rfc2866.txt

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Network Working Group                                          C. Rigney
Request for Comments: 2866                                    Livingston
Category: Informational                                        June 2000
Obsoletes: 2139


                           RADIUS Accounting

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

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

Abstract

   This document describes a protocol for carrying accounting
   information between a Network Access Server and a shared Accounting
   Server.

Implementation Note

   This memo documents the RADIUS Accounting protocol.  The early
   deployment of RADIUS Accounting was done using UDP port number 1646,
   which conflicts with the "sa-msg-port" service.  The officially
   assigned port number for RADIUS Accounting is 1813.

Table of Contents

   1.     Introduction ....................................    2
     1.1    Specification of Requirements .................    3
     1.2    Terminology ...................................    3
   2.     Operation .......................................    4
     2.1    Proxy .........................................    4
   3.     Packet Format ...................................    5
   4.     Packet Types ...................................     7
     4.1    Accounting-Request ............................    8
     4.2    Accounting-Response ...........................    9
   5.     Attributes ......................................   10
     5.1    Acct-Status-Type ..............................   12
     5.2    Acct-Delay-Time ...............................   13
     5.3    Acct-Input-Octets .............................   14
     5.4    Acct-Output-Octets ............................   15
     5.5    Acct-Session-Id ...............................   15



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     5.6    Acct-Authentic ................................   16
     5.7    Acct-Session-Time .............................   17
     5.8    Acct-Input-Packets ............................   18
     5.9    Acct-Output-Packets ...........................   18
     5.10   Acct-Terminate-Cause ..........................   19
     5.11   Acct-Multi-Session-Id .........................   21
     5.12   Acct-Link-Count ...............................   22
     5.13   Table of Attributes ...........................   23
   6.     IANA Considerations .............................   25
   7.     Security Considerations .........................   25
   8.     Change Log ......................................   25
   9.     References ......................................   26
   10.    Acknowledgements ................................   26
   11.    Chair's Address .................................   26
   12.    Author's Address ................................   27
   13.    Full Copyright Statement ........................   28

1.  Introduction

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

   The RADIUS (Remote Authentication Dial In User Service) document [2]
   specifies the RADIUS protocol used for Authentication and
   Authorization.  This memo extends the use of the RADIUS protocol to
   cover delivery of accounting information from the Network Access
   Server (NAS) to a RADIUS accounting server.

   This document obsoletes RFC 2139 [1].  A summary of the changes
   between this document and RFC 2139 is available in the "Change Log"
   appendix.

   Key features of RADIUS Accounting are:

      Client/Server Model

          A Network Access Server (NAS) operates as a client of the
          RADIUS accounting server.  The client is responsible for
          passing user accounting information to a designated RADIUS
          accounting server.





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          The RADIUS accounting server is responsible for receiving the
          accounting request and returning a response to the client
          indicating that it has successfully received the request.

          The RADIUS accounting server can act as a proxy client to
          other kinds of accounting servers.

      Network Security

          Transactions between the client and RADIUS accounting server
          are authenticated through the use of a shared secret, which is
          never sent over the network.

      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 RFC 2119 [3].  These
   key words mean the same thing whether capitalized or not.

1.2.  Terminology

   This document uses the following terms:

   service   The NAS provides a service to the dial-in user, such as PPP
             or Telnet.

   session   Each service provided by the NAS to a dial-in user
             constitutes a session, with the beginning of the session
             defined as the point where service is first provided and
             the end of the session defined as the point where service
             is ended.  A user may have multiple sessions in parallel or
             series if the NAS supports that, with each session
             generating a separate start and stop accounting record with
             its own Acct-Session-Id.

   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.



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2.  Operation

   When a client is configured to use RADIUS Accounting, at the start of
   service delivery it will generate an Accounting Start packet
   describing the type of service being delivered and the user it is
   being delivered to, and will send that to the RADIUS Accounting
   server, which will send back an acknowledgement that the packet has
   been received.  At the end of service delivery the client will
   generate an Accounting Stop packet describing the type of service
   that was delivered and optionally statistics such as elapsed time,
   input and output octets, or input and output packets.  It will send
   that to the RADIUS Accounting server, which will send back an
   acknowledgement that the packet has been received.

   The Accounting-Request (whether for Start or Stop) is submitted to
   the RADIUS accounting server via the network. It is recommended that
   the client continue attempting to send the Accounting-Request packet
   until it receives an acknowledgement, using some form of backoff.  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.

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

   If the RADIUS accounting server is unable to successfully record the
   accounting packet it MUST NOT send an Accounting-Response
   acknowledgment to the client.

2.1.  Proxy

   See the "RADIUS" RFC [2] for information on Proxy RADIUS.  Proxy
   Accounting RADIUS works the same way, as illustrated by the following
   example.

   1.    The NAS sends an accounting-request to the forwarding server.

   2.    The forwarding server logs the accounting-request (if desired),
         adds its Proxy-State (if desired) after any other Proxy-State
         attributes, updates the Request Authenticator, and forwards the
         request to the remote server.






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   3.    The remote server logs the accounting-request (if desired),
         copies all Proxy-State attributes in order and unmodified from
         the request to the response packet, and sends the accounting-
         response to the forwarding server.

   4.    The forwarding server strips the last Proxy-State (if it added
         one in step 2), updates the Response Authenticator and sends
         the accounting-response to the NAS.

   A forwarding server MUST not modify existing Proxy-State or Class
   attributes present in the packet.

   A forwarding server may either perform its forwarding function in a
   pass through manner, where it sends retransmissions on as soon as it
   gets them, or it may take responsibility for retransmissions, for
   example in cases where the network link between forwarding and remote
   server has very different characteristics than the link between NAS
   and forwarding server.

   Extreme care should be used when implementing a proxy server that
   takes responsibility for retransmissions so that its retransmission
   policy is robust and scalable.

3.  Packet Format

   Exactly one RADIUS Accounting packet is encapsulated in the UDP Data
   field [4], where the UDP Destination Port field indicates 1813
   (decimal).

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

   This memo documents the RADIUS Accounting protocol.  The early
   deployment of RADIUS Accounting was done using UDP port number 1646,
   which conflicts with the "sa-msg-port" service.  The officially
   assigned port number for RADIUS Accounting is 1813.

   A summary of the RADIUS data format is shown below.  The fields are
   transmitted from left to right.












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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                         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 Accounting Codes (decimal) are assigned as follows:

           4       Accounting-Request
           5       Accounting-Response

   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.

   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 4095.

   Authenticator

      The Authenticator field is sixteen (16) octets.  The most
      significant octet is transmitted first.  This value is used to
      authenticate the messages between the client and RADIUS accounting
      server.



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   Request Authenticator

      In Accounting-Request Packets, the Authenticator value is a 16
      octet MD5 [5] checksum, called the Request Authenticator.

      The NAS and RADIUS accounting server share a secret.  The Request
      Authenticator field in Accounting-Request packets contains a one-
      way MD5 hash calculated over a stream of octets consisting of the
      Code + Identifier + Length + 16 zero octets + request attributes +
      shared secret (where + indicates concatenation).  The 16 octet MD5
      hash value is stored in the Authenticator field of the
      Accounting-Request packet.

      Note that the Request Authenticator of an Accounting-Request can
      not be done the same way as the Request Authenticator of a RADIUS
      Access-Request, because there is no User-Password attribute in an
      Accounting-Request.

   Response Authenticator

      The Authenticator field in an Accounting-Response packet is called
      the Response Authenticator, and contains a one-way MD5 hash
      calculated over a stream of octets consisting of the Accounting-
      Response Code, Identifier, Length, the Request Authenticator field
      from the Accounting-Request packet being replied to, and the
      response attributes if any, followed by the shared secret.  The
      resulting 16 octet MD5 hash value is stored in the Authenticator
      field of the Accounting-Response packet.

   Attributes

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

4.  Packet Types

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