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Versions: 00 01 02 03 04 05 06 07 08 09 rfc4058                         
PANA Working Group                               Alper E. Yegin, Editor
INTERNET-DRAFT                                           Yoshihiro Ohba
Date: April 2003                                         Reinaldo Penno
Expires: October 2003                                   George Tsirtsis
                                                             Cliff Wang

                 Protocol for Carrying Authentication for
                           Network Access (PANA)
                       Requirements and Terminology
                   <draft-ietf-pana-requirements-05.txt>
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.
   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.
Abstract
   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 the
   PANA is to provide a link-layer agnostic and IPv4/IPv6 compatible
   client-server protocol that allows a host to be authenticated for
   network access. The protocol will run between a client's device and
   an agent device in the network where the agent might be a client of
   the AAA infrastructure. This document defines the common terminology
   and identifies the requirements for PANA.

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Table of Contents
   Status of this Memo...............................................1
   Abstract..........................................................1
   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.....................................6
   4.1.4. Identifiers................................................7
   4.2. IP Address Assignment........................................7
   4.3. EAP Lower Layer Requirements.................................7
   4.4. PAA-EP Protocol..............................................8
   4.5. Network......................................................8
   4.5.1. Multi-access...............................................8
   4.5.2. Disconnect Indication......................................8
   4.5.3. Location of PAA............................................9
   4.5.4. Secure Channel.............................................9
   4.6. Interaction with Other Protocols............................10
   4.7. Performance.................................................10
   4.8. Ordered-delivery, Congestion Control........................10
   4.9. Miscellaneous...............................................10
   4.9.1. IP Version Independence...................................10
   4.9.2. Denial of Service Attacks.................................10
   4.9.3. Location Privacy..........................................10
   5. Change Log....................................................11
   Acknowledgements.................................................11
   References.......................................................11
   Authors' Addresses...............................................13
   Appendix.........................................................14
   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 methods between the client and the access
   network. IETF PANA Working Group has been chartered with the goal of
   designing a network-layer access authentication protocol.
   Link-layer authentication mechanisms are used as enablers of secure
   network access. A higher-layer authentication is deemed necessary
   when link-layer authentication mechanisms are either not available
   for lack of technology or deployment difficulties, or not able to
   meet the overall 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. [USAGE] Internet-Draft describes the problem
   statement in detail.
   The protocol design will be limited to defining a client-server
   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 Working Group will not invent new security protocols and
   mechanisms but instead it will use the existing mechanisms. In
   particular, the Working Group will not define authentication
   protocols, key distribution or key agreement protocols, or key
   derivation. 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, Mobile IP Working Group has already defined such a
   carrier for Mobile IPv4 [MIPV4]. Mobile IPv4 registration request
   message is used as the carrier for authentication extensions (MN-FA
   [MIPV4], or MN-AAA [MNAAA]) to receive forwarding service from the
   foreign agents. In that sense, designing the equivalent of Mobile
   IPv4 registration request messages for general network access is the
   goal of this work, but not defining the equivalent of MN-FA or MN-
   AAA extensions.
   This document defines the common terminology and identifies the
   requirements of a protocol for PANA. These terminology and

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   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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].
3. Terminology
   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, identifier might contain any of IP address, link-
        layer address, switch port number, etc. of a connected device.
        PANA authentication agent keeps a table for binding device
        identifiers to the PANA clients. At most one PANA client
        should be associated with a DI on a PANA authentication agent.
   PANA Client (PaC)
        The entity wishing to obtain network access from a PANA
        authentication agent within a network. A PANA client is
        associated with a network device and a set of credentials to
        prove its identity for network access authorization.
   PANA Authentication Agent (PAA)
        The entity whose responsibility is to authenticate 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 authenticate a PaC for network access. A PaC can be
   identified by 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"). The current thinking is that a sufficient
   solution would be for PANA to carry EAP [EAP]. If PANA WG 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 (e.g., IPsec) ciphering can be
   used to provide such security. These mechanisms require presence of
   cryptographic keying material at PaC and EP, which can be generated
   by various EAP methods. Although PANA does not deal with key
   derivation or distribution, it indirectly enables this by the virtue
   of carrying EAP. The keying material produced by EAP methods cannot
   be directly used with IPsec. In that case these initial keys can be
   used with an IPsec key management protocol like IKE to generate the
   required security associations. Key distribution from PAA to EP
   SHOULD be handled by a separate protocol that takes care of
   provisioning in the network (see section 4.3). 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. Securing IPv6 router
   discovery and neighbor discovery protocols are within the scope of
   IETF SEND Working Group.
   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

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   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 authenticate each other for
   network access. Providing capability of only PAA authenticating the
   PaC is not sufficient.
   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 type of service theft is 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
   In addition to carrying authentication information, PANA MUST also
   provide only a binary authorization to indicate whether the PaC is
   allowed to access full IP services on the network (i.e., able to
   send and receive any IP packets). Providing finer granularity
   authorization, such as negotiating QoS parameters, authorizing
   individual services (e.g., http vs. ssh), individual users sharing
   the same device, etc. are outside the scope of PANA.
   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.
   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. 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), then it can still use
   a proprietary backend system, or rely on the information locally
   stored on the authentication agents.

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   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 for the
   PaC (e.g., NAI, IP address, 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,
   etc.)
   PAA MUST be able to create a binding between the PaC and the
   associated DI upon successful PANA exchange. The DI MUST 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 stored as an
   attribute of DI. The binding between DI and PaC is used for access
   control and accounting in the network as described in section 4.1.2.
4.2. IP Address Assignment
   Providing address assignment functionality is outside the scope of
   PANA. PANA protocol design MAY require the PaC to configure an IP
   address before using this protocol. Allocating an IP address to
   unauthenticated PaCs may create security vulnerabilities, such as IP
   address depletion attacks on the access network [SECTHREAT]. This
   threat may not be an issue for IPv6 because of the large address
   space, but it can affect IPv4 networks. This threat can be mitigated
   by allowing the protocol to run without an IP address 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
   EAP protocol itself imposes various requirements on its transport
   protocols. These requirements are based on the nature of the EAP
   protocol, and needs to be satisfied for correct operation. Please
   see [EAP] for the generic transport requirements that MUST be
   satisfied by PANA as well.


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4.4. PAA-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. This WG 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 not limited to COPS, SNMP, DIAMETER.
   This task is similar to what MIDCOM Working Group is trying to
   achieve, therefore some of that WG’s output might be useful here.
   It is assumed that the communication between PAA and EP(s) is
   secure. The objective of using this 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-EP protocol exchange
   per PaC) or the push model (i.e., PAA initiating the PAA-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 bypass even
   for unauthenticated PaCs, it should also allow and expect the PAA to
   send the filtering information at the end of successful PANA without
   EP ever sending a request.
4.5. Network
  4.5.1. Multi-access
   Protocol MUST support PaCs with multiple interfaces, and networks
   with multiple routers on multi-access links. In other words, PANA
   MUST not assume 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. When such indications
   are not protected by means of physical or link-layer mechanisms,

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   PANA MUST ensure this protection to prevent attackers 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 means, there must be no IP routers between 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 does not
   necessarily satisfy this requirement, as they can be more than one
   hop away from each other [MULTILINK]. 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.
   A PaC MAY not be pre-configured with the IP address of PAA.
   Therefore 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. First phase can be used for

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   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. Though, PANA MUST
   be able to co-exist and not 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
   [DHCP]. 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
   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.
4.8. Ordered-delivery, Congestion Control
   PANA MUST provide ordered-delivery for messages that carry EAP PDUs
   as described in [EAP]. PANA MUST provide congestion control for all
   messages. It can do so by using techniques like delayed
   initialization and exponential back off.
4.9. Miscellaneous
  4.9.1. IP Version Independence
   PANA MUST work with both IPv4 and IPv6.
  4.9.2. Denial of Service Attacks
   PANA MUST be robust against a class of DoS attacks such as blind
   masquerade attacks through IP spoofing that swamp the PAA in
   spending much resources and/or prevent legitimate clients' attempts
   of network access.
  4.9.3. Location Privacy
   Location privacy is outside the scope of PANA.

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5. Change Log
   Version 05
   * Definition of EP added.
   * Text is clarified to indicate some of the requirements are
   satisfied by EAP and EAP methods.
   * IP address pre-configuration requirement changed.
   * EAP lower layer requirements section added.
   * Location of PAA further clarified (link vs. subnet vs. IP hops).
   * PAA-EP protocol section added.
   Version 04
   * Minor Editorial corrections.
   * Inserted the PANA model appendix.
   Version 03
   * In section 4.2.2 the requirement for a heartbeat mechanism to
   provide disconnect indication was removed.  Rewording of the
   section was done.
   * In section 4.2.3 and 4.1.2 rewording was done to account for the
   separation of PAA and EP and the protocol between them.
   * In section 4.2.4 new text was added to account for the possibility
   to rely on the high layer protocol (EAP) to meet the requirements
   stated.
   * In section 4.5 new text was added to allow reliability and
   congestion control to be provided by the payload protocol, e.g.,
   EAP.
Acknowledgements
   We would like to thank Subir Das, Lionel Morand, Mohan
   Parthasarathy, Basavaraj Patil and the PANA Working Group members
   for their valuable contributions to the discussions and preparation
   of this document.
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-05.txt, April 2003. Work in progress.
   [8021X] "IEEE Standards for Local and Metropolitan Area Networks:
   Port Based Network Access Control", IEEE Draft 802.1X/D11, March

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   2001.
   [SECTHREAT] M. Parthasarathy, "PANA Threat Analysis and Security
   Requirements", draft-ietf-pana-threats-03.txt, April 2003. Work in
   progress.
   [EAP] L. Blunk, J. Vollbrecht, B. Aboba, J. Carlson, "Extensible
   Authentication Protocol (EAP)", draft-ietf-eap-rfc2284bis-01.txt,
   January 2003. Work in progress.
   [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.
   [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.
   [DHCP] R. Droms (editor), et. al., "Dynamic Host Configuration
   Protocol for IPv6", November 2002. Work in progress.
   [PRIVACY] T. Narten, R. Draves, "Privacy Extensions for Stateless
   Address Autoconfiguration in IPv6", RFC 3041, January 2001.




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Authors' Addresses
      Alper E. Yegin
      DoCoMo USA Labs
      181 Metro Drive, Suite 300
      San Jose, CA, 95110
      USA
      Phone: +1 408 451 4743
      Email: alper@docomolabs-usa.com
      Yoshihiro Ohba
      Toshiba America Research, Inc.
      P.O. Box 136
      Convent Station, NJ, 07961-0136
      USA
      Phone: +1 973 829 5174
      Email: yohba@tari.toshiba.com
      Reinaldo Penno
      Nortel Networks
      600 Technology Park
      Billerica, MA, 01821
      USA
      Phone: +1 978 288 8011
      Email: rpenno@nortelnetworks.com
      George Tsirtsis
      Flarion Technologies
      Bedminster One
      135 Route 202/206 South
      Bedminster, NJ, 07921
      USA
      Phone : +44 20 88260073
      E-mail: G.Tsirtsis@Flarion.com, gtsirt@hotmail.com
      Cliff Wang
      Smart Pipes
      565 Metro Place South
      Dublin, OH, 43017
      USA
      Phone: +1 614 923 6241
      Email: cwang@smartpipes.com




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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 PANA Client (PaC) and PANA Authentication Agent
   (PAA) w.r.t Enforcement Point (EP) and 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 access.
   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 understands 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-+
            [D2]
            Figure 1: PAA co-located with EP but separated from AR.
   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 are
   to be distributed to respective enforcement points so that the
   corresponding device on which PaC is authenticated must be able to
   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

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Internet Draft      PANA Requirements and Terminology        Apr 2003
   protocol is needed between PAA and EP to carry access control
   parameters.
           PaC  -------- EP --+
           [D1]               |
                              +--- AR/PAA --- (AAA)
                              |
           PaC  -------- EP --+
           [D2]
           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
   above. 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]                      |
                                     + -------(AAA)
                                     |
           PaC ---------- EP/PAA/AR--+
           [D2]
           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 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.



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Internet Draft      PANA Requirements and Terminology        Apr 2003
             PaC ----- EP -----+- AR -----+
                               |          |
             PaC ----- EP --- -+          |
                               |          |
             PaC ----- EP -----+- AR ---- + ----(AAA)
                               |
                               +- PAA
             Figure 4: PAA separated from EP and AR.
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