Network Working Group P. Congdon
Request for Comments: 3580 Hewlett Packard Company
Category: Informational B. Aboba
September 2003 IEEE 802.1X Remote Authentication Dial In User Service (RADIUS)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document provides suggestions on Remote Authentication Dial In
User Service (RADIUS) usage by IEEE 802.1X Authenticators. The
material in this document is also included within a non-normative
Appendix within the IEEE 802.1X specification, and is being presented
as an IETF RFC for informational purposes.
The service used to establish Access Point/Station mapping and
enable Station invocation of the distribution system services.
An Authenticator is an entity that requires authentication from
the Supplicant. The Authenticator may be connected to the
Supplicant at the other end of a point-to-point LAN segment or
802.11 wireless link.
An Authentication Server is an entity that provides an
Authentication Service to an Authenticator. This service
verifies, from the credentials provided by the Supplicant, the
claim of identity made by the Supplicant.
Port Access Entity (PAE)
The protocol entity associated with a physical or virtual
(802.11) Port. A given PAE may support the protocol
functionality associated with the Authenticator, Supplicant or
Any device that contains an IEEE 802.11 conformant medium
access control (MAC) and physical layer (PHY) interface to the
wireless medium (WM).
A Supplicant is an entity that is being authenticated by an
Authenticator. The Supplicant may be connected to the
Authenticator at one end of a point-to-point LAN segment or
802.11 wireless link.
1.2. Requirements Language
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. 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 [RFC2119].
2. RADIUS Accounting Attributes
With a few exceptions, the RADIUS accounting attributes defined in
[RFC2866], [RFC2867], and [RFC2869] have the same meaning within IEEE
802.1X sessions as they do in dialup sessions and therefore no
additional commentary is needed.
Attributes requiring more discussion include:
This attribute indicates how the session was terminated, as described
in [RFC2866]. [IEEE8021X] defines the following termination cause
values, which are shown with their RADIUS equivalents in the table on
the next page.
IEEE 802.1X RADIUS
SupplicantLogoff(1) User Request (1)
portFailure(2) Lost Carrier (2)
SupplicantRestart(3) Supplicant Restart (19)
reauthFailed(4) Reauthentication Failure (20)
authControlForceUnauth(5) Admin Reset (6)
portReInit(6) Port Reinitialized (21)
portAdminDisabled(7) Port Administratively Disabled (22)
When using this attribute, the User Request (1) termination cause
corresponds to the situation in which the session terminated due to
an EAPOL-Logoff received from the Supplicant. When a session is
moved due to roaming, the EAPOL state machines will treat this as a
A Lost Carrier (2) termination cause indicates session termination
due to loss of physical connectivity for reasons other than roaming
between Access Points. For example, if the Supplicant disconnects a
point-to-point LAN connection, or moves out of range of an Access
Point, this termination cause is used. Lost Carrier (2) therefore
equates to a Port Disabled condition in the EAPOL state machines.
A Supplicant Restart (19) termination cause indicates
re-initialization of the Supplicant state machines.
A Reauthentication Failure (20) termination cause indicates that a
previously authenticated Supplicant has failed to re-authenticate
successfully following expiry of the re-authentication timer or
explicit re-authentication request by management action.
Within [IEEE80211], periodic re-authentication may be useful in
preventing reuse of an initialization vector with a given key. Since
successful re-authentication does not result in termination of the
session, accounting packets are not sent as a result of
re-authentication unless the status of the session changes. For
a. The session is terminated due to re-authentication failure. In
this case the Reauthentication Failure (20) termination cause is
b. The authorizations are changed as a result of a successful
re-authentication. In this case, the Service Unavailable (15)
termination cause is used. For accounting purposes, the portion
of the session after the authorization change is treated as a
Where IEEE 802.1X authentication occurs prior to association,
accounting packets are not sent until an association occurs.
An Admin Reset (6) termination cause indicates that the Port has been
administratively forced into the unauthorized state.
A Port Reinitialized (21) termination cause indicates that the Port's
MAC has been reinitialized.
A Port Administratively Disabled (22) termination cause indicates
that the Port has been administratively disabled.
The purpose of this attribute is to make it possible to link together
multiple related sessions. While [IEEE8021X] does not act on
aggregated ports, it is possible for a Supplicant roaming between
Access Points to cause multiple RADIUS accounting packets to be sent
by different Access Points.
Where supported by the Access Points, the Acct-Multi-Session-Id
attribute can be used to link together the multiple related sessions
of a roaming Supplicant. In such a situation, if the session context
is transferred between Access Points, accounting packets MAY be sent
without a corresponding authentication and authorization exchange,
provided that Association has occurred. However, in such a situation
it is assumed that the Acct-Multi-Session-Id is transferred between
the Access Points as part of the Inter-Access Point Protocol (IAPP).
If the Acct-Multi-Session-Id were not unique between Access Points,
then it is possible that the chosen Acct-Multi-Session-Id will
overlap with an existing value allocated on that Access Point, and
the Accounting Server would therefore be unable to distinguish a
roaming session from a multi-link session.
As a result, the Acct-Multi-Session-Id attribute is unique among all
the bridges or Access Points, Supplicants and sessions. In order to
provide this uniqueness, it is suggested that the Acct-Multi-
Session-Id be of the form:
Original AP MAC Address | Supplicant MAC Address | NTP Timestamp
Here "|" represents concatenation, the original AP MAC Address is the
MAC address of the bridge or Access Point at which the session
started, and the 64-bit NTP timestamp indicates the beginning of the
original session. In order to provide for consistency of the Acct-
Multi-Session-Id between roaming sessions, the Acct-Multi-Session-Id
may be moved between Access Points as part of IAPP or another handoff
The use of an Acct-Multi-Session-Id of this form guarantees
uniqueness among all Access Points, Supplicants and sessions. Since
the NTP timestamp does not wrap on reboot, there is no possibility
that a rebooted Access Point could choose an Acct-Multi-Session-Id
that could be confused with that of a previous session.
Since the Acct-Multi-Session-Id is of type String as defined in
[RFC2866], for use with IEEE 802.1X, it is encoded as an ASCII string
of Hex digits. Example: "00-10-A4-23-19-C0-00-12-B2-
The Acct-Link-Count attribute may be used to account for the number
of ports that have been aggregated.
3. RADIUS Authentication
This section describes how attributes defined in [RFC2865],
[RFC2867], [RFC2868], [RFC2869], [RFC3162] and [RFC3579] are used in
IEEE 802.1X authentication.
In IEEE 802.1X, the Supplicant typically provides its identity via an
EAP-Response/Identity message. Where available, the Supplicant
identity is included in the User-Name attribute, and included in the
RADIUS Access-Request and Access-Reply messages as specified in
[RFC2865] and [RFC3579].
Alternatively, as discussed in [RFC3579] Section 2.1., the User-Name
attribute may contain the Calling-Station-ID value, which is set to
the Supplicant MAC address.
3.2. User-Password, CHAP-Password, CHAP-Challenge
Since IEEE 802.1X does not support PAP or CHAP authentication, the
User-Password, CHAP-Password or CHAP-Challenge attributes are not
used by IEEE 802.1X Authenticators acting as RADIUS clients.
3.3. NAS-IP-Address, NAS-IPv6-Address
For use with IEEE 802.1X, the NAS-IP-Address contains the IPv4
address of the bridge or Access Point acting as an Authenticator, and
the NAS-IPv6-Address contains the IPv6 address. If the IEEE 802.1X
Authenticator has more than one interface, it may be desirable to use
a loopback address for this purpose so that the Authenticator will
still be reachable even if one of the interfaces were to fail.
For use with IEEE 802.1X the NAS-Port will contain the port number of
the bridge, if this is available. While an Access Point does not
have physical ports, a unique "association ID" is assigned to every
mobile Station upon a successful association exchange. As a result,
for an Access Point, if the association exchange has been completed
prior to authentication, the NAS-Port attribute will contain the
association ID, which is a 16-bit unsigned integer. Where IEEE
802.1X authentication occurs prior to association, a unique NAS-Port
value may not be available.
For use with IEEE 802.1X, the Framed (2), Authenticate Only (8), and
Call Check (10) values are most commonly used.
A Service-Type of Framed indicates that appropriate 802 framing
should be used for the connection. A Service-Type of Authenticate
Only (8) indicates that no authorization information needs to be
returned in the Access-Accept. As described in [RFC2865], a
Service-Type of Call Check is included in an Access-Request packet to
request that the RADIUS server accept or reject the connection
attempt, typically based on the Called-Station-ID (set to the bridge
or Access Point MAC address) or Calling-Station-ID attributes (set to
the Supplicant MAC address). As noted in [RFC2865], it is
recommended that in this case, the User-Name attribute be given the
value of Calling-Station-Id.
Since there is no value for IEEE 802 media, the Framed-Protocol
attribute is not used by IEEE 802.1X Authenticators.
3.7. Framed-IP-Address, Framed-IP-Netmask
IEEE 802.1X does not provide a mechanism for IP address assignment.
Therefore the Framed-IP-Address and Framed-IP-Netmask attributes can
only be used by IEEE 802.1X Authenticators that support IP address
assignment mechanisms. Typically this capability is supported by
layer 3 devices.
The Framed-Routing attribute indicates the routing method for the
Supplicant. It is therefore only relevant for IEEE 802.1X
Authenticators that act as layer 3 devices, and cannot be used by a
bridge or Access Point.
This attribute indicates the name of the filter list to be applied to
the Supplicant's session. For use with an IEEE 802.1X Authenticator,
it may be used to indicate either layer 2 or layer 3 filters. Layer
3 filters are typically only supported on IEEE 802.1X Authenticators
that act as layer 3 devices.
This attribute indicates the maximum size of an IP packet that may be
transmitted over the wire between the Supplicant and the
Authenticator. IEEE 802.1X Authenticators set this to the value
corresponding to the relevant 802 medium, and include it in the
RADIUS Access-Request. The RADIUS server may send an EAP packet as
large as Framed-MTU minus four (4) octets, taking into account the
additional overhead for the IEEE 802.1X Version (1), Type (1) and
Body Length (2) fields. For EAP over IEEE 802 media, the Framed-MTU
values (which do not include LLC/SNAP overhead) and maximum frame
length values (not including the preamble) are as follows:
Media Framed-MTU Length
========= =============== ==============
Ethernet 1500 1522
802.3 1500 1522
802.4 8174 8193
802.5 (4 Mbps) 4528 4550
802.5 (16 Mbps) 18173 18200
802.5 (100 Mb/s) 18173 18200
802.6 9191 9240
802.9a 1500 1518
802.11 2304 2346
802.12 (Ethernet) 1500 1518
802.12 (Token Ring) 4502 4528
FDDI 4479 4500
NOTE - the Framed-MTU size for IEEE 802.11 media may change as a
result of ongoing work being undertaken in the IEEE 802.11 Working
Group. Since some 802.11 stations cannot handle an MTU larger than
1500 octets, it is recommended that RADIUS servers encountering a
NAS-Port-Type value of 802.11 send EAP packets no larger than 1496
[IEEE8021X] does not include compression support. Therefore this
attribute is not understood by [IEEE8021X] Authenticators.
3.12. Displayable Messages
The Reply-Message attribute, defined in section 5.18 of [RFC2865],
indicates text which may be displayed to the user. This is similar
in concept to the EAP Notification Type, defined in [RFC2284]. As
noted in [RFC3579], Section 2.6.5, when sending a displayable message
to an [IEEE8021X] Authenticator, displayable messages are best sent
within EAP-Message/EAP-Request/Notification attribute(s), and not
within Reply-Message attribute(s).
3.13. Callback-Number, Callback-ID
These attributes are not understood by IEEE 802.1X Authenticators.
3.14. Framed-Route, Framed-IPv6-Route
The Framed-Route and Framed-IPv6-Route attributes provide routes that
are to be configured for the Supplicant. These attributes are
therefore only relevant for IEEE 802.1X Authenticators that act as
layer 3 devices, and cannot be understood by a bridge or Access
3.15. State, Class, Proxy-State
These attributes are used for the same purposes as described in
Vendor-specific attributes are used for the same purposes as
described in [RFC2865]. The MS-MPPE-Send-Key and MS-MPPE-Recv-Key
attributes, described in section 2.4 of [RFC2548], MAY be used to
encrypt and authenticate the RC4 EAPOL-Key descriptor [IEEE8021X,
Section 7.6]. Examples of the derivation of the MS-MPPE-Send-Key and
MS-MPPE-Recv-Key attributes from the master key negotiated by an EAP
method are given in [RFC2716]. Details of the EAPOL-Key descriptor
are provided in Section 4.
When sent along in an Access-Accept without a Termination-Action
attribute or with a Termination-Action attribute set to Default, the
Session-Timeout attribute specifies the maximum number of seconds of
service provided prior to session termination.
When sent in an Access-Accept along with a Termination-Action value
of RADIUS-Request, the Session-Timeout attribute specifies the
maximum number of seconds of service provided prior to re-
authentication. In this case, the Session-Timeout attribute is used
to load the reAuthPeriod constant within the Reauthentication Timer
state machine of 802.1X. When sent with a Termination-Action value
of RADIUS-Request, a Session-Timeout value of zero indicates the
desire to perform another authentication (possibly of a different
type) immediately after the first authentication has successfully
When sent in an Access-Challenge, this attribute represents the
maximum number of seconds that an IEEE 802.1X Authenticator should
wait for an EAP-Response before retransmitting. In this case, the
Session-Timeout attribute is used to load the suppTimeout constant
within the backend state machine of IEEE 802.1X.
The Idle-Timeout attribute is described in [RFC2865]. For IEEE 802
media other than 802.11 the media are always on. As a result the
Idle-Timeout attribute is typically only used with wireless media
such as IEEE 802.11. It is possible for a wireless device to wander
out of range of all Access Points. In this case, the Idle-Timeout
attribute indicates the maximum time that a wireless device may
This attribute indicates what action should be taken when the service
is completed. The value RADIUS-Request (1) indicates that re-
authentication should occur on expiration of the Session-Time. The
value Default (0) indicates that the session should terminate.
For IEEE 802.1X Authenticators, this attribute is used to store the
bridge or Access Point MAC address in ASCII format (upper case only),
with octet values separated by a "-". Example: "00-10-A4-23-19-C0".
In IEEE 802.11, where the SSID is known, it SHOULD be appended to the
Access Point MAC address, separated from the MAC address with a ":".
For IEEE 802.1X Authenticators, this attribute is used to store the
Supplicant MAC address in ASCII format (upper case only), with octet
values separated by a "-". Example: "00-10-A4-23-19-C0".
This attribute contains a string identifying the IEEE 802.1X
Authenticator originating the Access-Request.
For use with IEEE 802.1X, NAS-Port-Type values of Ethernet (15)
Wireless - IEEE 802.11 (19), Token Ring (20) and FDDI (21) may be
This attribute has no meaning when sent to an [IEEE8021X]
In IEEE 802.1X, the Authenticator always transitions to the HELD
state after an authentication failure. Thus this attribute does not
make sense for IEEE 802.1X.
This attribute is sent by a bridge or Access Point to indicate the
nature of the Supplicant's connection. When sent in the Access-
Request it is recommended that this attribute contain information on
the speed of the Supplicant's connection. For 802.11, the following
format is recommended: "CONNECT 11Mbps 802.11b". If sent in the
Accounting STOP, this attribute may be used to summarize statistics
relating to session quality. For example, in IEEE 802.11, the
Connect-Info attribute may contain information on the number of link
layer retransmissions. The exact format of this attribute is
Since IEEE 802.1X provides for encapsulation of EAP as described in
[RFC2284] and [IEEE8021X], the EAP-Message attribute defined in
[RFC3579] is used to encapsulate EAP packets for transmission from
the IEEE 802.1X Authenticator to the Authentication Server. [RFC3579]
Section 2.2. describes how the Authentication Server handles invalid
EAP packets passed to it by the Authenticator.
As noted in [RFC3579] Section 3.1., the Message-Authenticator
attribute MUST be used to protect packets within a RADIUS/EAP
This attribute is used to identify the IEEE 802.1X Authenticator port
which authenticates the Supplicant. The NAS-Port-Id differs from the
NAS-Port in that it is a string of variable length whereas the NAS-
Port is a 4 octet value.
3.30. Framed-Pool, Framed-IPv6-Pool
IEEE 802.1X does not provide a mechanism for IP address assignment.
Therefore the Framed-Pool and Framed-IPv6-Pool attributes can only be
used by IEEE 802.1X Authenticators that support IP address assignment
mechanisms. Typically this capability is supported by layer 3
3.31. Tunnel Attributes
Reference [RFC2868] defines RADIUS tunnel attributes used for
authentication and authorization, and [RFC2867] defines tunnel
attributes used for accounting. Where the IEEE 802.1X Authenticator
supports tunneling, a compulsory tunnel may be set up for the
Supplicant as a result of the authentication.
In particular, it may be desirable to allow a port to be placed into
a particular Virtual LAN (VLAN), defined in [IEEE8021Q], based on the
result of the authentication. This can be used, for example, to
allow a wireless host to remain on the same VLAN as it moves within a
The RADIUS server typically indicates the desired VLAN by including
tunnel attributes within the Access-Accept. However, the IEEE 802.1X
Authenticator may also provide a hint as to the VLAN to be assigned
to the Supplicant by including Tunnel attributes within the Access-
For use in VLAN assignment, the following tunnel attributes are used:
Note that the VLANID is 12-bits, taking a value between 1 and 4094,
inclusive. Since the Tunnel-Private-Group-ID is of type String as
defined in [RFC2868], for use with IEEE 802.1X, the VLANID integer
value is encoded as a string.
When Tunnel attributes are sent, it is necessary to fill in the Tag
field. As noted in [RFC2868], section 3.1:
The Tag field is one octet in length and is intended to provide a
means of grouping attributes in the same packet which refer to the
same tunnel. Valid values for this field are 0x01 through 0x1F,
inclusive. If the Tag field is unused, it MUST be zero (0x00).
For use with Tunnel-Client-Endpoint, Tunnel-Server-Endpoint, Tunnel-
Private-Group-ID, Tunnel-Assignment-ID, Tunnel-Client-Auth-ID or
Tunnel-Server-Auth-ID attributes (but not Tunnel-Type, Tunnel-
Medium-Type, Tunnel-Password, or Tunnel-Preference), a tag field of
greater than 0x1F is interpreted as the first octet of the following
Unless alternative tunnel types are provided, (e.g. for IEEE 802.1X
Authenticators that may support tunneling but not VLANs), it is only
necessary for tunnel attributes to specify a single tunnel. As a
result, where it is only desired to specify the VLANID, the tag field
SHOULD be set to zero (0x00) in all tunnel attributes. Where
alternative tunnel types are to be provided, tag values between 0x01
and 0x1F SHOULD be chosen.
4. RC4 EAPOL-Key Frame
The RC4 EAPOL-Key frame is created and transmitted by the
Authenticator in order to provide media specific key information.
For example, within 802.11 the RC4 EAPOL-Key frame can be used to
distribute multicast/broadcast ("default") keys, or unicast ("key
mapping") keys. The "default" key is the same for all Stations
within a broadcast domain.
The RC4 EAPOL-Key frame is not acknowledged and therefore the
Authenticator does not know whether the Supplicant has received it.
If it is lost, then the Supplicant and Authenticator will not have
the same keying material, and communication will fail. If this
occurs, the problem is typically addressed by re-running the
The RC4 EAPOL-Key frame is sent from the Authenticator to the
Supplicant in order to provision the "default" key, and subsequently
in order to refresh the "default" key. It may also be used to
refresh the key-mapping key. Rekey is typically only required with
weak ciphersuites such as WEP, defined in [IEEE80211].
Where keys are required, an EAP method that derives keys is typically
selected. Therefore the initial "key mapping" keys can be derived
from EAP keying material, without requiring the Authenticator to send
an RC4 EAPOL-Key frame to the Supplicant. An example of how EAP
keying material can be derived and used is presented in [RFC2716].
While the RC4 EAPOL-Key frame is defined in [IEEE8021X], a more
complete description is provided on the next page.
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
| Version | Packet Type | Packet Body Length |
| Type | Key Length |Replay Counter...
| Replay Counter...
| Replay Counter | Key IV...
| Key IV...
| Key IV...
| Key IV...
| Key IV... |F| Key Index |
| Key Signature...
| Key Signature...
| Key Signature...
| Key Signature...
The Version field is one octet. For IEEE 802.1X, it contains the
The Packet Type field is one octet, and determines the type of
packet being transmitted. For an EAPOL-Key Descriptor, the Packet
Type field contains 0x03.
Packet Body Length
The Packet Body Length is two octets, and contains the length of
the EAPOL-Key descriptor in octets, not including the Version,
Packet Type and Packet Body Length fields.
The Type field is a single octet. The Key descriptor is defined
differently for each Type; this specification documents only the
RC4 Key Descriptor (Type = 0x01).
The Key Length field is two octets. If Packet Body Length = 44 +
Key Length, then the Key Field contains the key in encrypted form,
of length Key Length. This is 5 octets (40 bits) for WEP, and 13
octets (104 bits) for WEP-128. If Packet Body Length = 44, then
the Key field is absent, and Key Length represents the number of
least significant octets from the MS-MPPE-Send-Key attribute
[RFC2548] to be used as the keying material. Note that the MS-
MPPE-Send-Key and MS-MPPE-Recv-Key attributes are defined from the
point of view of the Authenticator. From the Supplicant point of
reference, the terms are reversed. Thus the MS-MPPE-Recv-Key on
the Supplicant corresponds to the MS-MPPE-Send-Key on the
Authenticator, and the MS-MPPE-Send-Key on the Supplicant
corresponds to the MS-MPPE-Recv-Key on the Authenticator.
The Replay Counter field is 8 octets. It does not repeat within
the life of the keying material used to encrypt the Key field and
compute the Key Signature field. A 64-bit NTP timestamp MAY be
used as the Replay Counter.
The Key IV field is 16 octets and includes a 128-bit
cryptographically random number.
The Key flag (F) is a single bit, describing the type of key that
is included in the Key field. Values are:
0 = for broadcast (default key)
1 = for unicast (key mapping key)
The Key Index is 7 bits.
The Key Signature field is 16 octets. It contains an HMAC-MD5
message integrity check computed over the EAPOL-Key descriptor,
starting from the Version field, with the Key field filled in if
present, but with the Key Signature field set to zero. For the
computation, the 32 octet (256 bit) MS-MPPE-Send-Key [RFC2548] is
used as the HMAC-MD5 key.
If Packet Body Length = 44 + Key Length, then the Key Field
contains the key in encrypted form, of length Key Length. If
Packet Body Length = 44, then the Key field is absent, and the
least significant Key Length octets from the MS-MPPE-Send-Key
attribute is used as the keying material. Where the Key field is
encrypted using RC4, the RC4 encryption key used to encrypt this
field is formed by concatenating the 16 octet (128 bit) Key-IV
field with the 32 octet MS-MPPE-Recv-Key attribute. This yields a
48 octet RC4 key (384 bits).
5. Security Considerations
Since this document describes the use of RADIUS for purposes of
authentication, authorization, and accounting in IEEE 802.1X-enabled
networks, it is vulnerable to all of the threats that are present in
other RADIUS applications. For a discussion of these threats, see
[RFC2607], [RFC2865], [RFC3162], [RFC3579], and [RFC3576].
Packet modification or forgery
Known plaintext attacks
Key management issues
5.1. Packet Modification or Forgery
RADIUS, defined in [RFC2865], does not require all Access-Requests to
be authenticated or integrity protected. However, IEEE 802.1X is
based on EAP. As described in , Section 3.1.:
The Message-Authenticator attribute MUST be used to protect all
Access-Request, Access-Challenge, Access-Accept, and Access-Reject
packets containing an EAP-Message attribute.
As a result, when used with IEEE 802.1X, all RADIUS packets MUST be
authenticated and integrity protected. In addition, as described in
, Section 4.2.:
To address the security vulnerabilities of RADIUS/EAP,
implementations of this specification SHOULD support IPsec
[RFC2401] along with IKE [RFC2409] for key management. IPsec ESP
[RFC2406] with non-null transform SHOULD be supported, and IPsec
ESP with a non-null encryption transform and authentication
support SHOULD be used to provide per-packet confidentiality,
authentication, integrity and replay protection. IKE SHOULD be
used for key management.
5.2. Dictionary Attacks
As discussed in [RFC3579] Section 4.3.3., the RADIUS shared secret is
vulnerable to offline dictionary attack, based on capture of the
Response Authenticator or Message-Authenticator attribute. In order
to decrease the level of vulnerability, [RFC2865], Section 3
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
In addition, the risk of an offline dictionary attack can be further
mitigated by employing IPsec ESP with a non-null transform in order
to encrypt the RADIUS conversation, as described in [RFC3579],
5.3. Known Plaintext Attacks
Since IEEE 802.1X is based on EAP, which does not support PAP, the
RADIUS User-Password attribute is not used to carry hidden user
passwords. The hiding mechanism utilizes MD5, defined in [RFC1321],
in order to generate a key stream based on the RADIUS shared secret
and the Request Authenticator. Where PAP is in use, it is possible
to collect key streams corresponding to a given Request Authenticator
value, by capturing RADIUS conversations corresponding to a PAP
authentication attempt using a known password. Since the User-
Password is known, the key stream corresponding to a given Request
Authenticator can be determined and stored.
The vulnerability is described in detail in [RFC3579], Section 4.3.4.
Even though IEEE 802.1X Authenticators do not support PAP
authentication, a security vulnerability can still exist where the
same RADIUS shared secret is used for hiding User-Password as well as
other attributes. This can occur, for example, if the same RADIUS
proxy handles authentication requests for both IEEE 802.1X (which may
hide the Tunnel-Password, MS-MPPE-Send-Key and MS-MPPE-Recv-Key
attributes) and GPRS (which may hide the User-Password attribute).
The threat can be mitigated by protecting RADIUS with IPsec ESP with
a non-null transform, as described in [RFC3579], Section 4.2. In
addition, the same RADIUS shared secret MUST NOT be used for both
IEEE 802.1X authentication and PAP authentication.
As noted in [RFC3579] Section 4.3.5., the RADIUS protocol provides
only limited support for replay protection. Replay protection for
RADIUS authentication and accounting can be provided by enabling
IPsec replay protection with RADIUS, as described in [RFC3579],
As with the Request Authenticator, for use with IEEE 802.1X
Authenticators, the Acct-Session-Id SHOULD be globally and temporally
5.5. Outcome Mismatches
[RFC3579] Section 2.6.3. discusses the issues that arise when the EAP
packet encapsulated in an EAP-Message attribute does not agree with
the RADIUS Packet Type. For example, an EAP Success packet might be
encapsulated within an Access-Reject; an EAP Failure might be sent
within an Access-Accept; or an EAP Success or Failure might be sent
within an Access-Challenge.
As described in [RFC3579] Section 2.6.3., these conflicting messages
are likely to cause confusion. To ensure that access decisions made
by IEEE 802.1X Authenticators conform to the wishes of the RADIUS
server, it is necessary for the Authenticator to make the decision
solely based on the authentication result (Access-Accept/Reject) and
not based on the contents of EAP-Message attributes, if present.
5.6. 802.11 Integration
[IEEE8021X] was developed for use on wired IEEE 802 networks such as
Ethernet, and therefore does not describe how to securely adapt IEEE
802.1X for use with 802.11. This is left to an enhanced security
specification under development within IEEE 802.11.
For example, [IEEE8021X] does not specify whether authentication
occurs prior to, or after association, nor how the derived keys are
used within various ciphersuites. It also does not specify
ciphersuites addressing the vulnerabilities discovered in WEP,
described in [Berkeley], [Arbaugh], [Fluhrer], and [Stubbl].
[IEEE8021X] only defines an authentication framework, leaving the
definition of the authentication methods to other documents, such as
Since [IEEE8021X] does not address 802.11 integration issues,
implementors are strongly advised to consult additional IEEE 802.11
security specifications for guidance on how to adapt IEEE 802.1X for
use with 802.11. For example, it is likely that the IEEE 802.11
enhanced security specification will define its own IEEE 802.11 key
hierarchy as well as new EAPOL-Key descriptors.
5.7. Key Management Issues
The EAPOL-Key descriptor described in Section 4. is likely to be
deprecated in the future, when the IEEE 802.11 enhanced security
group completes its work. Known security issues include:
 Default key-only support. IEEE 802.1X enables the derivation of
per-Station unicast keys, known in [IEEE80211] as "key mapping
keys." Keys used to encrypt multicast/broadcast traffic are
known as "default keys". However, in some 802.11
implementations, the unicast keys, derived as part of the EAP
authentication process, are used solely in order to encrypt,
authenticate and integrity protect the EAPOL-Key descriptor, as
described in Section 4. These implementations only support use
of default keys (ordinarily only used with multicast/broadcast
traffic) to secure all traffic, unicast or multicast/broadcast,
resulting in inherent security weaknesses.
Where per-Station key-mapping keys (e.g. unicast keys) are
unsupported, any Station possessing the default key can decrypt
traffic from other Stations or impersonate them. When used
along with a weak cipher (e.g. WEP), implementations supporting
only default keys provide more material for attacks such as
those described in [Fluhrer] and [Stubbl]. If in addition, the
default key is not refreshed periodically, IEEE 802.1X dynamic
key derivation provides little or no security benefit. For an
understanding of the issues with WEP, see [Berkeley], [Arbaugh],
[Fluhrer], and [Stubbl].
 Reuse of keying material. The EAPOL-Key descriptor specified in
section 4 uses the same keying material (MS-MPPE-Recv-Key) both
to encrypt the Key field within the EAPOL-Key descriptor, and to
encrypt data passed between the Station and Access Point.
Multi-purpose keying material is frowned upon, since multiple
uses can leak information helpful to an attacker.
 Weak algorithms. The algorithm used to encrypt the Key field
within the EAPOL-Key descriptor is similar to the algorithm used
in WEP, and as a result, shares some of the same weaknesses. As
with WEP, the RC4 stream cipher is used to encrypt the key. As
input to the RC4 engine, the IV and key are concatenated rather
than being combined within a mixing function. As with WEP, the
IV is not a counter, and therefore there is little protection
As a result of these vulnerabilities, implementors intending to use
the EAPOL-Key descriptor described in this document are urged to
consult the 802.11 enhanced security specification for a more secure
alternative. It is also advisable to consult the evolving literature
on WEP vulnerabilities, in order to better understand the risks, as
well as to obtain guidance on setting an appropriate re-keying
6. IANA Considerations
This specification does not create any RADIUS attributes nor any new
number spaces for IANA administration. However, it does require
assignment of new values to existing RADIUS attributes. These
Attribute Values Required
NAS-Port-Type Token-Ring (20), FDDI (21)
Tunnel-Type VLAN (13)
Acct-Terminate-Cause Supplicant Restart (19)
Reauthentication Failure (20)
Port Reinitialized (21)
Port Administratively Disabled (22)
7.1. Normative References
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
1321, April 1992.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2284] Blunk, L. and J. Vollbrecht, "PPP Extensible
Authentication Protocol (EAP)", RFC 2284, March 1998.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[RFC2867] Zorn, G., Aboba, B. and D. Mitton, "RADIUS Accounting
Modifications for Tunnel Protocol Support", RFC 2867,
[RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J.,
Holdrege, M. and I. Goyret, "RADIUS Attributes for
Tunnel Protocol Support", RFC 2868, June 2000.
[RFC2869] Rigney, C., Willats, W. and P. Calhoun, "RADIUS
Extensions", RFC 2869, June 2000.
[RFC3162] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6",
RFC 3162, August 2001.
[RFC3280] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC
3576, July 2003.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote
Authentication Dial In User Service) Support For
Extensible Authentication Protocol (EAP)", RFC 3579,
[IEEE8021X] IEEE Standards for Local and Metropolitan Area
Networks: Port based Network Access Control, IEEE Std
802.1X-2001, June 2001.
7.2. Informative References
[RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:
Keyed-Hashing for Message Authentication", RFC 2104,
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS
Attributes", RFC 2548, March 1999.
[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and
Policy Implementation in Roaming", RFC 2607, June
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[MD5Attack] Dobbertin, H., "The Status of MD5 After a Recent
Attack." CryptoBytes Vol.2 No.2, Summer 1996.
[IEEE802] IEEE Standards for Local and Metropolitan Area
Networks: Overview and Architecture, ANSI/IEEE Std
[IEEE8021Q] IEEE Standards for Local and Metropolitan Area
Networks: Draft Standard for Virtual Bridged Local
Area Networks, P802.1Q, January 1998.
[IEEE8023] ISO/IEC 8802-3 Information technology -
Telecommunications and information exchange between
systems - Local and metropolitan area networks -
Common specifications - Part 3: Carrier Sense
Multiple Access with Collision Detection (CSMA/CD)
Access Method and Physical Layer Specifications, (also
ANSI/IEEE Std 802.3- 1996), 1996.
[IEEE80211] Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific Requirements
Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications, IEEE Std.
[Berkeley] Borisov, N., Goldberg, I. and D. Wagner, "Intercepting
Mobile Communications: The Insecurity of 802.11", ACM
SIGMOBILE, Seventh Annual International Conference on
Mobile Computing and Networking, July 2001, Rome,
[Arbaugh] Arbaugh, W., Shankar, N. and J.Y.C. Wan, "Your 802.11
Wireless Network has No Clothes", Department of
Computer Science, University of Maryland, College
Park, March 2001.
[Fluhrer] Fluhrer, S., Mantin, I. and A. Shamir, "Weaknesses in
the Key Scheduling Algorithm of RC4", Eighth Annual
Workshop on Selected Areas in Cryptography, Toronto,
Canada, August 2001.
[Stubbl] Stubblefield, A., Ioannidis, J. and A. Rubin, "Using
the Fluhrer, Mantin and Shamir Attack to Break WEP",
2002 NDSS Conference.
8. Table of Attributes
The following table provides a guide to which attributes MAY be sent
and received as part of IEEE 802.1X authentication. L3 denotes
attributes that require layer 3 capabilities, and thus may not be
supported by all Authenticators. For each attribute, the reference
provides the definitive information on usage.
802.1X # Attribute
X 1 User-Name [RFC2865]
2 User-Password [RFC2865]
3 CHAP-Password [RFC2865]
X 4 NAS-IP-Address [RFC2865]
X 5 NAS-Port [RFC2865]
X 6 Service-Type [RFC2865]
7 Framed-Protocol [RFC2865]
L3 8 Framed-IP-Address [RFC2865]
L3 9 Framed-IP-Netmask [RFC2865]
L3 10 Framed-Routing [RFC2865]
X 11 Filter-Id [RFC2865]
X 12 Framed-MTU [RFC2865]
13 Framed-Compression [RFC2865]
L3 14 Login-IP-Host [RFC2865]
L3 15 Login-Service [RFC2865]
L3 16 Login-TCP-Port [RFC2865]
18 Reply-Message [RFC2865]
19 Callback-Number [RFC2865]
20 Callback-Id [RFC2865]
L3 22 Framed-Route [RFC2865]
L3 23 Framed-IPX-Network [RFC2865]
X 24 State [RFC2865]
X 25 Class [RFC2865]
X 26 Vendor-Specific [RFC2865]
X 27 Session-Timeout [RFC2865]
X 28 Idle-Timeout [RFC2865]
X 29 Termination-Action [RFC2865]
X 30 Called-Station-Id [RFC2865]
X 31 Calling-Station-Id [RFC2865]
X 32 NAS-Identifier [RFC2865]
X 33 Proxy-State [RFC2865]
34 Login-LAT-Service [RFC2865]
35 Login-LAT-Node [RFC2865]
36 Login-LAT-Group [RFC2865]
802.1X # Attribute
9. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards- related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
The authors would like to acknowledge Bob O'Hara of Airespace, David
Halasz of Cisco, Tim Moore, Sachin Seth and Ashwin Palekar of
Microsoft, Andrea Li, Albert Young and Dave Bagby of 3Com for
contributions to this document.
12. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Funding for the RFC Editor function is currently provided by the