Good guy:EAP-Response/EAP-Type=Foo ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        EAP-Type=Bar ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Request/                                               EAP-Type=Foo,                                               Error-Cause="Invalid EAP                                                Packet (Ignored)"                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        EAP-Type=Foo ->                                               <- Access-Accept/                                               EAP-Message/Success                        <- EAP SuccessAboba & Calhoun              Informational                     [Page 39]

RFC 3579                      RADIUS & EAP                September 2003   In the case where the client fails EAP authentication, and an error   message is sent prior to disconnection, the conversation would appear   as follows:Authenticating peer     NAS                    RADIUS server-------------------     ---                    -------------                        RADIUS Access-Request/                        EAP-Message/Start ->                                               <- RADIUS                                               Access-Challenge/                                               EAP-Message/EAP-Response/                                               Identity                        <- EAP-Request/                        IdentityEAP-Response/Identity (MyID) ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        (MyID) ->                                                <- RADIUS                                                Access-Challenge/                                                EAP-Message/EAP-Request                                                OTP/OTP Challenge                        <- EAP-Request/                        OTP/OTP ChallengeEAP-Response/OTP, OTPpw ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        OTP, OTPpw ->                                                <- RADIUS                                                Access-Challenge/                                                EAP-Message/EAP-Request/                                                Notification                        <- EAP-Request/                           NotificationEAP-Response/Notification ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        Notification ->                                                 <- RADIUS                                                 Access-Reject/                                                 EAP-Message/EAP-Failure                        <- EAP-Failure                        (client disconnected)Aboba & Calhoun              Informational                     [Page 40]

RFC 3579                      RADIUS & EAP                September 2003   In the case that the RADIUS server or proxy does not support EAP-   Message, but no error message is sent, the conversation would appear   as follows:Authenticating peer     NAS                       RADIUS server-------------------     ---                       -------------                        RADIUS Access-Request/                        EAP-Message/Start ->                                                  <- RADIUS                                                  Access-Reject                        (User Disconnected)In the case where the local RADIUS server does support EAP-Message, butthe remote RADIUS server does not, the conversation would appear asfollows:Authenticating peer     NAS                       RADIUS server-------------------     ---                       -------------                        RADIUS Access-Request/                        EAP-Message/Start ->                                                  <- RADIUS                                                  Access-Challenge/                                                  EAP-Message/                                                  EAP-Response/                                                  Identity                        <- EAP-Request/                        IdentityEAP-Response/Identity(MyID) ->                        RADIUS Access-Request/                        EAP-Message/EAP-Response/                        (MyID) ->                                                  <- RADIUS                                                  Access-Reject                                                  (proxied from remote                                                   RADIUS server)                        (User Disconnected)Aboba & Calhoun              Informational                     [Page 41]

RFC 3579                      RADIUS & EAP                September 2003   In the case where PPP is the link and the authenticating peer does   not support EAP, but where EAP is required for that user, the   conversation would appear as follows:Authenticating peer     NAS                       RADIUS server-------------------     ---                       -------------                        <- PPP LCP Request-EAP                        authPPP LCP NAK-EAPauth ->                        <- PPP LCP Request-CHAP                        authPPP LCP ACK-CHAPauth ->                        <- PPP CHAP ChallengePPP CHAP Response ->                        RADIUS Access-Request/                        User-Name,                        CHAP-Password ->                                                  <- RADIUS                                                  Access-Reject                        <-  PPP LCP Terminate                        (User Disconnected)In the case where PPP is the link, the NAS does not support EAP, butwhere EAP is required for that user, the conversation would appear asfollows:Authenticating peer     NAS                       RADIUS server-------------------     ---                       -------------                        <- PPP LCP Request-CHAP                        authPP LCP ACK-CHAPauth ->                        <- PPP CHAP ChallengePPP CHAP Response ->                        RADIUS Access-Request/                        User-Name,                        CHAP-Password ->                                                 <- RADIUS                                                 Access-Reject                        <-  PPP LCP Terminate                        (User Disconnected)Aboba & Calhoun              Informational                     [Page 42]

RFC 3579                      RADIUS & EAP                September 2003Appendix B - Change Log   The following changes have been made fromRFC 2869:   A NAS may simultaneously support both local authentication and   pass-through; once the NAS enters pass-through mode within a session,   it cannot revert back to local authentication.  Also EAP is   explicitly described as a 'lock step' protocol. (Section 2).   The NAS may initiate with an EAP-Request for an authentication Type.   If the Request is NAK'd, the NAS should send an initial   Access-Request with an EAP-Message attribute containing an   EAP-Response/Nak.   The RADIUS server may treat an invalid EAP Response as a non-fatal   error (Section 2.2)   For use with RADIUS/EAP, the Password-Retry (Section 2.3) and   Reply-Message (2.6.5) attributes are deprecated.   Each EAP session has a unique Identifier space (Section 2.6.1).   Role reversal is not supported (Section 2.6.2).   Message combinations (e.g. Access-Accept/EAP-Failure) that conflict   are discouraged (Section 2.6.3).   Only a single EAP packet may be encapsulated within a RADIUS message   (Section 3.1).   An Access-Request lacking explicit authentication as well as a   Message- Authenticator attribute SHOULD be silently discarded   (Section 3.3).   The Originating-Line-Info attribute is supported (Section 3.3).   IPsec ESP with non-null transform SHOULD be used and the usage model   is described in detail (Section 4.2).   Additional discussion of security vulnerabilities (Section 4.1) and   potential fixes (Section 4.3).   Separated normative (Section 6.1) and informative (Section 6.2)   references.Aboba & Calhoun              Informational                     [Page 43]

RFC 3579                      RADIUS & EAP                September 2003   Added additional examples (Appendix A): a NAS initiating with an   EAP-Request for an authentication Type; attempted role reversal.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 inBCP-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.Acknowledgments   Thanks to Dave Dawson and Karl Fox of Ascend, Glen Zorn of Cisco   Systems, Jari Arkko of Ericsson and Ashwin Palekar, Tim Moore and   Narendra Gidwani of Microsoft for useful discussions of this problem   space.  The authors would also like to acknowledge Tony Jeffree,   Chair of IEEE 802.1 for his assistance in resolving RADIUS/EAP issues   in IEEE 802.1X-2001.Aboba & Calhoun              Informational                     [Page 44]

RFC 3579                      RADIUS & EAP                September 2003Authors' Addresses   Bernard Aboba   Microsoft Corporation   One Microsoft Way   Redmond, WA 98052   Phone:  +1 425 706 6605   Fax:    +1 425 936 7329   EMail:   bernarda@microsoft.com   Pat R. Calhoun   Airespace   110 Nortech Parkway   San Jose, California, 95134   USA   Phone:  +1 408 635 2023   Fax:    +1 408 635 2020   EMail:  pcalhoun@airespace.comAboba & Calhoun              Informational                     [Page 45]

RFC 3579                      RADIUS & EAP                September 2003Full 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   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.Aboba & Calhoun              Informational                     [Page 46]