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rfc:rfc2865

Network Working Group C. Rigney Request for Comments: 2865 S. Willens Obsoletes: 2138 Livingston Category: Standards Track A. Rubens

                                                                 Merit
                                                            W. Simpson
                                                            Daydreamer
                                                             June 2000
        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.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

IESG Note:

 This protocol is widely implemented and used.  Experience has shown
 that it can suffer degraded performance and lost data when used in
 large scale systems, in part because it does not include provisions
 for congestion control.  Readers of this document may find it
 beneficial to track the progress of the IETF's AAA working group,
 which may develop a successor protocol that better addresses the
 scaling and congestion control issues.

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.  The early deployment of
 RADIUS was done using UDP port number 1645, which conflicts with the
 "datametrics" service.  The officially assigned port number for
 RADIUS is 1812.

Rigney, et al. Standards Track [Page 1] RFC 2865 RADIUS June 2000

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 ................    8
    2.3       Proxy ...........................................    8
    2.4       Why UDP? ........................................   11
    2.5       Retransmission Hints ............................   12
    2.6       Keep-Alives Considered Harmful ..................   13
 3.     Packet Format .........................................   13
 4.     Packet Types ..........................................   17
    4.1       Access-Request ..................................   17
    4.2       Access-Accept ...................................   18
    4.3       Access-Reject ...................................   20
    4.4       Access-Challenge ................................   21
 5.     Attributes ............................................   22
    5.1       User-Name .......................................   26
    5.2       User-Password ...................................   27
    5.3       CHAP-Password ...................................   28
    5.4       NAS-IP-Address ..................................   29
    5.5       NAS-Port ........................................   30
    5.6       Service-Type ....................................   31
    5.7       Framed-Protocol .................................   33
    5.8       Framed-IP-Address ...............................   34
    5.9       Framed-IP-Netmask ...............................   34
    5.10      Framed-Routing ..................................   35
    5.11      Filter-Id .......................................   36
    5.12      Framed-MTU ......................................   37
    5.13      Framed-Compression ..............................   37
    5.14      Login-IP-Host ...................................   38
    5.15      Login-Service ...................................   39
    5.16      Login-TCP-Port ..................................   40
    5.17      (unassigned) ....................................   41
    5.18      Reply-Message ...................................   41
    5.19      Callback-Number .................................   42
    5.20      Callback-Id .....................................   42
    5.21      (unassigned) ....................................   43
    5.22      Framed-Route ....................................   43
    5.23      Framed-IPX-Network ..............................   44
    5.24      State ...........................................   45
    5.25      Class ...........................................   46
    5.26      Vendor-Specific .................................   47
    5.27      Session-Timeout .................................   48
    5.28      Idle-Timeout ....................................   49
    5.29      Termination-Action ..............................   49

Rigney, et al. Standards Track [Page 2] RFC 2865 RADIUS June 2000

    5.30      Called-Station-Id ...............................   50
    5.31      Calling-Station-Id ..............................   51
    5.32      NAS-Identifier ..................................   52
    5.33      Proxy-State .....................................   53
    5.34      Login-LAT-Service ...............................   54
    5.35      Login-LAT-Node ..................................   55
    5.36      Login-LAT-Group .................................   56
    5.37      Framed-AppleTalk-Link ...........................   57
    5.38      Framed-AppleTalk-Network ........................   58
    5.39      Framed-AppleTalk-Zone ...........................   58
    5.40      CHAP-Challenge ..................................   59
    5.41      NAS-Port-Type ...................................   60
    5.42      Port-Limit ......................................   61
    5.43      Login-LAT-Port ..................................   62
    5.44      Table of Attributes .............................   63
 6.     IANA Considerations ...................................   64
    6.1       Definition of Terms .............................   64
    6.2       Recommended Registration Policies ...............   65
 7.     Examples ..............................................   66
    7.1       User Telnet to Specified Host ...................   66
    7.2       Framed User Authenticating with CHAP ............   67
    7.3       User with Challenge-Response card ...............   68
 8.     Security Considerations ...............................   71
 9.     Change Log ............................................   71
 10.    References ............................................   73
 11.    Acknowledgements ......................................   74
 12.    Chair's Address .......................................   74
 13.    Authors' Addresses ....................................   75
 14.    Full Copyright Statement ..............................   76

1. Introduction

 This document obsoletes RFC 2138 [1].  A summary of the changes
 between this document and RFC 2138 is available in the "Change Log"
 appendix.
 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).

Rigney, et al. Standards Track [Page 3] RFC 2865 RADIUS June 2000

 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.
 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

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14 [2].  These key
 words mean the same thing whether capitalized or not.
 An implementation is not compliant if it fails to satisfy one or more
 of the must or must not requirements for the protocols it implements.
 An implementation that satisfies all the must, must not, should and

Rigney, et al. Standards Track [Page 4] RFC 2865 RADIUS June 2000

 should not requirements for its protocols is said to be
 "unconditionally compliant"; one that satisfies all the must and must
 not requirements but not all the should or should not requirements
 for its protocols is said to be "conditionally compliant".
 A NAS that does not implement a given service MUST NOT implement the
 RADIUS attributes for that service.  For example, a NAS that is
 unable to offer ARAP service MUST NOT implement the RADIUS attributes
 for ARAP.  A NAS MUST treat a RADIUS access-accept authorizing an
 unavailable service as an access-reject instead.

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 [3].

Rigney, et al. Standards Track [Page 5] RFC 2865 RADIUS June 2000

 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.
 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 MUST 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 Proxy-State attributes were present in the Access-Request,
 they MUST be copied unmodified and in order into the response packet.
 Other Attributes can be placed before, after, or even between the
 Proxy-State attributes.
 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 (except Proxy-State) 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 Attribute SHOULD be

Rigney, et al. Standards Track [Page 6] RFC 2865 RADIUS June 2000

 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.

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 is 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

Rigney, et al. Standards Track [Page 7] RFC 2865 RADIUS June 2000

 came with the Access-Challenge.  The server then sends back either an
 Access-Accept or Access-Reject based on whether the response matches
 the required value, 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
 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 MUST 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. Proxy

 With proxy RADIUS, one RADIUS server receives an authentication (or
 accounting) request from a RADIUS client (such as a NAS), forwards
 the request to a remote RADIUS server, receives the reply from the
 remote server, and sends that reply to the client, possibly with
 changes to reflect local administrative policy.  A common use for
 proxy RADIUS is roaming.  Roaming permits two or more administrative
 entities to allow each other's users to dial in to either entity's
 network for service.

Rigney, et al. Standards Track [Page 8] RFC 2865 RADIUS June 2000

 The NAS sends its RADIUS access-request to the "forwarding server"
 which forwards it to the "remote server".  The remote server sends a
 response (Access-Accept, Access-Reject, or Access-Challenge) back to
 the forwarding server, which sends it back to the NAS.  The User-Name
 attribute MAY contain a Network Access Identifier [8] for RADIUS
 Proxy operations.  The choice of which server receives the forwarded
 request SHOULD be based on the authentication "realm". The
 authentication realm MAY be the realm part of a Network Access
 Identifier (a "named realm").  Alternatively, the choice of which
 server receives the forwarded request MAY be based on whatever other
 criteria the forwarding server is configured to use, such as Called-
 Station-Id (a "numbered realm").
 A RADIUS server can function as both a forwarding server and a remote
 server, serving as a forwarding server for some realms and a remote
 server for other realms.  One forwarding server can act as a
 forwarder for any number of remote servers.  A remote server can have
 any number of servers forwarding to it and can provide authentication
 for any number of realms.  One forwarding server can forward to
 another forwarding server to create a chain of proxies, although care
 must be taken to avoid introducing loops.
 The following scenario illustrates a proxy RADIUS communication
 between a NAS and the forwarding and remote RADIUS servers:
 1. A NAS sends its access-request to the forwarding server.
 2. The forwarding server forwards the access-request to the remote
    server.
 3. The remote server sends an access-accept, access-reject or
    access-challenge back to the forwarding server.  For this example,
    an access-accept is sent.
 4. The forwarding server sends the access-accept to the NAS.
 The forwarding server MUST treat any Proxy-State attributes already
 in the packet as opaque data.  Its operation MUST NOT depend on the
 content of Proxy-State attributes added by previous servers.
 If there are any Proxy-State attributes in the request received from
 the client, the forwarding server MUST include those Proxy-State
 attributes in its reply to the client.  The forwarding server MAY
 include the Proxy-State attributes in the access-request when it
 forwards the request, or MAY omit them in the forwarded request.  If
 the forwarding server omits the Proxy-State attributes in the
 forwarded access-request, it MUST attach them to the response before
 sending it to the client.

Rigney, et al. Standards Track [Page 9] RFC 2865 RADIUS June 2000

 We now examine each step in more detail.
 1. A NAS sends its access-request to the forwarding server.  The
    forwarding server decrypts the User-Password, if present, using
    the shared secret it knows for the NAS.  If a CHAP-Password
    attribute is present in the packet and no CHAP-Challenge attribute
    is present, the forwarding server MUST leave the Request-
    Authenticator untouched or copy it to a CHAP-Challenge attribute.
 '' The forwarding server MAY add one Proxy-State attribute to the
    packet.  (It MUST NOT add more than one.)  If it adds a Proxy-
    State, the Proxy-State MUST appear after any other Proxy-States in
    the packet.  The forwarding server MUST NOT modify any other
    Proxy-States that were in the packet (it may choose not to forward
    them, but it MUST NOT change their contents).  The forwarding
    server MUST NOT change the order of any attributes of the same
    type, including Proxy-State.
 2. The forwarding server encrypts the User-Password, if present,
    using the secret it shares with the remote server, sets the
    Identifier as needed, and forwards the access-request to the
    remote server.
 3. The remote server (if the final destination) verifies the user
    using User-Password, CHAP-Password, or such method as future
    extensions may dictate, and returns an access-accept, access-
    reject or access-challenge back to the forwarding server.  For
    this example, an access-accept is sent.  The remote server MUST
    copy all Proxy-State attributes (and only the Proxy-State
    attributes) in order from the access-request to the response
    packet, without modifying them.
 4. The forwarding server verifies the Response Authenticator using
    the secret it shares with the remote server, and silently discards
    the packet if it fails verification.  If the packet passes
    verification, the forwarding server removes the last Proxy-State
    (if it attached one), signs the Response Authenticator using the
    secret it shares with the NAS, restores the Identifier to match
    the one in the original request by the NAS, and sends the access-
    accept to the NAS.
 A forwarding server MAY need to modify attributes to enforce local
 policy.  Such policy is outside the scope of this document, with the
 following restrictions.  A forwarding server MUST not modify existing
 Proxy-State, State, or Class attributes present in the packet.

Rigney, et al. Standards Track [Page 10] RFC 2865 RADIUS June 2000

 Implementers of forwarding servers should consider carefully which
 values it is willing to accept for Service-Type.  Careful
 consideration must be given to the effects of passing along Service-
 Types of NAS-Prompt or Administrative in a proxied Access-Accept, and
 implementers may wish to provide mechanisms to block those or other
 service types, or other attributes.  Such mechanisms are outside the
 scope of this document.

2.4. 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.
    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.

Rigney, et al. Standards Track [Page 11] RFC 2865 RADIUS June 2000

 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
    than 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.

2.5. Retransmission Hints

 If the RADIUS server and alternate RADIUS server share the same
 shared secret, it is OK to retransmit the packet to the alternate
 RADIUS server with the same ID and Request Authenticator, because the
 content of the attributes haven't changed.  If you want to use a new
 Request Authenticator when sending to the alternate server, you may.
 If you change the contents of the User-Password attribute (or any
 other attribute), you need a new Request Authenticator and therefore
 a new ID.
 If the NAS is retransmitting a RADIUS request to the same server as
 before, and the attributes haven't changed, you MUST use the same
 Request Authenticator, ID, and source port.  If any attributes have
 changed, you MUST use a new Request Authenticator and ID.
 A NAS MAY use the same ID across all servers, or MAY keep track of
 IDs separately for each server, it is up to the implementer.  If a
 NAS needs more than 256 IDs for outstanding requests, it MAY use

Rigney, et al. Standards Track [Page 12] RFC 2865 RADIUS June 2000

 additional source ports to send requests from, and keep track of IDs
 for each source port.  This allows up to 16 million or so outstanding
 requests at one time to a single server.

2.6. Keep-Alives Considered Harmful

 Some implementers have adopted the practice of sending test RADIUS
 requests to see if a server is alive.  This practice is strongly
 discouraged, since it adds to load and harms scalability without
 providing any additional useful information.  Since a RADIUS request
 is contained in a single datagram, in the time it would take you to
 send a ping you could just send the RADIUS request, and getting a
 reply tells you that the RADIUS server is up.  If you do not have a
 RADIUS request to send, it does not matter if the server is up or
 not, because you are not using it.
 If you want to monitor your RADIUS server, use SNMP.  That's what
 SNMP is for.

3. Packet Format

 Exactly one RADIUS packet is encapsulated in the UDP Data field [4],
 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.  The early deployment of
 RADIUS was done using UDP port number 1645, which conflicts with the
 "datametrics" service.  The officially assigned port number for
 RADIUS is 1812.

Rigney, et al. Standards Track [Page 13] RFC 2865 RADIUS June 2000

 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
 Codes 4 and 5 are covered in the RADIUS Accounting document [5].
 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.  The RADIUS server can detect a duplicate request if
    it has the same client source IP address and source UDP port and
    Identifier within a short span of time.

Rigney, et al. Standards Track [Page 14] RFC 2865 RADIUS June 2000

 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
    MUST be treated as padding and ignored on reception.  If the
    packet is shorter than the Length field indicates, it MUST 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.
       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

Rigney, et al. Standards Track [Page 15] RFC 2865 RADIUS June 2000

       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.
    The secret MUST NOT be empty (length 0) since this would allow
    packets to be trivially forged.
    A RADIUS server MUST use the source IP address of the RADIUS UDP
    packet to decide which shared secret to use, so that RADIUS
    requests can be proxied.
    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 MAY add a Proxy-State Attribute,
    and when the proxy forwards a response, it MUST remove its Proxy-
    State Attribute if it added one.  Proxy-State is always added or
    removed after any other Proxy-States, but no other assumptions
    regarding its location within the list of attributes can be made.
    Since Access-Accept and Access-Reject replies are authenticated on
    the entire packet contents, the stripping of the Proxy-State
    attribute invalidates 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.

Rigney, et al. Standards Track [Page 16] RFC 2865 RADIUS June 2000

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 SHOULD contain a User-Name attribute.  It MUST
    contain either a NAS-IP-Address attribute or a NAS-Identifier
    attribute (or both).
    An Access-Request MUST contain either a User-Password or a CHAP-
    Password or a State.  An Access-Request MUST NOT contain both a
    User-Password and a CHAP-Password.  If future extensions allow
    other kinds of authentication information to be conveyed, the
    attribute for that can be used in an Access-Request instead of
    User-Password or CHAP-Password.
    An Access-Request 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 [3].

Rigney, et al. Standards Track [Page 17] RFC 2865 RADIUS June 2000

 A summary of the Access-Request 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             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                     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).

Rigney, et al. Standards Track [Page 18] RFC 2865 RADIUS June 2000

    On reception of an Access-Accept, the Identifier field is matched
    with a pending Access-Request.  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.

Rigney, et al. Standards Track [Page 19] RFC 2865 RADIUS June 2000

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.

Rigney, et al. Standards Track [Page 20] RFC 2865 RADIUS June 2000

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.
    Vendor-Specific, Idle-Timeout, Session-Timeout and Proxy-State
    attributes MAY also be included.  No other Attributes defined in
    this document 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
    dialing 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 MUST treat the Access-Challenge as though it had received
    an Access-Reject instead.

Rigney, et al. Standards Track [Page 21] RFC 2865 RADIUS June 2000

 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.
 The end of the list of Attributes is indicated by the Length of the
 RADIUS packet.
 Some Attributes MAY be included more than once.  The effect of this
 is Attribute specific, and is specified in each Attribute
 description.  A summary table is provided at the end of the
 "Attributes" section.

Rigney, et al. Standards Track [Page 22] RFC 2865 RADIUS June 2000

 If multiple Attributes with the same Type are present, the order of
 Attributes with the same Type MUST be preserved by any proxies.  The
 order of Attributes of different Types is not required to be
 preserved.  A RADIUS server or client MUST NOT have any dependencies
 on the order of attributes of different types.  A RADIUS server or
 client MUST NOT require attributes of the same type to be contiguous.
 Where an Attribute's description limits which kinds of packet it can
 be contained in, this applies only to the packet types defined in
 this document, namely Access-Request, Access-Accept, Access-Reject
 and Access-Challenge (Codes 1, 2, 3, and 11).  Other documents
 defining other packet types may also use Attributes described here.
 To determine which Attributes are allowed in Accounting-Request and
 Accounting-Response packets (Codes 4 and 5) refer to the RADIUS
 Accounting document [5].
 Likewise where packet types defined here state that only certain
 Attributes are permissible in them, future memos defining new
 Attributes should indicate which packet types the new Attributes may
 be present in.
 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 [6].
    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.
    A RADIUS server MAY ignore Attributes with an unknown Type.
    A RADIUS client MAY ignore Attributes with an unknown Type.

Rigney, et al. Standards Track [Page 23] RFC 2865 RADIUS June 2000

    This specification concerns the following values:
        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
       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

Rigney, et al. Standards Track [Page 24] RFC 2865 RADIUS June 2000

 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
    as 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 none of the types in RADIUS terminate with a NUL (hex
    00).  In particular, types "text" and "string" in RADIUS do not
    terminate with a NUL (hex 00).  The Attribute has a length field
    and does not use a terminator.  Text contains UTF-8 encoded 10646
    [7] characters and String contains 8-bit binary data.  Servers and
    servers and clients MUST be able to deal with embedded nulls.
    RADIUS implementers using C are cautioned not to use strcpy() when
    handling strings.
    The format of the value field is one of five data types.  Note
    that type "text" is a subset of type "string".
    text      1-253 octets containing UTF-8 encoded 10646 [7]
              characters.  Text of length zero (0) MUST NOT be sent;
              omit the entire attribute instead.
    string    1-253 octets containing binary data (values 0 through
              255 decimal, inclusive).  Strings of length zero (0)
              MUST NOT be sent; omit the entire attribute instead.
    address   32 bit value, most significant octet first.
    integer   32 bit unsigned value, most significant octet first.
    time      32 bit unsigned value, most significant octet first --
              seconds since 00:00:00 UTC, January 1, 1970.  The
              standard Attributes do not use this data type but it is
              presented here for possible use in future attributes.

Rigney, et al. Standards Track [Page 25] RFC 2865 RADIUS June 2000

5.1. User-Name

 Description
    This Attribute indicates the name of the user to be authenticated.
    It MUST be sent in Access-Request packets if available.
    It MAY be sent in an Access-Accept packet, in which case the
    client SHOULD use the name returned in the Access-Accept packet in
    all Accounting-Request packets for this session.  If the Access-
    Accept includes Service-Type = Rlogin and the User-Name attribute,
    a NAS MAY use the returned User-Name when performing the Rlogin
    function.
 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.
    The format of the username MAY be one of several forms:
    text      Consisting only of UTF-8 encoded 10646 [7] characters.
    network access identifier
              A Network Access Identifier as described in RFC 2486
              [8].
    distinguished name
              A name in ASN.1 form used in Public Key authentication
              systems.

Rigney, et al. Standards Track [Page 26] RFC 2865 RADIUS June 2000

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 [9] pages 109-110.  A more precise
    explanation of the method follows:
    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.

Rigney, et al. Standards Track [Page 27] RFC 2865 RADIUS June 2000

    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.
    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 ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Rigney, et al. Standards Track [Page 28] RFC 2865 RADIUS June 2000

 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, and SHOULD be
    unique to the NAS within the scope of the RADIUS server. NAS-IP-
    Address is only used in Access-Request packets.  Either NAS-IP-
    Address or NAS-Identifier MUST be present in an Access-Request
    packet.
    Note that NAS-IP-Address MUST NOT be used to select the shared
    secret used to authenticate the request.  The source IP address of
    the Access-Request packet MUST be used to select the shared
    secret.
 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.

Rigney, et al. Standards Track [Page 29] RFC 2865 RADIUS June 2000

 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.
  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.

Rigney, et al. Standards Track [Page 30] RFC 2865 RADIUS June 2000

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.
 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
    10      Call Check
    11      Callback Administrative

Rigney, et al. Standards Track [Page 31] RFC 2865 RADIUS June 2000

    The service types are defined as follows when used in an Access-
    Accept.  When used in an Access-Request, they MAY 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.
    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.
    Call Check          Used by the NAS in an Access-Request packet to
                        indicate that a call is being received and
                        that the RADIUS server should send back an
                        Access-Accept to answer the call, or an
                        Access-Reject to not accept the call,
                        typically based on the Called-Station-Id or
                        Calling-Station-Id attributes.  It is

Rigney, et al. Standards Track [Page 32] RFC 2865 RADIUS June 2000

                        recommended that such Access-Requests use the
                        value of Calling-Station-Id as the value of
                        the User-Name.
    Callback Administrative
                        The user should be disconnected and called
                        back, then granted access to the
                        administrative interface to the NAS from which
                        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
    6      X.75 Synchronous

Rigney, et al. Standards Track [Page 33] RFC 2865 RADIUS June 2000

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.

Rigney, et al. Standards Track [Page 34] RFC 2865 RADIUS June 2000

 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.

Rigney, et al. Standards Track [Page 35] RFC 2865 RADIUS June 2000

 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     |  Text ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
 Type
    11 for Filter-Id.
 Length
    >= 3
 Text
    The Text 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 UTF-8 encoded 10646 [7] characters.

Rigney, et al. Standards Track [Page 36] RFC 2865 RADIUS June 2000

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 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 value, but the server is not
    required to honor the hint.
 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.

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.

Rigney, et al. Standards Track [Page 37] RFC 2865 RADIUS June 2000

 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 [10]
     2      IPX header compression
     3      Stac-LZS 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-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.

Rigney, et al. Standards Track [Page 38] RFC 2865 RADIUS June 2000

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |            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 to use 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.
  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.

Rigney, et al. Standards Track [Page 39] RFC 2865 RADIUS June 2000

 Length
    6
 Value
    The Value field is four octets.
     0   Telnet
     1   Rlogin
     2   TCP Clear
     3   PortMaster (proprietary)
     4   LAT
     5   X25-PAD
     6   X25-T3POS
     8   TCP Clear Quiet (suppresses any NAS-generated connect string)

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.
 Length
    6
 Value
    The Value field is four octets.  Despite the size of the field,
    values range from 0 to 65535.

Rigney, et al. Standards Track [Page 40] RFC 2865 RADIUS June 2000

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     |  Text ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
 Type
    18 for Reply-Message.
 Length
    >= 3
 Text
    The Text 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 UTF-8 encoded 10646 [7] characters.

Rigney, et al. Standards Track [Page 41] RFC 2865 RADIUS June 2000

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
 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.

Rigney, et al. Standards Track [Page 42] RFC 2865 RADIUS June 2000

 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.

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     |  Text ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Rigney, et al. Standards Track [Page 43] RFC 2865 RADIUS June 2000

 Type
    22 for Framed-Route.
 Length
    >= 3
 Text
    The Text 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 UTF-8 encoded 10646 [7] characters.
    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 to use.
    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 defaults 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.

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)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Rigney, et al. Standards Track [Page 44] RFC 2865 RADIUS June 2000

 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.
    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, the client MUST NOT interpret the attribute
    locally.  A packet must have only zero or 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.

Rigney, et al. Standards Track [Page 45] RFC 2865 RADIUS June 2000

 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.  The client MUST NOT interpret the
    attribute locally.
 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.

Rigney, et al. Standards Track [Page 46] RFC 2865 RADIUS June 2000

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.
  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 [6].
 String
    The String field is one or more octets.  The actual format of the
    information is site or application specific, and a robust
    implementation SHOULD support the field as undistinguished octets.
    The codification of the range of allowed usage of this field is
    outside the scope of this specification.

Rigney, et al. Standards Track [Page 47] RFC 2865 RADIUS June 2000

    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...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
    Multiple subattributes MAY be encoded within a single Vendor-
    Specific attribute, although they do not have to be.

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

Rigney, et al. Standards Track [Page 48] RFC 2865 RADIUS June 2000

 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.
 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.

Rigney, et al. Standards Track [Page 49] RFC 2865 RADIUS June 2000

 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.
 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 ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Rigney, et al. Standards Track [Page 50] RFC 2865 RADIUS June 2000

 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.
    The actual format of the information is site or application
    specific.  UTF-8 encoded 10646 [7] characters are 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

Rigney, et al. Standards Track [Page 51] RFC 2865 RADIUS June 2000

 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.  UTF-8 encoded 10646 [7] characters are 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.

5.32. 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 MUST be present in an
    Access-Request packet.
    Note that NAS-Identifier MUST NOT be used to select the shared
    secret used to authenticate the request.  The source IP address of
    the Access-Request packet MUST be used to select the shared
    secret.
 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

Rigney, et al. Standards Track [Page 52] RFC 2865 RADIUS June 2000

 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.  When the proxy server receives the response to
    its request, it MUST remove its own Proxy-State (the last Proxy-
    State in the packet) before forwarding the response to the NAS.
    If a Proxy-State Attribute is added to a packet when forwarding
    the packet, the Proxy-State Attribute MUST be added after any
    existing Proxy-State attributes.
    The content of any Proxy-State other than the one added by the
    current server should be treated as opaque octets and MUST NOT
    affect operation of the protocol.
    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.

Rigney, et al. Standards Track [Page 53] RFC 2865 RADIUS June 2000

 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.
    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 ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Rigney, et al. Standards Track [Page 54] RFC 2865 RADIUS June 2000

 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 [11].  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.
  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

Rigney, et al. Standards Track [Page 55] RFC 2865 RADIUS June 2000

 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.
 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

Rigney, et al. Standards Track [Page 56] RFC 2865 RADIUS June 2000

 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)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 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.

Rigney, et al. Standards Track [Page 57] RFC 2865 RADIUS June 2000

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
 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.

Rigney, et al. Standards Track [Page 58] RFC 2865 RADIUS June 2000

 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.

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...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Rigney, et al. Standards Track [Page 59] RFC 2865 RADIUS June 2000

 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.
 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

Rigney, et al. Standards Track [Page 60] RFC 2865 RADIUS June 2000

    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
    6       PIAFS
    7       HDLC Clear Channel
    8       X.25
    9       X.75
    10      G.3 Fax
    11      SDSL - Symmetric DSL
    12      ADSL-CAP - Asymmetric DSL, Carrierless Amplitude Phase
            Modulation
    13      ADSL-DMT - Asymmetric DSL, Discrete Multi-Tone
    14      IDSL - ISDN Digital Subscriber Line
    15      Ethernet
    16      xDSL - Digital Subscriber Line of unknown type
    17      Cable
    18      Wireless - Other
    19      Wireless - IEEE 802.11
    PIAFS is a form of wireless ISDN commonly used in Japan, and
    stands for PHS (Personal Handyphone System) Internet Access Forum
    Standard (PIAFS).

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 [12] 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.
 A summary of the Port-Limit Attribute format is shown below.  The
 fields are transmitted from left to right.

Rigney, et al. Standards Track [Page 61] RFC 2865 RADIUS June 2000

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |             Value
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Value (cont)         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type
    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.
 Length
    >= 3

Rigney, et al. Standards Track [Page 62] RFC 2865 RADIUS June 2000

 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
 0-1       0-1      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 [Note 2]
 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
 0-1       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 [Note 1]
 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
 0-1       0        0        0           32   NAS-Identifier [Note 2]
 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

Rigney, et al. Standards Track [Page 63] RFC 2865 RADIUS June 2000

 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 or State.  An Access-Request MUST NOT contain both a
 User-Password and a CHAP-Password.  If future extensions allow other
 kinds of authentication information to be conveyed, the attribute for
 that can be used in an Access-Request instead of User-Password or
 CHAP-Password.
 [Note 2] An Access-Request MUST contain either a NAS-IP-Address or a
 NAS-Identifier (or 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. IANA Considerations

 This section provides guidance to the Internet Assigned Numbers
 Authority (IANA) regarding registration of values related to the
 RADIUS protocol, in accordance with BCP 26 [13].
 There are three name spaces in RADIUS that require registration:
 Packet Type Codes, Attribute Types, and Attribute Values (for certain
 Attributes).
 RADIUS is not intended as a general-purpose Network Access Server
 (NAS) management protocol, and allocations should not be made for
 purposes unrelated to Authentication, Authorization or Accounting.

6.1. Definition of Terms

 The following terms are used here with the meanings defined in
 BCP 26: "name space", "assigned value", "registration".

Rigney, et al. Standards Track [Page 64] RFC 2865 RADIUS June 2000

 The following policies are used here with the meanings defined in
 BCP 26: "Private Use", "First Come First Served", "Expert Review",
 "Specification Required", "IETF Consensus", "Standards Action".

6.2. Recommended Registration Policies

 For registration requests where a Designated Expert should be
 consulted, the IESG Area Director for Operations should appoint the
 Designated Expert.
 For registration requests requiring Expert Review, the ietf-radius
 mailing list should be consulted.
 Packet Type Codes have a range from 1 to 254, of which 1-5,11-13 have
 been allocated.  Because a new Packet Type has considerable impact on
 interoperability, a new Packet Type Code requires Standards Action,
 and should be allocated starting at 14.
 Attribute Types have a range from 1 to 255, and are the scarcest
 resource in RADIUS, thus must be allocated with care.  Attributes
 1-53,55,60-88,90-91 have been allocated, with 17 and 21 available for
 re-use.  Attributes 17, 21, 54, 56-59, 89, 92-191 may be allocated
 following Expert Review, with Specification Required.  Release of
 blocks of Attribute Types (more than 3 at a time for a given purpose)
 should require IETF Consensus.  It is recommended that attributes 17
 and 21 be used only after all others are exhausted.
 Note that RADIUS defines a mechanism for Vendor-Specific extensions
 (Attribute 26) and the use of that should be encouraged instead of
 allocation of global attribute types, for functions specific only to
 one vendor's implementation of RADIUS, where no interoperability is
 deemed useful.
 As stated in the "Attributes" section above:
    "[Attribute Type] 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."
 Therefore Attribute values 192-240 are considered Private Use, and
 values 241-255 require Standards Action.
 Certain attributes (for example, NAS-Port-Type) in RADIUS define a
 list of values to correspond with various meanings.  There can be 4
 billion (2^32) values for each attribute. Adding additional values to
 the list can be done on a First Come, First Served basis by the IANA.

Rigney, et al. Standards Track [Page 65] RFC 2865 RADIUS June 2000

7. 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.  Hexadecimal dumps of the
 example packets are given in network byte order, using the shared
 secret "xyzzy5461".

7.1. 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 with
 password "arctangent".
 The Request Authenticator is a 16 octet random number generated by
 the NAS.
 The User-Password is 16 octets of password padded at end with nulls,
 XORed with MD5(shared secret|Request Authenticator).
    01 00 00 38 0f 40 3f 94 73 97 80 57 bd 83 d5 cb
    98 f4 22 7a 01 06 6e 65 6d 6f 02 12 0d be 70 8d
    93 d4 13 ce 31 96 e4 3f 78 2a 0a ee 04 06 c0 a8
    01 10 05 06 00 00 00 03
     1 Code = Access-Request (1)
     1 ID = 0
     2 Length = 56
    16 Request Authenticator
    Attributes:
     6  User-Name = "nemo"
    18  User-Password
     6  NAS-IP-Address = 192.168.1.16
     6  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.
 The Response Authenticator is a 16-octet MD5 checksum of the code
 (2), id (0), Length (38), the Request Authenticator from above, the
 attributes in this reply, and the shared secret.

Rigney, et al. Standards Track [Page 66] RFC 2865 RADIUS June 2000

    02 00 00 26 86 fe 22 0e 76 24 ba 2a 10 05 f6 bf
    9b 55 e0 b2 06 06 00 00 00 01 0f 06 00 00 00 00
    0e 06 c0 a8 01 03
     1 Code = Access-Accept (2)
     1 ID = 0 (same as in Access-Request)
     2 Length = 38
    16 Response Authenticator
    Attributes:
     6  Service-Type (6) = Login (1)
     6  Login-Service (15) = Telnet (0)
     6  Login-IP-Host (14) = 192.168.1.3

7.2. 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.
 The Request Authenticator is a 16 octet random number generated by
 the NAS, and is also used as the CHAP Challenge.
 The CHAP-Password consists of a 1 octet CHAP ID, in this case 22,
 followed by the 16 octet CHAP response.
    01 01 00 47 2a ee 86 f0 8d 0d 55 96 9c a5 97 8e
    0d 33 67 a2 01 08 66 6c 6f 70 73 79 03 13 16 e9
    75 57 c3 16 18 58 95 f2 93 ff 63 44 07 72 75 04
    06 c0 a8 01 10 05 06 00 00 00 14 06 06 00 00 00
    02 07 06 00 00 00 01
     1 Code = 1     (Access-Request)
     1 ID = 1
     2 Length = 71
    16 Request Authenticator
    Attributes:
     8  User-Name (1) = "flopsy"
    19  CHAP-Password (3)
     6  NAS-IP-Address (4) = 192.168.1.16
     6  NAS-Port (5) = 20
     6  Service-Type (6) = Framed (2)
     6  Framed-Protocol (7) = PPP (1)

Rigney, et al. Standards Track [Page 67] RFC 2865 RADIUS June 2000

 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.
 The Response Authenticator is a 16-octet MD5 checksum of the code
 (2), id (1), Length (56), the Request Authenticator from above, the
 attributes in this reply, and the shared secret.
    02 01 00 38 15 ef bc 7d ab 26 cf a3 dc 34 d9 c0
    3c 86 01 a4 06 06 00 00 00 02 07 06 00 00 00 01
    08 06 ff ff ff fe 0a 06 00 00 00 02 0d 06 00 00
    00 01 0c 06 00 00 05 dc
     1 Code = Access-Accept (2)
     1 ID = 1 (same as in Access-Request)
     2 Length = 56
    16 Response Authenticator
    Attributes:
     6  Service-Type (6) = Framed (2)
     6  Framed-Protocol (7) = PPP (1)
     6  Framed-IP-Address (8) = 255.255.255.254
     6  Framed-Routing (10) = None (0)
     6  Framed-Compression (13) = VJ TCP/IP Header Compression (1)
     6  Framed-MTU (12) = 1500

7.3. 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.  The user
 enters the dummy password "challenge" in this example.  The challenge
 and response generated by the smart card for this example are
 "32769430" and "99101462".
 The Request Authenticator is a 16 octet random number generated by
 the NAS.
 The User-Password is 16 octets of password, in this case "challenge",
 padded at the end with nulls, XORed with MD5(shared secret|Request
 Authenticator).
    01 02 00 39 f3 a4 7a 1f 6a 6d 76 71 0b 94 7a b9
    30 41 a0 39 01 07 6d 6f 70 73 79 02 12 33 65 75
    73 77 82 89 b5 70 88 5e 15 08 48 25 c5 04 06 c0
    a8 01 10 05 06 00 00 00 07

Rigney, et al. Standards Track [Page 68] RFC 2865 RADIUS June 2000

     1 Code = Access-Request (1)
     1 ID = 2
     2 Length = 57
    16 Request Authenticator
    Attributes:
     7 User-Name (1) = "mopsy"
    18 User-Password (2)
     6  NAS-IP-Address (4) = 192.168.1.16
     6  NAS-Port (5) = 7
 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.
 The Response Authenticator is a 16-octet MD5 checksum of the code
 (11), id (2), length (78), the Request Authenticator from above, the
 attributes in this reply, and the shared secret.
 The Reply-Message is "Challenge 32769430.  Enter response at prompt."
 The State is a magic cookie to be returned along with user's
 response; in this example 8 octets of data (33 32 37 36 39 34 33 30
 in hex).
    0b 02 00 4e 36 f3 c8 76 4a e8 c7 11 57 40 3c 0c
    71 ff 9c 45 12 30 43 68 61 6c 6c 65 6e 67 65 20
    33 32 37 36 39 34 33 30 2e 20 20 45 6e 74 65 72
    20 72 65 73 70 6f 6e 73 65 20 61 74 20 70 72 6f
    6d 70 74 2e 18 0a 33 32 37 36 39 34 33 30
     1 Code = Access-Challenge (11)
     1 ID = 2 (same as in Access-Request)
     2 Length = 78
    16 Response Authenticator
    Attributes:
    48  Reply-Message (18)
    10  State (24)
 The user enters his response, and the NAS send a new Access-Request
 with that response, and includes the State Attribute.
 The Request Authenticator is a new 16 octet random number.
 The User-Password is 16 octets of the user's response, in this case
 "99101462", padded at the end with nulls, XORed with MD5(shared
 secret|Request Authenticator).

Rigney, et al. Standards Track [Page 69] RFC 2865 RADIUS June 2000

 The state is the magic cookie from the Access-Challenge packet,
 unchanged.
    01 03 00 43 b1 22 55 6d 42 8a 13 d0 d6 25 38 07
    c4 57 ec f0 01 07 6d 6f 70 73 79 02 12 69 2c 1f
    20 5f c0 81 b9 19 b9 51 95 f5 61 a5 81 04 06 c0
    a8 01 10 05 06 00 00 00 07 18 10 33 32 37 36 39
    34 33 30
     1 Code = Access-Request (1)
     1 ID = 3 (Note that this changes.)
     2 Length = 67
    16 Request Authenticator
    Attributes:
     7  User-Name = "mopsy"
    18  User-Password
     6  NAS-IP-Address (4) = 192.168.1.16
     6  NAS-Port (5) = 7
    10  State (24)
 The Response was incorrect (for the sake of example), so the RADIUS
 server tells the NAS to reject the login attempt.
 The Response Authenticator is a 16 octet MD5 checksum of the code
 (3), id (3), length(20), the Request Authenticator from above, the
 attributes in this reply (in this case, none), and the shared secret.
    03 03 00 14 a4 2f 4f ca 45 91 6c 4e 09 c8 34 0f
    9e 74 6a a0
     1 Code = Access-Reject (3)
     1 ID = 3 (same as in Access-Request)
     2 Length = 20
    16 Response Authenticator
    Attributes:
       (none, although a Reply-Message could be sent)

Rigney, et al. Standards Track [Page 70] RFC 2865 RADIUS June 2000

8. 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 [14], but such a mechanism is outside the scope of this
 specification.
 Other distribution methods are currently undergoing research and
 experimentation.  The SNMP Security document [14] also has an
 excellent overview of threats to network protocols.
 The User-Password hiding mechanism described in Section 5.2 has not
 been subjected to significant amounts of cryptanalysis in the
 published literature.  Some in the IETF community are concerned that
 this method might not provide sufficient confidentiality protection
 [15] to passwords transmitted using RADIUS.  Users should evaluate
 their threat environment and consider whether additional security
 mechanisms should be employed.

9. Change Log

 The following changes have been made from RFC 2138:
 Strings should use UTF-8 instead of US-ASCII and should be handled as
 8-bit data.
 Integers and dates are now defined as 32 bit unsigned values.

Rigney, et al. Standards Track [Page 71] RFC 2865 RADIUS June 2000

 Updated list of attributes that can be included in Access-Challenge
 to be consistent with the table of attributes.
 User-Name mentions Network Access Identifiers.
 User-Name may now be sent in Access-Accept for use with accounting
 and Rlogin.
 Values added for Service-Type, Login-Service, Framed-Protocol,
 Framed-Compression, and NAS-Port-Type.
 NAS-Port can now use all 32 bits.
 Examples now include hexadecimal displays of the packets.
 Source UDP port must be used in conjunction with the Request
 Identifier when identifying duplicates.
 Multiple subattributes may be allowed in a Vendor-Specific attribute.
 An Access-Request is now required to contain either a NAS-IP-Address
 or NAS-Identifier (or may contain both).
 Added notes under "Operations" with more information on proxy,
 retransmissions, and keep-alives.
 If multiple Attributes with the same Type are present, the order of
 Attributes with the same Type MUST be preserved by any proxies.
 Clarified Proxy-State.
 Clarified that Attributes must not depend on position within the
 packet, as long as Attributes of the same type are kept in order.
 Added IANA Considerations section.
 Updated section on "Proxy" under "Operations".
 Framed-MTU can now be sent in Access-Request as a hint.
 Updated Security Considerations.
 Text strings identified as a subset of string, to clarify use of
 UTF-8.

Rigney, et al. Standards Track [Page 72] RFC 2865 RADIUS June 2000

10. References

 [1]   Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote
       Authentication Dial In User Service (RADIUS)", RFC 2138, April
       1997.
 [2]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March, 1997.
 [3]   Rivest, R. and S. Dusse, "The MD5 Message-Digest Algorithm",
       RFC 1321, April 1992.
 [4]   Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
       1980.
 [5]   Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
 [6]   Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC
       1700, October 1994.
 [7]   Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
       2279, January 1998.
 [8]   Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
       2486, January 1999.
 [9]   Kaufman, C., Perlman, R., and Speciner, M., "Network Security:
       Private Communications in a Public World", Prentice Hall, March
       1995, ISBN 0-13-061466-1.
 [10]  Jacobson, V., "Compressing TCP/IP headers for low-speed serial
       links", RFC 1144, February 1990.
 [11]  ISO 8859. International Standard -- Information Processing --
       8-bit Single-Byte Coded Graphic Character Sets -- Part 1: Latin
       Alphabet No. 1, ISO 8859-1:1987.
 [12]  Sklower, K., Lloyd, B., McGregor, G., Carr, D. and T.
       Coradetti, "The PPP Multilink Protocol (MP)", RFC 1990, August
       1996.
 [13]  Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA
       Considerations Section in RFCs", BCP 26, RFC 2434, October
       1998.
 [14]  Galvin, J., McCloghrie, K. and J. Davin, "SNMP Security
       Protocols", RFC 1352, July 1992.

Rigney, et al. Standards Track [Page 73] RFC 2865 RADIUS June 2000

 [15]  Dobbertin, H., "The Status of MD5 After a Recent Attack",
       CryptoBytes Vol.2 No.2, Summer 1996.

11. Acknowledgements

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

12. Chair's Address

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

Rigney, et al. Standards Track [Page 74] RFC 2865 RADIUS June 2000

13. Authors' Addresses

 Questions about this memo can also be directed to:
 Carl Rigney
 Livingston Enterprises
 4464 Willow Road
 Pleasanton, California  94588
 Phone: +1 925 737 2100
 EMail: cdr@telemancy.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

Rigney, et al. Standards Track [Page 75] RFC 2865 RADIUS June 2000

14. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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

Rigney, et al. Standards Track [Page 76]

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