WDIFF

draft-aboba-radext-wlan-00.txt --> draft-aboba-radext-wlan-01.txt

Network Working Group Bernard Aboba
INTERNET-DRAFT Microsoft
Category: Proposed Standard
<draft-aboba-radext-wlan-00.txt>
3 July 2005
<draft-aboba-radext-wlan-01.txt>
13 February 2006

RADIUS Attributes for WLAN

By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.

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
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

This Internet-Draft will expire on December August 10, 2005. 2006.

Abstract

IEEE 802.11i defines the use of EAP authentication with IEEE 802.11
wireless LANs. Although AAA support is optional within IEEE 802.11i,
it is expected that many IEEE 802.11i authenticators will function as
AAA clients. This document proposes additional attributes for use by
IEEE 802.11 authenticators. The attributes defined in this document
are compatible with those used within Diameter EAP.

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Table of Contents

1. Introduction .......................................... 3
1.1 Terminology ..................................... 3
1.2 Requirements Language ........................... 4
2. RADIUS Attributes ..................................... 4
2.1 Allowed-SSID .................................... 4
2.2 Allowed-Called-Station-Id ....................... 5
2.3 EAP-Key-Name .................................... 5
2.4 EAP-Master-Session-Key .......................... 6
2.5 EAP-Peer-ID ..................................... 7
2.6 6
2.5 EAP-Server-ID ................................... 7
2.6 Mobility-Domain-ID .............................. 8
3. RADIUS Accounting ..................................... 9
3.1 Accounting-EAP-Auth-Method ...................... 9
4. Table of Attributes ................................... 10
5. 9
4. Diameter Considerations ............................... 11
6. 9
5. IANA Considerations ................................... 11
7. 10
6. Security Considerations ............................... 11
7.1 Dictionary Attacks .............................. 12
7.2 Key Management Issues ........................... 12
8. 10
7. References ............................................ 13
8.1 10
7.1 Normative References .................................. 13
8.2 10
7.2 Informative References ................................ 13 11
ACKNOWLEDGMENTS .............................................. 14 11
AUTHORS' ADDRESSES ........................................... 15 12
Intellectual Property Statement .............................. 15 12
Copyright Statement .......................................... 15 12
Disclaimer of Validity ....................................... 16 12

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1. Introduction

In situations where it is desirable to centrally manage
authentication, authorization and accounting (AAA) for IEEE 802.11
wireless LANs, deployment of a backend authentication and accounting
server is desirable. In such situations, it is expected that IEEE
802.11 authenticators will function as AAA clients. This document
defines additional attributes suitable for usage by IEEE 802.11
authenticators acting as AAA clients.

1.1. Terminology

This document uses the following terms:

Access Point (AP)
A Station that provides access to the distribution services
via the wireless medium for associated Stations.

Association
The service used to establish Access Point/Station mapping and
enable Station invocation of the distribution system services.

authenticator
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.

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.

Station (STA)
Any device that contains an IEEE 802.11 conformant medium
access control (MAC) and physical layer (PHY) interface to the
wireless medium (WM).

Supplicant
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.

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1.2. Requirements Language

In this document, several words are used to signify the requirements
of the specification. 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 Attributes

2.1. Allowed-SSID

Description

As described in [KEYFRAME] Section 2.5, it may be desirable for
the RADIUS server to be able to restrict the scope of the AAA-Key
provided to the RADIUS client. In particular, it may be desirable
to restrict the use of the key to a set of authorized SSIDs.

The Allowed-SSID attribute allows the RADIUS server to specify
which SSIDs the user is allowed to access. One or more Allowed-SSID Allowed-
SSID attributes MAY be included an Access-Accept packet. This
attribute is not allowed in other RADIUS packets. A summary of
the Allowed-
SSID Allowed-SSID 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 | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

TBD

Length

>=3

String

The String field contains one or more octets, encoding a single
SSID, as defined in [IEEE-802.11]. If the SSID included in the
Allowed-SSID attribute is not supported by the NAS, the attribute
is silently discarded. UTF-8 encoded 10646 characters are
recommended, but a robust implementation SHOULD support the field
as undistinguished octets.

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2.2. Allowed-Called-Station-Id Allowed-Called-Station-ID

Description

The Allowed-Called-Station-Id Allowed-Called-Station-ID attribute allows the RADIUS server
to specify which Called-Station-Ids Called-Station-IDs the user is allowed to access.
More than one Allowed-Called-Station-Id Allowed-Called-Station-ID attribute may MAY be included
in an Access-Accept packet. This attribute is not allowed in
other RADIUS packets. A summary of the Allowed-Called-Station-ID
Attribute format is shown below. The fields are transmitted from
left to right.

Code

TBD

Length

>=3

String

The String field is one or more octets, containing the layer 2
endpoint that the user's call terminated on. For details of the
encoding, see [RFC2865] and [RFC3580]. Note that this attribute
MUST NOT include the SSID. If the Called-Station-ID included in
the Allowed-Called-Station-ID attribute does not describe a layer
2 endpoint of the NAS, the attribute is silently discarded. A
robust implementation SHOULD support the field as undistinguished
octets.

2.3. EAP-Key-Name

Description

The EAP-Key-Name Attribute Attribute, defined in [RFC4072], contains the key name associated with
the EAP-Master-Session-Key attribute. EAP
Session-ID, as described in [KEYFRAME]. Exactly how this
attribute is used depends on the link layer in question. See [KEYFRAME] for
more discussion.

It should be noted that not all link layers use this name and
existing EAP method implementations do not generate it. An EAP-
Key-Name attribute MAY only be included within Access-Request and

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Key-Name attribute MAY only be included within Access-Request and 13 February 2006

Access-Accept packets. A summary of the EAP-Key-Name Attribute
format is shown below. The fields are transmitted from left to
right.

Code

TBD [DiamEAP]

102 [RFC4072]

Length

>=3

String

The String field, when present, is one or more octets, containing
the EAP Session-ID, as defined in [KEYFRAME] Section 2.4. [KEYFRAME]. Since the NAS
operates as a pass-through in EAP, it cannot know the EAP
Session-ID Session-
ID before receiving it from the RADIUS server. As a result, an
EAP-Key-Name attribute sent in an Access-Request MUST NOT contain
any data. A RADIUS server receiving an Access-Request with a EAP-Key-Name EAP-
Key-Name attribute with non-empty data MUST silently discard the
attribute. In addition, the RADIUS server SHOULD include this
attribute in an Access-Accept only if an empty EAP-
Key-Name EAP-Key-Name
attribute was present in the Access-Request.

2.4. EAP-Master-Session-Key

Description

The EAP-Master-Session-Key Attribute contains an EAP Master
Session Key (MSK), used as keying material for protecting the
communications between the user and the NAS. Exactly how this
keying material is used depends on the link layer in question, and
is beyond the scope of this document. For more discussion on the
MSK, see [RFC3748] and [KEYFRAME]. The EAP-Master-Session-Key
attribute MAY be included in a RADIUS Access-Accept. This
attribute is not allowed in other RADIUS packets.

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Code

TBD [DiamEAP]

Length

>=3

String

The String field is one or more octets, containing an EAP Master
Session Key (MSK), encrypted using AES Key Wrap with 128-bit KEK
as described in [RFC3394] Section 4.1.

The KEK is derived from the RADIUS shared secret (K) and the
Request Authenticator (R) as follows:

KEK = PRF(K, "EAP MSK KEK" || R, 128)

The PRF algorithm is based on PRF+ from IKEv2 shown below ("|"
denotes concatenation)

K = Key, S = Seed, LEN = output length, represented as binary
in a single octet.

PRF (K,S,LEN) = T1 | T2 | T3 | T4 | ... where:

T1 = HMAC-SHA256(K, S | LEN | 0x01)
T2 = HMAC-SHA256(K, T1 | S | LEN | 0x02)
T3 = HMAC-SHA256(K, T2 | S | LEN | 0x03)
T4 = HMAC-SHA256(K, T3 | S | LEN | 0x04)

2.5. EAP-Peer-ID EAP-Peer-ID

Description

The EAP-Peer-ID Attribute contains an the Peer-ID generated by the
EAP method. Exactly how this name is used depends on the link
layer in question. See [KEYFRAME] for more discussion. The EAP-
Peer-ID attribute is only allowed in Access-Request and Access-
Accept packets.

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It should be noted that not all link layers use this name, and
existing EAP method implementations do not generate it. Since the
NAS operates as a pass-through in EAP, it cannot know the EAP-
Peer-ID before receiving it from the RADIUS server. As a result,
an EAP-Peer-ID attribute sent in an Access-Request MUST NOT
contain any data. A home RADIUS server receiving an Access-
Request an EAP-Peer-ID attribute with non-empty data MUST silently

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discard the attribute. In addition, the home RADIUS server SHOULD
include this attribute an Access-Accept only if an empty EAP-Peer-
ID attribute was present in the Access-Request. An EAP-Peer-ID
attribute MUST NOT be included within an Access-Challenge. A summary of the
EAP-Peer-ID Attribute format is shown below. The fields are
transmitted from left to right.

Code

TBD

Length

>=3

String

The String field is one or more octets, containing the EAP Peer-ID
exported by the EAP method. For details, see [KEYFRAME] Appendix
E. A robust implementation SHOULD support the field as
undistinguished octets.

2.6.

2.5. EAP-Server-ID

Description

The EAP-Server-ID Attribute contains the Server-ID generated by
the EAP method. Exactly how this name is used depends on the link
layer in question. See [KEYFRAME] for more discussion. The EAP-
Server-ID attribute is only allowed in Access-Request and Access-
Accept packets.

It should be noted that not all link layers use this name, and
existing EAP method implementations do not generate it. Since the
NAS operates as a pass-through in EAP, it cannot know the EAP-

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Server-ID before receiving it from the RADIUS server. As a
result, an EAP-Server-ID attribute sent in an Access-Request MUST
NOT contain any data. A home RADIUS server receiving in an
Access-Request an EAP-Server-ID attribute with non-empty data MUST
silently discard the attribute. In addition, the home RADIUS
server SHOULD include this attribute an Access-Accept only if an
empty EAP-Server-ID attribute was present in the Access-Request.
An EAP-Server-ID attribute MUST NOT be included within an Access-
Challenge.
A summary of the EAP-Server-ID Attribute format is shown below.

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The fields are transmitted from left to right.

Code

TBD

Length

>=3

String

The String field is one or more octets, containing the EAP Server-
ID exported by the EAP method. For details, see [KEYFRAME]. [KEYFRAME]
Appendix E. A robust implementation SHOULD support the field as
undistinguished octets.

3. RADIUS Accounting

3.1. Accounting-EAP-Auth-Method

2.6. Mobility-Domain-ID

Description

Accounting-EAP-Auth-Method enables a RADIUS client to include the
EAP method utilized within an accounting packet. The semantics of
this

A single Mobility-Domain-ID attribute are identical MAY be included in an
Access-Request or Accounting-Request, in order to that of enable the NAS
to provide the RADIUS server with the Accounting-EAP-Auth-
Method AVP Mobility Domain Identifier,
defined in [DiamEAP], Section 4.1.5. The Accounting-
EAP-Auth-Method attribute is only allowed in Accounting-Request
packets.

The Accounting-EAP-Auth-Method attribute [IEEE-802.11r]. A summary of the Mobility-Domain-ID
Attribute format is shown below. The fields are transmitted from
left to right:

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Type

Code

TBD [DiamEAP]

Length

Vendor-ID

The Vendor-Id is 4 octets and represents the SMI Network
Management Private Enterprise Code of the Vendor in network byte
order, as allocated by IANA. A Vendor-Id of zero is reserved

>=3

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use by the IETF in providing an expanded global EAP Type space.

Vendor-Type WLAN 13 February 2006

String

The Vendor-Type String field is four octets and represents the vendor-
specific EAP method Type. If the Vendor-Id is zero, contains one or more octets, encoding a single
Mobility Domain Identifier as defined in [IEEE-802.11r]. UTF-8
encoded 10646 characters are recommended, but a robust
implementation SHOULD support the Vendor-
Type field is an extension and superset of the existing namespace
for EAP Types. For more information, see [RFC3748], Section 5.7.

4. as undistinguished octets.

3. Table of Attributes

The following table provides a guide to which attributes may be found
in which kinds of packets, and in what quantity.

Access- Access- Access- Access- CoA- CoA/Disconnect
Request Accept Reject Challenge Req # Attribute
0 0+ 0 0 0 TBD Allowed-SSID
0 0+ 0 0 0 TBD Allowed-Called-Station-Id
0-1 0-1 0 0 0 TBD 102 EAP-Key-Name
0 0-1 0 0 0 TBD EAP-Master-Session-Key
0-1 0-1 0 0 0 TBD EAP-Peer-ID
0-1 0-1 0 0 0 TBD EAP-Server-ID

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Actng- Actng-
Request Response # Attribute
0-1 0 0 0 0 TBD Accounting-EAP-Auth-Method Mobility-Domain-ID

The following table defines the meaning of the above table entries.

0 This attribute MUST NOT be present in packet.
0+ Zero or more instances of this attribute MAY be
present in the packet.
0-1 Zero or one instance of this attribute MAY be
present in the packet.

4. Diameter Considerations

Several of the attributes described in this document are already

The EAP-Key-Name attribute is aready defined as a RADIUS attributes
within Diameter EAP. These include EAP-
Key-Name [DiamEAP], EAP-Master-Session-Key [DiamEAP] and Accounting-
EAP-Auth-Method [DiamEAP].

Since Diameter packets are always encrypted, within Diameter EAP the
EAP-Master-Session-Key AVP is always sent in cleartext. However in
RADIUS encryption may not be used, so that the EAP-Master-Session-Key
attribute needs to be encrypted on a hop-by-hop basis, using the
RADIUS shared secret. [RFC4072].

New attributes not previously defined in Diameter EAP include EAP-
Peer-ID, EAP-Server-ID, Allowed-SSID Allowed-SSID, Allowed-Called-Station-ID, and Allowed-Called-Station-ID.
Mobility-Domain-ID. When used with Diameter EAP, all of these
attributes should be considered optional.

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5. IANA Considerations

This specification does not create any new registries.

This specification requires assignment of a RADIUS attribute types
for the following attributes:

Attribute Type
========= ====
Allowed-SSID TBD
Allowed-Called-Station-Id TBD
EAP-Peer-ID TBD
EAP-Server-ID TBD

7.
Mobility-Domain-ID TBD

6. Security Considerations

Since this document describes the use of RADIUS for purposes of
authentication, authorization, and accounting in WLANs, it is

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vulnerable to all of the threats that are present in other RADIUS
applications. For a discussion of these threats, see [RFC2607],
[RFC2865], [RFC3162], [RFC3576], [RFC3579], and [RFC3580].

However, there are several additional threats worth discussing:

Dictionary attacks
Key management issues

7.1. 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. The use
of AES Keywrap to protect the EAP-Master-Session-Key attribute does
not mitigate this vulnerability, since an attacker obtaining the
RADIUS shared secret will have all the information necessary to
obtain the EAP MSK.

In order to decrease the level of vulnerability, [RFC2865], Section 3
recommends:

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.

In addition, the risk of an offline dictionary attack can be reduced
by employing IPsec ESP with non-null transform in order to encrypt
the RADIUS conversation, as described in [RFC3579], Section 4.2.

7.2. Key Management Issues

As detailed in [Housley], AAA protocols transporting keys are
required to protect them against disclosure to third parties. In
Diameter EAP [DiamEAP] this is accomplished by use of the Diameter
re-direct mechanism, enabling transport of keys directly between the
NAS and the home AAA server.

Diameter redirect relies on scalable mechanisms for establishment of
security associations between the NAS and home AAA server, such as
provisioning of certificates. While this can be accommodated by use
of RADIUS over IPsec, as specified in [RFC3579], this is not yet
widely deployed. Given this, it does not appear practical at this
time to define an equivalent re-direct mechanism within RADIUS and
require its use with the attributes defined in this document.

Accordingly, the keying material included in the EAP-Master-Session-

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Key attribute is encrypted on a hop-by-hop basis and it is accessible
vulnerable to
RADIUS proxies in all of the path. The security requirements defined in
[Housley] can therefore only be satisfied if RADIUS clients threats that are
configured to talk directly to present in other RADIUS servers without proxies.

8.
applications. For a discussion of these threats, see [RFC2607],
[RFC2865], [RFC3162], [RFC3576], [RFC3579], and [RFC3580].

7. References

8.1.

7.1. Normative references

[IEEE-802.11]
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. 802.11-2003, 2003.

[IEEE-802.11r]
Draft Amendment to Standard for 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: Amendment 2: Fast BSS
Transition, IEEE P802.11r/D1.2, February 2006.

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

[RFC2865] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865, June
2000.

[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption

Aboba Proposed Standard (AES)
Key Wrap Algorithm", RFC 3394, September 2002. [Page 10]

INTERNET-DRAFT RADIUS Attributes for WLAN 13 February 2006

[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.

[DiamEAP]

[RFC4072] Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", draft-ietf-aaa-
eap-10.txt, Internet draft (work in progress), May RFC 4072, August
2005.

[KEYFRAME]
Aboba, B., Simon, D., Arkko, J., Eronen, P. and H. Levkowetz,
"EAP Key Management Framework", draft-ietf-eap-keying-06.txt,
March 2005.

8.2. draft-ietf-eap-keying-10.txt,
February 2006.

7.2. Informative references

[Housley] Housley, R. and B. Aboba, "AAA Key Management", draft-housley-
aaa-key-mgmt-00.txt, Internet draft (work in progress), June
2005.

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

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[IEEE-802.1X]
IEEE Standards for Local and Metropolitan Area Networks: Port
based Network Access Control, IEEE Std 802.1X-2004, December
2004.

[IEEE-802.11i]
Institute of Electrical and Electronics Engineers, "Supplement
to Standard for Telecommunications and Information Exchange
Between Systems - LAN/MAN Specific Requirements - Part 11:
Wireless LAN Medium Access Control (MAC) and Physical Layer
(PHY) Specifications: Specification for Enhanced Security",
IEEE 802.11i, July 2004.

[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999.

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

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

[RFC3575] Aboba, B., "IANA Considerations for RADIUS", RFC 3575, July
2003.

[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 Support for Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.

[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service
(RADIUS) Usage Guidelines", RFC 3580, September 2003.

[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., Arkko, J.,
"Diameter Base Protocol", RFC 3588, September 2003.

Acknowledgments

The authors would like to acknowledge Dorothy Stanley of Agere, and
Ashwin Palekar of Microsoft.

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Authors' Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

EMail: bernarda@microsoft.com
Phone: +1 425 706 6605
Fax: +1 425 936 7329

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Disclaimer of Validity

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Copyright (C) The Internet Society (2005). (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.

Acknowledgment

Funding for the RFC Editor function is currently provided by the
Internet Society.

Open issues

Open issues relating to this specification are tracked on the
following web site:

http://www.drizzle.com/~aboba/RADEXT/

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