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rfc:rfc2869

Network Working Group C. Rigney Request for Comments: 2869 Livingston Category: Informational W. Willats

                                                      Cyno Technologies
                                                             P. Calhoun
                                                       Sun Microsystems
                                                              June 2000
                         RADIUS Extensions

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 (2000).  All Rights Reserved.

Abstract

 This document describes additional attributes for carrying
 authentication, authorization and accounting information between a
 Network Access Server (NAS) and a shared Accounting Server using the
 Remote Authentication Dial In User Service (RADIUS) protocol
 described in RFC 2865 [1] and RFC 2866 [2].

Table of Contents

 1.     Introduction ..........................................    2
    1.1       Specification of Requirements ...................    3
    1.2       Terminology .....................................    3
 2.     Operation .............................................    4
    2.1       RADIUS support for Interim Accounting Updates....    4
    2.2       RADIUS support for Apple Remote Access
              Protocol ........................................    5
    2.3       RADIUS Support for Extensible Authentication
              Protocol (EAP) ..................................   11
       2.3.1  Protocol Overview ...............................   11
       2.3.2  Retransmission ..................................   13
       2.3.3  Fragmentation ...................................   14
       2.3.4  Examples ........................................   14
       2.3.5  Alternative uses ................................   19
 3.     Packet Format .........................................   19
 4.     Packet Types ..........................................   19
 5.     Attributes ............................................   20

Rigney, et al. Informational [Page 1] RFC 2869 RADIUS Extensions June 2000

    5.1       Acct-Input-Gigawords ............................   22
    5.2       Acct-Output-Gigawords ...........................   23
    5.3       Event-Timestamp .................................   23
    5.4       ARAP-Password ...................................   24
    5.5       ARAP-Features ...................................   25
    5.6       ARAP-Zone-Access ................................   26
    5.7       ARAP-Security ...................................   27
    5.8       ARAP-Security-Data ..............................   28
    5.9       Password-Retry ..................................   28
    5.10      Prompt ..........................................   29
    5.11      Connect-Info ....................................   30
    5.12      Configuration-Token .............................   31
    5.13      EAP-Message .....................................   32
    5.14      Message-Authenticator ...........................   33
    5.15      ARAP-Challenge-Response .........................   35
    5.16      Acct-Interim-Interval ...........................   36
    5.17      NAS-Port-Id .....................................   37
    5.18      Framed-Pool .....................................   37
    5.19      Table of Attributes .............................   38
 6.     IANA Considerations ...................................   39
 7.     Security Considerations ...............................   39
    7.1       Message-Authenticator Security ..................   39
    7.2       EAP Security ....................................   39
       7.2.1  Separation of EAP server and PPP authenticator ..   40
       7.2.2  Connection hijacking ............................   41
       7.2.3  Man in the middle attacks .......................   41
       7.2.4  Multiple databases ..............................   41
       7.2.5  Negotiation attacks .............................   42
 8.     References ............................................   43
 9.     Acknowledgements ......................................   44
 10.    Chair's Address .......................................   44
 11.    Authors' Addresses ....................................   45
 12.    Full Copyright Statement ..............................   47

1. Introduction

 RFC 2865 [1] describes the RADIUS Protocol as it is implemented and
 deployed today, and RFC 2866 [2] describes how Accounting can be
 performed with RADIUS.

Rigney, et al. Informational [Page 2] RFC 2869 RADIUS Extensions June 2000

 This memo suggests several additional Attributes that can be added to
 RADIUS to perform various useful functions.  These Attributes do not
 have extensive field experience yet and should therefore be
 considered experimental.
 The Extensible Authentication Protocol (EAP) [3] is a PPP extension
 that provides support for additional authentication methods within
 PPP.  This memo describes how the EAP-Message and Message-
 Authenticator attributes may be used for providing EAP support within
 RADIUS.
 All attributes are comprised of variable length Type-Length-Value 3-
 tuples.  New attribute values can be added without disturbing
 existing implementations of the protocol.

1.1. Specification of Requirements

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [4].
 An implementation is not compliant if it fails to satisfy one or more
 of the must or must not requirements for the protocols it implements.
 An implementation that satisfies all the must, must not, should and
 should not requirements for its protocols is said to be
 "unconditionally compliant"; one that satisfies all the must and must
 not requirements but not all the should or should not requirements
 for its protocols is said to be "conditionally compliant."
 A NAS that does not implement a given service MUST NOT implement the
 RADIUS attributes for that service.  For example, a NAS that is
 unable to offer ARAP service MUST NOT implement the RADIUS attributes
 for ARAP.  A NAS MUST treat a RADIUS access-request requesting an
 unavailable service as an access-reject instead.

1.2. Terminology

 This document uses the following terms:
 service   The NAS provides a service to the dial-in user, such as PPP
           or Telnet.
 session   Each service provided by the NAS to a dial-in user
           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

Rigney, et al. Informational [Page 3] RFC 2869 RADIUS Extensions June 2000

           is ended.  A user may have multiple sessions in parallel or
           series if the NAS supports that, with each session
           generating a separate start and stop accounting record.
 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.

2. Operation

 Operation is identical to that defined in RFC 2865 [1] and RFC 2866
 [2].

2.1. RADIUS support for Interim Accounting Updates

 When a user is authenticated, a RADIUS server issues an Access-Accept
 in response to a successful Access-Request. If the server wishes to
 receive interim accounting messages for the given user it must
 include the Acct-Interim-Interval RADIUS attribute in the message,
 which indicates the interval in seconds between interim messages.
 It is also possible to statically configure an interim value on the
 NAS itself. Note that a locally configured value on the NAS MUST
 override the value found in an Access-Accept.
 This scheme does not break backward interoperability since a RADIUS
 server not supporting this extension will simply not add the new
 Attribute. NASes not supporting this extension will ignore the
 Attribute.
 Note that all information in an interim message is cumulative (i.e.
 number of packets sent is the total since the beginning of the
 session, not since the last interim message).
 It is envisioned that an Interim Accounting record (with Acct-
 Status-Type = Interim-Update (3)) would contain all of the attributes
 normally found in an Accounting Stop message with the exception of
 the Acct-Term-Cause attribute.
 Since all the information is cumulative, a NAS MUST ensure that only
 a single generation of an interim Accounting message for a given
 session is present in the retransmission queue at any given time.

Rigney, et al. Informational [Page 4] RFC 2869 RADIUS Extensions June 2000

 A NAS MAY use a fudge factor to add a random delay between Interim
 Accounting messages for separate sessions. This will ensure that a
 cycle where all messages are sent at once is prevented, such as might
 otherwise occur if a primary link was recently restored and many
 dial-up users were directed to the same NAS at once.
 The Network and NAS CPU load of using Interim Updates should be
 carefully considered, and appropriate values of Acct-Interim-Interval
 chosen.

2.2. RADIUS support for Apple Remote Access Protocol

 The RADIUS (Remote Authentication Dial-In User Service) protocol
 provides a method that allows multiple dial-in Network Access Server
 (NAS) devices to share a common authentication database.
 The Apple Remote Access Protocol (ARAP) provides a method for sending
 AppleTalk network traffic over point-to-point links, typically, but
 not exclusively, asynchronous and ISDN switched-circuit connections.
 Though Apple is moving toward ATCP on PPP for future remote access
 services, ARAP is still a common way for the installed base of
 Macintosh users to make remote network connections, and is likely to
 remain so for some time.
 ARAP is supported by several NAS vendors who also support PPP, IPX
 and other protocols in the same NAS. ARAP connections in these
 multi-protocol devices are often not authenticated with RADIUS, or if
 they are, each vendor creates an individual solution to the problem.
 This section describes the use of additional RADIUS attributes to
 support ARAP. RADIUS client and server implementations that implement
 this specification should be able to authenticate ARAP connections in
 an interoperable manner.
 This section assumes prior knowledge of RADIUS, and will go into some
 detail on the operation of ARAP before entering a detailed discussion
 of the proposed ARAP RADIUS attributes.
 There are two features of ARAP this document does not address:
    1. User initiated password changing. This is not part of RADIUS,
       but can be implemented through a software process other than
       RADIUS.
    2. Out-of-Band messages. At any time, the NAS can send messages to
       an ARA client which appear in a dialog box on the dial-in
       user's screen.  These are not part of authentication and do not
       belong here. However, we note that a Reply-Message attribute in

Rigney, et al. Informational [Page 5] RFC 2869 RADIUS Extensions June 2000

       an Access-Accept may be sent down to the user as a sign-on
       message of the day string using the out-of-band channel.
 We have tried to respect the spirit of the existing RADIUS protocol
 as much as possible, making design decisions compatible with prior
 art.  Further, we have tried to strike a balance between flooding the
 RADIUS world with new attributes, and hiding all of ARAP operation
 within a single multiplexed ARAP attribute string or within Extended
 Authentication Protocol (EAP) [3] machinery.
 However, we feel ARAP is enough of a departure from PPP to warrant a
 small set of similarly named attributes of its own.
 We have assumed that an ARAP-aware RADIUS server will be able to do
 DES encryption and generate security module challenges.  This is in
 keeping with the general RADIUS goal of smart server / simple NAS.
 ARAP authenticates a connection in two phases. The first is a "Two-
 Way DES" random number exchange, using the user's password as a key.
 We say "Two-Way" because the ARAP NAS challenges the dial-in client
 to authenticate itself, and the dial-in client challenges the ARAP
 NAS to authenticate itself.
 Specifically, ARAP does the following:
    1. The NAS sends two 32-bit random numbers to the dial-in client
       in an ARAP msg_auth_challenge packet.
    2. The dial-in client uses the user's password to DES encrypt the
       two random numbers sent to it by the NAS. The dial-in client
       then sends this result, the user's name and two 32-bit random
       numbers of its own back to the NAS in an ARAP msg_auth_request
       packet.
    3. The NAS verifies the encrypted random numbers sent by the
       dial-in client are what it expected. If so, it encrypts the
       dial-in client's challenge using the password and sends it back
       to the dial-in client in an ARAP msg_auth_response packet.
 Note that if the dial-in client's response was wrong,  meaning the
 user has the wrong password, the server can initiate a retry sequence
 up to the maximum amount of retries allowed by the NAS. In this case,
 when the dial-in client receives the ARAP msg_auth_response packet it
 will acknowledge it with an ARAP msg_auth_again packet.
 After this first "DES Phase" the ARAP NAS MAY initiate a secondary
 authentication phase using what Apple calls "Add-In Security
 Modules."  Security Modules are small pieces of code which run on

Rigney, et al. Informational [Page 6] RFC 2869 RADIUS Extensions June 2000

 both the client and server and are allowed to read and write
 arbitrary data across the communications link to perform additional
 authentication functions.  Various security token vendors use this
 mechanism to authenticate ARA callers.
 Although ARAP allows security modules to read and write anything they
 like, all existing security modules use simple challenge and response
 cycles, with perhaps some overall control information.  This document
 assumes all existing security modules can be supported with one or
 more challenge/response cycles.
 To complicate RADIUS and ARAP integration, ARAP sends down some
 profile information after the DES Phase and before the Security
 Module phase.  This means that besides the responses to challenges,
 this profile information must also be present, at somewhat unusual
 times.  Fortunately the information is only a few  pieces of numeric
 data related to passwords, which this document packs into a single
 new attribute.
 Presenting an Access-Request to RADIUS on behalf of an ARAP
 connection is straightforward. The ARAP NAS generates the random
 number challenge, and then receives the dial-in client's response,
 the dial-in client's challenge, and the user's name. Assuming the
 user is not a guest, the following information is forwarded in an
 Access-Request packet:  User-Name (up to 31 characters long),
 Framed-Protocol (set to 3, ARAP), ARAP-Password, and any additional
 attributes desired, such as Service-Type, NAS-IP-Address, NAS-Id,
 NAS-Port-Type, NAS-Port, NAS-Port-Id, Connect-Info, etc.
 The Request Authenticator is a NAS-generated 16 octet random number.
 The low-order 8 octets of this number are sent to the dial-in user as
 the two 4 octet random numbers required in the ARAP
 msg_auth_challenge packet. Octets 0-3 are the first random number and
 Octets 4-7 are the second random number.
 The ARAP-Password in the Access-Request contains a 16 octet random
 number field, and is used to carry the dial-in user's response to the
 NAS challenge and the client's own challenge to the NAS.  The high-
 order octets contain the dial-in user's challenge to the NAS (2 32-
 bit numbers, 8 octets) and the low-order octets contain the dial-in
 user's response to the NAS challenge (2 32-bit numbers, 8 octets).
 Only one of User-Password, CHAP-Password, or ARAP-Password needs to
 be present in an Access-Request, or one or more EAP-Messages.
 If the RADIUS server does not support ARAP it SHOULD return an
 Access-Reject to the NAS.

Rigney, et al. Informational [Page 7] RFC 2869 RADIUS Extensions June 2000

 If the RADIUS server does support ARAP, it should verify the user's
 response using the Challenge (from the lower order 8 octets of the
 Request Authenticator) and the user's response (from the low order 8
 octets of the ARAP-Password).
 If that authentication fails, the RADIUS server should return an
 Access-Reject packet to the NAS, with optional Password-Retry and
 Reply-Messages attributes.  The presence of Password-Retry indicates
 the ARAP NAS MAY choose to initiate another challenge-response cycle,
 up to a total number of times equal to the integer value of the
 Password-Retry attribute.
 If the user is authenticated, the RADIUS server should return an
 Access-Accept packet (Code 2) to the NAS, with ID and Response
 Authenticator as usual, and attributes as follows:
    Service-Type of Framed-Protocol.
    Framed-Protocol of ARAP (3).
    Session-Timeout with the maximum connect time for the user in
    seconds.  If the user is to be given unlimited time,
    Session-Timeout should not be included in the Access-Accept
    packet, and ARAP will treat that as an unlimited timeout (-1).
    ARAP-Challenge-Response, containing 8 octets with the response to
    the dial-in client's challenge. The RADIUS server calculates this
    value by taking the dial-in client's challenge from the high order
    8 octets of the ARAP-Password attribute and  performing DES
    encryption on this value with the authenticating user's password
    as the key. If the user's password is less than 8 octets in
    length, the password is padded at the end with NULL octets to a
    length of 8 before using it as a key. If the user's password is
    greater than 8 octets in length, an Access-Reject MUST be sent
    instead.
    ARAP-Features, containing information that the NAS should send to
    the user in an ARAP "feature flags" packet.
       Octet 0: If zero, user cannot change their password. If non-
       zero user can.  (RADIUS does not handle the password changing,
       just the attribute which indicates whether ARAP indicates they
       can.)
       Octet 1: Minimum acceptable password length (0-8).

Rigney, et al. Informational [Page 8] RFC 2869 RADIUS Extensions June 2000

       Octet 2-5: Password creation date in Macintosh format, defined
       as 32 bits unsigned representing seconds since Midnight GMT
       January 1, 1904.
       Octet 6-9 Password Expiration Delta from create date in
       seconds.
       Octet 10-13: Current RADIUS time in Macintosh format
    Optionally, a single Reply-Message with a text string up to 253
    characters long which MAY be sent down to the user to be displayed
    in a sign-on/message of the day dialog.
    Framed-AppleTalk-Network may be included.
    Framed-AppleTalk-Zone, up to 32 characters in length, may be
    included.
    ARAP defines the notion of a list of zones for a user.  Along with
    a list of zone names, a Zone Access Flag is defined (and used by
    the NAS) which says how to use the list of zone names. That is,
    the dial-in user may only be allowed to see the Default Zone, or
    only the zones in the zone list (inclusive) or any zone except
    those in the zone list (exclusive).
    The ARAP NAS handles this by having a named filter which contains
    (at least) zone names.  This solves the problem where a single
    RADIUS server is managing disparate NAS clients who may not be
    able to "see" all of the zone names in a user zone list.  Zone
    names only have meaning "at the NAS." The disadvantage of this
    approach is that zone filters must be set up on the NAS somehow,
    then referenced by the RADIUS Filter-Id.
    ARAP-Zone-Access contains an integer which specifies how the "zone
    list" for this user should be used.  If this attribute is present
    and the value is 2 or 4 then a Filter-Id must also be present to
    name a zone list filter to apply the access flag to.
    The inclusion of a Callback-Number or Callback-Id attribute in the
    Access-Accept MAY cause the ARAP NAS to disconnect after sending
    the Feature Flags to begin callback processing in an ARAP specific
    way.

Rigney, et al. Informational [Page 9] RFC 2869 RADIUS Extensions June 2000

 Other attributes may be present in the Access-Accept packet as well.
 An ARAP NAS will need other information to finish bringing up the
 connection to the dial in client, but this information can be
 provided by the ARAP NAS without any help from RADIUS, either through
 configuration by SNMP, a NAS administration program, or deduced by
 the AppleTalk stack in the NAS. Specifically:
    1. AppearAsNet and AppearAsNode values, sent to the client to tell
       it what network and node numbers it should use in its datagram
       packets.  AppearAsNet can be taken from the Framed-AppleTalk-
       Network attribute or from the configuration or AppleTalk stack
       onthe NAS.
    2. The "default" zone - that is the name of the AppleTalk zone in
       which the dial-in client will appear.  (Or can be specified
       with the Framed-AppleTalk-Zone attribute.)
    3. Other very NAS specific stuff such as the name of the NAS, and
       smartbuffering information.  (Smartbuffering is an ARAP
       mechanism for replacing common AppleTalk datagrams with small
       tokens, to improve slow link performance in a few common
       traffic situations.)
    4. "Zone List" information for this user.  The ARAP specification
       defines a "zone count" field which is actually unused.
 RADIUS supports ARAP Security Modules in the following manner.
 After DES authentication has been completed, the RADIUS server may
 instruct the ARAP NAS to run one or more security modules for the
 dial-in user. Although the underlying protocol supports executing
 multiple security modules in series, in practice all current
 implementations only allow executing one.  Through the use of
 multiple Access-Challenge requests, multiple modules can be
 supported, but this facility will probably never be used.
 We also assume that, even though ARAP allows a free-form dialog
 between security modules on each end of the point-to-point link, in
 actual practice all security modules can be reduced to a simple
 challenge/response cycle.
 If the RADIUS server wishes to instruct the ARAP NAS to run a
 security module, it should send an Access-Challenge packet to the NAS
 with (optionally) the State attribute, plus the ARAP-Challenge-
 Response, ARAP-Features, and two more attributes:

Rigney, et al. Informational [Page 10] RFC 2869 RADIUS Extensions June 2000

 ARAP-Security: a four octet security module signature, containing a
 Macintosh OSType.
 ARAP-Security-Data, a string to carry the actual security module
 challenge and response.
 When the security module finishes executing, the security module
 response is passed  in an ARAP-Security-Data attribute from the NAS
 to the RADIUS server in a second Access-Request, also including the
 State from the Access-Challenge.  The authenticator field contains no
 special information in this case, and this can be discerned by the
 presence of the State attribute.

2.3. RADIUS Support for Extensible Authentication Protocol (EAP)

 The Extensible Authentication Protocol (EAP), described in [3],
 provides a standard mechanism for support of additional
 authentication methods within PPP.  Through the use of EAP, support
 for a number of authentication schemes may be added, including smart
 cards, Kerberos, Public Key, One Time Passwords, and others.  In
 order to provide for support of 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.
 In the proposed scheme, the RADIUS server is used to shuttle RADIUS-
 encapsulated EAP Packets between the NAS and a backend security
 server. While the conversation between the RADIUS server and the
 backend security server will typically occur using a proprietary
 protocol developed by the backend security server vendor, it is also
 possible to use RADIUS-encapsulated EAP via the EAP-Message
 attribute.  This has the advantage of allowing the RADIUS server to
 support EAP without the need for authentication-specific code, which
 can instead reside on the backend security server.

2.3.1. Protocol Overview

 The EAP conversation between the authenticating peer (dial-in user)
 and the NAS begins with the negotiation of EAP within LCP.  Once EAP
 has been negotiated, the NAS MUST send an EAP-Request/Identity
 message to the authenticating peer, unless identity is determined via
 some other means such as Called-Station-Id or Calling-Station-Id.
 The peer will then respond with an EAP-Response/Identity which the
 the NAS will then forward to the RADIUS server in the EAP-Message
 attribute of a RADIUS Access-Request packet. The RADIUS Server will
 typically use the EAP-Response/Identity to determine which EAP type
 is to be applied to the user.

Rigney, et al. Informational [Page 11] RFC 2869 RADIUS Extensions June 2000

 In order to permit non-EAP aware RADIUS proxies to forward the
 Access-Request packet, if the NAS sends the EAP-Request/Identity, the
 NAS MUST copy the contents of the EAP-Response/Identity into the
 User-Name attribute and MUST include the EAP-Response/Identity in the
 User-Name attribute in every subsequent Access-Request. NAS-Port or
 NAS-Port-Id SHOULD be included in the attributes issued by the NAS in
 the Access-Request packet, and either NAS-Identifier or NAS-IP-
 Address 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 very difficult to
 manage.
 If identity is determined via another means such as Called-Station-Id
 or Calling-Station-Id, the NAS MUST include these identifying
 attributes in every Access-Request.
 While this approach will save a round-trip, it cannot be universally
 employed.  There are circumstances in which the user's identity may
 not be needed (such as when authentication and accounting is handled
 based on Called-Station-Id or Calling-Station-Id), and therefore an
 EAP-Request/Identity packet may not necessarily be issued by the NAS
 to the authenticating peer. In cases where an EAP-Request/Identity
 packet will not be sent, the NAS will send to the RADIUS server a
 RADIUS Access-Request packet containing an EAP-Message attribute
 signifying EAP-Start. EAP-Start is indicated by sending an EAP-
 Message attribute with a length of 2 (no data). However, it should be
 noted that since no User-Name attribute is included in the Access-
 Request, this approach is not compatible with RADIUS as specified in
 [1], nor can it easily be applied in situations where proxies are
 deployed, such as roaming or shared use networks.
 If the RADIUS server supports EAP, it MUST respond with an Access-
 Challenge packet containing an EAP-Message attribute. If the RADIUS
 server does not support EAP, it MUST respond with an Access-Reject.
 The EAP-Message attribute includes an encapsulated EAP packet which
 is then passed on to the authenticating peer.  In the case where the
 NAS does not initially send an EAP-Request/Identity message to the
 peer, the Access-Challenge typically will contain an EAP-Message
 attribute encapsulating an EAP-Request/Identity message, requesting
 the dial-in user to identify themself. The NAS will then respond with
 a RADIUS Access-Request packet containing an EAP-Message attribute
 encapsulating an EAP-Response.  The conversation continues until
 either a RADIUS Access-Reject or Access-Accept packet is received.

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 Reception of a RADIUS Access-Reject packet, with or without an EAP-
 Message attribute encapsulating EAP-Failure, MUST result in the NAS
 issuing an LCP Terminate Request to the authenticating peer.  A
 RADIUS Access-Accept packet with an EAP-Message attribute
 encapsulating EAP-Success successfully ends the authentication phase.
 The RADIUS Access-Accept/EAP-Message/EAP-Success packet MUST contain
 all of the expected attributes which are currently returned in an
 Access-Accept packet.
 The above scenario creates a situation in which the NAS never needs
 to manipulate an EAP packet.  An alternative may be used in
 situations where an EAP-Request/Identity message will always be sent
 by the NAS to the authenticating peer.
 For proxied RADIUS requests there are two methods of processing.  If
 the domain is determined based on the Called-Station-Id, the RADIUS
 Server may proxy the initial RADIUS Access-Request/EAP-Start. If the
 domain is determined based on the user's identity, the local RADIUS
 Server MUST respond with a RADIUS Access-Challenge/EAP-Identity
 packet.  The response from the authenticating peer MUST be proxied to
 the final authentication server.
 For proxied RADIUS requests, the NAS may receive an Access-Reject
 packet in response to its Access-Request/EAP-Identity packet.  This
 would occur if the message was proxied to a RADIUS Server which does
 not support the EAP-Message extension. On receiving an Access-Reject,
 the NAS MUST send an LCP Terminate Request to the authenticating
 peer, and disconnect.

2.3.2. Retransmission

 As noted in [3], the EAP authenticator (NAS) is responsible for
 retransmission of packets between the authenticating peer and the
 NAS.  Thus if an EAP packet is lost in transit between the
 authenticating peer and the NAS (or vice versa), the NAS will
 retransmit. As in RADIUS [1], the RADIUS client is responsible for
 retransmission of packets between the RADIUS client and the RADIUS
 server.
 Note that 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 and Password-Retry attributes within the Access-
 Challenge packet.

Rigney, et al. Informational [Page 13] RFC 2869 RADIUS Extensions June 2000

 If Session-Timeout is present in an Access-Challenge packet that also
 contains an EAP-Message, the value of the Session-Timeout provides
 the NAS with the maximum number of seconds the NAS should wait for an
 EAP-Response before retransmitting the EAP-Message to the dial-in
 user.

2.3.3. 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.

2.3.4. Examples

 The example below shows the conversation between the authenticating
 peer, NAS, and RADIUS server, for the case of a One Time Password
 (OTP) authentication. OTP is used only for illustrative purposes;
 other authentication protocols could also have been used, although
 they might show somewhat different behavior.

Authenticating Peer NAS RADIUS Server ——————- — ————-

                      <- PPP LCP Request-EAP
                      auth

PPP LCP ACK-EAP auth →

                      <- PPP EAP-Request/
                      Identity

PPP EAP-Response/ Identity (MyID) →

                      RADIUS
                      Access-Request/
                      EAP-Message/
                      EAP-Response/
                      (MyID) ->
                                              <- RADIUS
                                              Access-Challenge/
                                              EAP-Message/EAP-Request
                                              OTP/OTP Challenge
                      <- PPP EAP-Request/
                      OTP/OTP Challenge

PPP EAP-Response/ OTP, OTPpw →

Rigney, et al. Informational [Page 14] RFC 2869 RADIUS Extensions June 2000

                      RADIUS
                      Access-Request/
                      EAP-Message/
                      EAP-Response/
                      OTP, OTPpw ->
                                               <- RADIUS
                                               Access-Accept/
                                               EAP-Message/EAP-Success
                                               (other attributes)
                      <- PPP EAP-Success

PPP Authentication Phase complete, NCP Phase starts

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 ——————- — ————-

                      <- PPP LCP Request-EAP
                      auth

PPP LCP ACK-EAP auth →

                      RADIUS
                      Access-Request/
                     EAP-Message/Start ->
                                             <- RADIUS
                                             Access-Challenge/
                                             EAP-Message/Identity
                      <- PPP EA-Request/
                      Identity

PPP EAP-Response/ Identity (MyID) →

                      RADIUS
                      Access-Request/
                      EAP-Message/
                      EAP-Response/
                      (MyID) ->
                                              <- RADIUS
                                              Access-Challenge/
                                              EAP-Message/EAP-Request
                                              OTP/OTP Challenge
                      <- PPP EAP-Request/
                      OTP/OTP Challenge

PPP EAP-Response/ OTP, OTPpw →

Rigney, et al. Informational [Page 15] RFC 2869 RADIUS Extensions June 2000

                      RADIUS
                      Access-Request/
                      EAP-Message/
                      EAP-Response/
                      OTP, OTPpw ->
                                               <- RADIUS
                                               Access-Accept/
                                               EAP-Message/EAP-Success
                                               (other attributes)
                      <- PPP EAP-Success

PPP Authentication Phase complete, NCP Phase starts

In the case where the client fails EAP authentication, the conversation would appear as follows:

Authenticating Peer NAS RADIUS Server ——————- — ————-

                      <- PPP LCP Request-EAP
                      auth

PPP LCP ACK-EAP auth →

                      Access-Request/
                      EAP-Message/Start ->
                                             <- RADIUS
                                             Access-Challenge/
                                             EAP-Message/Identity
                      <- PPP EAP-Request/
                      Identity

PPP EAP-Response/ Identity (MyID) →

                      RADIUS
                      Access-Request/
                      EAP-Message/
                      EAP-Response/
                      (MyID) ->
                                              <- RADIUS
                                              Access-Challenge/
                                              EAP-Message/EAP-Request
                                              OTP/OTP Challenge
                      <- PPP EAP-Request/
                      OTP/OTP Challenge

PPP EAP-Response/ OTP, OTPpw →

                      RADIUS
                      Access-Request/

Rigney, et al. Informational [Page 16] RFC 2869 RADIUS Extensions June 2000

                      EAP-Message/
                      EAP-Response/
                      OTP, OTPpw ->
                                               <- RADIUS
                                               Access-Reject/
                                               EAP-Message/EAP-Failure
                      <- PPP EAP-Failure
                      (client disconnected)

In the case that the RADIUS server or proxy does not support EAP-Message, the conversation would appear as follows:

Authenticating Peer NAS RADIUS Server ——————- — ————-

                      <- PPP LCP Request-EAP
                      auth

PPP LCP ACK-EAP auth →

                      RADIUS
                      Access-Request/
                      EAP-Message/Start ->
                                                <- RADIUS
                                                Access-Reject
                      <- PPP LCP Terminate
                      (User Disconnected)

In the case where the local RADIUS Server does support EAP-Message, but the remote RADIUS Server does not, the conversation would appear as follows:

Authenticating Peer NAS RADIUS Server ——————- — ————-

                      <- PPP LCP Request-EAP
                      auth

PPP LCP ACK-EAP auth →

                      RADIUS
                      Access-Request/
                      EAP-Message/Start ->
                                                <- RADIUS
                                                Access-Challenge/
                                                EAP-Message/Identity
                      <- PPP EAP-Request/
                      Identity

Rigney, et al. Informational [Page 17] RFC 2869 RADIUS Extensions June 2000

PPP EAP-Response/ Identity (MyID) →

                      RADIUS
                      Access-Request/
                      EAP-Message/EAP-Response/
                      (MyID) ->
                                                <- RADIUS
                                                Access-Reject
                                                (proxied from remote
                                                 RADIUS Server)
                      <- PPP LCP Terminate
                      (User Disconnected)

In the case where 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
                      auth

PPP LCP NAK-EAP auth →

                      <- PPP LCP Request-CHAP
                      auth

PPP LCP ACK-CHAP auth →

                      <- PPP CHAP Challenge

PPP CHAP Response →

                      RADIUS
                      Access-Request/
                      User-Name,
                      CHAP-Password ->
                                                <- RADIUS
                                                Access-Reject
                      <-  PPP LCP Terminate
                      (User Disconnected)

In the case where the NAS 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-CHAP
                      auth

Rigney, et al. Informational [Page 18] RFC 2869 RADIUS Extensions June 2000

PP LCP ACK-CHAP auth →

                      <- PPP CHAP Challenge

PPP CHAP Response →

                      RADIUS
                      Access-Request/
                      User-Name,
                      CHAP-Password ->
                                               <- RADIUS
                                               Access-Reject
                      <-  PPP LCP Terminate
                      (User Disconnected)

2.3.5. Alternative uses

 Currently the conversation between the backend security server and
 the RADIUS server is proprietary because of lack of standardization.
 In order to increase standardization and provide interoperability
 between Radius vendors and backend 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 backend
 security server instead.
 In the case where RADIUS-encapsulated EAP is used in a conversation
 between a RADIUS server and a backend security server, the security
 server will typically return an Access-Accept/EAP-Success 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/EAP-Success message to
 the NAS.

3. Packet Format

 Packet Format is identical to that defined in RFC 2865 [1] and 2866
 [2].

4. Packet Types

 Packet types are identical to those defined in RFC 2865 [1] and 2866
 [2].
 See "Table of Attributes" below to determine which types of packets
 can contain which attributes defined here.

Rigney, et al. Informational [Page 19] RFC 2869 RADIUS Extensions June 2000

5. Attributes

 RADIUS Attributes carry the specific authentication, authorization
 and accounting details for the request and response.
 Some attributes MAY be included more than once.  The effect of this
 is attribute specific, and is specified in each attribute
 description.  The order of attributes of the same type SHOULD be
 preserved.  The order of attributes of different types is not
 required to be preserved.
 The end of the list of attributes is indicated by the Length of the
 RADIUS packet.
 A summary of the attribute format is the same as in RFC 2865 [1] but
 is included here for ease of reference.  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     |  Value ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    The Type field is one octet.  Up-to-date values of the RADIUS Type
    field are specified in the most recent "Assigned Numbers" RFC [5].
    Values 192-223 are reserved for experimental use, values 224-240
    are reserved for implementation-specific use, and values 241-255
    are reserved and should not be used.  This specification concerns
    the following values:
         1-39   (refer to RFC 2865 [1], "RADIUS")
        40-51   (refer to RFC 2866 [2], "RADIUS Accounting")
        52      Acct-Input-Gigawords
        53      Acct-Output-Gigawords
        54      Unused
        55      Event-Timestamp
        56-59   Unused
        60-63   (refer to RFC 2865 [1], "RADIUS")
        64-67   (refer to [6])
        68      (refer to [7])
        69      (refer to [6])
        70      ARAP-Password
        71      ARAP-Features
        72      ARAP-Zone-Access

Rigney, et al. Informational [Page 20] RFC 2869 RADIUS Extensions June 2000

        73      ARAP-Security
        74      ARAP-Security-Data
        75      Password-Retry
        76      Prompt
        77      Connect-Info
        78      Configuration-Token
        79      EAP-Message
        80      Message-Authenticator
        81-83   (refer to [6])
        84      ARAP-Challenge-Response
        85      Acct-Interim-Interval
        86      (refer to [7])
        87      NAS-Port-Id
        88      Framed-Pool
        89      Unused
        90-91   (refer to [6])
        92-191  Unused
 Length
    The Length field is one octet, and indicates the length of this
    attribute including the Type, Length and Value fields.  If an
    attribute is received in a packet with an invalid Length, the
    entire request should be silently discarded.
 Value
    The Value field is zero or more octets and contains information
    specific to the attribute.  The format and length of the Value
    field is determined by the Type and Length fields.
    Note that none of the types in RADIUS terminate with a NUL (hex
    00).  In particular, types "text" and "string" in RADIUS do not
    terminate with a NUL (hex 00).  The Attribute has a length field
    and does not use a terminator.  Text contains UTF-8 encoded 10646
    [8] characters and String contains 8-bit binary data.  Servers and
    servers and clients MUST be able to deal with embedded nulls.
    RADIUS implementers using C are cautioned not to use strcpy() when
    handling strings.
    The format of the value field is one of five data types.  Note
    that type "text" is a subset of type "string."
    text      1-253 octets containing UTF-8 encoded 10646 [8]
              characters. Text of length zero (0) MUST NOT be sent;
              omit the entire attribute instead.

Rigney, et al. Informational [Page 21] RFC 2869 RADIUS Extensions June 2000

    string    1-253 octets containing binary data (values 0 through
              255 decimal, inclusive). Strings of length zero (0) MUST
              NOT be sent; omit the entire attribute instead.
    address   32 bit unsigned value, most significant octet first.
    integer   32 bit unsigned value, most significant octet first.
    time      32 bit unsigned value, most significant octet first --
                 seconds since 00:00:00 UTC, January 1, 1970.

5.1. Acct-Input-Gigawords

 Description
    This attribute indicates how many times the Acct-Input-Octets
    counter has wrapped around 2^32 over the course of this service
    being provided, and can only be present in Accounting-Request
    records where the Acct-Status-Type is set to Stop or Interim-
    Update.
 A summary of the Acct-Input-Gigawords attribute format is shown
 below.  The fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    52 for Acct-Input-Gigawords.
 Length
    6
 Value
    The Value field is four octets.

Rigney, et al. Informational [Page 22] RFC 2869 RADIUS Extensions June 2000

5.2. Acct-Output-Gigawords

 Description
    This attribute indicates how many times the Acct-Output-Octets
    counter has wrapped around 2^32 in the course of delivering this
    service, and can only be present in Accounting-Request records
    where the Acct-Status-Type is set to Stop or Interim-Update.
 A summary of the Acct-Output-Gigawords attribute format is shown
 below.  The fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    53 for Acct-Output-Gigawords.
 Length
    6
 Value
    The Value field is four octets.

5.3. Event-Timestamp

 Description
    This attribute is included in an Accounting-Request packet to
    record the time that this event occurred on the NAS, in seconds
    since January 1, 1970 00:00 UTC.
 A summary of the Event-Timestamp attribute format is shown below.
 The fields are transmitted from left to right.

Rigney, et al. Informational [Page 23] RFC 2869 RADIUS Extensions June 2000

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    55 for Event-Timestamp
 Length
    6
 Value
    The Value field is four octets encoding an unsigned integer with
    the number of seconds since January 1, 1970 00:00 UTC.

5.4. ARAP-Password

 Description
    This attribute is only present in an Access-Request packet
    containing a Framed-Protocol of ARAP.
    Only one of User-Password, CHAP-Password, or ARAP-Password needs
    to be present in an Access-Request, or one or more EAP-Messages.
 A summary of the ARAP-Password attribute format is shown below.  The
 fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |             Value2
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |             Value3
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |             Value4
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Rigney, et al. Informational [Page 24] RFC 2869 RADIUS Extensions June 2000

 Type
    70 for ARAP-Password.
 Length
    18
 Value
    This attribute contains a 16 octet string, used to carry the
    dial-in user's response to the NAS challenge and the client's own
    challenge to the NAS.  The high-order octets (Value1 and Value2)
    contain the dial-in user's challenge to the NAS (2 32-bit numbers,
    8 octets) and the low-order octets (Value3 and Value4) contain the
    dial-in user's response to the NAS challenge (2 32-bit numbers, 8
    octets).

5.5. ARAP-Features

 Description
    This attribute is sent in an Access-Accept packet with Framed-
    Protocol of ARAP, and includes password information that the NAS
    should sent to the user in an ARAP "feature flags" packet.
 A summary of the ARAP-Features attribute format is shown below.  The
 fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |     Value1    |    Value2     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Value3                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Value4                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Value5                              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    71 for ARAP-Features.
 Length
    16

Rigney, et al. Informational [Page 25] RFC 2869 RADIUS Extensions June 2000

 Value
    The Value field is a compound string containing information the
    NAS should send to the user in the ARAP "feature flags" packet.
       Value1: If zero, user cannot change their password. If non-zero
       user can.  (RADIUS does not handle the password changing, just
       the attribute which indicates whether ARAP indicates they can.)
       Value2: Minimum acceptable password length, from 0 to 8.
       Value3: Password creation date in Macintosh format, defined as
       32 unsigned bits representing seconds since Midnight GMT
       January 1, 1904.
       Value4: Password Expiration Delta from create date in seconds.
       Value5: Current RADIUS time in Macintosh format.

5.6. ARAP-Zone-Access

 Description
    This attribute is included in an Access-Accept packet with
    Framed-Protocol of ARAP to indicate how the ARAP zone list for the
    user should be used.
 A summary of the ARAP-Zone-Access attribute format is shown below.
 The fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    72 for ARAP-Zone-Access.
 Length
    6

Rigney, et al. Informational [Page 26] RFC 2869 RADIUS Extensions June 2000

 Value
    The Value field is four octets encoding an integer with one of the
    following values:
    1      Only allow access to default zone
    2      Use zone filter inclusively
    4      Use zone filter exclusively
    The value 3 is skipped, not because these are bit flags, but
    because 3 in some ARAP implementations means "all zones" which is
    the same as not specifying a list at all under RADIUS.
    If this attribute is present and the value is 2 or 4 then a
    Filter-Id must also be present to name a zone list filter to apply
    the access flag to.

5.7. ARAP-Security

 Description
    This attribute identifies the ARAP Security Module to be used in
    an Access-Challenge packet.
 A summary of the ARAP-Security attribute format is shown below.  The
 fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    73 for ARAP-Security.
 Length
    6

Rigney, et al. Informational [Page 27] RFC 2869 RADIUS Extensions June 2000

 Value
    The Value field is four octets, containing an integer specifying
    the security module signature, which is a Macintosh OSType.
    (Macintosh OSTypes are 4 ascii characters cast as a 32-bit
    integer)

5.8. ARAP-Security-Data

 Description
    This attribute contains the actual security module challenge or
    response, and can be found in Access-Challenge and Access-Request
    packets.
 A summary of the ARAP-Security-Data 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
    74 for ARAP-Security-Data.
 Length
    >=3
 String
    The String field contains the security module challenge or
    response associated with the ARAP Security Module specified in
    ARAP-Security.

5.9. Password-Retry

 Description
    This attribute MAY be included in an Access-Reject to indicate how
    many authentication attempts a user may be allowed to attempt
    before being disconnected.
    It is primarily intended for use with ARAP authentication.

Rigney, et al. Informational [Page 28] RFC 2869 RADIUS Extensions June 2000

 A summary of the Password-Retry attribute format is shown below.  The
 fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    75 for Password-Retry.
 Length
    6
 Value
    The Value field is four octets, containing an integer specifying
    the number of password retry attempts to permit the user.

5.10. Prompt

 Description
    This attribute is used only in Access-Challenge packets, and
    indicates to the NAS whether it should echo the user's response as
    it is entered, or not echo it.
 A summary of the Prompt attribute format is shown below.  The fields
 are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    76 for Prompt.

Rigney, et al. Informational [Page 29] RFC 2869 RADIUS Extensions June 2000

 Length
    6
 Value
    The Value field is four octets.
     0      No Echo
     1      Echo

5.11. Connect-Info

 Description
    This attribute is sent from the NAS to indicate the nature of the
    user's connection.
    The NAS MAY send this attribute in an Access-Request or
    Accounting-Request to indicate the nature of the user's
    connection.
 A summary of the Connect-Info 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     |     Text...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    77 for Connect-Info.
 Length
    >= 3
 Text
    The Text field consists of UTF-8 encoded 10646 [8] characters.
    The connection speed SHOULD be included at the beginning of the
    first Connect-Info attribute in the packet.  If the transmit and
    receive connection speeds differ, they may both be included in the
    first attribute with the transmit speed first (the speed the NAS
    modem transmits at), a slash (/), the receive speed, then
    optionally other information.

Rigney, et al. Informational [Page 30] RFC 2869 RADIUS Extensions June 2000

    For example, "28800 V42BIS/LAPM" or "52000/31200 V90"
    More than one Connect-Info attribute may be present in an
    Accounting-Request packet to accommodate expected efforts by ITU
    to have modems report more connection information in a standard
    format that might exceed 252 octets.

5.12. Configuration-Token

 Description
    This attribute is for use in large distributed authentication
    networks based on proxy.  It is sent from a RADIUS Proxy Server to
    a RADIUS Proxy Client in an Access-Accept to indicate a type of
    user profile to be used.  It should not be sent to a NAS.
 A summary of the Configuration-Token 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
    78 for Configuration-Token.
 Length
    >= 3
 String
    The String field is one or more octets.  The actual format of the
    information is site or application specific, and a robust
    implementation SHOULD support the field as undistinguished octets.
    The codification of the range of allowed usage of this field is
    outside the scope of this specification.

Rigney, et al. Informational [Page 31] RFC 2869 RADIUS Extensions June 2000

5.13. EAP-Message

 Description
    This attribute encapsulates Extended Access Protocol [3] packets
    so as to allow the NAS to authenticate dial-in users via EAP
    without having to understand the EAP protocol.
    The NAS places any EAP messages received from the user into one or
    more EAP attributes and forwards them to the RADIUS Server as part
    of the Access-Request, which can return EAP messages in Access-
    Challenge, Access-Accept and Access-Reject packets.
    A RADIUS Server receiving EAP messages that it does not understand
    SHOULD return an Access-Reject.
    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-
    Messages 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.  Access-Accept and Access-Reject packets SHOULD only have
    ONE EAP-Message attribute in them, containing EAP-Success or EAP-
    Failure.
    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 the EAP-Success
    or EAP-Failure packets) it is necessary that RADIUS/EAP provide
    integrity protection at least as strong as those used in the EAP
    methods themselves.
    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 an EAP-Message attribute without
    a Message-Authenticator attribute SHOULD be silently discarded by
    the RADIUS server.  A RADIUS Server supporting EAP-Message MUST
    calculate the correct value of the Message-Authenticator and
    silently discard the packet if it does not match the value sent.
    A RADIUS Server not supporting EAP-Message MUST return an Access-
    Reject if it receives an Access-Request containing an EAP-Message
    attribute. A RADIUS Server receiving an EAP-Message attribute that
    it does not understand MUST return an Access-Reject.

Rigney, et al. Informational [Page 32] RFC 2869 RADIUS Extensions June 2000

    Access-Challenge, Access-Accept, or Access-Reject packets
    including an EAP-Message attribute without a Message-Authenticator
    attribute SHOULD be silently discarded by the NAS. A NAS
    supporting EAP-Message MUST calculate the correct value of the
    Message-Authenticator and 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 EAP packets, as defined in [3].  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 passed by RADIUS.

5.14. Message-Authenticator

 Description
    This attribute MAY be used to sign Access-Requests to prevent
    spoofing Access-Requests using CHAP, ARAP or EAP authentication
    methods.  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.

Rigney, et al. Informational [Page 33] RFC 2869 RADIUS Extensions June 2000

    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.
    Earlier drafts of this memo used "Signature" as the name of this
    attribute, but Message-Authenticator is more precise.  Its
    operation has not changed, just the name.
 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 [9] checksum 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 checksum is calculated the signature string should be
    considered to be sixteen octets of zero.
    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)

Rigney, et al. Informational [Page 34] RFC 2869 RADIUS Extensions June 2000

    When the checksum 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 hash.  The is calculated and
    inserted in the packet before the Response Authenticator is
    calculated.
    This attribute is not needed if the User-Password attribute is
    present, 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.
    IP Security will eventually make this attribute unnecessary, so it
    should be considered an interim measure.

5.15. ARAP-Challenge-Response

 Description
    This attribute is sent in an Access-Accept packet with Framed-
    Protocol of ARAP, and contains the response to the dial-in
    client's challenge.
 A summary of the ARAP-Challenge-Response attribute format is shown
 below.  The fields are transmitted from left to right.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |     Value...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    84 for ARAP-Challenge-Response.
 Length
    10

Rigney, et al. Informational [Page 35] RFC 2869 RADIUS Extensions June 2000

 Value
    The Value field contains an 8 octet response to the dial-in
    client's challenge. The RADIUS server calculates this value by
    taking the dial-in client's challenge from the high order 8 octets
    of the ARAP-Password attribute and  performing DES encryption on
    this value with the authenticating user's password as the key. If
    the user's password is less than 8 octets in length, the password
    is padded at the end with NULL octets to a length of 8 before
    using it as a key.

5.16. Acct-Interim-Interval

 Description
    This attribute indicates the number of seconds between each
    interim update in seconds  for this specific session. This value
    can only appear in the Access-Accept message.
 A summary of the Acct-Interim-Interval attribute  format  is  shown
 below. The fields are transmitted from left to right.
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    85 for Acct-Interim-Interval.
 Length
    6
 Value
    The Value field contains the number of seconds between each
    interim update to be sent from the NAS for this session. The value
    MUST NOT be smaller than 60.  The value SHOULD NOT be smaller than
    600, and careful consideration should be given to its impact on
    network traffic.

Rigney, et al. Informational [Page 36] RFC 2869 RADIUS Extensions June 2000

5.17. NAS-Port-Id

 Description
    This Attribute contains a text string which identifies the port of
    the NAS which is authenticating the user.  It is only used in
    Access-Request and Accounting-Request packets.  Note that this is
    using "port" in its sense of a physical connection on the NAS, not
    in the sense of a TCP or UDP port number.
    Either NAS-Port or NAS-Port-Id SHOULD be present in an Access-
    Request packet, if the NAS differentiates among its ports.  NAS-
    Port-Id is intended for use by NASes which cannot conveniently
    number their ports.
 A summary of the NAS-Port-Id 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     |     Text...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    87 for NAS-Port-Id.
 Length
    >= 3
 Text
    The Text field contains the name of the port using UTF-8 encoded
    10646 [8] characters.

5.18. Framed-Pool

 Description
    This Attribute contains the name of an assigned address pool that
    SHOULD be used to assign an address for the user.  If a NAS does
    not support multiple address pools, the NAS should ignore this
    Attribute.  Address pools are usually used for IP addresses, but
    can be used for other protocols if the NAS supports pools for
    those protocols.

Rigney, et al. Informational [Page 37] RFC 2869 RADIUS Extensions June 2000

 A summary of the Framed-Pool 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
    88 for Framed-Pool
 Length
    >= 3
 String
    The string field contains the name of an assigned address pool
    configured on the NAS.

5.19. Table of Attributes

 The following table provides a guide to which attributes may be found
 in which kind of packets.  Acct-Input-Gigawords, Acct-Output-
 Gigawords, Event-Timestamp, and NAS-Port-Id may have 0-1 instances in
 an Accounting-Request packet.  Connect-Info may have 0+ instances in
 an Accounting-Request packet.  The other attributes added in this
 document must not be present in an Accounting-Request.

Request Accept Reject Challenge # Attribute 0-1 0 0 0 70 ARAP-Password [Note 1] 0 0-1 0 0-1 71 ARAP-Features 0 0-1 0 0 72 ARAP-Zone-Access 0-1 0 0 0-1 73 ARAP-Security 0+ 0 0 0+ 74 ARAP-Security-Data 0 0 0-1 0 75 Password-Retry 0 0 0 0-1 76 Prompt 0-1 0 0 0 77 Connect-Info 0 0+ 0 0 78 Configuration-Token 0+ 0+ 0+ 0+ 79 EAP-Message [Note 1] 0-1 0-1 0-1 0-1 80 Message-Authenticator [Note 1] 0 0-1 0 0-1 84 ARAP-Challenge-Response 0 0-1 0 0 85 Acct-Interim-Interval 0-1 0 0 0 87 NAS-Port-Id 0 0-1 0 0 88 Framed-Pool Request Accept Reject Challenge # Attribute

Rigney, et al. Informational [Page 38] RFC 2869 RADIUS Extensions June 2000

 [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.
 The following table defines 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.

6. IANA Considerations

 The Packet Type Codes, Attribute Types, and Attribute Values defined
 in this document are registered by the Internet Assigned Numbers
 Authority (IANA) from the RADIUS name spaces as described in the
 "IANA Considerations" section of [1], in accordance with BCP 26 [10].

7. Security Considerations

 The attributes other than Message-Authenticator and EAP-Message in
 this document have no additional security considerations beyond those
 already identified in [1].

7.1. Message-Authenticator Security

 Access-Request packets with a User-Password establish the identity of
 both the user and the NAS sending the Access-Request, because of the
 way the shared secret between NAS and RADIUS server is used.
 Access-Request packets with CHAP-Password or EAP-Message do not have
 a User-Password attribute, so the Message-Authenticator attribute
 should be used in access-request packets that do not have a User-
 Password, in order to establish the identity of the NAS sending the
 request.

7.2. EAP Security

 Since the purpose of EAP is to provide enhanced security for PPP
 authentication, it is critical that RADIUS support for EAP be secure.
 In particular, the following issues must be addressed:
    Separation of EAP server and PPP authenticator
    Connection hijacking
    Man in the middle attacks
    Multiple databases

Rigney, et al. Informational [Page 39] RFC 2869 RADIUS Extensions June 2000

    Negotiation attacks

7.2.1. Separation of EAP server and PPP authenticator

 It is possible for the EAP endpoints to mutually authenticate,
 negotiate a ciphersuite, and derive a session key for subsequent use
 in PPP encryption.
 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 pass the session key to the PPP encryption
 module.
 The situation is more complex when EAP is used with RADIUS, since the
 PPP authenticator will typically not reside on the same machine as
 the EAP server. For example, the EAP server may be a backend security
 server, or a module residing on the RADIUS server.
 In the case where the EAP server and PPP authenticator reside on
 different machines, there are several implications for security.
 Firstly, mutual authentication will occur between the peer and the
 EAP 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.
 As described earlier, when EAP/RADIUS is used to encapsulate EAP
 packets, the Message-Authenticator attribute is required in
 EAP/RADIUS Access-Requests sent from the NAS or tunnel server to the
 RADIUS server. Since the Message-Authenticator attribute involves a
 HMAC-MD5 hash, 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.  Similarly, Access-Challenge packets sent from the RADIUS
 server to the NAS are also authenticated and integrity protected
 using an HMAC-MD5 hash, enabling the NAS or tunnel server to
 determine the integrity of the packet and verify the identity of the
 RADIUS server.  Moreover, EAP packets sent via methods that contain
 their own integrity protection cannot be successfully modified by a
 rogue NAS or tunnel server.
 The second issue that arises in the case of an EAP server and PPP
 authenticator residing on different machines is that the session key
 negotiated between the peer and EAP server will need to be
 transmitted to the authenticator.  Therefore a mechanism needs to be
 provided to transmit the session key from the EAP server to the
 authenticator or tunnel server that needs to use the key. The
 specification of this transit mechanism is outside the scope of this
 document.

Rigney, et al. Informational [Page 40] RFC 2869 RADIUS Extensions June 2000

7.2.2. Connection hijacking

 In this form of attack, the attacker attempts to inject packets into
 the conversation between the NAS and the RADIUS server, or between
 the RADIUS server and the backend security server. RADIUS does not
 support encryption, and as described in [1], only Access-Reply and
 Access-Challenge packets are integrity protected. Moreover, the
 integrity protection mechanism described in [1] is weaker than that
 likely to be used by some EAP methods, making it possible to subvert
 those methods by attacking EAP/RADIUS.
 In order to provide for authentication of all packets in the EAP
 exchange, all EAP/RADIUS packets MUST be authenticated using the
 Message-Authenticator attribute, as described previously.

7.2.3. Man in the middle attacks

 Since RADIUS security is based on shared secrets, end-to-end security
 is not provided in the case where authentication or accounting
 packets are forwarded along a proxy chain.  As a result, attackers
 gaining control of a RADIUS proxy will be able to modify EAP packets
 in transit.

7.2.4. Multiple databases

 In many cases a backend security server will be deployed along with a
 RADIUS server in order to provide EAP services. Unless the backend
 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 backend 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 backend security server store information in the same backend
 database; by having the backend security server provide a full RADIUS
 implementation; or by consolidating both the backend security server
 and the RADIUS server onto the same machine.

Rigney, et al. Informational [Page 41] RFC 2869 RADIUS Extensions June 2000

7.2.5. Negotiation attacks

 In a negotiation attack, a rogue NAS, tunnel server, RADIUS proxy or
 RADIUS server causes the authenticating peer to choose a less secure
 authentication method so as to make it easier to obtain the user's
 password. For example, a session that would normally be authenticated
 with EAP would instead authenticated via CHAP or PAP; alternatively,
 a connection that would normally be authenticated via one EAP type
 occurs via a less secure EAP type, such as MD5. 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 [11].
 Protection against negotiation attacks requires the elimination of
 downward negotiations. This can be achieved via implementation of
 per-connection policy on the part of the authenticating peer, and
 per-user 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 EAP when calling one service, while negotiating
 CHAP for another service, even if both services are accessible via
 the same phone number.
 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 authenticating peer expecting
 EAP to be negotiated for a session MUST NOT negotiate CHAP or PAP.
 For a NAS, it may not be possible to determine whether a user is
 required to authenticate with EAP until the user's identity is known.
 For example, for shared-uses NASes it is possible for one reseller to
 implement EAP while another does not. In such cases, if any users of
 the NAS MUST do EAP, then the NAS MUST attempt to negotiate EAP for
 every call. This avoids forcing an EAP-capable client to do more than
 one authentication, which weakens 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 user 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

Rigney, et al. Informational [Page 42] RFC 2869 RADIUS Extensions June 2000

 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, the NAS MUST send an LCP-Terminate and disconnect the
 user.  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 user dialing in from one
 location (with an EAP-capable proxy) might be able to successfully
 authenticate via EAP, while the same user dialing into another
 location (and encountering an EAP-incapable proxy) might be
 consistently disconnected.

8. References

 [1]  Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
      Authentication Dial In User Service (RADIUS)", RFC 2865, June
      2000.
 [2]  Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
 [3]  Blunk, L. and J. Vollbrecht, "PPP Extensible Authentication
      Protocol (EAP)", RFC 2284, March 1998.
 [4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March, 1997.
 [5]  Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
      October 1994.
 [6]  Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M.  and
      I. Goyret, "RADIUS Attributes for Tunnel Protocol Support", RFC
      2868, June 2000.
 [7]  Zorn, G., Aboba, B. and D. Mitton, "RADIUS Accounting
      Modifications for Tunnel Protocol Support", RFC 2867, June 2000.
 [8]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
      2279, January 1998.

Rigney, et al. Informational [Page 43] RFC 2869 RADIUS Extensions June 2000

 [9]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
      for Message Authentication", RFC 2104, February 1997.
 [10] Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA
      Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
 [11] Slatalla, M., and  Quittner, J., "Masters of Deception."
      HarperCollins, New York, 1995.

9. Acknowledgements

 RADIUS and RADIUS Accounting were originally developed by Livingston
 Enterprises (now part of Lucent Technologies) for their PortMaster
 series of Network Access Servers.
 The section on ARAP is adopted with permission from "Using RADIUS to
 Authenticate Apple Remote Access Connections" by Ward Willats of Cyno
 Technologies (ward@cyno.com).
 The section on Acct-Interim-Interval is adopted with permission from
 an earlier work in progress by Pat Calhoun of Sun Microsystems, Mark
 Beadles of Compuserve, and Alex Ratcliffe of UUNET Technologies.
 The section on EAP is adopted with permission from an earlier work in
 progress by Pat Calhoun of Sun Microsystems, Allan Rubens of Merit
 Network, and Bernard Aboba of Microsoft.  Thanks also to Dave Dawson
 and Karl Fox of Ascend, and Glen Zorn and Narendra Gidwani of
 Microsoft for useful discussions of this problem space.

10. Chair's Address

 The RADIUS working group can be contacted via the current chair:
 Carl Rigney
 Livingston Enterprises
 4464 Willow Road
 Pleasanton, California  94588
 Phone: +1 925 737 2100
 EMail: cdr@telemancy.com

Rigney, et al. Informational [Page 44] RFC 2869 RADIUS Extensions June 2000

11. Authors' Addresses

 Questions about this memo can also be directed to:
 Carl Rigney
 Livingston Enterprises
 4464 Willow Road
 Pleasanton, California  94588
 EMail: cdr@telemancy.com
 Questions on ARAP and RADIUS may be directed to:
 Ward Willats
 Cyno Technologies
 1082 Glen Echo Ave
 San Jose, CA 95125
 Phone: +1 408 297 7766
 EMail: ward@cyno.com

Rigney, et al. Informational [Page 45] RFC 2869 RADIUS Extensions June 2000

 Questions on EAP and RADIUS may be directed to any of the following:
 Pat R. Calhoun
 Network and Security Research Center
 Sun Microsystems, Inc.
 15 Network Circle
 Menlo Park, CA 94025
 Phone: +1 650 786 7733
 EMail: pcalhoun@eng.sun.com
 Allan C. Rubens
 Tut Systems, Inc.
 220 E. Huron, Suite 260
 Ann Arbor, MI 48104
 Phone: +1 734 995 1697
 EMail: arubens@tutsys.com
 Bernard Aboba
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA 98052
 Phone: +1 425 936 6605
 EMail: bernarda@microsoft.com

Rigney, et al. Informational [Page 46] RFC 2869 RADIUS Extensions June 2000

12. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  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 assigns.
 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.

Rigney, et al. Informational [Page 47]

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