INTERNET DRAFT Pat R. Calhoun
Category: Standards Track Sun Laboratories, Inc.
Title: draft-calhoun-diameter-10.txt Allan C. Rubens
Date: October 1999 Tut Systems, Inc.
Haseeb Akhtar
Nortel Networks
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.
Abstract
The DIAMETER base protocol is intended to provide a framework for
access technology services that require AAA support. The protocol is
intended to be flexible enough to allow services to add building
blocks (or extensions) to DIAMETER in order to meet their
requirements.
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This draft specifies the message format and transport to be used by
all DIAMETER extensions and MUST be supported by all DIAMETER
implementations.
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Table of Contents
1.0 Introduction
1.1 Copyright Statement
1.2 Requirements language
1.3 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
2.3 Error Reporting
3.0 Reliable Transport
3.1 Flow Control
3.2 Peer failure recovery
4.0 DIAMETER AVPs
4.1 DIAMETER-Command AVP
4.1.1 Message-Reject-Ind
4.1.2 Device-Reboot-Ind
4.1.3 Device-Watchdog-Ind
4.2 Host-IP-Address
4.3 Host-Name
4.4 State
4.5 Class
4.6 Session-Timeout
4.7 Extension-Id
4.8 Integrity-Check-Value
4.9 Nonce
4.10 Timestamp
4.11 Session-Id
4.12 Vendor-Name
4.13 Firmware-Revision
4.14 Result-Code
4.15 Error-Code
4.16 Unrecognized-Command-Code
4.17 Reboot-Type
4.18 Reboot-Time
4.19 Failed-AVP-Code
4.20 User-Name
4.21 Receive-Window
4.22 Proxy-State
4.23 Redirected-Host
4.24 Broker-Issued-Certificate
5.0 Protocol Definition
5.1 Session Identifiers
5.2 DIAMETER Bootstrap Message
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5.2.1 State Machine
5.3 Keepalive Exchange
5.4 AVP Handling Rules
5.4.1 Unrecognized Command Support
5.4.2 The art of AVP Tagging
5.5 DIAMETER Message Security
5.5.1 Using the Integrity-Check-Value
5.5.2 AVP Encryption with Shared Secrets
5.6 DIAMETER Message Routing
5.6.1 DIAMETER Proxying
5.6.2 Message Redirection
6.0 IANA Considerations
6.1 AVP Attributes
6.2 Command Code AVP Values
6.3 Extension Identifier Values
6.4 Result Code AVP Values
6.5 Integrity Check Value Transform Values
6.7 AVP Header Bits
6.6 Reboot Type Values
7.0 Open Issues
8.0 DIAMETER protocol related configurable parameters
9.0 Security Considerations
10.0 References
11.0 Acknowledgements
12.0 Author's Address
13.0 Full Copyright Statement
Appendix A: Acknowledgment Timeouts
A.1 Calculating Adaptive Acknowledgment Timeout
A.2 Flow Control: Adjusting for Timeout
Appendix B: Examples of sequence numbering
B.1 Lock-step tunnel establishment
B.2 Multiple messages acknowledged
B.3 Lost message with retransmission
Appendix C: Backward Compatibility with RADIUS
Appendix D: Delayed Acknowledgement Optimization
Appendix E: Device-Reboot-Ind Message Flow
Appendix F: Device-Watchdog-Ind Message Flow
Appendix G: Message-Reject-Ind Message Flow
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1.0 Introduction
The DIAMETER is a peer to peer protocol that provides Authentication,
Authorization and Accounting (AAA) services for access technologies,
such as PPP dial-in, Mobile IP, etc.
This document describes the base DIAMETER protocol, which is used as
the transport for all DIAMETER extensions. This document in itself is
not complete and MUST be used with an accompanying applicability
extension document.
An example of such a document would be [7] that defines extensions to
the base protocol to support Dial-in PPP user authentication and
[15], which defines extensions to support accounting.
The DIAMETER protocol is recognized as a peer to peer protocol since
any node can initiate a request. However, a client is the device that
normally initiates a request for authentication and/or authorization
of a user. A server is the device that performs the actual
authentication and/or authorization of the user based on some
profile. A server can issue a request to a client, but this is
typically not a request for authentication and/or authorization, but
rather a different request, such as a request for an accounting
update.
1.1 Copyright Statement
Copyright (C) The Internet Society 1999. All Rights Reserved.
1.2 Requirements language
In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [13].
1.3 Terminology
Refer to [9] for terminology used in this document.
2.0 Protocol Overview
The DIAMETER protocol allows peers to exchange a variety of messages.
The base protocol provides the following facilities:
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- Sequenced in-order reliable delivery of UDP datagram messages
- Support for congestion control (receiver window)
- Timely detection of failed or unresponsive peers
- Delivery of AVPs (attribute value pairs)
- Extensibility, through addition of new commands and AVPs
All data delivered by the is protocol 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:
- All messages carry either an Integrity Check Vector (ICV) or a
digital signature[11]. They 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 can be used for
accounting purposes, capacity planning, etc.
The DIAMETER base protocol provides the minimum requirements needed
for an AAA transport protocol. 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.
2.1 Header Format
The base DIAMETER protocol is run over UDP port 1812. Implementations
MAY send packets from any source port, but SHOULD 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 summary of the DIAMETER 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RADIUS PCC |Flags|A|W| Ver | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Send (Ns) | Next Received (Nr) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVPs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
RADIUS PCC (Packet Compatibility Code)
The RADIUS PCC field is a one octet field which is used for
backward compatibility with RADIUS. In order to easily distinguish
DIAMETER messages from RADIUS a special value has been reserved
and allows an implementation to support both protocols
concurrently using the first octet in the header. The RADIUS PCC
field MUST be set as follows:
254 DIAMETER message
PKT 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
following flag may be set:
The 'W' bit (Window-Present) is set when the Next Send (Ns) and
Next Received (Nr) fields are present in the header. Should
DIAMETER be implemented over a reliable transport, the 'W'
should not be set.
The 'A' bit is set to indicate that the message is an
acknowledgement only and does not contain a Command-Code AVP
following the header. Note that the Security AVPs MUST still be
present within an acknowledgment message.
Version
This field MUST be set to 1 to indicate DIAMETER Version 1.
Message Length
The Message Length field is two octets. It indicates the length
of the DIAMETER message including the header fields.
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
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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.
Ss is incremented after copying if the message is not a ZLB ACK.
Next Received
This field is present when the Window-Present bit is set in the
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
3.0 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 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 will be as follows:
<ZLB Message> ::= <DIAMETER Header>
<Timestamp AVP>
<Nonce AVP>
{<Integrity-Check-Value AVP> ||
<Digital-Signature AVP> [11] }
2.2 AVP Format
DIAMETER AVPs carry specific authentication, accounting and
authorization 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
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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
byte boundary. Zero bytes are added to the end of the AVP value till
a word boundary is reached.
2.2.1 AVP Header
The AVP format is shown below and MUST be sent 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Length | Cmd Flags | Reserved |T|V|H|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
AVP Code
The AVP Code identifies the attribute uniquely. If the Vendor-
Specific-AVP 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 6.0).
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.
Command Flags
The Command Flag field is a bit-field that can be used by
individual command codes. Any Command Code that makes use of these
bits MUST define their value, and how they are used. Note that
only AVPs with the AVP Code set to Command-Code may use these
bits, otherwise the bits MUST be set to zero (0).
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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. Reserved bits should be set to
0 and ignored on receipt.
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.
When the 'H' bit is enabled it indicates that the AVP data is
encrypted using hop-by-hop encryption. See section 4.5 for more
information.
The 'V' bit, known as the Vendor-Specific bit, indicates whether
the optional Vendor ID field is present in the AVP header. When
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 'H'
and 'T' bits 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 can use their own Vendor ID along
with private Attribute values, guaranteeing that they will not
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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
UDP limits messages to 2^16 bytes.
The format of the value field MAY be one of six data types. It is
possible for an attribute to have a structure and this MUST be
defined along with the attribute.
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 variable length string using the UTF-8
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, most significant octet first. The AVP Length
field MUST be set to 12.
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Integer64
64 bit value, most significant octet first. The AVP Length
field MUST be set to 16.
Time
32 bit unsigned value, most significant octet first -- seconds
since 00:00:00 GMT, January 1, 1900. The AVP Length field MUST
be set to 12.
2.3 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 DIAMETER-Command 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
Response to the message MUST be sent with the Result-Code or Error-
Code AVP set to a value that enables the peer to understand the
nature of the problem.
3.0 Reliable Transport
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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 in appropriate.
-The retransmission scheme required is more agressive than
TCP provides.
3.1 Flow Control
ZLB messages are used to acknowledge DIAMETER messages to the
communicating peer.
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.
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
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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. Appendix D 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 acknowlegment. Messages SHOULD be retransmitted
at least three times. Appendix A recommends a retransmission
timer 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- Vector 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 number of unacknowledged packets which can
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 can 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 Appendix B for some examples of how sequence numbers progress.
3.2 Peer failure recovery
A DIAMETER message with the Command-Code AVP set to Device-Reboot-Ind
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
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same identifier as the last processed Device-Reboot-Ind is considered
a retransmission and SHOULD NOT change the peer's state to inactive.
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.
4.0 DIAMETER AVPs
This section will define the mandatory AVPs that MUST be supported by
all DIAMETER implementations.
The following AVPs are defined in this document:
Attribute Name Attribute Code Definition in Section
------------------------------------------------------------
DIAMETER-Command 256 4.1
Host-IP-Address 4 [1], 4.2
Host-Name 32 [1], 4.3
State 24 [1], 4.4
Class 25 [1], 4.5
Session-Timeout 27 [1], 4.6
Extension-Id 258 4.7
Integrity-Check-Value 259 4.8
Nonce 261 4.9
Timestamp 262 4.10
Session-Id 263 4.11
Vendor-Name 266 4.12
Firmware-Revision 267 4.13
Result-Code 268 4.14
Error-Code 269 4.15
Unrecognized-Command-Code 270 4.16
Reboot-Type 271 4.17
Reboot-Time 272 4.18
Failed-AVP-Code 279 4.19
User-Name 1 [1], 4.20
Receive-Window 277 4.21
Proxy-State 33 [1], 4.22
Redirect-Host 278 4.23
Broker-Issued-Certificate 280 4.24
4.1 DIAMETER-Command AVP
Description
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The DIAMETER-Command AVP MUST be the first AVP following the
DIAMETER header. This AVP is used in order to communicate the
command associated with the message. A DIAMETER message can have
at most one DIAMETER-Command AVP. Unless noted otherwise, all
command codes defined in this document will use the following
format:
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 = 256)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AVP Length
The length of this attribute MUST be at least 12. The exact
length of the AVP is determined by the actual Command and is
defined with each command.
AVP Flags
The 'M' bit MUST be set. The 'V' MAY be set if the Command Code
is vendor specific. The 'H', 'T' bits MUST NOT be set.
Command Code
The Command Code field contains the command number. The
following commands are defined and MUST be supported by all
DIAMETER implementations in order to conform to the base
protocol specification:
Command Name Command Code
-----------------------------------
Message-Reject-Ind 256
Device-Reboot-Ind 257
Device-Watchdog-Ind 258
4.1.1 Message-Reject-Ind (MRI)
Description
The Message-Reject-Ind command provides a generic means of
completing transactions by indicating errors in the messages which
initiated them. The Message-Reject-Ind command is a possible
response to any DIAMETER command. Some some DIAMETER commands MAY
expect more specialized error messages, depending on the error
type.
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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 message is defined as follows:
<Message-Reject-Ind message> ::= <DIAMETER Header>
<Message-Reject-Ind Command AVP>
<Host-IP-Address AVP>
[<Host-Name AVP>]
[<Session-Id AVP>]
<Result-Code AVP>
[<Error-Code AVP> ]
{<Failed-AVP-Code AVP> ||
<Unrecognized-Command-Code AVP>}
<Timestamp AVP>
<Nonce AVP>
{<Integrity-Check-Value AVP> ||
<Digital-Signature AVP> [11]}
where the Identifier value in the message header and optionally
the Session-Id AVP are copied from the message being rejected and
the DIAMETER-Command AVP has the format described below. The
Result-Code and conditionally-present Error-Code AVPs indicate the
nature of the error causing rejection, and the conditionally-
present Failed-AVP-Code 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
Error-Code and/or Failed-AVP-Code AVPs will be present in the
message. The Unrecognized-Command-Code AVP is present only when
the reason for message rejection is an unrecognized or unsupported
command code.
The length of the DIAMETER Command AVP must be 12 when the Command
Code is set to 256 (Message-Reject-Ind).
4.1.2 Device-Reboot-Ind (DRI)
Description
A DIAMETER device sends the Device-Reboot-Ind message to inform
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all of its peers 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 once it is able to receive network
traffic.
This message is also used by a DIAMETER device in order to
exchange the supported protocol version number as well as all
supported extensions. The originator of this message SHOULD insert
it's highest supported version number within the DIAMETER header.
Similarly the originator of this message MUST include all
supported extensions within the message.
It is desirable for a DIAMETER device to retain the supported
extensions in order to ensure that only requests/responses are
sent to peers that support the extension in question.
This message MUST contain the Vendor-Name and Extension-Id AVPs.
In the case where a DIAMETER device is configured to communicate
with many peers, this message MUST be issued to each peer. The DRI
SHOULD be periodically retransmitted until an acknowledgement is
received. This retransmission timer MAY be different from the
timer used when the communication has been established, and SHOULD
be configurable.
No explicit DIAMETER message is necessary to acknowledge this
message since it is handled by DIAMETER's reliable transport.
Message Format
<Device-Reboot-Ind> ::= <DIAMETER Header>
<Device-Reboot-Ind Command AVP>
<Reboot-Type AVP>
[<Reboot-Time AVP>]
<Host-IP-Address AVP>
[<Host-Name AVP>]
<Vendor-Name AVP>
<Extension-Id AVPs>
<Firmware-Revision AVP>
[<X509-Certificate AVP>]
[<X509-Certificate-URL AVP>]
<Timestamp AVP>
<Nonce AVP>
{<Integrity-Check-Value AVP> ||
<Digital-Signature AVP> [11]}
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The length of the DIAMETER Command AVP must be 12 when the Command
Code is set to 257 (Device-Reboot-Ind).
4.1.3 Device-Watchdog-Ind (DWI)
Description
The Device-Watchdog-Ind is used as a keepalive mechanism between
two DIAMETER peers, and SHOULD be sent during after a configurable
period of inactivity. The lower the timer value is set to, the
quicker a host can 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. This message MUST contain the Host-IP-
Address or Host-Name AVP as well as any security related AVPs.
No explicit DIAMETER message is necessary to acknowledge this
message since it is handled by DIAMETER's reliable transport.
Message Format
<Device-Watchdog-Ind> ::= <DIAMETER Header>
<Device-Watchdog-Ind Command AVP>
{<Host-IP-Address AVP> ||
<Host-Name AVP> }
<Timestamp AVP>
<Nonce AVP>
{<Integrity-Check-Value AVP> ||
<Digital-Signature AVP> [11]}
The length of the Command Code AVP MUST be 12 when the Command Code
field is set to 258 (Device-Watchdog-Ind).
4.2 Host-IP-Address
The Host-IP-Address AVP (AVP Code 4) is of type Address and is used
to inform a DIAMETER peer of the sender's identity. The data portion
of this AVP contains the IP address of the originator of the DIAMETER
message.
The AVP flags for this AVP are different from the default value, and
have the following rules:
The 'M' bit MUST be set. The 'H' SHOULD NOT be set since
implementations could use this information to determine the shared
secret information necessary to authenticate the message. The 'T'
and 'V' bits MUST NOT be set.
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4.3 Host-Name
The Host-Name AVP (AVP Code 32) is of type String, and is used to
inform a DIAMETER peer of the sender's identity. The data portion of
this AVP contains the host name of the originator of the DIAMETER
message. The host name MUST follow the NAI [8] naming conventions.
The AVP flags for this AVP are different from the default value, and
have the following rules:
The 'M' bit MUST be set. The 'H' SHOULD NOT be set since
implementations could use this information to determine the shared
secret information necessary to authenticate the message. The 'T'
and 'V' bits MUST NOT be set.
4.4 State
The State AVP (AVP Code 24) is sent by the server to the client when
the DIAMETER exchange can span multiple round-trip messages and is
used to maintain server state information. The opaque data MUST be
sent unmodified by the client to the server in subsequent messages
for the same Session-Id.
The data portion of the AVP is of type Data and the format of the
information is site or application specific, and SHOULD be treated as
opaque octets.
4.5 Class
The server sends the Class AVP (AVP Code 25) to the client during
authentication or authorization and MUST be sent unmodified by the
client to the accounting server as part of the accounting message if
accounting is supported. No interpretation of the opaque data should
be made by the client.
The data portion of the AVP is of type Data and the format of the
information is site or application specific, and SHOULD be treated as
opaque octets.
4.6 Session-Timeout
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.
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This AVP can 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 can return any value. A value of zero
provided by a client DOES NOT imply that service is being terminated.
4.7 Extension-Id
The Extension-Id AVP (AVP Code 258) is of type Integer32 and is used
in order to identify a specific DIAMETER extension. This AVP SHOULD
be 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
it by the IANA (see section 6.3). The base protocol does not require
a Extension-Id since its support is mandatory.
There MAY be more than one Extension-Id AVP within a DIAMETER
message.
4.8 Integrity-Check-Value
The Integrity-Check-Value AVP (AVP Code 259) 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 AVP MUST be present to
provide replay protection and the Nonce AVP must be present to add
randomness to the message. All AVPs following this AVP must be
ignored.
The Integrity-Check-Value is generated in the method described in
section 5.5.1
All DIAMETER implementations MUST support this AVP.
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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 Header (AVP Code = 259)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transform ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
AVP Length
The length of this attribute MUST be at least 13.
AVP Flags
The 'M' bit MUST be set and the 'T' bit MAY be set. The 'V' and
'H' bits MUST NOT be set.
Transform ID
The Transform ID field contains a value that identifies the
transform that was used to compute the ICV. The following
values are defined in this document:
HMAC-MD5-96[6] 1
Data
The Data field contains an ICV of the message up to this AVP.
4.9 Nonce
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.
The AVP flags for this AVP are different from the default value, and
have the following rules:
The 'M' bit MUST be set and the 'T' bit MAY be set. The 'V' and
'H' bits MUST NOT be set.
4.10 Timestamp
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 Integrity AVP
defined in separate extensions. The value of time is the most
significant four octets returned from an NTP server that indicates
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the number of seconds expired since Jan. 1, 1900.
The AVP flags for this AVP are different from the default value, and
have the following rules:
The 'M' bit MUST be set and the 'T' bit MAY be set. The 'V' and
'H' bits MUST NOT be set.
Messages which are older than a certain maximum age SHOULD be
rejected and a MRI message with the Result-Code AVP value set to
DIAMETER_SEE_ERROR_CODE and the Error-Code AVP set to
DIAMETER_TIMEOUT. The recommended value for the maximum age of an
outstanding message is 4 seconds.
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.
4.11 Session-Id
The Session-Id AVP (AVP Code 263) is of type Data and is used to
identify a specific session (see section 5.1). 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
DIAMETER-Command AVP.
For any other messages that does 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><monotonically increasing 32 bit value><optional
value>
It is suggested that the monotonically increasing 32 bit value NOT
start at zero 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.
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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 can be used by more than one extension.
4.12 Vendor-Name
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 AVPs can provide very
useful debugging information.
The AVP flags for this AVP are different from the default value, and
have the following rules:
The 'H' bits MAY be set. The 'T', 'V' and 'M' bits MUST NOT be
set.
4.13 Firmware-Revision
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 which 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.
The AVP flags for this AVP are different from the default value, and
have the following rules:
The 'H' bits MAY be set. The 'T', 'V' and 'M' bits MUST NOT be
set.
4.14 Result-Code
The Result-Code AVP (AVP Code 268) is of type Integer32 and indicates
whether a particular request was completed successfully or whether an
error occurred. The Result-Code AVP MUST be present in all DIAMETER
messages of type *-Response or *-Answer. The following codes have
been defined:
DIAMETER_SUCCESS 0
The Request was successfully completed.
DIAMETER_FAILURE 1
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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-Code AVPs indicating the attributes which caused the
failure.
DIAMETER_POOR_REQUEST 2
The Request was poorly constructed. A DIAMETER Message-Reject
message returning this result SHOULD whenever possible also
contain one or more Failed-AVP-Code AVPs indicating the
attributes which caused the failure.
DIAMETER_INVALID_AUTH 3
The Request did not contain a valid Integrity-Check-Value or
Digital-Signature [11].
DIAMETER_UNKNOWN_SESSION_ID 4
The Request contained an unknown Session-Id.
DIAMETER_SEE_ERROR_CODE 5
The Request failed. The message MUST also contain an Error-Code
AVP which provides command-specific information on the failure.
A DIAMETER Message-Reject-Ind message returning this result
SHOULD whenever possible also contain one or more Failed-AVP-
Code AVPs indicating the attributes which caused the failure.
DIAMETER_COMMAND_UNSUPPORTED 6
The Request contained a command code which the DIAMETER
implementation does not recognize or does not support. The
Message-Reject-Ind message MUST also contain an Unrecognized-
Command-Code AVP which contains the Command Code value which
was rejected.
DIAMETER_TIMEOUT
This error MAY be returned if a request if a message has been
received that has a Timestamp AVP that is older than the
maximum age that the communicating peer accepts.
DIAMETER_ATTRIBUTE_UNSUPPORTED 8
The Request contained an AVP with an AVP Code which the
DIAMETER implementation does not recognize or does not support.
An DIAMETER Message-Reject-Ind message returning this result
MUST also contain one or more Failed-AVP-Code AVPs indicating
the AVP Codes which 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
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direct the request directly to the server, whose contact
information has been added to the response.
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 domain
requested is unknown.
DIAMETER_INVALID_TRANSFORM 11
A message was received that included an Integrity-Check-Value
or Digital-Signature that made use of an unsupported transform.
4.15 Error-Code
The Error-Code AVP (AVP Code 269) is of type Integer32 and contains
the message specific error code, if any. This AVP only needs to be
present if the Result-Code AVP is present with the
DIAMETER_SEE_ERROR_CODE.
Error-Code values and corresponding semantics are specific to the
command to which the Error-Code is a response, and MUST therefore be
documented as part of the description of that command.
4.16 Unrecognized-Command-Code
The Unrecognized-Command-Code AVP (AVP Code 270) is of type Integer32
and contains the offending Command Code that resulted in sending the
Message-Reject-Ind message.
4.17 Reboot-Type
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 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 besides the
acknowledgement.
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
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ready to accept new DIAMETER messages.
4.18 Reboot-Time
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 MAY 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.
4.19 Failed-AVP-Code
The Failed-AVP-Code 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
documentation of the Result-Code AVP and of the Message-Reject-Ind
command provide information on the use of the Failed-AVP-Code AVP.
The Data field contains the complete AVP that could not be processed
successfully. Possible reasons for this are an improperly-constructed
AVP, an unsupported or unrecognized AVP Code, or an invalid value.
4.20 User-Name
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.
4.21 Receive-Window
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 node MUST stop sending messages when it detects that the number of
unacknowledged messages is equal to the peer's receive window size.
4.22 Proxy-State
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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, only one such AVP may
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.
The Proxy-State AVP's Address field is intended to be used by
DIAMETER hosts in order to assist in determining if the AVP was
locally generated.
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 ...
+-+-+-+-+-+-+-+-+
AVP Flags
The 'M' bit MUST be set. The 'V', 'H' and 'T' bits MUST NOT be
set.
Address
The Address field is a 128-bit field that contains the IP
address of the system that created the Proxy-State AVP. If the
host creating the AVP has an IPv4 address, the leading 96 bits
MUST be set to zero. This field is intended to assist hosts in
determining if a Proxy-State AVP in a message was locally
created.
Data
The Data field is one or more octets. The actual format of the
information is site or application specific, and SHOULD be
treated as undistinguished octets.
4.23 Redirect-Host
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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
about 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 a group of
DIAMETER servers that can satisfy the request.
4.24 Broker-Issued-Certificate
The Broker-Issued-Certificate AVP (AVP Code 280) is typically added
by a broker in a network where the broker's organization also
provides certificate authority services. In such networks,
certificates are issued to all DIAMETER servers within the roaming
consortium. The Broker-Issued-Certificate AVP contains a timestamp
and an expiration time, which CAN be used by DIAMETER hosts in order
to determine whether they should further validate the certificate
against a certification validation infrastructure (see section 5.6.2
for more information).
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 = 280)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expiration Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Certificate Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Digital Signature Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Certificate ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Digital Signature ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AVP Length
The length of this attribute MUST be at least 24.
Timestamp
The Timestamp field contains the time when the AVP was created.
This field is in the data format defined in Section 2.2.3.
Expiration
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The Expiration field contains the time after which the broker
recommends that a new Broker-Certificate be retrieved. This
field is in the data format defined in Section 2.2.3.
Certificate Length
The Certificate Length field contains the number of octets of
the certificate in the certificate field.
Digital-Signature Length
The Digital-Signature Length field contains the number of
octets of the signature found in the Digital Signature field.
Certificate
The certificate field contains the X.509 certificate [19].
Digital-Signature
The Digital-Signature field contains the broker's digital
signature [11].
5.0 Protocol Definition
The base DIAMETER protocol is never used on its own. It is always
extended for a particular application. The base DIAMETER protocol
concerns 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 requires that every message
includes some AVPs (Nonce, Timestamp, Integrity-Check-Vector or
Digital-Signature).
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 and Error-Code AVPs
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 ZLB, or by piggybacking an
acknowledgement in a non-ZLB message.
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Communicating DIAMETER peers retain state relating to transport
(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 the peer
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). This can only be done according to
rules established in a particular extension/application of DIAMETER.
DIAMETER extensions MUST define an explicit exchange of messages
which allow a peer to inform the other party that a session has been
terminated.
5.1 Session Identifiers
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
typically adds the Session-Timeout AVP to the response. The Session-
Timeout AVP defines how long the user can make use of the resources
before another authorization request is sent to the server. Should
the server not receive another authorization request before the
timeout occurs, it SHOULD release any state information related to
the user's session.
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.
5.2 DIAMETER Bootstrap Message
DIAMETER provides a message that is used to indicate either an
imminent reboot, or that a reboot has occurred. The DRI message MUST
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be sent to all known DIAMETER peers both previous to a reboot when
possible as well as following a reboot.
The Reboot-Type AVP is used to indicate the type of reboot associated
with the DRI. When set to REBOOT_IMMINENT, all peers should be warned
that any new DIAMETER requests sent to the issuer will probably not
be received or processed. If a request MUST be sent it would be
preferable to issue the request to an alternate peer if available.
The message includes an optional Reboot-Time AVP that specifies an
estimate of how long before the issuer is available to receive new
DIAMETER messages.
Upon reboot, the host MUST issue a DRI message with the Reboot-Type
AVP set to REBOOTED. This is an indication that new DIAMETER messages
may be sent to the transmitter of the DRI.
Note that the Reboot-Time AVP is not required, and when present
provides an estimate and should not be used as a hard value. 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.
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 appendix E
for more information.
5.2.1 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 acknowledgements and the DRI. Once the DIAMETER peer is
set to the open state, any DIAMETER message may be accepted and
processed. The following is a suggested 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.
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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
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 no ACK received cleanup closed
5.3 Keepalive Exchange
DIAMETER uses the Device-Watchdog-Ind message as a keepalive
mechanism. DIAMETER entities that need to ensure that connectivity
with a peer is not lost may use this mechanism. Each node is
responsible for sending their own Device-Watchdog-Ind message to its
peer when no activity is present for some time, which can be
configurable. Note that it is possible for each node in the network
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to have a different inactivity timer configured. The more aggressive
the timer, the more traffic is generated, but the quicker it can
detect if a peer is no longer reachable.
A DIAMETER Client can use this mechanism to ensure that fail-over to
an alternate server occurs even without any AAA traffic. DIAMETER
Servers use this mechanism to identify when a particular client is no
longer reachable. Redundant DIAMETER Servers can use this mechanism
to identify when the primary server is no longer available. Proxy
Servers can equally use this method to identify when a particular
domain's server is no longer reachable.
The DIAMETER Device-Watchdog-Ind message does not require a reply.
The message is acknowledged using DIAMETER's reliable transport. See
appendix F for more information.
5.4 AVP Handling Rules
5.4.1 Unrecognized Command Support
The DIAMETER protocol provides a message that is used to inform a
peer that a DIAMETER message was received with an unrecognized
command (see appendix G for more information). The following provides
a DIAMETER message that is sent to a peer:
<Take-A-Hike-Req> ::= <DIAMETER Header>
<Take-A-Hike-Req Command AVP>
<Host-IP-Address AVP>
[<Host-Name AVP>]
<Timestamp AVP>
<Nonce AVP>
{<Integrity-Check-Value AVP> ||
<Digital-Signature AVP> [11] }
Upon receipt of the above message, the receiver notices that it does
not support the command and sends the following message:
<Message-Reject-Ind> ::= <DIAMETER Header>
<Message-Reject-Ind Command AVP>
<Unrecognized-Command-Code AVP>
<Host-IP-Address AVP>
[<Host-Name AVP>]
<Timestamp AVP>
<Nonce AVP>
{<Integrity-Check-Value AVP> ||
<Digital-Signature AVP> [11] }
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5.4.2 The art of AVP Tagging
The AVP Header provides the 'T' bit that is used for grouping AVPs
together. Although the base protocol does not define any AVPs that
need to be grouped, it is envisioned that DIAMETER extensions will
require tag support.
In the case where multiple AVPs are needed to indicate a specific
authorization "rule" tagging is appropriate. Such an example is taken
from [10] that discusses Tunneling attributes. In this case multiple
AVPs are required in order to specify tunnel parameter, and more than
one set of AVPs MAY be present in the message. This is necessary in
order to support redundant tunnel servers.
In this case, the AVPs that need to be grouped together would have a
specific tag value, and each group would use a different tag value.
5.5 DIAMETER Message Security
5.5.1 Using the Integrity-Check-Value
The use of the Integrity-Check-Value (ICV) AVP requires a pre-
configured shared secret. Although this mechanism does not scale as
well as the Digital Signature, it may be desirable to use this
mechanism in the case where asymmetric technology is not required or
available. It is recommended that the key size used in the
computation of the ICV be sufficiently long (e.g. 128 bits), and that
different keys be used for both authentication and encryption (see
section 5.5.2).
Note that in the case where two DIAMETER nodes need to communicate
through an intermediate node (i.e. Proxy) it does not offer any end-
to-end data integrity or encryption as each node must re-compute the
Integrity-Check-Value AVP.
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.
The Data field of the AVP contains an HMAC-MD5-96[6] of the message
up to the ICV AVP. Prior to computing the hash value, the Message
Length field in the DIAMETER header (see section 2.1) MUST be set to
zero. 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,
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Output)
The following is an example of a message that include hop-by-hop
security:
<DIAMETER Message> ::= <DIAMETER Header>
<DIAMETER-Command AVP>
[<Additional AVPs>]
<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>
Any AVPs in a message that is not succeeded by the Integrity-Check-
Value AVP MUST be ignored.
5.5.2 AVP Encryption with Shared Secrets
This method of encrypting AVP data is the simplest to use and MUST be
supported by all DIAMETER implementations. However, local policy MAY
determine that the use of this mechanism is not permitted.
The 'H' bit MUST only be set if a shared secret exists between both
DIAMETER peers. If the 'H' bit is set in any DIAMETER AVP, the Nonce
AVP MUST be present prior to the first encrypted AVP.
The length of the AVP value to be encrypted is first encoded in the
following Subformat, which is included in the AVP's data field.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| length of plain text data | plain text data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length
The Length field contains the length of the decrypted data.
plain text data
Data of AVP that is to be obscured.
Padding
If the plain text does not align on the byte boundary required by
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the hashing algorithm (e.g. 16 octets for MD5), it is highly
recommended that random padding be added to obscure the length of
the plain text data.
The resulting subformat MAY be padded to a multiple of 16 octets in
length. For example, if the plain text data to be obscured is a
string containing 6 characters (e.g. password 'foobar'), then 8 + n *
16 octets of padding would be applied. Padding does NOT alter the
value placed in the Length of the ClearText Data, only the length of
the AVP itself.
Next, An MD5 hash is performed on the concatenation of:
- the four octet Command Code of the AVP
- the shared authentication secret
- an arbitrary length random vector
The value of the random vector used in this hash is passed in the
Data field of a Nonce AVP. This Nonce AVP must appear in the message
before any hidden AVPs. The same Nonce may be used for more than one
hidden AVP in the same message. If a different Nonce is used for the
hiding of subsequent AVPs then a new Nonce AVP must be placed before
the first AVP to which it applies.
The MD5 hash value is then XORed with the first 16 octet or less
segment of the AVP Subformat and placed in the Data field of the AVP.
If the AVP Subformat is less than 16 octets, the Subformat is
transformed as if the Value field had been padded to 16 octets before
the XOR, but only the actual octets present in the Subformat are
modified, and the length of the AVP is not altered.
If the Subformat is longer than 16 octets, a second one-way MD5 hash
is calculated over a stream of octets consisting of the shared secret
followed by the result of the first XOR. That hash is XORed with the
second 16 octet or less segment of the Subformat and placed in the
corresponding octets of the Data field of the AVP.
If necessary, this operation is repeated, with each XOR result being
used along with the shared secret to generate the next hash to XOR
the next segment of the value with. This technique results in the
content of the AVP being obscured, although the length of the AVP is
still known.
On receipt, the Nonce is taken from the last Nonce AVP encountered in
the message prior to the AVP to be decrypted. The above process is
then reversed to yield the original value. For more details on this
hiding method, consult RFC2138 [1].
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Please note that in the case where the DIAMETER message needs to be
processed by an intermediate non-trusted DIAMETER server (also known
as a proxy server, depicted as DIA2 in the figure below) the AVP
needs to be decrypted using Shared-Secret-1 and re-encrypted by DIA2
using Shared-Secret-2.
(Shared-Secret-1) (Shared-Secret-2)
+------+ -----> +------+ ------> +------+
| | | | | |
| DIA1 +-------------------+ DIA2 +-------------------+ DIA3 |
| | | | | |
+------+ +------+ +------+
Figure 1: Message Forwarding
Unfortunately in this case the non-trusted server DIA2 has access to
sensitive information (such as a password). It is recommended that
the key size used in the encryption of AVPs be sufficiently long
(e.g. 128 bits), and that different keys be used for both
authentication and encryption (see section 5.5.1).
5.6 DIAMETER Message Routing
5.6.1 DIAMETER Proxying
This section will describe how DIAMETER server implementations can
proxy requests to upstream servers. Consider the following diagram,
which depicts DIA1 sending a request to DIA2. Typically, the request
will contain the User-Name AVP (section 4.20), which conforms to the
format defined in the NAI specification [8]. Server DIA2 will extract
that realm portion of the NAI to determine if the request can be
locally processed, or if the request must be proxied to an upstream
server (in this case DIA3).
(Request) (Request)
(User-Name = joe@abc.com) (Proxy-State=1)
+------+ ------> +------+ ------> +------+
| | | | | |
| DIA1 +-------------------+ DIA2 +-------------------+ DIA3 |
| | | | | |
+------+ <------ +------+ <------ +------+
(Response) (Response)
(Proxy-State=1)
mno.net xyz.com abc.com
Figure 2: DIAMETER Proxying
Prior to forwarding the request, DIA2 must establish some state
information in order to be able to forward the corresponding response
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from DIA3 to DIA1. There are two methods of doing so:
1. DIA2 can maintain state information locally, and using the
session-Id and possible the Identifier in the header, can match
the request with the response. The state information would contain
sufficient information for it to know where the response should be
forwarded. Additionally, it may be necessary for DIA2 to attach
AVPs to the response that were created when the request was
received. These AVPs could be kept in the state table.
2. DIA2 can attach a Proxy-State AVP (section 4.22), which may
contain any information, including information regarding the
source of the request, additional AVPs that must be attached to
the response, etc. Upon receipt of the response, DIA2 must find
the Proxy-State AVP, determine if the AVP was created locally, and
if so use the information included within the AVP. If AVPs were
found within the Proxy-State AVP, they could easily be attached to
the response. Finally, the Proxy-State AVP is removed from the
response before being forwarded to DIA1.
Although both methods work, the latter is much simpler as it
reduces the amount of state information each proxy must maintain
on a per request basis.
When DIA3 receives a request that includes the Proxy-State AVP, it
MUST include the same AVP in the corresponding response.
Furthermore, should DIA3 have to proxy the request to another
upstream server, it would have to replace the existing Proxy-State
AVP with its own. It must, however, be able to replace the Proxy-
State AVP in the corresponding response back to the one it had
received in the request. One suggested implementation is to
include the Proxy-State AVPs in a newly created Proxy-State AVP,
allowing a server to easily replace the Proxy-State AVPs in the
responses.
5.6.2 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 3). This is typically done when the
broker provides simple NAI to Home DIAMETER Server address resolution
services.
In the example provided in figure 3, 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
4.14). When a response is received with such a value, the message
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MUST also include one or more Redirect-Host AVPs. These AVPs contain
address information that can be then used to directly communicate
with the Home DIAMETER Server. Note that the servers COULD cache the
home server information in order to reduce the latency involved in
any future messages destined for that home server.
+------------------+ +---------+
| DIAMETER | | CRL DB/ |
| Broker | | OCSP |
+------------------+ +---------+
/|\
Request | Response w+
| Result Code =
| Redirect
\|/
+----------+ +----------+
| abc.net |/ \| xyz.net |
| DIAMETER |--------------| DIAMETER |
| Server |\ /| Server |
+----------+ Direct +----------+
Communication
Figure 3: DIAMETER Broker Returning Redirect Indication
When returning the response with the Result-Code set to indicate a
redirect indication, the broker can also include the certificates of
both the requesting server, and the target server. These certificates
are encapsulated in the Broker-Certificate AVP, which also includes a
timestamp and an expiration time. The requesting server can forward
the Broker-Certificate that belongs to it in the subsequent request
to the home DIAMETER server. The Broker-Certificate is intended to
allow the peers to communicate without having to validate the
certificate against a certificate validation infrastructure, such as
Certificate Revocation Lists (CRLs) or using Online Certificate
Status Protocol (OCSP) [14]. Local policy at the individual servers
will dictate whether they can trust the Broker-Certificate, or
whether they must validate the certificate themselves.
6.0 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
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.
6.1 AVP Attributes
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As defined in Section 4.0, AVPs contain vendor ID, Attribute and
Value fields. For vendor ID value of 0, IANA will maintain a registry
of assigned Attributes and in some case also values. Attribute 0-254
are assigned from the RADIUS protocol [1], whose attributes are also
maintained through IANA. Attributes 256-280 are assigned within this
document in section 4.0. The remaining values are available for
assignment through Designated Expert [12].
6.2 Command Code AVP Values
As defined in Section 4.1, 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].
6.3 Extension Identifier Values
as defined in Section 4.7, 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].
6.4 Result Code AVP Values
As defined in Section 4.14, the Result Code AVP (AVP Code 268)
defines the values 0-8. All remaining values are available for
assignment via IETF Consensus [12].
6.5 Integrity Check Value Transform Values
Section 4.8 defines the Integrity-Check-Value AVP (AVP Code 259)
which contains a field called the Transform. This document reserves
the value 1. All remaining values are available for assignment via
Designated Expert [12].
6.6 Reboot Type Values
Section 4.17 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].
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6.7 AVP Header Bits
There are six remaining reserved bits in the AVP header. Additional
bits should only be assigned via a Standards Action [12].
7.0 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 can 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.
8.0 DIAMETER protocol related configurable parameters
This section contains the configurable parameters that can be 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.
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.
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Receive Window
The Receive window determines how many DIAMETER messages a node
can handle from a communicating peer. This is normally
configured to a value that allows the node to effectively
manage its receive buffers.
Retransmission Timer
The retransmission timer is the time period that a node will
retransmit a message if not transport level acknowledgement was
received.
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.
Delayed Acknowlegement Timer
This is an optional timer, described in appendix D, that
specifies how long an implementation could wait before sending
a ZLB. The idea is that if there is a non-ZLB message that
would be sent within this window, an acknowledgement would be
piggybacked onto the message.
Shared Secret
The shared secret is a value that is known by two communicating
peers, and is used to generate the Integrity-Check-Value.
9.0 Security Considerations
Security issues are the primary topic of this document.
10.0 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] Calhoun, Bulley, "DIAMETER User Authentication Extensions",
draft-calhoun-diameter-authen-06.txt, Work in Progress,
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August 1999.
[8] Aboba, Beadles "The Network Access Identifier." RFC 2486.
January 1999.
[9] Calhoun, Zorn, Pan, Akhtar, "DIAMETER Framework",
draft-calhoun-diameter-framework-04.txt, Work in Progress,
October 1999.
[10] Zorn, Leifer, Rubens, Shriver, "RADIUS attributes for
Tunnel Protocol Support",
draft-ietf-radius-tunnel-auth-05.txt, Work in Progress,
April 1998.
[11] Calhoun, Bulley, "DIAMETER Secure Proxy Extension",
draft-calhoun-diameter-proxy-03.txt, Work in Progress,
October 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.
[15] Arkko, Calhoun, Patel, Zorn, "DIAMETER Accounting
Extension", draft-calhoun-diameter-accounting-00.txt,
IETF Work in Progress, September 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.
11.0 Acknowledgements
The authors would like to thank Nenad Trifunovic, Tony Johansson and
Pankaj Patel for their participation in the Document Reading Party.
Erik Guttman provided alot of good suggestions that were instrumental
in reducing the size of the document, while making the text generally
clearer.
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, Sumit Vakil, John
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R. Vollbrecht, Jeff Weisberg and Glen Zorn
12.0 Author's Address
Questions about this memo can be directed to:
Pat R. Calhoun
Network and Security Research Center, Sun Labs
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
13.0 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
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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."
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Appendix A: Acknowledgment Timeouts
DIAMETER uses sliding windows and timeouts to provide flow-control
across the underlying medium and to perform efficient data buffering
to keep two DIAMETER peers' receive window full without causing
receive buffer overflow. DIAMETER requires that a timeout be used to
recover from dropped messages.
When the timeout for a peer expires, the previously transmitted
message with Ns value equal to the highest in-sequence value of Nr
received from the peer is retransmitted. The receiving peer does not
advance its value for the receive sequence number state, Sr, until it
receives a message with Ns equal to its current value of Sr.
This rule assures that all subsequent acknowledgements to this peer
will contain an Nr value equal to the Ns value of the first missing
message until a message with the missing Ns value is received.
The exact implementation of the acknowledgment timeout is vendor-
specific. It is suggested that an adaptive timeout be implemented
with back-off for flow control. The timeout mechanism proposed here
has the following properties:
Independent timeouts for each peer. A device will have to
maintain and calculate timeouts for every active peer.
An administrator-adjustable maximum timeout, MaxTimeOut, unique to
each device.
An adaptive timeout mechanism that compensates for changing
throughput. To reduce message processing overhead, vendors may
choose not to recompute the adaptive timeout for every received
acknowledgment. The result of this overhead reduction is that the
timeout will not respond as quickly to rapid network changes.
Timer back-off on timeout to reduce congestion. The backed-off
timer value is limited by the configurable maximum timeout value.
Timer back-off is done every time an acknowledgment timeout
occurs.
In general, this mechanism has the desirable behavior of quickly
backing off upon a timeout and of slowly decreasing the timeout value
as messages are delivered without errors.
A.1 Calculating Adaptive Acknowledgment Timeout
We must decide how much time to allow for acknowledgments to return.
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If the timeout is set too high, we may wait an unnecessarily long
time for dropped messages. If the timeout is too short, we may time
out just before the acknowledgment arrives. The acknowledgment
timeout should also be reasonable and responsive to changing network
conditions.
The suggested adaptive algorithm detailed below is based on the TCP
1989 implementation and is explained in Richard Steven's book TCP/IP
Illustrated, Volume 1 (page 300). 'n' means this iteration of the
calculation, and 'n-1' refers to values from the last calculation.
DIFF[n] = SAMPLE[n] - RTT[n-1]
DEV[n] = DEV[n-1] + (beta * (|DIFF[n]| - DEV[n-1]))
RTT[n] = RTT[n-1] + (alpha * DIFF[n])
ATO[n] = MIN (RTT[n] + (chi * DEV[n]), MaxTimeOut)
DIFF represents the error between the last estimated round-trip time
and the measured time. DIFF is calculated on each iteration.
DEV is the estimated mean deviation. This approximates the standard
deviation. DEV is calculated on each iteration and stored for use in
the next iteration. Initially, it is set to 0.
RTT is the estimated round-trip time of an average message. RTT is
calculated on each iteration and stored for use in the next
iteration. Initially, it is set to PPD.
ATO is the adaptive timeout for the next transmitted message. ATO is
calculated on each iteration. Its value is limited, by the MIN
function, to be a maximum of the configure MaxTimeOut value.
Alpha is the gain for the round trip estimate error and is typically
1/8 (0.125).
Beta is the gain for the deviation and is typically 1/4 (0.250).
Chi is the gain for the timeout and is typically set to 4.
To eliminate division operations for fractional gain elements, the
entire set of equations can be scaled. With the suggested gain
constants, they should be scaled by 8 to eliminate all division. To
simplify calculations, all gain values are kept to powers of two so
that shift operations can be used in place of multiplication or
division. The above calculations are carried out each time an
acknowledgment is received for a message that was not retransmitted
(no timeout occurred).
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A.2 Flow Control: Adjusting for Timeout
This section describes how the calculation of ATO is modified in the
case where a timeout does occur. When a timeout occurs, the timeout
value should be adjusted rapidly upward. To compensate for shifting
internetwork time delays, a strategy must be employed to increase the
timeout when it expires. A simple formula called Karn's Algorithm is
used in TCP implementations and may be used in implementing the
back-off timers for the DIAMETER peers. Notice that in addition to
increasing the timeout, we also shrink the size of the window as
described in the next section.
Karn's timer back-off algorithm, as used in TCP, is:
NewTIMEOUT = delta * TIMEOUT
Adapted to our timeout calculations, for an interval in which a
timeout occurs, the new timeout interval ATO is calculated as:
RTT[n] = delta * RTT[n-1]
DEV[n] = DEV[n-1]
ATO[n] = MIN (RTT[n] + (chi * DEV[n]), MaxTimeOut)
In this modified calculation of ATO, only the two values that
contribute to ATO and that are stored for the next iteration are
calculated. RTT is scaled by delta, and DEV is unmodified. DIFF is
not carried forward and is not used in this scenario. A value of 2
for Delta, the timeout gain factor for RTT, is suggested.
Appendix B: Examples of sequence numbering
This appendix uses several common scenarios to illustrate how
sequence number state progresses and is interpreted.
B.1 Lock-step session establishment
In this example, a DIAMETER host establishes communication with a
peer, with the exchange involving each side alternating in the
sending of messages. This example is contrived, in that the final
acknowledgement typically would be included in the Device-Watchdog-
Ind message.
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DIAMETER Host A DIAMETER Host B
-> Device-Reboot-Ind
Nr: 0, Ns: 0
(ZLB) <-
Nr: 1, Ns: 0
-> Device-Watchdog-Ind
Nr: 0, Ns: 1
(delay)
(ZLB) <-
Nr: 2, Ns: 0
B.2 Multiple messages acknowledged
This example shows a flow of messages from DIAMETER Host B to Host A,
with Host A having no traffic of its own. Host A is waiting 1/4 of
its timeout interval, and then acknowledging all messages seen since
the last interval.
DIAMETER Host A DIAMETER Host B
(previous message flow precedes this)
-> (ZLB)
Nr: 7000, Ns: 1000
(non-ZLB) <-
Nr: 1000, Ns: 7000
(non-ZLB) <-
Nr: 1000, Ns: 7001
(non-ZLB) <-
Nr: 1000, Ns: 7002
(Host A's timer indicates it should acknowledge pending
traffic)
-> (ZLB)
Nr: 7003, Ns: 1000
B.3 Lost message with retransmission
Host A attempts to communicate with Host B. The Device-Reboot-Ind
sent from B to A is lost and must be retransmitted by Host B.
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DIAMETER Host A DIAMETER Host B
-> Device-Reboot-Ind
Nr: 0, Ns: 0
(message lost) Device-Reboot-Ind <-
Nr: 1, Ns: 0
(pause; Host A's timer started first, so fires first)
-> Device-Reboot-Ind
Nr: 0, Ns: 0
(Host B realizes it has already seen this message)
(Host B might use this as a cue to retransmit, as in this
example)
Device-Reboot-Ind <-
Nr: 1, Ns: 0
-> Device-Watchdog-Ind
Nr: 1, Ns: 1
(delay)
(ZLB) <-
Nr: 2, Ns: 1
Appendix C Backward Compatibility with RADIUS
The DIAMETER protocol was designed with RADIUS [1] compatibility in
mind. A DIAMETER node MAY listen for incoming RADIUS and DIAMETER
packets on the same UDP port. The first octet in the message would
indicate whether the message is of type RADIUS or DIAMETER.
The RADIUS protocol defines a one octet attribute space, and the
DIAMETER protocol reserves the first 255 attribute identifiers to be
the same as those defined in RADIUS. This allows DIAMETER servers to
easily perform protocol conversion, since a dictionary lookup would
not be necessary in order to map a RADIUS attribute to a DIAMETER
AVP.
By re-using the RADIUS attribute space, a DIAMETER server could
easily read a typical RADIUS user profile without any additional
conversions. This reduces the need to create duplicate user profiles
for both protocols, and also does not require any database conversion
while reading the profiles.
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Appendix D Delayed Acknowledgement Optimization
This optimization will potentially reduce the amount of traffic sent
between DIAMETER peers. This optimization affects when
acknowledgments are sent, as presented in Section 3.1.
If a peer does not have a message queued to transmit at the time a
non-ZLB message is received then it should delay a short time before
sending a ZLB message containing the latest values of Sr and Ss, as
described above. This short delay is to allow for the possible
arrival of a message to be transmitted back to its peer, thus
avoiding the need to issue a ZLB. The suggested value for this time
delay is 1/4 the receiving peer's value of Round-Trip-Time (RTT - see
Appendix A), if it computes RTT, or a maximum of 1/2 of its fixed
acknowledgment timeout interval otherwise. This timeout should
provide a reasonable opportunity for the receiving peer to obtain a
payload message destined for its peer, upon which the ACK of the
received message can be piggybacked. Note that if a peer's window is
full, it MAY advertise an older Nr value if it is not ready to accept
new messages.
This delay value should be treated as a suggested maximum; an
implementation could make this delay quite small without adversely
affecting the protocol. The default time delay is 2 seconds. To
provide for better throughput, the receiving peer should skip this
delay entirely and send a ZLB message immediately in the case where
its receive window is filled and it has no queued data to send for
this connection or it can't send queued data because the transmit
window is closed.
Appendix E Device-Reboot-Ind Message Flow
The following figure depicts a sample flow of Device-Reboot-Ind
between three DIAMETER peers, one being a proxy or broker server. In
this example DIA1 initiates the bootstrap sequence with DIA2, and
later DIA3 initiates the bootstrap sequence with DIA2. After some
time DIA1 needs to reboot and informs DIA2. The details of each
message is provided below.
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+-------+ +-------+ +-------+
| DIA1 | | PROXY | | DIA3 |
| | | DIA2 | | |
+-------+ +-------+ +-------+
| | |
|DRI (ns=0, nr=0) | |
| Rebooted | |
| version 1, | |
| extensions 1, 4 | |
(a) |------------------->| |
|DRI (ns=0, nr=1) | |
| Rebooted | |
| version 1, | |
| extension 1 | |
(b) |<-------------------| |
|ZLB (ns=0, nr=1) | |
(c) |------------------->| |
| . |DRI (ns=0, nr=0) |
| . | Rebooted |
| | version 1, |
| | extensions 1, 2 |
(d) | |<------------------|
| |DRI (ns=0, nr=1) |
| | Rebooted |
| | version 1, |
| | extension 1 |
(e) | |------------------>|
| |ZLB (ns=0, nr=1) |
(f) | |<------------------|
|DRI (ns=x, nr=y) | . |
| Upcoming Reboot | . |
(g) |------------------->| |
| . | |
| . | |
|DRI (ns=0, nr=0) | |
| Rebooted | |
| version 1, | |
| extensions 1, 4 | |
(h) |------------------->| |
| | |
Figure 4: Sample DRI Message Flow in a Proxy Environment
(a) DIA1 sends a DRI message to DIA2 indicating that its version
is one (1) and that its supported extensions are 1 (Roamops) and 4
(Mobile-IP).
(b) DIA2 sends a DRI message to DIA1 indicating that its version
is one (1) and that its supported extension is 1 (Roamops). This
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message also includes a piggy-backed acknowledgement of (a).
(c) DIA1 sends an acknowledgement of (b)
(d) DIA3 sends a DRI message to DIA2 indicating that its version
is one (1) and that its supported extensions are 1 (Roamops) and 2
(Secure Proxy).
(e) DIA2 sends a DRI message to DIA3 indicating that its version
is one (1) and that its supported extension is 1 (Roamops). This
message also includes a piggy-backed acknowledgement of (d).
(f) DIA3 sends an acknowledgement of (e)
(g) after some time DIA1 sends an indication to DIA2 that it is
about to reboot. All messages destined to the domain for which
DIA1 is responsible for should be redirected to an alternate
DIAMETER Server.
(h) Once the reboot is complete, DIA sends the DRI, which causes
steps (a) through (c) to be repeated.
Appendix F Device-Watchdog-Ind Message Flow
The following figure provides an example of how the Device-Watchdog-
Ind message is used in a proxy environment. The details of each
message is provided below.
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+-------+ +-------+ +-------+
| DIA1 | | PROXY | | DIA3 |
| | | DIA2 | | |
+-------+ +-------+ +-------+
| | |
|CMD-X (ns=23, nr=40)| |
(a) |------------------->| |
|ZLB (ns=40, nr=24) | |
(b) |<-------------------| |
| . | |
| . | |
| |CMD-Y (ns=12, nr=20)|
(c) | |------------------->|
| |ZLB (ns=20, nr=13) |
(d) | |<-------------------|
|WDI (ns=24, nr=40) | . |
(e) |------------------->| . |
|ZLB (ns=40, nr=25) | |
(f) |<-------------------| |
| |WDI (ns=21, nr=13) |
(g) | |<-------------------|
| |ZLB (ns=13, nr=22) |
(h) | |------------------->|
| | |
Figure 5: Sample WDI Message in a Proxy Environment
(a) DIA1 issues a message to DIA2
(b) DIA2 acknowledges the receipt of (a)
(c) DIA2 issues a message to DIA3
(d) DIA3 acknowleges the receipt of (c)
(e) After some time of inactivity, DIA1 issues a WDI to DIA2
(f) DIA2 acknowledges the receipt of (e)
(g) After some period of inactivity, DIA3 issues a WDI to DIA2
(h) DIA2 acknowledges the receipt of (g)
Appendix G Message-Reject-Ind Message Flow
The following figure show sample flows of MRI command between two
DIAMETER peers.In this example DIA1 and DIA2 servers generates error
messages. The details of the messages are provided below.
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+-------+ +-------+
| DIA1 | | DIA2 |
+-------+ +-------+
| |
|Unknown command |
(a) |------------------------------------>|
|MRI(Unrecognized Command Code) |
(b) |<------------------------------------|
| . |
| . |
|Unknown AVP |
(c) |<------------------------------------|
|MRI(Failed AVP Code) |
(d) |------------------------------------>|
| . |
| . |
|Bad value in a valid AVP |
(e) |------------------------------------>|
|MRI (Error Code | Failed AVP Code) |
(f) |<------------------------------------|
Figure 6: Sample MRI Message Flow
(a) DIA2 receives an unknown command from DIA1.
(b) DIA2 recognizes that it received an unknown command and
hence sends an MRI with Unrecognized Command Code AVP.
(c) DIA1 receives an unknown AVP in a message sent by DIA2.
(d) DIA1 recognizes that it received an unknown AVP and
returns an MRI with Failed AVP Code to DIA2.
(e) DIA2 receives a bad parameter within a otherwise
valid AVP from DIA1.
(f) As soon as it discovers that it has received a bad
parameter, it returns an MRI message to DIA1 with
Error Code AVP and Failed AVP Code.
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