RFC2138 - Remote Authentication Dial In User Service (RADIUS)

Network Working Group C. Rigney

Request for Comments: 2138 Livingston

Obsoletes: 2058 A. Rubens

Category: Standards Track Merit

W. Simpson

Daydreamer

S. Willens

Livingston

April 1997

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.

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. There has been some

confusion in the assignment of port numbers for this protocol. The

early deployment of RADIUS was done using the erroneously chosen port

number 1645, which conflicts with the "datametrics" service. The

officially assigned port number for RADIUS is 1812.

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 ................ 7

2.3 Why UDP? ........................................ 8

3. Packet Format ......................................... 10

4. Packet Types .......................................... 13

4.1 Access-Request .................................. 13

4.2 Access-Accept ................................... 14

4.3 Access-Reject ................................... 15

4.4 Access-Challenge ................................ 17

5. Attributes ............................................ 18

5.1 User-Name ....................................... 21

5.2 User-PassWord ................................... 22

5.3 CHAP-Password ................................... 23

5.4 NAS-IP-Address .................................. 24

5.5 NAS-Port ........................................ 25

5.6 Service-Type .................................... 26

5.7 Framed-Protocol ................................. 28

5.8 Framed-IP-Address ............................... 29

5.9 Framed-IP-Netmask ............................... 29

5.10 Framed-Routing .................................. 30

5.11 Filter-Id ....................................... 31

5.12 Framed-MTU ...................................... 32

5.13 Framed-Compression .............................. 33

5.14 Login-IP-Host ................................... 33

5.15 Login-Service ................................... 34

5.16 Login-TCP-Port .................................. 35

5.17 (unassigned) .................................... 36

5.18 Reply-Message ................................... 36

5.19 Callback-Number ................................. 37

5.20 Callback-Id ..................................... 38

5.21 (unassigned) .................................... 38

5.22 Framed-Route .................................... 39

5.23 Framed-IPX-Network .............................. 40

5.24 State ........................................... 40

5.25 Class ........................................... 41

5.26 Vendor-Specific ................................. 42

5.27 Session-Timeout ................................. 44

5.28 Idle-Timeout .................................... 44

5.29 Termination-Action .............................. 45

5.30 Called-Station-Id ............................... 46

5.31 Calling-Station-Id .............................. 47

5.32 NAS-Identifier .................................. 48

5.33 Proxy-State ..................................... 48

5.34 Login-LAT-Service ............................... 49

5.35 Login-LAT-Node .................................. 50

5.36 Login-LAT-Group ................................. 51

5.37 Framed-AppleTalk-Link ........................... 52

5.38 Framed-AppleTalk-Network ........................ 53

5.39 Framed-AppleTalk-Zone ........................... 54

5.40 CHAP-Challenge .................................. 55

5.41 NAS-Port-Type ................................... 55

5.42 Port-Limit ...................................... 56

5.43 Login-LAT-Port .................................. 57

5.44 Table of Attributes ............................. 58

6. Examples .............................................. 59

6.1 User Telnet to Specified Host ................... 60

6.2 Framed User Authenticating with CHAP ............ 60

6.3 User with Challenge-Response card ............... 61

Security Considerations ...................................... 63

References ................................................... 64

Acknowledgements ............................................. 64

Chair's Address .............................................. 65

Author's Addresses ........................................... 65

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).

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

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

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:

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 [1].

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 should 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 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 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

Attributes should be 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 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 (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

came with the Access-Challenge. The server then sends back either an

Access-Accept or Access-Reject based on whether the response matches

what it should be, 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 should 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. 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.

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 that 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.

3. Packet Format

Exactly one RADIUS packet is encapsulated in the UDP Data field [2],

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. There has been some

confusion in the assignment of port numbers for this protocol. The

early deployment of RADIUS was done using the erroneously chosen port

number 1645, which conflicts with the "datametrics" service. The

officially assigned port number for RADIUS is 1812.

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 [9], and

are not further mentioned here. 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.

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

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 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. A RADIUS

server SHOULD 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 can add a Proxy-State Attribute, and

when the proxy forwards a response, it removes the Proxy-State

Attribute. Since Access-Accept and Access-Reject replies are

authenticated on the entire packet contents, the stripping of the

Proxy-State attribute would invalidate 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.

Attributes

Many 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.

In the section below on "Attributes" where the text refers to which

packets an attribute is allowed in, only packets with Codes 1, 2, 3

and 11 and attributes defined in this document are covered in this

document. A summary table is provided at the end of the "Attributes"

section. To determine which Attributes are allowed in packets with

codes 4 and 5 refer to the RADIUS Accounting document [9].

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 MUST contain a User-Name attribute. It SHOULD

contain either a NAS-IP-Address attribute or NAS-Identifier

attribute (or both, although that is not recommended). It MUST

contain either a User-Password attribute or CHAP-Password

attribute. It 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 [1].

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).

On reception of an Access-Accept, 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.

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.

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.

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. 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 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

dialin 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

should treat the Access-Challenge as though it had received an

Access-Reject instead.

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.

Some Attributes MAY be included more than once. The effect of this

is Attribute specific, and is specified in each 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[3].

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:

A RADIUS server MAY ignore Attributes with an unknown Type.

A RADIUS client MAY ignore Attributes with an unknown Type.

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

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

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 a "string" in RADIUS does not require termination by an

ASCII NUL because the Attribute already has a length field.

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. The standard

Attributes do not use this data type but it is presented

here for possible use within Vendor-Specific attributes.

5.1. 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.

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:

monolithic Consisting only of alphanumeric characters. This

simple form might be used to locally manage a NAS.

simple Consisting only of printable ASCII characters.

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.

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 [4] 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.

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 ...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Type

3 for CHAP-Password.

Length

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. It is only used

in Access-Request packets. Either NAS-IP-Address or NAS-

Identifier SHOULD be present in an Access-Request packet.

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.

Length

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

Value

The Value field is four octets. Despite the size of the field,

values range from 0 to 65535.

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

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

The service types are defined as follows when used in an Access-

Accept. When used in an Access-Request, they should 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.

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.

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

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

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

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.

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

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.

Length

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 String ...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Type

11 for Filter-Id.

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 from the range 32

through 126 decimal.

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 is only used in Access-Accept packets.

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

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.

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

Value

The Value field is four octets.

0 None

1 VJ TCP/IP header compression [5]

2 IPX header 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.

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

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 which should be used 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.

Length

Value

The Value field is four octets.

0 Telnet

1 Rlogin

2 TCP Clear

3 PortMaster (proprietary)

4 LAT

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

Value

The Value field is four octets. Despite the size of the field,

values range from 0 to 65535.

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 String ...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Type

18 for Reply-Message.

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 from the

range 10, 13, and 32 through 126 decimal. Mechanisms for

extension to other character sets are beyond the scope of this

specification.

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.

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 String...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Type

22 for Framed-Route.

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 from the range 32

through 126 decimal.

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 should be

used. 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 should default 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)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

23 for Framed-IPX-Network.

Length

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, 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

24 for State.

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. No interpretation by the client should

be made.

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.

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[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.

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...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

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

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

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.

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

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 ...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

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. Printable ASCII is 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

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. Printable ASCII is 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 SHOULD be present in an

Access-Request packet.

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

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. This attribute should be removed by the proxy

server before the response is forwarded to the NAS.

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.

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 ...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

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 [6]. 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

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

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

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.

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

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.

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...

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

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

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

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

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 [7] 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.

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

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

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

1 0 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

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 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

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

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

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, and MUST NOT contain 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. 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.

6.1. 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.

Code = 1 (Access-Request)

ID = 0

Length = 56

Request Authenticator = {16 octet random number}

Attributes:

User-Name = "nemo"

User-Password = {16 octets of Password padded at end with nulls,

XORed with MD5(shared secretRequest Authenticator)}

NAS-IP-Address = 192.168.1.16

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.

Code = 2 (Access-Accept)

ID = 0 (same as in Access-Request)

Length = 38

Response Authenticator = {16-octet MD-5 checksum of the code (2),

id (0), Length (38), the Request Authenticator from

above, the attributes in this reply, and the shared

secret}

Attributes:

Service-Type = Login-User

6.2. 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.

Code = 1 (Access-Request)

ID = 1

Length = 71

Request Authenticator = {16 octet random number also used as

CHAP challenge}

Attributes:

User-Name = "flopsy"

CHAP-Password = {1 octet CHAP ID followed by 16 octet

CHAP response}

NAS-IP-Address = 192.168.1.16

NAS-Port = 20

Service-Type = Framed-User

Framed-Protocol = PPP

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.

Code = 2 (Access-Accept)

ID = 1 (same as in Access-Request)

Length = 56

Response Authenticator = {16-octet MD-5 checksum of the code (2),

id (1), Length (56), the Request Authenticator from

above, the attributes in this reply, and the shared

secret}

Attributes:

Service-Type = Framed-User

Framed-Protocol = PPP

Framed-IP-Address = 255.255.255.254

Framed-Routing = None

Framed-Compression = 1 (VJ TCP/IP Header Compression)

Framed-MTU = 1500

6.3. 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.

Code = 1 (Access-Request)

ID = 2

Length = 57

Request Authenticator = {16 octet random number}

Attributes:

User-Name = "mopsy"

User-Password = {16 octets of Password padded at end with nulls,

XORed with MD5(shared secretRequest Authenticator)}

NAS-IP-Address = 192.168.1.16

NAS-Port = 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.

Code = 11 (Access-Challenge}

ID = 2 (same as in Access-Request)

Length = 78

Response Authenticator = {16-octet MD-5 checksum of the code (11),

id (2), length (78), the Request Authenticator from

above, the attributes in this reply, and the shared

secret}

Attributes:

Reply-Message = "Challenge 32769430. Enter response at prompt."

State = {Magic Cookie to be returned along with user's response;

in this example 8 octets of data}

The user enters his response, and the NAS send a new Access-Request

with that response, and includes the State Attribute.

Code = 1 (Access-Request)

ID = 3 (Note that this changes)

Length = 67

Request Authenticator = {NEW 16 octet random number}

Attributes:

User-Name = "mopsy"

User-Password = {16 octets of Response padded at end with

nulls, XORed with MD5 checksum of shared secret

plus above Request Authenticator}

NAS-IP-Address = 192.168.1.16

NAS-Port = 7

State = {Magic Cookie from Access-Challenge packet, unchanged}

The Response was incorrect, so the RADIUS server tells the NAS to

reject the login attempt.

Code = 3 (Access-Reject)

ID = 3 (same as in Access-Request)

Length = 20

Response Authenticator = {16-octet MD-5 checksum of the code (3),

id (3), length(20), the Request Authenticator from

above, the attributes in this reply if any, and the

shared secret}

Attributes:

(none, although a Reply-Message could be sent)

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 [8], but such a mechanism is outside the scope of this

specification.

Other distribution methods are currently undergoing research and

experimentation. The SNMP Security document [8] also has an

Excellent overview of threats to network protocols.

References

[1] Rivest, R., and S. Dusse, "The MD5 Message-Digest Algorithm",

RFC1321, MIT Laboratory for Computer Science, RSA Data

Security Inc., April 1992.

[2] Postel, J., "User Datagram Protocol", STD 6, RFC768,

USC/Information Sciences Institute, August 1980.

[3] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC

1700, USC/Information Sciences Institute, October 1994.

[4] Kaufman, C., Perlman, R., and Speciner, M., "Network Security:

Private Communications in a Public World", Prentice Hall, March

1995, ISBN 0-13-061466-1.

[5] Jacobson, V., "Compressing TCP/IP headers for low-speed serial

links", RFC1144, Lawrence Berkeley Laboratory, February 1990.

[6] ISO 8859. International Standard -- Information Processing --

8-bit Single-Byte Coded Graphic Character Sets -- Part 1: Latin

Alphabet No. 1, ISO 8859-1:1987.

<URL:http://www.iso.ch/cate/d16338.Html>

[7] Sklower, K., Lloyd, B., McGregor, G., and Carr, D., "The PPP

Multilink Protocol (MP)", RFC1717, University of California

Berkeley, Lloyd Internetworking, Newbridge Networks

Corporation, November 1994.

[8] Galvin, J., McCloghrie, K., and Davin, J., "SNMP Security

Protocols", RFC1352, Trusted Information Systems, Inc., Hughes

LAN Systems, Inc., MIT Laboratory for Computer Science, July

1992.

[9] Rigney, C., "RADIUS Accounting", RFC2139, April 1997.

Acknowledgments

RADIUS was originally developed by Livingston Enterprises for their

PortMaster series of Network Access Servers.

Chair's Address

The working group can be contacted via the current chair:

Carl Rigney

Livingston Enterprises

4464 Willow Road

Pleasanton, California 94588

Phone: +1 510 426 0770

EMail: cdr@livingston.com

Authors' Addresses

Questions about this memo can also be directed to:

Carl Rigney

Livingston Enterprises

4464 Willow Road

Pleasanton, California 94588

Phone: +1 510 426 0770

EMail: cdr@livingston.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