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RFC 2904

AAA Authorization Framework

Pages: 35

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Network Working Group                                      J. Vollbrecht
Request for Comments: 2904                      Interlink Networks, Inc.
Category: Informational                                       P. Calhoun
                                                  Sun Microsystems, Inc.
                                                              S. Farrell
                                                  Baltimore Technologies
                                                              L. Gommans
                                                 Enterasys Networks EMEA
                                                                G. Gross
                                                     Lucent Technologies
                                                            B. de Bruijn
                                                 Interpay Nederland B.V.
                                                              C. de Laat
                                                      Utrecht University
                                                             M. Holdrege
                                                               D. Spence
                                                Interlink Networks, Inc.
                                                             August 2000

                      AAA Authorization Framework

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.


This memo serves as the base requirements for Authorization of Internet Resources and Services (AIRS). It presents an architectural framework for understanding the authorization of Internet resources and services and derives requirements for authorization protocols.
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Table of Contents

1. Introduction ................................................ 2 2. Authorization Entities and Trust Relationships .............. 4 3. Message Sequences ........................................... 7 3.1. Single Domain Case ..................................... 7 3.1.1. The Agent Sequence .............................. 7 3.1.2. The Pull Sequence ............................... 8 3.1.3. The Push Sequence ............................... 9 3.2. Roaming ................................................ 10 3.3. Distributed Services ................................... 13 3.4. Combining Roaming and Distributed Services ............. 15 4. Relationship of Authorization and Policy .................... 16 4.1. Policy Retrieval ....................................... 16 4.2. Policy Evaluation ...................................... 17 4.3. Policy Enforcement ..................................... 17 4.4. Distributed Policy ..................................... 18 5. Use of Attribute Certificates ............................... 19 6. Resource Management ......................................... 22 6.1. Session Management ..................................... 23 6.2. The Resource Manager ................................... 24 7. AAA Message Forwarding and Delivery ......................... 25 8. End-to-End Security ......................................... 26 9. Streamlined Authorization Process ........................... 27 10. Summary of the Authorization Framework ..................... 28 11. Security Considerations .................................... 28 Glossary ....................................................... 29 References ..................................................... 31 Authors' Addresses ............................................. 32 Full Copyright Statement ....................................... 35

1. Introduction

This document is one of a series of three documents under consideration by the AAAarch RG dealing with the authorization requirements for AAA protocols. The three documents are: AAA Authorization Framework (this document) AAA Authorization Requirements [2] AAA Authorization Application Examples [3] There is a demonstrated need for a common scheme which covers all Internet services which offer Authorization. This common scheme will address various functional architectures which meet the requirements of basic services. We attempt to describe these architectures and functions as a basis for deriving requirements for an authorization protocol [2].
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   These architectures include Policy structures, Certificate
   Authorities, Resource Managers, Inter-Domain and Multi-Domain
   schemes, and Distributed Services.  The requirements are for the
   expected use of Authorization services across these architectures.

   A representative set of applications that may use this architecture
   to support their authorization needs is presented in [3].  The
   examples in [3] show how this framework may be used to meet a wide
   variety of different authorization needs.

   We expect that this work may be extended in the future to a more
   comprehensive model and that the scheme described here will be
   incorporated into a framework that includes authentication,
   accounting and auditing.  We have referenced a number of
   authorization sources, but also recognize that there may be some that
   we have missed and that should be included.  Please notify one of the
   authors of any such oversight so it can be corrected in a future

   In general, it is assumed that the parties who are participating in
   the authorization process have already gone through an authentication
   phase.  The authentication method used by those parties is outside
   the scope of this document except to the extent that it influences
   the requirements found in a subsequent authorization process.
   Likewise, accounting requirements are outside the scope of this
   document other than recording accounting data or establishing trust
   relationships during an authorization that will facilitate a
   subsequent accounting phase.

   The work for this memo was done by a group that originally was the
   Authorization subgroup of the AAA Working Group of the IETF.  When
   the charter of the AAA working group was changed to focus on MobileIP
   and NAS requirements, the AAAarch Research Group was chartered within
   the IRTF to continue and expand the architectural work started by the
   Authorization subgroup.  This memo is one of four which were created
   by the subgroup.  This memo is a starting point for further work
   within the AAAarch Research Group.  It is still a work in progress
   and is published so that the work will be available for the AAAarch
   subgroup and others working in this area, not as a definitive
   description of architecture or requirements.

   This document uses the terms 'MUST', 'SHOULD' and 'MAY', and their
   negatives, in the way described in RFC 2119 [4].
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2. Authorization Entities and Trust Relationships

The following framework is being presented in order to provide a framework for discussing authorization requirements for a large number of applications. The intent is to provide some common vocabulary for the discussion. Terminology is introduced for basic elements in the authorization transaction and for concepts that appear to be common to all (or at least many) authorization proposals. Figure 1, below, identifies the basic conceptual entities that may be participants in an authorization: 1. A User who wants access to a service or resource. 2. A User Home Organization (UHO) that has an agreement with the user and checks whether the user is allowed to obtain the requested service or resource. This entity may carry information required to authorize the User, which might not be known to the Service Provider (such as a credit limit). 3. A Service Provider's AAA Server which authorizes a service based on an agreement with the User Home Organization without specific knowledge about the individual User. This agreement may contain elements that are not relevant to an individual user (e.g., the total agreed bandwidth between the User Home Organization and the Service Provider). 4. A Service Provider's Service Equipment which provides the service itself. This might, for example, be a NAS in dial service, or a Router in the QoS service, or a print server in the Internet Printing service.
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               +------+      +-------------------------+
               |      |      | User Home Organization  |
               |      |      |  +-------------------+  |
               |      |      |  |    AAA Server     |  |
               |      |      |  |                   |  |
               |      |      |  +-------------------+  |
               |      |      |                         |
               |      |      +-------------------------+
               |      |
               |      |
               |      |
               | User |      +-------------------------+
               |      |      | Service Provider        |
               |      |      |  +-------------------+  |
               |      |      |  |    AAA Server     |  |
               |      |      |  |                   |  |
               |      |      |  +-------------------+  |
               |      |      |                         |
               |      |      |  +-------------------+  |
               |      |      |  |      Service      |  |
               |      |      |  |     Equipment     |  |
               |      |      |  +-------------------+  |
               |      |      |                         |
               +------+      +-------------------------+

              Fig. 1 -- The Basic Authorization Entities

   These entities will be referenced in the authorization requirements.

   There may be bilateral agreements between pairs of organizations
   involved in an authorization transaction.  Agreements between
   organizations may take the form of formal contracts or Service Level
   Agreements.  Figure 2 uses double lines to show relationships that
   may exist between the User and the User Home Organization and between
   the User Home Organization and the Service Provider.
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              +------+      +-------------------------+
              |      |      | User Home Organization  |
              |      |======|  +-------------------+  |
              |      |      |  |    AAA Server     |  |
              |      |      |  |                   |  |
              |      |      |  +-------------------+  |
              |      |      |                         |
              |      |      +-------------------------+
              |      |                  ||
              |      |                  ||
              |      |                  ||
              | User |      +-------------------------+
              |      |      | Service Provider        |
              |      |      |  +-------------------+  |
              |      |      |  |    AAA Server     |  |
              |      |      |  |                   |  |
              |      |      |  +-------------------+  |
              |      |      |                         |
              |      |      |  +-------------------+  |
              |      |      |  |      Service      |  |
              |      |      |  |     Equipment     |  |
              |      |      |  +-------------------+  |
              |      |      |                         |
              +------+      +-------------------------+

                     Fig. 2 -- Service Agreements

   Authorization is based on these bilateral agreements between
   entities. Agreements may be chained, as shown in figure 2.  The User
   has an agreement with the User Home Organization (e.g., the User may
   have access to the service between 9:00 a.m. and 11:00 a.m. daily).
   The User Home Organization has an agreement with the Service Provider
   (e.g., that all requests for access will be granted, except between
   5:00 a.m. and 10:00 a.m. on Sunday).  The fulfillment of the User's
   request depends on both agreements being honored.

   Note that these agreements may be implemented by hand configuration
   or by evaluation of Policy data stored in a Policy database.  The
   point is that there must be a set of known rules in place between
   entities in order for authorization transactions to be executed.

   Trust is necessary to allow each entity to "know" that the policy it
   is authorizing is correct.  This is a business issue as well as a
   protocol issue.  Trust is often established through third party
   authentication servers (such as Kerberos), via a certificate
   authority, by configuring shared secrets or passwords, or by sharing
   a common facility (such as a connecting wire between processors).
   These "static" trust relationships are necessary for authorization
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   transactions to take place.  Static trust relationships are used in
   an authorization sequence to establish a "dynamic" relationship
   between the User and the Service Equipment.  Several possible
   authorization sequences are possible, each of which use the static
   trust "chain" to have the user first be approved by the User Home
   Organization, and then have the Service Provider accept the request
   based on its trust of the User Home Organization.

3. Message Sequences

In general, the User Home Organization and the Service Provider are different entities or different "administrative domains". In the simplest case, however, the User Home Organization and the Service Provider may be combined as a single entity. This case will be used to describe three authorization sequences possible with the simple case. In following sections these concepts will be applied to more complicated cases involving separate User Home Organization and Service Provider entities (as in roaming) and multiple Service Providers each with their own AAA Servers and Service Equipment (as in distributed services).

3.1. Single Domain Case

This case includes the User, the Service Provider's AAA Server, and the Service Provider's Service Equipment. Examples of this case include a NAS supported by a standalone RADIUS server, or a QoS Router supported by a local bandwidth broker. The sequences considered in the following figures are the "agent", "pull", and "push" sequences for the single domain case.

3.1.1. The Agent Sequence

In the agent sequence (see figure 3), the Service Provider AAA Server functions as an agent between the User and the service itself. The AAA Server receives a request from the User and forwards authorization and possibly configuration information to the Service Equipment. In this model, the User sends a request to the Service Provider's AAA Server (1), which will apply a policy associated with the User and the particular service being requested. The AAA Server sends a request to the Service Equipment, and the Service Equipment sets up whatever is requested (2). The Service Equipment then responds to the AAA Server acknowledging that it has set up the Service for the user (3). The AAA Server replies to the User telling it that the Service is set up (4).
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   Depending on the nature of the service, further communication may
   take place between the User and the Service Equipment.  For this to
   occur, there needs to be a binding between the User and the
   authorized service.  This requires further study.

            +------+      | Service Provider        |
            |      |   1  |  +-------------------+  |
            |      |------+->|    AAA Server     |  |
            |      |<-----+--|                   |  |
            |      |   4  |  +-------------------+  |
            | User |      |          |  /|\         |
            |      |      |          |2  |3         |
            |      |      |         \|/  |          |
            |      |      |  +-------------------+  |
            |      |      |  |      Service      |  |
            |      |      |  |     Equipment     |  |
            |      |      |  +-------------------+  |
            +------+      |                         |

                     Fig. 3 -- Agent Sequence

   Example: A regular user may ask for 1 Mb/s bandwidth (1).  The
   bandwidth broker (AAA Server) tells the router (Service Equipment) to
   set this user into the 1Mb/s "queue" (2).  The router responds that
   it has done so (3), and the bandwidth broker tells the User the
   bandwidth is set up (4).

3.1.2. The Pull Sequence

The pull sequence (figure 4) is what is typically used in the Dialin application, in the Mobile-IP proposal, and in some QoS proposals. The User sends a request to the Service Equipment (1), which forwards it to the Service Provider's AAA Server (2), which evaluates the request and returns an appropriate response to the Service Equipment (3), which sets up the service and tells the User it is ready (4).
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            +------+      | Service Provider        |
            |      |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |      |  |                   |  |
            |      |      |  +-------------------+  |
            | User |      |         /|\  |          |
            |      |      |          |2  |3         |
            |      |      |          |  \|/         |
            |      |   1  |  +-------------------+  |
            |      |------+->|      Service      |  |
            |      |<-----+--|     Equipment     |  |
            |      |   4  |  +-------------------+  |
            +------+      |                         |

                     Fig. 4 -- Pull Sequence

3.1.3. The Push Sequence

The push sequence (figure 5) requires that the User get from the Service Provider's AAA Server a ticket or certificate verifying that it is o.k. for the User to have access to the service (1,2). The User includes the ticket in the request (3) to the Service Equipment. The Service Equipment uses the ticket to verify that the request is approved by the Service Provider's AAA Server. The Service Equipment then sends an o.k. to the User (4). The ticket the user gets from the Service Provider's AAA Server will typically have some time limit on it. It may contain an indication of service location, and in some applications, it might be used for more than one request. In the push sequence the communication between the AAA Server and the Service Equipment is relayed through the User rather than directly between themselves.
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              +------+      | Service Provider        |
              |      |   1  |  +-------------------+  |
              |      |------+->|    AAA Server     |  |
              |      |<-----+--|                   |  |
              |      |   2  |  +-------------------+  |
              | User |      |                         |
              |      |      |                         |
              |      |      |                         |
              |      |   3  |  +-------------------+  |
              |      |------+->|      Service      |  |
              |      |<-----+--|     Equipment     |  |
              |      |   4  |  +-------------------+  |
              +------+      |                         |

                     Fig. 5 -- Push Sequence

3.2. Roaming -- the User Home Organization is not the Service Provider

In many interesting situations, the organization that authorizes and authenticates the User is different from the organization providing the service. This situation has been explored in the Roaming Operations (roamops) Working Group. For purposes of this discussion, any situation in which the User Home Organization is different from the Service Provider is considered to be roaming. Examples of roaming include an ISP selling dialin ports to other organizations or a Mobile-IP provider allowing access to a user from another domain. The same agent, pull and push sequences are possible with roaming. If the Service Provider's AAA Server and the Service Equipment are grouped as a logical entity for purposes of description, then the following figures illustrate these cases.
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            +------+      +-------------------------+
            |      |   1  | User Home Organization  |
            |      |----->|  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |<-----|  |                   |  |
            |      |   4  |  +-------------------+  |
            |      |      |                         |
            |      |      +-------------------------+
            |      |                 |  /|\
            |      |                 |2  |3
            |      |                \|/  |
            | User |      +-------------------------+
            |      |      | Service Provider        |
            |      |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |      |  |                   |  |
            |      |      |  +-------------------+  |
            |      |      |                         |
            |      |      |  +-------------------+  |
            |      |      |  |      Service      |  |
            |      |      |  |     Equipment     |  |
            |      |      |  +-------------------+  |
            |      |      |                         |
            +------+      +-------------------------+

                 Fig. 6 -- Roaming Agent Sequence
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            +------+      +-------------------------+
            |      |      | User Home Organization  |
            |      |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |      |  |                   |  |
            |      |      |  +-------------------+  |
            |      |      |                         |
            |      |      +-------------------------+
            |      |                /|\  |
            |      |                 |2  |3
            |      |                 |  \|/
            |      |      +-------------------------+
            |      |      | Service Provider        |
            | User |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |   1  |  |                   |  |
            |      |----->|  +-------------------+  |
            |      |      |                         |
            |      |<-----|  +-------------------+  |
            |      |   4  |  |      Service      |  |
            |      |      |  |     Equipment     |  |
            |      |      |  +-------------------+  |
            |      |      |                         |
            +------+      +-------------------------+

                 Fig. 7 -- Roaming Pull Sequence
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            +------+      +-------------------------+
            |      |   1  | User Home Organization  |
            |      |----->|  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |<-----|  |                   |  |
            |      |   2  |  +-------------------+  |
            |      |      |                         |
            |      |      +-------------------------+
            |      |
            |      |
            |      |
            | User |      +-------------------------+
            |      |      | Service Provider        |
            |      |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |   3  |  |                   |  |
            |      |----->|  +-------------------+  |
            |      |      |                         |
            |      |<-----|  +-------------------+  |
            |      |   4  |  |      Service      |  |
            |      |      |  |     Equipment     |  |
            |      |      |  +-------------------+  |
            |      |      |                         |
            +------+      +-------------------------+

               Fig. 8 -- Roaming Push Sequence

3.3. Distributed Services

To provide a complete service to a user, offerings from several service providers may need to be combined. An example would be a user who requires a QoS service for a session that crosses multiple ISPs. Any service that is provided by more than one Service Provider acting in concert is a distributed service. Figure 9 illustrates distributed services.
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                 +-------------------+      +-------------------+
   +------+      | Org1              |      | Org2              |
   |      |      |  +-------------+  |      |  +-------------+  |
   |      |      |  | AAA Server  |  |      |  | AAA Server  |  |
   |      |      |  |             |  |      |  |             |  |
   |      |      |  +-------------+  |      |  +-------------+  |
   | User |======|                   |======|                   |
   |      |      |  +-------------+  |      |  +-------------+  |
   |      |      |  |   Service   |  |      |  |   Service   |  |
   |      |      |  |  Equipment  |  |      |  |  Equipment  |  |
   |      |      |  +-------------+  |      |  +-------------+  |
   +------+      |                   |      |                   |
                 +-------------------+      +-------------------+

                  Fig. 9 -- Distributed Services

   The agreements between entities in figure 9 imply that the request
   from the User will be authenticated and authorized by the first
   organization, then forwarded to the second organization.  Note that
   the sequence between User and Org1 may be different than between Org1
   and Org2.  The first might use a pull sequence, and the second might
   use an agent sequence.  This example is illustrated in figure 10.

                 +-------------------+      +-------------------+
   +------+      | Org1              |      | Org2              |
   |      |      |  +-------------+  |   3  |  +-------------+  |
   |      |      |  | AAA Server  |--+------+->| AAA Server  |  |
   |      |      |  |             |<-+------+--|             |  |
   |      |      |  +-------------+  |   6  |  +-------------+  |
   | User |      |       /|\  |      |      |        |  /|\     |
   |      |      |        |2  |7     |      |        |4  |5     |
   |      |      |        |  \|/     |      |       \|/  |      |
   |      |   1  |  +-------------+  |      |  +-------------+  |
   |      |------+->|   Service   |  |      |  |   Service   |  |
   |      |<-----+--|  Equipment  |  |      |  |  Equipment  |  |
   |      |   8  |  +-------------+  |      |  +-------------+  |
   +------+      |                   |      |                   |
                 +-------------------+      +-------------------+

             Fig. 10 -- A Possible Distributed Sequence

   There are a number of other ways that authorization sequences for
   distributed services can be set up.  For example, it is possible
   that, in order to reduce delay time in setting up a session, Org1
   could send a response to the user before receiving a verification
   that Org2 has authorized the service.  In that case Org1 would need
   to be able to revoke the authorization sent earlier if Org2 does not
   send the authorization in some amount of time.
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3.4. Combining Roaming and Distributed Services

Figure 11 shows a combination of Roaming and Distributed Services. Contract and trust relationships may be set up in number of ways, depending on a variety of factors, especially the business model. +------+ +-------------------+ +-------------------+ | | | User Home Org | | SuperOrg | | | | +-------------+ | | +-------------+ | | | | | AAA Server | | | | AAA Server | | | | | | | | | | | | | | | +-------------+ | | +-------------+ | | | | | | | | | +-------------------+ +-------------------+ | | | | | | +-------------------+ +-------------------+ | User | | Org1 | | Org2 | | | | +-------------+ | | +-------------+ | | | | | AAA Server | | | | AAA Server | | | | | | | | | | | | | | | +-------------+ | | +-------------+ | | | | | | | | | | +-------------+ | | +-------------+ | | | | | Service | | | | Service | | | | | | Equipment | | | | Equipment | | | | | +-------------+ | | +-------------+ | | | | | | | +------+ +-------------------+ +-------------------+ Fig. 11 -- Roaming and Distributed Services New entities that combine or add capabilities can be created to meet business needs. In figure 11, one such possibility, a SuperOrg entity is shown. The idea is that this entity would provide authentication and authorization for organizations that are providing services to end-users. It could be considered to be a wholesaler or broker. While not all authorization will require having a broker, authorization protocols should allow such entities to be created to meet legitimate requirements. Having considered the basic players and how they interact, we will now consider different ways that authorization data may be stored in the network.
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4. Relationship of Authorization and Policy

The Policy Framework (policy) Working Group is seeking to provide a framework to represent, manage, and share policies and policy information in a vendor-independent, interoperable, scalable manner. [5],[6],[7]. This section explores the relationship of policy and authorization and sets the stage for defining protocol requirements for supporting policy when included as part of multi-domain authorization. The work presented here builds on the policy framework, extending it to support policy across multiple domains. One view of an authorization is that it is the result of evaluating policies of each organization that has an interest in the authorization decision. In this document the assumption is that each administration may have policies which may be indexed by user, by service, or by other attributes of the request. The policies of each administration are defined independently of other administrations. Each independent policy must be 1) retrieved, 2) evaluated, and 3) enforced.

4.1. Policy Retrieval

Policy definitions are maintained and stored in a policy repository [5] by (or on behalf of) the organization that requires them. The Policy Framework WG is working on a way to describe policy [7]. Other implementations describe policy as a set of ACL lists. Policy definitions must be retrieved in order to be evaluated and enforced. Policy Definitions can be indexed by requester, by service attribute, or by some other key. The organization requiring the policy is also responsible for determining which policy is to be applied to a specific authorization request. Policy retrieval is typically done by the administration that defines the policy or by an agent acting for that administration. Thus a policy defining the times of day that a particular User is allowed to connect to the network is maintained and retrieved by the User Organization. A policy defining a time that ports will be unusable because of maintenance is maintained and retrieved by the Service Provider. Note that some implementation may choose to have the Service Provider retrieve a policy from the User Home Organization using a distributed directory access protocol. This may be appropriate in some cases, but is not a general solution. To understand why, suppose the remote administration and the home administration communicate via a broker which proxies their communications. In this case the remote and home
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   administrations have no prior relationship, and therefore the home
   administration directory is unlikely to be open for access by the
   remote administration and vice versa.

4.2. Policy Evaluation

Evaluation of policy requires access to information referenced by the policy. Often the information required is not available in the administration where the policy is retrieved. For example, checking that a user is allowed to login at the current time can readily be done by the User Home Organization because the User Home Organization has access to current time. But authorizing a user requiring a 2Mb/s path with less than 4 hops requires information available at a Service Provider and not directly available to the UHO, so the UHO must either 1) have a way to query a remote administration for the needed information or 2) forward the policy to the remote administration and have the remote administration do the actual evaluation or 3) attempt somehow to "shadow" the authoritative source of the information (e.g by having the Service Provider send updates to the UHO). Applications might support either 1) or 2), and a general authorization protocol must allow both. Case 3) is not considered further as shadowing seems too "expensive" to be supported by an AAA protocol. An example of case 1 is when a Service Provider forwards a request to a UHO which includes a query for the clearance code of the User. The Service Provider policy includes reference to the clearance code and the information in the reply is used as input to that policy. An example of case 2 is when the UHO approves an authorization conditional on the Service Provider confirming that there is currently a specific resource available for its use. The UHO includes the "policy" along with a conditional authorization to the Service Provider.

4.3. Policy Enforcement

Policy Enforcement is typically done by the Service Provider on the Service Equipment. The Service Equipment is equivalent to the Policy Target described in the Policy Framework [5]. Thus a NAS may enforce destination IP address limits via "filters" and a Router may enforce QoS restrictions on incoming packets. The protocol that sends the information between the Service Equipment and the Service Provider AAA Server may be specific to the Service Equipment, but it seems that the requirements are not different in kind from what is required between other AAA servers.
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   In particular, an AAA Server could send a "policy" to the Service
   Equipment stating what the equipment should do under various
   situations.  The Service equipment should either set up to "enforce"
   the policy or reject the request.

   The AAA Server could also send a query to the Service Equipment for
   information it requires to evaluate a policy.

4.4. Distributed Policy

A policy is retrieved by a Policy Retrieval Point (PRP) from a Policy Repository, evaluated at a Policy Decision Point (PDP) or Policy Consumer, and enforced at a Policy Enforcement Point (PEP) or Policy Target [5]. Generally, any of the AAA Servers involved in an authorization transaction may retrieve a policy or evaluate a policy, and any of the Service Equipment may enforce a policy. Policy Repositories may reside on any of the AAA Servers or be located elsewhere in the network. Information against which policy conditions are evaluated (such as resource status, session state, or time of day) are accessible at Policy Information Points (PIPs) and might be accessed using Policy Information Blocks (PIBs). An interesting question in any authorization application that uses policy is where are the PDPs, PRPs, PIPs and PEPs? Figure 12 shows which policy elements may be available at different points in the model. In distributed services, there may be multiple Service Providers involved in the authorization transaction, and each may act as the policy elements shown below. Note that the User (or requester) may also be a PRP (e.g. use policy description to specify what service is being requested), a PIP (have information needed by other entities to evaluate their policy), and a PDP (decide if it will accept a service with specific parameters).
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            +------+      +------------------------------+
            |      |      | User Home Organization       |
            |      |      |  +-------------------+  PRP  |
            |      |      |  |    AAA Server     |  PIP  |
            |      |      |  |                   |  PDP  |
            |      |      |  +-------------------+       |
            |      |      |                              |
            |      |      +------------------------------+
            |      |
            |      |
            |      |      +------------------------------+
            | User |      | Service Provider             |
            |      |      |  +-------------------+  PRP  |
            | PRP  |      |  |    AAA Server     |  PIP  |
            | PIP  |      |  |                   |  PDP  |
            | PDP  |      |  +-------------------+       |
            |      |      |                              |
            |      |      |  +-------------------+       |
            |      |      |  |      Service      |  PIP  |
            |      |      |  |     Equipment     |  PEP  |
            |      |      |  +-------------------+       |
            |      |      |                              |
            +------+      +------------------------------+

              PRP = Policy Retrieval Point
              PIP = Policy Information Point
              PDP = Policy Decision Point
              PEP = Policy Enforcement Point

       Fig. 12 -- Where Different Policy Elements May be Located

   An AAA protocol must be able to transport both policy definitions and
   the information needed to evaluate policies.  It must also support
   queries for policy information.

5. Use of Attribute Certificates to Store Authorization Data

This section outlines another mechanism that could be used for securely transporting the attributes on which an authorization decision is to be made. Work on X.509 Attribute Certificates is currently being undertaken in the Public Key Infrastructure (PKIX) Working Group [8]. This proposal is largely based on that work. When considering authorization using certificate-based mechanisms, one is often less interested in the identity of the entity than in some other attributes, (e.g. roles, account limits etc.), which should be used to make an authorization decision.
Top   ToC   RFC2904 - Page 20
   In many such cases, it is better to separate this information from
   the identity for management, security, interoperability or other
   reasons. However, this authorization information may also need to be
   protected in a fashion similar to a public key certificate.  The name
   used here for such a structure is an Attribute Certificate (AC) which
   is a digitally signed (certified) set of attributes.

   An AC is a structure that is similar to an X.509 public key
   certificate [9] with the main difference being that it contains no
   public key.  The AC typically contains group membership, role,
   clearance and other access control information associated with the AC
   owner.  A syntax for ACs is also defined in the X.509 standard.

   When making an access decision based on an AC, an access decision
   function (in a PEP, PDP or elsewhere) may need to ensure that the
   appropriate AC owner is the entity that has requested access.  The
   linkage between the request and the AC can be achieved if the AC has
   a "pointer" to a Public Key Certificate (PKC) for the requester and
   that the PKC has been used to authenticate the request.  Other forms
   of linkage can be defined which work with other authentication

   As there is often confusion about the difference between public key
   certificates (PKC's) and attribute certificates (ACs), an analogy may
   help. A PKC can be considered to be like a passport: it identifies
   the owner, it tends to be valid for a long period, it is difficult to
   forge, and it has a strong authentication process to establish the
   owner's identity.  An AC is more like an entry visa in that it is
   typically issued by a different authority than the passport issuing
   authority, and it doesn't have as long a validity period as a
   passport.  Acquiring an entry visa typically requires presenting a
   passport that authenticates that owner's identity.  As a consequence,
   acquiring the entry visa becomes a simpler procedure.  The entry visa
   will refer to the passport as a part of how that visa specifies the
   terms under which the passport owner is authorized to enter a

   In conjunction with authentication services, ACs provide a means to
   transport authorization information securely to applications.
   However, there are a number of possible communication paths that an
   AC may take.

   In some environments, it is suitable for a client to "push" an AC to
   a server.  This means that no new connections between the client and
   server domains are required.  It also means that no search burden is
   imposed on servers, which improves performance.
Top   ToC   RFC2904 - Page 21
   In other cases, it is more suitable for a client simply to
   authenticate to the server and for the server to request the client's
   AC from an AC issuer or a repository.  A major benefit of the this
   model is that it can be implemented without changes to the client and
   client/server protocol.  It is also more suitable for some inter-
   domain cases where the client's rights should be assigned within the
   server's domain, rather than within the client's "home" domain.

   There are a number of possible exchanges that can occur, and there
   are three entities involved: client, server, and AC issuer.  In
   addition the use of a directory service as a repository for AC
   retrieval may be supported.

   Figure 13 shows an abstract view of the exchanges that may involve
   ACs. Note that the lines in the diagram represent protocols which
   must be defined, not data flows.  The PKIX working group will define
   the required acquisition protocols.  One candidate for the lookup
   protocols is LDAP (once an LDAP schema exists which states where an
   AC is to be found).

      +--------------+                        +---------------+
      |  AAA Server/ |                        |               |
      |  AC Issuer   +----+                   |   Directory   |
      |              |    |                   |               |
      +--+-----------+    | Server            +-------+-------+
         |                | Acquisition               |
         |Client          |                           |Server
         |Acquisition     +----------------------+    |Lookup
         |                                       |    |
      +--+-----------+                        +--+----+-------+
      |              |     AC in application  |   Service     |
      |     User     +------------------------+  Equipment/   |
      |              |        protocol        | AAA Server    |
      +--+-----------+                        +---------------+
         | Client Lookup
      |              |
      |  Directory   |
      |              |

                       Fig. 13 -- AC Exchanges
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   Figure 14 shows the data flows which may occur in one particular
   case, that termed "push" above (section 2.1.3).

      |  AAA Server/ |
      |  AC Issuer   |
      |              |
         |Acquisition (1)
      +--+-----------+                        +---------------+
      |              |     AC in application  |   Service     |
      |     User     +------------------------+  Equipment/   |
      |              |        protocol (2)    | AAA Server    |
      +--------------+                        +---------------+

              Fig. 14 -- One example of an AC exchange

   In the diagram, the user first contacts the AC Issuer and then
   incorporates the AC into the application protocol.  The Service
   Equipment must then validate the AC and use it as the basis for the
   access decision (this functionality may be distributed between a PEP
   and PDP).

6. Resource Management

Authorization requests may be chained through a set of servers, as described in previous sections. Each of the servers may have a contractual relationship with servers on either side of it in the chain. In many of the applications being considered, the authorization results in establishing of an ongoing service which we call a session. Each of the servers involved in the authorization may also want to keep track of the state of the session, and be able to effect changes to the session if required. To make it simple to discuss this capability, we assume that each AAA Server MAY have a Resource Manager component. Resource Managers tracking the same session need to be able to initiate changes to the session, and to inform other Resource Managers when changes occur. Communication between Resource Managers creates requirements for an authorization protocol. An example of the use of resource management might be a user which sets up a QoS path through two ISPs, and while this path is active, one of the ISPs gets a request for more bandwidth from a higher priority user. The ISP may need to take some bandwidth from a the lower priority user's previously allocated session and give it to the
Top   ToC   RFC2904 - Page 23
   new request.  To do this, each of the administrations in the
   authorization path must be informed and agree to the change (this
   could be considered to be "authorizing the new value").

6.1. Session Management and State Synchronization

When an AAA Server grants authorization of some resource to an AAA requester (either a User or another AAA Server), the server may need to maintain session state information. This is used to make decisions about new sessions based on the state of current sessions, and to allow monitoring of sessions by all interested AAA Servers. Each session is identified by a session identifier, which must be unique within each AAA Server. Communication between AAA Servers must include the session identifier. It is desirable that the session identifier is the same across all AAA servers, otherwise each server will have to map identifiers from other servers to its own identifiers. A single session identifier significantly simplifies auditing and session control functions. Maintaining session state across AAA administrative boundaries increases the complexity of the problem, especially if each AAA Server in the trust chain must keep state as well. This can be viewed as an interdomain database replication problem. The protocol must include tools to help manage replicated state. Some of the problems to be addressed are: a) Service Equipment must be able to notify its Resource Manager when a session terminates or changes state in some other way. The Resource Manager must inform other Resource Managers which keep state for this session. b) The Resource Manager will need to set a time limit for each session which must be refreshed by having the Resource Manager query for authoritative status or by having the authoritative source send periodic keep alive messages that are forwarded to all Resource Managers in the authorization chain. Determining the appropriate session lifetime may be application specific and depends on the acceptable level of risk. If the service being offered is billed based on time, the session lifetime may need to be relatively small; if the service is billed on usage, the lifetime may be relatively large. c) Any Resource Manager in the chain must have the ability to terminate a session. This requires the Resource Manager to have knowledge of at least the adjacent AAA Servers in the authorization chain.
Top   ToC   RFC2904 - Page 24
   An example of how resource management can be used is in the PPP
   dialin application.  A home ISP may wish to restrict the number of
   concurrent sessions that a user can have at any given time.  This is
   particularly important when service providers give all-you-can-eat
   Internet access.  The possibility for fraud is quite large, since a
   user could provide his or her username/password to many people,
   causing a loss of revenue.  Resource management would allow the home
   ISP AAA server to identify when a user is active and to reject any
   authorization request for the user until termination indication is
   received from the NAS or until the session expires.

6.2. The Resource Manager

This section describes the functions of the Resource Manager in more detail. The Resource Manager is the component which tracks the state of sessions associated with an AAA Server or Service Equipment. It also may allocate resources to a session (e.g. IP addresses) and may track use of resources allocated by peer resource managers to a session (e.g. bandwidth in a foreign administrative domain). The resource manager also provides interfaces to allow the User to acquire or release authorized sessions. The Resource Manager maintains all session specific AAA state information required by the AAA Server. That state information may include pointers to peer Resource Managers in other administrative domains that possess additional AAA state information that refers to the same session. The Resource Manager is the anchor point in the AAA Server from which a session can be controlled, monitored, and coordinated even if that session is consuming network resources or services across multiple Service Provider administrative domains. The Resource Manager has several important functions: a) It allows a Service Provider operations staff to inspect the status of any of the allocated resources and services including resources that span foreign Service Provider administrative boundaries. The peer Resource Managers will cooperatively share only the state information subset that is required to assist in diagnosing cross-domain trouble tickets. The network operator may also modify or altogether cancel one of the User's active authorizations. b) It is the process contacted by other Resource Managers to inform the AAA Server that a specific session has been cancelled. This information is relayed to the other peer Resource Managers that also know about that session and hence must cancel it.
Top   ToC   RFC2904 - Page 25
   c) The Resource Manager conceals the identity and location of its
      private internal AAA components from other administrative domains
      and from the User, while at the same time facilitating cooperation
      between those domains.

   d) The Resource Manager cooperates with "policy servers" or Policy
      Decision Points (PDPs).  The Resource Manager maintains internal
      state information, possibly complex cross-administrative domain
      information, supported by dialogues with its peer Resource
      Managers.  A policy server can use the state information when
      evaluating a particular policy.

   e) The separation of the Resource Manager and the policy server into
      two distinct architectural components allows a single session to
      span multiple administrative domains, where each administrative
      domain has one or more policy server cooperating with its Resource

   AAA resource managers will normally use the same trust relationships
   needed for authorization sequences.  It is possible for independent
   relationships to be established, but that is discouraged.

7. AAA Message Forwarding and Delivery

An AAA Server is responsible for securely forwarding AAA messages to the correct destination system or process in the AAA infrastructure. Two well known examples are forwarding AAA messages for a roaming AAA service, and forwarding AAA messages for a distributed AAA service. The same principle can also be applied to intra-domain communications. The message forwarding is done in one of two modes. The first mode is when an AAA server needs to forward a message to a peer AAA server that has a known "logical destination address" that must be resolved by an application-specific procedure into its actual network address. Typically the forwarding procedure indexes into a database by an application-specific identifier to discover the peer's network address. For example, in the roaming dialin application, the application-specific identifier may be an NAI. A bandwidth brokerage application would use other search indices unique to its problem domain to select the addressed peer AAA server. After the address resolution procedure has completed successfully, then the AAA server transmits the message to its peer over the connection associated with that destination network address. The second mode is when the AAA server already has an established session representing an authorization. The session's state contains the addressing and context used to direct the message to its destination peer AAA server, PDP, PEP, or User. The message is sent
Top   ToC   RFC2904 - Page 26
   over the AAA server's connection to that destination peer,
   multiplexed with other session's messages. The message must be
   qualified by a session identifier that is understood by both end
   points.  The AAA message's destination may be either intra-
   administrative domain, or inter-administrative domain.  In the former
   case, the destination process may reside on the same system as the
   AAA server.

   In addition to the above message forwarding processing, the
   underlying message delivery service must meet the following

   -  Unicast capability -- An end system can send a message to any
      other end system with minimal latency of session setup/disconnect
      overhead messages, and no end system overhead of keeping state
      information about every potential peer.

   -  Data integrity and error detection -- This data transport protocol
      assumes an underlying datagram network layer service that includes
      packet discard on error detection, and data integrity protection
      against third party modifications.

   -  Reliable data transport assurance -- When an end system
      successfully receives a message marked receipt requested, it must
      acknowledge that message to the sending system by either
      piggybacking the acknowledgement on an application-specific reply
      message, or else as a standalone acknowledgement message.  The
      sending system maintains a retry timer; when the timer expires,
      the sending system retransmits a copy of its original message. It
      gives up after a configurable number of unsuccessful retries.

   -  Sequenced data delivery -- If multiple messages are sent between a
      pair of end systems, those messages are delivered to the addressed
      application in the same order as they were transmitted.
      Duplicates are silently suppressed.

   -  Responsive to network congestion feedback -- When the network
      enters into congestion, the end systems must detect that
      condition, and they must back off their transmission rate until
      the congestion subsides.  The back off and recovery algorithms
      must avoid oscillations.

8. End-to-End Security

When AAA servers communicate through intermediate AAA servers, such as brokers, it may be necessary that a part of the payload be secure between the originator and the target AAA server. The security requirement may consist of one or more of the following: end-to-end
Top   ToC   RFC2904 - Page 27
   message integrity, confidentiality, replay protection, and
   nonrepudiation.  Furthermore, it is a requirement that intermediate
   AAA servers be able to append information such as local policy to a
   message before forwarding the message to its intended destination.
   It may also be required that an intermediate AAA Server sign such
   appended information.

   This requirement has been clearly documented in [10], which describes
   many current weaknesses of the RADIUS protocol [11] in roaming
   networks since RADIUS does not provide such functionality.  One
   well-known attack is the ability for the intermediate nodes to modify
   critical accounting information, such as a session time.

   Most popular security protocols (e.g. IPSec, SSL, etc.) do not
   provide the ability to secure a portion of the payload. Therefore, it
   may be necessary for the AAA protocol to implement its own security
   extensions to provide end-to-end security.

9. Streamlined Authorization Process

The techniques described above allow for great flexibility in distributing the components required for authentication and authorization. However, working groups such as Roamops and MobileIP have identified requirements to minimize Internet traversals in order to reduce latency. To support these requirements, data fields necessary for both authentication and authorization SHOULD be able to be carried in a single message set. This is especially important when there are intermediate servers (such as Brokers) in the AAA chain. Furthermore, it should be possible for the Brokers to allow end-to- end (direct) authentication and authorization. This can be done as follows. The User Home Organization generates a ticket which is signed using the UHO's private key. The ticket is carried in the accounting messages. The accounting messages must flow through the Broker since the Broker is acting as the settlement agent and requires this information. There are Brokers that will require to be in the authentication and authorization path as well since they will use this information to detect fraudulent activity, so the above should be optional. In order for end-to-end authentication and authorization to occur, it may be necessary for the Broker to act as a certificate authority. All members of the roaming consortium would be able to trust each other (to an extent) using the certificates. A Service Provider's AAA server that sends a request to the Broker should be able to receive a redirect message which would allow the two peers (Service Provider and UHO) to interact directly. The redirect message from
Top   ToC   RFC2904 - Page 28
   the Broker should include the UHO's certificate, which eliminates the
   Service Provider from accessing the certificate archive.  The request
   from the Service Provider could include its own certificate, and a
   token from the Broker's redirect message that is timestamped and
   guarantees that the Service Provider is in good standing with the
   Broker.  This eliminates the home domain from accessing the
   Certificate Revocation List (CRL).

10. Summary of the Authorization Framework

The above has introduced the basic players in an authorization transaction as User, User Home Organization, Service Provider's AAA Server, and Service Equipment. It has discussed relationships between entities based on agreements or contracts, and on "trust". Examples of authorization sequences have been given. Concepts of roaming and distributed services have been briefly described. Combination of roaming and distributed services was also considered and the concept of a "wholesaler" or Broker was introduced. We have considered the use of policies and attribute certificates to store and transmit authorization data. We discussed the problem of managing the resources to which access has been authorized including the problem of tracking state information for session-oriented services, and we defined the Resource Manager component of a AAA Server. We considered the problem of forwarding AAA messages among servers in possibly different administrative domains. We considered the need for end-to-end security of portions of the payload of authorization messages that pass through intermediate AAA Servers. Finally we stressed the need for support of a streamlined authorization process that minimizes delay for latency-sensitive applications. The intent is that this will provide support for discussing and understanding requirements of specific applications that need authorization services.

11. Security Considerations

Authorization is itself a security mechanism. As such, it is important that authorization protocols cannot easily be abused to circumvent the protection they are intended to ensure. It is the responsibility of protocol designers to design their protocols to be resilient against well-known types of attacks. The following are some considerations that may guide protocol designers in the development of authorization protocols.
Top   ToC   RFC2904 - Page 29
   Authorization protocols must not be susceptible to replay attacks.
   If authentication data is carried with the authorization data, for
   example, the authentication protocol used must either be impervious
   to replay or else the confidentiality of the authentication data must
   be protected.

   If proxying is required, the authorization protocol must not be
   susceptible to man-in-the-middle attacks.

   If the push model is used, the confidentiality of the authorization
   data must be ensured so that it may not be hijacked by third parties
   and used to obtain a service fraudulently.

   If the agent model is used, the binding between the authorization and
   the service itself must be protected to prevent service authorized to
   one party from being fraudulently received by another.

   In addition to guarding against circumvention, authorization
   protocols designed according to this framework will have some
   intrinsic security requirements.  These are included among the
   requirements in [2] and summarized briefly below.

   Among the intrinsic security needs is the fact that authorization
   protocols may carry sensitive information.  It is necessary to
   protect such information from disclosure to unauthorized parties
   including (as discussed in section 8) even certain parties involved
   in the authorization decision.

   We have discussed the use of multi-party trust chains involving
   relaying of authorization data through brokers or other parties.  In
   such cases, the integrity of the chain must be maintained.  It may be
   necessary to protect the data exchanged between parties using such
   mechanisms as encryption and digital signatures.

   Finally, because authorization will be necessary to gain access to
   many Internet services, a denial of service attack against an
   authorization server can be just as effective as a denial of service
   attack against the service equipment itself in preventing access to
   Internet services.


Attribute Certificate -- structure containing authorization attributes which is digitally signed using public key cryptography.
Top   ToC   RFC2904 - Page 30
   Contract Relationship -- a relation established between two or more
      business entities where terms and conditions determine the
      exchange of goods or services.

   Distributed Service -- a service that is provided by more than one
      Service Provider acting in concert.

   Dynamic Trust Relationship -- a secure relationship which is
      dynamically created between two entities who may never have had
      any prior relationship. This relationship can be created if the
      involved entities have a mutually trusted third party. Example: A
      merchant trusts a cardholder at the time of a payment transaction
      because they both are known by a credit card organization.

   Policy Decision Point (PDP) -- The point where policy decisions are

   Policy Enforcement Point (PEP) -- The point where the policy
      decisions are actually enforced.

   Resource Manager -- the component of an AAA Server which tracks the
      state of sessions associated with the AAA Server or its associated
      Service Equipment and provides an anchor point from which a
      session can be controlled, monitored, and coordinated.

   Roaming -- An authorization transaction in which the Service Provider
      and the User Home Organization are two different organizations.
      (Note that the dialin application is one for which roaming has
      been actively considered, but this definition encompasses other
      applications as well.)

   Security Association -- a collection of security contexts, between a
      pair of nodes, which may be applied to protocol messages exchanged
      between them. Each context indicates an authentication algorithm
      and mode, a secret (a shared key, or appropriate public/private
      key pair), and a style of replay protection in use. [12]

   Service Equipment -- the equipment which provides a service.

   Service Provider -- an organization which provides a service.

   Static Trust Relationship -- a pre-established secure relationship
      between two entities created by a trusted party.  This
      relationship facilitates the exchange of AAA messages with a
      certain level of security and traceability. Example: A network
      operator (trusted party) who has access to the wiring closet
Top   ToC   RFC2904 - Page 31
      creates a connection between a user's wall outlet and a particular
      network port.  The user is thereafter trusted -- to a certain
      level -- to be connected to this particular network port.

   User -- the entity seeking authorization to use a resource or a

   User Home Organization (UHO) -- An organization with whom the User
      has a contractual relationship which can authenticate the User and
      may be able to authorize access to resources or services.


[1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Farrell, S., Vollbrecht, J., Calhoun, P., Gommans, L., Gross, G., de Bruijn, B., de Laat, C., Holdrege, M. and D. Spence, "AAA Authorization Requirements", RFC 2906, August 2000. [3] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., Gross, G., de Bruijn, B., de Laat, C., Holdrege, M. and D. Spence, "AAA Authorization Application Examples", RFC 2905, August 2000. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [5] Stevens, M., "Policy Framework", Work in Progress. [6] Strassner, John, Ed Ellesson, and Bob Moore, "Policy Core Information Model -- Version 1 Specification", Work in Progress. [7] Strassner, John, et al, "Policy Framework LDAP Core Schema", Work in Progress. [8] Farrell, Stephen and Russell Housley, "An Internet Attribute Certificate Profile for Authorization", Work in Progress. [9] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet X.509 Public Key Infrastructure -- Certificate and CRL Profile", RFC 2459, January 1999. [10] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy Implementation in Roaming", RFC 2607, June 1999. [11] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote Authentication Dial In User Service (RADIUS)", RFC 2138, April 1997.
Top   ToC   RFC2904 - Page 32
   [12] Perkins, C., "IP Mobility Support", RFC 2002, October 1996.

   [13] Yavatkar, R., Pendarakis, D. and R. Guerin, "A Framework for
        Policy-based Admission Control", RFC 2753, January 2000.

Authors' Addresses

John R. Vollbrecht Interlink Networks, Inc. 775 Technology Drive, Suite 200 Ann Arbor, MI 48108 USA Phone: +1 734 821 1205 Fax: +1 734 821 1235 Mail: 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 EMail: Stephen Farrell Baltimore Technologies 61 Fitzwilliam Lane Dublin 2 Ireland Phone: +353 1 647 7406 Fax: +353 1 647 7499 EMail:
Top   ToC   RFC2904 - Page 33
   Leon Gommans
   Enterasys Networks EMEA
   Kerkplein 24
   2841 XM  Moordrecht
   The Netherlands

   Phone: +31 182 379279
          or at University of Utrecht:

   George M. Gross
   Lucent Technologies
   184 Liberty Corner Road, m.s. LC2N-D13
   Warren, NJ 07059

   Phone:  +1 908 580 4589
   Fax:    +1 908-580-4991

   Betty de Bruijn
   Interpay Nederland B.V.
   Eendrachtlaan 315
   3526 LB Utrecht
   The Netherlands

   Phone: +31 30 2835104

   Cees T.A.M. de Laat
   Physics and Astronomy dept.
   Utrecht University
   Pincetonplein 5,
   3584CC Utrecht

   Phone: +31 30 2534585
   Phone: +31 30 2537555
Top   ToC   RFC2904 - Page 34
   Matt Holdrege
   223 Ximeno Ave.
   Long Beach, CA 90803


   David W. Spence
   Interlink Networks, Inc.
   775 Technology Drive, Suite 200
   Ann Arbor, MI  48108

   Phone: +1 734 821 1203
   Fax:   +1 734 821 1235
Top   ToC   RFC2904 - Page 35
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