One document matched: draft-calhoun-diameter-framework-00.txt
INTERNET DRAFT Pat R. Calhoun
Category: Standards Track Sun Microsystems, Inc.
Title: draft-calhoun-diameter-framework-00.txt Glen Zorn
Date: May 1998 Microsoft Corporation
Ping Pan
IBM T. J. Watson Research Center
DIAMETER Framework Document
<draft-calhoun-diameter-framework-00.txt>
Status of this Memo
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Abstract
As the number of new internet services has increased in the past cou-
ple of years, routers and network access servers (NAS) have had to
undergo re-engineering to support them.
These new services could often benefit from an Authentication,
Authorization and Accounting (AAA) protocol to facilitate off-loading
policy information to an external server.
The DIAMETER protocol defines a policy protocol used by clients to
perform Policy, AAA and Resource Control. This allows a single server
to handle policies for many services.
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Table of Contents
1.0 Introduction
1.1 Terminology
1.2 Specification Language
2.0 DIAMETER Architecture
2.1 DIAMETER Base Protocol
2.1.1 DIAMETER Security
2.2 Resource Management Extension
2.3 Accounting Extension
2.5 QOS Extension
2.6 Mobile IP Extension
3.0 Why not LDAP?
4.0 References
5.0 Acknowledgements
6.0 Author's Address
Appendix A. "Drinks" Policy Extension
1.0 Introduction
As the number of new internet services has increased in the past cou-
ple of years, routers and network access servers (NAS) have had to
undergo re-engineering to support them.
These new services could often benefit from an Authentication,
Authorization and Accounting (AAA) protocol to facilitate off-loading
policy information to an external server.
An example of such a service is dial-up PPP Internet access. Large
ISPs cannot bear the administrative burden to configure all of their
users on each NAS everytime a new device is deployed. In this case
RADIUS [1] has been used successfully by many such ISPs.
New services such as Voice over IP, Fax over IP [6], Mobile IP [7]
and RAP [5] also require similar services in order to be able to
authenticate, retrieve authorization information, and generate
accounting records for billing purposes.
The current trend is for each working groups to define its own policy
protocol for a specific service, each with their own nuances. This
requires requires customers to deploy several policy servers, which
increases the cost of administration and complicates deployment.
DIAMETER offers a common solution by defining a base protocol that
defines the header formats, security extensions and requirements as
well as a small number of mandatory commands and AVPs. A new service
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can extend DIAMETER by extending the base protocol to support new
functionality.
1.1 Terminology
AAA
Authentication, Authorization and Accounting.
AVP
The DIAMETER protocol consists of a header followed by objects.
Each object is encapsulated in a header known as an Attribute-
Value-Pair.
Commands
The DIAMETER Protocol is a request/response protocol. Each DIAME-
TER message includes a Command AVP that is used to identify the
type of request or response.
Integrity Check Vector (ICV)
An Integrity Check Vector is an unforgeable or secure hash of the
packet with a shared secret.
1.2 Specification Language
In this document, several words are used to signify the requirements
of the specification [8]. These words are often capitalized.
MUST This word, or the adjective "required", means that
the definition is an absolute requirement of the
specification.
MUST NOT This phrase means that the definition is an absolute
prohibition of the specification.
SHOULD This word, or the adjective "recommended", means
that, in some circumstances, valid reasons may exist to
ignore this item, but the full implications must be
understood and carefully weighed before choosing a
different course. Unexpected results may result
otherwise.
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MAY This word, or the adjective "optional", means that this
item is one of an allowed set of alternatives. An
implementation which does not include this option MUST
be prepared to interoperate with another implementation
which does include the option.
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2.0 DIAMETER Architecture
The Base DIAMETER Architecture consists of three modules, which
defines a small set of primitives that MUST be implemented by all
DIAMETER entities.
Many applications require that the policy server maintain session
state information. The Resource Management extension provides this
capability between client and a server as well as between two
servers.
Most services using DIAMETER require accounting. The current IETF's
standard protocol for accounting is SNMP, but experience indicates
that SNMP often is not the correct protocol for service accounting.
Many applications and services use RADIUS Accounting [4] as their
accounting protocol, however RADIUS accounting is not a standard pro-
tocol and is informational only. A standard accounting protocol is
required.
The following diagram provides a representation of the DIAMETER
Architecture. As an example, a fictional Policy Extension has been
added to the architecture. This fictional service is described here
in order to to illustrate how a service could make use of DIAMETER.
+------------+
| Policy |
| |
| Extension |
+------------+
+------------+ / \ +------------+
| Resource | | | Accounting |
| | | | |
| Management | | | Extension |
+------------+ | +------------+
/ \ | / \
| | |
\ / \ / \ /
+--------------------------------------------------+
| |
| DIAMETER Base Protocol |
| |
+--------------------------------------------------+
Figure 1: DIAMETER Protocol Architecture
Design direction for more extensions will be taken from the user (ISP
and network operations) community.
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2.1 DIAMETER Base Protocol
The Base Protocol defines a set of primitives and the security model
used between DIAMETER peers. The following goals motivate the defini-
tion of the base protocol:
- Base protocol MUST be lightweight and simple to implement.
- Allow unsolicited messages from the Policy Server to the client.
- Feature discovery.
- Version negotiation.
- unsupported extension notification instead of silent discard.
- Efficient encoding of Attributes.
- The AVP address space MUST be large (i.e. 32 bits)
- The protocol MUST ensure that 32 bit alignment is observed.
- Support for vendor specific AVPs and Commands.
- The protocol MUST support both TCP and UDP.
- client to server as well as server to server communication (as
in figure 2) is needed.
- Authentication and privacy for policy messages.
- Communication with a DIAMETER entity through an intermediate
DIAMETER entity.
Feature Discovery is intended to dramatically reduce the administra-
tive overhead associated with Policy Server configuration. A DIAMETER
client can use the a DIAMETER service-type request over SLP [2] to
locate Policy Servers within the network, and then a set of DIAMETER
messages to retrieve the supported extensions.
DIAMETER version negotiation will also reduce the administrative
overhead in policy server configuration. DIAMETER entities SHOULD
agree to use the higher DIAMETER protocol version number that they
commonly support.
UDP is preferable for policy applications that require "fine tuned"
retransmission strategies. For applications that require support for
larger messages and are not as concerned with the retransmission
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policy, TCP can be used. Each individual extension may specify the
underlying transport requirements.
As mentioned above, DIAMETER supports server to server communication
(see figure 2). Servers can either belong to the same administrative
domain, or they may belong to different domains. This is commonly
called "proxying" DIAMETER requests, where a proxy server is used in
order to reach the end policy server. This functionality is described
in [3] and has many different applications besides Internet dial-up
access.
+--------+ +--------+
| proxy | | policy |
| policy |<--------------->| |
| server | server-server | server |
+--------+ communication +--------+
/ /|\
/ | client-server
/ | communication
|/_ \|/
+--------+ +--------+
| router | | router |
+--------+ +--------+
Figure 2: Client through a Proxy Server
2.1.1 DIAMETER Security
The protocol presents three different security methods. The first and
most obvious method requires no security and can be used with IPSEC.
The second method is to make use of shared secrets between two enti-
ties. In this case the protocol could include an HMAC-MD5-96 [8]
Integrity Check Vector (ICV) within an AVP to provide integrity of
the message.
Figure 3 depicts an example of Hop-by-Hop security where Policy
Server 1 (PS1) and Proxy Server 2 (PS2) share a secret as well as PS2
and Policy Server 3 (PS3). In this example PS1 sends a message to PS3
through PS2 with an ICV that is computed using the secret it shares
with PS2. Upon receipt of the message, PS2 validates the ICV, removes
it and adds an ICV that is computed using the secret it shares with
PS3. This is commonly called Hop-by-Hop security since it does not
provide message integrity between PS1 and PS3.
The third method, called End-to-End security, allows a DIAMETER
entity to communicate with a Server through a set of intermediate
Proxies (see figure 3). In this case the initiator MUST sign the
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message using public key cryptography since it is the only way for
the end server to ensure that a proxy has not modified the original
message.
+----------+ +----------+
| policy |<--------------->| proxy |
| server 1 | server-server | server 2 |
+----------+ communication +----------+
/|\
| server-server
| communication
\|/
+----------+
| policy |
| server 3 |
+----------+
Figure 3: Proxy Server Communication
If certificates are not statically configured or retrieved through
some other means (i.e. Certificate Authority), it requires that both
the client and the server exchange certificates as part of the DIAME-
TER bootstrap protocol.
For both the second and the third method the base protocol MUST pro-
vide replay protection.
2.2 Resource Management Extension
The Resource Management Extension enables Servers to maintain session
state information. Many applications require the policy server to
make decisions not only based on a static policy, but also based on
network events.
The Resource Management Extension allows a client and server to
exchange state information as well as two Servers. Some servers may
also use a distributed back-end database to share state information.
The Resource Management extension does not provide a message to
create a session. This is handled through an extension's authoriza-
tion response message.
An example would be when the server authorizes the allocation of
bandwidth through a successful response message. A response message
would then create state information within the client and the server
that can be handled through the resource management extensions at a
later time, using the session identifier assigned to the session.
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The following abilities supported by the Resource Management exten-
sion:
- Associating resources with clients.
- Identifying when a session is terminated.
- Session termination by servers.
- State update/refresh from the client or other servers.
In order for the server to maintain accurate state information, it
MUST be notified when a session is terminated.
State update and refresh is very important in the case where the
server has lost state information (i.e. reboot). The server MUST be
able to request information about a specific session as well as a
generic request to retrieve all state information. For services that
require fault tolerance, servers SHOULD share state information.
The server must be able to request that a client terminate a session.
This is required in services where policy can pre-empt a low priority
session.
Because multiple servers need to share state information, the server
MUST generate resource tokens. These resource tokens are returned by
the server at authorization time by the appropriate extension. The
resource token is sent by the client to the server when it receives a
request for a state update, and must contain enough information for
the server to rebuild session state information.
Furthermore since state information is shared amongst servers it is
required that each session have a universally unique session identif-
ier associated with it that is assigned by the client.
2.3 Accounting Extension
The Accounting Extension defines the messages used for service
accounting. The accounting extension MUST provide the following func-
tionality (a separate effort is in place to define the exact require-
ments of the accounting extension):
- Negotiable transfer mechanism.
- Provide general purpose AVPs.
- Flexible to allows new extensions to use the accounting
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extension.
- Scalable to allows millions to users and thousands of sites.
- Secure accounting data transfer.
The accounting extension must be able to transfer accounting records
in an event-driven or batch manner. The selected transfer mechanism
must be negotiable, and it must be possible to initiate batch
transfer from either peer.
The extension MUST Support accounting finite and infinite sessions as
well indivisible events. Other detailed requirements call for sup-
porting service name/id, amount and length of attributes.
It must also be flexible to work in many applications areas. This
requires extensibility, application defined level of security,
minimal storage and code size requirements, and the ability to work
in both real-time and non-real time situations.
The accounting protocol must be scalable to the size of global
shared-use networks with millions of users and thousands of sites and
accounting systems.Transmission, header, and security overhead MUST
be amortized over several accounting records. Only a per-entity state
needs to be held by the accounting systems (as opposed to a per-
session state).
The accounting protocol must be secure. End-to-end and hop-by-hop
integrity and confidentiality, data-based access control are all
needed. Standard Internet security protocols are to be used where
possible.
3.0 Why not LDAP?
Many people have asked whether LDAP would provide the functionality
required.
A Server MAY wish to access policies using LDAP, but the use of LDAP
between the client and the server is not possible. The use of LDAP in
this case would require that all routers have write access to the
directory. Most customers would not accept this requirements and it
is not efficient.
In the case of roaming, customers would have to open up their direc-
tory so outside routers have writeable access. Moreover, having
1000's of routers constantly write to the directory would cause some
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additional problems to the Directory Service.
Finally, LDAP does not provide server initiated messages which is a
requirement for an AAA protocol.
4.0 References
[1] Rigney, et alia, "RADIUS", RFC-2138, Livingston, April 1997
[2] Veizades, Guttman, Perkins, Kaplan, "Service Location
Protocol", RFC-2165, June 1997.
[3] Aboba, Zorn, "Roaming Requirements", draft-ietf-roamops-
roamreq-08.txt, March 1998.
[4] Rigney, "RADIUS Accounting", RFC-2139, April 1997.
[5] Yavatkar, Pendarakis, Guerin, "A Framework for Policy-based
Admission Control", draft-ietf-rap-framework-00.txt,
November 1997.
[6] Masinter, "Terminology and Goals for Internet Fax",
draft-ietf-fax-goals-02.txt, March 1998.
[7] C. Perkins, Editor. IP Mobility Support. RFC 2002, October
1996.
[8] Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for
Message Authentication", RFC 2104, January 1997.
[9] Bradner, "Key words for use in RFCs to Indicate Requirements
Levels", BCP 14, RFC 2119, March 1997.
5.0 Acknowledgements
The Authors would like to thanks Bernard Aboba and Jari Arkko for
their Accounting Requirements contribution.
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6.0 Author's Address
Questions about this memo can be directed to:
Pat R. Calhoun
Technology Development
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
Glen Zorn
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Phone: 1-425-703-1559
E-Mail: glennz@microsoft.com
Ping Pan
IBM T. J. Watson Research Center
30 Saw Mill River Road,
Hawthorne, NY 10532
Phone: 1-914-784-6579
Fax: 1-914-784-6205
E-mail: pan@watson.ibm.com
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Appendix A. "Drinks" Policy Extension
This section is provided as an example only and is intended to pro-
vide the reader with a better understanding of how DIAMETER could be
used by services.
This protocol will provide authentication, authorization and account-
ing services for bar customers. Each user will be provided with a
smart card that contains the user's identity and private key.
When a user enters a bar he may use the automated facility by insert-
ing his card into a card slot and wait for the appropriate retina
scan to be performed. The user also selects a drink, and may simply
hit the "favorite drink" button on the machine.
The DIAMETER Client then issues the authentication request to the
Server which authenticates the user. The message MUST contain a
unique session identifier that will be used while the user is present
in the bar. The authentication phase consists of a check that the key
and retina scan matches the user's identity and that the user is of
age (this is a local decision since each state has different minimum
age requirements).
If the user is successfully authenticated the server adds authoriza-
tion information. Authorization information MAY include the user's
favorite drinks, whether the user's martini should be shaken or
stirred, any known allergic reactions to peanuts or other assorted
snacks, etc.
Upon receipt of the response, the DIAMETER client dispenses the drink
to the customer and generates and accounting request to the DIAMETER
accounting server (which MAY be different from the authentication and
authorization server).
Since the Policy server adapts itself according to the user's drink-
ing habits, it knows how often to send a message to the DIAMETER
Client to offer another drink to the customer. Since the policy
server also knows about the user's favorite drinks, it may even "sug-
gest" a list of drinks to the user periodically. This is achieved
using the Resource Management extensions defined earlier.
When the user wishes to order a new drink, the same mechanism occurs
as defined above, but the Session Identifier is constant. When the
user leaves the bar, the DIAMETER Client sends a message to the
server stating that it is terminating a session (based on the Session
ioni
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