Network Working Group S Willens
Internet Draft Livingston
A Rubens
Merit
W A Simpson
Daydreamer
C Rigney
Livingston
expires in six months May 1994
Remote Authentication Dial In User Service (RADIUS)
draft-ietf-nasreq-radius-01.txt (c)
Status of this Memo
This document is a submission to the Network-Access-Server-
Requirements Working Group of the Internet Engineering Task Force
(IETF). Comments should be submitted to the nas-req@merit.edu
mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet-Drafts Shadow
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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.
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Table of Contents
1. Introduction .......................................... 1
1.1 Specification of Requirements ................... 2
1.2 Terminology ..................................... 2
2. Operation ............................................. 3
2.1 Challenge/Response .............................. 4
3. Packet Format ......................................... 5
3.1 Access-Request .................................. 8
3.2 Access-Ack ...................................... 9
3.3 Access-Reject ................................... 10
3.4 Access-Challenge ................................ 11
4. Attributes ............................................ 13
4.1 User-Name ....................................... 14
4.2 User-Password ................................... 15
4.3 Challenge-Response .............................. 16
4.4 NAS-Identifier .................................. 17
4.5 NAS-Port ........................................ 18
4.6 User-Service .................................... 19
4.7 Framed-Protocol ................................. 19
4.8 Framed-Address .................................. 20
4.9 Framed-Netmask .................................. 21
4.10 Framed-Routing .................................. 22
4.11 Framed-Filter ................................... 23
4.12 Framed-MTU ...................................... 23
4.13 Framed-Compression .............................. 24
4.14 Login-Host ...................................... 25
4.15 Login-Service ................................... 26
4.16 Login-TCP-Port .................................. 27
4.17 Change-Password ................................. 27
4.18 Reply-Message ................................... 27
4.19 Callback-Number ................................. 28
4.20 Callback-Name ................................... 29
4.21 (unassigned) .................................... 30
4.22 Framed-Route .................................... 30
4.23 Framed-IPX-Network .............................. 31
4.24 State ........................................... 32
SECURITY CONSIDERATIONS ...................................... 33
REFERENCES ................................................... 34
ACKNOWLEDGEMENTS ............................................. 34
CHAIR'S ADDRESS .............................................. 35
AUTHOR'S ADDRESS ............................................. 35
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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 (that is, SLIP, PPP, telnet, rlogin).
Key features of RADIUS are:
Client/Server Model
A Network Access Server (NAS) operates as a client of RADIUS. The
NAS 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 NAS to deliver service
to the user.
The RADIUS servers can act as proxy clients to other
authentication servers, such as Kerberos.
Network Security
Transactions between the NAS 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 NAS 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 supports 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 available through
published API's such as Kerberos and SafeWord.
Extensible Protocol
All transactions are comprised of variable length attribute-value
tuples. Adding new attribute values can be achieved without
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disturbing existing implementations of the protocol.
Source Code Availability
Livingston Enterprises is making the C source code for RADIUS
available without use restrictions.
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.
1.2. Terminology
This document frequently uses the following terms:
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 NAS is configured to use RADIUS, any user of the NAS presents
authentication information to the NAS. 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 NAS has obtained such information, it first looks in its
local database of users for the username. If found, the user is
locally authenticated. If not found, the NAS will create an
"Access-Request" containing such attributes as the user's name, the
user's password, the ID of the NAS 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].
The Access-Request is submitted to the RADIUS server via the network.
If no response is returned within a configurable length of time, the
request is re-sent a configurable number of times. After several
failed attempts, the NAS can also forward requests to an alternate
server in the event that the primary server is down or unreachable.
Once the RADIUS server receives the request, it validates the sending
client. The RADIUS server consults a local 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 NAS or Port to which the user is
allowed access.
The RADIUS server MAY make requests of other servers in order to
satisfy the request.
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 also send a text message which MAY be
displayed by the NAS to the user. No other attributes are permitted
in an "Access-Reject".
If all conditions are met and the RADIUS server wishes to issue a
challenge to which the user must respond, the RADIUS server sends an
"Access-Challenge" response.
If the NAS 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. It then re-submits
its original Access-Request with a new request ID, with the Password
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attribute replaced by the response (encrypted), and including the
State attribute from the "Access-Challenge", if any. Only 0 or 1
State attributes should be present in a request.
If all conditions are met, the list of configuration values for the
user are placed into an "Access Ack" response. These values include
the type of usage (SLIP, PPP, Login User), and all necessary values
to deliver the desired service. For SLIP and PPP, this includes such
values as IP addresses, subnet masks, MTU, desired compression, and
desired packet filters. For character mode users, this includes
things such as desired protocol, host, and access control filter.
2.1. Challenge/Response
In challenge/response authentication, individual users are 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 that facilitate calculation of the correct response with
ease. Unauthorized users, lacking the appropriate device and lacking
knowledge of the secret key necessary to emulate such a device, can
only guess at the response.
The Access-Challenge packet typically contains a Reply-Message
including a challenge to be displayed to the user, such as a numeric
value unlikely ever to be repeated. Typically this is obtained from
an external server that knows what type of authenticator should be in
the possession of the authorized user and can therefore choose a
random or non-repeating pseudorandom number of an appropriate radix
and length.
The user then enters the challenge into his device and it calculates
a response, which the user enters into the NAS 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-Ack, otherwise an Access-Reject.
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3. Packet Format
Exactly one RADIUS packet is encapsulated in the UDP Data field [1],
where the UDP Destination Port field indicates 1645, and the UDP
Source Port field is used to indicate the specific request which was
made. Each new request MUST use a new UDP Source Port. A
retransmitted request does not need to be considered a new request.
An Access-Request sent in reply to an Access-Challenge does not need
to be considered a new request and can use the same UDP Source Port
as the Access-Request that resulted in the Access-Challenge.
When a reply is generated, the Ports are reversed.
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-Ack
3 Access-Reject
11 Access-Challenge
Identifier
The Identifier field is one octet, and aids in matching requests and
replies.
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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.
Authenticator
The Authenticator field is sixteen 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.
The Request Authenticator value depends upon the method used to
generate the octets, and is independent of the hash algorithm used to
generate any response. The value SHOULD be unique and unpredictable.
The Ack, Reject, or Challenge Authenticator field 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, and the response Attributes,
followed by (concatenated with) a "shared secret".
The one-way hash algorithm is chosen such that it is computationally
infeasible to determine the secret from the known request and
response values.
The secret SHOULD be at least as large and unguessable as a well-
chosen password. It is preferred that the secret be at least the
length of the hash value for the hashing algorithm chosen (16 octets
for MD5). This is to ensure a sufficiently large range for the
secret to provide protection against exhaustive search attacks.
Each Request Authenticator value SHOULD be unique over the lifetime
of a secret, 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 SHOULD exhibit global and temporal uniqueness.
Each Request Authenticator value 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
another authenticator.
Although protocols such as RADIUS are incapable of protecting against
theft of an authenticated session via realtime active wiretapping
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attacks, generation of unique unpredictable requests can protect
against a wide range of active attacks against authentication.
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3.1. 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, an appropriate reply MUST be
transmitted.
This request MUST contain attributes containing the ID of the NAS
and the user's name, and SHOULD contain attributes with the user's
password and the Port ID which the user is accessing. It MAY
contain additional attributes as a hint to the server. When a
password is present, it is hidden using a method based on the RSA
Message Digest Algorithm MD5 [3].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| 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 MAY remain unchanged.
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Authenticator
The 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.
3.2. Access-Ack
Description
Access-Ack packets are sent by the RADIUS server, and provide
specific configuration information necessary to begin delivery of
services to the user. If every Attribute received in an Access-
Request is recognizable and all values are acceptable, then the
RADIUS implementation MUST transmit a packet with the Code field
set to 2 (Access-Ack).
On reception of an Access-Ack, the Identifier field is matched
with a pending Access-Request. Additionally, the Authenticator
field MUST contain the correct response for the pending Access-
Request. Invalid packets are silently discarded.
A summary of the Access-Ack 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authenticator |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
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Code
2 for Access-Ack.
Identifier
The Identifier field is a copy of the Identifier field of the
Access-Request which caused this Access-Ack.
Authenticator
The 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.
3.3. 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 a Reply-Message Attribute
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authenticator |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
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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.
Authenticator
The 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.
3.4. 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 4 (Access-Challenge).
The Attributes field MAY have a Reply-Message Attribute. and MAY
have a State Attribute. No other attributes are permitted in an
Access-Challenge.
On receipt of an Access-Challenge, the Identifier field is matched
with a pending Access-Request. Additionally, the Authenticator
field MUST contain the correct response for the pending Access-
Request. Invalid packets are silently discarded.
If the NAS supports challenge/response, receipt of a valid
Access-Challenge indicates that a new Access-Request SHOULD be
submitted. The NAS MAY display the text message, if any, to the
user, and then prompt the user for a response. It then re-submits
its original Access-Request with a new request ID, with the
Password attribute replaced by the user's response (encrypted),
and including the State attribute from the "Access-Challenge", if
any. Only 0 or 1 State attributes should be present in a request.
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A NAS which supports PAP MAY forward the Reply-Message to the
dialin client and accept a PAP response which it can use as though
the user had entered the response.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| 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.
Authenticator
The 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.
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4. Attributes
RADIUS Attributes carry the specific authentication, authorization,
information and configuration details for the request and reply.
Some Attributes MAY be listed more than once. The effect of this is
Attribute specific, and is specified by each such Attribute
description.
The end of the list of Attributes is indicated by the length of the
RADIUS packet.
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 [2].
Values 192-223 are reserved for experimental use, values 224-240
are reserved for implementation-specific use, and values 241-255
are reserved and should not be used. This specification concerns
the following values:
1 User-Name
2 User-Password
3 Challenge-Response
4 NAS-Identifier
5 NAS-Port
6 User-Service
7 Framed-Protocol
8 Framed-Address
9 Framed-Netmask
10 Framed-Routing
11 Framed-Filter
12 Framed-MTU
13 Framed-Compression
14 Login-Host
15 Login-Service
16 Login-TCP-Port
17 (deprecated)
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18 Reply-Message
19 Callback-Number
20 Callback-Name
21 (unassigned)
22 Framed-Route
23 Framed-IPX-Network
24 State
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 a Access-Request but with an invalid
Length, an Access-Reject SHOULD be transmitted.
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.
The format of the value field is one of four data types.
string 0-253 octets
address 32 bit value, most significant octet first.
integer 32 bit value, most significant octet first.
time 32 bit value, most significant octet first -- seconds
since 00:00:00 GMT, January 1, 1970.
4.1. User-Name
Description
This attribute indicates the name of the user to be authenticated.
It is only used in Access-Request packets.
A summary of the User-Name attribute format is shown below. The
fields are transmitted from left to right.
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0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
1
Length
>= 3
String
The String field is one or more octets.
The format of the username may be one of several forms:
monolithic Consisting only of alphanumeric characters. This
simple form might be used to locally manage a NAS.
provider/name
Two monolithic portions separated by a slash. The
provider part indicates the realm in which the name part
applies.
name@fqdn SMTP address. The Fully Qualified Domain Name (with or
without trailing dot) indicates the realm in which the
name part applies.
distinguished name
A name in ASN.1 form used in Public Key authentication
systems.
4.2. User-Password
Description
This attribute indicates the password of the user to be
authenticated. It is only used in Access-Request packets.
On transmission, the password is hidden. A one-way MD5 hash is
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calculated over a stream of octets consisting of the "shared
secret", followed by (concatenated with) the Request
Authenticator. This value is xor'd with each successive 16 octet
segment of the password.
On receipt, the same mask is created. Repeating the xor function
yields 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
Length
>= 3
String
The String field is one or more octets.
4.3. Challenge-Response
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 RADIUS Authenticator
field.
A summary of the Challenge-Response attribute format is shown below.
The fields are transmitted from left to right.
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0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | CHAP Ident | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
3
Length
>= 18
CHAP Ident
This field is one octet, and contains the CHAP Identifier from the
CHAP Response packet.
String
The String field is 16 octets when MD5 is used for CHAP.
4.4. NAS-Identifier
Description
This attribute indicates the Identifying Address of the NAS which
is authenticating the user. It is only used in Access-Request
packets.
A summary of the NAS-Identifier 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
4
Length
6
Address
The Address field is four octets.
4.5. NAS-Port
Description
This attribute indicates the port number of the NAS which is
authenticating the user. It is only used in Access-Request
packets.
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
Length
6
Value
The Value field is four octets. Despite the rather large size of
the field, values range from 0 to 65535.
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4.6. User-Service
Description
This attribute indicates the type of link the user has requested,
or a change in the type of link to be configured. It is used in
both Access-Request and Access-Ack packets.
A summary of the User-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
6
Length
6
Value
The Value field is four octets.
1 Login
2 Framed
3 Callback Login
4 Callback Framed
5 Outbound User
6 Shell User
4.7. Framed-Protocol
Description
This attribute indicates the framing to be used for framed access.
It is used in both Access-Request and Access-Ack packets.
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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
Length
6
Value
The Value field is four octets.
1 PPP
2 SLIP
4.8. Framed-Address
Description
This attribute indicates the address to be configured for the
user. It is only used in Access-Ack packets.
A summary of the Framed-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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
8
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).
4.9. Framed-Netmask
Description
This attribute indicates the IP netmask to be configured for the
user when the user is a router to a network. It is unnecessary
when routing is used. It is only used in Access-Ack packets.
A summary of the Framed-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 | Netmask
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Netmask (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
9
Length
6
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Netmask
The Netmask field is four octets.
4.10. 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-Ack
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
Length
6
Value
The Value field is four octets.
0 None
1 Send routing packets
2 Listen for routing packets
3 Send and Listen
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4.11. Framed-Filter
Description
This attribute indicates the name of the filter list for this
user.
Using a name for a filter list allows independence from multiple
NAS implementations. However, the name used might be dependent on
the NAS making the request, rather than the user.
A summary of the Framed-Filter attribute format is shown below. The
fields are transmitted from left to right.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
11
Length
>= 3
String
The String field is one or more octets.
4.12. Framed-MTU
Description
This attribute indicates the Maximum Transmission Unit to be
configured for the user, when it is not negotiated by some other
means (such as PPP). It is only used in Access-Ack packets.
A summary of the Framed-MTU attribute format is shown below. The
fields are transmitted from left to right.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
12
Length
6
Value
The Value field is four octets. Despite the rather large size of
the field, values range from 64 to 65535.
4.13. Framed-Compression
Description
This attribute indicates a compression protocol to be used for the
link.
More than one compression protocol attribute MAY be sent. It is
the responsibility of the NAS to apply the proper compression
protocol to appropriate link traffic.
A summary of the Framed-Compression attribute format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
13
Length
6
Value
The Value field is four octets.
1 VJ TCP/IP header compression
2 IPX header compression
4.14. Login-Host
Description
This attribute indicates the system with which the user is to be
automatically connected, when the Login-Service attribute is
listed. It is only used in Access-Ack packets.
A summary of the Login-Host attribute format is shown below. The
fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
14
Length
6
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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.
4.15. Login-Service
Description
This attribute indicates the service with which the user is to be
automatically connected. It is only used in Access-Ack 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
Length
6
Value
The Value field is four octets.
0 Telnet
1 Rlogin
2 TCP
3 Portmaster (proprietary)
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4.16. Login-TCP-Port
Description
This attribute indicates the TCP port with which the user is to be
automatically connected, when the Login-Service attribute is
listed. It is only used in Access-Ack 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
Length
6
Value
The Value field is four octets. Despite the rather large size of
the field, values range from 0 to 65535.
4.17. Change-Password
Description
THIS ATTRIBUTE HAS BEEN DEPRECATED.
4.18. Reply-Message
Description
This attribute indicates text which MAY be displayed to the user.
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When used in an Access-Ack, it is the success message.
When used in an Access-Reject, it is the failure message. It MAY
indicate a dialog message to prompt the user before another
Access-Request attempt.
When used in an Access-Challenge, it MAY indicate a dialog message
to prompt the user for a response.
Multiple Reply-Message's MAY be included and if any are displayed,
they MUST be displayed in the same order as they appear in the
packet.
A summary of the Reply-Message attribute format is shown below. The
fields are transmitted from left to right.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
18
Length
>= 3
String
The String field is one or more octets, and its contents are
implementation dependent. It is intended to be human readable,
and MUST NOT affect operation of the protocol. It is recommended
that the message contain displayable ASCII characters 32 through
126 decimal. Mechanisms for extension to other character sets are
the topic of future research.
4.19. Callback-Number
Description
This attribute indicates a dialing string to be used for callback.
It is used in both Access-Request and Access-Ack packets.
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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
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.
It is intended that only an authorized user will have correct site
specific information to make use of the Callback. The
codification of the range of allowed usage of this field is
outside the scope of this specification.
4.20. Callback-Name
Description
This attribute indicates the name of a place to be called. It is
used in both Access-Request and Access-Ack packets.
A summary of the Callback-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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
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Type
20
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.
It is intended that only an authorized user will have correct site
specific information to make use of the Callback. The
codification of the range of allowed usage of this field is
outside the scope of this specification.
4.21. (unassigned)
Description
THIS ATTRIBUTE CODE HAS NOT BEEN ASSIGNED.
4.22. Framed-Route
Description
This attribute provides routing information to be configured for
the user. It is used in the Access-Ack packet and can appear
multiple times.
A summary of the Framed-Route attribute format is shown below. The
fields are transmitted from left to right.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
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Type
22
Length
>= 3
String
The String field is one or more octets, and its contents are
implementation dependent. It is intended to be human readable and
MUST NOT affect operation of the protocol. It is recommended that
the message contain displayable ASCII characters 32 through 126
decimal.
It MAY contain a destination address in dotted quad form, a space,
a gateway address in dotted quad form, a space, and a decimal
metric.
4.23. Framed-IPX-Network
Description
This attribute indicates the IPX Network number to be configured
for the user. It is used in Access-Ack packets.
A summary of the Framed-IPX-Network attribute format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
23
Length
6
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Value
The Value field is four octets.
4.24. State
Description
This attribute is available to be sent by the server to the client
in an Access-Challenge and should be sent unmodified from the
client to the server in an Access-Ack reply to that Challenge. No
interpretation by the client should be made. A packet may have
only one State attribute. Usage of the State attribute is
implementation dependent.
A summary of the State attribute format is shown below. The fields
are transmitted from left to right.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
20
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.
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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 (such as PAP rather than CHAP). 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 [4], but such a mechanism is outside the scope of this
specification.
Other distribution methods are currently undergoing research and
experimentation. The SNMP Security document [4] also has an
excellent overview of threats to network protocols.
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References
[1] Postel, J., "User Datagram Protocol", RFC 768, USC/Information
Sciences Institute, August 1980.
[2] Reynolds, J., and J. Postel, "Assigned Numbers", RFC 1340,
USC/Information Sciences Institute, July 1992.
[3] Rivest, R., and S. Dusse, "The MD5 Message-Digest Algorithm",
MIT Laboratory for Computer Science and RSA Data Security,
Inc., RFC 1321, April 1992.
[4] Galvin, J., McCloghrie, K., and J. Davin, "SNMP Security
Protocols", Trusted Information Systems, Inc., Hughes LAN
Systems, Inc., MIT Laboratory for Computer Science, RFC 1352,
July 1992.
Acknowledgments
RADIUS was originally developed by Livingston Enterprises for their
PortMaster series of Network Access Servers.
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Chair's Address
The working group can be contacted via the current chair:
John Vollbrecht
Merit Network, Inc.
1071 Beal Ave.
Ann Arbor, MI 48109
EMail: jrv@merit.edu
Author's Address
Questions about this memo can also be directed to:
Steve Willens
Livingston Enterprises
6920 Koll Center Parkway, Suite 220
Pleasanton, CA 94566
EMail: steve@livingston.com
Allan C. Rubens
Merit Network, Inc.
1071 Beal Ave.
Ann Arbor, MI 48109
EMail: acr@merit.edu
William Allen Simpson
Daydreamer
Computer Systems Consulting Services
1384 Fontaine
Madison Heights, Michigan 48071
EMail: Bill.Simpson@um.cc.umich.edu
Carl Rigney
Livingston Enterprises
6920 Koll Center Parkway, Suite 220
Pleasanton, CA 94566
EMail: cdr@livingston.com
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