rfc2138.txt

Network Working Group                                          C. Rigney
Request for Comments: 2138                                    Livingston
Obsoletes: 2058                                                A. Rubens
Category: Standards Track                                          Merit
                                                              W. Simpson
                                                              Daydreamer
                                                              S. Willens
                                                              Livingston
                                                              April 1997


          Remote Authentication Dial In User Service (RADIUS)

Status of this Memo

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

Abstract

   This document describes a protocol for carrying authentication,
   authorization, and configuration information between a Network Access
   Server which desires to authenticate its links and a shared
   Authentication Server.

Implementation Note

   This memo documents the RADIUS protocol.  There has been some
   confusion in the assignment of port numbers for this protocol.  The
   early deployment of RADIUS was done using the erroneously chosen port
   number 1645, which conflicts with the "datametrics" service.  The
   officially assigned port number for RADIUS is 1812.

Table of Contents

   1.     Introduction ..........................................    3
      1.1       Specification of Requirements ...................    4
      1.2       Terminology .....................................    5
   2.     Operation .............................................    5
      2.1       Challenge/Response ..............................    7
      2.2       Interoperation with PAP and CHAP ................    7
      2.3       Why UDP? ........................................    8
   3.     Packet Format .........................................   10
   4.     Packet Types ..........................................   13
      4.1       Access-Request ..................................   13



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      4.2       Access-Accept ...................................   14
      4.3       Access-Reject ...................................   15
      4.4       Access-Challenge ................................   17
   5.     Attributes ............................................   18
      5.1       User-Name .......................................   21
      5.2       User-Password ...................................   22
      5.3       CHAP-Password ...................................   23
      5.4       NAS-IP-Address ..................................   24
      5.5       NAS-Port ........................................   25
      5.6       Service-Type ....................................   26
      5.7       Framed-Protocol .................................   28
      5.8       Framed-IP-Address ...............................   29
      5.9       Framed-IP-Netmask ...............................   29
      5.10      Framed-Routing ..................................   30
      5.11      Filter-Id .......................................   31
      5.12      Framed-MTU ......................................   32
      5.13      Framed-Compression ..............................   33
      5.14      Login-IP-Host ...................................   33
      5.15      Login-Service ...................................   34
      5.16      Login-TCP-Port ..................................   35
      5.17      (unassigned) ....................................   36
      5.18      Reply-Message ...................................   36
      5.19      Callback-Number .................................   37
      5.20      Callback-Id .....................................   38
      5.21      (unassigned) ....................................   38
      5.22      Framed-Route ....................................   39
      5.23      Framed-IPX-Network ..............................   40
      5.24      State ...........................................   40
      5.25      Class ...........................................   41
      5.26      Vendor-Specific .................................   42
      5.27      Session-Timeout .................................   44
      5.28      Idle-Timeout ....................................   44
      5.29      Termination-Action ..............................   45
      5.30      Called-Station-Id ...............................   46
      5.31      Calling-Station-Id ..............................   47
      5.32      NAS-Identifier ..................................   48
      5.33      Proxy-State .....................................   48
      5.34      Login-LAT-Service ...............................   49
      5.35      Login-LAT-Node ..................................   50
      5.36      Login-LAT-Group .................................   51
      5.37      Framed-AppleTalk-Link ...........................   52
      5.38      Framed-AppleTalk-Network ........................   53
      5.39      Framed-AppleTalk-Zone ...........................   54
      5.40      CHAP-Challenge ..................................   55
      5.41      NAS-Port-Type ...................................   55
      5.42      Port-Limit ......................................   56
      5.43      Login-LAT-Port ..................................   57
      5.44      Table of Attributes .............................   58



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   6.     Examples ..............................................   59
      6.1       User Telnet to Specified Host ...................   60
      6.2       Framed User Authenticating with CHAP ............   60
      6.3       User with Challenge-Response card ...............   61
   Security Considerations ......................................   63
   References ...................................................   64
   Acknowledgements .............................................   64
   Chair's Address ..............................................   65
   Author's Addresses ...........................................   65

1.  Introduction

   Managing dispersed serial line and modem pools for large numbers of
   users can create the need for significant administrative support.
   Since modem pools are by definition a link to the outside world, they
   require careful attention to security, authorization and accounting.
   This can be best achieved by managing a single "database" of users,
   which allows for authentication (verifying user name and password) as
   well as configuration information detailing the type of service to
   deliver to the user (for example, SLIP, PPP, telnet, rlogin).

   Key features of RADIUS are:

   Client/Server Model

      A Network Access Server (NAS) operates as a client of RADIUS.  The
      client is responsible for passing user information to designated
      RADIUS servers, and then acting on the response which is returned.

      RADIUS servers are responsible for receiving user connection
      requests, authenticating the user, and then returning all
      configuration information necessary for the client to deliver
      service to the user.

      A RADIUS server can act as a proxy client to other RADIUS servers
      or other kinds of authentication servers.

   Network Security

      Transactions between the client and RADIUS server are
      authenticated through the use of a shared secret, which is never
      sent over the network.  In addition, any user passwords are sent
      encrypted between the client and RADIUS server, to eliminate the
      possibility that someone snooping on an unsecure network could
      determine a user's password.






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   Flexible Authentication Mechanisms

      The RADIUS server can support a variety of methods to authenticate
      a user.  When it is provided with the user name and original
      password given by the user, it can support PPP PAP or CHAP, UNIX
      login, and other authentication mechanisms.

   Extensible Protocol

      All transactions are comprised of variable length Attribute-
      Length-Value 3-tuples.  New attribute values can be added without
      disturbing existing implementations of the protocol.

1.1.  Specification of Requirements

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

   MUST      This word, or the adjective "required", means that the
             definition is an absolute requirement of the specification.

   MUST NOT  This phrase means that the definition is an absolute
             prohibition of the specification.

   SHOULD    This word, or the adjective "recommended", means that there
             may exist valid reasons in particular circumstances to
             ignore this item, but the full implications must be
             understood and carefully weighed before choosing a
             different course.

   MAY       This word, or the adjective "optional", means that this
             item is one of an allowed set of alternatives.  An
             implementation which does not include this option MUST be
             prepared to interoperate with another implementation which
             does include the option.
















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1.2.  Terminology

   This document frequently 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
             is ended.  A user may have multiple sessions in parallel or
             series if the NAS supports that.

   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

   When a client is configured to use RADIUS, any user of the client
   presents authentication information to the client.  This might be
   with a customizable login prompt, where the user is expected to enter
   their username and password.  Alternatively, the user might use a
   link framing protocol such as the Point-to-Point Protocol (PPP),
   which has authentication packets which carry this information.

   Once the client has obtained such information, it may choose to
   authenticate using RADIUS.  To do so, the client creates an "Access-
   Request" containing such Attributes as the user's name, the user's
   password, the ID of the client and the Port ID which the user is
   accessing.  When a password is present, it is hidden using a method
   based on the RSA Message Digest Algorithm MD5 [1].

   The Access-Request is submitted to the RADIUS server via the network.
   If no response is returned within a length of time, the request is
   re-sent a number of times.  The client can also forward requests to
   an alternate server or servers in the event that the primary server
   is down or unreachable.  An alternate server can be used either after
   a number of tries to the primary server fail, or in a round-robin
   fashion.  Retry and fallback algorithms are the topic of current
   research and are not specified in detail in this document.






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   Once the RADIUS server receives the request, it validates the sending
   client.  A request from a client for which the RADIUS server does not
   have a shared secret should be silently discarded.  If the client is
   valid, the RADIUS server consults a database of users to find the
   user whose name matches the request.  The user entry in the database
   contains a list of requirements which must be met to allow access for
   the user.  This always includes verification of the password, but can
   also specify the client(s) or port(s) to which the user is allowed
   access.

   The RADIUS server MAY make requests of other servers in order to
   satisfy the request, in which case it acts as a client.

   If any condition is not met, the RADIUS server sends an "Access-
   Reject" response indicating that this user request is invalid.  If
   desired, the server MAY include a text message in the Access-Reject
   which MAY be displayed by the client to the user.  No other
   Attributes are permitted in an Access-Reject.

   If all conditions are met and the RADIUS server wishes to issue a
   challenge to which the user must respond, the RADIUS server sends an
   "Access-Challenge" response.  It MAY include a text message to be
   displayed by the client to the user prompting for a response to the
   challenge, and MAY include a State attribute.  If the client receives
   an Access-Challenge and supports challenge/response it MAY display
   the text message, if any, to the user, and then prompt the user for a
   response.  The client then re-submits its original Access-Request
   with a new request ID, with the User-Password Attribute replaced by
   the response (encrypted), and including the State Attribute from the
   Access-Challenge, if any.  Only 0 or 1 instances of the State
   Attributes should be present in a request.  The server can respond to
   this new Access-Request with either an Access-Accept, an Access-
   Reject, or another Access-Challenge.

   If all conditions are met, the list of configuration values for the
   user are placed into an "Access-Accept" response.  These values
   include the type of service (for example: SLIP, PPP, Login User) and
   all necessary values to deliver the desired service.  For SLIP and
   PPP, this may include values such as IP address, subnet mask, MTU,
   desired compression, and desired packet filter identifiers.  For
   character mode users, this may include values such as desired
   protocol and host.









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2.1.  Challenge/Response

   In challenge/response authentication, the user is given an
   unpredictable number and challenged to encrypt it and give back the
   result. Authorized users are equipped with special devices such as
   smart cards or software that facilitate calculation of the correct
   response with ease. Unauthorized users, lacking the appropriate
   device or software and lacking knowledge of the secret key necessary
   to emulate such a device or software, can only guess at the response.

   The Access-Challenge packet typically contains a Reply-Message
   including a challenge to be displayed to the user, such as a numeric
   value unlikely ever to be repeated. Typically this is obtained from
   an external server that knows what type of authenticator should be in
   the possession of the authorized user and can therefore choose a
   random or non-repeating pseudorandom number of an appropriate radix
   and length.

   The user then enters the challenge into his device (or software) and
   it calculates a response, which the user enters into the client which
   forwards it to the RADIUS server via a second Access-Request.  If the
   response matches the expected response the RADIUS server replies with
   an Access-Accept, otherwise an Access-Reject.

   Example: The NAS sends an Access-Request packet to the RADIUS Server
   with NAS-Identifier, NAS-Port, User-Name, User-Password (which may
   just be a fixed string like "challenge" or ignored).  The server
   sends back an Access-Challenge packet with State and a Reply-Message
   along the lines of "Challenge 12345678, enter your response at the
   prompt" which the NAS displays.  The NAS prompts for the response and
   sends a NEW Access-Request to the server (with a new ID) with NAS-
   Identifier, NAS-Port, User-Name, User-Password (the response just
   entered by the user, encrypted), and the same State Attribute that
   came with the Access-Challenge.  The server then sends back either an
   Access-Accept or Access-Reject based on whether the response matches
   what it should be, or it can even send another Access-Challenge.

2.2.  Interoperation with PAP and CHAP

   For PAP, the NAS takes the PAP ID and password and sends them in an
   Access-Request packet as the User-Name and User-Password. The NAS MAY
   include the Attributes Service-Type = Framed-User and Framed-Protocol
   = PPP as a hint to the RADIUS server that PPP service is expected.

   For CHAP, the NAS generates a random challenge (preferably 16 octets)
   and sends it to the user, who returns a CHAP response along with a
   CHAP ID and CHAP username.  The NAS then sends an Access-Request
   packet to the RADIUS server with the CHAP username as the User-Name



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   and with the CHAP ID and CHAP response as the CHAP-Password
   (Attribute 3).  The random challenge can either be included in the
   CHAP-Challenge attribute or, if it is 16 octets long, it can be
   placed in the Request Authenticator field of the Access-Request
   packet.  The NAS MAY include the Attributes Service-Type = Framed-
   User and Framed-Protocol = PPP as a hint to the RADIUS server that
   PPP service is expected.

   The RADIUS server looks up a password based on the User-Name,
   encrypts the challenge using MD5 on the CHAP ID octet, that password,
   and the CHAP challenge (from the CHAP-Challenge attribute if present,
   otherwise from the Request Authenticator), and compares that result
   to the CHAP-Password.  If they match, the server sends back an
   Access-Accept, otherwise it sends back an Access-Reject.

   If the RADIUS server is unable to perform the requested
   authentication it should return an Access-Reject.  For example, CHAP
   requires that the user's password be available in cleartext to the
   server so that it can encrypt the CHAP challenge and compare that to
   the CHAP response.  If the password is not available in cleartext to
   the RADIUS server then the server MUST send an Access-Reject to the
   client.

2.3.  Why UDP?

   A frequently asked question is why RADIUS uses UDP instead of TCP as
   a transport protocol.  UDP was chosen for strictly technical reasons.

   There are a number of issues which must be understood.  RADIUS is a
   transaction based protocol which has several interesting
   characteristics:

   1.   If the request to a primary Authentication server fails, a
        secondary server must be queried.

         To meet this requirement, a copy of the request must be kept
         above the transport layer to allow for alternate transmission.
         This means that retransmission timers are still required.

   2.   The timing requirements of this particular protocol are
        significantly different than TCP provides.

         At one extreme, RADIUS does not require a "responsive"
         detection of lost data.  The user is willing to wait several
         seconds for the authentication to complete.  The generally
         aggressive TCP retransmission (based on average round trip
         time) is not required, nor is the acknowledgement overhead of
         TCP.



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         At the other extreme, the user is not willing to wait several
         minutes for authentication.  Therefore the reliable delivery of
         TCP data two minutes later is not useful.  The faster use of an
         alternate server allows the user to gain access before giving
         up.

   3.   The stateless nature of this protocol simplifies the use of UDP.

         Clients and servers come and go.  Systems are rebooted, or are
         power cycled independently.  Generally this does not cause a
         problem and with creative timeouts and detection of lost TCP
         connections, code can be written to handle anomalous events.
         UDP however completely eliminates any of this special handling.
         Each client and server can open their UDP transport just once
         and leave it open through all types of failure events on the
         network.

   4.   UDP simplifies the server implementation.

         In the earliest implementations of RADIUS, the server was
         single threaded.  This means that a single request was
         received, processed, and returned.  This was found to be
         unmanageable in environments where the back-end security
         mechanism took real time (1 or more seconds).  The server
         request queue would fill and in environments where hundreds of
         people were being authenticated every minute, the request
         turn-around time increased to longer that users were willing to
         wait (this was especially severe when a specific lookup in a
         database or over DNS took 30 or more seconds).  The obvious
         solution was to make the server multi-threaded.  Achieving this
         was simple with UDP.  Separate processes were spawned to serve
         each request and these processes could respond directly to the
         client NAS with a simple UDP packet to the original transport
         of the client.

         It's not all a panacea.  As noted, using UDP requires one thing
         which is built into TCP: with UDP we must artificially manage
         retransmission timers to the same server, although they don't
         require the same attention to timing provided by TCP.  This one
         penalty is a small price to pay for the advantages of UDP in
         this protocol.

         Without TCP we would still probably be using tin cans connected
         by string.  But for this particular protocol, UDP is a better
         choice.






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3.  Packet Format

   Exactly one RADIUS packet is encapsulated in the UDP Data field [2],
   where the UDP Destination Port field indicates 1812 (decimal).

   When a reply is generated, the source and destination ports are
   reversed.

   This memo documents the RADIUS protocol.  There has been some
   confusion in the assignment of port numbers for this protocol.  The
   early deployment of RADIUS was done using the erroneously chosen port
   number 1645, which conflicts with the "datametrics" service.  The
   officially assigned port number for RADIUS is 1812.

   A summary of the RADIUS data 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                         Authenticator                         |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attributes ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

Code

   The Code field is one octet, and identifies the type of RADIUS
   packet.  When a packet is received with an invalid Code field, it is
   silently discarded.

   RADIUS Codes (decimal) are assigned as follows:

        1       Access-Request
        2       Access-Accept
        3       Access-Reject
        4       Accounting-Request
        5       Accounting-Response
       11       Access-Challenge
       12       Status-Server (experimental)
       13       Status-Client (experimental)
      255       Reserved




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   Codes 4 and 5 are covered in the RADIUS Accounting document [9], and
   are not further mentioned here.  Codes 12 and 13 are reserved for
   possible use, but are not further mentioned here.

Identifier

   The Identifier field is one octet, and aids in matching requests and
   replies.

Length

   The Length field is two octets.  It indicates the length of the
   packet including the Code, Identifier, Length, Authenticator and
   Attribute fields.  Octets outside the range of the Length field
   should be treated as padding and should be ignored on reception.  If
   the packet is shorter than the Length field indicates, it should be
   silently discarded.  The minimum length is 20 and maximum length is
   4096.

Authenticator

   The Authenticator field is sixteen (16) octets.  The most significant
   octet is transmitted first.  This value is used to authenticate the
   reply from the RADIUS server, and is used in the password hiding
   algorithm.

Request Authenticator

      In Access-Request Packets, the Authenticator value is a 16 octet
      random number, called the Request Authenticator.  The value SHOULD
      be unpredictable and unique over the lifetime of a secret (the
      password shared between the client and the RADIUS server), since
      repetition of a request value in conjunction with the same secret
      would permit an attacker to reply with a previously intercepted
      response.  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.

      The Request Authenticator value in an Access-Request packet SHOULD
      also be unpredictable, lest an attacker trick a server into
      responding to a predicted future request, and then use the
      response to masquerade as that server to a future Access-Request.








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      Although protocols such as RADIUS are incapable of protecting
      against theft of an authenticated session via realtime active
      wiretapping attacks, generation of unique unpredictable requests
      can protect against a wide range of active attacks against
      authentication.

      The NAS and RADIUS server share a secret.  That shared secret
      followed by the Request Authenticator is put through a one-way MD5
      hash to create a 16 octet digest value which is xored with the
      password entered by the user, and the xored result placed in the
      User-Password attribute in the Access-Request packet.  See the
      entry for User-Password in the section on Attributes for a more
      detailed description.

   Response Authenticator

      The value of the Authenticator field in Access-Accept, Access-
      Reject, and Access-Challenge packets is called the Response
      Authenticator, and contains a one-way MD5 hash calculated over a
      stream of octets consisting of: the RADIUS packet, beginning with
      the Code field, including the Identifier, the Length, the Request
      Authenticator field from the Access-Request packet, and the
      response Attributes, followed by the shared secret.  That is,
      ResponseAuth = MD5(Code+ID+Length+RequestAuth+Attributes+Secret)
      where + denotes concatenation.

Administrative Note

   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.
   This is to ensure a sufficiently large range for the secret to
   provide protection against exhaustive search attacks.  A RADIUS
   server SHOULD use the source IP address of the RADIUS UDP packet to
   decide which shared secret to use, so that RADIUS requests can be
   proxied.

   When using a forwarding proxy, the proxy must be able to alter the
   packet as it passes through in each direction - when the proxy
   forwards the request, the proxy can add a Proxy-State Attribute, and
   when the proxy forwards a response, it removes the Proxy-State
   Attribute. Since Access-Accept and Access-Reject replies are
   authenticated on the entire packet contents, the stripping of the
   Proxy-State attribute would invalidate the signature in the packet -
   so the proxy has to re-sign it.

   Further details of RADIUS proxy implementation are outside the scope
   of this document.



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Attributes

   Many Attributes may have multiple instances, in such a case the order
   of Attributes of the same Type SHOULD be preserved.  The order of
   Attributes of different Types is not required to be preserved.

   In the section below on "Attributes" where the text refers to which
   packets an attribute is allowed in, only packets with Codes 1, 2, 3
   and 11 and attributes defined in this document are covered in this
   document.  A summary table is provided at the end of the "Attributes"
   section.  To determine which Attributes are allowed in packets with
   codes 4 and 5 refer to the RADIUS Accounting document [9].

4.  Packet Types

   The RADIUS Packet type is determined by the Code field in the first
   octet of the Packet.

4.1.  Access-Request

   Description

      Access-Request packets are sent to a RADIUS server, and convey
      information used to determine whether a user is allowed access to
      a specific NAS, and any special services requested for that user.
      An implementation wishing to authenticate a user MUST transmit a
      RADIUS packet with the Code field set to 1 (Access-Request).

      Upon receipt of an Access-Request from a valid client, an
      appropriate reply MUST be transmitted.

      An Access-Request MUST contain a User-Name attribute.  It SHOULD
      contain either a NAS-IP-Address attribute or NAS-Identifier
      attribute (or both, although that is not recommended).  It MUST
      contain either a User-Password attribute or CHAP-Password
      attribute.  It SHOULD contain a NAS-Port or NAS-Port-Type
      attribute or both unless the type of access being requested does
      not involve a port or the NAS does not distinguish among its
      ports.

      An Access-Request MAY contain additional attributes as a hint to
      the server, but the server is not required to honor the hint.

      When a User-Password is present, it is hidden using a method based
      on the RSA Message Digest Algorithm MD5 [1].

   A summary of the Access-Request packet format is shown below.  The
   fields are transmitted from left to right.



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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Request Authenticator                     |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attributes ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

   Code

      1 for Access-Request.

   Identifier

      The Identifier field MUST be changed whenever the content of the
      Attributes field changes, and whenever a valid reply has been
      received for a previous request.  For retransmissions, the
      Identifier MUST remain unchanged.

   Request Authenticator

      The Request Authenticator value MUST be changed each time a new
      Identifier is used.

   Attributes

      The Attribute field is variable in length, and contains the list
      of Attributes that are required for the type of service, as well
      as any desired optional Attributes.

4.2.  Access-Accept

   Description

      Access-Accept packets are sent by the RADIUS server, and provide
      specific configuration information necessary to begin delivery of
      service to the user.  If all Attribute values received in an
      Access-Request are acceptable then the RADIUS implementation MUST
      transmit a packet with the Code field set to 2 (Access-Accept).







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      On reception of an Access-Accept, the Identifier field is matched
      with a pending Access-Request.  Additionally, the Response
      Authenticator field MUST contain the correct response for the
      pending Access-Request.  Invalid packets are silently discarded.

   A summary of the Access-Accept packet 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Response Authenticator                    |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attributes ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

   Code

      2 for Access-Accept.

   Identifier

      The Identifier field is a copy of the Identifier field of the
      Access-Request which caused this Access-Accept.

   Response Authenticator

      The Response Authenticator value is calculated from the Access-
      Request value, as described earlier.

   Attributes

      The Attribute field is variable in length, and contains a list of
      zero or more Attributes.












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4.3.  Access-Reject

   Description

      If any value of the received Attributes is not acceptable, then
      the RADIUS server MUST transmit a packet with the Code field set
      to 3 (Access-Reject).  It MAY include one or more Reply-Message
      Attributes with a text message which the NAS MAY display to the
      user.

   A summary of the Access-Reject packet 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Response Authenticator                    |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attributes ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

   Code

      3 for Access-Reject.

   Identifier

      The Identifier field is a copy of the Identifier field of the
      Access-Request which caused this Access-Reject.

   Response Authenticator

      The Response Authenticator value is calculated from the Access-
      Request value, as described earlier.

   Attributes

      The Attribute field is variable in length, and contains a list of
      zero or more Attributes.







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4.4.  Access-Challenge

   Description

      If the RADIUS server desires to send the user a challenge
      requiring a response, then the RADIUS server MUST respond to the
      Access-Request by transmitting a packet with the Code field set to
      11 (Access-Challenge).

      The Attributes field MAY have one or more Reply-Message
      Attributes, and MAY have a single State Attribute, or none.  No
      other Attributes are permitted in an Access-Challenge.

      On receipt of an Access-Challenge, the Identifier field is matched
      with a pending Access-Request.  Additionally, the Response
      Authenticator field MUST contain the correct response for the
      pending Access-Request.  Invalid packets are silently discarded.

      If the NAS does not support challenge/response, it MUST treat an
      Access-Challenge as though it had received an Access-Reject
      instead.

      If the NAS supports challenge/response, receipt of a valid
      Access-Challenge indicates that a new Access-Request SHOULD be
      sent.  The NAS MAY display the text message, if any, to the user,
      and then prompt the user for a response.  It then sends its
      original Access-Request with a new request ID and Request
      Authenticator, with the User-Password Attribute replaced by the
      user's response (encrypted), and including the State Attribute
      from the Access-Challenge, if any.  Only 0 or 1 instances of the
      State Attribute can be present in an Access-Request.

      A NAS which supports PAP MAY forward the Reply-Message to the
      dialin client and accept a PAP response which it can use as though
      the user had entered the response.  If the NAS cannot do so, it
      should treat the Access-Challenge as though it had received an
      Access-Reject instead.














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   A summary of the Access-Challenge packet 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Response Authenticator                    |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attributes ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

   Code

      11 for Access-Challenge.

   Identifier

      The Identifier field is a copy of the Identifier field of the
      Access-Request which caused this Access-Challenge.

   Response Authenticator

      The Response Authenticator value is calculated from the Access-
      Request value, as described earlier.

   Attributes

      The Attributes field is variable in length, and contains a list of
      zero or more Attributes.

5.  Attributes

   RADIUS Attributes carry the specific authentication, authorization,
   information and configuration details for the request and reply.

   Some Attributes MAY be included more than once.  The effect of this
   is Attribute specific, and is specified in each Attribute
   description.

   The end of the list of Attributes is indicated by the Length of the
   RADIUS packet.





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   A summary of the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     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 [3].
      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:

      A RADIUS server MAY ignore Attributes with an unknown Type.

      A RADIUS client MAY ignore Attributes with an unknown Type.

          1      User-Name
          2      User-Password
          3      CHAP-Password
          4      NAS-IP-Address
          5      NAS-Port
          6      Service-Type
          7      Framed-Protocol
          8      Framed-IP-Address
          9      Framed-IP-Netmask
         10      Framed-Routing
         11      Filter-Id
         12      Framed-MTU
         13      Framed-Compression
         14      Login-IP-Host
         15      Login-Service
         16      Login-TCP-Port
         17      (unassigned)
         18      Reply-Message
         19      Callback-Number
         20      Callback-Id
         21      (unassigned)
         22      Framed-Route
         23      Framed-IPX-Network
         24      State
         25      Class
         26      Vendor-Specific



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         27      Session-Timeout
         28      Idle-Timeout
         29      Termination-Action
         30      Called-Station-Id
         31      Calling-Station-Id
         32      NAS-Identifier
         33      Proxy-State
         34      Login-LAT-Service
         35      Login-LAT-Node
         36      Login-LAT-Group
         37      Framed-AppleTalk-Link
         38      Framed-AppleTalk-Network
         39      Framed-AppleTalk-Zone
         40-59   (reserved for accounting)
         60      CHAP-Challenge
         61      NAS-Port-Type
         62      Port-Limit
         63      Login-LAT-Port

   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 an Access-Request but with an invalid
      Length, an Access-Reject SHOULD be transmitted.  If an Attribute
      is received in an Access-Accept, Access-Reject or Access-Challenge
      packet with an invalid length, the packet MUST either be treated
      an Access-Reject or else 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 a "string" in RADIUS does not require termination by an
      ASCII NUL because the Attribute already has a length field.














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      The format of the value field is one of four data types.

      string    0-253 octets

      address   32 bit value, most significant octet first.

      integer   32 bit value, most significant octet first.

      time      32 bit value, most significant octet first -- seconds
                since 00:00:00 GMT, January 1, 1970.  The standard
                Attributes do not use this data type but it is presented
                here for possible use within Vendor-Specific attributes.


5.1.  User-Name

   Description

      This Attribute indicates the name of the user to be authenticated.
      It is only used in Access-Request packets.

   A summary of the User-Name 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      1 for User-Name.

   Length

      >= 3

   String

      The String field is one or more octets.  The NAS may limit the
      maximum length of the User-Name but the ability to handle at least
      63 octets is recommended.








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      The format of the username MAY be one of several forms:

      monolithic Consisting only of alphanumeric characters.  This
                 simple form might be used to locally manage a NAS.

      simple    Consisting only of printable ASCII characters.

      name@fqdn SMTP address.  The Fully Qualified Domain Name (with or
                without trailing dot) indicates the realm in which the
                name part applies.

      distinguished name
                A name in ASN.1 form used in Public Key authentication
                systems.

5.2.  User-Password

   Description

      This Attribute indicates the password of the user to be
      authenticated, or the user's input following an Access-Challenge.
      It is only used in Access-Request packets.

      On transmission, the password is hidden.  The password is first
      padded at the end with nulls to a multiple of 16 octets.  A one-
      way MD5 hash is calculated over a stream of octets consisting of
      the shared secret followed by the Request Authenticator.  This
      value is XORed with the first 16 octet segment of the password and
      placed in the first 16 octets of the String field of the User-
      Password Attribute.

      If the password is longer than 16 characters, a second one-way MD5
      hash is calculated over a stream of octets consisting of the
      shared secret followed by the result of the first xor.  That hash
      is XORed with the second 16 octet segment of the password and
      placed in the second 16 octets of the String field of the User-
      Password Attribute.

      If necessary, this operation is repeated, with each xor result
      being used along with the shared secret to generate the next hash
      to xor the next segment of the password, to no more than 128
      characters.

      The method is taken from the book "Network Security" by Kaufman,
      Perlman and Speciner [4] pages 109-110.  A more precise
      explanation of the method follows:





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      Call the shared secret S and the pseudo-random 128-bit Request
      Authenticator RA.  Break the password into 16-octet chunks p1, p2,
      etc.  with the last one padded at the end with nulls to a 16-octet
      boundary.  Call the ciphertext blocks c(1), c(2), etc.  We'll need
      intermediate values b1, b2, etc.

         b1 = MD5(S + RA)       c(1) = p1 xor b1
         b2 = MD5(S + c(1))     c(2) = p2 xor b2
                .                       .
                .                       .
                .                       .
         bi = MD5(S + c(i-1))   c(i) = pi xor bi

      The String will contain c(1)+c(2)+...+c(i) where + denotes
      concatenation.

      On receipt, the process is reversed to yield the original
      password.

   A summary of the User-Password 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      2 for User-Password.

   Length

      At least 18 and no larger than 130.

   String

      The String field is between 16 and 128 octets long, inclusive.

5.3.  CHAP-Password

   Description

      This Attribute indicates the response value provided by a PPP
      Challenge-Handshake Authentication Protocol (CHAP) user in
      response to the challenge.  It is only used in Access-Request
      packets.



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      The CHAP challenge value is found in the CHAP-Challenge Attribute
      (60) if present in the packet, otherwise in the Request
      Authenticator field.

   A summary of the CHAP-Password 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 4 5 6 7 8 9
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  CHAP Ident   |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      3 for CHAP-Password.

   Length

      19

   CHAP Ident

      This field is one octet, and contains the CHAP Identifier from the
      user's CHAP Response.

   String

      The String field is 16 octets, and contains the CHAP Response from
      the user.

5.4.  NAS-IP-Address

   Description

      This Attribute indicates the identifying IP Address of the NAS
      which is requesting authentication of the user.  It is only used
      in Access-Request packets.  Either NAS-IP-Address or NAS-
      Identifier SHOULD be present in an Access-Request packet.












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   A summary of the NAS-IP-Address 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     |            Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Address (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      4 for NAS-IP-Address.

   Length

      6

   Address

      The Address field is four octets.

5.5.  NAS-Port

   Description

      This Attribute indicates the physical port number of the NAS which
      is authenticating the user.  It is only used in Access-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-Type (61) or both SHOULD
      be present in an Access-Request packet, if the NAS differentiates
      among its ports.

   A summary of the NAS-Port Attribute format is shown below.  The
   fields are transmitted from left to right.














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    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

      5 for NAS-Port.

   Length

      6

   Value

      The Value field is four octets.  Despite the size of the field,
      values range from 0 to 65535.

5.6.  Service-Type

   Description

      This Attribute indicates the type of service the user has
      requested, or the type of service to be provided.  It MAY be used
      in both Access-Request and Access-Accept packets.  A NAS is not
      required to implement all of these service types, and MUST treat
      unknown or unsupported Service-Types as though an Access-Reject
      had been received instead.

   A summary of the Service-Type 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

      6 for Service-Type.





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   Length

      6

   Value

      The Value field is four octets.

       1      Login
       2      Framed
       3      Callback Login
       4      Callback Framed
       5      Outbound
       6      Administrative
       7      NAS Prompt
       8      Authenticate Only
       9      Callback NAS Prompt


      The service types are defined as follows when used in an Access-
      Accept.  When used in an Access-Request, they should be considered
      to be a hint to the RADIUS server that the NAS has reason to
      believe the user would prefer the kind of service indicated, but
      the server is not required to honor the hint.

      Login               The user should be connected to a host.

      Framed              A Framed Protocol should be started for the
                          User, such as PPP or SLIP.

      Callback Login      The user should be disconnected and called
                          back, then connected to a host.

      Callback Framed     The user should be disconnected and called
                          back, then a Framed Protocol should be started
                          for the User, such as PPP or SLIP.

      Outbound            The user should be granted access to outgoing
                          devices.

      Administrative      The user should be granted access to the
                          administrative interface to the NAS from which
                          privileged commands can be executed.

      NAS Prompt          The user should be provided a command prompt
                          on the NAS from which non-privileged commands
                          can be executed.




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      Authenticate Only   Only Authentication is requested, and no
                          authorization information needs to be returned
                          in the Access-Accept (typically used by proxy
                          servers rather than the NAS itself).

      Callback NAS Prompt The user should be disconnected and called
                          back, then provided a command prompt on the
                          NAS from which non-privileged commands can be
                          executed.

5.7.  Framed-Protocol

   Description

      This Attribute indicates the framing to be used for framed access.
      It MAY be used in both Access-Request and Access-Accept packets.

   A summary of the Framed-Protocol 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

      7 for Framed-Protocol.

   Length

      6

   Value

      The Value field is four octets.

       1      PPP
       2      SLIP
       3      AppleTalk Remote Access Protocol (ARAP)
       4      Gandalf proprietary SingleLink/MultiLink protocol
       5      Xylogics proprietary IPX/SLIP






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5.8.  Framed-IP-Address

   Description

      This Attribute indicates the address to be configured for the
      user.  It MAY be used in Access-Accept packets.  It MAY be used in
      an Access-Request packet as a hint by the NAS to the server that
      it would prefer that address, but the server is not required to
      honor the hint.

   A summary of the Framed-IP-Address 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     |            Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Address (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      8 for Framed-IP-Address.

   Length

      6

   Address

      The Address field is four octets.  The value 0xFFFFFFFF indicates
      that the NAS should allow the user to select an address (e.g.
      Negotiated).  The value 0xFFFFFFFE indicates that the NAS should
      select an address for the user (e.g. Assigned from a pool of
      addresses kept by the NAS).  Other valid values indicate that the
      NAS should use that value as the user's IP address.

5.9.  Framed-IP-Netmask

   Description

      This Attribute indicates the IP netmask to be configured for the
      user when the user is a router to a network.  It MAY be used in
      Access-Accept packets.  It MAY be used in an Access-Request packet
      as a hint by the NAS to the server that it would prefer that
      netmask, but the server is not required to honor the hint.




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   A summary of the Framed-IP-Netmask 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     |            Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Address (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      9 for Framed-IP-Netmask.

   Length

      6

   Address

      The Address field is four octets specifying the IP netmask of the
      user.

5.10.  Framed-Routing

   Description

      This Attribute indicates the routing method for the user, when the
      user is a router to a network.  It is only used in Access-Accept
      packets.

   A summary of the Framed-Routing 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

      10 for Framed-Routing.





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   Length

      6

   Value

      The Value field is four octets.

       0      None
       1      Send routing packets
       2      Listen for routing packets
       3      Send and Listen

5.11.  Filter-Id

   Description

      This Attribute indicates the name of the filter list for this
      user.  Zero or more Filter-Id attributes MAY be sent in an
      Access-Accept packet.

      Identifying a filter list by name allows the filter to be used on
      different NASes without regard to filter-list implementation
      details.

   A summary of the Filter-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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      11 for Filter-Id.

   Length

      >= 3










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   String

      The String field is one or more octets, and its contents are
      implementation dependent.  It is intended to be human readable and
      MUST NOT affect operation of the protocol.  It is recommended that
      the message contain displayable ASCII characters from the range 32
      through 126 decimal.

5.12.  Framed-MTU

   Description

      This Attribute indicates the Maximum Transmission Unit to be
      configured for the user, when it is not negotiated by some other
      means (such as PPP).  It is only used in Access-Accept packets.

      A summary of the Framed-MTU 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

      12 for Framed-MTU.

   Length

      6

   Value

      The Value field is four octets.  Despite the size of the field,
      values range from 64 to 65535.












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5.13.  Framed-Compression

   Description

      This Attribute indicates a compression protocol to be used for the
      link.  It MAY be used in Access-Accept packets.  It MAY be used in
      an Access-Request packet as a hint to the server that the NAS
      would prefer to use that compression, but the server is not
      required to honor the hint.

      More than one compression protocol Attribute MAY be sent.  It is
      the responsibility of the NAS to apply the proper compression
      protocol to appropriate link traffic.

   A summary of the Framed-Compression 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

      13 for Framed-Compression.

   Length

      6

   Value

      The Value field is four octets.

       0      None
       1      VJ TCP/IP header compression [5]
       2      IPX header compression

5.14.  Login-IP-Host

   Description

      This Attribute indicates the system with which to connect the
      user, when the Login-Service Attribute is included.  It MAY be
      used in Access-Accept packets.  It MAY be used in an Access-



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      Request packet as a hint to the server that the NAS would prefer
      to use that host, but the server is not required to honor the
      hint.

   A summary of the Login-IP-Host 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     |            Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Address (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      14 for Login-IP-Host.

   Length

      6

   Address

      The Address field is four octets.  The value 0xFFFFFFFF indicates
      that the NAS SHOULD allow the user to select an address.  The
      value 0 indicates that the NAS SHOULD select a host to connect the
      user to.  Other values indicate the address the NAS SHOULD connect
      the user to.

5.15.  Login-Service

   Description

      This Attribute indicates the service which should be used to
      connect the user to the login host.  It is only used in Access-
      Accept packets.

   A summary of the Login-Service Attribute format is shown below.  The
   fields are transmitted from left to right.










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    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

      15 for Login-Service.

   Length

      6

   Value

      The Value field is four octets.

       0      Telnet
       1      Rlogin
       2      TCP Clear
       3      PortMaster (proprietary)
       4      LAT

5.16.  Login-TCP-Port

   Description

      This Attribute indicates the TCP port with which the user is to be
      connected, when the Login-Service Attribute is also present.  It
      is only used in Access-Accept packets.

   A summary of the Login-TCP-Port 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

      16 for Login-TCP-Port.



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   Length

      6

   Value

      The Value field is four octets.  Despite the size of the field,
      values range from 0 to 65535.

5.17.  (unassigned)

   Description

      ATTRIBUTE TYPE 17 HAS NOT BEEN ASSIGNED.

5.18.  Reply-Message

   Description

      This Attribute indicates text which MAY be displayed to the user.

      When used in an Access-Accept, it is the success message.

      When used in an Access-Reject, it is the failure message.  It MAY
      indicate a dialog message to prompt the user before another
      Access-Request attempt.

      When used in an Access-Challenge, it MAY indicate a dialog message
      to prompt the user for a response.

      Multiple Reply-Message's MAY be included and if any are displayed,
      they MUST be displayed in the same order as they appear in the
      packet.

   A summary of the Reply-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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-


   Type

      18 for Reply-Message.




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   Length

      >= 3

   String

      The String field is one or more octets, and its contents are
      implementation dependent.  It is intended to be human readable,
      and MUST NOT affect operation of the protocol.  It is recommended
      that the message contain displayable ASCII characters from the
      range 10, 13, and 32 through 126 decimal.  Mechanisms for
      extension to other character sets are beyond the scope of this
      specification.

5.19.  Callback-Number

   Description

      This Attribute indicates a dialing string to be used for callback.
      It MAY be used in Access-Accept packets.  It MAY be used in an
      Access-Request packet as a hint to the server that a Callback
      service is desired, but the server is not required to honor the
      hint.

   A summary of the Callback-Number 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      19 for Callback-Number.

   Length

      >= 3











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   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.

5.20.  Callback-Id

   Description

      This Attribute indicates the name of a place to be called, to be
      interpreted by the NAS.  It MAY be used in Access-Accept packets.

   A summary of the Callback-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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      20 for Callback-Id.

   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.

5.21.  (unassigned)

   Description

      ATTRIBUTE TYPE 21 HAS NOT BEEN ASSIGNED.





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5.22.  Framed-Route

   Description

      This Attribute provides routing information to be configured for
      the user on the NAS.  It is used in the Access-Accept packet and
      can appear multiple times.

   A summary of the Framed-Route 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

      22 for Framed-Route.

   Length

      >= 3

   String

      The String field is one or more octets, and its contents are
      implementation dependent.  It is intended to be human readable and
      MUST NOT affect operation of the protocol.  It is recommended that
      the message contain displayable ASCII characters from the range 32
      through 126 decimal.

      For IP routes, it SHOULD contain a destination prefix in dotted
      quad form optionally followed by a slash and a decimal length
      specifier stating how many high order bits of the prefix should be
      used.  That is followed by a space, a gateway address in dotted
      quad form, a space, and one or more metrics separated by spaces.
      For example, "192.168.1.0/24 192.168.1.1 1 2 -1 3 400". The length
      specifier may be omitted in which case it should default to 8 bits
      for class A prefixes, 16 bits for class B prefixes, and 24 bits
      for class C prefixes.  For example, "192.168.1.0 192.168.1.1 1".

      Whenever the gateway address is specified as "0.0.0.0" the IP
      address of the user SHOULD be used as the gateway address.






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5.23.  Framed-IPX-Network

   Description

      This Attribute indicates the IPX Network number to be configured
      for the user.  It is used in Access-Accept packets.

   A summary of the Framed-IPX-Network 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

      23 for Framed-IPX-Network.

   Length

      6

   Value

      The Value field is four octets.  The value 0xFFFFFFFE indicates
      that the NAS should select an IPX network for the user (e.g.
      assigned from a pool of one or more IPX networks kept by the NAS).
      Other values should be used as the IPX network for the link to the
      user.

5.24.  State

   Description

      This Attribute is available to be sent by the server to the client
      in an Access-Challenge and MUST be sent unmodified from the client
      to the server in the new Access-Request reply to that challenge,
      if any.









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      This Attribute is available to be sent by the server to the client
      in an Access-Accept that also includes a Termination-Action
      Attribute with the value of RADIUS-Request.  If the NAS performs
      the Termination-Action by sending a new Access-Request upon
      termination of the current session, it MUST include the State
      attribute unchanged in that Access-Request.

      In either usage, no interpretation by the client should be made.
      A packet may have only one State Attribute.  Usage of the State
      Attribute is implementation dependent.

   A summary of the State 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      24 for State.

   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.

5.25.  Class

   Description

      This Attribute is available to be sent by the server to the client
      in an Access-Accept and should be sent unmodified by the client to
      the accounting server as part of the Accounting-Request packet if
      accounting is supported.  No interpretation by the client should
      be made.





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   A summary of the Class 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      25 for Class.

   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.

5.26.  Vendor-Specific

   Description

      This Attribute is available to allow vendors to support their own
      extended Attributes not suitable for general usage.  It MUST not
      affect the operation of the RADIUS protocol.

      Servers not equipped to interpret the vendor-specific information
      sent by a client MUST ignore it (although it may be reported).
      Clients which do not receive desired vendor-specific information
      SHOULD make an attempt to operate without it, although they may do
      so (and report they are doing so) in a degraded mode.

   A summary of the Vendor-Specific Attribute format is shown below.
   The fields are transmitted from left to right.









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    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       |            Vendor-Id
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        Vendor-Id (cont)           |  String...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      26 for Vendor-Specific.

   Length

       >= 7

   Vendor-Id

      The high-order octet is 0 and the low-order 3 octets are the SMI
      Network Management Private Enterprise Code of the Vendor in
      network byte order, as defined in the Assigned Numbers RFC [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.

      It SHOULD be encoded as a sequence of vendor type / vendor length
      / value fields, as follows.  The Attribute-Specific field is
      dependent on the vendor's definition of that attribute.  An
      example encoding of the Vendor-Specific attribute using this
      method follows:

       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       |            Vendor-Id
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Vendor-Id (cont)           | Vendor type   | Vendor length |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Attribute-Specific...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-





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5.27.  Session-Timeout

   Description

      This Attribute sets the maximum number of seconds of service to be
      provided to the user before termination of the session or prompt.
      This Attribute is available to be sent by the server to the client
      in an Access-Accept or Access-Challenge.

   A summary of the Session-Timeout 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

      27 for Session-Timeout.

   Length

      6

   Value

      The field is 4 octets, containing a 32-bit unsigned integer with
      the maximum number of seconds this user should be allowed to
      remain connected by the NAS.

5.28.  Idle-Timeout

   Description

      This Attribute sets the maximum number of consecutive seconds of
      idle connection allowed to the user before termination of the
      session or prompt.  This Attribute is available to be sent by the
      server to the client in an Access-Accept or Access-Challenge.









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   A summary of the Idle-Timeout 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

      28 for Idle-Timeout.

   Length

      6

   Value

      The field is 4 octets, containing a 32-bit unsigned integer with
      the maximum number of consecutive seconds of idle time this user
      should be permitted before being disconnected by the NAS.

5.29.  Termination-Action

   Description

      This Attribute indicates what action the NAS should take when the
      specified service is completed.  It is only used in Access-Accept
      packets.

   A summary of the Termination-Action 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

      29 for Termination-Action.




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   Length

      6

   Value

      The Value field is four octets.

       0      Default
       1      RADIUS-Request

      If the Value is set to RADIUS-Request, upon termination of the
      specified service the NAS MAY send a new Access-Request to the
      RADIUS server, including the State attribute if any.

5.30.  Called-Station-Id

   Description

   This Attribute allows the NAS to send in the Access-Request packet
   the phone number that the user called, using Dialed Number
   Identification (DNIS) or similar technology.  Note that this may be
   different from the phone number the call comes in on.  It is only
   used in Access-Request packets.

   A summary of the Called-Station-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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-


   Type

      30 for Called-Station-Id.

   Length

      >= 3

   String

      The String field is one or more octets, containing the phone
      number that the user's call came in on.




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      The actual format of the information is site or application
      specific.  Printable ASCII is recommended, but 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.

5.31.  Calling-Station-Id

   Description

      This Attribute allows the NAS to send in the Access-Request packet
      the phone number that the call came from, using Automatic Number
      Identification (ANI) or similar technology.  It is only used in
      Access-Request packets.

   A summary of the Calling-Station-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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      31 for Calling-Station-Id.

   Length

      >= 3

   String

      The String field is one or more octets, containing the phone
      number that the user placed the call from.

      The actual format of the information is site or application
      specific.  Printable ASCII is recommended, but 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.







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5.32.  NAS-Identifier

   Description

      This Attribute contains a string identifying the NAS originating
      the Access-Request.  It is only used in Access-Request packets.
      Either NAS-IP-Address or NAS-Identifier SHOULD be present in an
      Access-Request packet.

   A summary of the NAS-Identifier 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      32 for NAS-Identifier.

   Length

      >= 3

   String

      The String field is one or more octets, and should be unique to
      the NAS within the scope of the RADIUS server.  For example, a
      fully qualified domain name would be suitable as a NAS-Identifier.

      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.

5.33.  Proxy-State

   Description

      This Attribute is available to be sent by a proxy server to
      another server when forwarding an Access-Request and MUST be
      returned unmodified in the Access-Accept, Access-Reject or
      Access-Challenge.  This attribute should be removed by the proxy
      server before the response is forwarded to the NAS.



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      Usage of the Proxy-State Attribute is implementation dependent.  A
      description of its function is outside the scope of this
      specification.

   A summary of the Proxy-State 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      33 for Proxy-State.

   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.

5.34.  Login-LAT-Service

   Description

      This Attribute indicates the system with which the user is to be
      connected by LAT.  It MAY be used in Access-Accept packets, but
      only when LAT is specified as the Login-Service.  It MAY be used
      in an Access-Request packet as a hint to the server, but the
      server is not required to honor the hint.

      Administrators use the service attribute when dealing with
      clustered systems, such as a VAX or Alpha cluster. In such an
      environment several different time sharing hosts share the same
      resources (disks, printers, etc.), and administrators often
      configure each to offer access (service) to each of the shared
      resources. In this case, each host in the cluster advertises its
      services through LAT broadcasts.




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      Sophisticated users often know which service providers (machines)
      are faster and tend to use a node name when initiating a LAT
      connection.  Alternately, some administrators want particular
      users to use certain machines as a primitive form of load
      balancing (although LAT knows how to do load balancing itself).

   A summary of the Login-LAT-Service 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-


   Type

      34 for Login-LAT-Service.

   Length

      >= 3

   String

      The String field is one or more octets, and contains the identity
      of the LAT service to use.  The LAT Architecture allows this
      string to contain $ (dollar), - (hyphen), . (period), _
      (underscore), numerics, upper and lower case alphabetics, and the
      ISO Latin-1 character set extension [6].  All LAT string
      comparisons are case insensitive.

5.35.  Login-LAT-Node

   Description

      This Attribute indicates the Node with which the user is to be
      automatically connected by LAT.  It MAY be used in Access-Accept
      packets, but only when LAT is specified as the Login-Service.  It
      MAY be used in an Access-Request packet as a hint to the server,
      but the server is not required to honor the hint.

   A summary of the Login-LAT-Node Attribute format is shown below.  The
   fields are transmitted from left to right.






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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      35 for Login-LAT-Node.

   Length

      >= 3

   String

      The String field is one or more octets, and contains the identity
      of the LAT Node to connect the user to.  The LAT Architecture
      allows this string to contain $ (dollar), - (hyphen), . (period),
      _ (underscore), numerics, upper and lower case alphabetics, and
      the ISO Latin-1 character set extension.  All LAT string
      comparisons are case insensitive.

5.36.  Login-LAT-Group

   Description

      This Attribute contains a string identifying the LAT group codes
      which this user is authorized to use.  It MAY be used in Access-
      Accept packets, but only when LAT is specified as the Login-
      Service.  It MAY be used in an Access-Request packet as a hint to
      the server, but the server is not required to honor the hint.

      LAT supports 256 different group codes, which LAT uses as a form
      of access rights.  LAT encodes the group codes as a 256 bit
      bitmap.

      Administrators can assign one or more of the group code bits at
      the LAT service provider; it will only accept LAT connections that
      have these group codes set in the bit map. The administrators
      assign a bitmap of authorized group codes to each user; LAT gets
      these from the operating system, and uses these in its requests to
      the service providers.








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   A summary of the Login-LAT-Group 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      36 for Login-LAT-Group.

   Length

      34

   String

      The String field is a 32 octet bit map, most significant octet
      first.  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.

5.37.  Framed-AppleTalk-Link

   Description

      This Attribute indicates the AppleTalk network number which should
      be used for the serial link to the user, which is another
      AppleTalk router.  It is only used in Access-Accept packets.  It
      is never used when the user is not another router.

   A summary of the Framed-AppleTalk-Link 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)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   Type

      37 for Framed-AppleTalk-Link.

   Length

      6

   Value

      The Value field is four octets.  Despite the size of the field,
      values range from 0 to 65535.  The special value of 0 indicates
      that this is an unnumbered serial link.  A value of 1-65535 means
      that the serial line between the NAS and the user should be
      assigned that value as an AppleTalk network number.

5.38.  Framed-AppleTalk-Network

   Description

      This Attribute indicates the AppleTalk Network number which the
      NAS should probe to allocate an AppleTalk node for the user.  It
      is only used in Access-Accept packets.  It is never used when the
      user is another router.  Multiple instances of this Attribute
      indicate that the NAS may probe using any of the network numbers
      specified.

   A summary of the Framed-AppleTalk-Network 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

      38 for Framed-AppleTalk-Network.

   Length

      6






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   Value

      The Value field is four octets.  Despite the size of the field,
      values range from 0 to 65535.  The special value 0 indicates that
      the NAS should assign a network for the user, using its default
      cable range.  A value between 1 and 65535 (inclusive) indicates
      the AppleTalk Network the NAS should probe to find an address for
      the user.

5.39.  Framed-AppleTalk-Zone

   Description

      This Attribute indicates the AppleTalk Default Zone to be used for
      this user.  It is only used in Access-Accept packets.  Multiple
      instances of this attribute in the same packet are not allowed.

   A summary of the Framed-AppleTalk-Zone 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 4
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      39 for Framed-AppleTalk-Zone.

   Length

      >= 3

   String

      The name of the Default AppleTalk Zone to be used for this user.
      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.









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5.40.  CHAP-Challenge

   Description

      This Attribute contains the CHAP Challenge sent by the NAS to a
      PPP Challenge-Handshake Authentication Protocol (CHAP) user.  It
      is only used in Access-Request packets.

      If the CHAP challenge value is 16 octets long it MAY be placed in
      the Request Authenticator field instead of using this attribute.

   A summary of the CHAP-Challenge 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

      60 for CHAP-Challenge.

   Length

      >= 7

   String

      The String field contains the CHAP Challenge.

5.41.  NAS-Port-Type

   Description

      This Attribute indicates the type of the physical port of the NAS
      which is authenticating the user.  It can be used instead of or in
      addition to the NAS-Port (5) attribute.  It is only used in
      Access-Request packets.  Either NAS-Port (5) or NAS-Port-Type or
      both SHOULD be present in an Access-Request packet, if the NAS
      differentiates among its ports.









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   A summary of the NAS-Port-Type 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

      61 for NAS-Port-Type.

   Length

      6

   Value

      The Value field is four octets.  "Virtual" refers to a connection
      to the NAS via some transport protocol, instead of through a
      physical port.  For example, if a user telnetted into a NAS to
      authenticate himself as an Outbound-User, the Access-Request might
      include NAS-Port-Type = Virtual as a hint to the RADIUS server
      that the user was not on a physical port.

      0       Async
      1       Sync
      2       ISDN Sync
      3       ISDN Async V.120
      4       ISDN Async V.110
      5       Virtual

5.42.  Port-Limit

   Description

      This Attribute sets the maximum number of ports to be provided to
      the user by the NAS.  This Attribute MAY be sent by the server to
      the client in an Access-Accept packet.  It is intended for use in
      conjunction with Multilink PPP [7] or similar uses.  It MAY also
      be sent by the NAS to the server as a hint that that many ports
      are desired for use, but the server is not required to honor the
      hint.





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   A summary of the Port-Limit 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

      62 for Port-Limit.

   Length

      6

   Value

      The field is 4 octets, containing a 32-bit unsigned integer with
      the maximum number of ports this user should be allowed to connect
      to on the NAS.

5.43.  Login-LAT-Port

   Description

      This Attribute indicates the Port with which the user is to be
      connected by LAT.  It MAY be used in Access-Accept packets, but
      only when LAT is specified as the Login-Service.  It MAY be used
      in an Access-Request packet as a hint to the server, but the
      server is not required to honor the hint.

   A summary of the Login-LAT-Port 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      63 for Login-LAT-Port.




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   Length

      >= 3

   String

      The String field is one or more octets, and contains the identity
      of the LAT port to use.  The LAT Architecture allows this string
      to contain $ (dollar), - (hyphen), . (period), _ (underscore),
      numerics, upper and lower case alphabetics, and the ISO Latin-1
      character set extension.  All LAT string comparisons are case
      insensitive.

5.44.  Table of Attributes

   The following table provides a guide to which attributes may be found
   in which kinds of packets, and in what quantity.

   Request   Accept   Reject   Challenge   #    Attribute
   1         0        0        0            1   User-Name
   0-1       0        0        0            2   User-Password [Note 1]
   0-1       0        0        0            3   CHAP-Password [Note 1]
   0-1       0        0        0            4   NAS-IP-Address
   0-1       0        0        0            5   NAS-Port
   0-1       0-1      0        0            6   Service-Type
   0-1       0-1      0        0            7   Framed-Protocol
   0-1       0-1      0        0            8   Framed-IP-Address
   0-1       0-1      0        0            9   Framed-IP-Netmask
   0         0-1      0        0           10   Framed-Routing
   0         0+       0        0           11   Filter-Id
   0         0-1      0        0           12   Framed-MTU
   0+        0+       0        0           13   Framed-Compression
   0+        0+       0        0           14   Login-IP-Host
   0         0-1      0        0           15   Login-Service
   0         0-1      0        0           16   Login-TCP-Port
   0         0+       0+       0+          18   Reply-Message
   0-1       0-1      0        0           19   Callback-Number
   0         0-1      0        0           20   Callback-Id
   0         0+       0        0           22   Framed-Route
   0         0-1      0        0           23   Framed-IPX-Network
   0-1       0-1      0        0-1         24   State
   0         0+       0        0           25   Class
   0+        0+       0        0+          26   Vendor-Specific
   0         0-1      0        0-1         27   Session-Timeout
   0         0-1      0        0-1         28   Idle-Timeout
   0         0-1      0        0           29   Termination-Action
   0-1       0        0        0           30   Called-Station-Id
   0-1       0        0        0           31   Calling-Station-Id



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   0-1       0        0        0           32   NAS-Identifier
   0+        0+       0+       0+          33   Proxy-State
   0-1       0-1      0        0           34   Login-LAT-Service
   0-1       0-1      0        0           35   Login-LAT-Node
   0-1       0-1      0        0           36   Login-LAT-Group
   0         0-1      0        0           37   Framed-AppleTalk-Link
   0         0+       0        0           38   Framed-AppleTalk-Network
   0         0-1      0        0           39   Framed-AppleTalk-Zone
   0-1       0        0        0           60   CHAP-Challenge
   0-1       0        0        0           61   NAS-Port-Type
   0-1       0-1      0        0           62   Port-Limit
   0-1       0-1      0        0           63   Login-LAT-Port


   Request   Accept   Reject   Challenge   #    Attribute


   [Note 1] An Access-Request MUST contain either a User-Password or a
   CHAP-Password, and MUST NOT contain both.

   The following table defines the meaning of the above table entries.

 0     This attribute MUST NOT be present in packet.
 0+    Zero or more instances of this attribute MAY be present in packet.
 0-1   Zero or one instance of this attribute MAY be present in packet.
 1     Exactly one instance of this attribute MUST be present in packet.

6.  Examples

   A few examples are presented to illustrate the flow of packets and
   use of typical attributes.  These examples are not intended to be
   exhaustive, many others are possible.



















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6.1.  User Telnet to Specified Host

   The NAS at 192.168.1.16 sends an Access-Request UDP packet to the
   RADIUS Server for a user named nemo logging in on port 3.

      Code = 1        (Access-Request)
      ID = 0
      Length = 56
      Request Authenticator = {16 octet random number}
      Attributes:
          User-Name = "nemo"
          User-Password = {16 octets of Password padded at end with nulls,
                      XORed with MD5(shared secret|Request Authenticator)}
          NAS-IP-Address = 192.168.1.16
          NAS-Port = 3

   The RADIUS server authenticates nemo, and sends an Access-Accept UDP
   packet to the NAS telling it to telnet nemo to host 192.168.1.3.

      Code = 2        (Access-Accept)
      ID = 0          (same as in Access-Request)
      Length = 38
      Response Authenticator = {16-octet MD-5 checksum of the code (2),
                      id (0), Length (38), the Request Authenticator from
                      above, the attributes in this reply, and the shared
                      secret}
      Attributes:
          Service-Type = Login-User
          Login-Service = Telnet
          Login-Host = 192.168.1.3

6.2.  Framed User Authenticating with CHAP

   The NAS at 192.168.1.16 sends an Access-Request UDP packet to the
   RADIUS Server for a user named flopsy logging in on port 20 with PPP,
   authenticating using CHAP.  The NAS sends along the Service-Type and
   Framed-Protocol attributes as a hint to the RADIUS server that this
   user is looking for PPP, although the NAS is not required to do so.













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      Code = 1        (Access-Request)
      ID = 1
      Length = 71
      Request Authenticator = {16 octet random number also used as
                               CHAP challenge}
      Attributes:
          User-Name = "flopsy"
          CHAP-Password = {1 octet CHAP ID followed by 16 octet
                           CHAP response}
          NAS-IP-Address = 192.168.1.16
          NAS-Port = 20
          Service-Type = Framed-User
          Framed-Protocol = PPP

   The RADIUS server authenticates flopsy, and sends an Access-Accept
   UDP packet to the NAS telling it to start PPP service and assign an
   address for the user out of its dynamic address pool.

      Code = 2        (Access-Accept)
      ID = 1          (same as in Access-Request)
      Length = 56
      Response Authenticator = {16-octet MD-5 checksum of the code (2),
                      id (1), Length (56), the Request Authenticator from
                      above, the attributes in this reply, and the shared
                      secret}
      Attributes:
          Service-Type = Framed-User
          Framed-Protocol = PPP
          Framed-IP-Address = 255.255.255.254
          Framed-Routing = None
          Framed-Compression = 1      (VJ TCP/IP Header Compression)
          Framed-MTU = 1500

6.3.  User with Challenge-Response card

   The NAS at 192.168.1.16 sends an Access-Request UDP packet to the
   RADIUS Server for a user named mopsy logging in on port 7.

      Code = 1        (Access-Request)
      ID = 2
      Length = 57
      Request Authenticator = {16 octet random number}
      Attributes:
          User-Name = "mopsy"
          User-Password = {16 octets of Password padded at end with nulls,
                      XORed with MD5(shared secret|Request Authenticator)}
          NAS-IP-Address = 192.168.1.16
          NAS-Port = 7



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   The RADIUS server decides to challenge mopsy, sending back a
   challenge string and looking for a response.  The RADIUS server
   therefore and sends an Access-Challenge UDP packet to the NAS.

      Code = 11       (Access-Challenge}
      ID = 2          (same as in Access-Request)
      Length = 78
      Response Authenticator = {16-octet MD-5 checksum of the code (11),
                      id (2), length (78), the Request Authenticator from
                      above, the attributes in this reply, and the shared
                      secret}
      Attributes:
          Reply-Message = "Challenge 32769430.  Enter response at prompt."
          State =     {Magic Cookie to be returned along with user's response;
                       in this example 8 octets of data}

   The user enters his response, and the NAS send a new Access-Request
   with that response, and includes the State Attribute.

      Code = 1        (Access-Request)
      ID = 3          (Note that this changes)
      Length = 67
      Request Authenticator = {NEW 16 octet random number}
      Attributes:
          User-Name = "mopsy"
          User-Password = {16 octets of Response padded at end with
                      nulls, XORed with MD5 checksum of shared secret
                      plus above Request Authenticator}
          NAS-IP-Address = 192.168.1.16
          NAS-Port = 7
          State =     {Magic Cookie from Access-Challenge packet, unchanged}

   The Response was incorrect, so the RADIUS server tells the NAS to
   reject the login attempt.

      Code = 3        (Access-Reject)
      ID = 3          (same as in Access-Request)
      Length = 20
      Response Authenticator = {16-octet MD-5 checksum of the code (3),
                      id (3), length(20), the Request Authenticator from
                      above, the attributes in this reply if any, and the
                      shared secret}
      Attributes:
              (none, although a Reply-Message could be sent)







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RFC 2138                         RADIUS                       April 1997


Security Considerations

   Security issues are the primary topic of this document.

   In practice, within or associated with each RADIUS server, there is a
   database which associates "user" names with authentication
   information ("secrets").  It is not anticipated that a particular
   named user would be authenticated by multiple methods.  This would
   make the user vulnerable to attacks which negotiate the least secure
   method from among a set.  Instead, for each named user there should
   be an indication of exactly one method used to authenticate that user
   name.  If a user needs to make use of different authentication
   methods under different circumstances, then distinct user names
   SHOULD be employed, each of which identifies exactly one
   authentication method.

   Passwords and other secrets should be stored at the respective ends
   such that access to them is as limited as possible.  Ideally, the
   secrets should only be accessible to the process requiring access in
   order to perform the authentication.

   The secrets should be distributed with a mechanism that limits the
   number of entities that handle (and thus gain knowledge of) the
   secret.  Ideally, no unauthorized person should ever gain knowledge
   of the secrets.  It is possible to achieve this with SNMP Security
   Protocols [8], but such a mechanism is outside the scope of this
   specification.

   Other distribution methods are currently undergoing research and
   experimentation.  The SNMP Security document [8] also has an
   excellent overview of threats to network protocols.




















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References

   [1]   Rivest, R., and S. Dusse, "The MD5 Message-Digest Algorithm",
         RFC 1321, MIT Laboratory for Computer Science, RSA Data
         Security Inc., April 1992.

   [2]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
         USC/Information Sciences Institute, August 1980.

   [3]   Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
         1700, USC/Information Sciences Institute, October 1994.

   [4]   Kaufman, C., Perlman, R., and Speciner, M., "Network Security:
         Private Communications in a Public World", Prentice Hall, March
         1995, ISBN 0-13-061466-1.

   [5]   Jacobson, V., "Compressing TCP/IP headers for low-speed serial
         links", RFC 1144, Lawrence Berkeley Laboratory, February 1990.

   [6]   ISO 8859. International Standard -- Information Processing --
         8-bit Single-Byte Coded Graphic Character Sets -- Part 1: Latin
         Alphabet No. 1, ISO 8859-1:1987.
         <URL:http://www.iso.ch/cate/d16338.html>

   [7]   Sklower, K., Lloyd, B., McGregor, G., and Carr, D., "The PPP
         Multilink Protocol (MP)", RFC 1717, University of California
         Berkeley, Lloyd Internetworking, Newbridge Networks
         Corporation, November 1994.

   [8]   Galvin, J., McCloghrie, K., and Davin, J., "SNMP Security
         Protocols", RFC 1352, Trusted Information Systems, Inc., Hughes
         LAN Systems, Inc., MIT Laboratory for Computer Science, July
         1992.

   [9]   Rigney, C., "RADIUS Accounting", RFC 2139, April 1997.

Acknowledgments

   RADIUS was originally developed by Livingston Enterprises for their
   PortMaster series of Network Access Servers.











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Chair's Address

   The working group can be contacted via the current chair:

   Carl Rigney
   Livingston Enterprises
   4464 Willow Road
   Pleasanton, California  94588

   Phone: +1 510 426 0770
   EMail: cdr@livingston.com

Authors' Addresses

   Questions about this memo can also be directed to:

   Carl Rigney
   Livingston Enterprises
   4464 Willow Road
   Pleasanton, California  94588

   Phone: +1 510 426 0770
   EMail: cdr@livingston.com

   Allan C. Rubens
   Merit Network, Inc.
   4251 Plymouth Road
   Ann Arbor, Michigan  48105-2785

   EMail: acr@merit.edu

   William Allen Simpson
   Daydreamer
   Computer Systems Consulting Services
   1384 Fontaine
   Madison Heights, Michigan  48071

   EMail: wsimpson@greendragon.com

   Steve Willens
   Livingston Enterprises
   4464 Willow Road
   Pleasanton, California  94588

   EMail: steve@livingston.com






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