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Versions: 00 01                                                         
RADIUS Working Group                                          Pat Calhoun
INTERNET DRAFT                                           3Com Corporation
Category: Internet Draft                                     Mark Beadles
Title: draft-ietf-radius-acct-interim-01.txt       Compuserve Corporation
Date: January 1998                                          Alex Ratcliff

                                  RADIUS Accounting
                         Interim Accounting Record Extension

Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working  doc-
   uments  of  the Internet Engineering Task Force (IETF), its areas, and
   its working groups.  Note that other groups may also distribute  work-
   ing documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months.
   Internet-Drafts  may  be  updated,  replaced,  or  obsoleted  by other
   documents at any time.  It is not appropriate to use Internet-  Drafts
   as  reference  material  or  to  cite them other than as a ``work- ing
   draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft,  please  check  the
   1id-abstracts.txt  listing  contained  in  the  Internet-Drafts Shadow
   Directories on ds.internic.net,  nic.nordu.net,  ftp.nisc.sri.com,  or


   The RADIUS Accounting document [1] defines a mechanism which  is  used
   by  a  Network Access Server (NAS) to send accounting information to a
   RADIUS server. The current protocol defines a Start and  Stop  record.
   This  document  defines  an  interim  record which is used to make the
   RADIUS accounting protocol more robust.

1.0 Introduction

   The current protocol defines a message which a NAS sends to the RADIUS
   server when a session begins, and a message when the session ends. All
   information which is necessary for the billing process  (i.e.  session
   time,  number  of  bytes  transfered,  etc)  are only available in the
   Accounting Stop message. Therefore if a NAS  becomes  unavailable  for
   some  time  (i.e.  power  failure, reboot, network problem, etc...) it
   becomes impossible  for  a  service  provider  to  bill  for  sessions

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   initiated on the NAS (this is especially  important  with  long  lived

   This document introduces a new accounting message which is  sent  from
   NAS  to  the  RADIUS  server  which  is  called the interim accounting
   message. This message is sent in  order  to  periodically  update  the
   RADIUS server with information pertaining to a specific session.

1.1 Specification of Requirements

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

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

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

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

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

2.0 Operation

   When a user is authenticated, a RADIUS server issues an  Access-Accept
   in  response  to  a successful Access-Request. If the server wishes to
   receive interim accounting messages for the given user it must include
   the  Acct-Interim-Interval  RADIUS  attribute  in  the  message, which
   indicates the interval in seconds between interim messages.

   It is also possible to statically configure an interim  value  on  the
   NAS  itself. Note that a locally configured value on the NAS overrides
   a value found in an Access-Accept.

   This scheme does not break backward interoperability  since  a  RADIUS
   server  not  supporting  this  extension  will  simply not add the new
   Attribute. On the other hand, NAS' not supporting this extension  will
   simply  ignore  the Attribute. This means that if a RADIUS Server uses
   the interim extension for other purposes (i.e. resource management) it

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   MUST be aware of NAS' which do not support this extension.

   Note that all information in an interim message  is  cumulative  (i.e.
   number  of  packets  sent  is  the  total  since  the beginning of the
   session, not since the last interim message).

   It is envisioned that an Interim Accounting record would  contain  all
   of  the  attributes  normally found in an Accounting Stop message with
   the exception of the Acct-Term-Cause attribute.

   Since all the information is cumulative, a NAS MUST ensure that only a
   single generation of an interim Accounting message for a given session
   is present in the retransmission queue at any given time.  This  means
   that  the  NAS  MUST first delete any pending interim messages for the
   given  session  (whose  information  is   now   obsolete)   from   the
   retransmissions  before  issuing a new interim message. Note that this
   event would only  occur  if  the  RADIUS  accounting  server  was  not

   A NAS MAY use a fudge factor to add a  random  delay  between  Interim
   Accounting  messages  for  separate  sessions. This will ensure that a
   cycle where all messages are sent at once  is  prevented  (this  could
   occur  if  a primary link was recently restored and many dial-up users
   were directed to the same NAS at once).

   Although this extension allows control from a central  RADIUS  Server,
   the authors wish to strongly caution against using low interval values
   (i.e. less than 60 seconds). In a NAS with large  port  densities,  it
   can  become  a  CPU  intensive  task  as  well  as  a waste of network

3.0 Attributes

   This section defines the new RADIUS Attributes  necessary  to  support
   the Interim Accounting extension.

3.1 Acct-Status-Type


      This attribute indicates whether this Accounting-Request marks  the
      beginning of the user service (Start) or the end (Stop).

      It MAY be used by the client to mark the start of  accounting  (for
      example,  upon booting) by specifying Accounting-On and to mark the
      end of accounting (for example, just before a scheduled reboot)  by
      specifying Accounting-Off.

      Additionally this attribute MAY indicate an interim update.

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      A summary of the Acct-Status-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)         |


      40 for Acct-Status-Type.




      The Value field is four octets and can have one  of  the  following

         1      Start
         2      Stop
         3      Interim Update
         7      Accounting-On
         8      Accounting-Off

3.2 Acct-Interim-Interval


      This attribute indicates the number of seconds between each interim
      update  in  seconds  for this specific session. This value can only
      appear in the Access-Accept RADIUS message.

      A summary of the Acct-Interim-Interval attribute  format  is  shown
      below. The fields are transmitted from left to right.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       |     Type      |    Length     |             Value
       |          Value (cont)         |

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      85 for Acct-Interim-Interval.




      The Value field contains the number of seconds between each interim
      update to be sent from the NAS for this session. The value MUST NOT
      be smaller than 60 and SHOULD NOT be less than 600.

4.0 Contacts

   Pat R. Calhoun
   3Com Corporation
   1800 Central Ave.
   Mount Prospect, Il, 60056
   (847) 342-6898

   Mark A. Beadles,
   Compuserve Corporation
   CompuServe, Inc.
   5000 Britton Rd.
   Hilliard, OH, 43026
   (614) 723-1941

   Alex Ratcliffe,
   UUNET Technologies, Inc,
   3060 Williams Drive,
   Fairfax, VA, 22032
   (703) 206 5698

  5.0 References

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

   [2]   Rigney, C., Rubens, A., Simpson, W., and Willens, S., "Remote
         Authentication Dial In User Service (RADIUS)", RFC 2138,
         April 1997.

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