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Network Working Group C. Rigney
Request for Comments: 2865 S. Willens
Obsoletes: 2138 Livingston
Category: Standards Track A. Rubens
Merit
W. Simpson
Daydreamer
June 2000
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.
Copyright Notice
IESG Note:
This protocol is widely implemented and used. Experience has shown
that it can suffer degraded performance and lost data when used in
large scale systems, in part because it does not include provisions
for congestion control. Readers of this document may find it
beneficial to track the progress of the IETF's AAA working group,
which may develop a successor protocol that better addresses the
scaling and congestion control issues.
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. The early deployment of
RADIUS was done using UDP port number 1645, which conflicts with the
"datametrics" service. The officially assigned port number for
RADIUS is 1812.
Rigney, et al. Standards Track [Page 1]
RFC 2865 RADIUS June 2000
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 ................ 8
2.3 Proxy ........................................... 8
2.4 Why UDP? ........................................ 11
2.5 Retransmission Hints ............................ 12
2.6 Keep-Alives Considered Harmful .................. 13
3. Packet Format ......................................... 13
4. Packet Types .......................................... 17
4.1 Access-Request .................................. 17
4.2 Access-Accept ................................... 18
4.3 Access-Reject ................................... 20
4.4 Access-Challenge ................................ 21
5. Attributes ............................................ 22
5.1 User-Name ....................................... 26
5.2 User-Password ................................... 27
5.3 CHAP-Password ................................... 28
5.4 NAS-IP-Address .................................. 29
5.5 NAS-Port ........................................ 30
5.6 Service-Type .................................... 31
5.7 Framed-Protocol ................................. 33
5.8 Framed-IP-Address ............................... 34
5.9 Framed-IP-Netmask ............................... 34
5.10 Framed-Routing .................................. 35
5.11 Filter-Id ....................................... 36
5.12 Framed-MTU ...................................... 37
5.13 Framed-Compression .............................. 37
5.14 Login-IP-Host ................................... 38
5.15 Login-Service ................................... 39
5.16 Login-TCP-Port .................................. 40
5.17 (unassigned) .................................... 41
5.18 Reply-Message ................................... 41
5.19 Callback-Number ................................. 42
5.20 Callback-Id ..................................... 42
5.21 (unassigned) .................................... 43
5.22 Framed-Route .................................... 43
5.23 Framed-IPX-Network .............................. 44
5.24 State ........................................... 45
5.25 Class ........................................... 46
5.26 Vendor-Specific ................................. 47
5.27 Session-Timeout ................................. 48
5.28 Idle-Timeout .................................... 49
5.29 Termination-Action .............................. 49
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RFC 2865 RADIUS June 2000
5.30 Called-Station-Id ............................... 50
5.31 Calling-Station-Id .............................. 51
5.32 NAS-Identifier .................................. 52
5.33 Proxy-State ..................................... 53
5.34 Login-LAT-Service ............................... 54
5.35 Login-LAT-Node .................................. 55
5.36 Login-LAT-Group ................................. 56
5.37 Framed-AppleTalk-Link ........................... 57
5.38 Framed-AppleTalk-Network ........................ 58
5.39 Framed-AppleTalk-Zone ........................... 58
5.40 CHAP-Challenge .................................. 59
5.41 NAS-Port-Type ................................... 60
5.42 Port-Limit ...................................... 61
5.43 Login-LAT-Port .................................. 62
5.44 Table of Attributes ............................. 63
6. IANA Considerations ................................... 64
6.1 Definition of Terms ............................. 64
6.2 Recommended Registration Policies ............... 65
7. Examples .............................................. 66
7.1 User Telnet to Specified Host ................... 66
7.2 Framed User Authenticating with CHAP ............ 67
7.3 User with Challenge-Response card ............... 68
8. Security Considerations ............................... 71
9. Change Log ............................................ 71
10. References ............................................ 73
11. Acknowledgements ...................................... 74
12. Chair's Address ....................................... 74
13. Authors' Addresses .................................... 75
14. Full Copyright Statement .............................. 76
1. Introduction
This document obsoletes RFC 2138 [1]. A summary of the changes
between this document and RFC 2138 is available in the "Change Log"
appendix.
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).
Rigney, et al. Standards Track [Page 3]
RFC 2865 RADIUS June 2000
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
login, and other authentication mechanisms.
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
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [2]. These key
words mean the same thing whether capitalized or not.
An implementation is not compliant if it fails to satisfy one or more
of the must or must not requirements for the protocols it implements.
An implementation that satisfies all the must, must not, should and
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RFC 2865 RADIUS June 2000
should not requirements for its protocols is said to be
"unconditionally compliant"; one that satisfies all the must and must
not requirements but not all the should or should not requirements
for its protocols is said to be "conditionally compliant".
A NAS that does not implement a given service MUST NOT implement the
RADIUS attributes for that service. For example, a NAS that is
unable to offer ARAP service MUST NOT implement the RADIUS attributes
for ARAP. A NAS MUST treat a RADIUS access-accept authorizing an
unavailable service as an access-reject instead.
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 [3].
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RFC 2865 RADIUS June 2000
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 MUST 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 Proxy-State attributes were present in the Access-Request,
they MUST be copied unmodified and in order into the response packet.
Other Attributes can be placed before, after, or even between the
Proxy-State attributes.
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 (except Proxy-State) 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 Attribute SHOULD be
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RFC 2865 RADIUS June 2000
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 is 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
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came with the Access-Challenge. The server then sends back either an
Access-Accept or Access-Reject based on whether the response matches
the required value, 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 MUST 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. Proxy
With proxy RADIUS, one RADIUS server receives an authentication (or
accounting) request from a RADIUS client (such as a NAS), forwards
the request to a remote RADIUS server, receives the reply from the
remote server, and sends that reply to the client, possibly with
changes to reflect local administrative policy. A common use for
proxy RADIUS is roaming. Roaming permits two or more administrative
entities to allow each other's users to dial in to either entity's
network for service.
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RFC 2865 RADIUS June 2000
The NAS sends its RADIUS access-request to the "forwarding server"
which forwards it to the "remote server". The remote server sends a
response (Access-Accept, Access-Reject, or Access-Challenge) back to
the forwarding server, which sends it back to the NAS. The User-Name
attribute MAY contain a Network Access Identifier [8] for RADIUS
Proxy operations. The choice of which server receives the forwarded
request SHOULD be based on the authentication "realm". The
authentication realm MAY be the realm part of a Network Access
Identifier (a "named realm"). Alternatively, the choice of which
server receives the forwarded request MAY be based on whatever other
criteria the forwarding server is configured to use, such as Called-
Station-Id (a "numbered realm").
A RADIUS server can function as both a forwarding server and a remote
server, serving as a forwarding server for some realms and a remote
server for other realms. One forwarding server can act as a
forwarder for any number of remote servers. A remote server can have
any number of servers forwarding to it and can provide authentication
for any number of realms. One forwarding server can forward to
another forwarding server to create a chain of proxies, although care
must be taken to avoid introducing loops.
The following scenario illustrates a proxy RADIUS communication
between a NAS and the forwarding and remote RADIUS servers:
1. A NAS sends its access-request to the forwarding server.
2. The forwarding server forwards the access-request to the remote
server.
3. The remote server sends an access-accept, access-reject or
access-challenge back to the forwarding server. For this example,
an access-accept is sent.
4. The forwarding server sends the access-accept to the NAS.
The forwarding server MUST treat any Proxy-State attributes already
in the packet as opaque data. Its operation MUST NOT depend on the
content of Proxy-State attributes added by previous servers.
If there are any Proxy-State attributes in the request received from
the client, the forwarding server MUST include those Proxy-State
attributes in its reply to the client. The forwarding server MAY
include the Proxy-State attributes in the access-request when it
forwards the request, or MAY omit them in the forwarded request. If
the forwarding server omits the Proxy-State attributes in the
forwarded access-request, it MUST attach them to the response before
sending it to the client.
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RFC 2865 RADIUS June 2000
We now examine each step in more detail.
1. A NAS sends its access-request to the forwarding server. The
forwarding server decrypts the User-Password, if present, using
the shared secret it knows for the NAS. If a CHAP-Password
attribute is present in the packet and no CHAP-Challenge attribute
is present, the forwarding server MUST leave the Request-
Authenticator untouched or copy it to a CHAP-Challenge attribute.
'' The forwarding server MAY add one Proxy-State attribute to the
packet. (It MUST NOT add more than one.) If it adds a Proxy-
State, the Proxy-State MUST appear after any other Proxy-States in
the packet. The forwarding server MUST NOT modify any other
Proxy-States that were in the packet (it may choose not to forward
them, but it MUST NOT change their contents). The forwarding
server MUST NOT change the order of any attributes of the same
type, including Proxy-State.
2. The forwarding server encrypts the User-Password, if present,
using the secret it shares with the remote server, sets the
Identifier as needed, and forwards the access-request to the
remote server.
3. The remote server (if the final destination) verifies the user
using User-Password, CHAP-Password, or such method as future
extensions may dictate, and returns an access-accept, access-
reject or access-challenge back to the forwarding server. For
this example, an access-accept is sent. The remote server MUST
copy all Proxy-State attributes (and only the Proxy-State
attributes) in order from the access-request to the response
packet, without modifying them.
4. The forwarding server verifies the Response Authenticator using
the secret it shares with the remote server, and silently discards
the packet if it fails verification. If the packet passes
verification, the forwarding server removes the last Proxy-State
(if it attached one), signs the Response Authenticator using the
secret it shares with the NAS, restores the Identifier to match
the one in the original request by the NAS, and sends the access-
accept to the NAS.
A forwarding server MAY need to modify attributes to enforce local
policy. Such policy is outside the scope of this document, with the
following restrictions. A forwarding server MUST not modify existing
Proxy-State, State, or Class attributes present in the packet.
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RFC 2865 RADIUS June 2000
Implementers of forwarding servers should consider carefully which
values it is willing to accept for Service-Type. Careful
consideration must be given to the effects of passing along Service-
Types of NAS-Prompt or Administrative in a proxied Access-Accept, and
implementers may wish to provide mechanisms to block those or other
service types, or other attributes. Such mechanisms are outside the
scope of this document.
2.4. 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.
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RFC 2865 RADIUS June 2000
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
than 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.
2.5. Retransmission Hints
If the RADIUS server and alternate RADIUS server share the same
shared secret, it is OK to retransmit the packet to the alternate
RADIUS server with the same ID and Request Authenticator, because the
content of the attributes haven't changed. If you want to use a new
Request Authenticator when sending to the alternate server, you may.
If you change the contents of the User-Password attribute (or any
other attribute), you need a new Request Authenticator and therefore
a new ID.
If the NAS is retransmitting a RADIUS request to the same server as
before, and the attributes haven't changed, you MUST use the same
Request Authenticator, ID, and source port. If any attributes have
changed, you MUST use a new Request Authenticator and ID.
A NAS MAY use the same ID across all servers, or MAY keep track of
IDs separately for each server, it is up to the implementer. If a
NAS needs more than 256 IDs for outstanding requests, it MAY use
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RFC 2865 RADIUS June 2000
additional source ports to send requests from, and keep track of IDs
for each source port. This allows up to 16 million or so outstanding
requests at one time to a single server.
2.6. Keep-Alives Considered Harmful
Some implementers have adopted the practice of sending test RADIUS
requests to see if a server is alive. This practice is strongly
discouraged, since it adds to load and harms scalability without
providing any additional useful information. Since a RADIUS request
is contained in a single datagram, in the time it would take you to
send a ping you could just send the RADIUS request, and getting a
reply tells you that the RADIUS server is up. If you do not have a
RADIUS request to send, it does not matter if the server is up or
not, because you are not using it.
If you want to monitor your RADIUS server, use SNMP. That's what
SNMP is for.
3. Packet Format
Exactly one RADIUS packet is encapsulated in the UDP Data field [4],
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. The early deployment of
RADIUS was done using UDP port number 1645, which conflicts with the
"datametrics" service. The officially assigned port number for
RADIUS is 1812.
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RFC 2865 RADIUS June 2000
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 [5].
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. The RADIUS server can detect a duplicate request if
it has the same client source IP address and source UDP port and
Identifier within a short span of time.
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RFC 2865 RADIUS June 2000
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
MUST be treated as padding and ignored on reception. If the
packet is shorter than the Length field indicates, it MUST 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
Rigney, et al. Standards Track [Page 15]
RFC 2865 RADIUS June 2000
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.
The secret MUST NOT be empty (length 0) since this would allow
packets to be trivially forged.
A RADIUS server MUST 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 MAY add a Proxy-State Attribute,
and when the proxy forwards a response, it MUST remove its Proxy-
State Attribute if it added one. Proxy-State is always added or
removed after any other Proxy-States, but no other assumptions
regarding its location within the list of attributes can be made.
Since Access-Accept and Access-Reject replies are authenticated on
the entire packet contents, the stripping of the Proxy-State
attribute invalidates 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.
Rigney, et al. Standards Track [Page 16]
RFC 2865 RADIUS June 2000
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 SHOULD contain a User-Name attribute. It MUST
contain either a NAS-IP-Address attribute or a NAS-Identifier
attribute (or both).
An Access-Request MUST contain either a User-Password or a CHAP-
Password or a State. An Access-Request MUST NOT contain both a
User-Password and a CHAP-Password. If future extensions allow
other kinds of authentication information to be conveyed, the
attribute for that can be used in an Access-Request instead of
User-Password or CHAP-Password.
An Access-Request 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 [3].
Rigney, et al. Standards Track [Page 17]
RFC 2865 RADIUS June 2000
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).
Rigney, et al. Standards Track [Page 18]
RFC 2865 RADIUS June 2000
On reception of an Access-Accept, the Identifier field is matched
with a pending Access-Request. 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.
Rigney, et al. Standards Track [Page 19]
RFC 2865 RADIUS June 2000
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.
Rigney, et al. Standards Track [Page 20]
RFC 2865 RADIUS June 2000
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.
Vendor-Specific, Idle-Timeout, Session-Timeout and Proxy-State
attributes MAY also be included. No other Attributes defined in
this document 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
dialing 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 MUST treat the Access-Challenge as though it had received
an Access-Reject instead.
Rigney, et al. Standards Track [Page 21]
RFC 2865 RADIUS June 2000
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.
The end of the list of Attributes is indicated by the Length of the
RADIUS packet.
Some Attributes MAY be included more than once. The effect of this
is Attribute specific, and is specified in each Attribute
description. A summary table is provided at the end of the
"Attributes" section.
Rigney, et al. Standards Track [Page 22]
RFC 2865 RADIUS June 2000
If multiple Attributes with the same Type are present, the order of
Attributes with the same Type MUST be preserved by any proxies. The
order of Attributes of different Types is not required to be
preserved. A RADIUS server or client MUST NOT have any dependencies
on the order of attributes of different types. A RADIUS server or
client MUST NOT require attributes of the same type to be contiguous.
Where an Attribute's description limits which kinds of packet it can
be contained in, this applies only to the packet types defined in
this document, namely Access-Request, Access-Accept, Access-Reject
and Access-Challenge (Codes 1, 2, 3, and 11). Other documents
defining other packet types may also use Attributes described here.
To determine which Attributes are allowed in Accounting-Request and
Accounting-Response packets (Codes 4 and 5) refer to the RADIUS
Accounting document [5].
Likewise where packet types defined here state that only certain
Attributes are permissible in them, future memos defining new
Attributes should indicate which packet types the new Attributes may
be present in.
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 [6].
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.
A RADIUS server MAY ignore Attributes with an unknown Type.
A RADIUS client MAY ignore Attributes with an unknown Type.
Rigney, et al. Standards Track [Page 23]
RFC 2865 RADIUS June 2000
This specification concerns the following values:
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
Rigney, et al. Standards Track [Page 24]
RFC 2865 RADIUS June 2000
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
as 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 none of the types in RADIUS terminate with a NUL (hex
00). In particular, types "text" and "string" in RADIUS do not
terminate with a NUL (hex 00). The Attribute has a length field
and does not use a terminator. Text contains UTF-8 encoded 10646
[7] characters and String contains 8-bit binary data. Servers and
servers and clients MUST be able to deal with embedded nulls.
RADIUS implementers using C are cautioned not to use strcpy() when
handling strings.
The format of the value field is one of five data types. Note
that type "text" is a subset of type "string".
text 1-253 octets containing UTF-8 encoded 10646 [7]
characters. Text of length zero (0) MUST NOT be sent;
omit the entire attribute instead.
string 1-253 octets containing binary data (values 0 through
255 decimal, inclusive). Strings of length zero (0)
MUST NOT be sent; omit the entire attribute instead.
address 32 bit value, most significant octet first.
integer 32 bit unsigned value, most significant octet first.
time 32 bit unsigned value, most significant octet first --
seconds since 00:00:00 UTC, January 1, 1970. The
standard Attributes do not use this data type but it is
presented here for possible use in future attributes.
Rigney, et al. Standards Track [Page 25]
RFC 2865 RADIUS June 2000
5.1. User-Name
Description
This Attribute indicates the name of the user to be authenticated.
It MUST be sent in Access-Request packets if available.
It MAY be sent in an Access-Accept packet, in which case the
client SHOULD use the name returned in the Access-Accept packet in
all Accounting-Request packets for this session. If the Access-
Accept includes Service-Type = Rlogin and the User-Name attribute,
a NAS MAY use the returned User-Name when performing the Rlogin
function.
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:
text Consisting only of UTF-8 encoded 10646 [7] characters.
network access identifier
A Network Access Identifier as described in RFC 2486
[8].
distinguished name
A name in ASN.1 form used in Public Key authentication
systems.
Rigney, et al. Standards Track [Page 26]
RFC 2865 RADIUS June 2000
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 [9] 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.
Rigney, et al. Standards Track [Page 27]
RFC 2865 RADIUS June 2000
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Rigney, et al. Standards Track [Page 28]
RFC 2865 RADIUS June 2000
Type
3 for CHAP-Password.
Length
19
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, and SHOULD be
unique to the NAS within the scope of the RADIUS server. NAS-IP-
Address is only used in Access-Request packets. Either NAS-IP-
Address or NAS-Identifier MUST be present in an Access-Request
packet.
Note that NAS-IP-Address MUST NOT be used to select the shared
secret used to authenticate the request. The source IP address of
the Access-Request packet MUST be used to select the shared
secret.
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.
Rigney, et al. Standards Track [Page 29]
RFC 2865 RADIUS June 2000
Length
6
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
6
Value
The Value field is four octets.
Rigney, et al. Standards Track [Page 30]
RFC 2865 RADIUS June 2000
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
6
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
10 Call Check
11 Callback Administrative
Rigney, et al. Standards Track [Page 31]
RFC 2865 RADIUS June 2000
The service types are defined as follows when used in an Access-
Accept. When used in an Access-Request, they MAY 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.
Login The user should be connected to a host.
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.
Call Check Used by the NAS in an Access-Request packet to
indicate that a call is being received and
that the RADIUS server should send back an
Access-Accept to answer the call, or an
Access-Reject to not accept the call,
typically based on the Called-Station-Id or
Calling-Station-Id attributes. It is
Rigney, et al. Standards Track [Page 32]
RFC 2865 RADIUS June 2000
recommended that such Access-Requests use the
value of Calling-Station-Id as the value of
the User-Name.
Callback Administrative
The user should be disconnected and called
back, then granted access to the
administrative interface to the NAS from which
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
6
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
6 X.75 Synchronous
Rigney, et al. Standards Track [Page 33]
RFC 2865 RADIUS June 2000
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
6
Address
The Address field is four octets. The value 0xFFFFFFFF indicates
that the NAS Should allow the user to select an address (e.g.
Negotiated). The value 0xFFFFFFFE indicates that the NAS should
select an address for the user (e.g. Assigned from a pool of
addresses kept by the NAS). 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.
Rigney, et al. Standards Track [Page 34]
RFC 2865 RADIUS June 2000
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
6
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.
Rigney, et al. Standards Track [Page 35]
RFC 2865 RADIUS June 2000
Length
6
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 | Text ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
11 for Filter-Id.
Length
>= 3
Text
The Text 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 UTF-8 encoded 10646 [7] characters.
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RFC 2865 RADIUS June 2000
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 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 value, but the server is not
required to honor the hint.
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
6
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.
Rigney, et al. Standards Track [Page 37]
RFC 2865 RADIUS June 2000
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
6
Value
The Value field is four octets.
0 None
1 VJ TCP/IP header compression [10]
2 IPX header compression
3 Stac-LZS 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.
Rigney, et al. Standards Track [Page 38]