Network Working Group G. Zorn

Network Working Group G. Zorn
Request for Comments: 2548 Microsoft Corporation
Category: Informational March 1999

Microsoft Vendor-specific RADIUS Attributes

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 Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

This document describes the set of Microsoft vendor-specific RADIUS
attributes. These attributes are designed to support Microsoft
proprietary dial-up protocols and/or provide support for features
which is not provided by the standard RADIUS attribute set [3]. It
is expected that this memo will be updated whenever Microsoft defines
a new vendor-specific attribute, since its primary purpose is to
provide an open, easily accessible reference for third-parties
wishing to interoperate with Microsoft products.

1. Specification of Requirements

In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT" are to be interpreted as
described in [2].

2. Attributes

The following sections describe sub-attributes which may be
transmitted in one or more RADIUS attributes of type Vendor-Specific
[3]. More than one sub-attribute MAY be transmitted in a single
Vendor-Specific Attribute; if this is done, the sub-attributes SHOULD
be packed as a sequence of Vendor-Type/Vendor-Length/Value triples
following the inital Type, Length and Vendor-ID fields. The Length
field of the Vendor-Specific Attribute MUST be set equal to the sum
of the Vendor-Length fields of the sub-attributes contained in the
Vendor-Specific Attribute, plus six. The Vendor-ID field of the
Vendor-Specific Attribute(s) MUST be set to decimal 311 (Microsoft).

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

2.1. Attributes for Support of MS-CHAP Version 1

2.1.1. Introduction

Microsoft created Microsoft Challenge-Handshake Authentication
Protocol (MS-CHAP) [4] to authenticate remote Windows workstations,
providing the functionality to which LAN-based users are accustomed.
Where possible, MS-CHAP is consistent with standard CHAP [5], and the
differences are easily modularized. Briefly, the differences between
MS-CHAP and standard CHAP are:

* MS-CHAP is enabled by negotiating CHAP Algorithm 0x80 in LCP
option 3, Authentication Protocol.

* The MS-CHAP Response packet is in a format designed for
compatibility with Microsoft Windows NT 3.5, 3.51 and 4.0,
Microsoft Windows95, and Microsoft LAN Manager 2.x networking
products. The MS-CHAP format does not require the authenticator
to store a clear-text or reversibly encrypted password.

* MS-CHAP provides an authenticator-controlled authentication
retry mechanism.

* MS-CHAP provides an authenticator-controlled password changing
mechanism.

* MS-CHAP defines an extended set of reason-for-failure codes,
returned in the Failure packet Message field.

The attributes defined in this section reflect these differences.

2.1.2. MS-CHAP-Challenge

Description

This Attribute contains the challenge sent by a NAS to a Microsoft
Challenge-Handshake Authentication Protocol (MS-CHAP) user. It
MAY be used in both Access-Request and Access-Challenge packets.

A summary of the MS-CHAP-Challenge Attribute format is shown below.
The fields are transmitted from left to right.

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
11 for MS-CHAP-Challenge.

Vendor-Length
> 2

String
The String field contains the MS-CHAP challenge.

2.1.3. MS-CHAP-Response

Description

This Attribute contains the response value provided by a PPP
Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP)
user in response to the challenge. It is only used in Access-
Request packets.

A summary of the MS-CHAP-Response Attribute format is shown below.
The fields are transmitted from left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Ident | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LM-Response
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response(cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NT-Response
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
1 for MS-CHAP-Response.

Vendor-Length
52

Ident
Identical to the PPP CHAP Identifier.

Flags
The Flags field is one octet in length. If the Flags field is one
(0x01), the NT-Response field is to be used in preference to the
LM-Response field for authentication. The LM-Response field MAY
still be used (if non-empty), but the NT-Response SHOULD be tried
first. If it is zero, the NT-Response field MUST be ignored and
the LM-Response field used.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

LM-Response
The LM-Response field is 24 octets in length and holds an encoded
function of the password and the received challenge. If this
field is empty, it SHOULD be zero-filled.

NT-Response

The NT-Response field is 24 octets in length and holds an encoded
function of the password and the received challenge. If this
field is empty, it SHOULD be zero-filled.

2.1.4. MS-CHAP-Domain

Description

The MS-CHAP-Domain Attribute indicates the Windows NT domain in
which the user was authenticated. It MAY be included in both
Access-Accept and Accounting-Request packets.

A summary of the MS-CHAP-Domain Attribute format is given below. The
fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Ident | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
10 for MS-CHAP-Domain.

Vendor-Length
> 3

Ident
The Ident field is one octet and aids in matching requests and
replies.

String
This field contains the name in ASCII of the Windows NT domain in
which the user was authenticated.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

2.1.5. MS-CHAP-Error

Description

The MS-CHAP-Error Attribute contains error data related to the
preceding MS-CHAP exchange. This Attribute may be used in both
MS-CHAP-V1 and MS-CHAP-V2 (see below) exchanges. It is only used
in Access-Reject packets.

A summary of the MS-CHAP-Error Attribute format is given below. The
fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Ident | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
2 for MS-CHAP-Error.

Vendor-Length
> 3

Ident
The Ident field is one octet and aids in matching requests and
replies.

String
This field contains specially formatted ASCII text, which is
interpreted by the authenticating peer.

2.1.6. MS-CHAP-CPW-1

Description

This Attribute allows the user to change their password if it has
expired. This Attribute is only used in Access-Request packets, and
should only be included if an MS-CHAP-Error attribute was included in
the immediately preceding Access-Reject packet, the String field of
the MS-CHAP-Error attribute indicated that the user password had
expired, and the MS-CHAP version is less than 2.

A summary of the MS-CHAP-CPW-1 Attribute format is shown below. The
fields are transmitted from left to right.

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Code | Ident |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LM-Old-Password
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Old-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Old-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Old-Password (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LM-New-Password
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-New-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-New-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-New-Password (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NT-Old-Password
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Old-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Old-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Old-Password (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NT-New-Password
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-New-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-New-Password (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-New-Password (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New-LM-Password-Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
3 for MS-CHAP-PW-1

Vendor-Length
72

Code
The Code field is one octet in length. Its value is always 5.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Ident
The Ident field is one octet and aids in matching requests and
replies.

LM-Old-Password
The LM-Old-Password field is 16 octets in length. It contains the
encrypted Lan Manager hash of the old password.

LM-New-Password
The LM-New-Password field is 16 octets in length. It contains the
encrypted Lan Manager hash of the new password.

NT-Old-Password
The NT-Old-Password field is 16 octets in length. It contains the
encrypted Lan Manager hash of the old password.

NT-New-Password
The NT-New-Password field is 16 octets in length. It contains the
encrypted Lan Manager hash of the new password.

New-LM-Password-Length
The New-LM-Password-Length field is two octets in length and
contains the length in octets of the new LAN Manager-compatible
password.

Flags
The Flags field is two octets in length. If the least significant
bit of the Flags field is one, this indicates that the NT-New-
Password and NT-Old-Password fields are valid and SHOULD be used.
Otherwise, the LM-New-Password and LM-Old-Password fields MUST be
used.

2.1.7. MS-CHAP-CPW-2

Description

This Attribute allows the user to change their password if it has
expired. This Attribute is only used in Access-Request packets,
and should only be included if an MS-CHAP-Error attribute was
included in the immediately preceding Access-Reject packet, the
String field of the MS-CHAP-Error attribute indicated that the
user password had expired, and the MS-CHAP version is equal to 2.

A summary of the MS-CHAP-CPW-2 Attribute format is shown below. The
fields are transmitted from left to right.

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Code | Ident |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Old-NT-Hash
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Old-NT-Hash (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Old-NT-Hash (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Old-NT-Hash (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Old-LM-Hash
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Old-LM-Hash(cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Old-LM-Hash(cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Old-LM-Hash(cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LM-Response
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Response (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NT-Response
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--++-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--++-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Vendor-Type
4 for MS-CHAP-PW-2

Vendor-Length
86

Code
6

Ident
The Ident field is one octet and aids in matching requests and
replies. The value of this field MUST be identical to that in the
Ident field in all instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-
Enc-PW and MS-CHAP-PW-2 attributes contained in a single Access-
Request packet.

Old-NT-Hash
The Old-NT-Hash field is 16 octets in length. It contains the old
Windows NT password hash encrypted with the new Windows NT
password hash.

Old-LM-Hash
The Old-LM-Hash field is 16 octets in length. It contains the old
Lan Manager password hash encrypted with the new Windows NT
password hash.

LM-Response
The LM-Response field is 24 octets in length and holds an encoded
function of the password and the received challenge. If this
field is empty, it SHOULD be zero-filled.

NT-Response
The NT-Response field is 24 octets in length and holds an encoded
function of the password and the received challenge. If this
field is empty, it SHOULD be zero-filled.

Flags
The Flags field is two octets in length. If the least significant
bit (bit 0) of this field is one, the NT-Response field is to be
used in preference to the LM-Response field for authentication.
The LM-Response field MAY still be used (if present), but the NT-
Response SHOULD be tried first. If least significant bit of the
field is zero, the NT-Response field MUST be ignored and the LM-
Response field used instead. If bit 1 of the Flags field is one,
the Old-LM-Hash field is valid and SHOULD be used. If this bit is
set, at least one instance of the MS-CHAP-LM-Enc-PW attribute MUST
be included in the packet.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

2.1.8. MS-CHAP-LM-Enc-PW

Description

This Attribute contains the new Windows NT password encrypted with
the old LAN Manager password hash. The encrypted Windows NT
password is 516 octets in length; since this is longer than the
maximum lengtth of a RADIUS attribute, the password must be split
into several attibutes for transmission. A 2 octet sequence
number is included in the attribute to help preserve ordering of
the password fragments.

This Attribute is only used in Access-Request packets, in
conjunction with the MS-CHAP-CPW-2 attribute. It should only be
included if an MS-CHAP-Error attribute was included in the
immediately preceding Access-Reject packet, the String field of
the MS-CHAP-Error attribute indicated that the user password had
expired, and the MS-CHAP version is 2 or greater.

A summary of the MS-CHAP-LM-Enc-PW 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Code | Ident |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence-Number | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
5 for MS-CHAP-LM-Enc-PW

Vendor-Length
> 6

Code 6. Code is the same as for the MS-CHAP-PW-2 attribute.

Ident
The Ident field is one octet and aids in matching requests and
replies. The value of this field MUST be identical in all
instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-Enc-PW and MS-
CHAP-PW-2 attributes which are present in the same Access-Request
packet.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Sequence-Number
The Sequence-Number field is two octets in length and indicates
which "chunk" of the encrypted password is contained in the
following String field.

String The String field contains a portion of the encrypted password.

2.2. MS-CHAP-NT-Enc-PW

Description

This Attribute contains the new Windows NT password encrypted with
the old Windows NT password hash. The encrypted Windows NT
password is 516 octets in length; since this is longer than the
maximum lengtth of a RADIUS attribute, the password must be split
into several attibutes for transmission. A 2 octet sequence
number is included in the attribute to help preserve ordering of
the password fragments.

This Attribute is only used in Access-Request packets, in conjunc-
tion with the MS-CHAP-CPW-2 and MS-CHAP2-CPW attributes. It
should only be included if an MS-CHAP-Error attribute was included
in the immediately preceding Access-Reject packet, the String
field of the MS-CHAP-Error attribute indicated that the user
password had expired, and the MS-CHAP version is 2 or greater.

A summary of the MS-CHAP-NT-Enc-PW 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Code | Ident |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence-Number | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
6 for MS-CHAP-NT-Enc-PW

Vendor-Length
> 6

Code
6. Code is the same as for the MS-CHAP-PW-2 attribute.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Ident
The Ident field is one octet and aids in matching requests and
replies. The value of this field MUST be identical in all
instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-Enc-PW and MS-
CHAP-PW-2 attributes which are present in the same Access-Request
packet.

Sequence-Number
The Sequence-Number field is two octets in length and indicates
which "chunk" of the encrypted password is contained in the
following String field.

String
The String field contains a portion of the encrypted password.

2.3. Attributes for Support of MS-CHAP Version 2

2.3.1. Introduction

This section describes RADIUS attributes supporting version two of
Microsoft's PPP CHAP dialect (MS-CHAP-V2) [14]. MS-CHAP-V2 is
similar to, but incompatible with, MS-CHAP version one (MS-CHAP-V1)
[4]. Certain protocol fields have been deleted or reused but with
different semantics. Where possible, MS-CHAP-V2 is consistent with
both MS-CHAP-V1 and standard CHAP [1]. Briefly, the differences
between MS-CHAP-V2 and MS-CHAP-V1 are:

* MS-CHAP-V2 is enabled by negotiating CHAP Algorithm 0x81 in LCP
option 3, Authentication Protocol.

* MS-CHAP-V2 provides mutual authentication between peers by
piggybacking a peer challenge on the Response packet and an
authenticator response on the Success packet.

* The calculation of the "Windows NT compatible challenge
response" sub-field in the Response packet has been changed to
include the peer challenge and the user name.

* In MS-CHAP-V1, the "LAN Manager compatible challenge response"
sub-field was always sent in the Response packet. This field
has been replaced in MS-CHAP-V2 by the Peer-Challenge field.

* The format of the Message field in the Failure packet has been
changed.

* The Change Password (version 1) and Change Password (version 2)
packets are no longer supported. They have been replaced with a
single Change-Password packet.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

The attributes defined in this section reflect these differences.

2.3.2. MS-CHAP2-Response

Description

This Attribute contains the response value provided by an MS-
CHAP-V2 peer in response to the challenge. It is only used in
Access-Request packets.

A summary of the MS-CHAP2-Response 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Ident | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peer-Challenge
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Response
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Response (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
25 for MS-CHAP2-Response.

Vendor-Length
52

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Ident
Identical to the PPP MS-CHAP v2 Identifier.

Flags
The Flags field is one octet in length. It is reserved for future
use and MUST be zero.

Peer-Challenge
The Peer-Challenge field is a 16-octet random number.

Reserved
This field is reserved for future use and MUST be zero.

Response
The Response field is 24 octets in length and holds an encoded
function of the password, the Peer-Challenge field and the
received challenge.

2.3.3. MS-CHAP2-Success

Description

This Attribute contains a 42-octet authenticator response string.
This string MUST be included in the Message field of the MS-CHAP-
V2 Success packet sent from the NAS to the peer. This Attribute
is only used in Access-Accept packets.

A summary of the MS-CHAP2-Success 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Ident | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
26 for MS-CHAP2-Success.

Vendor-Length
45

Ident
Identical to the PPP MS-CHAP v2 Identifier.

String
The 42-octet authenticator string (see above).

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2.3.4. MS-CHAP2-CPW

Description

This Attribute allows the user to change their password if it has
expired. This Attribute is only used in conjunction with the MS-
CHAP-NT-Enc-PW attribute in Access-Request packets, and should
only be included if an MS-CHAP-Error attribute was included in the
immediately preceding Access-Reject packet, the String field of
the MS-CHAP-Error attribute indicated that the user password had
expired, and the MS-CHAP version is equal to 3.

A summary of the MS-CHAP-CPW-2 Attribute format is shown below. The
fields are transmitted from left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Code | Ident |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encrypted-Hash
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Encrypted-Hash (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Encrypted-Hash (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Encrypted-Hash (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peer-Challenge
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Peer-Challenge (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NT-Response
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--++-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--++-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Response (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
27 for MS-CHAP2-PW

Vendor-Length
70

Code
7

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Ident
The Ident field is one octet and aids in matching requests and
replies. The value of this field MUST be identical to that in the
Ident field in all instances of the MS-CHAP-NT-Enc-PW contained in
the Access-Request packet.

Encrypted-Hash
The Encrypted-Hash field is 16 octets in length. It contains the
old Windows NT password hash encrypted with the new Windows NT
password hash.

NT-Response
The NT-Response field is 24 octets in length and holds an encoded
function of the new password, the Peer-Challenge field and the
received challenge.

Flags
The Flags field is two octets in length. This field is reserved
for future use and MUST be zero.

2.4. Attributes for MPPE Support

This section describes a set of Attributes designed to support the
use of Microsoft Point-to-Point Encryption (MPPE) [6] in dial-up
networks. MPPE is a means of representing Point to Point Protocol
(PPP) [7] packets in a encrypted form. MPPE uses the RSA RC4 [8]
algorithm for encryption. The length of the session key to be used
for initializing encryption tables can be negotiated; MPPE currently
supports 40 bit and 128 bit session keys. MPPE is negotiated within
option 18 in the PPP Compression Control Protocol (CCP)[9], [10].

2.4.1. MS-CHAP-MPPE-Keys

Description

The MS-CHAP-MPPE-Keys Attribute contains two session keys for use
by the Microsoft Point-to-Point Encryption Protocol (MPPE). This
Attribute is only included in Access-Accept packets.

A summary of the MS-CHAP-MPPE-Keys Attribute format is given below.
The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Keys
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Keys (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
12 for MS-CHAP-MPPE-Keys.

Vendor-Length
34

Keys
The Keys field consists of two logical sub-fields: the LM-Key and
the NT-Key. The LM-Key is eight octets in length and contains the
first eight bytes of the output of the function LmPasswordHash(P,
This hash is constructed as follows: let the plain-text password
be represented by P.

The NT-Key sub-field is sixteen octets in length and contains the
first sixteen octets of the hashed Windows NT password. The
format of the plaintext Keys field is illustrated in the following
diagram:

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LM-Key
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LM-Key (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NT-Key
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Key (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Key (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NT-Key (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Padding (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Keys field MUST be encrypted by the RADIUS server using the
same method defined for the User-Password Attribute [3]. Padding
is required because the method referenced above requires the field
to be encrypted to be a multiple of sixteen octets in length.

Implementation Note
This attribute should only be returned in response to an
Access-Request packet containing MS-CHAP attributes.

2.4.2. MS-MPPE-Send-Key

Description

The MS-MPPE-Send-Key Attribute contains a session key for use by
the Microsoft Point-to-Point Encryption Protocol (MPPE). As the
name implies, this key is intended for encrypting packets sent
from the NAS to the remote host. This Attribute is only included
in Access-Accept packets.

A summary of the MS-MPPE-Send-Key Attribute format is given below.
The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Salt
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
16 for MS-MPPE-Send-Key.

Vendor-Length
> 4

Salt
The Salt field is two octets in length and is used to ensure the
uniqueness of the keys used to encrypt each of the encrypted
attributes occurring in a given Access-Accept packet. The most
significant bit (leftmost) of the Salt field MUST be set (1). The
contents of each Salt field in a given Access-Accept packet MUST
be unique.

String
The plaintext String field consists of three logical sub-fields:
the Key-Length and Key sub-fields (both of which are required),
and the optional Padding sub-field. The Key-Length sub-field is
one octet in length and contains the length of the unencrypted Key
sub-field. The Key sub-field contains the actual encryption key.
If the combined length (in octets) of the unencrypted Key-Length
and Key sub-fields is not an even multiple of 16, then the Padding
sub-field MUST be present. If it is present, the length of the
Padding sub-field is variable, between 1 and 15 octets. The
String field MUST be encrypted as follows, prior to transmission:

Construct a plaintext version of the String field by concate-
nating the Key-Length and Key sub-fields. If necessary, pad
the resulting string until its length (in octets) is an even
multiple of 16. It is recommended that zero octets (0x00) be
used for padding. Call this plaintext P.

Call the shared secret S, the pseudo-random 128-bit Request
Authenticator (from the corresponding Access-Request packet) R,
and the contents of the Salt field A. Break P into 16 octet
chunks p(1), p(2)...p(i), where i = len(P)/16. Call the
ciphertext blocks c(1), c(2)...c(i) and the final ciphertext C.
Intermediate values b(1), b(2)...c(i) are required. Encryption
is performed in the following manner ('+' indicates
concatenation):

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

b(1) = MD5(S + R + A) c(1) = p(1) xor b(1) C = c(1)
b(2) = MD5(S + c(1)) c(2) = p(2) xor b(2) C = C + c(2)
. .
. .
. .
b(i) = MD5(S + c(i-1)) c(i) = p(i) xor b(i) C = C + c(i)

The resulting encrypted String field will contain
c(1)+c(2)+...+c(i).

On receipt, the process is reversed to yield the plaintext String.

Implementation Notes
It is possible that the length of the key returned may be larger
than needed for the encryption scheme in use. In this case, the
RADIUS client is responsible for performing any necessary
truncation.

This attribute MAY be used to pass a key from an external (e.g.,
EAP [15]) server to the RADIUS server. In this case, it may be
impossible for the external server to correctly encrypt the key,
since the RADIUS shared secret might be unavailable. The external
server SHOULD, however, return the attribute as defined above; the
Salt field SHOULD be zero-filled and padding of the String field
SHOULD be done. When the RADIUS server receives the attribute
from the external server, it MUST correctly set the Salt field and
encrypt the String field before transmitting it to the RADIUS
client. If the channel used to communicate the MS-MPPE-Send-Key
attribute is not secure from eavesdropping, the attribute MUST be
cryptographically protected.

2.4.3. MS-MPPE-Recv-Key

Description

The MS-MPPE-Recv-Key Attribute contains a session key for use by
the Microsoft Point-to-Point Encryption Protocol (MPPE). As the
name implies, this key is intended for encrypting packets received
by the NAS from the remote host. This Attribute is only included
in Access-Accept packets.

A summary of the MS-MPPE-Recv-Key Attribute format is given below.
The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Salt
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
17 for MS-MPPE-Recv-Key.

Vendor-Length
> 4

Salt
The Salt field is two octets in length and is used to ensure the
uniqueness of the keys used to encrypt each of the encrypted
attributes occurring in a given Access-Accept packet. The most
significant bit (leftmost) of the Salt field MUST be set (1). The
contents of each Salt field in a given Access-Accept packet MUST
be unique.

String
The plaintext String field consists of three logical sub-fields:
the Key-Length and Key sub-fields (both of which are required),
and the optional Padding sub-field. The Key-Length sub-field is
one octet in length and contains the length of the unencrypted Key
sub-field. The Key sub-field contains the actual encryption key.
If the combined length (in octets) of the unencrypted Key-Length
and Key sub-fields is not an even multiple of 16, then the Padding
sub-field MUST be present. If it is present, the length of the
Padding sub-field is variable, between 1 and 15 octets. The
String field MUST be encrypted as follows, prior to transmission:

Construct a plaintext version of the String field by
concatenating the Key-Length and Key sub-fields. If necessary,
pad the resulting string until its length (in octets) is an
even multiple of 16. It is recommended that zero octets (0x00)
be used for padding. Call this plaintext P.

Call the shared secret S, the pseudo-random 128-bit Request
Authenticator (from the corresponding Access-Request packet) R,
and the contents of the Salt field A. Break P into 16 octet
chunks p(1), p(2)...p(i), where i = len(P)/16. Call the
ciphertext blocks c(1), c(2)...c(i) and the final ciphertext C.
Intermediate values b(1), b(2)...c(i) are required. Encryption
is performed in the following manner ('+' indicates
concatenation):

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

b(1) = MD5(S + R + A) c(1) = p(1) xor b(1) C = c(1)
b(2) = MD5(S + c(1)) c(2) = p(2) xor b(2) C = C + c(2)
. .
. .
. .
b(i) = MD5(S + c(i-1)) c(i) = p(i) xor b(i) C = C + c(i)

The resulting encrypted String field will contain
c(1)+c(2)+...+c(i).

On receipt, the process is reversed to yield the plaintext String.

Implementation Notes
It is possible that the length of the key returned may be larger
than needed for the encryption scheme in use. In this case, the
RADIUS client is responsible for performing any necessary
truncation.

This attribute MAY be used to pass a key from an external (e.g.,
EAP [15]) server to the RADIUS server. In this case, it may be
impossible for the external server to correctly encrypt the key,
since the RADIUS shared secret might be unavailable. The external
server SHOULD, however, return the attribute as defined above; the
Salt field SHOULD be zero-filled and padding of the String field
SHOULD be done. When the RADIUS server receives the attribute
from the external server, it MUST correctly set the Salt field and
encrypt the String field before transmitting it to the RADIUS
client. If the channel used to communicate the MS-MPPE-Recv-Key
attribute is not secure from eavesdropping, the attribute MUST be
cryptographically protected.

2.4.4. MS-MPPE-Encryption-Policy

Description

The MS-MPPE-Encryption-Policy Attribute may be used to signify
whether the use of encryption is allowed or required. If the
Policy field is equal to 1 (Encryption-Allowed), any or none of
the encryption types specified in the MS-MPPE-Encryption-Types
Attribute MAY be used. If the Policy field is equal to 2
(Encryption-Required), any of the encryption types specified in
the MS-MPPE-Encryption-Types Attribute MAY be used, but at least
one MUST be used.

A summary of the MS-MPPE-Encryption-Policy Attribute format is given
below. The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Policy
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Policy (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
7 for MS-MPPE-Encryption-Policy.

Vendor-Length
6

Policy
The Policy field is 4 octets in length. Defined values are:

1 Encryption-Allowed 2 Encryption-Required

2.4.5. MS-MPPE-Encryption-Types

Description

The MS-MPPE-Encryption-Types Attribute is used to signify the
types of encryption available for use with MPPE. It is a four
octet integer that is interpreted as a string of bits.

A summary of the MS-MPPE-Encryption-Policy Attribute format is given
below. The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Types
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Types (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
8 for MS-MPPE-Encryption-Types.

Vendor-Length
6

Policy
The Types field is 4 octets in length. The following diagram
illustrates the Types field.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

3 2 1
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |S|L| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

If the L bit is set, RC4[5] encryption using a 40-bit key is
allowed. If the S bit is set, RC4 encryption using a 128-bit key
is allowed. If both the L and S bits are set, then either 40- or
128-bit keys may be used with the RC4 algorithm.

2.5. Attributes for BAP Support

This section describes a set of vendor-specific RADIUS attributes
designed to support the dynamic control of bandwidth allocation in
multilink PPP [11]. Attributes are defined that specify whether use
of the PPP Bandwidth Allocation Protocol (BAP) [12] is allowed or
required on incoming calls, the level of line capacity (expressed as
a percentage) below which utilization must fall before a link is
eligible to be dropped, and the length of time (in seconds) that a
link must be under-utilized before it is dropped.

2.5.1. MS-BAP-Usage

Description

This Attribute describes whether the use of BAP is allowed,
disallowed or required on new multilink calls. It MAY be used in
Access-Accept packets.

A summary of the MS-BAP-Usage 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
13 for MS-BAP-Usage.

Vendor-Length
6

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Value
The Value field is four octets.

0 BAP usage not allowed
1 BAP usage allowed
2 BAP usage required

2.5.2. MS-Link-Utilization-Threshold

Description

This Attribute represents the percentage of available bandwidth
utilization below which the link must fall before the link is
eligible for termination. Permissible values for the MS-Link-
Utilization-Threshold Attribute are in the range 1-100, inclusive.
It is only used in Access-Accept packets.

A summary of the MS-Link-Utilization-Threshold 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
14 for MS-Link-Utilization-Threshold

Vendor-Length 6

Value The Value field is four octets in length and represents the
percentage of available bandwidth utilization below which the link
must fall before the link is eligible for termination.
Permissible values are in the range 1-100, inclusive.

2.5.3. MS-Link-Drop-Time-Limit

Description

The MS-Link-Drop-Time-Limit Attribute indicates the length of time
(in seconds) that a link must be underutilized before it is
dropped. It MAY only be included in Access-Accept packets.

A summary of the MS-Link-Drop-Time-Limit Attribute format is given
below. The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
15 for MS-Link-Drop-Time-Limit

Vendor-Length
6

Value
The Value field represents the number of seconds that a link must
be underutilized (i.e., display bandwidth utilization below the
threshold specified in the MS-Link-Utilization-Threshold
Attribute) before the link is dropped.

2.6. Attributes for ARAP Support

This section describes a set of Attributes designed to support the
Apple Remote Access Protocol (ARAP).

2.6.1. MS-Old-ARAP-Password

Description

The MS-Old-ARAP-Password Attribute is used to transmit the old
ARAP password during an ARAP password change operation. It MAY be
included in Access-Request packets.

A summary of the MS-Old-ARAP-Password Attribute Attribute format is
given below. The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
19 for MS-Old-ARAP-Password Attribute

Vendor-Length
> 3

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

String
The String field is one or more octets. It contains the old ARAP
password DES-encrypted using itself as the key.

2.6.2. MS-New-ARAP-Password

Description

The MS-New-ARAP-Password Attribute is used to transmit the new
ARAP password during an ARAP password change operation. It MAY be
included in Access-Request packets.

A summary of the MS-New-ARAP-Password Attribute Attribute format is
given below. The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
20 for MS-New-ARAP-Password Attribute

Vendor-Length
> 3

String
The String field is one or more octets. It contains the new ARAP
password DES-encrypted using the old ARAP password as the key.

2.6.3. MS-ARAP-Password-Change-Reason

Description

The MS-ARAP-Password-Change-Reason Attribute is used to indicate
reason for a server-initiated password change. It MAY be included
in Access-Challenge packets.

A summary of the MS-ARAP-Password-Change-Reason Attribute format is
given below. The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Why
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Why (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
21 for MS-ARAP-Password-Change-Reason

Vendor-Length
6

Why
The Why field is 4 octets in length. The following values are
defined:
Just-Change-Password 1
Expired-Password 2
Admin-Requires-Password-Change 3
Password-Too-Short 4

2.6.4. MS-ARAP-Challenge

Description

This attribute is only present in an Access-Request packet
containing a Framed-Protocol Attribute with the value 3 (ARAP).

A summary of the MS-ARAP-Challenge Attribute format is given below.
The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Challenge
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Challenge (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Challenge (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
33 for MS-ARAP-Challenge

Vendor-Length
10

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Value
The Challenge Field is 8 octets in length. It contains the
challenge (as two 4-octet quantities) sent by the NAS to the peer.

2.7. Miscellaneous Attributes

This section describes attributes which do not fall into any
particular category, but are used in the identification and operation
of Microsoft remote access products.

2.7.1. MS-RAS-Vendor

Description

The MS-RAS-Vendor Attribute is used to indicate the manufacturer
of the RADIUS client machine. It MAY be included in both Access-
Request and Accounting-Request packets.

A summary of the MS-RAS-Vendor Attribute format is given below. The
fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Vendor-ID
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Vendor-ID (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
9 for MS-RAS-Vendor

Vendor-Length
6

Vendor-ID
The Vendor-ID field is 4 octets in length. The high-order octet
is 0 and the low-order 3 octets are the SMI Network Management
Private Enterprise Code of the Vendor in network byte order, as
defined in the Assigned Numbers RFC [13].

2.7.2. MS-RAS-Version

Description

The MS-RAS-Version Attribute is used to indicate the version of
the RADIUS client software. This attribute SHOULD be included in
packets containing an MS-RAS-Vendor Attribute; it SHOULD NOT be

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

sent in packets which do not contain an MS-RAS-Vendor Attribute.
It MAY be included in both Access-Request and Accounting-Request
packets.

A summary of the MS-RAS-Version Attribute format is given below. The
fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
18 for MS-RAS-Version

Vendor-Length
> 3

String
The String field is one or more octets. The actual format of the
information is vendor specific, and a robust implementation SHOULD
support the field as undistinguished octets.

2.7.3. MS-Filter

Description

The MS-Filter Attribute is used to transmit traffic filters. It
MAY be included in both Access-Accept and Accounting-Request
packets.

If multiple MS-Filter Attributes are contained within a packet,
they MUST be in order and they MUST be consecutive attributes in
the packet.

A summary of the MS-Filter Attribute format is given below. The
fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Filter...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
22 for MS-Filter Attribute

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

Vendor-Length
> 3

Filter
The Filter field is one or more octets. It contains a sequence of
undifferentiated octets.

If multiple MS-Filter Attributes occur in a single Access-Accept
packet, the Filter field from each MUST be concatenated in the
order received to form the actual filter.

2.7.4. MS-Acct-Auth-Type

Description

The MS-Acct-Auth-Type Attribute is used to represent the method
used to authenticate the dial-up user. It MAY be included in
Accounting-Request packets.

A summary of the MS-Acct-Auth-Type Attribute format is given below.
The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | Auth-Type
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Auth-Type (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
23 for MS-Acct-Auth-Type

Vendor-Length
6

Auth-Type
The Auth-Type field is 4 octets in length. The following values
are defined for this field:

PAP 1
CHAP 2
MS-CHAP-1 3
MS-CHAP-2 4
EAP 5

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

2.7.5. MS-Acct-EAP-Type

Description

The MS-Acct-EAP-Type Attribute is used to represent the Extensible
Authentication Protocol (EAP) [15] type used to authenticate the
dial-up user. It MAY be included in Accounting-Request packets.

A summary of the MS-Acct-EAP-Type Attribute format is given below.
The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | EAP-Type
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EAP-Type (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
24 for MS-Acct-EAP-Type

Vendor-Length
6

Auth-Type
The EAP-Type field is 4 octets in length. The following values
are currently defined for this field:

MD5 4
OTP 5
Generic Token Card 6
TLS 13

2.7.6. MS-Primary-DNS-Server

Description

The MS-Primary-DNS-Server Attribute is used to indicate the
address of the primary Domain Name Server (DNS) [16, 17] server to
be used by the PPP peer. It MAY be included in both Access-Accept
and Accounting-Request packets.

A summary of the MS-Primary-DNS-Server Attribute format is given
below. The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | IP-Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP-Address (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
28 for MS-Primary-DNS-Server

Vendor-Length
6

IP-Address
The IP-Address field is 4 octets in length. It contains the IP
address of the primary DNS server.

2.7.7. MS-Secondary-DNS-Server

Description

The MS-Secondary-DNS-Server Attribute is used to indicate the
address of the secondary DNS server to be used by the PPP peer.
It MAY be included in both Access-Accept and Accounting-Request
packets.

A summary of the MS-Secondary-DNS-Server Attribute format is given
below. The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | IP-Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP-Address (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
29 for MS-Secondary-DNS-Server

Vendor-Length
6

IP-Address
The IP-Address field is 4 octets in length. It contains the IP
address of the secondary DNS server.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

2.7.8. MS-Primary-NBNS-Server

Description

The MS-Primary-NBNS-Server Attribute is used to indicate the
address of the primary NetBIOS Name Server (NBNS) [18] server to
be used by the PPP peer. It MAY be included in both Access-Accept
and Accounting-Request packets.

A summary of the MS-Primary-MBNS-Server Attribute format is given
below. The fields are transmitted 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | IP-Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP-Address (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
30 for MS-Primary-NBNS-Server

Vendor-Length
6

IP-Address
The IP-Address field is 4 octets in length. It contains the IP
address of the primary NBNS server.

2.7.9. MS-Secondary-NBNS-Server

Description

The MS-Secondary-NBNS-Server Attribute is used to indicate the
address of the secondary DNS server to be used by the PPP peer.
It MAY be included in both Access-Accept and Accounting-Request
packets.

A summary of the MS-Secondary-NBNS-Server Attribute format is given
below. The fields are transmitted left to right.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Type | Vendor-Length | IP-Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP-Address (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Vendor-Type
31 for MS-Secondary-NBNS-Server

Vendor-Length
6

IP-Address
The IP-Address field is 4 octets in length. It contains the IP
address of the secondary NBNS server.

3. Table of Attributes

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

Request Accept Reject Challenge Acct-Request # Attribute
0-1 0 0 0 0 1 MS-CHAP-Response
0 0 0-1 0 0 2 MS-CHAP-Error
0-1 0 0 0 0 3 MS-CHAP-CPW-1
0-1 0 0 0 0 4 MS-CHAP-CPW-2
0+ 0 0 0 0 5 MS-CHAP-LM-Enc-PW
0+ 0 0 0 0 6 MS-CHAP-NT-Enc-PW
0 0-1 0 0 0 7 MS-MPPE-Encryption-
Policy
0 0-1 0 0 0 8 MS-MPPE-Encryption-Type
0-1 0 0 0 0-1 9 MS-RAS-Vendor
0 0-1 0 0 0-1 10 MS-CHAP-Domain
0-1 0 0 0-1 0 11 MS-CHAP-Challenge
0 0-1 0 0 0 12 MS-CHAP-MPPE-Keys
0 0-1 0 0 0 13 MS-BAP-Usage
0 0-1 0 0 0 14 MS-Link-Utilization-
Threshold
0 0-1 0 0 0 15 MS-Link-Drop-Time-Limit
0 0-1 0 0 0 16 MS-MPPE-Send-Key
0 0-1 0 0 0 17 MS-MPPE-Recv-Key
0-1 0 0 0 0-1 18 MS-RAS-Version
0-1 0 0 0 0 19 MS-Old-ARAP-Password
0-1 0 0 0 0 20 MS-New-ARAP-Password
0 0 0 0-1 0 21 MS-ARAP-PW-Change-
Reason

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

0 0+ 0 0 0+ 22 MS-Filter
0 0 0 0 0-1 23 MS-Acct-Auth-Type
0 0 0 0 0-1 24 MS-Acct-EAP-Type
0-1 0 0 0 0 25 MS-CHAP2-Response
0 0-1 0 0 0 26 MS-CHAP2-Success
0-1 0 0 0 0 27 MS-CHAP2-CPW
0 0-1 0 0 0-1 28 MS-Primary-DNS-Server
0 0-1 0 0 0-1 29 MS-Secondary-DNS-Server
0 0-1 0 0 0-1 30 MS-Primary-NBNS-Server
0 0-1 0 0 0-1 31 MS-Secondary-NBNS-
Server
0-1 0 0 0 0 33 MS-ARAP-Challenge

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 packet.
0-1 Zero or one instance of this attribute MAY be present in packet.

4. Security Considerations

MS-CHAP, like PPP CHAP, is susceptible to dictionary attacks. User
passwords should be chosen with care, and be of sufficient length to
deter easy guessing.

Although the scheme used to protect the Keys field of the MS-CHAP-
MPPE-Keys, MS-MPPE-Send-Key and MS-MPPE-Recv-Key Attributes is
believed to be relatively secure on the wire, RADIUS proxies will
decrypt and re-encrypt the field for forwarding. Therefore, these
attributes SHOULD NOT be used on networks where untrusted RADIUS
proxies reside.

5. Acknowledgements

Thanks to Carl Rigney ([email protected]), Ashwin Palekar (ash-
[email protected]), Aydin Edguer ([email protected]), Narendra
Gidwani ([email protected]), Steve Cobb ([email protected]),
Pat Calhoun ([email protected]), Dave Mitton
([email protected]), Paul Funk ([email protected]), Gurdeep Singh
Pall ([email protected]), Stephen Bensley ([email protected]),
and Don Rule ([email protected]) for useful suggestions and
editorial feedback.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

6. Editor's Address

Questions about this memo can be directed to:

Glen Zorn
Microsoft Corporation
One Microsoft Way
Redmond, Washington 98052

Phone: +1 425 703 1559
Fax: +1 425 936 7329
EMail: [email protected]

7. References

[1] Simpson, W., "PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC 1994, August 1996.

[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[3] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote
Access Dial In User Service", RFC 2138, April 1997.

[4] Zorn, G. and S. Cobb, "Microsoft PPP CHAP Extensions", RFC 2433,
October 1998.

[5] Simpson, W., "PPP Challenge Handshake Authentication Protocol
(CHAP)", RFC 1994, August 1996.

[6] Zorn, G. and G. Pall, "Microsoft Point-to-Point Encryption
(MPPE) Protocol", Work in Progress.

[7] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
1661, July 1994.

[8] RC4 is a proprietary encryption algorithm available under
license from RSA Data Security Inc. For licensing information,
contact:
RSA Data Security, Inc.
100 Marine Parkway
Redwood City, CA 94065-1031

[9] Pall, G., "Microsoft Point-to-Point Compression (MPPC)
Protocol", RFC 2118, March 1997.

[10] Rand, D., "The PPP Compression Control Protocol (CCP)", RFC
1962, June 1996.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

[11] Sklower, K., Lloyd, B., McGregor, G., Carr, D. and T. Coradetti,
"The PPP Multilink Protocol (MP)", RFC 1990, August 1996.

[12] Richards, C. and K. Smith, "The PPP Bandwidth Allocation
Protocol (BAP) The PPP Bandwidth Allocation Control Protocol
(BACP)", RFC 2125, March 1997.

[13] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
October 1994.

[14] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2", Work in
Progress.

[15] Blunk, L. and J. Vollbrecht, "PPP Extensible Authentication
Protocol (EAP)", RFC 2284, March 1998.

[16] Mockapetris, P., "Domain Names - Concepts and Facilities", STD
13, RFC 1034, USC/ISI, November 1987.

[17] Mockapetris, P., "Domain Names - Implementation and
Specification", STD 13, RFC 1035, November 1987.

[18] Auerbach, K., and A. Aggarwal, "Protocol Standard for a NetBIOS
Service on a TCP/UDP Transport", STD 19, RFCs 1001 and 1002,
March 1987.

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RFC 2548 Microsoft Vendor-specific RADIUS Attributes March 1999

10. Full Copyright Statement

Copyright (C) The Internet Society (1999). 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
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

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.

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