As per Relevance of the word indicate, we have this rfc below:
Network Working Group C.
Request for Comments: 2138
Obsoletes: 2058 A.
Category: Standards Track
W.
S.
April 1997
Remote Authentication Dial In User Service (RADIUS
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
This document describes a protocol for carrying authentication
authorization, and configuration information between a Network
Server which desires to authenticate its links and a
Authentication Server
Implementation
This memo documents the RADIUS protocol. There has been
confusion in the assignment of port numbers for this protocol.
early deployment of RADIUS was done using the erroneously chosen
number 1645, which conflicts with the "datametrics" service.
officially assigned port number for RADIUS is 1812.
Table of
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
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RFC 2138 RADIUS April 1997
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
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RFC 2138 RADIUS April 1997
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.
Managing dispersed serial line and modem pools for large numbers
users can create the need for significant administrative support
Since modem pools are by definition a link to the outside world,
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)
well as configuration information detailing the type of service
deliver to the user (for example, SLIP, PPP, telnet, rlogin).
Key features of RADIUS are
Client/Server
A Network Access Server (NAS) operates as a client of RADIUS.
client is responsible for passing user information to
RADIUS servers, and then acting on the response which is returned
RADIUS servers are responsible for receiving user
requests, authenticating the user, and then returning
configuration information necessary for the client to
service to the user
A RADIUS server can act as a proxy client to other RADIUS
or other kinds of authentication servers
Network
Transactions between the client and RADIUS server
authenticated through the use of a shared secret, which is
sent over the network. In addition, any user passwords are
encrypted between the client and RADIUS server, to eliminate
possibility that someone snooping on an unsecure network
determine a user's password
Rigney, et. al. Standards Track [Page 3]
RFC 2138 RADIUS April 1997
Flexible Authentication
The RADIUS server can support a variety of methods to
a user. When it is provided with the user name and
password given by the user, it can support PPP PAP or CHAP,
login, and other authentication mechanisms
Extensible
All transactions are comprised of variable length Attribute
Length-Value 3-tuples. New attribute values can be added
disturbing existing implementations of the protocol
1.1. Specification of
In this document, several words are used to signify the
of the specification. These words are often capitalized
MUST This word, or the adjective "required", means that
definition is an absolute requirement of the specification
MUST NOT This phrase means that the definition is an
prohibition of the specification
SHOULD This word, or the adjective "recommended", means that
may exist valid reasons in particular circumstances
ignore this item, but the full implications must
understood and carefully weighed before choosing
different course
MAY This word, or the adjective "optional", means that
item is one of an allowed set of alternatives.
implementation which does not include this option MUST
prepared to interoperate with another implementation
does include the option
Rigney, et. al. Standards Track [Page 4]
RFC 2138 RADIUS April 1997
1.2.
This document frequently uses the following terms
service The NAS provides a service to the dial-in user, such as
or Telnet
session Each service provided by the NAS to a dial-in
constitutes a session, with the beginning of the
defined as the point where service is first provided
the end of the session defined as the point where
is ended. A user may have multiple sessions in parallel
series if the NAS supports that
silently
This means the implementation discards the packet
further processing. The implementation SHOULD provide
capability of logging the error, including the contents
the silently discarded packet, and SHOULD record the
in a statistics counter
2.
When a client is configured to use RADIUS, any user of the
presents authentication information to the client. This might
with a customizable login prompt, where the user is expected to
their username and password. Alternatively, the user might use
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
authenticate using RADIUS. To do so, the client creates an "Access
Request" containing such Attributes as the user's name, the user'
password, the ID of the client and the Port ID which the user
accessing. When a password is present, it is hidden using a
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
re-sent a number of times. The client can also forward requests
an alternate server or servers in the event that the primary
is down or unreachable. An alternate server can be used either
a number of tries to the primary server fail, or in a round-
fashion. Retry and fallback algorithms are the topic of
research and are not specified in detail in this document
Rigney, et. al. Standards Track [Page 5]
RFC 2138 RADIUS April 1997
Once the RADIUS server receives the request, it validates the
client. A request from a client for which the RADIUS server does
have a shared secret should be silently discarded. If the client
valid, the RADIUS server consults a database of users to find
user whose name matches the request. The user entry in the
contains a list of requirements which must be met to allow access
the user. This always includes verification of the password, but
also specify the client(s) or port(s) to which the user is
access
The RADIUS server MAY make requests of other servers in order
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.
desired, the server MAY include a text message in the Access-
which MAY be displayed by the client to the user. No
Attributes are permitted in an Access-Reject
If all conditions are met and the RADIUS server wishes to issue
challenge to which the user must respond, the RADIUS server sends
"Access-Challenge" response. It MAY include a text message to
displayed by the client to the user prompting for a response to
challenge, and MAY include a State attribute. If the client
an Access-Challenge and supports challenge/response it MAY
the text message, if any, to the user, and then prompt the user for
response. The client then re-submits its original Access-
with a new request ID, with the User-Password Attribute replaced
the response (encrypted), and including the State Attribute from
Access-Challenge, if any. Only 0 or 1 instances of the
Attributes should be present in a request. The server can respond
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
user are placed into an "Access-Accept" response. These
include the type of service (for example: SLIP, PPP, Login User)
all necessary values to deliver the desired service. For SLIP
PPP, this may include values such as IP address, subnet mask, MTU
desired compression, and desired packet filter identifiers.
character mode users, this may include values such as
protocol and host
Rigney, et. al. Standards Track [Page 6]
RFC 2138 RADIUS April 1997
2.1. Challenge/
In challenge/response authentication, the user is given
unpredictable number and challenged to encrypt it and give back
result. Authorized users are equipped with special devices such
smart cards or software that facilitate calculation of the
response with ease. Unauthorized users, lacking the
device or software and lacking knowledge of the secret key
to emulate such a device or software, can only guess at the response
The Access-Challenge packet typically contains a Reply-
including a challenge to be displayed to the user, such as a
value unlikely ever to be repeated. Typically this is obtained
an external server that knows what type of authenticator should be
the possession of the authorized user and can therefore choose
random or non-repeating pseudorandom number of an appropriate
and length
The user then enters the challenge into his device (or software)
it calculates a response, which the user enters into the client
forwards it to the RADIUS server via a second Access-Request. If
response matches the expected response the RADIUS server replies
an Access-Accept, otherwise an Access-Reject
Example: The NAS sends an Access-Request packet to the RADIUS
with NAS-Identifier, NAS-Port, User-Name, User-Password (which
just be a fixed string like "challenge" or ignored). The
sends back an Access-Challenge packet with State and a Reply-
along the lines of "Challenge 12345678, enter your response at
prompt" which the NAS displays. The NAS prompts for the response
sends a NEW Access-Request to the server (with a new ID) with NAS
Identifier, NAS-Port, User-Name, User-Password (the response
entered by the user, encrypted), and the same State Attribute
came with the Access-Challenge. The server then sends back either
Access-Accept or Access-Reject based on whether the response
what it should be, or it can even send another Access-Challenge
2.2. Interoperation with PAP and
For PAP, the NAS takes the PAP ID and password and sends them in
Access-Request packet as the User-Name and User-Password. The NAS
include the Attributes Service-Type = Framed-User and Framed-
= 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
CHAP ID and CHAP username. The NAS then sends an Access-
packet to the RADIUS server with the CHAP username as the User-
Rigney, et. al. Standards Track [Page 7]
RFC 2138 RADIUS April 1997
and with the CHAP ID and CHAP response as the CHAP-
(Attribute 3). The random challenge can either be included in
CHAP-Challenge attribute or, if it is 16 octets long, it can
placed in the Request Authenticator field of the Access-
packet. The NAS MAY include the Attributes Service-Type = Framed
User and Framed-Protocol = PPP as a hint to the RADIUS server
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
to the CHAP-Password. If they match, the server sends back
Access-Accept, otherwise it sends back an Access-Reject
If the RADIUS server is unable to perform the
authentication it should return an Access-Reject. For example,
requires that the user's password be available in cleartext to
server so that it can encrypt the CHAP challenge and compare that
the CHAP response. If the password is not available in cleartext
the RADIUS server then the server MUST send an Access-Reject to
client
2.3. Why UDP
A frequently asked question is why RADIUS uses UDP instead of TCP
a transport protocol. UDP was chosen for strictly technical reasons
There are a number of issues which must be understood. RADIUS is
transaction based protocol which has several
characteristics
1. If the request to a primary Authentication server fails,
secondary server must be queried
To meet this requirement, a copy of the request must be
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
significantly different than TCP provides
At one extreme, RADIUS does not require a "responsive
detection of lost data. The user is willing to wait
seconds for the authentication to complete. The
aggressive TCP retransmission (based on average round
time) is not required, nor is the acknowledgement overhead
TCP
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RFC 2138 RADIUS April 1997
At the other extreme, the user is not willing to wait
minutes for authentication. Therefore the reliable delivery
TCP data two minutes later is not useful. The faster use of
alternate server allows the user to gain access before
up
3. The stateless nature of this protocol simplifies the use of UDP
Clients and servers come and go. Systems are rebooted, or
power cycled independently. Generally this does not cause
problem and with creative timeouts and detection of lost
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
and leave it open through all types of failure events on
network
4. UDP simplifies the server implementation
In the earliest implementations of RADIUS, the server
single threaded. This means that a single request
received, processed, and returned. This was found to
unmanageable in environments where the back-end
mechanism took real time (1 or more seconds). The
request queue would fill and in environments where hundreds
people were being authenticated every minute, the
turn-around time increased to longer that users were willing
wait (this was especially severe when a specific lookup in
database or over DNS took 30 or more seconds). The
solution was to make the server multi-threaded. Achieving
was simple with UDP. Separate processes were spawned to
each request and these processes could respond directly to
client NAS with a simple UDP packet to the original
of the client
It's not all a panacea. As noted, using UDP requires one
which is built into TCP: with UDP we must artificially
retransmission timers to the same server, although they don'
require the same attention to timing provided by TCP. This
penalty is a small price to pay for the advantages of UDP
this protocol
Without TCP we would still probably be using tin cans
by string. But for this particular protocol, UDP is a
choice
Rigney, et. al. Standards Track [Page 9]
RFC 2138 RADIUS April 1997
3. Packet
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
reversed
This memo documents the RADIUS protocol. There has been
confusion in the assignment of port numbers for this protocol.
early deployment of RADIUS was done using the erroneously chosen
number 1645, which conflicts with the "datametrics" service.
officially assigned port number for RADIUS is 1812.
A summary of the RADIUS data format is shown below. The fields
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
The Code field is one octet, and identifies the type of
packet. When a packet is received with an invalid Code field, it
silently discarded
RADIUS Codes (decimal) are assigned as follows
1 Access-
2 Access-
3 Access-
4 Accounting-
5 Accounting-
11 Access-
12 Status-Server (experimental
13 Status-Client (experimental
255
Rigney, et. al. Standards Track [Page 10]
RFC 2138 RADIUS April 1997
Codes 4 and 5 are covered in the RADIUS Accounting document [9],
are not further mentioned here. Codes 12 and 13 are reserved
possible use, but are not further mentioned here
The Identifier field is one octet, and aids in matching requests
replies
The Length field is two octets. It indicates the length of
packet including the Code, Identifier, Length, Authenticator
Attribute fields. Octets outside the range of the Length
should be treated as padding and should be ignored on reception.
the packet is shorter than the Length field indicates, it should
silently discarded. The minimum length is 20 and maximum length
4096.
The Authenticator field is sixteen (16) octets. The most
octet is transmitted first. This value is used to authenticate
reply from the RADIUS server, and is used in the password
algorithm
Request
In Access-Request Packets, the Authenticator value is a 16
random number, called the Request Authenticator. The value
be unpredictable and unique over the lifetime of a secret (
password shared between the client and the RADIUS server),
repetition of a request value in conjunction with the same
would permit an attacker to reply with a previously
response. Since it is expected that the same secret MAY be
to authenticate with servers in disparate geographic regions,
Request Authenticator field SHOULD exhibit global and
uniqueness
The Request Authenticator value in an Access-Request packet
also be unpredictable, lest an attacker trick a server
responding to a predicted future request, and then use
response to masquerade as that server to a future Access-Request
Rigney, et. al. Standards Track [Page 11]
RFC 2138 RADIUS April 1997
Although protocols such as RADIUS are incapable of
against theft of an authenticated session via realtime
wiretapping attacks, generation of unique unpredictable
can protect against a wide range of active attacks
authentication
The NAS and RADIUS server share a secret. That shared
followed by the Request Authenticator is put through a one-way MD
hash to create a 16 octet digest value which is xored with
password entered by the user, and the xored result placed in
User-Password attribute in the Access-Request packet. See
entry for User-Password in the section on Attributes for a
detailed description
Response
The value of the Authenticator field in Access-Accept, Access
Reject, and Access-Challenge packets is called the
Authenticator, and contains a one-way MD5 hash calculated over
stream of octets consisting of: the RADIUS packet, beginning
the Code field, including the Identifier, the Length, the
Authenticator field from the Access-Request packet, and
response Attributes, followed by the shared secret. That is
ResponseAuth = MD5(Code+ID+Length+RequestAuth+Attributes+Secret
where + denotes concatenation
Administrative
The secret (password shared between the client and the RADIUS server
SHOULD be at least as large and unguessable as a well-
password. It is preferred that the secret be at least 16 octets
This is to ensure a sufficiently large range for the secret
provide protection against exhaustive search attacks. A
server SHOULD use the source IP address of the RADIUS UDP packet
decide which shared secret to use, so that RADIUS requests can
proxied
When using a forwarding proxy, the proxy must be able to alter
packet as it passes through in each direction - when the
forwards the request, the proxy can add a Proxy-State Attribute,
when the proxy forwards a response, it removes the Proxy-
Attribute. Since Access-Accept and Access-Reject replies
authenticated on the entire packet contents, the stripping of
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
of this document
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RFC 2138 RADIUS April 1997
Many Attributes may have multiple instances, in such a case the
of Attributes of the same Type SHOULD be preserved. The order
Attributes of different Types is not required to be preserved
In the section below on "Attributes" where the text refers to
packets an attribute is allowed in, only packets with Codes 1, 2, 3
and 11 and attributes defined in this document are covered in
document. A summary table is provided at the end of the "Attributes
section. To determine which Attributes are allowed in packets
codes 4 and 5 refer to the RADIUS Accounting document [9].
4. Packet
The RADIUS Packet type is determined by the Code field in the
octet of the Packet
4.1. Access-
Access-Request packets are sent to a RADIUS server, and
information used to determine whether a user is allowed access
a specific NAS, and any special services requested for that user
An implementation wishing to authenticate a user MUST transmit
RADIUS packet with the Code field set to 1 (Access-Request).
Upon receipt of an Access-Request from a valid client,
appropriate reply MUST be transmitted
An Access-Request MUST contain a User-Name attribute. It
contain either a NAS-IP-Address attribute or NAS-
attribute (or both, although that is not recommended). It
contain either a User-Password attribute or CHAP-
attribute. It SHOULD contain a NAS-Port or NAS-Port-
attribute or both unless the type of access being requested
not involve a port or the NAS does not distinguish among
ports
An Access-Request MAY contain additional attributes as a hint
the server, but the server is not required to honor the hint
When a User-Password is present, it is hidden using a method
on the RSA Message Digest Algorithm MD5 [1].
A summary of the Access-Request packet format is shown below.
fields are transmitted from left to right
Rigney, et. al. Standards Track [Page 13]
RFC 2138 RADIUS April 1997
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
1 for Access-Request
The Identifier field MUST be changed whenever the content of
Attributes field changes, and whenever a valid reply has
received for a previous request. For retransmissions,
Identifier MUST remain unchanged
Request
The Request Authenticator value MUST be changed each time a
Identifier is used
The Attribute field is variable in length, and contains the
of Attributes that are required for the type of service, as
as any desired optional Attributes
4.2. Access-
Access-Accept packets are sent by the RADIUS server, and
specific configuration information necessary to begin delivery
service to the user. If all Attribute values received in
Access-Request are acceptable then the RADIUS implementation
transmit a packet with the Code field set to 2 (Access-Accept).
Rigney, et. al. Standards Track [Page 14]
RFC 2138 RADIUS April 1997
On reception of an Access-Accept, the Identifier field is
with a pending Access-Request. Additionally, the
Authenticator field MUST contain the correct response for
pending Access-Request. Invalid packets are silently discarded
A summary of the Access-Accept packet format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
2 for Access-Accept
The Identifier field is a copy of the Identifier field of
Access-Request which caused this Access-Accept
Response
The Response Authenticator value is calculated from the Access
Request value, as described earlier
The Attribute field is variable in length, and contains a list
zero or more Attributes
Rigney, et. al. Standards Track [Page 15]
RFC 2138 RADIUS April 1997
4.3. Access-
If any value of the received Attributes is not acceptable,
the RADIUS server MUST transmit a packet with the Code field
to 3 (Access-Reject). It MAY include one or more Reply-
Attributes with a text message which the NAS MAY display to
user
A summary of the Access-Reject packet format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
3 for Access-Reject
The Identifier field is a copy of the Identifier field of
Access-Request which caused this Access-Reject
Response
The Response Authenticator value is calculated from the Access
Request value, as described earlier
The Attribute field is variable in length, and contains a list
zero or more Attributes
Rigney, et. al. Standards Track [Page 16]
RFC 2138 RADIUS April 1997
4.4. Access-
If the RADIUS server desires to send the user a
requiring a response, then the RADIUS server MUST respond to
Access-Request by transmitting a packet with the Code field set
11 (Access-Challenge).
The Attributes field MAY have one or more Reply-
Attributes, and MAY have a single State Attribute, or none.
other Attributes are permitted in an Access-Challenge
On receipt of an Access-Challenge, the Identifier field is
with a pending Access-Request. Additionally, the
Authenticator field MUST contain the correct response for
pending Access-Request. Invalid packets are silently discarded
If the NAS does not support challenge/response, it MUST treat
Access-Challenge as though it had received an Access-
instead
If the NAS supports challenge/response, receipt of a
Access-Challenge indicates that a new Access-Request SHOULD
sent. The NAS MAY display the text message, if any, to the user
and then prompt the user for a response. It then sends
original Access-Request with a new request ID and
Authenticator, with the User-Password Attribute replaced by
user's response (encrypted), and including the State
from the Access-Challenge, if any. Only 0 or 1 instances of
State Attribute can be present in an Access-Request
A NAS which supports PAP MAY forward the Reply-Message to
dialin client and accept a PAP response which it can use as
the user had entered the response. If the NAS cannot do so,
should treat the Access-Challenge as though it had received
Access-Reject instead
Rigney, et. al. Standards Track [Page 17]
RFC 2138 RADIUS April 1997
A summary of the Access-Challenge packet format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
11 for Access-Challenge
The Identifier field is a copy of the Identifier field of
Access-Request which caused this Access-Challenge
Response
The Response Authenticator value is calculated from the Access
Request value, as described earlier
The Attributes field is variable in length, and contains a list
zero or more Attributes
5.
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
is Attribute specific, and is specified in each
description
The end of the list of Attributes is indicated by the Length of
RADIUS packet
Rigney, et. al. Standards Track [Page 18]
RFC 2138 RADIUS April 1997
A summary of the Attribute format is shown below. The fields
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
The Type field is one octet. Up-to-date values of the RADIUS
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
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-
2 User-
3 CHAP-
4 NAS-IP-
5 NAS-
6 Service-
7 Framed-
8 Framed-IP-
9 Framed-IP-
10 Framed-
11 Filter-
12 Framed-
13 Framed-
14 Login-IP-
15 Login-
16 Login-TCP-
17 (unassigned
18 Reply-
19 Callback-
20 Callback-
21 (unassigned
22 Framed-
23 Framed-IPX-
24
25
26 Vendor-
Rigney, et. al. Standards Track [Page 19]
RFC 2138 RADIUS April 1997
27 Session-
28 Idle-
29 Termination-
30 Called-Station-
31 Calling-Station-
32 NAS-
33 Proxy-
34 Login-LAT-
35 Login-LAT-
36 Login-LAT-
37 Framed-AppleTalk-
38 Framed-AppleTalk-
39 Framed-AppleTalk-
40-59 (reserved for accounting
60 CHAP-
61 NAS-Port-
62 Port-
63 Login-LAT-
The Length field is one octet, and indicates the length of
Attribute including the Type, Length and Value fields. If
Attribute is received in an Access-Request but with an
Length, an Access-Reject SHOULD be transmitted. If an
is received in an Access-Accept, Access-Reject or Access-
packet with an invalid length, the packet MUST either be
an Access-Reject or else silently discarded
The Value field is zero or more octets and contains
specific to the Attribute. The format and length of the
field is determined by the Type and Length fields
Note that a "string" in RADIUS does not require termination by
ASCII NUL because the Attribute already has a length field
Rigney, et. al. Standards Track [Page 20]
RFC 2138 RADIUS April 1997
The format of the value field is one of four data types
string 0-253
address 32 bit value, most significant octet first
integer 32 bit value, most significant octet first
time 32 bit value, most significant octet first --
since 00:00:00 GMT, January 1, 1970. The
Attributes do not use this data type but it is
here for possible use within Vendor-Specific attributes
5.1. User-
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.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
1 for User-Name
>= 3
The String field is one or more octets. The NAS may limit
maximum length of the User-Name but the ability to handle at
63 octets is recommended
Rigney, et. al. Standards Track [Page 21]
RFC 2138 RADIUS April 1997
The format of the username MAY be one of several forms
monolithic Consisting only of alphanumeric characters.
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
without trailing dot) indicates the realm in which
name part applies
distinguished
A name in ASN.1 form used in Public Key
systems
5.2. User-
This Attribute indicates the password of the user to
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
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
the shared secret followed by the Request Authenticator.
value is XORed with the first 16 octet segment of the password
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 MD
hash is calculated over a stream of octets consisting of
shared secret followed by the result of the first xor. That
is XORed with the second 16 octet segment of the password
placed in the second 16 octets of the String field of the User
Password Attribute
If necessary, this operation is repeated, with each xor
being used along with the shared secret to generate the next
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
explanation of the method follows
Rigney, et. al. Standards Track [Page 22]
RFC 2138 RADIUS April 1997
Call the shared secret S and the pseudo-random 128-bit
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-
boundary. Call the ciphertext blocks c(1), c(2), etc. We'll
intermediate values b1, b2, etc
b1 = MD5(S + RA) c(1) = p1 xor b
b2 = MD5(S + c(1)) c(2) = p2 xor b
. .
. .
. .
bi = MD5(S + c(i-1)) c(i) = pi xor
The String will contain c(1)+c(2)+...+c(i) where +
concatenation
On receipt, the process is reversed to yield the
password
A summary of the User-Password Attribute format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
2 for User-Password
At least 18 and no larger than 130.
The String field is between 16 and 128 octets long, inclusive
5.3. CHAP-
This Attribute indicates the response value provided by a
Challenge-Handshake Authentication Protocol (CHAP) user
response to the challenge. It is only used in Access-
packets
Rigney, et. al. Standards Track [Page 23]
RFC 2138 RADIUS April 1997
The CHAP challenge value is found in the CHAP-Challenge
(60) if present in the packet, otherwise in the
Authenticator field
A summary of the CHAP-Password Attribute format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
3 for CHAP-Password
19
CHAP
This field is one octet, and contains the CHAP Identifier from
user's CHAP Response
The String field is 16 octets, and contains the CHAP Response
the user
5.4. NAS-IP-
This Attribute indicates the identifying IP Address of the
which is requesting authentication of the user. It is only
in Access-Request packets. Either NAS-IP-Address or NAS
Identifier SHOULD be present in an Access-Request packet
Rigney, et. al. Standards Track [Page 24]
RFC 2138 RADIUS April 1997
A summary of the NAS-IP-Address Attribute format is shown below.
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 for NAS-IP-Address
6
The Address field is four octets
5.5. NAS-
This Attribute indicates the physical port number of the NAS
is authenticating the user. It is only used in Access-
packets. Note that this is using "port" in its sense of
physical connection on the NAS, not in the sense of a TCP or
port number. Either NAS-Port or NAS-Port-Type (61) or both
be present in an Access-Request packet, if the NAS
among its ports
A summary of the NAS-Port Attribute format is shown below.
fields are transmitted from left to right
Rigney, et. al. Standards Track [Page 25]
RFC 2138 RADIUS April 1997
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 for NAS-Port
6
The Value field is four octets. Despite the size of the field
values range from 0 to 65535.
5.6. Service-
This Attribute indicates the type of service the user
requested, or the type of service to be provided. It MAY be
in both Access-Request and Access-Accept packets. A NAS is
required to implement all of these service types, and MUST
unknown or unsupported Service-Types as though an Access-
had been received instead
A summary of the Service-Type Attribute format is shown below.
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 for Service-Type
Rigney, et. al. Standards Track [Page 26]
RFC 2138 RADIUS April 1997
6
The Value field is four octets
1
2
3 Callback
4 Callback
5
6
7 NAS
8 Authenticate
9 Callback NAS
The service types are defined as follows when used in an Access
Accept. When used in an Access-Request, they should be
to be a hint to the RADIUS server that the NAS has reason
believe the user would prefer the kind of service indicated,
the server is not required to honor the hint
Login The user should be connected to a host
Framed A Framed Protocol should be started for
User, such as PPP or SLIP
Callback Login The user should be disconnected and
back, then connected to a host
Callback Framed The user should be disconnected and
back, then a Framed Protocol should be
for the User, such as PPP or SLIP
Outbound The user should be granted access to
devices
Administrative The user should be granted access to
administrative interface to the NAS from
privileged commands can be executed
NAS Prompt The user should be provided a command
on the NAS from which non-privileged
can be executed
Rigney, et. al. Standards Track [Page 27]
RFC 2138 RADIUS April 1997
Authenticate Only Only Authentication is requested, and
authorization information needs to be
in the Access-Accept (typically used by
servers rather than the NAS itself).
Callback NAS Prompt The user should be disconnected and
back, then provided a command prompt on
NAS from which non-privileged commands can
executed
5.7. Framed-
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 for Framed-Protocol
6
The Value field is four octets
1
2
3 AppleTalk Remote Access Protocol (ARAP
4 Gandalf proprietary SingleLink/MultiLink
5 Xylogics proprietary IPX/
Rigney, et. al. Standards Track [Page 28]
RFC 2138 RADIUS April 1997
5.8. Framed-IP-
This Attribute indicates the address to be configured for
user. It MAY be used in Access-Accept packets. It MAY be used
an Access-Request packet as a hint by the NAS to the server
it would prefer that address, but the server is not required
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 for Framed-IP-Address
6
The Address field is four octets. The value 0xFFFFFFFF
that the NAS should allow the user to select an address (e.g
Negotiated). The value 0xFFFFFFFE indicates that the NAS
select an address for the user (e.g. Assigned from a pool
addresses kept by the NAS). Other valid values indicate that
NAS should use that value as the user's IP address
5.9. Framed-IP-
This Attribute indicates the IP netmask to be configured for
user when the user is a router to a network. It MAY be used
Access-Accept packets. It MAY be used in an Access-Request
as a hint by the NAS to the server that it would prefer
netmask, but the server is not required to honor the hint
Rigney, et. al. Standards Track [Page 29]
RFC 2138 RADIUS April 1997
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9 for Framed-IP-Netmask
6
The Address field is four octets specifying the IP netmask of
user
5.10. Framed-
This Attribute indicates the routing method for the user, when
user is a router to a network. It is only used in Access-
packets
A summary of the Framed-Routing Attribute format is shown below.
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
10 for Framed-Routing
Rigney, et. al. Standards Track [Page 30]
RFC 2138 RADIUS April 1997
6
The Value field is four octets
0
1 Send routing
2 Listen for routing
3 Send and
5.11. Filter-
This Attribute indicates the name of the filter list for
user. Zero or more Filter-Id attributes MAY be sent in
Access-Accept packet
Identifying a filter list by name allows the filter to be used
different NASes without regard to filter-list
details
A summary of the Filter-Id Attribute format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
11 for Filter-Id
>= 3
Rigney, et. al. Standards Track [Page 31]
RFC 2138 RADIUS April 1997
The String field is one or more octets, and its contents
implementation dependent. It is intended to be human readable
MUST NOT affect operation of the protocol. It is recommended
the message contain displayable ASCII characters from the range 32
through 126 decimal
5.12. Framed-
This Attribute indicates the Maximum Transmission Unit to
configured for the user, when it is not negotiated by some
means (such as PPP). It is only used in Access-Accept packets
A summary of the Framed-MTU Attribute format is shown below.
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12 for Framed-MTU
6
The Value field is four octets. Despite the size of the field
values range from 64 to 65535.
Rigney, et. al. Standards Track [Page 32]
RFC 2138 RADIUS April 1997
5.13. Framed-
This Attribute indicates a compression protocol to be used for
link. It MAY be used in Access-Accept packets. It MAY be used
an Access-Request packet as a hint to the server that the
would prefer to use that compression, but the server is
required to honor the hint
More than one compression protocol Attribute MAY be sent. It
the responsibility of the NAS to apply the proper
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
13 for Framed-Compression
6
The Value field is four octets
0
1 VJ TCP/IP header compression [5]
2 IPX header
5.14. Login-IP-
This Attribute indicates the system with which to connect
user, when the Login-Service Attribute is included. It MAY
used in Access-Accept packets. It MAY be used in an Access
Rigney, et. al. Standards Track [Page 33]
RFC 2138 RADIUS April 1997
Request packet as a hint to the server that the NAS would
to use that host, but the server is not required to honor
hint
A summary of the Login-IP-Host Attribute format is shown below.
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
14 for Login-IP-Host
6
The Address field is four octets. The value 0xFFFFFFFF
that the NAS SHOULD allow the user to select an address.
value 0 indicates that the NAS SHOULD select a host to connect
user to. Other values indicate the address the NAS SHOULD
the user to
5.15. Login-
This Attribute indicates the service which should be used
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.
fields are transmitted from left to right
Rigney, et. al. Standards Track [Page 34]
RFC 2138 RADIUS April 1997
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
15 for Login-Service
6
The Value field is four octets
0
1
2 TCP
3 PortMaster (proprietary
4
5.16. Login-TCP-
This Attribute indicates the TCP port with which the user is to
connected, when the Login-Service Attribute is also present.
is only used in Access-Accept packets
A summary of the Login-TCP-Port Attribute format is shown below.
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 (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16 for Login-TCP-Port
Rigney, et. al. Standards Track [Page 35]
RFC 2138 RADIUS April 1997
6
The Value field is four octets. Despite the size of the field
values range from 0 to 65535.
5.17. (unassigned
ATTRIBUTE TYPE 17 HAS NOT BEEN ASSIGNED
5.18. Reply-
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
indicate a dialog message to prompt the user before
Access-Request attempt
When used in an Access-Challenge, it MAY indicate a dialog
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
packet
A summary of the Reply-Message Attribute format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
18 for Reply-Message
Rigney, et. al. Standards Track [Page 36]
RFC 2138 RADIUS April 1997
>= 3
The String field is one or more octets, and its contents
implementation dependent. It is intended to be human readable
and MUST NOT affect operation of the protocol. It is
that the message contain displayable ASCII characters from
range 10, 13, and 32 through 126 decimal. Mechanisms
extension to other character sets are beyond the scope of
specification
5.19. Callback-
This Attribute indicates a dialing string to be used for callback
It MAY be used in Access-Accept packets. It MAY be used in
Access-Request packet as a hint to the server that a
service is desired, but the server is not required to honor
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
19 for Callback-Number
>= 3
Rigney, et. al. Standards Track [Page 37]
RFC 2138 RADIUS April 1997
The String field is one or more octets. The actual format of
information is site or application specific, and a
implementation SHOULD support the field as undistinguished octets
The codification of the range of allowed usage of this field
outside the scope of this specification
5.20. Callback-
This Attribute indicates the name of a place to be called, to
interpreted by the NAS. It MAY be used in Access-Accept packets
A summary of the Callback-Id Attribute format is shown below.
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
20 for Callback-Id
>= 3
The String field is one or more octets. The actual format of
information is site or application specific, and a
implementation SHOULD support the field as undistinguished octets
The codification of the range of allowed usage of this field
outside the scope of this specification
5.21. (unassigned
ATTRIBUTE TYPE 21 HAS NOT BEEN ASSIGNED
Rigney, et. al. Standards Track [Page 38]
RFC 2138 RADIUS April 1997
5.22. Framed-
This Attribute provides routing information to be configured
the user on the NAS. It is used in the Access-Accept packet
can appear multiple times
A summary of the Framed-Route Attribute format is shown below.
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...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
22 for Framed-Route
>= 3
The String field is one or more octets, and its contents
implementation dependent. It is intended to be human readable
MUST NOT affect operation of the protocol. It is recommended
the message contain displayable ASCII characters from the range 32
through 126 decimal
For IP routes, it SHOULD contain a destination prefix in
quad form optionally followed by a slash and a decimal
specifier stating how many high order bits of the prefix should
used. That is followed by a space, a gateway address in
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
specifier may be omitted in which case it should default to 8
for class A prefixes, 16 bits for class B prefixes, and 24
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
address of the user SHOULD be used as the gateway address
Rigney, et. al. Standards Track [Page 39]
RFC 2138 RADIUS April 1997
5.23. Framed-IPX-
This Attribute indicates the IPX Network number to be
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-