INTERNET DRAFT Pat R. Calhoun
Category: Standards Track Sun Microsystems, Inc.
Title: draft-calhoun-diameter-11.txt Allan C. Rubens
Date: December 1999 Tut Systems, Inc.
Haseeb Akhtar
Nortel Networks
Erik Guttman
Sun Microsystems, Inc.
DIAMETER Base Protocol
Status of this Memo
This document is an individual contribution for consideration by the
AAA Working Group of the Internet Engineering Task Force. Comments
should be submitted to the diameter@ipass.com mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at:
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.
Copyright (C) The Internet Society 1999. All Rights Reserved.
Abstract
The DIAMETER base protocol is intended to provide a AAA framework for
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Mobile-IP, NASREQ and ROAMOPS. This draft specifies the message
format, transport, error reporting and security services to be used
by all DIAMETER extensions and MUST be supported by all DIAMETER
implementations.
Table of Contents
1.0 Introduction
1.1 Requirements language
1.2 Terminology
2.0 Protocol Overview
2.1 Header Format
2.1.1 ZLB Message Format
2.2 AVP Format
2.2.1 AVP Header
2.2.2 Optional Header Elements
2.2.3 AVP Value Formats
2.2.4 DIAMETER Base Protocol AVPs
2.3 Mandatory AVPs
2.3.1 Command-Code AVP
2.3.2 Host-IP-Address AVP
2.3.3 Host-Name AVP
2.4 The art of AVP Tagging
2.5 State Machine
2.6 Device-Reboot-Ind (DRI) Command
2.6.1 Vendor-Name AVP
2.6.2 Firmware-Revision AVP
2.6.3 Reboot-Type AVP
2.6.4 Reboot-Time AVP
2.6.5 Extension-Id AVP
2.7 Device-Watchdog-Ind (DWI) Command
3.0 "User" Sessions
3.1 Session-Id AVP
3.2 Session-Timeout AVP
3.3 User-Name AVP
4.0 Reliable Transport
4.1 Flow Control
4.1.1 Receive-Window AVP
4.2 Peer failure recovery
5.0 Error Reporting
5.1 Message-Reject-Ind (MRI) Command
5.1.1 Failed-AVP AVP
5.2 Result-Code AVP
6.0 DIAMETER Message Routing
6.1 Message Proxying
6.1.1 Proxy-State AVP
6.1.2 Destination-NAI AVP
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6.2 Message Redirection
6.2.1 Redirected-Host AVP
7.0 DIAMETER Message Security
7.1 Hop-by-Hop Security
7.1.1 Integrity-Check-Value AVP
7.1.2 Encrypted-Payload AVP
7.2 Nonce AVP
7.3 Timestamp AVP
8.0 IANA Considerations
8.1 AVP Attributes
8.2 Command Code AVP Values
8.3 Extension Identifier Values
8.4 Result-Code AVP Values
8.5 Integrity-Check-Value AVP Transform Values
8.6 Reboot-Type AVP Values
8.7 AVP Header Bits
9.0 Open Issues
10.0 DIAMETER protocol related configurable parameters
11.0 Security Considerations
12.0 References
13.0 Acknowledgements
14.0 Author's Addresses
15.0 Full Copyright Statement
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1.0 Introduction
The DIAMETER protocol allows peers to exchange a variety of messages.
The base protocol provides the following facilities:
- Delivery of AVPs (attribute value pairs)
- Capabilities negotiation, as required in [20]
- Error notification
- Sequenced in-order reliable delivery of UDP datagram messages
- Support for congestion control (receiver window), as required in
[21]
- Timely detection of failed or unresponsive peers, as required in
[21, 22, 23]
- Extensibility, through addition of new commands and AVPs, as
required in [21]
All data delivered by the protocol is in the form of an AVP. Some of
these AVP values are used by the DIAMETER protocol itself, while
others deliver data associated with particular applications which
employ DIAMETER. AVPs may be added arbitrarily to DIAMETER messages,
so long as the required AVPs are included and AVPs which are
explicitly excluded are not included. AVPs are used by base DIAMETER
protocol to support the following required features:
- If application-level security is required, all messages MUST
include an Integrity Check Vector (ICV). If the ICV is present,
the message MUST also carry a timestamp and a nonce to aid in
providing replay protection.
- To carry user authentication information, for the purposes of
enabling the DIAMETER server to authenticate the user.
- To allow authorization information to be exchanged for a
particular user's session between a DIAMETER client and server.
- To exchange resource usage information, which MAY be used for
accounting purposes, capacity planning, etc.
The DIAMETER base protocol provides the minimum requirements needed
for an AAA transport protocol, as required by NASREQ [21], Mobile IP
[22, 23], and ROAMOPS [20]. The base protocol is not intended to be
used by itself, and must be used with an application-specific
extension, such as Mobile IP. The DIAMETER protocol was heavily
inspired and builds upon the tradition of the RADIUS [1] protocol.
Any node can initiate a request. In that sense, DIAMETER is a peer to
peer protocol. In this document, a DIAMETER client is the device that
normally initiates a request for authentication and/or authorization
of a user. A DIAMETER server is the device that performs the actual
authentication and/or authorization of the user based on some
profile. A server MAY issue an unsolicited message to a client, but
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this is typically not a request for authentication and/or
authorization, but rather for something else, such as an accounting
update.
1.1 Requirements language
In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [13].
1.2 Terminology
Refer to [9] for terminology used in this document.
2.0 Protocol Overview
The base DIAMETER protocol is never used on its own. It is always
extended for a particular application. The base DIAMETER protocol
concerns itself with capabilities negotiation, and how messages are
sent, resent and how peers may eventually be abandoned. The base
protocol also defines certain rules which apply to all exchanges of
messages between DIAMETER peers. It is important to note that the
base protocol provides an optional application-level security AVPs
(Integrity-Check-Value) which MAY be used in absence of an underlying
security protocol (e.g. IP Security).
Communication between DIAMETER peers begins with one peer sending a
message to another DIAMETER peer. The set of AVPs included in the
message is determined by a particular application of or extension to
DIAMETER. (We will refer to this as the DIAMETER extension). One
AVP which is included in the initial communication is the Session-Id.
The communicating party may accept or reject the request which
contains a new Session-Id, or return Result-Code if the request
cannot be processed. The behavior of the communicating peer depends
on the DIAMETER extension employed.
Exchanges of messages are either request/reply oriented, or in some
special cases, do not require replies. All such messages which do
not require replies (or acknowledgments) have names which end with
'-Ind' (short for Indication). All messages require a transport
level acknowledgement, either through a Zero Length Body (ZLB), or by
piggybacking an acknowledgement in a non-ZLB message.
Communicating DIAMETER peers retain state relating to transport
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(sequence numbers and the like). This state information may be
discarded when the communicating peer is determined to be
unreachable. This occurs when the peer does not acknowledge receipt
of a DIAMETER message that has been retransmitted a maximum number of
times. The Device-Watchdog-Ind is used to pro-actively probe peers to
ensure that communication is still possible.
Freeing the transport state associated with a communication with a
DIAMETER peer is entirely independent of freeing session state
(associated with a Session-Id). The latter MUST only be done
according to rules established in a particular extension/application
of DIAMETER.
DIAMETER extensions SHOULD define an explicit exchange of messages
which allow a peer to inform the other party that a session has been
terminated.
2.1 Header Format
The base DIAMETER protocol is run over UDP port 1812. Implementations
MAY send packets from any source port, but MUST be prepared to
receive packets on port 1812. When a request is received, in order to
send a reply, the source and destination ports in the reply are
reversed.
A given DIAMETER process SHOULD use the same port number to send all
messages to aid in identifying which process sent a given message.
More than one DIAMETER process MAY exist within a single host, so the
sender's port number is needed to discriminate them.
A summary of the DIAMETER data format is shown below. The fields are
transmitted in network byte order.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RADIUS PCC=254|Flags|A|W| Ver | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Send (Ns) | Next Received (Nr) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVPs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
RADIUS PCC
The RADIUS Packet Compatibility Code (PCC) field is a one octet
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field which is used for backward compatibility with RADIUS and
MUST be set to 254. In order to easily distinguish DIAMETER
messages from RADIUS, the value of 254 has been reserved and
allows implementations to support both protocols by using the
first octet in the header.
Flags
The Message Flags field is five bits, and is used in order to
identify any options. This field MUST be initialized to zero. The
'W' bit (Window-Present) is set when the Next Send (Ns) and Next
Received (Nr) fields are present in the header. The 'A' bit is set
to indicate that the message is an acknowledgement only (ZLB) and
does not contain a Command-Code AVP following the header. Note
that the Security AVPs, if required, MUST still be present within
a ZLB.
In the event that the DIAMETER protocol is implemented over a
reliable transport, the 'W' and 'A' bits MUST NOT be set.
Version
This Version field MUST be set to 1 to indicate DIAMETER Version
1.
Message Length
The Message Length field is two octets and indicates the length of
the DIAMETER message including the header fields. DIAMETER
implementations MUST be ready to receive UDP packets of at least
8192 octets in length.
Identifier
The Identifier field is four octets, and aids in matching requests
and replies. The sender MUST ensure that the identifier in a
message is locally unique (to the sender) at any given time, and
MAY attempt to ensure that the number is unique across reboots.
The identifier is normally a monotonically increasing number,
whose start value was randomly generated. DIAMETER servers should
consider a message to be unique by examining the source address,
source port and Identifier field of the message.
Next Send
This field is present when the Window-Present bit is set in the
header flags. The Next Send (Ns) is copied from the send sequence
number state variable, Ss, at the time the message is transmitted.
The variable Ss is incremented after copying into the header if
the message is not a ZLB.
Next Received
This field is present when the Window-Present bit is set in the
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header flags. Nr is copied from the receive sequence number state
variable, Sr, and indicates the sequence number, Ns, +1 of the
highest (modulo 2^16) in-sequence message received. See section
4.0 for more information.
AVPs
AVPs is a method of encapsulating information relevant to the
DIAMETER message. See section 2.2 for more information on AVPs.
2.1.1 ZLB Message Format
Zero Length Body (ZLB) messages are used to explicitly acknowledge
one or more DIAMETER message, and contain no additional
Authentication, Authorization or Accounting related AVPs. ZLB
messages must contain authentication AVPs, otherwise attacks could be
mounted against DIAMETER nodes.
The format of a ZLB message is as follows:
<ZLB Message> ::= <DIAMETER Header>
[<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>]
2.2 AVP Format
DIAMETER AVPs carry specific authentication, accounting and
authorization information, security information as well as
configuration details for the request and reply.
Some AVPs MAY be listed more than once. The effect of this is AVP
specific, and is specified in each case by the AVP description.
Each AVP of type 'string' and 'data' MUST be padded to align on a 32
bit boundary, while other AVP types align naturally. Zero bytes are
added to the end of the AVP value till a word boundary is reached.
The length of the padding is not reflected in the AVP Length field.
2.2.1 AVP Header
The AVP format is shown below and MUST be sent in network byte order.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Length | Reserved |P|T|V|R|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
AVP Code
The AVP Code identifies the attribute uniquely. If the Vendor-
Specific bit is set, the AVP Code is allocated from the vendor's
private address space.
The first 256 AVP numbers are reserved for backward compatibility
with RADIUS and are to be interpreted as per RADIUS [1]. AVP
numbers 256 and above are used for DIAMETER, which are allocated
by IANA (see section 8.1).
AVP Length
The AVP Length field is two octets, and indicates the length of
this Attribute including the AVP Code, AVP Length, AVP Flags,
Reserved, the Tag and Vendor ID fields if present and the AVP
data. If a message is received with an Invalid attribute length,
the message SHOULD be rejected.
AVP Flags
The AVP Flags field informs the DIAMETER host how each attribute
must be handled. Note that subsequent DIAMETER extensions MAY
define bits to be used within the AVP Header, and an unrecognized
bit should be considered an error. The 'R' and the reserved bits
should be set to 0 and ignored on receipt, while the 'P' bit is
defined in [11].
The 'M' Bit, known as the Mandatory bit, indicates whether support
of the AVP is required. If an AVP is received with the 'M' bit
enabled and the receiver does not support the AVP, the message
MUST be rejected. AVPs without the 'M' bit enabled are
informational only and a receiver that receives a message with
such an AVP that is not supported MAY simply ignore the AVP.
The 'V' bit, known as the Vendor-Specific bit, indicates whether
the optional Vendor ID field is present in the AVP header. When
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set the AVP Code belongs to the specific vendor code address
space.
The 'T' bit, known as the Tag bit, is used to group sets of AVPs
together. Grouping of AVPs is necessary when more than one AVP is
needed to express a condition. If this bit is set, the optional
Tag field will be present.
Unless otherwise noted, AVPs will have the following default AVP
Flags field settings:
The 'M' bit MUST be set. The 'V' bit MUST NOT be set. The 'T'
bit MAY be set.
2.2.2 Optional Header Elements
The AVP Header consists of several optional fields. These fields are
only present if their respective bit-flags are enabled.
Vendor ID
The Vendor ID field is present in the 'V' bit is set in the AVP
Flags field. The optional four octet Vendor ID field contains the
IANA assigned "SMI Network Management Private Enterprise Codes"
[2] value, encoded in network byte order. Any vendor wishing to
implement DIAMETER extensions MUST use their own Vendor ID along
with private Attribute values, guaranteeing that they will not
collide with any other vendor's extensions, nor with future IETF
extensions.
A vendor ID value of zero (0) corresponds to the IETF adopted AVP
values, as managed by the IANA. Since the absence of the vendor ID
field implies that the AVP in question is not vendor specific,
implementations SHOULD not use the zero (0) vendor ID.
Tag
The Tag field is four octet in length and is intended to provide a
means of grouping attributes in the same message which refer to
the same set. If the Tag field is unused, the 'T' bit MUST NOT be
set.
2.2.3 AVP Value Formats
The Data field is zero or more octets and contains information
specific to the Attribute. The format and length of the Data field is
determined by the AVP Code and AVP Length fields. Note that messages
which are larger than the path MTU will cause IP fragmentation and
messages SHOULD be kept to that size wherever possible. In any case
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UDP limits messages to 2^16 bytes.
The format of the value field MAY be one of seven data types.
Data
The data contains a variable length of arbitrary data. Unless
otherwise noted, the AVP Length field MUST be set to at least
9.
String
The data contains a non-NULL terminated variable length string
using the UTF-8 [24] character set. Unless otherwise noted,
the AVP Length field MUST be set to at least 9.
Address
32 bit (IPv4) [17] or 128 bit (IPv6) [16] address, most
significant octet first. The format of the address (IPv4 or
IPv6) is determined by the length. If the attribute value is an
IPv4 address, the AVP Length field MUST be 12, otherwise the
AVP Length field MUST be set to 24 for IPv6 addresses.
Integer32
32 bit value, in network byte order. The AVP Length field MUST
be set to 12.
Integer64
64 bit value, in network byte order. The AVP Length field MUST
be set to 16.
Time
32 bit unsigned value, In network byte order, and contains the
seconds since 00:00:00 GMT, January 1, 1900. The AVP Length
field MUST be set to 12.
Complex
The complex data type is reserved for AVPs that includes
multiple information fields, and therefore do not fit within
any of the AVP types defined above. Complex AVPs MUST provide
the data format, and the expected length of the AVP.
2.2.4 DIAMETER Base Protocol AVPs
The following table describes the DIAMETER AVPs defined in the base
protocol, their AVP Code values, types, possible flag values and
whether the AVP MAY be encrypted.
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Irregular AVP Flag rules
+-----+-----+------+-----+----+
Attribute Section Value | | |SHOULD| MUST|Encr|
Attribute Name Code Defined Type | MUST| MAY | NOT | NOT|Cand|
--------------------------------------------------+-----+------+----------+
User-Name [1] 1 3.3 String | | | | | Y |
Host-IP-Address[1] 4 2.3.2 Address | M | | | T,V | N |
Session-Timeout[1] 27 3.2 Integer32| | | | | Y |
Host-Name [1] 32 2.3.3 String | M | | | T,V | N |
Proxy-State [1] 33 6.1.1 Complex | M | | | T,V | N |
Command-Code 256 2.3.1 Integer32| M | V | | T | N |
Extension-Id 258 2.6.5 Integer32| | | | | Y |
Integrity-Check 259 7.1.1 Complex | | | | | N |
-Value | | | | | |
Encrypted-Payload 260 7.1.2 Data | | | | | N |
Nonce 261 7.2 Data | | | | | N |
Timestamp 262 7.3 Time | | | | | N |
Session-Id 263 3.3 Data | | | | | Y |
Vendor-Name 266 2.6.1 String | | | |T,V,M| Y |
Firmware 267 2.6.2 Integer32| | | |T,V,M| Y |
-Revision | | | | | |
Result-Code 268 5.2 Complex | | | | | N |
Destination-NAI 269 6.1.2 String | | | | | Y |
Reboot-Type 271 2.6.3 Integer32| | | | | N |
Reboot-Time 272 2.6.4 Integer32| | | | | N |
Failed-AVP 279 5.1.1 Data | | | | | Y |
Receive-Window 277 4.1.1 Integer32| | | | | Y |
Redirect-Host 278 6.2.1 Address | | | | | Y |
2.3 Mandatory AVPs
This section defines the DIAMETER AVPs that MUST be present in all
DIAMETER messages, with the exception of the ZLB.
2.3.1 Command-Code AVP
The Command-Code AVP (AVP Code 256) is of type Integer32 and MUST be
the first AVP following the DIAMETER header (except for ZLB
messages). A DIAMETER message MUST have at most one Command-Code
AVP, and it is used in order to communicate the command associated
with the message. The Command Code 32-bit address space is managed
by IANA (see section 8.2).
The following Command Codes are currently defined in the DIAMETER
protocol:
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Command-Name Abbrev. Code Reference
--------------------------------------------------------
Device-Reboot-Ind DRI 257 2.6
Device-Watchdog-Ind DWI 258 2.7
Message-Reject-Ind MRI 259 5.1
AA-Mobile-Node-Request AMR 260 [10]
AA-Mobile-Node-Answer AMA 261 [10]
Home-Agent-MIP-Request HAR 262 [10]
Home-Agent-MIP-Answer HAA 263 [10]
Mobile-Node-Terminate-Ind MTI 264 [10]
AA-Request AAR 265 [7]
AA-Answer AAA 266 [7]
AA-Challenge-Ind ACI 267 [7]
DIAMETER-EAP-Request DER 268 [7]
DIAMETER-EAP-Answer DEA 269 [7]
DIAMETER-EAP-Ind DEI 270 [7]
Accounting-Request ACR 271 [15]
Accounting-Answer ACA 272 [15]
Accounting-Poll-Ind ACP 273 [15]
2.3.2 Host-IP-Address AVP
The Host-IP-Address AVP (AVP Code 4) is of type Address and is used
to inform a DIAMETER peer of the sender's IP address. All DIAMETER
messages, except for ZLBs, MUST include either the Host-IP-Address or
the Host-Name (section 2.3.3) AVPs, or both.
2.3.3 Host-Name AVP
The Host-Name AVP (AVP Code 32) is of type String, and is used to
inform a DIAMETER peer of the sender's identity. All DIAMETER
messages, except for ZLBs, MUST include either the Host-IP-Address or
the Host-Name (section 2.3.2) AVPs, or both. This AVP contains the
host name of the originator of the DIAMETER message that MUST follow
the NAI [8] naming conventions.
2.4 The art of AVP Tagging
The AVP Header provides the 'T' bit, which is used to group AVPs
together. All AVPs with the same tag value are part of the same
"group", and there are no guidelines or rules on which tag values are
used. The base protocol defines the Redirect-Host AVP (see section
6.2.1), and [11] defines how the associated certificate MAY be
carried within the DIAMETER protocol. This allows a single request to
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include information about more than one host. In the case where
multiple AVPs are needed to indicate a specific authorization "rule"
tagging is appropriate. In some cases, more than one such rule MAY be
present, and the tagging mechanism allows the sets of AVPs to be
easily grouped.
Some Command Codes require certain AVPs to be tagged and use the '('
and ')' characters in the BNF command definition, such as:
<Device-Reboot-Ind> ::= <DIAMETER Header>
<Command Code AVP>
(<Tagged AVP #1>
<Tagged AVP #2>
<Tagged AVP n>)
2.5 State Machine
A DIAMETER node initially considers all known peers to be in the
closed state, and should not process any DIAMETER message with the
exception of the Device-Reboot-Ind (DRI). Once the DIAMETER peer is
set to the open state, any DIAMETER message may be accepted and
processed. This section provides the DIAMETER base protocol state
machine.
If at any time no transport level acknowledgement is received and the
message was retransmitted the maximum number of times, the session
with the peer MUST be closed, and all associated state with the peer
MUST be freed.
State Event Action New State
----- ----- ------ ---------
closed Local Open send DRI wait-ack1
Request
closed receive DRI send ACK wait-ack2
send DRI
closed receive invalid cleanup closed
DRI
wait-ack1 receive ACK accept Incoming wait-ack1
Messages
wait-ack1 receive DRI send ACK open
Accept Incoming
Messages
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wait-ack1 no ACK received cleanup closed
wait-ack2 received ACK Accept Incoming open
Messages
wait-ack2 no ACK received cleanup closed
open receive DRI send ACK wait-ack2
Rebooted send DRI
open receive DRI cleanup closed
Imminent-Reboot
open receive DWI send ACK open
open receive other send ACK open
messages
open inactivity period send DWI open
hits watchdog
timer
open no ACK received cleanup closed
2.6 Device-Reboot-Ind (DRI) Command
A DIAMETER device sends the Device-Reboot-Ind message, by including
the Command-Code AVP with a value of 257, to inform a peer either of
an upcoming reboot, or that it has just rebooted. The Reboot-Type AVP
MUST be present and indicates the type of reboot associated with this
command. Note that a DIAMETER device should only send this message
when it is able to receive network traffic.
The receiver of a DRI message with the Reboot-Type AVP set to
REBOOT_IMMINENT SHOULD make an attempt to send packets to an
alternate peer, if one is available. The optional Reboot-Time AVP
will contain an estimate of how long before the peer will be ready to
re-establish communication. In the case of a software implementation
(server) running on a general purpose operating system, the Reboot-
Time AVP will probably not be present since it is possible that the
DIAMETER server has been stopped and it is not possible to know how
long before (and if) it will be restarted.
The DRI message is also used for capabilities negotiation, such as
the supported protocol version number, and the locally supported
extensions. The receiver uses the extensions advertised in order to
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determine whether it SHOULD send certain application-specific
DIAMETER commands. A DIAMETER node MUST retain the supported
extensions in order to ensure that unrecognized commands and/or AVPs
are not sent to a peer. Note that in a proxy environment, it is still
possible for this problem to occur, and the DIAMETER base protocol
provides this error reporting message.
Upon reboot, the host MUST issue a DRI message with the Reboot-Type
AVP set to REBOOTED to all configured peers. If a peer is no longer
reachable, a DIAMETER device SHOULD periodically transmit a DRI until
an acknowledgement is received. The retransmission timer SHOULD be
different from the retransmission timer used when communication has
been established, and SHOULD be configurable.
Upon receipt of this message the peer's Ss and Sr variables MUST be
reset. It is possible for this message to be received outside the
window (Ns and Nr set to zero) when it follows a reboot.
The DIAMETER Reboot-Ind message does not require a reply. The message
is acknowledged using DIAMETER's reliable transport. See [25] for
more information.
Message Format
<Device-Reboot-Ind> ::= <DIAMETER Header>
<Command Code AVP = 257>
{<Host-IP-Address AVP> ||
<Host-Name AVP>}
<Vendor-Name AVP>
<Extension-Id AVPs>
<Reboot-Type AVP>
[<Reboot-Time AVP>]
[<Receive-Window AVP>]
[<Firmware-Revision AVP>]
[<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>]
2.6.1 Vendor-Name AVP
The Vendor-Name AVP (AVP Code 266) is of type String and is used to
inform a DIAMETER peer of the Vendor Name of the DIAMETER device.
This MAY be used in order to know which vendor specific attributes
may be sent to the peer. It is also envisioned that the combination
of the Vendor-Name and the Firmware-Revision (section 2.6.2) AVPs MAY
provide very useful debugging information.
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2.6.2 Firmware-Revision AVP
The Firmware-Revision AVP (AVP Code 267) is of type Integer32 and is
used to inform a DIAMETER peer of the firmware revision of the
issuing device.
For devices that do not have a firmware revision (general purpose
computers running DIAMETER software modules, for instance), the
revision of the DIAMETER software module may be reported instead.
2.6.3 Reboot-Type AVP
The Reboot-Type AVP (AVP Code 271) is of type Integer32 and MUST be
present in the Device-Reboot-Indication message. This AVP contains an
indication of the type of reboot that has or will occur. The
following values are currently supported:
REBOOT_IMMINENT 1
When the Reboot-Type AVP is set to this value it is an
indication that the DIAMETER peer is about to reboot and should
not be sent any additional DIAMETER messages after the
acknowledgement for this Device-Reboot-Ind message.
REBOOTED 2
When the Reboot-Type AVP is set to this value it is an
indication that the DIAMETER peer has recently rebooted and is
ready to accept new DIAMETER messages.
2.6.4 Reboot-Time AVP
The Reboot-Time AVP (AVP Code 272) is of type Integer32 and MAY be
present in the DRI. The value of this AVP indicates the number of
seconds before the issuer expects to be ready to receive new DIAMETER
messages. This AVP MUST only be present when the Reboot-Type AVP is
set to REBOOT_IMMINENT. The value indicated by this AVP should be
used as an estimate and is not a hard rule.
2.6.5 Extension-Id AVP
The Extension-Id AVP (AVP Code 258) is of type Integer32 and is used
in order to identify a specific DIAMETER extension. This AVP is used
in the Device-Reboot-Ind command in order to inform the peer what
extensions are locally supported.
Each DIAMETER extension draft MUST have an Extension-Id assigned to
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it by the IANA (see section 8.3). The base protocol does not require
an Extension-Id since its support is mandatory.
There MAY be more than one Extension-Id AVP within a DIAMETER
Device-Reboot-Ind message. The following values are recognized:
NASREQ 1 [7]
Strong Security 2 [11]
Mobile-IP 4 [10]
Accounting 5 [15]
2.7 Device-Watchdog-Ind (DWI) Command
The Device-Watchdog-Ind (DWI), indicated by the Command-Code AVP set
to 258, is OPTIONAL and is used as a keepalive mechanism between two
DIAMETER peers. If implemented, it SHOULD be sent during after a
configurable period of inactivity. Communicating peers are not
required to have the same DWI timer values set, as each entity MAY
have different requirements.
A DIAMETER node MAY use this mechanism to ensure that fail-over to an
alternate server occurs in the absence of AAA traffic. This pro-
active approach may minimize the possible latency involved in the
fail-over that would otherwise occur.
The lower the timer value is set to, the quicker a host will pro-
actively detect that a peer is no longer reachable. However, the
timer SHOULD NOT be set to a value that is considered too low (e.g. 2
seconds), since it will generate considerable traffic.
The DIAMETER Device-Watchdog-Ind message does not require a reply.
The message is acknowledged using DIAMETER's reliable transport. See
[25 for more information.
Message Format
<Device-Watchdog-Ind> ::= <DIAMETER Header>
<Command Code AVP = 258>
{<Host-IP-Address AVP> ||
<Host-Name AVP> }
[<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>]
3.0 "User" Sessions
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When a user requests access to the network, a DIAMETER client issues
an authentication and authorization request to its local server. The
request contains a Session-Id AVP, which is used in subsequent
messages (e.g. subsequent authorization, accounting, etc) relating to
the user's session. The Session-Id AVP is a means for the client and
servers to correlate a DIAMETER message with a user session.
When a DIAMETER server authorizes a user to use network resources, it
SHOULD add the Session-Timeout AVP to the response. The Session-
Timeout AVP defines the maximum amount of time a user MAY make use of
the resources before another authorization request is to be
transmitted to the server. If the server does not receive another
authorization request before the timeout occurs, it SHOULD release
any state information related to the user's session. Note that the
Session-Timeout AVP implies how long the DIAMETER server is willing
to pay for the services rendered, therefore a DIAMETER client SHOULD
NOT expect payment for services rendered past the session expiration
time.
The base protocol does not include any authorization request
messages, since these are largely application-specific and are
defined in a DIAMETER protocol extension document. Such extensions
SHOULD provide a message that allows a client to inform a server that
the user's session has been released. This would enable the server to
free state information instead of having to wait for the timeout to
occur.
3.1 Session-Id AVP
The Session-Id AVP (AVP Code 263) is of type Data and is used to
identify a specific session (see section 3.0). All messages
pertaining to a specific session MUST include only one Session-Id AVP
and the same value MUST be used throughout the life of a session.
When present, the Session-Id SHOULD appear immediately following the
Command-Code AVP.
For messages that do not pertain to a specific session, multiple
Session-Id AVPs MAY be present as long as the 'T' bit is set.
The Session-Id MUST be globally unique at any given time since it is
used by the server to identify the session (or flow). The format of
the session identifier SHOULD be as follows:
<Sender's IP Address><sender's port number> <monotonically increasing
32 bit value><optional value>
The monotonically increasing 32 bit value SHOULD NOT start at zero
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upon reboot, but rather start at a random value. This will minimize
the possibility of overlapping Session-Ids after a reboot.
Alternatively, an implementation MAY keep track of the increasing
value in non-volatile memory. The optional value is implementation
specific but may include a modem's device Id, a layer 2 address,
timestamp, etc.
The session Id is created by the DIAMETER device initiating the
session, which in most cases is done by the client. Note that a
Session-Id MAY be used by more than one extension (e.g.
authentication for a specific service and accounting, both of which
have separate extensions).
3.2 Session-Timeout AVP
The Session-Timeout AVP (AVP Code 27) is of type Integer32 and
contains the maximum number of seconds of service to be provided to
the user before termination of the session. A value of zero means
that this session has an unlimited number of seconds before
termination.
This AVP MAY be provided by the client as a hint of the maximum
duration that it is willing to accept. However, the server DOES NOT
have to observe the hint and MAY return any value. A value of zero
provided by a client DOES NOT imply that service is being terminated.
3.3 User-Name AVP
The User-Name AVP (AVP Code 1) is of type String and contains the
User-Name in a format consistent with the NAI specification [8]. All
DIAMETER systems SHOULD support usernames of at least 72 octets in
length.
4.0 Reliable Transport
This section provides a detailed overview of how DIAMETER is reliably
transported over UDP. DIAMETER provides its own reliable transport
due to its unique requirements, which include:
- Rapid discovery of the failure of a communicating peer.
- Transactions of few messages will be the norm, so the TCP slow
start algorithm is not appropriate.
- The retransmission scheme required is more aggressive than TCP
provides.
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4.1 Flow Control
The DIAMETER header contains two fields used for reliable transport:
Nr (Next Received) and Ns (Next Send). The sequence number state for
each peer is represented (for clarity of discussion) as Sr (the next
in-sequence message expected to be received) and Ss (the next in-
sequence message to be sent). Sr and Ss are initialized to 0.
The sequence number is a free ranging counter modulo 65536. For
purposes of detecting duplication, a received sequence value is
considered less than or equal to the last received value if its value
lies in the range of the last value and its 32767 successor values.
For example if the last received sequence number was 15, the packets
received with Ns values in the range 32783..65535, or 0..15 would be
considered duplicates. Duplicate messages are silently discarded.
ZLB messages are used to acknowledge DIAMETER messages to the
communicating peer. Each subsequent non-ZLB message is sent with a
sequence number incremented by one (modulo 2^16). The following rules
apply:
- When a non-ZLB message is received with a Ns value which matches
the peer's Sr value, Sr is incremented by one. Sr is not
modified if a message is received with a Ns value greater than
the current Sr value.
- In messages which are sent to a peer, Nr is set to reflect one
higher than the Ns value of the highest (module 2^16) in-order
message received from the peer.
- Every time a peer sends a non-ZLB message, it sends the message
with Ns set to the current value of Ss. The value of Ss for
that peer is then incremented by one (modulo 2^16).
- Every time a peer receives an in-order non-ZLB message, the
receiving peer must increment its Sr value. The peer MUST
acknowledge the message, either by sending a ZLB message with
the updated Nr value, or by piggybacking the acknowledgement in
any outgoing message sent to the communicating peer. In this
piggybacked message, the Nr field will be set to its updated
value. The implementation guidelines [25] defines an OPTIONAL
algorithm for delaying acknowledgments, to wait for outgoing
messages to piggyback acknowledgements on.
- Messages which are sent MUST be queued and retransmitted till
the peer sends an acknowledgement. Messages SHOULD be
retransmitted at least three times. The implmentation
guidelines specification [25] recommends a retransmission timer
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algorithm.
Retransmitted messages SHOULD include the current value of Sr in the
Nr field. An implementation MAY choose not to update Nr field (and
Timestamp AVP) for retransmitted messages, in order to avoid having
to perform another hash in the Integrity-Check- Value AVP. The
message identifier in the retransmitted message MUST NOT be changed.
A DIAMETER implementation MAY queue out of order DIAMETER messages
for subsequent processing.
The receive window is the maximum number of unacknowledged packets
that are to be outstanding to a DIAMETER peer. When transmitting
packets, a DIAMETER peer must obey the receive window size offered by
its peer. The default window size is 7. Once the number of
unacknowledged messages equals the window size, the window is
'closed.' Previously transmitted packets may be retransmitted when
the peer's window is closed. A peer MAY explicitly specify its
window size in the Device-Reboot-Ind message in the Receive-Window
AVP.
A peer MAY return a Nr value in a ZLB or piggybacked in a non-ZLB
message which is less than the latest Sr value, due to congestion.
Returning a value in Nr of the first value in the window will have
the effect of preventing the communicating peer from sending any new
messages.
See [25] for some examples of how sequence numbers progress.
4.1.1 Receive-Window AVP
The Receive-Window AVP (AVP Code 277) is of type Integer32 and
contains the maximum number of outstanding unacknowledged messages
that it is willing to accept for a given peer. Once the number of
unacknowledged messages has reached this number, the receive window
is considered closed. The default value for the receive window is 7,
and SHOULD be configurable. A simple implementation that does not
require a high number of transactions per second MAY send a Receive-
Window AVP set to one (1).
A node MUST stop sending messages when it detects that the number of
unacknowledged messages is equal to the peer's receive window size.
4.2 Peer failure recovery
A DIAMETER message with the Command-Code AVP set to Device-Reboot-Ind
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and the Ns and Nr values set to zero (0) indicates that the peer has
rebooted. This message MUST be recognized and supported by a
DIAMETER implementation. When this event occurs, the Ss and Sr values
must be reset and the retransmission queue MUST be cleared. Since the
protocol requires that all new messages include a random identifier
in the protocol header, a Device-Reboot-Ind that is received with the
same identifier as the last processed Device-Reboot-Ind is considered
a retransmission and SHOULD NOT change the peer's state to closed.
Messages other than the Device-Reboot-Ind MUST NOT be sent to the
peer until both the acknowledgement for the transmitted Device-
Reboot-Ind AND the peer's Device-Reboot-Ind have been received. When
both of these have been received, the peer is considered to be in the
active state.
5.0 Error Reporting
There are five different types of errors within DIAMETER. The first
being where a DIAMETER message is poorly formatted and
unrecognizable, indicated below by "Bad Message". This error
condition applies if a received message creates a fatal error (e.g.
fails transport level authentication, cannot be parsed, etc).
The second case involves receiving a Command-Code AVP that is not
supported, which is shown below by "Unknown Command". The third case
is where an AVP is received, marked mandatory and is unknown by the
receiver, which is labeled below as "Unknown AVP".
This fourth case involves receiving a message with a known AVP, yet
the value is either unknown or illegal, which is shown below as "Bad
Value". The last case occurs when an error occurs while processing a
specific extension command, which is not related to the message
format and is labeled "Extension Error" below.
Error Type Ignore Message Send Extension
Message-Reject-Ind Response +
Result-Code
Bad Message X
Unknown Command X
Unknown AVP X
Bad Value X
Extension Error X
"Ignore Message" indicates that the message is simply dropped. The
"Message-Reject-Ind" indicates that a Message-Reject-Ind message MUST
be sent to the peer as described in the appropriate section. The
"Extension Response + Result-Code" indicates that the appropriate
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Response to the message MUST be sent with the Result-Code AVP set to
a value that enables the peer to understand the nature of the
problem.
5.1 Message-Reject-Ind (MRI) Command
The Message-Reject-Ind (MRI), indicated by the Command-Code AVP set
to 256, provides a generic means of completing transactions by
indicating errors in the messages that initiated them. The Message-
Reject-Ind command is a possible response to any DIAMETER command.
Some DIAMETER commands MAY expect more specialized error messages,
depending on the error type.
The Message-Reject-Ind message MUST contain the same identification
in the header and include the Session-Id if it was present in the
original message that it is responding to, even if the identification
is erroneous. The receiver of a Message-Reject-Ind SHOULD examine the
Result-Code AVP provided before processing the identification, in
order to handle the latter appropriately.
Message Format
The structure of the Message-Reject-Ind message is defined as
follows:
<Message-Reject-Ind message> ::= <DIAMETER Header>
<Command-Code AVP = 256>
<Host-IP-Address AVP>
[<Host-Name AVP>]
[<Session-Id AVP>]
<Result-Code AVP>
<Failed-AVP AVP>
[<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>]
where the Identifier value in the message header and optionally
the Session-Id AVP are copied from the message being rejected. The
Result-Code AVP indicate the nature of the error causing
rejection, and the Failed-AVP AVP provides some minimal debugging
data by indicating a specific AVP type which caused the problem.
See the description of the Result-Code AVP for indication of when
the Failed-AVP AVP MUST be present in the message. See [25] for
more information.
5.1.1 Failed-AVP AVP
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The Failed-AVP AVP (AVP Code 279) is of type Data and provides
debugging information in cases where a request is rejected or not
fully processed due to erroneous information in a specific AVP. The
value of the Result-Code AVP will provide information on the reason
for the Failed-AVP AVP.
A DIAMETER message MAY contain one or more Failed-AVP, each
containing a complete AVP that could not be processed successfully.
The possible reasons for this AVP are the presence of an improperly
constructed AVP, an unsupported or unrecognized AVP or an invalid AVP
value (e.g. unknown Command-Code AVP).
5.2 Result-Code AVP
The Result-Code AVP (AVP Code 268) is of type Complex and indicates
whether a particular request was completed successfully or whether an
error occurred. All DIAMETER messages of type *-Response or *-Answer
MUST include one Result-Code AVP.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AVP Header (AVP Code = 268)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| String ...
+-+-+-+-+-+-+-+-+
The Result Code field contains an IANA-managed 32-bit address space
representing errors. The String field contains an OPTIONAL string
field containing a human readable error message. The base protocol
defines the following error codes, and others MAY be defined in
separate DIAMETER extensions:
DIAMETER_SUCCESS 0
The Request was successfully completed.
DIAMETER_FAILURE 1
The Request was not successfully completed for an unspecified
reason. A DIAMETER Message-Reject message returning this
result SHOULD whenever possible also contain one or more
Failed-AVP AVPs indicating the attributes which caused the
failure.
DIAMETER_POOR_REQUEST 2
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The Request was poorly constructed.
DIAMETER_INVALID_AUTH 3
The Request did not contain a valid Integrity-Check-Value or
CMS-Data [11] AVP.
DIAMETER_UNKNOWN_SESSION_ID 4
The Request contained an unknown Session-Id. This error is sent
only due to conditions that arise due to command messages in
DIAMETER extensions, the base protocol does not include command
codes that require the Session-Id AVP.
DIAMETER_USER_UNKNOWN 5
A request was received for a user that is unknown, therefore
authentication failed. This error is sent only due to
conditions that arise due to command messages in DIAMETER
extensions, the base protocol does not include command codes
that require the User-Name AVP.
DIAMETER_COMMAND_UNSUPPORTED 6
The Request contained a Command-Code AVP that the receiver did
not recognize or support. The Message-Reject-Ind message MUST
also contain a Failed-AVP AVP containing the unrecognized
Command-Code AVP.
DIAMETER_TIMEOUT 7
This error MAY be returned if a request has been received that
has a Timestamp AVP that is older than the maximum age that the
communicating peer is willing to accept.
DIAMETER_AVP_UNSUPPORTED 8
The peer received a message that contained an AVP that is not
recognized or supported and was marked with the Mandatory bit.
A Message-Reject-Ind message with this error MUST contain one
or more Failed-AVP AVP containing the AVPs that caused the
failure.
DIAMETER_REDIRECT_INDICATION 9
A proxy or broker has determined that the request could not be
satisfied locally and the initiator of the request should
direct the request directly to the server, whose contact
information has been added to the response. This error code
MUST NOT be sent in a Message-Reject-Ind message.
DIAMETER_DOMAIN_NOT_SERVED 10
A proxy or broker has determined that it is unable to forward
the request or provide redirect information since the realm
portion of the NAI requested is unknown.
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DIAMETER_UNSUPPORTED_TRANSFORM 11
A message was received that included an Integrity-Check-Value
or CMS-Data AVP [11] that made use of an unsupported transform.
DIAMETER_AUTHENTICATION_REJECTED 12
The authentication process for the user failed, most likely due
to an invalid password used by the user.
DIAMETER_AUTHORIZATION_REJECTED 13
A request was received for which the user could not be
authorized. This error could occur when the user has already
expended allowed resources, or if the service requested is not
permitted to the user.
DIAMETER_INVALID_AVP_VALUE 14
The request contained an AVP with an invalid value in its data
portion. A DIAMETER message with this result code MUST include
the offending AVPs within a Failed-AVP AVP.
DIAMETER_MISSING_AVP 15
The request did not contain an AVP which the Command Code
requires be present. If this result code is sent, a Failed-AVP
AVP should be included in the Message-Reject-Ind message. The
AVP 'Data' in the Failed-AVP has its AVP Code set to the value
of the missing and required AVP, but does not include any data
of its own.
6.0 DIAMETER Message Routing
The DIAMETER base protocol supports two basic message routing
methods; proxying and brokering. A DIAMETER proxy is a server that
simply forwards the request based on the user's identity, or through
some other means. A DIAMETER broker is a server that provides
redirect services, allowing all servers in a roaming consortium to
interact directly.
6.1 Message Proxying
A DIAMETER proxy is a server that provides message forwarding
functions to other DIAMETER Servers. Proxies are typically used when
a hierarchical DIAMETER network is deployed, where some DIAMETER
servers can authenticate and authorize a set of users. Such an
example is a roaming consortium, where each ISP has a user base,
which they can authenticate and authorize. It is important to note
that proxy servers MUST NOT attempt to re-order AVPs in a DIAMETER
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message.
The example provided in figure 1 shows a request issued by DIA1,
requesting authentication and authorization for a user that belongs
to DIA3's network. When DIA1 receives the request from the access
device (e.g. NAS), it checks whether the Destination-NAI AVP is
present, which MUST be in a format consistent with the NAI [8]
specification. If the Destination-NAI is not present, the server MUST
use the information found in the User-Name AVP.
The NAI has a format of user@realm, and DIAMETER servers typically
have a list of locally supported realms, and MAY have a list of
externally supported realms with associated DIAMETER servers.
DIAMETER servers that interface with brokers SHOULD allow for a
"default" destination for all requests received that are not locally
configured.
In the example below, DIA1 looks up the user's realm, and determines
that the request is to be forwarded to DIA2. When DIA2 receives the
request, it MAY decide that some state information needs to be kept
in order to process the response in a particular fashion. An example
would be that DIA2 determines that certain authorization information
is to be added to the response, when received.
(Request) (Request)
(User-Name=joe@abc.com) (User-Name=joe@abc.com)
(Host-Name=DIA1@nmo.net) (Host-Name=DIA1@nmo.net)
(Proxy-State=x) (Proxy-State=y)
+------+ ------> +------+ ------> +------+
| | | | | |
| DIA1 +-------------------+ DIA2 +-------------------+ DIA3 |
| | | | | |
+------+ <------ +------+ <------ +------+
(Response) (Response)
(User-Name=joe@abc.com) (User-Name=joe@abc.com)
(Dest-NAI=DIA1@mno.net) (Dest-NAI=DIA1@mno.net)
(Proxy-State=x) (Proxy-State=y)
mno.net xyz.com abc.com
Figure 1: DIAMETER Proxying
There are two methods that MAY be implemented by DIAMETER servers in
order to keep per-request state information.
1. DIA2 MAY maintain a state control block, and using the
session-Id and possibly the Identifier in the header, can match
the request with the response. The state control block MAY
include AVPs that need to be added to the corresponding
response, or any additional policy decisions that will need to
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be done when the response is received.
2. DIA2 MAY add a Proxy-State AVP (see section 6.1.1), which can
contain ANY information that will be needed when the
corresponding response is received. A DIAMETER message MUST
only include one Proxy-State AVP, so if a new Proxy-State AVP
is added, the old one MUST be removed. The new Proxy-State AVP
MAY include AVPs that are to be added to the response, the
existing Proxy-State AVP, etc.
Once DIA2 has completed processing the request, it forwards the
request to DIA3 following the same procedures defined for DIA1.
When DIA3 receives the request, and it determines that the
request is to be processed locally, it authenticates and
authorizes the user. DIA3 MUST add the Destination-NAI AVP,
with the same contents as the Host-Name AVP that was found in
the corresponding request. If the request contained a Proxy-
State AVP, the same AVP MUST be present in the response.
When DIA2 receives the response from DIA3, it MUST first
determine whether the Proxy-State AVP was created locally by
looking at the address field of the AVP. Since it is the same
AVP as the one that it added to the request, it will extract
any embedded information within the Proxy-State AVP. If AVPs
were encapsulated within the Proxy-State AVP, these SHOULD be
extracted and added to the response. If the request from DIA1
included a Proxy-State AVP, the same AVP MUST be present in the
response back to DIA1.
6.1.1 Proxy-State AVP
The Proxy-State AVP (AVP Code 33) is used by proxy servers when
forwarding requests and contains opaque data that is used by the
proxy to further process the response. Such data may include AVPs
that are to be added to the response, information about the
downstream peer, etc.
A DIAMETER node that receives such an AVP in a request MUST return
the identical AVP in the response. Furthermore, no more than one
Proxy-State AVP MUST be present in a message at any given time, so
implementations MUST ensure that they remove any Proxy-State AVPs
before adding their own.
If the Proxy-State AVP was removed from a request, the same AVP MUST
be inserted in the corresponding response before forwarding the
message to the downstream peer.
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The Proxy-State AVP's Address field is 128-bits in length contains
the IP address of the system created the AVP. If the host creating
the AVP has an IPv4 address, the leading 96 bits MUST be set to zero
(0). This field is intended to assist hosts in determining whether a
Proxy-State AVP is intended for the local host.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AVP Header (AVP Code = 33)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 128-bit Address...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
6.1.2 Destination-NAI AVP
The Destination-NAI AVP (AVP Code 269) is of type String and MAY be
included in a request or response message, and MUST be in a format
consistent with the NAI specification. When found in a response, the
AVP SHOULD contain the value of the Host-Name AVP that was found in
the request. This AVP SHOULD be used by intermediate proxies in the
message routing process.
6.2 Message Redirection
There are cases where a DIAMETER proxy, known as a broker, may wish
to request that a server contact another directly instead of
forwarding the message (figure 2). This is typically done when the
broker provides simple NAI to Home DIAMETER Server address resolution
services.
In the example provided in figure 2, abc.net's DIAMETER server issues
a request to its broker, which in turn returns a response that
includes the Result-Code AVP set to a specific value (see section
5.2). When a response is received with such a value, the message MUST
also include one or more Redirect-Host AVPs. These AVPs contain
address information that SHOULD be used to directly communicate with
the Home DIAMETER Server. Note that the servers MAY cache the home
server information in order to reduce the latency involved in any
future messages destined for that home server.
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+------------------+ +---------+
| DIAMETER | | CRL DB/ |
| Broker | | OCSP |
+------------------+ +---------+
/|\
Request | Response +
| Result Code =
| Redirect
\|/
+----------+ +----------+
| abc.net |/ \| xyz.net |
| DIAMETER |--------------| DIAMETER |
| Server |\ /| Server |
+----------+ Direct +----------+
Communication
Figure 2: DIAMETER Broker Returning Redirect Indication
When returning the response with the Result-Code set to indicate a
redirect indication, the broker MAY also include the certificates of
both the requesting server, and the target server. These certificates
are encapsulated in a CMS-Data AVP [11]. The requesting server SHOULD
forward the certificate that belongs to it in the subsequent request
to the home DIAMETER server.
6.2.1 Redirect-Host AVP
The Redirect-Host AVP (AVP Code 278) is of type Address and is
returned in a response that has the Result-Code AVP set to
DIAMETER_REDIRECT_REQUEST. This AVP includes address information of
the DIAMETER host to which the request must be redirected. Upon
receipt of such a Result-Code, and this AVP, a DIAMETER host SHOULD
send the request directly to the host. A proxy server or broker MAY
return more than one Redirect-Host AVP if there is more than one
DIAMETER server that can satisfy the request.
The broker MAY wish to return the certificate associated with a given
Redirect-Host AVP. This can be returned in a CMS-Data AVP, as defined
in [11].
7.0 DIAMETER Message Security
The DIAMETER Base protocol MAY be secured in one of three ways. The
first method does not involve any security mechanisms in the DIAMETER
protocol, but relies on an underlying security mechanism, such as IP
Security. The second method is hop-by-hop security, which SHOULD be
supported by all DIAMETER implementations. The third method is
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optional and requires a Public Key Infrastructure [14], and is
documented in [11].
7.1 Hop-by-Hop Security
DIAMETER Hop-by-Hop security provides message integrity and per AVP
encryption, and requires that the communicating entities have a pre-
configured shared secret, similar to the method employed by the
RADIUS protocol. Hop-by-Hop security does not have the scaling
properties associated with a public key infrastructure (PKI), which
is used in end-to-end security, but MAY be desirable in environments
where asymmetric technology is not required, or available.
Hop-by-Hop security implies that each hop along a proxy chain is
responsible for the following tasks:
- Validating the message's integrity using the shared secret with
the sender.
- Decrypting any encrypted AVPs using the secret shared with the
sender.
- Re-encrypting AVPs using the secret shared with the next server.
- Computing the message hash using the secret shared with the next
server, and adding it to the ICV AVP in the DIAMETER message.
(Shared-Secret-1) (Shared-Secret-2)
+------+ -----> +------+ ------> +------+
| | | | | |
| DIA1 +-------------------+ DIA2 +-------------------+ DIA3 |
| | | | | |
+------+ +------+ +------+
Figure 3: Hop-by-Hop Security in Proxy Environments
The above steps that each proxy MUST perform in a proxy chain clearly
describes the security issues associated with hop-by-hop security in
a proxy environment. Since the message integrity is re-computed at
each node in the chain, it is very difficult to detect if a proxy
modified information in the message (e.g. session time). Furthermore,
any sensitive information would be known to all proxies in the chain,
since each node must decrypt AVPs. Therefore, Any AVPs that require
strong authentication and/or confidentiality in a proxy environment
SHOULD be protected via the mechanism described in the strong
security extension [11].
It is highly recommended that the size of the shared secrets used be
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sufficiently long (e.g. 128 bits), and that different shared secrets
be used for both authentication and encryption.
7.1.1 Integrity-Check-Value AVP
The Integrity-Check-Value AVP (AVP Code 259) is of type data and is
used for hop-by-hop authentication and integrity, and is not
recommended for use with untrusted proxy servers.
The DIAMETER header as well as all AVPs (including padding) up to
this AVP is protected by the Integrity-Check-Value. Note that the
Message Length field in the DIAMETER header MUST be set to zero (0)
prior to the ICV calculation. The Timestamp and Nonce AVPs MUST be
present in the message PRIOR to the Integrity-Check-Value AVP. The
Timestamp AVP provides replay protection and the Nonce AVP provides
randomness. Any AVPs in a message that is not succeeded by the
Integrity-Check-Value AVP MUST be ignored.
The following is an example of a message that include hop-by-hop
security:
<DIAMETER Message> ::= <DIAMETER Header>
<Command-Code AVP>
[<Additional AVPs>]
<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>
All DIAMETER implementations SHOULD support this AVP.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AVP Header (AVP Code = 259)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transform ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
AVP Length
The length of this attribute MUST be at least 13.
Transform ID
The Transform ID field contains a value that identifies the
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transform that was used to compute the ICV. The following
values are defined in this document:
HMAC-MD5-96[6] 1
The ICV is computed using the HMAC-MD5 algorithm, and the
first 12 bytes of the hash output is included in the data
portion of the ICV AVP. All DIAMETER implementations
supporting this AVP MUST support this transform. Using the
example code provided in [6], the following call would be
used to generate the Integrity-Check-Value:
hmac_md5(DiameterMessage, MessageLength, Secret,
Secretlength, Output)
Key ID
The Key ID field contains a key identifier, which is used to
identify the keying information used to generate the AVP's data
field.
Data
The data field contains the output from the hashing algorithm.
7.1.2 Encrypted-Payload AVP
The Encrypted-Payload AVP (AVP Code 260) is of type data and is used
to encapsulate encrypted AVPs for privacy during transmission.
Hop-by-Hop confidentiality is achieved by encapsulating all AVPs
which are to be encrypted into an Encrypted-Payload AVP. This
feature SHOULD be supported by DIAMETER implementations.
The plain text (which is a buffer containing one or more AVPs) is
first padded to a sixteen (16) byte boundary with 0 bytes. Since the
encapsulated AVPs have length fields, it is possible to detect their
boundaries, whether or not padding has been done.
One or more Nonce AVPs MUST precede an Encrypted-Payload AVP. An MD5
hash is performed on the:
- last Nonce AVP which precedes the Encrypted-Payload AVP
- the shared authentication secret
This MD5 hash value is then XORed with the first 16 octet segment of
the buffer to encrypt. The resulting 16 octet result is saved as the
first 16 octets of the encrypted buffer. The result is also used to
calculate a new value using MD5:
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- the 16 byte result of the previous XOR
- the shared authentication secret
This value is then XORed with the next 16 bytes. This is done for
each 16 bytes successively in the buffer to encrypt, producing an
equal sized encrypted buffer.
The receiver of a DIAMETER message with an Encrypted-Payload AVP MUST
first check the integrity of the message, either through the ICV, or
the CMS-Data AVP [11] if it protects the Encrypted-Payload AVP. Then
the Encrypted-Payload AVP is decrypted, using the same algorithm as
above, which applied to the buffer will reproduce the plain text
version. The decapsulated AVPs are then used to process the DIAMETER
message in the normal manner.
7.2 Nonce AVP
The Nonce AVP (AVP Code 261) is of type Data and MUST be present
prior to the Integrity-Check-Value AVPs within a message and is used
to ensure randomness within a message. The content of this AVP MUST
be a random value of at least 128 bits.
7.3 Timestamp AVP
The Timestamp AVP (AVP Code 262) is of type Time and is used to add
replay protection to the DIAMETER protocol. This AVP MUST appear
prior to the Integrity-Check-Value AVP or any other message integrity
AVP defined in separate extensions. The value of time is the most
significant four octets returned from an NTP server that indicates
the number of seconds expired since Jan. 1, 1900.
Messages which are older than a certain maximum age SHOULD be
rejected and a response SHOULD be returned with the Result-Code AVP
value set to DIAMETER_TIMEOUT.
Note that the larger the value, the more susceptible one is to a
replay attack. However, one does have to take into account the
possibility for clock drift, and the latency involved in the
transmission of the message over the network. The timestamp AVP
SHOULD be updated prior to retransmission.
8.0 IANA Considerations
This document defines a number of assigned numbers to be maintained
by the IANA. This section explains the criteria to be used by the
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IANA to assign additional numbers in each of these lists. The
following subsections describe the assignment policy for the
namespaces defined elsewhere in this document.
8.1 AVP Attributes
As defined in section 2.2, AVPs contain vendor ID, attribute and
value fields. For vendor ID value of 0, IANA will maintain a registry
of assigned AVP codes and in some case also values. Attribute 0-254
are assigned from the RADIUS protocol [1], whose attributes are also
maintained through IANA. AVP Codes 256-280 are assigned within this
document. The remaining values are available for assignment through
Designated Expert [12].
8.2 Command Code AVP Values
As defined in section 2.3.1, the Command Code AVPs (AVP Code 256)
have an associated value maintained by IANA. Values 0-255 are
reserved for backward RADIUS compatibility, and values 256-258 are
defined in this specification. The remaining values are available for
assignment via Designated Expert [12].
8.3 Extension Identifier Values
As defined in section 2.6.5, the Extension Identifier is used to
identify a specific DIAMETER Extension. All values, other than zero
(0) are available for assignment via Designated Expert [12].
Note that the DIAMETER protocol is not inteded to be extended for any
purpose. Any extensions added to the protocol MUST ensure that they
fit within the existing framework, and that no changes to the base
protocol are required.
8.4 Result-Code AVP Values
As defined in Section 5.2, the Result Code AVP (AVP Code 268) defines
the values 0-8. All remaining values are available for assignment via
IETF Consensus [12].
8.5 Integrity-Check-Value AVP Transform Values
Section 7.1.1 defines the Integrity-Check-Value AVP (AVP Code 259)
which contains a field called the Transform. This document reserves
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the value 1. All remaining values are available for assignment via
Designated Expert [12].
8.6 Reboot-Type AVP Values
Section 2.6.3 defines the Reboot-Type AVP (AVP Code 271), which is
used to inform the peer of the cause for the reboot. This document
defines the values 1-3. All remaining values are available for
assignment via Designated Expert [12].
8.7 AVP Header Bits
There are six remaining reserved bits in the AVP header. Additional
bits should only be assigned via a Standards Action [12].
9.0 Open Issues
The following are the open issues that SHOULD be addressed in future
versions of the DIAMETER protocol:
- AVPs of type 'Time" are 32 bits in size and contain the a
timestamp consistent with NTP [18]. This field is expected to
expire sometime in 2038. Future investigation SHOULD be done to
determine if a 64 bit time format could be used.
- The fact that the Sender's IP Address is used in the
construction of the Session-Id means that the introduction of
Network Address Translation MAY cause two hosts to represent the
same Session Identifier. This area needs to be investigated
further to be able to support DIAMETER hosts on a private
network.
- Some crypto algorithms are known to have weaknesses if a random
value is not found early within the plaintext, therefore it is
recommended that the Nonce AVP be added early in a message if
possible. More investigation on this subject is needed in order
to determine if there exists any possibility for such attacks.
- When additional hashing transforms are supporting by the
DIAMETER base protocol, there SHOULD be a method to negotiate
the transform to be used. This negotiation MUST NOT be prone to
a bidding down attack to the lowest secure transform.
10.0 DIAMETER protocol related configurable parameters
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This section contains the configurable parameters that are found
throughout this document:
Device-Reboot-Ind Timer
This timer is used to determine how long an implementation
should issue another DRI message if no response is received.
Default is 20 seconds.
Device-Watchdog-Ind Timer
This is the timer that determines the period of inactivity that
must occur before a DWI is transmitted to the communicating
peer. Default is 60 seconds, if DWI messages are sent.
Receive Window
The Receive window determines how many unacknowledged DIAMETER
messages MAY be pending with a communicating peer. This is
normally configured to a value that allows the node to
effectively manage its receive buffers. Default is 7.
Retransmission Timer
The retransmission timer is the time period that a node will
retransmit a message if no transport level acknowledgement was
received. Default is 3 seconds.
Maximum Retransmissions
This is the maximum number of times a DIAMETER message will be
retransmitted before it is determined that the communicating
peer is no longer reachable. Default is 3.
Delayed Acknowledgement Timer
This timer is defined in [25].
Shared Secret
The shared secret is a value that is known by two communicating
peers, and is used to generate the Integrity-Check-Value AVP.
There is no default.
Maximum Age of an outstanding message
Messages older than the maximum age SHOULD be rejected, as
described in section 7.3. The recommended value is 4 seconds.
11.0 Security Considerations
The DIAMETER base protocol requires that two communicating peers
exchange messages in a secure fashion. This document documents two
security methods that can be used. The first requires no security at
the application layer, but rather relies on an underlying security
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mechanism, such as IP Security.
When IP Security is not available, or desirable, the DIAMETER
protocol MAY use hop-by-hop security, which requires communicating
peers to share a long-lived secret. Hop-by-Hop security provides
replay protection by requiring that the communicating peers share a
time source, such as an NTP server.
When the DIAMETER protocol is used in an inter-domain network, strong
application level security MAY be required, such as non-repudiation.
This the communicating peers do require this level of security either
for legal or business purposes, the extension defined in [11] MAY be
used.
12.0 References
[1] Rigney, et alia, "RADIUS", RFC-2138, April 1997
[2] Reynolds, Postel, "Assigned Numbers", RFC 1700, October 1994.
[3] Postel, "User Datagram Protocol", RFC 768, August 1980.
[4] Rivest, "The MD5 Message-Digest Algorithm", RFC 1321, April
1992.
[5] Kaufman, Perlman, Speciner, "Network Security: Private
Communications in a Public World", Prentice Hall, March 1995,
ISBN 0-13-061466-1.
[6] Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for Message
Authentication", RFC 2104, January 1997.
[7] P. Calhoun, W. Bulley, "DIAMETER NASREQ Extension", draft-
calhoun-diameter-nasreq-00.txt (work in progress), December
1999.
[8] Aboba, Beadles "The Network Access Identifier." RFC 2486.
January 1999.
[9] Calhoun, Zorn, Pan, Akhtar, "DIAMETER Framework", draft-
calhoun-diameter-framework-05.txt (work in progress), December
1999.
[10] P. Calhoun, C. Perkins, "DIAMETER Mobile IP Extensions",
draft-calhoun-diameter-mobileip-04.txt (work in progress),
December 1999.
[11] P. Calhoun, W. Bulley, S. Farrell, "DIAMETER Strong Security
Extension", draft-calhoun-diameter-strong-security-00.txt (work
in progress), December 1999.
[12] Narten, Alvestrand,"Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998
[13] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[14] Myers, Ankney, Malpani, Galperin, Adams, "X.509 Internet Public
Key Infrastructure Online Certificate Status Protocol (OCSP)",
RFC 2560, June 1999.
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[15] Arkko, Calhoun, Patel, Zorn, "DIAMETER Accounting Extension",
draft-calhoun-diameter-accounting-02.txt (work in progress),
December 1999.
[16] Hinden, Deering, "IP Version 6 Addressing Architecture", RFC
2373, July 1998.
[17] ISI, "Internet Protocol", RFC 791, September 1981.
[18] Mills, "Simple Network Time Protocol (SNTP) Version 4 for IPv4,
IPv6 and OSI, RFC 2030, October 1996.
[19] Housley, Ford, Polk, Solo, "Internet X.509 Public Key
Infrastructure Certificate and CRL Profile", RFC 2459, January
1999.
[20] B. Aboba, G. Zorn, "Criteria for Evaluating Roaming Protocols",
RFC 2477, January 1999.
[21] M. Beadles, "Criteria for Evaluating Network Access Server
Protocols", draft-ietf-nasreq-criteria-03.txt (work in
progress), October 1999.
[22] T. Hiller et al., "Cdma2000 Wireless Data Requirements for
AAA", draft-hiller-cdma2000-AAA-00.txt (work in progress),
October 1999.
[23] S. Glass, S. Jacobs, C. Perkin, "Mobile IP Authentication,
Authorization, and Accounting Requirements", draft-ietf-
mobileip-aaa-reqs-01.txt (work in progress), October 1999.
[24] F. Yergeau, "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[25] P. Calhoun, A. Rubens, H. Akhtar, E. Guttman, W. Bulley, J.
Haag, "DIAMETER Implementation Guidelines", draft-calhoun-
diameter-impl-guide-00.txt (work in progress), December 1999.
13.0 Acknowledgements
The authors would like to thank Nenad Trifunovic, Tony Johansson and
Pankaj Patel for their participation in the Document Reading Party.
The authors would also like to acknowledge the following people for
their contribution in the development of the DIAMETER protocol:
Bernard Aboba, Jari Arkko, William Bulley, Daniel C. Fox, Lol Grant,
Ignacio Goyret, Nancy Greene, Peter Heitman, Paul Krumviede, Fergal
Ladley, Ryan Moats, Victor Muslin, Kenneth Peirce, Stephen
Farrell,Sumit Vakil, John R. Vollbrecht, Jeff Weisberg and Glen Zorn
14.0 Author's Addresses
Questions about this memo can be directed to:
Pat R. Calhoun
Calhoun et al. expires May 2000 [Page 40]
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Network and Security Research Center, Sun Laboratories
Sun Microsystems, Inc.
15 Network Circle
Menlo Park, California, 94025
USA
Phone: 1-650-786-7733
Fax: 1-650-786-6445
E-mail: pcalhoun@eng.sun.com
Allan C. Rubens
Tut Systems, Inc.
220 E. Huron, Suite 260
Ann Arbor, MI 48104
USA
Phone: 1-734-995-1697
E-Mail: arubens@tutsys.com
Haseeb Akhtar
Wireless Technology Labs
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082-4399
USA
Phone: 1-972-684-8850
E-Mail: haseeb@nortelnetworks.com
Erik Guttman
Network and Security Research Center, Sun Laboratories
Sun Microsystems, Inc.
15 Network Circle
Menlo Park, California, 94025
USA
Phone: 49-7263-911-701
E-mail: erik.guttman@germany.sun.com
15.0 Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished
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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 docu- ment itself may not be modified in any
way, such as by removing the copyright notice or references to the
Internet Society or other Inter- net 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 permis- sions 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 WAR- RANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Calhoun et al. expires May 2000 [Page 42]