rfc2059.txt
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Network Working Group C. Rigney
Request for Comments: 2059 Livingston
Category: Informational January 1997
RADIUS Accounting
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
This document describes a protocol for carrying accounting
information between a Network Access Server and a shared Accounting
Server.
Table of Contents
1. Introduction .......................................... 2
1.1 Specification of Requirements ................... 3
1.2 Terminology ..................................... 3
2. Operation ............................................. 3
3. Packet Format ......................................... 4
4. Packet Types .......................................... 6
4.1 Accounting-Request .............................. 7
4.2 Accounting-Response ............................. 8
5. Attributes ............................................ 9
5.1 Acct-Status-Type ................................ 11
5.2 Acct-Delay-Time ................................. 12
5.3 Acct-Input-Octets ............................... 13
5.4 Acct-Output-Octets .............................. 13
5.5 Acct-Session-Id ................................. 14
5.6 Acct-Authentic .................................. 15
5.7 Acct-Session-Time ............................... 16
5.8 Acct-Input-Packets .............................. 17
5.9 Acct-Output-Packets ............................. 17
5.10 Acct-Terminate-Cause ............................ 18
5.11 Acct-Multi-Session-Id ........................... 20
5.12 Acct-Link-Count ................................. 21
5.13 Table of Attributes ............................. 22
Security Considerations ...................................... 24
References ................................................... 24
Acknowledgements ............................................. 24
Chair's Address .............................................. 25
Author's Address ............................................. 25
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RFC 2059 RADIUS Accounting January 1997
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 [4]
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.
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.
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.
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.
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RFC 2059 RADIUS Accounting January 1997
1.1 Specification of Requirements
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.
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.
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
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RFC 2059 RADIUS Accounting January 1997
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.
3. Packet Format
Exactly one RADIUS Accounting packet is encapsulated in the UDP Data
field [1], where the UDP Destination Port field indicates 1813
(decimal).
When a reply is generated, the source and destination ports are
reversed.
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RFC 2059 RADIUS Accounting January 1997
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 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.
Length
The Length field is two octets. It indicates the length of the
packet including the Code, Identifier, Length, Authenticator and
Attribute fields. Octets outside the range of the Length field
should be treated as padding and should be ignored on reception. If
the packet is shorter than the Length field indicates, it should be
silently discarded. The minimum length is 20 and maximum length is
4096.
Authenticator
The Authenticator field is sixteen (16) octets. The most significant
octet is transmitted first. This value is used to authenticate the
messages between the client and RADIUS accounting server.
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RFC 2059 RADIUS Accounting January 1997
Request Authenticator
In Accounting-Request Packets, the Authenticator value is a 16
octet MD5 [3] 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.
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RFC 2059 RADIUS Accounting January 1997
4.1. Accounting-Request
Description
Accounting-Request packets are sent from a client (typically a
Network Access Server or its proxy) to a RADIUS accounting server,
and convey information used to provide accounting for a service
provided to a user. The client transmits a RADIUS packet with the
Code field set to 4 (Accounting-Request).
Upon receipt of an Accounting-Request, the server MUST transmit an
Accounting-Response reply if it successfully records the
accounting packet, and MUST NOT transmit any reply if it fails to
record the accounting packet.
Any attribute valid in a RADIUS Access-Request or Access-Accept
packet is valid in a RADIUS Accounting-Request packet, except that
the following attributes MUST NOT be present in an Accounting-
Request: User-Password, CHAP-Password, Reply-Message, State.
Either NAS-IP-Address or NAS-Identifier MUST be present in a
RADIUS Accounting-Request. It SHOULD contain a NAS-Port or NAS-
Port-Type attribute or both unless the service does not involve a
port or the NAS does not distinguish among its ports.
A summary of the Accounting-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
4 for Accounting-Request.
Identifier
The Identifier field MUST be changed whenever the content of the
Attributes field changes, and whenever a valid reply has been
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RFC 2059 RADIUS Accounting January 1997
received for a previous request. For retransmissions where the
contents are identical, the Identifier MUST remain unchanged.
Note that if Acct-Delay-Time is included in the attributes of an
Accounting-Request then the Acct-Delay-Time value will be updated
when the packet is retransmitted, changing the content of the
Attributes field and requiring a new Identifier and Request
Authenticator.
Request Authenticator
The Request Authenticator of an Accounting-Request contains a 16-
octet MD5 hash value calculated according to the method described
in "Request Authenticator" above.
Attributes
The Attributes field is variable in length, and contains a list of
Attributes.
4.2. Accounting-Response
Description
Accounting-Response packets are sent by the RADIUS accounting
server to the client to acknowledge that the Accounting-Request
has been received and recorded successfully. If the Accounting-
Request was recorded successfully then the RADIUS accounting
server MUST transmit a packet with the Code field set to 5
(Accounting-Response). On reception of an Accounting-Response by
the client, the Identifier field is matched with a pending
Accounting-Request. Invalid packets are silently discarded.
A RADIUS Accounting-Response is not required to have any
attributes in it.
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RFC 2059 RADIUS Accounting January 1997
A summary of the Accounting-Response 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 ...
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