IETF PANA Working Group                          Alper E. Yegin, Editor
INTERNET-DRAFT                                           Yoshihiro Ohba
Expires: December 2003                                   Reinaldo Penno
                                                        George Tsirtsis
                                                             Cliff Wang
                                                              June 2003

                 Protocol for Carrying Authentication for
                    Network Access (PANA) Requirements

Status of this Memo
    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 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

   The list of Internet-Draft Shadow Directories can be accessed at


   It is expected that future IP devices will have a variety of access
   technologies to gain network connectivity. Currently there are
   access-specific mechanisms for providing client information to the
   network for authentication and authorization purposes. In addition
   to being limited to specific access media (e.g., 802.1X for IEEE 802
   links), some of these protocols are limited to specific network
   topologies (e.g., PPP for point-to-point links). The goal of this
   document is to identify the requirements for a link-layer agnostic
   protocol that allows a host and a network to authenticate each other
   for network access. This protocol will run between a client's device
   and an agent in the network where the agent might be a client of the
   AAA infrastructure.

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Table of Contents

   Table of Contents.................................................2
   1. Introduction...................................................3
   2. Key Words......................................................4
   3. Terminology....................................................4
   4. Requirements...................................................5
   4.1. Authentication...............................................5
   4.1.1. Authentication of Client...................................5
   4.1.2. Authorization, Accounting and Access Control...............6
   4.1.3. Authentication Backend.....................................7
   4.1.4. Identifiers................................................7
   4.2. IP Address Assignment........................................7
   4.3. EAP Lower Layer Requirements.................................8
   4.4. PAA-to-EP Protocol...........................................8
   4.5. Network......................................................9
   4.5.1. Multi-access...............................................9
   4.5.2. Disconnect Indication......................................9
   4.5.3. Location of PAA............................................9
   4.5.4. Secure Channel............................................10
   4.6. Interaction with Other Protocols............................10
   4.7. Performance.................................................10
   4.8. Congestion Control..........................................11
   4.9. IP Version Independence.....................................11
   4.10. Denial of Service Attacks..................................11
   4.11. Client Identity Privacy....................................11
   5. Security Considerations.......................................11
   6. Acknowledgements..............................................11
   7. References....................................................12
   7.1. Normative References........................................12
   7.2. Informative References......................................12
   8. Authors' Addresses............................................13
   9. Appendix......................................................14
   10. Full Copyright Statement.....................................16

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1. Introduction

   Providing secure network access service requires access control
   based on the authentication and authorization of the clients and the
   access networks. Initial and subsequent client-to-network
   authentication provides parameters that are needed to police the
   traffic flow through the enforcement points. A protocol is needed to
   carry authentication parameters between the client and the access

   Link-layer authentication mechanisms are used as enablers of secure
   network access. A higher-layer authentication protocol is deemed
   necessary when link-layer authentication mechanisms either do not
   exist in terms of specifications/standards for a specific technology
   or present deployment difficulties; when link-layer mechanisms are
   not able to meet the overall authentication and security
   requirements; or when multi-layer (e.g., link-layer and
   network-layer) authentication is needed. Currently there is no
   standard network-layer solution for authenticating clients for
   network access. In the absence of such a solution, some inadequate
   standards-based solutions are deployed or non-standard ad-hoc
   solutions are invented. The usage scenarios Internet-Draft [USAGE]
   describes the problem statement in detail.

   The protocol design will be limited to defining a messaging protocol
   (i.e., a carrier) that will allow authentication payload to be
   carried between the host/client and an agent/server in the access
   network for authentication and authorization purposes regardless of
   the AAA infrastructure that may (or may not) reside on the network.
   As a network-layer protocol, it will be independent of the
   underlying access technologies. It will also be applicable to any
   network topology.

   The intent is not to invent new security protocols and mechanisms
   but to reuse existing mechanisms such as EAP [EAP]. In particular,
   the requirements do not mandate the need to define new
   authentication protocols (e.g., EAP-TLS [EAPTLS]), key distribution
   or key agreement protocols, or key derivation methods. The desired
   protocol can be viewed as the front-end of the AAA protocol or any
   other protocol/mechanisms the network is running at the background
   to authenticate its clients. It will act as a carrier for an already
   defined security protocol or mechanism.

   As an example, the Mobile IP Working Group has already defined such
   a carrier for Mobile IPv4 [MIPV4]. A Mobile IPv4 registration
   request message is used as a carrier for authentication extensions
   (MN-FA [MIPv4] or MN-AAA [MNAAA]) that allow a foreign agent to
   authenticate mobile nodes before providing forwarding service. The
   goal of PANA is similar in that it aims to define a network-layer
   transport for authentication information; however, PANA will be
   decoupled from mobility management and it will rely on other
   specifications for the definition of authentication payloads.

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   This document defines the common terminology and identifies the
   requirements of a protocol for PANA. These terminology and
   requirements will be used to define and limit the scope of the work
   to be done in this group.

2. Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [KEYWORDS].

3. Terminology

   PANA Client (PaC)

        The client side of the protocol that resides in the host device
        which is responsible for providing the credentials to prove its
        identity for network access authorization.

   PANA Client Identifier (PaCI)

        The identifier that is presented by the PaC to the PAA for
        network access authentication. A simple username and NAI [NAI]
        are examples of PANA client identifiers.

   Device Identifier (DI)

        The identifier used by the network as a handle to control and
        police the network access of a client. Depending on the access
        technology, this identifier might contain any of IP address,
        link-layer address, switch port number, etc. of a connected

   PANA Authentication Agent (PAA)

        The access network side entity of the protocol whose
        responsibility is to verify the credentials provided by a PANA
        client and grant network access service to the device
        associated with the client and identified by a DI.

   Enforcement Point (EP)

        A node on the access network where per-packet enforcement
        policies (i.e., filters) are applied on the inbound
        and outbound traffic of client devices. Information such as DI
        and (optionally) cryptographic keys are provided by PAA per
        client for constructing filters on the EP.

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4. Requirements

4.1. Authentication

  4.1.1. Authentication of Client

   PANA MUST enable authentication of PaCs for network access. A PaC's
   identity can be authenticated by verifying the credentials (e.g.,
   identifier, authenticator) supplied by one of the users of the
   device or the device itself. PANA MUST only grant network access
   service to the device identified by the DI, rather than granting
   separate access to multiple simultaneous users of the device. Once
   the network access is granted to the device, the methods used by the
   device on arbitrating which one of its users can access the network
   is outside the scope of PANA.

   PANA MUST NOT define new security protocols or mechanisms. Instead,
   it MUST be defined as a "carrier" for such protocols. PANA MUST
   identify which specific security protocol(s) or mechanism(s) it can
   carry (the "payload"). EAP [EAP] is a candidate protocol that
   satisfies many of the requirements for authentication. PANA would be
   a carrier protocol for EAP. If the PANA Working Group decides that
   extensions to EAP are needed, it will define requirements for the
   EAP WG instead of designing such extensions.

   Providing authentication, integrity and replay protection for data
   traffic after a successful PANA exchange is outside the scope of
   this protocol. In networks where physical layer security is not
   present, link-layer or network-layer ciphering (e.g., IPsec) can be
   used to provide such security. These mechanisms require presence of
   cryptographic keying material at PaC and EP. Although PANA does not
   deal with key derivation or distribution, it enables this by the
   virtue of carrying EAP and allowing appropriate EAP method
   selection. Various EAP methods are capable of generating basic
   keying material. The keying material produced by EAP methods cannot
   be directly used with IPsec as it lacks the properties of an IPsec
   SA (security association) which include secure cipher suite
   negotiation, mutual proof of possession of keying material,
   freshness of transient session keys, key naming, etc. These basic
   (initial) EAP keys can be used with an IPsec key management protocol
   like IKE to generate the required security associations. A separate
   protocol, called secure association protocol, is required to
   generate IPsec SAs based on the basic EAP keys. This protocol MUST
   be capable of enabling IPsec-based access control on the EPs. IPsec
   SAs MUST enable authentication, integrity and replay protection of
   data packets as they are sent between the EP and PaC.

   Providing a complete secure network access solution by also securing
   router discovery  [RDISC], neighbor discovery [NDISC], and address
   resolution protocols [ARP] is outside the scope as well.

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   Some access networks might require or allow their clients to get
   authenticated and authorized by the NAP (network access provider)
   and ISP before the clients gain network access. NAP is the owner of
   the access network who provides physical and link-layer connectivity
   to the clients. PANA MUST be capable of enabling two independent
   authentication operations (i.e., execution of two separate EAP
   methods) for the same client. Determining the authorization
   parameters as a result of two separate authentications is an
   operational issue and therefore it is outside the scope of PANA.

   Both the PaC and the PAA MUST be able to perform mutual
   authentication for network access. Providing only the capability of
   a PAA authenticating the PaC is not sufficient. Mutual
   authentication capability is required in some environments but not
   in all of them. For example, clients might not need to authenticate
   the access network when physical security is available (e.g.,
   dial-up networks).
    PANA MUST be capable of carrying out both periodic and on-demand
   re-authentication. Both the PaC and the PAA MUST be able to initiate
   both the initial authentication and the re-authentication process.

   Certain types of service theft are possible when the DI is not
   protected during or after the PANA exchange [SECTHREAT]. PANA MUST
   have the capability to exchange DI securely between the PAC and PAA
   where the network is vulnerable to man-in-the-middle attacks. While
   PANA MUST provide such a capability, its utility relies on the use
   of an authentication method that can generate keys for cryptographic
   computations on PaC and PAA.

  4.1.2. Authorization, Accounting and Access Control

   After a device is authenticated using PANA, it MUST be authorized
   for "network access." That is, the core requirement of PANA is to
   verify the authorization of a PaC so that PaC's device may send and
   receive any IP packets. It may also be possible to provide finer
   granularity authorization, such as authorization for QoS or
   individual services (e.g., http vs. ssh). However, while a backend
   authorization infrastructure (e.g., Diameter) might provide such
   indications to the PAA, explicit support for them is outside the
   scope of PANA. For instance, PANA is not required to carry any
   indication of which services are authorized for the authenticated

   Providing access control functionality in the network is outside the
   scope of PANA. Client access authentication SHOULD be followed by
   access control to make sure only authenticated and authorized
   clients can send and receive IP packets via access network. Access
   control can involve setting access control lists on the EPs.
   Identification of clients that are authorized to access the network
   is done by the PANA protocol exchange. If IPsec-based access control

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   is deployed in an access network, PaC and EPs should have the
   required IPsec SA in place. Generating the IPsec SAs based on EAP
   keys is outside the scope of PANA protocol. This transformation MUST
   be handled by a separate secure association protocol (see section
    Carrying accounting data is outside the scope of PANA.

  4.1.3. Authentication Backend

   PANA protocol MUST NOT make any assumptions on the backend
   authentication protocol or mechanisms. A PAA MAY interact with
   backend AAA infrastructures such as RADIUS or Diameter, but it is
   not a requirement. When the access network does not rely on an
   IETF-defined AAA protocol (e.g., RADIUS, Diameter), it can still use
   a proprietary backend system, or rely on the information locally
   stored on the authentication agents.

   The interaction between the PAA and the backend authentication
   entities is outside the scope of PANA.

  4.1.4. Identifiers

   PANA SHOULD allow various types of identifiers to be used as the
   PaCI (e.g., username, NAI, FQDN, etc.). This requirement generally
   relies on the client identifiers supported by various EAP methods.

   PANA SHOULD allow various types of identifiers to be used as the DI
   (e.g., IP address, link-layer address, port number of a switch,

   A PAA MUST be able to create a binding between the PaCI and the
   associated DI upon successful PANA exchange. This can be achieved by
   PANA communicating the PaCI and DI to the PAA during the protocol
   exchange. The DI can be carried either explicitly as part of the
   PANA payload, or implicitly as the source of the PANA message, or
   both. Multi-access networks also require use of a cryptographic
   protection along with DI filtering to prevent unauthorized access
   [SECTHREAT]. The keying material required by the cryptographic
   methods needs to be indexed by the DI. The binding between DI and
   PaCI is used for access control and accounting in the network as
   described in section 4.1.2.

4.2. IP Address Assignment

   Assigning an IP address to the client is outside the scope of PANA.
   PANA protocol design MAY require the PaC to configure an IP address
   before using this protocol. Allocating IP addresses to
   unauthenticated PaCs may create security vulnerabilities, such as IP

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   address depletion attacks on the access network [SECTHREAT]. IPv4
   networks with limited address space are the main targets of such
   attacks. Launching a successful attack that can deplete the
   addresses in an IPv6 network is relatively harder.

   This threat can be mitigated by allowing the protocol to run without
   an IP address configured on the PaC (i.e., using unspecified source
   address). Such a design choice might limit the re-use of existing
   security mechanisms, and impose additional implementation
   complexity. This trade off should be taken into consideration in
   designing PANA.

 4.3. EAP Lower Layer Requirements

   The EAP protocol itself imposes various requirements on its
   transport protocols. These requirements are based on the nature of
   the EAP protocol, and they need to be satisfied for correct
   operation. Please see [EAP] for the generic transport requirements
   that MUST be satisfied by PANA as well.

4.4. PAA-to-EP Protocol

   PANA does not assume that the PAA is always co-located with the
   EP(s). Network access enforcement can be provided by one or more
   nodes on the same IP subnet as the client (e.g., multiple routers),
   or on another subnet in the access domain (e.g., gateway to the
   Internet, depending on the network architecture). When the PAA and
   the EP(s) are separated, there needs to be another transport for
   client provisioning. This transport is needed to create access
   control lists to allow authenticated and authorized clients' traffic
   through the EPs. PANA Working Group will preferably identify an
   existing protocol solution that allows the PAA to deliver the
   authorization information to one or more EPs when the PAA is
   separated from EPs. Possible candidates include but are not limited
   to COPS, SNMP, Diameter, etc. This task is similar to what the
   MIDCOM Working Group is trying to achieve, therefore some of that
   working group's output might be useful here.

   It is assumed that the communication between PAA and EP(s) is
   secure. The objective of using a PAA-to-EP protocol is to provide
   filtering rules to EP(s) for allowing network access of a recently
   authenticated and authorized PaC. The chosen protocol MUST be
   capable of carrying DI and cryptographic keys for a given PaC from
   PAA to EP. Depending on the PANA protocol design, support for either
   of the pull model (i.e., EP initiating the PAA-to-EP protocol
   exchange per PaC) or the push model (i.e., PAA initiating the
   PAA-to-EP protocol exchange per PaC), or both may be required. For
   example, if the design is such that the EP allows the PANA traffic
   to pass through even for unauthenticated PaCs, the EP should also
   allow and expect the PAA to send the filtering information at the

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   end of a successful PANA exchange without the EP ever sending a

4.5. Network

  4.5.1. Multi-access

   PANA MUST support PaCs with multiple interfaces, and networks with
   multiple routers on multi-access links. In other words, PANA MUST
   NOT assume the PaC has only one network interface, or the access
   network has only one first hop router, or the PaC is using a
   point-to-point link.

  4.5.2. Disconnect Indication

   PANA MUST NOT assume that the link is connection-oriented. Links may
   or may not provide disconnect indication. Such notification is
   desirable in order for the PAA to cleanup resources when a client
   moves away from the network (e.g., inform the enforcement points
   that the client is no longer connected). PANA SHOULD have a
   mechanism to provide disconnect indication. PANA MUST be capable of
   securing disconnect messages in order to prevent malicious nodes
   from leveraging this extension for DoS attacks.
    This mechanism MUST allow the PAA to be notified about the departure
   of a PaC from the network. This mechanism MUST also allow a PaC to
   be notified about the discontinuation of the network access service.
   Access discontinuation can happen due to various reasons such as
   network systems going down, or a change in access policy.

   In case the clients cannot send explicit disconnect messages to the
   PAA, PAA can still detect their departure by relying on periodic
   authentication requests.

  4.5.3. Location of PAA

   The PAA and PaC MUST be exactly one IP hop away from each other.
   That is, there must be no IP routers between the two. Note that this
   does not mean they are on the same physical link. Bridging
   techniques can place two nodes just exactly one IP hop away from
   each other although they might be connected to separate physical
   links. Furthermore, two nodes on the same IP subnet do not
   necessarily satisfy this requirement, as they can be more than one
   hop away from each other [MULTILINK]. A PAA can be on the NAS
   (network access server) or WLAN access point or first hop router.
   The use of PANA when the PAA is multiple IP hops away from the PaC
   is outside the scope of PANA.

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   A PaC may or may not be pre-configured with the IP address of PAA.
   Therefore the PANA protocol MUST define a dynamic discovery method.
   Given that the PAA is one hop away from the PaC, there are a number
   of discovery techniques that could be used (e.g., multicast or
   anycast) by the PaC to find out the address of the PAA.

  4.5.4. Secure Channel

   PANA MUST NOT assume presence of a secure channel between the PaC
   and the PAA. PANA MUST be able to provide authentication especially
   in networks which are not protected against eavesdropping and
   spoofing. PANA MUST enable protection against replay attacks on both
   PaCs and PAAs.

   This requirement partially relies on the EAP protocol and the EAP
   methods carried over PANA. Use of EAP methods that provide mutual
   authentication and key derivation/distribution is essential for
   satisfying this requirement. EAP does not make a secure channel
   assumption, and supports various authentication methods that can be
   used in such environments. Additionally, PANA MUST ensure its design
   does not contain vulnerabilities that can be exploited when it is
   used over insecure channels. PANA MAY provide a secure channel by
   deploying a two-phase authentication. The first phase can be used
   for creation of the secure channel, and the second phase is for
   client and network authentication.

4.6. Interaction with Other Protocols

   Mobility management is outside the scope of PANA. However, PANA MUST
   be able to co-exist and MUST NOT unintentionally interfere with
   various mobility management protocols, such as Mobile IPv4 [MIPV4],
   Mobile IPv6 [MIPV6], fast handover protocols [FMIPV4, FMIPV6], and
   other standard protocols like IPv6 stateless address
   auto-configuration  [ADDRCONF] (including privacy extensions
   [PRIVACY]), and DHCP [DHCPV4, DHCPV6]. It MUST NOT make any
   assumptions on the protocols or mechanisms used for IP address
   configuration of the PaC.

4.7. Performance

   PANA design SHOULD give consideration to efficient handling of the
   authentication process. This is important for gaining network access
   with minimum latency. As an example, a method like minimizing the
   protocol signaling by creating local security associations can be
   used for this purpose.

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4.8. Congestion Control

   PANA MUST provide congestion control for the protocol messaging.
   Under certain conditions PaCs might unintentionally get synchronized
   when sending their requests to the PAA (e.g., upon recovering from a
   power outage on the access network). The network congestion
   generated from such events can be avoided by using techniques like
   delayed initialization and exponential back off.

4.9. IP Version Independence

   PANA MUST work with both IPv4 and IPv6.

4.10. Denial of Service Attacks

   PANA MUST be robust against a class of DoS attacks such as blind
   masquerade attacks through IP spoofing that would swamp the PAA,
   causing it to spend resources and prevent network access by
   legitimate clients.

4.11. Client Identity Privacy

   Some clients might prefer hiding their identity from visited access
   networks for privacy reasons. Providing identity protection for
   clients is outside the scope of PANA. Note that some authentication
   methods may already have this capability. Where necessary, identity
   protection can be achieved by letting PANA carry such authentication

5. Security Considerations

   This document identifies requirements for the PANA protocol design.
   Due to the nature of this protocol most of the requirements are
   security related. The actual protocol design is not specified in
   this document. A thorough discussion on PANA security threats can be
   found in PANA Threat Analysis and Security Requirements document
   [SECTHREAT]. Security threats identified in that document are
   already included in this general PANA requirements document.

6. Acknowledgements

   We would like to thank Subir Das, Lionel Morand, Mohan
   Parthasarathy, Basavaraj Patil, Pete McCann, Derek Atkins, Dan
   Forsberg, Francis Dupont, Bernard Aboba and the PANA Working Group
   members for their valuable contributions to the discussions and
   preparation of this document.

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7. References

7.1. Normative References

   [KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate
   Requirement Levels", RFC 2119, March 1997.

   [USAGE] Y. Ohba, S. Das, B. Patil, H. Soliman, A. Yegin, "Problem
   Statement and Usage Scenarios for PANA",
   draft-ietf-pana-usage-scenarios-06.txt, April 2003. Work in

   [SECTHREAT] M. Parthasarathy, "PANA Threat Analysis and Security
   Requirements", draft-ietf-pana-threats-04.txt, May 2003. Work in

   [EAP] L. Blunk, J. Vollbrecht, B. Aboba, J. Carlson, H. Levkowetz,
   "Extensible Authentication Protocol (EAP)",
   draft-ietf-eap-rfc2284bis-04.txt, June 2003. Work in progress.

 7.2. Informative References

   [8021X] "IEEE Standards for Local and Metropolitan Area Networks:
   Port Based Network Access Control", IEEE Std 802.1X-2001.
    [EAPTLS] B. Aboba, D. Simon, "PPP EAP TLS Authentication Protocol",
   RFC 2716, October 1999.

   [MULTILINK] D. Thaler, C. Huitema, "Multi-link Subnet Support in
   IPv6", draft-ietf-ipv6-multilink-subnets-00.txt, December 2002. Work
   in progress.

   [PPP] W. Simpson (editor), "The Point-To-Point Protocol (PPP)", STD
   51, RFC 1661, July 1994.

   [MIPV4] C. Perkins (editor), "IP Mobility Support for IPv4", RFC
   3344, August 2002.

   [MIPV6] D. Johnson and C. Perkins, "Mobility Support in IPv6",
   draft-ietf-mobileip-ipv6-21.txt, February 2003. Work in progress.

   [MNAAA] C. Perkins, P. Calhoun, "Mobile IPv4 Challenge/Response
   Extensions", RFC3012, November 2000.

   [NDISC] T. Narten, E. Nordmark, and W. Simpson, "Neighbor Discovery
   for IP Version 6 (IPv6)",RFC 2461, December 1998.

   [ARP] D. Plummer, "An Ethernet Address Resolution Protocol", STD 37,
   RFC 826, November 1982.

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   [FMIPV4] K. ElMalki (editor), et. al., "Low latency Handoffs in
   Mobile IPv4", November 2001. Work in progress.

   [FMIPV6] R. Koodli (editor), et. al., "Fast Handovers for Mobile
   IPv6", March 2003. Work in progress.

   [DHCPV4] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
   March 1997.

   [DHCPV6] R. Droms (editor), et. al., "Dynamic Host Configuration
   Protocol for IPv6 (DHCPv6)", November 2002. Work in progress.

   [PRIVACY] T. Narten, R. Draves, "Privacy Extensions for Stateless
   Address Autoconfiguration in IPv6", RFC 3041, January 2001.

8. Authors' Addresses

      Alper E. Yegin
      DoCoMo USA Labs
      181 Metro Drive, Suite 300
      San Jose, CA, 95110
      Phone: +1 408 451 4743

      Yoshihiro Ohba
      Toshiba America Research, Inc.
      P.O. Box 136
      Convent Station, NJ, 07961-0136
      Phone: +1 973 829 5174

      Reinaldo Penno
      Nortel Networks
      600 Technology Park
      Billerica, MA, 01821
      Phone: +1 978 288 8011
       George Tsirtsis
      Flarion Technologies
      Bedminster One
      135 Route 202/206 South
      Bedminster, NJ, 07921
      Phone : +44 20 88260073

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      Cliff Wang
      Smart Pipes
      565 Metro Place South
      Dublin, OH, 43017
      Phone: +1 614 923 6241

9. Appendix

   A. PANA Model

   Following sub-sections capture the PANA usage model in different
   network architectures with reference to its placement of logical
   elements such as the PANA Client (PaC) and the PANA Authentication
   Agent (PAA) with respect to the Enforcement Point (EP) and the
   Access Router (AR). Four different scenarios are described in
   following sub-sections.  Note that PAA may or may not use AAA
   infrastructure to verify the credentials of PaC to authorize network

   A.1.  PAA Co-located with EP but Separated from AR

   In this scenario (Figure 1), PAA is co-located with the enforcement
   point on which access control is performed.  PaCs communicate with
   the PAA for network access on behalf of a device (D1, D2, etc.).
   PANA in this case provides a means to transport the authentication
   parameters from the PaC to PAA.  PAA knows how to verify the
   credentials.  After verification, PAA sends back the success or
   failure response to PaC.  However, PANA does not play any explicit
   role in performing access control except that it provides a hook to
   access control mechanisms. This might be the case where PAA is
   co-located with the access point (an IP-capable L2 access device).

            PaC -----EP/PAA--+
            [D1]             |
                             +------ AR ----- (AAA)
            PaC -----EP/PAA--+

            Figure 1: PAA co-located with EP but separated from AR.

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   A.2.  PAA Co-located with AR but Separated from EP

   Figure 2 describes this model. In this scenario, PAA is not
   co-located with EPs but it is placed on the AR. Although we have
   shown only one AR here there could be multiple ARs, one of which is
   co-located with the PAA. PaC exchanges the same messages with PAA as
   discussed earlier. The difference here is when the initial
   authentication for the PaC succeeds, access control parameters have
   to be distributed to respective enforcement points so that the
   corresponding device on which PaC is authenticated can access to the
   network. Similar to the earlier case, PANA does not play any
   explicit role in performing access control except that it provides a
   hook to access control mechanisms.  However, a separate protocol is
   needed between PAA and EP to carry access control parameters.

           PaC  ----- EP --+
           [D1]            |
                           +------ AR/PAA --- (AAA)
           PaC  ----- EP --+

           Figure 2: PAA co-located with AR but separated from EP.

   A.3.  PAA Co-located with EP and AR

   In this scenario (Figure 3), PAA is co-located with the EP and AR on
   which access control and routing are performed.  PaC exchanges the
   same messages with PAA and PAA performs similar functionalities as
   before. PANA in this case also does not play any explicit role in
   performing access control except that it provides a hook to access
   control mechanisms.

           PaC ----- EP/PAA/AR--+
           [D1]                 |
           PaC ----- EP/PAA/AR--+

           Figure 3: PAA co-located with EP and AR.

   A.4.  PAA Separated from EP and AR

   Figure 4 represents this model. In this scenario, PAA is neither
   co-located with EPs nor with ARs. It still resides on the same IP
   link as ARs. PaC does similar exchanges with PAA as discussed

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   earlier. Similar to model in A.2, after successful authentication,
   access control parameters will be distributed to respective
   enforcement points via a separate protocol and PANA does not play
   any explicit role in this.

             PaC ----- EP -----+--- AR ---+
                               |          |
             PaC ----- EP --- -+          |
                               |          |
             PaC ----- EP -----+--- AR -- + ----(AAA)
                               +--- PAA

             Figure 4: PAA separated from EP and AR.

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