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Network Working Group                                      Bernard Aboba
INTERNET-DRAFT                                                 Tim Moore
Category: Informational                                        Microsoft
6 April 2002

                A Model for Context Transfer in IEEE 802

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet- Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at

The list of Internet-Draft Shadow Directories can be accessed at

Copyright Notice

Copyright (C) The Internet Society (2002).  All Rights Reserved.


The IEEE 802 Inter-Access Point Protocol (IAPP), under development
within the IEEE 802.11 TgF working group, supports the transfer of
context between access points implementing IEEE 802 technology.  This
document describes how IAPP can be used to support transfer of
authentication, authorization and accounting (AAA) context between
devices supporting IEEE 802.1X network port authentication.  This
specification is currently being developed within the IEEE 802.11 TgF
working group and is being presented to the IETF for informational

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1.  Introduction

[IEEE8021X] enables authenticated access to [IEEE802] media, including
Ethernet [IEEE8023], Token Ring, and 802.11 wireless LANs [IEEE80211].
Although Authentication, Authorization and Accounting (AAA) support is
optional within IEEE 802.1X, it is expected that many IEEE 802.1X
Authenticators will function as AAA clients. Behavior of IEEE 802.1X
Authenticators acting as RADIUS clients is described in [Congdon].

The IEEE 802 Inter-Access Point Protocol (IAPP), under development
within the IEEE 802.11 TgF working group, supports the transfer of
context between access points implementing IEEE 802 technology.  This
document describes how IAPP can be used to support transfer of
authentication, authorization and accounting (AAA) context between
devices supporting IEEE 802.1X network port authentication [IEEE8021X].

In terms of organization, this document first develops a general model
for AAA context transfer.  Central to the model is the notion of a
"correct" context transfer -- a transfer resulting in the same context
on the new access point as would have resulted had a AAA conversation
been completed.

The circumstances in which "correct" context transfer can be achieved
are analyzed -- demonstrating that this can only be achieved in a
limited set of circumstances. As a result, it is suggested that context
transfer protocols restrict the domain of applicability to scenarios
involving a high degree of homogeneity.

For example, layer 2 context transfer solutions are most likely to be
successful transferring context within media families, such as IEEE 802.
While the IAPP protocol is expected to be used primarily for transfer of
context between IEEE 802.11 access points, it is also possible for it to
be used to transfer context between access points supporting other IEEE
802 media, such as IEEE 802.15 or 802.16. Where context transfer between
dissimilar media is required, then higher layer homogeneity is needed.
This can be achieved, for example, by restricting applicability to
access points supporting Mobile IP.

1.1.  Terminology

This document uses the following terms:

          An Authenticator is an entity that require 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.

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Authentication Server
          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

          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, the key words "MAY", "MUST,  "MUST  NOT",  "OPTIONAL",
"RECOMMENDED",  "SHOULD",  and  "SHOULD  NOT",  are to be interpreted as
described in [RFC2119].

2.  Context transfer model

In attempting to transfer context between devices, the first task is to
understand how "context" is defined, and what the goal of the context
transfer is. For the purpose of this document "context" will refer to
the set of state defining the service to be provided to the user.

To date, a number of protocols have been proposed for defining and
managing services provided on a per-user basis. RADIUS, defined in
[RFC2865], [RFC2866], [RFC2867], [RFC2868],[RFC2869], and [RFC3162] is a
first-generation protocol for Authentication, Authorization and
Accounting (AAA). Diameter and COPS have also been proposed for use in

In each of these protocols, exchanges are used to establish, and
possibly to remove, state from devices. In thinking about transfer of
context initially established through such protocols, we propose the
"Equivalency Principle":

   For context established via protocol exchanges, transfer of context
   to a new device can be accomplished by transferring the protocol
   exchanges that created the context on the original device, and
   processing them on the new device. For such a context transfer to be
   successful, the the state created on the new device by processing

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   such an exchange MUST be equivalent to the state that would have been
   created by having the new device engage in a fresh protocol

For the equivalency principle to be satisfied, it is necessary for the
new device to be able to process the protocol exchanges from the old
device, and for those exchanges to result in the same state on the new
device. This requires that the protocol messages completely describe the
context to be created on the device, and that the effect of processing
these messages not depend on state that exists uniquely on the old
device, but may not exist on the new device.

For example, a protocol message that describes the state to be attained
in terms of deltas from a previous state would not be suitable for use
in context transfer, since the effect of the protocol message would
differ depending on the previous device state. Similarly, if a protocol
message were conditionally executed based on dynamic data, such as the
number of users on the device, then the message might have a different
effect on the new device than on the old device.

To a large extent, AAA protocols meet the criteria, since the desired
device state is completely described by the authorizations. Conditional
execution, if it occurs, is usually confined to the AAA server.

The messages that establish service context differ, depending on the AAA
protocol that is being considered.  Within RADIUS, service context is
only established via an Access-Accept. Access-Reject messages do not
establish context since their purpose is to deny access. Similarly,
Access-Challenge messages do not establish context since they represent
an intermediate stage within the authentication conversation.  Since
only one RADIUS message (Access-Accept) establishes service context, to
re-establish context on a new device, to first order it is only
necessary to transfer Access-Accept messages to the new device, and
process them as if they were sent by the RADIUS server.

Note that since only one RADIUS message type can establish context, the
message type need not be included explicitly, since it is implicit. As a
result, devices supporting transfer of RADIUS context need only transfer
attributes, not the entire RADIUS message.

2.1.  "Correct" context transfer

Given this model for context establishment, it is worthwhile to examine
when the transfer of context between devices produces a "correct"

One way to define correctness in a context transfer is that the transfer
establishes on the new device the same context as would have been

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created had the new device completed a AAA conversation with the
authentication server.  Ideally, a context transfer should only succeed
if it is "correct" in this way. If a successful context transfer would
establish "incorrect" state, it would be preferable for such a transfer
to fail.

Not all AAA and access device configurations are capable of meeting this
definition of "correctness".  Implicit within our context transfer model
is trust between devices transferring context.  Since the new device
acts on the context transfer as though it had been instructed by a
trusted AAA server, it is necessary for the new device to trust the old

In transfer of context across administrative domains, such a level of
trust may not be possible or appropriate. As a result, a context
transfer may fail even in situations where the devices are homogeneous,
due to lack of trust between administrative domains.

If the deployment is heterogeneous, it also may be difficult to meet
this definition of correctness.  In these situations, AAA servers often
perform conditional evaluation, in which the authorizations returned in
an Access-Accept message are contingent on characteristics of the AAA
client or the user.  For example, in a heterogeneous deployment, the AAA
server might return different authorizations depending on the type of
device making the request, in order to make sure that the requested
service is consistent with device capabilities.

If differences between the new and old device would result in the AAA
server sending a different set of messages to the new device than were
sent to the old device, then a context transfer between the devices
cannot be carried out correctly.

For example, if some access points within a deployment support dynamic
VLANs while others do not, then attributes present in the Access-Request
(such as the NAS-IP-Address, NAS-Identifier, Vendor-Identifier, etc.)
could be examined to determine when VLAN attributes will be returned, as
described in [Condgon]. VLAN support is defined in [IEEE8021Q].

In practice, this limits the situations in which context transfer can be
expected to be successful. Where the deployed devices implement the same
set of services, it may be possible to transfer context successfully.
However, where the supported services differ between devices, the
context transfer may not succeed. For example, [RFC2865], section 1.1

   "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

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   for ARAP.  A NAS MUST treat a RADIUS access-accept authorizing an
   unavailable service as an access-reject instead."

Note that this behavior is only applies to attributes that are known,
but not implemented. For attributes that are unknown, section of 5 of
[RFC2865] states:

   "A RADIUS server MAY ignore Attributes with an unknown Type.  A
   RADIUS client MAY ignore Attributes with an unknown Type."

Obeying the Equivalency Principle, if a new device is provided with
RADIUS context for a known but unavailable service, then it MUST process
this context the same way it would handle a RADIUS Access-Accept
requesting an unavailable service. This MUST cause the context transfer
to fail. However, if a new device is provided with RADIUS context that
indicates an unknown attribute, then this attribute MAY be ignored.

Although it may seem somewhat counter-intuitive, failure is indeed the
"correct" result where a known but unsupported service is requested.
Presumably a correctly configured AAA server would not request that a
device carry out a service that it does not implement. This implies that
if the new device were to complete a AAA conversation that it would be
likely to receive different service instructions than those present in
the context transfer. In such a case, failure of the context transfer is
the desired result. This will cause the new device to go back to the AAA
server in order to receive the appropriate service definition.

Thus in practice, context transfer is most likely to be successful
within a homogeneous device deployment within a single administrative
domain. For example, where all the devices support IEEE 802.1X, success
is possible, as long as the same set of security services are supported.
For example, it would not be advisable to attempt to transfer context
between an 802.11 access point implementing WEP to an 802.15 access
point without security support. The correct result of such a transfer
would be a failure, since if the transfer were blindly carried out, then
the user would be moved from a secure to an insecure channel without
permission from the AAA server. Thus the definition of a "known but
unsupported service" MUST encompass requests for unavailable security
services. This includes vendor-specific attributes related to security,
such as those described in [RFC2548].

In general, context transfers between media with different service
models should not be expected to be successful. For example, attempts to
transfer context between cellular devices and 802.11 access points
cannot be "correct" within this model, unless the cellular access points
implement the same set of services as the 802.11 access points. Where
the implemented services differ, the correct behavior would be for such
context transfers to fail, and for the 802.11 AP to pick up the correct

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service definition by going back to the AAA server. Thus while attempted
context transfers between heterogeneous technologies may fail, context
transfers between homogeneous devices have a higher probability of

2.2.  Context handling

AAA is not mandatory to implement for IEEE 802.1X Authenticators.  The
IEEE 802.1X [IEEE8021X] specification provides guidelines for usage of
RADIUS [RFC2865], a revised version of which can be found in [Congdon].
However, support for other protocols is feasible. Since a IEEE 802.1X
Authenticator may support zero or more AAA protocols and implementation
of AAA is non-mandatory, an IEEE 802.1X Authenticator cannot be assumed
to implement any particular AAA protocol.

Therefore it is important that the context transfer protocol be agnostic
with respect to AAA protocols.  If two devices share support for a given
AAA protocol, then the context transfer mechanism should enable the
devices to interoperate. One way to accomplish this is to enable the
context transfer mechanism to support multiple AAA protocols within the
same message. This allows a device that speaks multiple protocols to
interoperate with a device that only supports one of them.

Through addition of a AAA Information Element, and unique sub-elements
for each AAA protocol, it is possible to support transfer of context for
multiple AAA protocols within the same message.  Assigning only one
Information Element for AAA ensures against exhaustion of the IAPP
element space. Since the number of AAA attributes may be substantial,
assignment of Information Elements to individual attributes is to be

Packaging each AAA protocol message within its own individual sub-
element enables compatibility with the definition of correctness
described earlier. Within IAPP, a device that receives Information
Elements or sub-elements that it does not support will ignore those
elements, and process those that it does support.

However, as described earlier, our model of context transfer requires
that if a device supports a AAA protocol, that transferred AAA messages
MUST be processed according to the rules of the protocol. For RADIUS,
this implies that the context transfer MUST fail if known but
unavailable services are requested, but that unknown attributes MAY be
ignored. As a result, individual RADIUS attributes MUST NOT be encoded
as Information Elements or sub-elements within IAPP. Rather, RADIUS
attribues are encoded as a unit within the RADIUS sub-element.  This
enables  the correct processing to occur. While a device may ignore an
entire Information Element or sub-element, once the Information Element
or sub-element is recognized it must be processed in its entirety.

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Among other things, this approach enables the context transfer operation
to be independent of the supported AAA protocol.  For example, a device
supporting both Diameter and RADIUS could include sub-elements for both
protocols. This would enable transfer of context to a new device
supporting either protocol.

2.3.  Information Element format

Within IAPP, Information Elements have the following structure:

 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
|       Element Identifier        |            Length           |
|                          Information...

Element Identifier

   The Element Identifier field is two octets. It identifies the
   enclosed Information Element.

   TBD - Element Identifier for AAA


   The Length field is two octets. It encodes the length of the
   Information Element, including the Element Identifier, Length and
   Information fields.


   The Information field is variable length. It encodes the Information

AAA sub-elements are encoded within the Information field as follows:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|       Organization Unique Identifier            |     Type    |
|                             Data...

Organization Unique Identifier (OUI)

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   The OUI is a three octet field, encoding the Organization Unique
   Identifier. An OUI of zero is used for standardized sub-elements.
   Non-zero OUIs can be used to support vendor-specific sub-elements.


   The type field is one octet, and represents the AAA protocol type:

   1 = RADIUS
   2 = Diameter


   The Data field is of variable length, and contains the context to be
   transferred. For RADIUS this consists of a list of attributes.

2.4.  Usage guidelines for the RADIUS sub-element

RADIUS context is established solely by Access-Accept messages, and
therefore the bulk of RADIUS attributes within the RADIUS sub-element
are those that may be included within an Access-Accept.

There are three classes of exception:

[1]  Authentication attributes not relevant to IEEE 802 or to IEEE
     802.1X context transfer.

[2]  Accounting attributes such as the Acct-Authentic and Acct-Multi-
     SessionId accounting attributes.

[3]  Attributes included within an Access Request that provide
     additional information relating to the previous session on the old
     AP. This includes NAS-IP-Address, NAS-IPv6-Address, NAS-Port,NAS-
     Identifier, Called-Station-Id, Calling-Station-Id, and NAS-Port-Id.

The attributes allowable for use with transfers of IEEE 802.1X context
are described in Appendix A.

As noted in [Congdon], some attributes are not relevant to IEEE 802,
while others that are relevant are not useful for context transfer.  For
example, where an IAPP protocol provides support for integrity
protection, transfer of an additional integrity check (Message-
Authenticator attribute) is not  necessary.  Similarly, since the IEEE
802.1X backend state machine is driven purely by the authentication
outcome, not by the contents of the EAP-Message attribute, transferring
this attribute is not necessary.

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Acct-Authentic encodes the authentication technique utilized on the old
access point: RADIUS, Local or Remote. A value of RADIUS denotes
authentication against a backend RADIUS server; Local means that the
user authenticated against the local database on the old device; Remote
means that a AAA protocol other than RADIUS was used.

Typically, it does not make sense to transfer context of sessions
established by local authentication.  This violates the Equivalency
Principle because context established via local authentication will not
in general be the same as the context that would be established by
carrying out a conversation with the AAA server.  In order to guard
against inappropriate context transfers, the new device MUST examine the
authentication status prior to deciding to accept the context transfer.

Acct-Multi-SessionId enables linkage of accounting records from related
sessions. As described in [Congdon], it is possible to maintain the same
Acct-Multi-SessionId as a user moves between devices.  To enable this,
it is necessary to include the Acct-Multi-SessionId in the context

3.  Security considerations

3.1.  Trust issues

Implicit within our context transfer model is trust between devices
engaging in a context transfer.  Since the new device will act on the
context transfer as though it had been given the service instructions by
a trusted AAA server, it is necessary for the new device to trust the
old device, at least sufficiently to allow transfer of AAA context.

In transfer of context across administrative domains, such a level of
trust may not be possible or appropriate. Therefore it is possible for
context transfer to fail even in situations where the devices are
homogeneous, due to lack of trust between administrative domains.

Note however, that even where the required trust exists, it SHOULD NOT
extend to enabling the new Access Point to obtain the keys used for
encrypting traffic on the old Access Point. This would enable a rogue
new Access Point to decrypt traffic previously captured on the old
Access Point. A variety of mechanisms can be used to prevent this and a
specific mechanism is not mandated in this specification. For example,
it is possible for the old Access Point to transfer to the new Access
Point a "transfer key" derived via a one-way function from the old key,
so that the old key cannot be easily obtained from the "transfer key".
Alternatively, where perfect forward secrecy (PFS) is desired, a new key
can be derived that does not depend on the old key.

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Another implication of the "Equivalency Principle" is that the context
transfer protocol SHOULD provide the same level of security as the AAA
protocol whose context is being transferred.  For example, AAA protocol
messages may include attributes requiring confidentiality.  This
includes user passwords, encryption keys, or tunnel passwords. In order
to transfer these attributes securely, confidentiality is required.
Similarly, where the AAA protocol is using IPsec [RFC2401] to provide
confidentiality, it does not make sense for the context transfer
protocol to use a less secure mechanism, such as the shared secret-based
hiding described in [RFC2865].

4.  IANA Considerations

This specification does not create any RADIUS attributes nor any new
number spaces for IANA administration.

5.  References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", RFC 2119, March, 1997.

[RFC2401] Kent, S., Atkinson, R., "Security Architecture for the
          Internet Protocol", RFC 2401, November 1998.

[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS attributes", RFC
          2548, March 1999.

[RFC2865] Rigney, C., Rubens, A., Simpson, W., Willens, S.,  "Remote
          Authentication Dial In User Service (RADIUS)", RFC 2865, June

[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.

[RFC2867] Zorn, G., Mitton, D., Aboba, B., "RADIUS Accounting
          Modifications for Tunnel Protocol Support", RFC 2867, June

[RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M.,
          Goyret, I., "RADIUS Attributes for Tunnel Protocol Support",
          RFC 2868, June 2000.

[RFC2869] Rigney, C., Willats, W., Calhoun, P., "RADIUS Extensions", RFC
          2869, June 2000.

[RFC3162] Aboba, B., Zorn, G., Mitton, D.,"RADIUS and IPv6", RFC 3162,
          August 2001.

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[Congdon] Congdon, P., Et al. "IEEE 802.1X Usage Guidelines", Internet
          draft (work in progress), draft-congdon-radius-8021x-17.txt,
          November 2001.

[IEEE802] IEEE Standards for Local and Metropolitan Area Networks:
          Overview and Architecture, ANSI/IEEE Std 802, 1990.

          IEEE Standards for Local and Metropolitan Area Networks: Draft
          Standard for Virtual Bridged Local Area Networks, P802.1Q/D8,
          January 1998.

          IEEE Standards for Local and Metropolitan Area Networks: Port
          based Network Access Control, IEEE Std 802.1X-2001, June 2001.

          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.

          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. 802.11-1997, 1997.

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Appendix A - Table of Attributes

The following table provides a guide to which attributes are sent and
received as part of IEEE 802.1X authentication, and which attributes are
considered part of the "context" to be transferred during roaming. L3
denotes attributes that will be understood only by switches or access
points implementing Layer 3 capabilities.

802.1X     Context    #    Attribute
  X           X       1   User-Name [RFC2865]
                      2   User-Password [RFC2865]
                      3   CHAP-Password [RFC2865]
  X           R       4   NAS-IP-Address [RFC2865]
  X           R       5   NAS-Port [RFC2865]
  X           X       6   Service-Type [RFC2865]
                      7   Framed-Protocol [RFC2865]
                      8   Framed-IP-Address [RFC2865]
                      9   Framed-IP-Netmask [RFC2865]
  L3          X      10   Framed-Routing [RFC2865]
  X           X      11   Filter-Id [RFC2865]
  X           X      12   Framed-MTU [RFC2865]
                     13   Framed-Compression [RFC2865]
  L3          X      14   Login-IP-Host [RFC2865]
  L3          X      15   Login-Service [RFC2865]
  L3          X      16   Login-TCP-Port [RFC2865]
  X           X      18   Reply-Message [RFC2865]
                     19   Callback-Number [RFC2865]
                     20   Callback-Id [RFC2865]
  L3          X      22   Framed-Route [RFC2865]
  L3          X      23   Framed-IPX-Network [RFC2865]
  X           X      24   State [RFC2865]
  X           X      25   Class [RFC2865]
  X           X      26   Vendor-Specific [RFC2865]
  X           X      27   Session-Timeout [RFC2865]
  X           X      28   Idle-Timeout [RFC2865]
  X           X      29   Termination-Action [RFC2865]
  X           R      30   Called-Station-Id [RFC2865]
  X           R      31   Calling-Station-Id [RFC2865]
  X           R      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

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802.1X        #   Attribute
  L3          X      37   Framed-AppleTalk-Link [RFC2865]
  L3          X      38   Framed-AppleTalk-Network [RFC2865]
  L3          X      39   Framed-AppleTalk-Zone [RFC2865]
  X                  40   Acct-Status-Type [RFC2866]
  X                  41   Acct-Delay-Time [RFC2866]
  X                  42   Acct-Input-Octets [RFC2866]
  X                  43   Acct-Output-Octets [RFC2866]
  X                  44   Acct-Session-Id [RFC2866]
  X           X      45   Acct-Authentic [RFC2866]
  X                  46   Acct-Session-Time [RFC2866]
  X                  47   Acct-Input-Packets [RFC2866]
  X                  48   Acct-Output-Packets [RFC2866]
  X                  49   Acct-Terminate-Cause [RFC2866]
  X           X      50   Acct-Multi-Session-Id [RFC2866]
                     51   Acct-Link-Count [RFC2866]
  X                  52   Acct-Input-Gigawords [RFC2869]
  X                  53   Acct-Output-Gigawords [RFC2869]
  X                  55   Event-Timestamp [RFC2869]
                     60   CHAP-Challenge [RFC2865]
  X           X      61   NAS-Port-Type [RFC2865]
                     62   Port-Limit [RFC2865]
                     63   Login-LAT-Port [RFC2865]
  X           X      64   Tunnel-Type [RFC2868]
  X           X      65   Tunnel-Medium-Type [RFC2868]
  L3          X      66   Tunnel-Client-Endpoint [RFC2868]
  L3          X      67   Tunnel-Server-Endpoint [RFC2868]
  L3          X      68   Acct-Tunnel-Connection [RFC2867]
  L3          X      69   Tunnel-Password [RFC2868]
                     70   ARAP-Password [RFC2869]
                     71   ARAP-Features [RFC2869]
                     72   ARAP-Zone-Access [RFC2869]
                     73   ARAP-Security [RFC2869]
                     74   ARAP-Security-Data [RFC2869]
                     75   Password-Retry [RFC2869]
                     76   Prompt [RFC2869]
  X                  77   Connect-Info [RFC2869]
  X                  78   Configuration-Token [RFC2869]
  X                  79   EAP-Message [RFC2869]
  X                  80   Message-Authenticator [RFC2869]
  X           X      81   Tunnel-Private-Group-ID [RFC2868]
  L3          X      82   Tunnel-Assignment-ID [RFC2868]
  X           X      83   Tunnel-Preference [RFC2868]
                     84   ARAP-Challenge-Response [RFC2869]
802.1X        #   Attribute

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802.1X        #   Attribute
  X                  85   Acct-Interim-Interval [RFC2869]
  X                  86   Acct-Tunnel-Packets-Lost [RFC2867]
  X           R      87   NAS-Port-Id [RFC2869]
                     88   Framed-Pool [RFC2869]
  L3          X      90   Tunnel-Client-Auth-ID [RFC2868]
  L3          X      91   Tunnel-Server-Auth-ID [RFC2868]
  X           R      95   NAS-IPv6-Address [RFC3162]
                     96   Framed-Interface-Id [RFC3162]
  L3          X      97   Framed-IPv6-Prefix [RFC3162]
  L3          X      98   Login-IPv6-Host [RFC3162]
  L3          X      99   Framed-IPv6-Route [RFC3162]
  L3          X     100   Framed-IPv6-Pool [RFC3162]
802.1X     Context    #    Attribute


802.1X    = Allowed for use with IEEE 802.1X
Context   = Transferred during roaming if available
L3        = implemented only on switches/access points with Layer 3
R         = Attributes acceptable for context transfer that are
            included only within an Access-Request


The authors would like to acknowledge Bob O'Hara of Informed Technology
and Dave Bagby of 3Com for contributions to this document.

Authors' Addresses

Bernard Aboba
Tim Moore
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

EMail: {bernarda, timmoore}@microsoft.com
Phone: +1 425 882 8080
Fax:   +1 425 936 7329

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