Network Working Group G. Zorn, Ed.
Internet-Draft Network Zen
Updates: 2865, 2866 November 17, 2008
(if approved)
Intended status: Informational
Expires: May 21, 2009
RADIUS Error Messages
draft-zorn-radius-err-msg-10.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document describes new RADIUS protocol elements designed to
allow the communication of packet and attribute errors between RADIUS
servers and clients.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification of Requirements . . . . . . . . . . . . . . . . 3
3. RADIUS Packet Format . . . . . . . . . . . . . . . . . . . . . 3
4. Packet Types . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Error-Notification . . . . . . . . . . . . . . . . . . . . 6
5. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Error-Code . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Attribute Values . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Acct-Error-Notification . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
The RADIUS protocol [RFC2865] is defined to allow most errors to be
ignored and to silently discard unrecognized or erroneous packets.
In many cases, this behavior is beneficial or at least innocuous.
For example, it's probably a good idea to discard messages from
unknown clients and server messages having incorrect authenticators,
and discarding short packets doesn't seem to hurt anything. In some
cases, however, this policy can cause interoperability problems and
may result in the provision of incorrect services to users,
particularly in roaming situations.
Because RADIUS packets having unknown values in the Code field of the
header are silently discarded it is difficult to ascertain whether a
new packet type is considered invalid by the remote client/server or
if the message was simply lost. Similarly, RFC 2865 allows clients
to ignore unrecognized attributes, which can lead to incorrect
service provisioning.
This document defines a set of messages and attributes that can be
used to notify a RADIUS client or server of various message errors.
Discussion of this draft may be directed to the author.
2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. RADIUS Packet Format
Exactly one RADIUS packet is encapsulated in the UDP Data field
[RFC0768] where the UDP Destination Port field indicates 1812
(decimal).
When a reply is generated, the source and destination ports are
reversed.
A summary of the RADIUS data 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authenticator |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
Code
The Code field is one octet, and identifies the type of RADIUS
packet. When a client receives a packet with an invalid Code
field, it is silently discarded. If a server receives a packet
with an invalid Code field from a valid client, it SHOULD reply
with an Error-Notification packet (section 4.1); if the server
does not support the Error Notification packet, it MUST
silently discard the received packet.
The RADIUS Codes (decimal) defined in this document are as
follows:
<MSG1> Error-Notification
Identifier
The Identifier field is one octet, and aids in matching
requests, replies and notifications. The RADIUS server can
detect a duplicate request if it has the same client source IP
address, source UDP port and Identifier within a short span of
time.
Length
The Length field is two octets. It indicates the length of the
packet including the Code, Identifier, Length, Authenticator
and Attribute fields. Octets outside the range of the Length
field MUST be treated as padding and ignored on reception. If
the packet is shorter than the Length field indicates, it MUST
be silently discarded. The minimum length is 20 and maximum
length is 4096.
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Authenticator
The Authenticator field is sixteen (16) octets. The most
significant octet is transmitted first. This value is used to
authenticate the reply from the RADIUS server.
Notification Authenticator
The value of the Authenticator field in the Error-
Notification packet is called the Notification
Authenticator, and contains a one-way MD5 hash calculated
over a stream of octets consisting of: the RADIUS packet,
beginning with the Code field, including the Identifier, the
Length, the Authenticator field from the packet to which
this packet is a response, and the response Attributes,
followed by the shared secret. That is,
Notification Auth =
MD5(Code+ID+Length+RequestAuth+Attributes+Secret)
where '+' denotes concatenation.
Administrative Note
The secret shared between the client and the RADIUS server
SHOULD be at least as large and unguessable as a well-chosen
password. It is preferred that the secret be at least 16
octets. This is to ensure a sufficiently large range for the
secret to provide protection against exhaustive search attacks.
The secret MUST NOT be empty (length 0) since this would allow
packets to be trivially forged.
A RADIUS server MUST use the source IP address of the RADIUS
UDP packet to decide which shared secret to use, so that RADIUS
requests can be proxied.
When using a forwarding proxy, the proxy must be able to alter
the packet as it passes through in each direction - when the
proxy forwards the request, the proxy MAY add a Proxy-State
Attribute, and when the proxy forwards a response, it MUST
remove its Proxy-State Attribute if it added one. Proxy-State
is always added or removed after any other Proxy-States, but no
other assumptions regarding its location within the list of
attributes can be made. Since Access-Accept and Access-Reject
replies are authenticated on the entire packet contents, the
stripping of the Proxy-State attribute invalidates the
signature in the packet - so the proxy has to re-sign it.
Further details of RADIUS proxy implementation are outside the
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scope of this document.
4. Packet Types
The RADIUS Packet type is determined by the Code field in the first
octet of the Packet.
4.1. Error-Notification
Description
Error-Notification packets are sent by a RADIUS server as an
indication that a previous request contained one or more errors.
A RADIUS server wishing to notify a client that one or more errors
occurred MUST transmit a RADIUS packet with the Code field set to
<MSG1> (Error-Notification).
Error-Notification packets MUST contain at least one Error-Code
Attribute.
A summary of the Error-Notification packet format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Notification Authenticator |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
Code
<MSG1> for Error-Notification
Identifier
The Identifier field is a copy of the Identifier field of the
packet which caused this Error-Notification packet to be
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created.
Notification Authenticator
The Notification Authenticator value is calculated from the
Error-Notification packet, as described above.
Attributes
The Attribute field is variable in length, and contains any
desired optional Attributes in addition to the required
Attributes.
5. Attributes
5.1. Error-Code
Description
This attribute contains a code identifying the class of error that
occurred, a code signifying the error itself and an optional text
description of the error.
The Error-Code Attribute MUST be included in Error-Notification
packets sent from a server.
RADIUS Accounting [RFC2866] clients MUST include this Attribute in
Accounting-Request packets in which the Acct-Status-Type Attribute
has a value of Acct-Error-Notification (see below).
A summary of the Error-Code 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 | Class | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code (cont'd.)| String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
<ATR> for Error-Code.
Length
>= 4
Class
The CLASS field contains a single ASCII character indicating
the severity of the error. This document defines the following
error classes:
F The error was fatal and the message causing the error was
discarded.
W Warning error: the message was processed, but the result may
not be as anticipated.
Code
The Code field contains an unsigned integer representing the
type of error that occurred. This document defines the
following decimal values for the Code field:
1 Unrecognized Packet Type
2 Unrecognized Vendor OUI
3 Unrecognized Attribute
4 Unknown Session Identifier
5 Unknown Key Identifier
String
The optional String field contains a text description of the
error. When the Error-Code Attribute is used in Accounting-
Request packets, the String field SHOULD contain a message
describing the error.
6. Attribute Values
The following sub-sections defines a new value for the Acct-Status-
Type Attribute [RFC2866].
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6.1. Acct-Error-Notification
Description
When the value <VAL> is present in the Value field of an Acct-
Status-Type Attribute in an Accounting-Request packet, it
signifies that one or more errors have occurred on the client
side.
7. IANA Considerations
The criteria to be used by the Internet Assigned Numbers Authority
(IANA) for assignment of numbers within namespaces defined within
this document are identical to those given in [RFC3575].
8. Security Considerations
None.
9. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote
Authentication Dial In User Service)", RFC 3575,
July 2003.
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Author's Address
Glen Zorn (editor)
Network Zen
1310 East Thomas Street
Seattle, Washington 98102
US
Phone: +1 (206) 377-9035
Email: gwz@net-zen.net
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