PANA Working Group
   Internet Draft                                           D. Forsberg
Internet-Draft                                                     Nokia
Expires: April 23, 2004                                          Y. Ohba
                                                                 Toshiba
                                                                B. Patil
                                                                   Nokia
                                                           H. Tschofenig
                                                                 Siemens
                                                                A. Yegin
                                                         DoCoMo USA Labs
   Document: draft-ietf-pana-pana-01.txt
   Expires: December 2003                                     June
                                                        October 24, 2003

     Protocol for Carrying Authentication for Network Access (PANA)
                       <draft-ietf-pana-pana-01.txt>
                        draft-ietf-pana-pana-02

Status of this Memo

   This document is an Internet-Draft and is subject to in full conformance with
   all provisions of Section 10 of RFC2026.

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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   This document defines the Protocol for Carrying Authentication for
   Network Access (PANA), a link-layer agnostic transport for Extensible
   Authentication Protocol (EAP) to enable network access authentication
   between clients and access networks. PANA can carry any
   authentication method that can be specified as an EAP method, and can
   be used on any link that can carry IP. PANA covers the
   client-to-network access authentication part of an overall secure
   network access framework, which additionally includes other protocols
   and mechanisms for service provisioning, access control as a result
   of initial authentication, and accounting.

Table of Contents

   1  Introduction..................................................3
   2  Terminology...................................................4
   3  Protocol Overview.............................................5

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   4
   2.     Terminology  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.     Protocol Overview  . . . . . . . . . . . . . . . . . . . .   6
   4.     Protocol Details..............................................6 Details . . . . . . . . . . . . . . . . . . . . .   8
   4.1    Common Processing Rules.................................6
      4.2  Discovery and Initial Handshake Phase..................10
      4.3  Authentication Phase...................................12
      4.4  Re-authentication......................................14
      4.5  Termination Phase......................................16
      4.6  Illustration of a Complete Message Sequence............16
      4.7  Device ID choice.......................................18
      4.8  Refresh Interval Negotiation...........................18
      4.9  Mobility Handling......................................19
      4.10   Event Notification...................................19
      4.11   PaC Implications.....................................20
      4.12   PAA Implications.....................................20
   5  PANA Security Association Establishment......................20
   6  Authentication Method Choice.................................21
   7  Filter Rule Installation.....................................21 Rules  . . . . . . . . . . . . . . . . .   8  Data Traffic Protection......................................22
   9  Message Formats..............................................23
      9.1  PANA Header............................................23
      9.2  AVP Header.............................................24
      9.3  PANA Messages..........................................26
      9.4  AVPs in PANA...........................................29
      9.5  AVP Occurrence Table...................................32
   10   Security Considerations...................................33
   11   Open Issues...............................................39
   12   Acknowledgments...........................................39
   13   References................................................39
   Change History..................................................42
   Appendix A.  Adding sequence number to PANA for carrying EAP....43
   Full Copyright Statement........................................52

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
   4.1.1  Payload Encoding . . . . . . . . . . . . . . . . . . . . .   8
   4.1.2  Transport Layer Protocol . . . . . . . . . . . . . . . . .   8
   4.1.3  Fragmentation  . . . . . . . . . . . . . . . . . . . . . .   9
   4.1.4  Sequence Number and Retransmission . . . . . . . . . . . .   9
   4.1.5  PANA Security Association  . . . . . . . . . . . . . . . .  10
   4.1.6  Message Authentication Code  . . . . . . . . . . . . . . .  11
   4.1.7  Message Validity Check . . . . . . . . . . . . . . . . . .  11
   4.1.8  Error Handling . . . . . . . . . . . . . . . . . . . . . .  12
   4.2    Discovery and Initial Handshake Phase  . . . . . . . . . .  12
   4.3    Authentication Phase when PANA-PAA-Discover is sent by
          EP . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   4.4    Re-authentication  . . . . . . . . . . . . . . . . . . . .  17
   4.5    Termination Phase  . . . . . . . . . . . . . . . . . . . .  18
   4.6    Illustration of a Complete Message Sequence  . . . . . . .  18
   4.7    Device ID Choice . . . . . . . . . . . . . . . . . . . . .  20
   4.8    Session Lifetime . . . . . . . . . . . . . . . . . . . . .  20
   4.9    Mobility Handling  . . . . . . . . . . . . . . . . . . . .  21
   4.10   Event Notification . . . . . . . . . . . . . . . . . . . .  22
   4.11   PaC Implications . . . . . . . . . . . . . . . . . . . . .  22
   4.12   PAA Implications . . . . . . . . . . . . . . . . . . . . .  22
   5.     PANA Security Association Establishment  . . . . . . . . .  23
   6.     Authentication Method Choice . . . . . . . . . . . . . . .  24
   7.     Filter Rule Installation . . . . . . . . . . . . . . . . .  25
   8.     Data Traffic Protection  . . . . . . . . . . . . . . . . .  26
   9.     Message Formats  . . . . . . . . . . . . . . . . . . . . .  27
   9.1    PANA Header  . . . . . . . . . . . . . . . . . . . . . . .  27
   9.2    AVP Header . . . . . . . . . . . . . . . . . . . . . . . .  28
   9.3    PANA Messages  . . . . . . . . . . . . . . . . . . . . . .  30
   9.3.1  Message Specifications . . . . . . . . . . . . . . . . . .  31
   9.3.2  PANA-PAA-Discover (PDI)  . . . . . . . . . . . . . . . . .  31
   9.3.3  PANA-Start-Request (PSR) . . . . . . . . . . . . . . . . .  31
   9.3.4  PANA-Start-Answer (PSA)  . . . . . . . . . . . . . . . . .  31
   9.3.5  PANA-Auth-Request (PAR)  . . . . . . . . . . . . . . . . .  32
   9.3.6  PANA-Auth-Answer (PAN) . . . . . . . . . . . . . . . . . .  32
   9.3.7  PANA-Bind-Request (PBR)  . . . . . . . . . . . . . . . . .  32
   9.3.8  PANA-Bind-Answer (PBA) . . . . . . . . . . . . . . . . . .  33
   9.3.9  PANA-Reauth-Request (PRAR) . . . . . . . . . . . . . . . .  33
   9.3.10 PANA-Reauth-Answer (PRAA)  . . . . . . . . . . . . . . . .  33
   9.3.11 PANA-Termination-Request (PTR) . . . . . . . . . . . . . .  33
   9.3.12 PANA-Termination-Answer (PTA)  . . . . . . . . . . . . . .  34
   9.3.13 PANA-Error (PER) . . . . . . . . . . . . . . . . . . . . .  34
   9.4    AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . .  34
   9.4.1  MAC AVP  . . . . . . . . . . . . . . . . . . . . . . . . .  34
   9.4.2  Device-Id AVP  . . . . . . . . . . . . . . . . . . . . . .  35
   9.4.3  Session-Id AVP . . . . . . . . . . . . . . . . . . . . . .  35
   9.4.4  Cookie AVP . . . . . . . . . . . . . . . . . . . . . . . .  35
   9.4.5  Protection-Capability AVP  . . . . . . . . . . . . . . . .  36
   9.4.6  Termination-Cause AVP  . . . . . . . . . . . . . . . . . .  36
   9.4.7  Result-Code AVP  . . . . . . . . . . . . . . . . . . . . .  36
   9.4.8  EAP-Payload AVP  . . . . . . . . . . . . . . . . . . . . .  39
   9.4.9  Session-Lifetime AVP . . . . . . . . . . . . . . . . . . .  39
   9.4.10 Failed-AVP AVP . . . . . . . . . . . . . . . . . . . . . .  39
   9.4.11 NAP-Information AVP  . . . . . . . . . . . . . . . . . . .  40
   9.4.12 ISP-Information AVP  . . . . . . . . . . . . . . . . . . .  40
   9.4.13 Provider-Identifier AVP  . . . . . . . . . . . . . . . . .  40
   9.4.14 Provider-Name AVP  . . . . . . . . . . . . . . . . . . . .  40
   9.5    AVP Occurrence Table . . . . . . . . . . . . . . . . . . .  40
   10.    PANA Protocol Message Retransmissions  . . . . . . . . . .  43
   10.1   Transmission and Retransmission Parameters . . . . . . . .  45
   11.    Security Considerations  . . . . . . . . . . . . . . . . .  46
   12.    Open Issues  . . . . . . . . . . . . . . . . . . . . . . .  52
   13.    Change History . . . . . . . . . . . . . . . . . . . . . .  53
   14.    Acknowledgments  . . . . . . . . . . . . . . . . . . . . .  54
          Normative References . . . . . . . . . . . . . . . . . . .  55
          Informative References . . . . . . . . . . . . . . . . . .  58
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  59
   A.     Adding sequence number to PANA for carrying EAP  . . . . .  61
   A.1    Why is sequence number needed for PANA to carry EAP? . . .  61
   A.2    Single sequence number approach  . . . . . . . . . . . . .  62
   A.2.1  Single sequence number with EAP retransmission method  . .  62
   A.2.2  Single sequence number with PANA-layer retransmission
          method . . . . . . . . . . . . . . . . . . . . . . . . . .  63
   A.3    Dual sequence number approach  . . . . . . . . . . . . . .  66
   A.3.1  Dual sequence number with orderly-delivery method  . . . .  66
   A.3.2  Dual sequence number with reliable-delivery method . . . .  68
   A.3.3  Comparison of the dual sequence number methods . . . . . .  69
   A.4    Consensus  . . . . . . . . . . . . . . . . . . . . . . . .  69
          Intellectual Property and Copyright Statements . . . . . .  70

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 enforcement points. A protocol is needed to carry
   authentication methods between the client and the access network.

   Currently there is no standard network-layer solution for
   authenticating clients for network access.
   [I-D.ietf-pana-usage-scenarios] describes the problem statement that
   led to the development of PANA.

   Scope of this working group is identified as designing a link-layer
   agnostic transport for network access authentication methods. PANA
   Working Group has identified EAP [RFC2284] as the payload for this
   protocol and carrier for authentication methods. In other words, PANA
   will carry EAP which can carry various authentication methods.  By
   the virtue of enabling transport of EAP above IP, any authentication
   method that can be carried as an EAP method is made available to PANA
   and hence to any link-layer technology. There is a clear division of
   labor between PANA, EAP and EAP methods.

   Various environments and usage models for PANA are identified in the
   [I-D.ietf-pana-usage-scenarios] Internet-Draft. Potential security
   threats for network-layer access authentication protocol is discussed
   in [I-D.ietf-pana-threats-eval] draft.  These two drafts have been
   essential in defining the requirements [I-D.ietf-pana-requirements]
   on the PANA protocol. Note that some of these requirements are
   imposed by the chosen payload, EAP [RFC2284].

   This Internet-Draft makes an attempt for defining the PANA protocol
   based on the other drafts discussed above. Special care has been
   given to ensure the currently stated scope is observed and to keep
   the protocol as simple as possible. The current state of this draft
   is not complete, but it should be regarded as a work in progress.
   The authors made effort to capture the common understanding developed
   within the working group as much as possible. The design choices
   being made in this draft should not be considered as cast in stone.

2. Terminology

   This section describes some terms introduced in this document:

   PANA Session:

      PANA session is defined as the exchange of messages between the
      PANA Client (PaC) and the PANA Authentication Agent (PAA) to
      authenticate a user (PaC) for network access. If the
      authentication is unsuccessful, the session is terminated. The
      session is considered as active until there is a disconnect
      indication by the PaC or the PAA terminates it.

   Session Identifier:

      This identifier is used to uniquely identify a PANA session on the
      PAA and PaC. It is included in PANA messages to bind the message
      to a specific PANA session.

   PANA Security Association:

      The representation of the trust relation between the PaC and the
      PAA that is created at the end of the authentication phase. This
      security association includes the device identifier of the peer,
      and a shared key when available.

   The definition of the terms PANA Client (PaC), PANA Authentication
   Agent (PAA), Enforcement Point (EP) and Device Identifier (DI) can be
   found in [I-D.ietf-pana-requirements].

3. Protocol Overview

   The PANA protocol involves two functional entities namely the PaC and
   the PAA. The EP, mentioned in the context with PANA, is a logical
   entity. There is, however, the option that the EP is not physically
   co-located with the PAA. In case that the PAA and the EP are
   co-located only an API is required for intercommunication instead of
   a separate protocol. In the case where the PAA is separated from the
   EP, a separate protocol will be used between the PAA and the EP for
   managing access control. The protocol and messaging between the PAA
   and EP for access authorization is outside the scope of this draft
   and will be dealt separately.

   The PANA protocol (PaC<->PAA) resides above the transport layer and
   the details are explained in Section 4. Although this document
   describes the interaction with a number of entities and with other
   protocol which enable network access authentication; the PANA
   protocol itself is needed to
   carry authentication methods executed between the client PaC and the access
   network. IETF PAA.

   The placement of the entities used in PANA Working Group has been chartered largely depends on a
   certain architecture. The PAA may optionally interact with a AAA
   backend to authenticate the goal
   of designing user (PaC). And in the case where the PAA
   and EP are co-located, the intercommunication may not require a network-layer access authentication
   separate protocol.

   Link-layer authentication mechanisms Figure 1 illustrates the interactions in a
   simplified manner:

           PaC                   EP            PAA           AAA
           ---                   ---           ---           ---

                         PAA Discovery
            <---------------------o------------> (1)
                      PANA Authentication       AAA interaction
            <----------------------------------><------------> (2)

                                     Authorization
                                  <-------------  (3)

                        Figure 1: PANA Framework

   The details of each of these aspects of the protocol are used as enablers described in
   Section 4 of secure
   network access. A higher-layer authentication is deemed necessary
   when link-layer this document. PANA supports authentication mechanisms are either not available
   for lack of technology or deployment difficulties, or not able to
   meet a PaC
   using various EAP methods. The EAP method used depends on 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 level
   of security required for authenticating clients the EAP messaging itself. PANA does not
   secure the data traffic itself. However, EAP methods that enable key
   exchange may allow other protocols to be bootstrapped for
   network access. In securing
   the absence of such data traffic [I-D.ietf-pana-ipsec].

   From a solution, some inadequate
   standards-based solutions are deployed or non-standard ad-hoc
   solutions are invented. [USAGE] describes the problem statement in
   detail.

   Scope state machine aspect, PANA protocol consists of three phases
   1.  Discovery and initial handshake phase

   2.  Authentication phase

   3.  Termination phase

   In the first phase, an IP address of this working group PAA is identified as designing discovered and a link-layer
   agnostic transport for network access authentication methods. PANA
   Working Group has identified
   session is established between PaC and PAA.  EAP [RFC2284] messages are
   exchanged and a PANA SA is established in the second phase. The
   established PANA session as well as a PANA SA is deleted in the third
   phase.

4. Protocol Details

4.1 Common Processing Rules

4.1.1 Payload Encoding

   The payload for this
   protocol and carrier for authentication methods. In other words, of any PANA will carry EAP which can carry various authentication methods.
   By the virtue message consists of enabling transport zero or more AVPs
   (Attribute Value Pairs).  A brief description of EAP above IP, any
   authentication method the AVPs defined in
   this document is listed below:

   o  Cookie AVP: contains a random value that can be carried as an EAP method is
   made available to used for making
      initial handshake robust against blind resource consumption DoS
      attacks.

   o  Protection-Capability AVP: contains information which protection
      should be initiated after the PANA and hence to any exchange (e.g. link-layer technology. There or
      network layer protection).

   o  Device-Id AVP: contains a device identifier of the sender of the
      message. A device identifier is represented as a clear division pair of labor between PANA, EAP device
      identifier type and EAP methods.
   Defining new authentication methods, device identifier value.  Either a layer-2
      address or deriving/distributing keys an IP address is outside used for the device identifier value.

   o  EAP AVP: contains an EAP PDU.

   o  MAC AVP: contains a Message Authentication Code that protects a
      PANA message PDU.

   o  Termination-Cause AVP: contains the reason of session termination.

   o  Result-Code AVP: contains information about the scope protocol execution
      results.

   o  Session-Id AVP: contains the session identifier value.

   o  Session-Lifetime AVP: contains the duration of PANA. Providing a secure channel authorized access.

   o  Failed-AVP: contains the offending AVP that
   protects EAP and EAP methods against eavesdropping caused a failure.

   o  NAP-Information AVP, ISP-Information AVP: contains the information
      on a NAP and spoofing an ISP, respectively.

4.1.2 Transport Layer Protocol

   PANA uses UDP as its transport layer protocol.  The UDP port number
   is TBD.  All messages except for PANA-PAA-Discover are always
   unicast.  PaC MAY use unspecified IP address for communicating with
   PAA.

4.1.3 Fragmentation

   PANA does not an objective provide fragmentation of the PANA design.

   While messages. Instead, it
   relies on fragmentation provided by EAP methods and IP layer when
   needed.

4.1.4 Sequence Number and Retransmission

   PANA is a fundamental part of a complete secure network access
   solution, its responsibility is limited uses sequence numbers to authentication and
   authorization provide ordered delivery of the client and the network. Providing access
   control is outside the scope EAP
   messages. The design involves use of PANA. A separate provisioning
   protocol is needed for passing filtering  information to access
   control nodes in the network. Additionally, mechanisms two sequence numbers to provide
   data traffic protection in terms prevent
   some of authentication, integrity and
   replay protection, and encryption are outside the scope as well.

   Various environments and usage models for DoS attacks on the sequencing scheme.  Every PANA are identified packet
   include one transmitted sequence number (tseq) and one received
   sequence number (rseq) in the
   [USAGE] Internet-Draft. Potential security threats PANA header.  See Appendix A for network-layer
   access authentication protocol is discussed in [THREATS] draft.

   These
   detailed explanation on why two sequence numbers are needed.

   The two drafts sequence number fields have been essential in defining the requirements
   [PY+02] on the PANA protocol. Note that some same length of these requirements
   are imposed 32 bits and
   appear in PANA header.  tseq starts from initial sequence number
   (ISN) and is monotonically increased by the chosen payload, EAP [RFC2284].

   This Internet-Draft makes an attempt 1. The serial number
   arithmetic defined in [RFC1982] is used for defining sequence number
   operation. The ISNs are exchanged between PaC and PAA during the PANA protocol
   based on
   discovery and initial handshake phase (see Section 4.2). The rules
   that govern the sequence numbers in other drafts discussed above. Special care has been
   given to ensure the currently stated scope phases are described as
   follows.

   o  When a message is observed and to keep sent, a new sequence number is placed on the protocol as simple as possible. The current state
      tseq field of this draft
   is not complete, but message regardless of whether it should be regarded is sent as a work in progress.
   The authors made effort to capture result
      of retransmission or not.  When a message is sent, rseq is copied
      from the common understanding
   developed within tseq field of the working group as much as possible. The design
   choices being made in this draft should not be last accepted message.

   o  When a message is received, it is considered as cast valid in
   stone.

2  Terminology

   This section describes some terms introduced in this document:

   PANA Session:

        PANA session of
      sequence numbers if and only if (i) its tseq is defined as greater than the
      tseq of the last accepted message and (ii) its rseq falls in the exchange of messages
      range between the
        PANA Client (PaC) tseq of the last acknowledged message + 1 and
      the tseq of the last transmitted message.

   PANA Authentication Agent (PAA) to
        authenticate a user (PaC) relies on EAP-layer retransmissions, or for network access. If the
        authentication is unsuccessful, example NAS
   functionality [I-D.ietf-aaa-eap], for retransmitting EAP Requests
   based on timer.  Other PANA layer messages that require a response
   from the session is terminated. The
        session is considered as active communicating peer are retransmitted based on timer at
   PANA-layer until there is a disconnect
        indication by response is received (in which case the PaC
   retransmission timer is stopped) or the PAA terminates it.

   Session Identifier:

        This identifier is used to uniquely identify a number of retransmission
   reaches the maximum value (in which case the PANA session on MUST be
   deleted immediately).  For PANA-layer retransmission, the PAA and PaC. It is included
   retransmission timer SHOULD be calculated as described in PANA messages to bind the
        message [RFC2988]
   to a specific provide congestion control.  See Section 10 for default timer and
   maximum retransmission count parameters.

4.1.5 PANA session. Security Association

   A PANA Disconnect Indication: SA is created as an attribute of a PANA session termination when EAP
   authentication succeeds with explicit notification from a PaC
        sent to the PAA. The PDI also includes the session identifier.

   PANA creation of a Master Session Revocation: Key (MSK)
   [I-D.ietf-eap-rfc2284bis].  A PANA session termination with explicit notification sent from SA is not created when the PAA to PANA
   authentication fails or no MSK is produced by any EAP authentication
   method. In the PaC. The PSR includes case where two EAP authentications are performed in a
   sequence in a single PANA authentication, it is possible that two
   MSKs are derived. If this happens, the session identifier. PANA Security Association:

        The representation of SA MUST be bound to the trust relation between
   MSK derived from the PaC and first EAP authentication.  When a new MSK is
   derived as a result of EAP-based re-authentication, any key derived
   from the PAA old MSK MUST be updated to a new one that is derived from
   the new MSK.

   The created at PANA SA is deleted when the end corresponding PANA session is
   deleted.  The lifetime of the authentication phase
        (PH2). This security association includes PANA SA is the device identifier
        of same as the peer, and a shared key when available.

   The definition lifetime of
   the terms PANA Client (PaC), session for simplicity.

   PANA Authentication
   Agent (PAA), Enforcement Point (EP) and Device Identifier (DI) can
   be found in [PY+02].

3  Protocol Overview

   The SA attributes as well as PANA protocol involves two functional entities namely the session attributes are listed
   below:

   PANA Session attributes:

      *  Session-Id

      *  Device-Id of PaC
   and the PAA.

      *  Device-Id of PAA

      *  Initial tseq of PaC (ISN_pac)

      *  Initial tseq of PAA (ISN_paa)

      *  Last transmitted tseq value

      *  Last received rseq value

      *  Last transmitted message payload

      *  Retransmission interval

      *  Session lifetime

      *  Protection-Capability

      *  PANA SA attributes:

         +  MSK
         +  PANA_MAC_Key

   The EP, mentioned in the context with PANA, is a
   logical entity. There is, however, the option that the EP PANA_MAC_Key is not
   physically co-located with the PAA. In case that the PAA used to integrity protect PANA messages and
   derived from the EP
   are co-located only an API is required instead of a separate
   protocol. In MSK in the case following way:

      PANA_MAC_KEY = The first N-bit of
                     HMAC_SHA1(MSK, ISN_pac | ISN_paa | Session-ID)

   where the PAA is separated from the EP, a
   separate protocol will be used between value of N depends on the PAA integrity protection algorithm in
   use, i.e., N=128 for HMAC-MD5 and the EP N=160 for
   managing access control. HMAC-SHA1.

   The protocol and messaging between the PAA
   and EP length of MSK MUST be N-bit or longer.  See Section 4.1.6 for access authorization is outside the scope
   detailed usage of this draft
   and will be dealt separately.

   The PANA protocol (PaC<->PAA) resides above the transport layer and PANA_MAC_Key.

4.1.6 Message Authentication Code

   A PANA message can contain a MAC (Message Authentication Code) AVP
   for cryptographically protecting the details are explained message.

   When a MAC AVP is included in Section 4.2. Although this document
   describes the interaction with a number PANA message, the value field of entities and with other
   protocol which enable network access authentication; the PANA
   protocol itself
   MAC AVP is executed between the PaC and calculated by using the PAA.

   The protocol has three primary functions:

   1. The PaC discovering PANA_MAC_Key in the address of following way:

      MAC AVP value = HMAC_SHA1(PANA_MAC_Key, PANA_PDU)

   where PANA_PDU is the PAA
   2. The transport of EAP payloads between PANA message including the PaC and PANA header, with
   the PAA
   3. Access authorization by MAC AVP value field first initialized to 0.

4.1.7 Message Validity Check

   When a PANA message is received, the PAA message is considered to be
   invalid at least when one of the following conditions are not met:

   o  Each field in the message header contains a valid value including
      sequence number, message length, message type, version number,
      flags, etc.

   o  When a device identifier of the EP [Note that this aspect communication peer is outside the scope of bound to the
      PANA protocol.]

   The placement of session, it matches the entities used device identifier carried in PANA largely depend on a
   certain architecture. MAC and/
      or IP header(s).

   o  The PAA may optionally interact with a AAA
   backend to authenticate message type is one of the user (PaC). And expected types in the case where the
   PAA and EP are co-located, step 3 mentioned above may not require a
   separate protocol. Figure 1 illustrates the interactions in a
   simplified manner:

        PaC                   EP            PAA           AAA
        ---                   ---           ---           ---

          PAA Discovery
        <---------------------o-----------------> (1)
      |               PANA_REQUEST
      | ---------------------------------------->
      |                          AAA interaction
      |(2)                                      ----------->
      |                                         <-----------
      |         PANA_RESPONSE
      | <---------------------------------------
      |
                                Authorization
                              <-----------------  (3)

                          Figure 1: PANA Protocol current
      state.

   o  The details of each of these aspects of the protocol are described
   in section 4 of this document. PANA supports authentication of message payload contains a PaC
   using various EAP methods. The EAP method used depends on the level valid set of security required AVPs allowed for the EAP messaging itself. PANA does not
   secure the data traffic itself. However, EAP methods
      message type and there is no missing AVP that enable key
   exchange may allow other protocols needs to be bootstrapped for securing included
      in the data traffic.

   From payload.

   o  Each AVP is decoded correctly.

   o  When a state machine aspect, PANA protocol consists of three phases

   1. Discovery and initial handshake phase
   2. Authentication phase
   3. Termination phase

   In MAC AVP is included, the AVP value matches the MAC value
      computed against the received message.

   o  When a Device-Id AVP is included, the AVP is valid if the device
      identifier type contained in the first phase, an IP address of PAA AVP is discovered and a PANA
   session supported (this check is established between
      for both PaC and PAA.  EAP messages are
   exchanged PAA) and a PANA SA is established in the second phase. The
   established PANA session as well as a PANA SA requested one (this check is deleted for
      PAA only) and the device identifier value contained in the
   third phase.

4  Protocol Details

4.1 Common Processing Rules

4.1.1 Payload Encoding

   The payload of any PANA message consists of zero or more AVPs
   (Attribute Value Pairs).  A brief description of AVP
      matches the AVPs defined in
   this document is listed below:

   - Cookie AVP: contains a random value extracted from the lower-layer encapsulation
      header corresponding to the device identifier type contained in
      the AVP.  Note that is used for making
     initial handshake robust a Device-Id AVP carries the PaC's device
      identifier in messages from PaC to PAA and PAA's device identifier
      in messages from PAA to PaC.

   Invalid messages MUST be discarded in order to provide robustness
   against blind resource consumption DoS
     attacks.

   - Protection-Cap. AVP: contains information which protection should attacks and an unprotected.  In addition, a
   non-acknowledged error notification message MAY be initiated after returned to the PANA exchange (e.g. link-layer
   sender. See Section 4.1.8 for details.

4.1.8 Error Handling

   PANA-Error message MAY be sent by either PaC or network
   layer protection).
   - Device-Id AVP: contains PAA when a device identifier badly
   formed PANA message is received or in case of other errors.  If the
   cause of this error message was a request message (e.g.,
   PANA-PAA-Discover or *-Request), then the request MAY be
   retransmitted immediately without waiting for its retransmission
   timer to go off. If the sender cause of the
     message. A device identifier is represented as error was a pair response message,
   the receiver of device
     identifier type and device identifier value.  Either a layer-2
     address or an IP address is used for the device identifier value.

   - EAP AVP: contains an EAP PDU.

   - MAC AVP: contains PANA-Error message SHOULD NOT resend the same
   response until it receives the next request.

   To defend against DoS attacks a Message Authentication Code that protects timer MAY be used. One (1) error
   notification is sent to each different sender each N seconds. N is a
     PANA
   configurable parameter.

   When an error message PDU.

   - Termination-Cause AVP: contains is sent unprotected with MAC AVP and the reason
   lower-layer is insecure, the error message is treated as an
   informational message.  The receiver of session termination.

   - Result-Code AVP: contains information about such an error message MUST
   NOT change its state unless the protocol execution
   results.

   - Session-Id AVP: contains error persists and the session identifier value.

4.1.2 Transport Layer Protocol PANA uses UDP as its transport layer protocol.  The UDP port number session
   is TBD.  All messages except for PANA-PAA-Discover are always
   unicast.  PaC MAY use unspecified IP address for communicating with
   PAA.

4.1.3 Fragmentation

   PANA does not provide fragmentation of PANA messages.  Instead, it
   relies on fragmentation provided by EAP methods making any progress.

4.2 Discovery and IP layer when
   needed.

4.1.4 Sequence Number Initial Handshake Phase

   When a PaC attaches to a network, and Retransmission

   PANA uses sequence numbers knows that it has to provide ordered delivery of EAP
   messages. discover
   PAA for PANA, it SHOULD send a PANA-PAA-Discover message to a well-
   known link local multicast address (TBD) and UDP port (TBD). The design involves use of two sequence numbers
   source address is set to prevent
   some of the DoS attacks on unspecified IP address if the sequencing scheme.  Every PaC has
   not configured an address yet. PANA packet
   include one transmitted sequence number (tseq) PAA discovery assumes that PaC
   and PAA are one received
   sequence number (rseq) in hop away from each other. If PaC knows the IP address
   of the PAA (some pre-configuration), it MAY unicast the PANA header.  See Appendix
   discovery message to that address. PAA SHOULD answer to the
   PANA-PAA-Discover message with a PANA-Start-Request message.

   When the PAA receives such a request, or upon receiving some lower
   layer indications of a new PaC, PAA SHOULD unicast a
   PANA-Start-Request message. The destination address may be
   unspecified IP address, but the L2 destination would be a unicast
   address (something for
   detailed explanation the implementations to deal with).

   There can be multiple PAAs on why two sequence numbers are needed.

   The two sequence number fields have the same length of N (TBD:
   possibly 32) bits and appear in PANA header.  tseq starts from
   initial sequence number (ISN) link. The authentication and
   authorization result does not depend on which PAA is monotonically increased chosen by 1.
   The serial number arithmetic defined in [RFC1982] is used for
   sequence number operation.  The ISNs are exchanged between the
   PaC. By default the PaC MAY choose the PAA that sent the that sent
   the first response.

   PaC may also choose to start sending packets before getting
   authenticated. In that case, the network should detect this and send
   an unsolicited PANA-Start-Request message to PaC. EP is the node that
   can detect such activity. If EP and PAA during are co-located, then an
   internal mechanism (e.g. API) between the discovery and initial handshake phase (see section
   "Discovery EP module and Initial Handshake Phase").  The rules that govern the
   sequence numbers in other phases PAA
   module on the same host can prompt PAA to start PANA. In case they
   are described as follows.

   o When a separate, there needs to be an explicit message is sent, to prompt PAA.
   Upon detecting the need to authenticate a new sequence number is placed on client, EP can send a
   PANA-PAA-Discover message to the
   tseq field PAA on behalf of the PaC. This
   message regardless of whether it is sent as carries a result device identifier of retransmission or not.  When the PaC in a Device-ID AVP. So
   that, the PAA can send the unsolicited PANA-Start-Request message
   directly to the PaC.  If the link between the EP and PAA is sent, rseq is copied not
   secure, the PANA-PAA-Discover message sent from the EP to the PAA
   MUST be protected by using, e.g., IPsec.

   A PANA-Start-Request message contains a cookie carried in a Cookie
   AVP in the payload, respectively.  The rseq field of the header is
   set to zero (0).  The tseq field of the last accepted message.

   o When a message header contains the initial
   sequence number.  The cookie is received, used for preventing the PAA from
   resource consumption DoS attacks by blind attackers.  The cookie is
   computed in such a way that it does not require any per-session state
   maintenance on the PAA in order to verify the cookie returned in a
   PANA-Start-Answer message. The exact algorithms and syntax used for
   generating cookies does not affect interoperability and hence is not
   specified here.  An example algorithm is considered as valid in terms described below.

      Cookie =
        <secret-version> | HMAC_SHA1( <Device-Id of
   sequence numbers if and PaC> | <secret> )

   where <secret> is a randomly generated secret known only if (i) its tseq to the PAA,
   <secret-version> is greater than an index used for choosing the
   tseq of secret for
   generating the last accepted message cookie and (ii) its rseq falls in '|' indicates concatenation.  The secret-
   version should be changed frequently enough to prevent replay
   attacks. The secret key is locally known to the
   range between PAA only and valid
   for a certain time frame.

   PAA MAY enable NAP-ISP authentication separation by setting the tseq
   S-flag of the last acknowledged message + 1 and the
   tseq header of the last transmitted message.

   PANA relies on EAP-layer retransmission for retransmitting EAP
   Request based on timer.  Other PANA layer messages that require a
   response from PANA-Start-Request. Also, the communicating peer are retransmitted based
   PANA-Start-Request MAY contain zero or one NAP-Information AVP and
   zero or more ISP-Information AVPs to advertise the information on
   timer at PANA-layer until a response is received (in which case the
   retransmission timer is stopped) or
   NAP and/or ISPs.

   When a PaC receives the number of retransmission
   reaches PANA-Start-Request message in response to the maximum value (in which case
   PANA-PAA-Discover message, it responds with a PANA-Start-Answer
   message if it wishes to enter the PANA session MUST be
   deleted immediately).  For PANA-layer retransmission, authentication phase.  The
   PANA-Start-Answer message contains the
   retransmission timer SHOULD be calculated as described initial sequence numbers in [RFC2988]
   to provide congestion control (TBD: default timer
   the tseq and maximum
   retransmission count suggestions).

4.1.5 PANA Security Association

   A PANA SA is created as an attribute rseq fields of a the PANA session when EAP
   authentication succeeds with header, a creation copy of a Master Session Key
   (MSK) [RFC2284bis].  A the received
   Cookie (if any) as the PANA SA payload.

   If the S-flag of the received PANA-Start-Request message is not created when set,
   PaC MUST NOT set the PANA
   authentication fails or no MSK is produced by any EAP authentication
   method. In S-flag in the case where two EAP authentications are performed PANA-Start-Answer message sent
   back to the PAA.  In this case, PaC can indicate its choice of ISP by
   including its ISP-Information AVP in a
   sequence the PANA-Start-Answer message.
   AAA routing will be based on the ISP choice if an ISP-Information AVP
   is specified in a single PANA authentication, the PANA-Start-Answer message, otherwise it is possible that two
   MSKs are derived. will be
   based on EAP identifier.

   If the S-flag of the received PANA-Start-Request message is set, PaC
   can indicate its desire to perform separate EAP authentication for
   NAP and ISP by setting the S-flag in the PANA-Start-Answer message.
   In this happens, case, PaC can also indicate its choice of ISP by including
   its ISP-Information AVP in the PANA SA MUST PANA-Start-Answer message.  AAA
   routing for NAP authentication will be bound to based on the
   MSK derived from NAP.  AAA routing
   for ISP authentication will be based on the first ISP choice if an
   ISP-Information AVP is specified in the PANA-Start-Answer message,
   otherwise it will be based on EAP authentication. identifier."

   When a new MSK the PAA receives the PANA-Start-Answer message from the PaC, it
   verifies the cookie.  The cookie is
   derived considered as a result of EAP-based re-authentication, any key derived
   from valid if the old MSK MUST be updated to a new one that
   received cookie has the expected value.  If the computed cookie is derived from
   valid, the new MSK. protocol enters the authentication phase.  Otherwise, it
   MUST silently discard the received message.

   The created PANA SA PANA-Start-Request/Answer exchange is deleted needed before entering
   authentication phase even when the corresponding PANA session PaC is deleted.  The lifetime of pre-configured with PAAs IP
   address and the PANA SA PANA-PAA-Discover message is unicast.

   A PANA-Start-Request message is never retransmitted. A
   PANA-Start-Answer message is retransmitted based on timer in the same
   manner as the lifetime
   of the PANA session for simplicity.

   PANA SA attributes as well as PANA session attributes are listed
   below:

    PANA Session attributes:
      - Session-Id
      - Device-Id of PaC
      - Device-Id of PAA
      - Initial tseq of other messages retransmitted at PANA-layer.

      PaC (ISN_pac)
      - Initial tseq of      PAA (ISN_paa)
      - Last transmitted tseq value
      - Last received rseq value
      - Last transmitted message payload
      - Retransmission interval
      - Session lifetime
      - Protection-Capability
      - PANA SA attributes:
          + MSK
          + PANA_MAC_Key

   The PANA_MAC_Key is used         Message
      ------------------------------------------------------
         ----->            PANA-PAA-Discover(0,0)
         <-----            PANA-Start-Request(x,0)[Cookie]
         ----->            PANA-Start-Answer(x,y)[Cookie]
                           (continued to integrity protect PANA messages and
   derived from the MSK in the following way:

      PANA_MAC_KEY = The first N-bit of
                     HMAC_SHA1(MSK, ISN_pac | ISN_paa | Session-ID)
   where the value of N depends on the integrity protection  algorithm
   in use, i.e., N=128 authentication phase)

  Figure 2: Example Sequence for HMAC-MD5 Discovery and N=160 for HMAC-SHA1.

   The length of MSK MUST be N-bit or longer.  See section 4.1.6 for
   the detailed usage of the PANA_MAC_Key.

4.1.6 Initial Handshake Phase

      PaC   EP      PAA    Message Authentication Code

   A PANA message can contain a MAC (Message Authentication Code) AVP
      ------------------------------------------------------
       ---->o              (Data packet arrival or L2 trigger)
             ------>       PANA-PAA-Discover(0,0)[Device-Id]
       <------------       PANA-Start-Request(x,0)[ Cookie]
       ------------>       PANA-Start-Answer(y,x)[ Cookie]
                           (continued to authentication phase)

  Figure 3: Example Sequence for cryptographically protecting the message.

   When a MAC AVP Discovery and Initial Handshake Phase
                 when PANA-PAA-Discover is included in a PANA message, the value field of the
   MAC AVP sent by PaC

4.3 Authentication Phase when PANA-PAA-Discover is calculated sent by using the PANA_MAC_Key EP

   The main task in the following
   way:

     MAC AVP value = HMAC_SHA1(PANA_MAC_Key, PANA_PDU)

   where PANA_PDU is the PANA message including the PANA header, with
   the MAC AVP value field first initialized to 0.

4.1.7 Message Validity Check

   When a PANA message is received, the message authentication phase is considered to be
   invalid at least when one of the following conditions carry EAP messages
   between PaC and PAA. All EAP messages except for EAP Success/Failure
   messages are not met:

   o Each field carried in the message header contains a valid value including
   sequence number, message length, message type, version number,
   flags, etc.

   o PANA-Auth-Request/PANA-Auth-Answer
   messages.  When a device identifier of the communication peer an EAP Success/Failure message is bound to the
   PANA session, it matches sent from a PAA,
   the device identifier carried in MAC and/or
   IP header(s).

   o The message type is one of the expected types carried in the current
   state.

   o PANA-Bind-Request message.  The PANA-
   Bind-Request message payload contains is acknowledged with a valid set of AVPs allowed for the
   message type and there PANA-Bind-Answer.  It is no missing AVP that needs
   possible to be included carry multiple EAP sequences in the payload.

   o Each AVP is decoded correctly.

   o a single PANA session.

   When PaC and PAA negotiated during the discovery and initial
   handshake phase to perform separate NAP and ISP authentications in a MAC AVP is included,
   single PANA session, the AVP value matches PAA determines the MAC value
   computed against execution order of NAP
   authentication and ISP authentication.  In this case, the received message.

   o When a Device-Id AVP PAA can
   indicate which EAP authentication is included, the currently occurring by including
   a NAP-Information or an ISP-Information AVP is valid if of the device
   identifier type contained corresponding EAP
   authentication in the AVP matches the expected one (this
   check is for PAA only) and the device identifier value contained in first PANA-Auth-Request message sent to the AVP matches
   PaC. In the value extracted from case where the lower-layer
   encapsulation header corresponding PaC agreed to the device identifier type
   contained perform separate
   authentications but did not specify its ISP choice in
   PANA-Start-Answer message, the AVP.

   Invalid messages PAA MUST be discarded in order to provide robustness
   against DoS attacks and an unprotected.  (TBD: include its NAP-Information
   AVP in addition, a
   non-acknowledged error notification PANA-Auth-Request message MAY be returned to the
   sender.)

4.2 Discovery and Initial Handshake Phase

   When a PaC attaches to a network, and knows that when it has to discover
   PAA for PANA, performs NAP authentication
   and MUST NOT include any service provider information AVP when it
   performs ISP authentication so that the PaC can send always distinguish
   ISP authentication from NAP authentication.  The PAA SHOULD stop
   including a PANA-PAA-Discover NAP-Information or an ISP-Information AVP once it
   receives the first PANA-Auth-Answer message to a well-
   known link local multicast address (TBD) and UDP port (TBD). The
   source address is set to of the unspecified IP address if current EAP
   authentication.

   Currently, use of multiple EAP methods in PANA is designed only for
   NAP-ISP authentication separation.  It is not for arbitrary EAP
   method sequencing, or giving the PaC has
   not configured another chance when an address yet. PANA PAA discovery assumes that PaC
   authentication method fails.  The NAP and PAA ISP authentication are one hop away from each other. If PaC knows the IP
   address
   considered completely independent. Presence or success of one should
   not effect the PAA (some pre-configuration), it can unicast the PANA
   discovery message to that address. PAA answers to the PANA-PAA-
   Discover message with a PANA-Start-Request message.

   When other. Making an authentication decision based on the PAA receives such a request,
   success or upon receiving some lower
   layer indications failure of each authentication is a new PaC, PAA can unicast a PANA-Start-Request
   message. The destination address may be unspecified IP address, but
   the L2 destination would be a unicast address (something for the
   implementations to deal with).

   There can be multiple PAAs on network policy issue.
   PANA signals only the link. The result does not depend
   on which PAA PaC chooses. By default PaC chooses of the PAA immediately preceding EAP
   authentication method in PANA-Bind-Request messages.

   When an EAP method that sent is capable of deriving keys is used during
   the first response.

   PaC may also choose to start sending packets before getting
   authenticated. In that case, authentication phase and the network should detect this keys are successfully derived the
   PANA-Bind-Request and send
   an unsolicited PANA-Start-Request PANA-Bind-Answer messages and all subsequent
   PANA messages MUST contain a MAC AVP.  The PANA-Bind-Request and the
   PANA-Bind-Answer message to PaC. EP exchange is also used for binding device
   identifiers of the node
   that can detect such activity. If EP and PAA are co-located, then an
   internal mechanism (e.g. API) between the EP module PaC and the PAA
   module on the same host can prompt PAA to start PANA. In case they
   are separate, there needs to an explicit message to prompt PAA. Upon
   detecting the need to authenticate a client, EP can send a PANA-PAA-
   Discover message to PANA SA. To achieve this,
   the PAA on behalf of PANA-Bind-Request and the PaC.  This message
   carries PANA-Bind-Answer SHOULD contain a
   device identifier of the PaC PAA and the PaC, respectively, in a Device-ID
   Device-Id AVP. So that,  The PaC MUST use the PAA can send same type of device identifier
   as contained in the unsolicited PANA-Start-Request PANA-Bind-Request message.  The PANA-Bind-Request
   message directly MAY also contain a Protection-Capability AVP to indicate if
   link-layer or network-layer ciphering should be initiated after PANA.
   No link layer or network layer specific information is included in
   the PaC.  If Protection-Capability AVP. When the link between information is preconfigured
   on the EP PaC and the PAA this AVP can be omitted. It is assumed that at
   least PAA is aware of the security capabilities of the access
   network. The PANA protocol does not secure, specify how the
   PANA-PAA-Discover message sent from PANA SA and the EP
   Protection-Capability AVP will be used to the PAA provide per-packet
   protection for data traffic.

   PANA-Bind-Request and PANA-Bind-Answer messages MUST be
   protected by using.

   A PANA-Start-Request message contains a cookie carried retransmitted
   based on the retransmission rule described in a Cookie
   AVP Appendix A.

      PaC      PAA  Message(tseq,rseq)[AVPs]
      -------------------------------------------------
                    (continued from discovery and initial handshake phase)
         <-----     PANA-Auth-Request(x+1,y)[EAP{Request}]
         ----->>     PANA-Auth-Answer(y+1,x+1)[EAP{Response}]
           .
           .
         <-----     PANA-Auth-Request (x+2,y+1)[EAP{Request}]
         ----->     PANA-Auth-Answer (y+2,x+2)[EAP{Response}]
         <-----     PANA-Bind-Request(x+3,y+2)
                       [EAP{Success}, Device-Id, Lifetime, Protection-Cap., MAC]
         ----->     PANA-Bind-Answer(y+3,x+3)
                       [Device-Id, Protection-Cap., MAC]

           Figure 4: Example Sequence in the payload, respectively.  The rseq field Authentication Phase

4.4 Re-authentication

   There are two types of the header is
   set to zero (0). re-authentication supported by PANA.

   The tseq field first type of the header contains the initial
   sequence number.  The cookie re-authentication is used for preventing the PAA from
   resource consumption DoS attacks based on EAP by blind attackers.  The cookie is
   computed entering an
   authentication phase.  In this case, some or all message exchanges
   for discovery and initial handshake phase MAY be omitted in such the
   following way.  When a way as not to require any saved per-session state PaC wants to recognize its valid cookie when initiate EAP-based
   re-authentication, it sends a particular unicast PANA-PAA-Discovery message sent by the
   PaC in response to
   the PANA-Start-Request PAA.  This message arrives.  The
   exact algorithms and syntax used for generating cookies does not
   affect interoperability and hence is not specified here.  An example
   algorithm is described below.

   Cookie =
     <secret-version> | HMAC_SHA1( <Device-Id of PaC> | <secret> )

   where <secret> is MUST contain a randomly generated secret known only to  the
   PAA, <secret-version> Session-Id AVP which is an index used
   for choosing identifying the secret for
   generating PANA session on the cookie and '|' indicates concatenation.  The secret-
   version should be changed frequently enough to prevent replay
   attacks. The secret key is locally known to PAA. If the PAA only and valid already has
   an established PANA session for a certain time frame.

   When a PaC receives the PANA-Start-Request message in response to PaC with the PANA-PAA-Discover message, matching identifier,
   it responds with sends a PANA-Start-Answer
   message. The PANA-Start-Answer PANA-Auth-Request message contains the initial sequence
   numbers in the tseq and rseq fields of containing the PANA header, a copy of same identifier
   to start an authentication phase.  If the received Cookie as PAA can not recognize the PANA payload.
   session identifier, it proceeds with regular authentication by
   sending back PANA-Start-Request.  When the PAA receives the PANA-Start-Request initiates EAP-based
   re-authentication, it sends a PANA-Auth-Request message from containing
   the PaC,
   it verifies session identifier for the cookie.  The cookie is considered as valid if PaC to enter an authentication phase.
   PAA SHOULD initiate EAP authentication before the
   received cookie has current session
   lifetime expires. In both cases, the expected value.  If tseq and rseq values are
   inherited from the computed cookie previous (re-)authentication.  For any EAP-based
   re-authentication, if there is
   valid, the protocol enters the authentication phase.  Otherwise, it
   MUST silently discard the received an established PANA SA,
   PANA-Auth-Request and PANA-Auth-Answer messages SHOULD be protected
   by adding a MAC AVP to each message.

   The PANA-Start-Request/Answer exchange second type of re-authentication is needed before based on a single protected
   message exchange without entering the authentication phase even when phase.
   PANA-Reauth-Request and PANA-Reauth-Answer messages are used for this
   purpose.  If there is an established PANA SA, both the PaC is pre-configured with PAAs
   IP address and the PANA-PAA-Discover message is unicast.

   A PANA-Start-Request message is never retransmitted. A PANA-Start-
   Answer
   PAA are allowed to send a PANA-Reauth-Request message is retransmitted based to the
   communicating peer whenever it needs to make sure the availability of
   the PANA SA on timer in the same manner as
   other peer and expect the peer to return a PANA-
   Reauth-Answer message.  Both PANA-Reauth-Request/ PANA-Reauth-Answer
   messages retransmitted at PANA-layer. MUST be protected with a MAC AVP.

   Implementations MUST limit the rate of performing re-authentication
   for both types of re-authentication.

      PaC      PAA         Message     Message(tseq,rseq)[AVPs]
      ------------------------------------------------------
         ----->            PANA-PAA-Discover(0,0)        PANA-Reauth-Request(q,p)[MAC]
         <-----            PANA-Start-Request(x,0)[Cookie]
      ----->            PANA-Start-Answer(x,y)[ Cookie]
                        (continued to authentication phase)

                 (PANA-PAA-Discover sent by PaC)        PANA-Reauth-Answer(p+1,q)[MAC]

        Figure 2: 5: Example Sequence for Discovery and Initial Handshake Phase PaC-initiated second type
                           Re-authentication

      PaC   EP      PAA    Message     Message(tseq,rseq)[AVPs]
      ------------------------------------------------------
    ---->o              (Data packet arrival or L2 trigger)
          ------>       PANA-PAA-Discover(0,0)[Device-Id]
    <------------       PANA-Start-Request(x,0)[ Cookie]
    ------------>       PANA-Start-Answer(y,x)[ Cookie]
                        (continued to authentication phase)

                 (PANA-PAA-Discover sent by EP)
         <-----        PANA-Reauth-Request(p,q)[MAC]
         ----->        PANA-Reauth-Answer(q+1,p)[MAC]

        Figure 3: 6: Example Sequence for Discovery and Initial Handshake Phase

4.3 Authentication PAA-initiated second type
                           Re-authentication

4.5 Termination Phase

   A procedure for explicitly terminating a PANA session can be
   initiated either from PaC (i.e., disconnect indication) or from PAA
   (i.e., session revocation).  The main task PANA-Termination-Request and the
   PANA-Termination-Answer message exchanges are used for disconnect
   indication and session revocation procedures.

   The reason for termination is indicated in authentication phase the Termination-Cause AVP.
   When there is to carry EAP messages an established PANA SA established between the PaC and PAA. All EAP messages except for EAP Success/Failure
   the PAA, all messages are carried in exchanged during the PANA-Auth-Request/PANA-Auth-Answer
   messages.  When an EAP Success/Failure message is sent from termination phase MUST be
   protected with a PAA, MAC AVP.  When the message is carried in sender of the PANA-Bind-Request message.  The PANA-
   Bind-Request message is acknowledged with a PANA-Bind-Answer.  It is
   possible to carry multiple EAP sequences in
   Termination-Request receives a single valid acknowledgment, all states
   maintained for the PANA sequence. session MUST be deleted immediately.

      PaC      PAA     Message(tseq,rseq)[AVPs]
      ------------------------------------------------------
         ----->        PANA-Termination-Request(q,p)[MAC]
         <-----        PANA-Termination-Answer(p+1,q)[MAC]

           Figure 7: Example Sequence for Session Termination

4.6 Illustration of a Complete Message Sequence

   A single complete PANA session can enable more than one EAP authentication.
   This message sequence is illustrated in Figure 8. The
   example assumes the following scenario:

   o  PaC multicasts PANA-PAA-Discover message

   o  The ISNs used to satisfy by the separate NAP PAA and the PaC are x and ISP authentications
   scenario.  Each y, respectively.

   o  A single EAP authentication sequence is delineated from the subsequent
   one.  The F-flag used in the PANA header indicates if this was the final authentication from sender's perspective.  If the PAA enables two
   separate authentication, it should not set the F-flag in after the
   first phase.

   o  An EAP method.  This indicates PAA's willingness to offer another authentication method for NAP-ISP separation.  PaC can respond with
   the F-flag unset, indicating PaC's willingness to go through a
   second single round trip is used in
      the EAP sequence.

   o  The EAP authentication method. method derives keys. The PaC can optionally decline PANA SA is
      established based on the unique and fresh session key provided by
   setting
      the F-flag, EAP method.

   o  After PANA SA is established, all messages are integrity and this concludes
      replay protected with the MAC AVP.

   o  Re-authentication based on the PANA-Reauth-Request/ PANA-Reauth-
      Answer exchange is performed.

   o  The PANA authentication.  If session is terminated as a result of the PANA-
      Termination-Request indication from the PaC.

      PaC      PAA does not offer two levels of authentication, then  Message(tseq,rseq)[AVPs]
      -----------------------------------------------------
      // Discovery and initial handshake phase
         ----->     PANA-PAA-Discover (0,0)
         <-----     PANA-Start-Request (x,0)[Cookie]
         ----->     PANA-Start-Request-Answer (y,x)[Cookie]

      // Authentication phase
         <-----     PANA-Auth-Request(x+1,y)[EAP]
         ----->     PANA-Auth-Answer(y+1,x+1)[EAP]
         <-----     PANA-Auth-Request(x+2,y+1)[EAP]
         ----->     PANA-Auth-Answer(y+2,x+2)[EAP]
         <-----     PANA-Bind-Request(x+3,y+2)
                      [EAP{Success}, Device-Id, Lifetime, Protection-Cap., MAC]
         ----->     PANA-Bind-Answer(y+3,x+3)
                      [Device-Id, Protection-Cap., MAC]

      // Re-authentication
         <-----     PANA-Reauth-Request (x+4,y+3)[MAC]
         ----->     PANA-Reauth-Answer (y+4,x+4)[MAC]

      // Termination phase
         ----->     PANA-Termination-Request(y+5,x+4)[MAC]
         <-----     PANA-Termination-Answer (x+5,y+5)[MAC]
                 Figure 8: A Complete Message Sequence

4.7 Device ID Choice

   A PaC SHOULD configure an IP address before PANA if it sets
   the F-flag even at can. It might
   either have a pre-configured IP address, or have to obtain one via
   dynamic methods such as DHCP or stateless address autoconfiguration.
   Dynamic methods may or may not succeed depending on the end of first EAP exchange. local
   security policy.  In that case the
   PaC has no other option but networks where clients have to set the F-flag be authorized
   before they are allowed to mark obtain an IP address, EPs will detect the end of
   PANA authentication.

   Currently, use of multiple EAP methods in
   associated activity and PANA is designed only for
   NAP-ISP authentication separation. protocol will be engaged before the
   clients can configure a valid IP address.

   Either an IP address or a link-layer address SHOULD be used as device
   ID at any time. It is not for arbitrary EAP
   method sequencing, or giving assumed that PAA knows the PaC another chance when an
   authentication method fails.  The NAP and ISP authentication are
   considered completely independent.  Presence security mechanisms
   being provided or success of one
   should not effect required on the other. Making a decision access network (e.g., based on the success
   physical security, link-layer ciphers enabled before or failure of each authentication after PANA,
   or IPsec). When IPsec-based mechanism [I-D.ietf-pana-ipsec] is a network policy issue.  PANA
   signals only the result
   choice of access control, PAA SHOULD provide its IP address as device
   ID, and expect the immediately preceding EAP
   authentication method. PaC to provide its IP address in return.  In all
   other cases, link-layer addresses can be provided from both sides.

   When an EAP method that is capable of deriving keys IPsec-based access control is used during but the authentication phase and PaC is using an
   unspecified IP address in the keys are successfully derived all
   subsequent PANA messages MUST contain a MAC AVP.  The PANA-Bind-
   Request and authentication phase, the PANA-Bind-Answer message exchange is also used for
   binding device identifiers of ID
   reported by the PaC MUST be either 0.0.0.0 or 0::0. This device ID
   MUST be recorded as a temporary one by the PAA until the PaC obtains
   a valid one and informs the PAA to PAA. Eventually PaC MUST obtain an IP
   address, possibly by relying on the newly-created PANA SA.
   To achieve this, session
   [I-D.tschofenig-pana-bootstrap-rfc3118], in order to gain full access
   to the PANA-Bind-Request and network. PaC MUST update the PANA-Bind-Answer
   SHOULD contain a device identifier of registered on
   the PAA and from unspecified to the PaC,
   respectively, in valid IP address by initiating a Device-Id AVP.  The PaC MUST use
   PANA-Reauth-Request/PANA-Reauth-Answer exchange in which the same type IP
   address of
   device identifier as the PaC is contained in the PANA-Bind-Request message. Device-Id AVP.

4.8 Session Lifetime

   The PANA-Bind-Request message MAY also contain a Protection-Capability authentication phase determines the PANA session lifetime when
   the network access authorization succeeds. The Session-Lifetime AVP to indicate if link-layer or network-layer ciphering should
   MAY be
   initiated after PANA.  No link layer or network layer specific
   information is optionally included in the Protection-Capability AVP. When the
   information is preconfigured on the PANA-Bind-Request message to inform
   PaC and about the PAA valid lifetime of the PANA session. It MUST be ignored
   when included in other PANA messages. When there are multiple EAP
   authentication taking place, this AVP can SHOULD be
   omitted. It included after the
   final authentication.

   The lifetime is assumed a non-negotiable parameter that at least can be used by PaC to
   manage PANA-related state. PaC does not have to perform any actions
   when the lifetime expires, other than optionally purging local state.

   PAA is aware of SHOULD initiate EAP authentication before the security
   capabilities current session
   lifetime expires.

   PaC and PAA MAY optionally rely on lower-layer indications to
   expedite the detection of a disconnected peer. Availability and
   reliability of such indications depend on the specific access
   technologies. PANA peer can use PANA-Reauth-Request message to verify
   the access network. disconnection before taking an action.

   The PANA protocol does session lifetime parameter is not
   specify how the PANA SA and related to the Protection-Capability AVP will transmission of
   PANA-Reauth-Request messages. These messages can be used to provide per-packet protection for data traffic.

   PANA-Bind-Request and PANA-Bind-Answer messages MUST be
   retransmitted based on
   asynchronously verifying the retransmission rule described in Appendix
   A.

   PaC      PAA  Message(tseq,rseq)[AVPs]
   -------------------------------------------------
                 (continued from discovery and initial handshake phase)
      <-----     PANA-Auth-Request(x+1,y)[EAP{Request}]
      ----->     PANA-Auth-Answer(y+1,x+1)[EAP{Response}]
        .
        .
      <-----     PANA-Auth-Request (x+2,y+1)[EAP{Request}]
      ----->     PANA-Auth-Answer (y+2,x+2)[EAP{Response}]
      <-----     PANA-Bind-Request(x+3,y+2)                // F-flag
   set
                   [EAP{Success}, Device-Id, Protection-Cap., MAC]
      ----->     PANA-Bind-Answer(y+3,x+3)
                   [Device-Id, Protection-Cap., MAC]  // F-flag set

            Figure 4: Example Sequence in Authentication Phase

4.4 Re-authentication

   There are two types liveness of re-authentication supported by PANA. the peer and enabling
   mobility optimizations. The first type of re-authentication is based on EAP by entering an
   authentication phase.  In this case, some or all decision to send PANA-Reauth-Request
   message exchanges
   for discovery is taken locally and initial handshake phase MAY be omitted in does not require coordination between
   the
   following way. peers.

4.9 Mobility Handling

   When a PaC initiates EAP-based re-authentication, it
   sends a PANA-PAA-Discovery message wants to resume an ongoing PANA session after connecting
   to another link in the PAA.  If same access network, it MAY send the PAA already
   has an established unexpired
   PANA session for identifier in its PANA-Start-Answer message. In the PaC with
   absence of a device Session-Id AVP in this message, PAA MUST assume this is
   a fresh session and continue its normal execution.

   If PAA receives a session identifier
   that matches in the one extracted PANA-Start-Answer
   message, and it is configured to enable fast re-authentication, it
   SHOULD retrieve the PANA session attributes from the MAC header and/or IP header previous PAA of
   the PaC.  The mechanism required to determine the previous PAA of the PANA-PAA-Discover message, it sends a PANA-Auth-Request
   message with
   PaC by relying on the PANA session identifier for that is outside the scope of
   PANA session protocol. A possible solution is to start
   an authentication phase.  When embed the PAA initiates EAP-based re-
   authentication, it sends a PANA-Auth-Request message with identifier in
   the PANA session identifier for identifier. Furthermore, the PaC mechanism required to enter an authentication phase.  In
   both cases,
   retrieve the tseq and rseq values are inheritated session attributes from the previous (re-)authentication.  For any EAP-based re-authentication,
   if there is an established PANA SA, PANA-Auth-Request and PANA-Auth-
   Answer messages MAY be protected by adding a MAC AVP to each
   message.

   The second type of re-authentication PAA is based on a single protected
   message exchange without entering outside the authentication phase.
   PANA-Reauth-Request and PANA-Reauth-Answer messages are used
   scope of this protocol. Seamoby Context Transfer Protocol
   [I-D.ietf-seamoby-ctp] might be useful for this purpose.  If there is an established PANA SA, both the PaC and

   When the PAA are allowed to send a PANA-Reauth-Request message to the
   communicating peer whenever it needs to make sure the availability
   of the PANA SA on the peer and expect the peer is not configured to return a PANA-
   Reauth-Answer message.  Both PANA-Reauth-Request/ PANA-Reauth-Answer
   messages MUST be protected with a MAC AVP.

   Implementations MUST limit enable fast re-authentication, or
   can not retrieve the rate of performing re-authentication
   for both types of re-authentication.

   PaC      PAA     Message(tseq,rseq)[AVPs]
   ------------------------------------------------------
      ----->        PANA-Reauth-Request(q,p)[MAC]
      <-----        PANA-Reauth-Answer(p+1,q)[MAC]

   Figure 5: Example Sequence for PaC-initiated Re-authentication

   PaC      PAA     Message(tseq,rseq)[AVPs]
   ------------------------------------------------------
      <-----        PANA-Reauth-Request(p,q)[MAC]
      ----->        PANA-Reauth-Answer(q+1,p)[MAC]

   Figure 6: Example Sequence for PAA-initiated Re-authentication

4.5 Termination Phase

   A procedure for explicitly terminating a PANA session can be
   initiated either from PaC (i.e., disconnect indication) attributes, or from PAA the PANA session has
   already expired (i.e., session revocation).  The PANA-Termination-Request  and lifetime is zero), the
   PANA-Termination-Answer PAA MUST send
   the PANA-Auth-Request message exchanges are used for
   disconnect indication and with the new session revocation procedures.

   The reason for termination is indicated in identifier and let
   the Termination-Cause
   AVP. When there is an established PANA SA established between the
   PaC exchange take its usual course. This action will engage EAP
   authentication and the PAA, all messages exchanged during the termination phase
   MUST be protected with create a MAC AVP.  When fresh PANA session from scratch.

   In case the sender of new PAA retrieves the PANA-
   Termination-Request  receives a valid acknowledgment, all states
   maintained for on-going PANA session attributes
   from the previous PAA, the PANA session MUST be deleted immediately.

   PaC      PAA     Message(tseq,rseq)[AVPs]
   ------------------------------------------------------
      ----->        PANA-Termination-Request(q,p)[MAC]
      <-----        PANA-Termination-Answer(p+1,q)[MAC]

   Figure 7: Example Sequence for Session Termination

4.6 Illustration of continues with a Complete Message Sequence

   A complete PANA message sequence is illustrated in Figure 8. PANA-Reauth
   exchange.  The
   example assumes MAC AVP contained in the following scenario:

   - PaC multicasts PANA-PAA-Discover message

   - The ISNs used PANA-Reauth messages MUST be
   generated and verified by using the PAA and retrieved PANA SA attributes.
   This exchange MUST also include Session-Id AVP that contains the PaC are x
   newly assigned session identifier, and y, respectively.

   - Device-Id AVP. A single EAP sequence is used in authentication phase.

   - An EAP authentication method with a single round trip is used in
   the EAP sequence.

   - The EAP authentication method derives keys. The new PANA SA
   session is
   established created upon successful completion of this exchange. This
   session inherits only the session lifetime, protection capability,
   and MSK attributes from the previous session. Other attributes are
   generated based on the unique and fresh session key provided by
   the EAP method.

   - After PANA SA is established, all messages are integrity and
   replay protected with the MAC AVP.

   - Re-authentication based exchanges on the PANA-Reauth-Request/ PANA-Reauth-
   Answer exchange new link. While MSK
   stays the same, a new PANA_MAC_Key is performed.

   - The computed using the new
   parameters. Subsequent MAC-AVPs are processed using this new PANA session is terminated as SA.

4.10 Event Notification

   Upon detecting the need to authenticate a result client, EP can send a
   trigger message to the PAA on behalf of the PANA-
   Termination-Request indication from PaC. This can be one of
   the messages provided by the PAA-to-EP protocol, or, in the absence
   of such a facility, PANA-PAA_Discover can be used as well. This
   message MUST carry the device identifier of the PaC.

   PaC So that, the PAA  Message(tseq,rseq)[AVPs]
   -----------------------------------------------------
   // Discovery and initial handshake phase
      ----->     PANA-PAA-Discover (0,0)
      <-----
   can send the unsolicited PANA-Start-Request (x,0)[Cookie]
      ----->     PANA-Start-Request-Answer (y,x)[Cookie]

   // Authentication phase
      <-----     PANA-Auth-Request(x+1,y)[EAP]
      ----->     PANA-Auth-Answer(y+1,x+1)[EAP]
      <-----     PANA-Auth-Request(x+2,y+1)[EAP]
      ----->     PANA-Auth-Answer(y+2,x+2)[EAP]
      <-----     PANA-Bind-Request(x+3,y+2)        // F-flag set
                   [EAP, Device-Id, Data-Protection, MAC]

      ----->     PANA-Bind-Answer(y+3,x+3)         // F-flag set
                   [Device-Id, Data-Protection, MAC]

   // Re-authentication
      <-----     PANA-Reauth-Request (x+4,y+3)[MAC]
      ----->     PANA-Reauth-Answer (y+4,x+4)[MAC]

   // Termination phase
      ----->     PANA-Termination-Request(y+5,x+4)[MAC]
      <-----     PANA-Termination-Answer (x+5,y+5)[MAC]

                   Figure 8: A Complete Message Sequence

4.7 Device ID choice

   PaC has message directly to pick a device identifier the
   PaC.  If the link between the EP and PAA is not physically secured,
   this message sent from EP to provide for PAA MUST be cryptographically protected
   (e.g., by using IPsec).

4.11 PaC Implications

   o  PaC state machine. [TBD]

4.12 PAA Implications

   o  PAA state machine. [TBD]

5. PANA Security Association Establishment

   When PANA exchanges.
   In this version of the specification, device ID is considered to be
   fixed.  Future versions might enable changing it during a PANA
   session.

   A PaC will configure used over an IP address before PANA if it can. It might
   either have a pre-configured IP address, or have to obtain one via
   dynamic methods already established secure channel, such as DHCP
   physically secured wires or stateless address autoconfiguration.
   Dynamic methods may ciphered link-layers, we can reasonably
   assume that man-in-the-middle attack or may service theft is not succeed depending on the local
   security policy.  In networks possible
   [I-D.ietf-pana-threats-eval].

   Anywhere else where there is no secure channel prior to PANA, the PaCs need
   protocol needs to use PANA prior protect itself against such attacks. The device
   identifier that is used during the authentication needs to address configuration, EPs will detect be
   verified at the PaCs attempt end of the authentication to get IP
   address prevent service theft
   and help PAA to initiate authentication.

   Either an IP address or link-layer address DoS attacks. Additionally, a free loader should be used as prevented from
   spoofing data packets by using the device
   DI identifier of an already
   authorized legitimate client. Both of these requirements necessitate
   generation of a security association between the PaC and the PAA at any time.  The
   the end of the authentication. This can only case an IP address should be used as
   device ID is done when IPsec will be the
   authentication method used for protecting data traffic
   after initial authentication.  Any other time a link-layer address can be used by both PAA and PaC as device ID. It is assumed that PAA
   knows the security mechanisms being provided or required generate cryptographic keys. Use of
   secret keys can prevent attacks which would otherwise be very easy to
   launch by eavesdropping on and spoofing traffic over an insecure
   link.

   PANA relies on EAP and the
   access network (e.g., physical security, link-layer ciphers prior EAP methods to
   PANA, link-layer ciphers enabled after PANA, IPsec).  When IPsec provide a session key in
   order to establish a PANA security association. An example of such a
   method is
   the EAP-TLS [RFC2716], whereas EAP-MD5 [RFC2284] is an example
   of a method that cannot create such keying material. The choice of data ciphering, PAA should provide its IP address
   EAP method becomes important, as
   device ID, and expect already discussed in the PaC to provide its IP address if it has
   one.  In all other cases, link-layer addresses can be provided from
   both sides.

   When IPsec ciphering next
   section.

   This keying material is already used but the PaC uses an unspecified IP
   address in within PANA during the authentication phase, it MUST use its MAC address for final
   handshake. This handshake ensures that the device identifier until that is
   bound to the PaC at the end of the authentication process is configured with a specified
   IP address that is used for IPsec ciphering. Once such not
   coming from a specified
   IP address is configured, man-in-the-middle, but from the PaC MUST update legitimate PaC.
   Knowledge of the device identifier
   registered same keying material on both PaC and the PAA from helps
   prove this. The other use of the MAC address keying material will be discussed in
   Section 7 and Section 8.

6. Authentication Method Choice

   Authentication methods' capabilities and therefore applicability to
   various environments differ among them. Not all methods provide
   support for mutual authentication, key derivation or distribution,
   and DoS attack resiliency that are necessary for operating in
   insecure networks. Such networks might be susceptible to the IP address by
   initiating
   eavesdropping and spoofing, therefore a PANA-Reauth-Request/PANA-Reauth-Answer exchange in
   which the IP address of the PaC is contained in the Device-Id AVP
   contained in the PANA-Reauth-Request message sent from the PaC.

4.8 Refresh Interval Negotiation

   The stronger authentication phase also determines the PANA session lifetime
   when authorization succeeds. The Session-Lifetime AVP (to
   method needs to be
   defined, Code XXX) is used to determine the valid lifetime of PANA
   session. This AVP MUST NOT be included in any message other than prevent attacks on the
   PANA-Bind-Request client and PANA-Bind-Anser message. It MUST be ignored
   when received in other messages or the authorization result
   network.

   The authentication method choice is a
   failure.

   This AVP carries function of the maximum session lifetime offered by underlying
   security of the network
   when included in (e.g., physically secured, shared link,
   etc.). It is the PANA-Bind-Request sent by responsibility of the PAA. If it is
   omitted, or contains user and the value 0xFFFFFFFF, this means network operator
   to pick the session
   lifetime is infinity. This AVP right method for authentication. PANA carries EAP
   regardless of the requested session
   lifetime when it EAP method used. It is sent by outside the PaC. If requested session lifetime
   is greater than scope of PANA to
   mandate, recommend, or limit use of any authentication methods.  PANA
   cannot increase the offered lifetime, then strength of a weak authentication method to make
   it is ignored and the
   offered lifetime becomes the session lifetime. The requested
   lifetime becomes the session lifetime if suitable for an insecure environment. There are some EAP- based
   approaches to achieve this goal (see
   [I-D.josefsson-pppext-eap-tls-eap],[I-D.ietf-pppext-eap-ttls],[I-D.tschofenig-eap-ikev2]
   ). PANA can carry these EAP encapsulating methods but it is less than or equal to does not
   concern itself with how they achieve protection for the offered lifetime. The PaC MUST perform a weak methods
   (i.e., their EAP method payloads).

7. Filter Rule Installation

   PANA protocol provides client authentication (by
   sending a PANA-Auth-Request andnot a PANA-Reauth-Request) before the
   session lifetime expires. Failure to do so yields in PaC losing and authorization
   functionality for securing network access.

4.9 Mobility Handling

   If PaC wants to resume an ongoing PANA session after connecting to
   another link in The other component of a
   complete solution is the same access network, it control which ensures that only
   authenticated and authorized clients can send gain access to the unexpired network.
   PANA session id in its PANA-Start-Request message. In enables access control by identifying legitimate clients and
   generating filtering information for access control mechanisms.
   Getting this filtering information to the absence EPs (Enforcement Points)
   and performing filtering are outside the scope of
   session id AVP in this message, PAA PANA.

   Access control can assume this is a fresh
   session and assigns a new session ID be achieved by placing EPs in the first PANA-Auth-Request
   message.

   If PAA receives a session id in network for
   policing the PANA-Start-Request message, traffic flow. EPs should prevent data traffic from and
   it
   to any unauthorized client unless it's PANA traffic. When a client is configured
   authenticated and authorized, PAA should notify EP(s) and ask for
   changing filtering rules to enable fast re-authentication, allow traffic for a recently authorized
   client. There needs to be a protocol between PAA and EP(s) when these
   entities are not co-located. PANA Working Group will not be defining
   a new protocol for this interaction. Instead, it SHOULD
   retrieve the PANA SA from the previous PAA of the PaC. Determining
   the previous PAA will (preferably)
   identify one of the PaC by using the PANA session id is outside existing protocols that can fit the scope of this protocol. A possible solution is requirements.
   Possible candidates include but not limited to embed thePAA
   identifier into the message. Furthermore, the mechanism required COPS, SNMP, DIAMETER.
   This task is similar to
   retrieve the PANA SA from the previous PAA what MIDCOM Working Group is outside the scope trying to
   achieve, therefore some of
   PANA protocol. Seamoby Context Transfer Protocol [CTP] the MIDCOM's output might be useful here.

   If the PAA is not configured to enable fast re-authentication, or
   can not retrieve the PANA SA, or the PANA SA has expired, the PAA
   MUST send the PANA-Start-Request message with a new session id and
   let the PANA exchange take its usual course. Otherwise, PAA MUST
   continue the PANA session with a PANA_Reauth exchange (rather than
   PANA_Auth exchange which,

   EPs' location in most of the times, means full
   authentication). Device ID AVPs MUST network topology should be included in this exchange to
   bind the new DIs appropriate for
   performing access control functionality. The closest IP-capable
   access device to the PANA SA.

   TBD: This client devices is a proposal and requires further thoughts.

4.10 Event Notification

   Upon detecting the need to authenticate a client, EP can send a
   trigger message to the logical choice. PAA and
   EPs on behalf an access network should be aware of the PaC. This each other as this is
   necessary for access control. Generally this can be one of
   the messages provided achieved by
   manual configuration. Dynamic discovery is another possibility, but
   this is clearly outside the PAA-to-EP protocol, or, in the absence scope of such PANA.

   Filtering rules generally include device identifiers for a facility, PANA-PAA_Discover client,
   and also cryptographic keying material when needed. Such keys are
   needed when attackers can be used as well. This
   message MUST carry eavesdrop and spoof on the device identifier
   identifiers easily. They are used with link-layer or network-layer
   ciphering to provide additional protection. For issues regarding
   data-origin authentication see Section 8.

8. Data Traffic Protection

   Protecting data traffic of the PaC. So that, the
   PAA can send the unsolicited PANA-Start-Request  message directly authenticated and authorized clients from
   others is another component of providing a complete secure network
   access solution. Authentication, integrity and replay protection of
   data packets are needed to prevent spoofing when the PaC.  If the link between the EP and PAA underlying
   network is not physically
   secured, this message sent from EP to PAA MUST be cryptographically
   protected (e.g., by using IPsec).

4.11 PaC Implications

   - PaC state machine. [TBD]

4.12 PAA Implications

   - PAA state machine. [TBD]

5  PANA Security Association Establishment secured. Encryption is needed when
   eavesdropping is a concern in the network.

   When PANA the network is used over an already established secure channel, such
   as physically secured wires or ciphered link-layers, we can
   reasonably assume that man-in-the-middle attack secured, or service theft is
   not possible [THREATS].

   Anywhere else where there the link-layer ciphering
   is no secure channel already enabled prior to PANA, the
   protocol needs to protect itself against such attacks. data traffic protection is already
   in place. In other cases, enabling link-layer ciphering or network-
   layer ciphering might rely on PANA authentication. The device
   identifier user and
   network have to make sure an appropriate EAP method that can generate
   required keying materials is used during used. Once the authentication keying material is
   available, it needs to be
   verified at the end of the authentication provided to prevent service theft
   and DoS attacks. Additionally, a free loader should the EP(s) for use with
   ciphering.

   Network-layer ciphering, i.e., IPsec, can be prevented
   from spoofing used when data packets traffic
   protection is required but link-layer ciphering capability is not
   available. Note that a simple shared secret generated by using the device identifier of an
   already authorized legitimate client. Both of these requirements
   necessitate generation of a security association between the
   PaC EAP
   method is not readily usable by IPsec for authentication and the PAA at the end
   encryption of IP packets. Fresh and unique session key derived from
   the authentication. This can only be
   done when the authentication EAP method used can generate cryptographic
   keys. Use of is still insufficient to produce an IPsec SA since
   both traffic selectors and other IPsec SA parameters are missing.
   The shared secret keys can prevent attacks which would otherwise be very easy used in conjunction with a key management
   protocol like IKE [RFC2409] to launch by eavesdropping on and spoofing traffic over
   an insecure link.

   PANA relies on EAP and turn a simple shared secret into the
   required IPsec SA. The details of this mechanism is outside the scope
   of PANA protocol [I-D.ietf-pana-ipsec], PANA provides bootstrapping
   functionality for such a mechanism by carrying EAP methods to provide that can
   generate initial keying material.

   Using network-layer ciphers should be regarded as a session key substitute for
   link-layer ciphers when the latter is not available. IKE involves
   several message exchanges which can incur additional delay in
   order to establish getting
   basic IP connectivity for a PANA security association. An example of such mobile device. Such a
   method latency is EAP-TLS [EAPTLS], whereas EAP-MD5 [RFC2284]
   inevitable when there is an example
   of a method that cannot create such keying material. The choice no other alternative and this level of
   EAP method becomes important, as already discussed in the next
   section.

   This keying material
   protection is already required. Network-layer ciphering can also be used within PANA during the final
   handshake. This handshake ensures that in
   addition to link-layer ciphering if the device identifier that is
   bound added benefits outweigh its
   cost to the PaC at user and the end network.

9. Message Formats

   This section defines message formats for PANA protocol.

9.1 PANA Header

   A summary of the authentication process PANA header format is not
   coming from a man-in-the-middle, but from the legitimate PaC.
   Knowledge of the same keying material on both PaC and the PAA helps
   prove this. shown below.  The other use of the keying material will be discussed fields are
   transmitted in sections network byte order.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 and 8. 8 9 0 1 2 3 4 5 6  Authentication Method Choice

   Authentication methods' capabilities and therefore applicability to
   various environments differ among them. Not all methods provide
   support for mutual authentication, key derivation or distribution,
   and DoS attack resiliency that are necessary for operating in
   insecure networks. Such networks might 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Version    |                 Message Length                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Flags      |                 Message Type                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Transmitted Sequence Number                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Received Sequence Number                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  AVPs ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-

   Version

      This Version field MUST be susceptible to
   eavesdropping and spoofing, therefore a stronger authentication
   method needs set to be used 1 to prevent attacks on the client and
   the network. indicate PANA Version 1.

   Message Length

      The authentication method choice is a function of the underlying
   security of the network (e.g., physically secured, shared link,
   etc.). It Message Length field is the responsibility of the user three octets and indicates the network operator
   to pick length
      of the right method for authentication. PANA carries EAP
   regardless of message including the EAP method used. It header fields.

   Flags

      The Flags field is outside eight bits.  The following bits are assigned:

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |R r r r S r r r|
      +-+-+-+-+-+-+-+-+

      R(equest)

         If set, the scope of PANA
   to mandate, recommend, or limit use of any authentication methods.
   PANA cannot increase message is a request. If cleared, the strength of message is an
         answer.

      S(eparate)

         When the S-flag is set in a weak authentication method to
   make PANA-Start-Request message it suitable for an insecure environment. There are some EAP-
   based approaches
         indicates that PAA is willing to achieve this goal (see [PEAP],[TTLS],[EAP-
   IKEv2]). PANA can carry these offer separate EAP encapsulating methods but it does
   not concern itself with how they achieve protection
         authentication for NAP and ISP.  When the weak
   methods (i.e., their S-flag is set in a
         PANA-Start-Answer message it indicates that PaC accepts on
         performing separate EAP method payloads).

7  Filter Rule Installation

   PANA protocol provides client authentication for NAP and authorization
   functionality ISP."

      r(eserved)

         these flag bits are reserved for securing network access. future use, and MUST be set to
         zero, and ignored by the receiver.

   Message Type

      The other component of a
   complete solution Message Type field is the access control which ensures that only
   authenticated three octets, and authorized clients can gain access is used in order to
      communicate the network.
   PANA enables access control message type with the message. The 24-bit address
      space is managed by identifying legitimate clients and
   generating filtering information IANA [ianaweb].  PANA uses its own address
      space for access control mechanisms.
   Getting this filtering information to field.

   Transmitted Sequence Number

      The Transmitted Sequence Number field contains the EPs (Enforcement Points)
   and performing filtering are outside monotonically
      increasing 32 bit sequence number that the scope of PANA.

   Access control can be achieved by placing EPs in message sender
      increments every time a new PANA message is sent.

   Received Sequence Number

      The Received Sequence Number field contains the network for
   policing 32 bit transmitted
      sequence number that the traffic flow. EPs should prevent data traffic message sender has last received from and
   to any unauthorized client unless it's PANA traffic. When a client
   is authenticated and authorized, PAA should notify EP(s) and ask for
   changing filtering rules to allow traffic for its
      peer.

   AVPs

      AVPs are a recently authorized
   client. There needs method of encapsulating information relevant to be a protocol between PAA and EP(s) when
   these entities are not co-located. the
      PANA Working Group will not message.  See section Section 9.2 for more information on
      AVPs.

9.2 AVP Header

   Each AVP of type OctetString MUST be
   defining padded to align on a new protocol for this interaction. Instead, it will
   (preferably) identify one 32-bit
   boundary, while other AVP types align naturally. A number of
   zero-valued bytes are added to the existing protocols that can fit end of the
   requirements. Possible candidates include but not limited to COPS,
   SNMP, DIAMETER. This task is similar to what MIDCOM Working Group AVP Data field till a
   word boundary is
   trying to achieve, therefore some reached. The length of the MIDCOM's output might be
   useful here.

   EPs location padding is not reflected
   in the network topology should be appropriate for
   performing access control functionality. AVP Length field [RFC3588].

   The closest IP-capable
   access device to the client devices is fields in the logical choice. PAA and
   EPs on an access network should AVP header MUST be aware sent in network byte order. The
   format of each other as this is
   necessary the header is:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           AVP Code                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   AVP Flags   |                  AVP Length                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Vendor-Id (opt)                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Data ...
      +-+-+-+-+-+-+-+-+

   AVP Code

      The AVP Code, combined with the Vendor-Id field, identifies the
      attribute uniquely. AVP numbers are allocated by IANA [ianaweb].
      PANA uses its own address space for access control. Generally this can be achieved by
   manual configuration. Dynamic discovery field although some of
      the AVP formats are borrowed from Diameter protocol [RFC3588].

   AVP Flags

      The AVP Flags field is eight bits.  The following bits are
      assigned:

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |V M r r r r r r|
      +-+-+-+-+-+-+-+-+

      M(andatory)

         The 'M' Bit, known as the Mandatory bit, indicates whether
         support of the AVP is another possibility, but
   this required.

      V(endor)

         The 'V' bit, known as the Vendor-Specific bit, indicates
         whether the optional Vendor-Id field is clearly outside present in the scope of PANA.

   Filtering rules generally include device identifiers for a client,
   and also cryptographic keying material when needed. Such keys AVP
         header.

      r(eserved)

         these flag bits are
   needed when attackers can eavesdrop reserved for future use, and spoof on the device
   identifiers easily. They are used with link-layer or network-layer
   ciphering MUST be set to provide additional protection. For issues regarding
   data-origin authentication see Section 8.

8  Data Traffic Protection

   Protecting data traffic of authenticated
         zero, and authorized clients from
   others ignored by the receiver.

   AVP Length

      The AVP Length field is another component of providing a complete secure network
   access solution. Authentication, integrity three octets, and replay protection of
   data packets are needed to prevent spoofing when indicates the underlying
   network is not physically secured. Encryption is needed when
   eavesdropping is a concern number of
      octets in this AVP including the network.

   When the network is physically secured, or AVP Code, AVP Length, AVP Flags,
      and the link-layer ciphering
   is already enabled prior to PANA, AVP data traffic protection is already
   in place. In other cases, enabling link-layer ciphering or network-
   layer ciphering might rely on PANA authentication.

   Vendor-Id

      The user and
   network have to make sure an appropriate EAP method that can
   generate required keying materials Vendor-Id field is used. Once present if the keying material 'V' bit is available, it needs to be provided to set in the AVP
      Flags field. The optional four-octet Vendor-Id field contains the EP(s) for
      uniquely assigned id value, encoded in network byte order.  Any
      vendor wishing to implement a vendor-specific PANA AVP MUST use
      their own Vendor-Id along with
   ciphering.

   Network-layer ciphering, i.e., IPsec, can be used when data traffic
   protection is required but link-layer ciphering capability is not
   available. Note their privately managed AVP address
      space, guaranteeing that a simple shared secret generated by an EAP
   method is they will not readily usable by IPsec for authentication collide with any other
      vendor's vendor-specific AVP(s), nor with future IETF
      applications.

   Data

      The Data field is zero or more octets and
   encryption of IP packets. Fresh contains information
      specific to the Attribute. The format and unique session key derived from length of the EAP method Data field
      is still insufficient to produce an IPsec SA since
   both traffic selectors determined by the AVP Code and other IPsec SA parameters are missing.
   The shared secret AVP Length fields.

9.3 PANA Messages

   Figure 9 lists all PANA messages defined in this document

                 Message       Direction: PaC---PAA
                 ----------------------------------
                 PANA-PAA-Discover        -------->

                 PANA-Start-Request       <--------
                 PANA-Start-Answer        -------->

                 PANA-Auth-Request        <--------
                 PANA-Auth-Answer         -------->

                 PANA-Bind-Request        <--------
                 PANA-Bind-Answer         -------->

                 PANA-Reauth-Request      <------->
                 PANA-Reauth-Answer       <------->

                 PANA-Termination-Request <------->
                 PANA-Termination-Answer  <------->

                 PANA-Error               <------->
                    Figure 9: PANA Message Overview

   Additionally the EP can be used also send a PANA-PAA-Discover message to the
   PAA.

9.3.1 Message Specifications

   Every PANA message MUST include a corresponding ABNF [RFC2234]
   specification found in conjunction with [RFC3588].  Note that PANA messages have a key management
   protocol like IKE [RFC2409]
   different header format compared to Diameter.

   Example:

      message ::= < PANA-Header: <Message type>, [REQ] [SEP] >
                                    * [ AVP ]

9.3.2 PANA-PAA-Discover (PDI)

   The PANA-PAA-Discover (PDI) message is used to turn a simple shared secret into discover the
   required IPsec SA. The details address
   of PAA(s). Both sequence numbers in this mechanism is outside message are set to zero (0).
   If the
   scope of PANA protocol, EP detects a new PaC and sends the PANA-PAA-Discover to the
   PAA, it can be outlined in a separate
   Internet-Draft. PANA provides bootstrapping functionality for such a
   mechanism MUST include the Device-Id of the PaC.

         PANA-PAA-Discover ::= < PANA-Header: 1 >
                   0*1 < Device-Id >
                    *  [ AVP ]

9.3.3 PANA-Start-Request (PSR)

   PANA-Start-Request (PSR) is sent by carrying EAP methods that can generate initial keying
   material.

   Using network-layer ciphers should be regarded as a substitute for
   link-layer ciphers when the latter PAA to the PaC. The PAA sets
   the transmission sequence number to an initial random value.  The
   received sequence number is not available. IKE involves
   several message exchanges which can incur additional delay set to zero (0).

         PANA-Start-Request ::= < PANA-Header: 2, REQ [SEP] >
                       [ Cookie ]
                       [ NAP-Information ]
                    *  [ ISP-Information ]
                    *  [ AVP ]

9.3.4 PANA-Start-Answer (PSA)

   PANA-Start-Answer (PSA) is sent by the PaC to the PAA in
   getting basic IP connectivity for a mobile device. Such response to
   a latency is
   inevitable when there PANA-Start-Request message.  The PANA_start message transmission
   sequence number field is no other alternative and this level of
   protection copied to the received sequence number
   field.  The transmission sequence number is required. Network-layer ciphering can also be used in
   addition set to link-layer ciphering if initial random
   value.

         PANA-Start-Answer ::= < PANA-Header: 2 [SEP] >
                       [ Cookie ]
                       [ ISP-Information ]
                    *  [ AVP ]

9.3.5 PANA-Auth-Request (PAR)

   PANA-Auth-Request (PAR) is sent by the added benefits outweigh its
   cost PAA to the user PaC.

         PANA-Auth-Request ::= < PANA-Header: 3, REQ >
                       < Session-Id >
                       < EAP-Payload >
                   0*1 [ NAP-Information ]
                   0*1 [ ISP-Information ]
                    *  [ AVP ]
                   0*1 < MAC >

   (Both NAP-Information and the network.

9  Message Formats

   This section defines message formats for PANA protocol.

9.1 PANA Header

   A summary of the PANA header format is shown below.  The fields are
   transmitted in network byte order.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Version    |                 Message Length                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Flags      |                 Message Type                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Transmitted Sequence Number                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Received Sequence Number                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  AVPs ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-

   Version

     This Version field ISP-Information MUST NOT be set included at the
   same time)"

9.3.6 PANA-Auth-Answer (PAN)

   PANA-Auth-Answer (PAN) is sent by the PaC to 1 the PAA in response to indicate PANA Version 1.

   Message Length

     The Message Length field a
   PANA-Auth-Request message.

         PANA-Auth-Answer ::= < PANA-Header: 3 >
                       < Session-Id >
                       < EAP-Payload >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.7 PANA-Bind-Request (PBR)

   PANA-Bind-Request (PBR) is three octets and indicates sent by the
     length of PAA to the PaC.

         PANA-Bind-Request ::= < PANA-Header: 4, REQ >
                       < Session-Id >
                       < Device-Id >
                       { EAP-Payload }
                       { Result-Code }
                       [ Session-Lifetime ]
                       [ Protection-Capability ]
                    *  [ AVP ]
                   0*1 < MAC >

9.3.8 PANA-Bind-Answer (PBA)

   PANA-Bind-Answer (PBA) is sent by the PANA message including PaC to the header fields.

   Flags

     The Flags field is eight bits.  The following bits are assigned:

     0 1 2 3 PAA in response to a
   PANA-Result-Request message.

         PANA-Bind-Answer ::= < PANA-Header: 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |R r r r F r r r|
    +-+-+-+-+-+-+-+-+
       R(equest)

                   - If set, >
                       < Session-Id >
                       < Device-Id >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.9 PANA-Reauth-Request (PRAR)

   PANA-Reauth-Request (PRAR) is either sent by the message PaC or the PAA.

         PANA-Reauth-Request ::= < PANA-Header: 5, REQ >
                       < Session-Id >
                       < Device-Id >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.10 PANA-Reauth-Answer (PRAA)

   PANA-Reauth-Answer (PRAA) is sent in response to a request. If cleared,
   PANA-Reauth-Request.

         PANA-Reauth-Answer ::= < PANA-Header: 5 >
                       < Session-Id >
                       < Device-Id >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.11 PANA-Termination-Request (PTR)

   PANA-Termination-Request (PTR) is sent either by the message PaC or the PAA.

         PANA-Termination-Request ::= < PANA-Header: 6, REQ >
                       < Session-Id >
                       < Termination-Cause >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.12 PANA-Termination-Answer (PTA)

   PANA-Termination-Answer (PTA) is an answer.

       F(inish)
                   - F-flag in sent either by the PANA header indicates if this  was PaC or the final authentication from sender's
                     perspective.  If PAA enables two separate
                     authentication, it should not set F-flag in
   response to PANA-Termination-Request.

         PANA-Termination-Answer ::= < PANA-Header: 6 >
                       < Session-Id >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.13 PANA-Error (PER)

   PANA-Error is sent either by the PaC or the PAA.

         PANA-Error ::= < PANA-Header: 7 >
                        < Session-Id >
                        < Result-Code >
                        { Failed-AVP }
                     *  [ AVP ]
                    0*1 < MAC >

9.4 AVPs in PANA

   Some of the
                     PANA-Bind-Request message after the first EAP
                     method.

       r(eserved)

                   - these flag bits used AVPs are reserved for future use,
                     and MUST be set to zero, and ignored by the
                     receiver.

   Message Type

     The Message Type field is three octets, defined in this document and is used some of them
   are defined in order other documents like [RFC3588]. PANA proposes to
     communicate use
   the message type same name space with the message. Diameter spec. For temporary allocation,
   PANA uses AVP type numbers starting from 1024.

9.4.1 MAC AVP

   The 24-bit
     address first octet (8 bits) of the MAC (Code 1024) AVP data contains the
   MAC algorithm type. Rest of the AVP data payload contains the MAC
   encoded in network byte order. The Algorithm 8 bit name space is
   managed by IANA [IANAWEB].

   Transmitted Sequence Number [ianaweb]. The Transmitted Sequence Number field contains the monotonically
     increasing 32 bit sequence number that AVP length varies depending on the message sender
     increments every time a new packet
   used algorithm.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Algorithm   |           MAC...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Algorithm

         1              HMAC-MD5 (16 bytes)
         2              HMAC-SHA1 (20 bytes)
   MAC

      The Message Authentication Code is sent.

   Received Sequence Number encoded in network byte order.

9.4.2 Device-Id AVP

   The Received Sequence Number field first octet (8 bits) of the Device-Id (Code 1025) AVP data
   contains the 32 bit
     transmitted sequence number that device type. Rest of the peer has last received.

   AVPs

     AVPs are a method AVP data payload contains the
   device data.  The content and format of encapsulating information relevant data (including byte and bit
   ordering) for L2_ADDRESS is expected to the
     PANA message.  See section 9.2 be specified in specific
   documents that describe how IP operates over different link-layers.
   For instance, [RFC2464].

            RESERVED                          0
            IPV4_ADDRESS                      1
            IPV6_ADDRESS                      2
            L2_ADDRESS                        3

   For type 1 (IPv4 address), data size is 32 bits and for more information on AVPs.

9.2 AVP Header type 2 (IPv6
   address), data size is 128 bits.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           AVP Code     Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+           Data...                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9.4.3 Session-Id AVP Flags   |

   Session-Id AVP Length                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Vendor-Id (opt)                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Data ...
      +-+-+-+-+-+-+-+-+ (Code 1026) has an opaque data field, which is
   assigned by the PAA. All messages pertaining to a specific PANA
   Session MUST include only one Session-Id AVP and the same value MUST
   be used throughout the lifetime of a session.  When present, the
   Session-Id SHOULD appear immediately following the PANA header.

   The Session-Id MUST be globally and eternally unique, as it is meant
   to identify a PANA Session without reference to any other
   information, and may be needed to correlate historical authentication
   information with accounting information.

   The Session-Id AVP MAY use Diameter [RFC3588] message formatting. In
   this case the AVP code is 263.

9.4.4 Cookie AVP

   The Cookie AVP (Code 1027) is of type OctetString. The data is opaque
   and the exact content is outside the scope of this protocol.

9.4.5 Protection-Capability AVP

   The Protection-Capability AVP (Code 1028) is of type Unsigned32.  The
   AVP data is used as a collection of flags for different data
   protection capability indications. Below is a list of specified data
   protection capabilities:

         0          UNKNOWN
         1          L2_PROTECTION
         2          IPSEC_PROTECTION

9.4.6 Termination-Cause AVP Code

   The Termination-Cause AVP Code, combined with (Code 1029) is of type of type Enumerated,
   and is used to indicate the Vendor-Id field, identifies reason why a session was terminated on
   the
      attribute uniquely. AVP numbers are allocated by IANA [IANAWEB].

   AVP Flags access device.  The AVP Flags field data is eight bits. used as a collection of flags The
   following bits Termination-Cause AVP defined in [RFC3588] are
      assigned:

       0 used for
   PANA.

   LOGOUT                   1 2 3  (PaC -> PAA)

      The client initiated a disconnect

   ADMINISTRATIVE           4 5 6 7
      +-+-+-+-+-+-+-+-+
      |V M r r r r r r|
      +-+-+-+-+-+-+-+-+

         M(andatory)

                   -  (PAA -> Pac)

      The 'M' Bit, known client was not granted access, or was disconnected, due to
      administrative reasons, such as the Mandatory bit,
                     indicates whether support receipt of the AVP is
                     required.

         V(endor)

                   - a
      Abort-Session-Request message.

   SESSION_TIMEOUT          8  (PAA -> PaC)

      The 'V' bit, known as the Vendor-Specific bit,
                     indicates whether the optional Vendor-Id field
                     is present in the AVP header.

         r(eserved)

                   - these flag bits are reserved for future use,
                     and MUST be set to zero, session has timed out, and ignored by the
                     receiver. service has been terminated.

9.4.7 Result-Code AVP Length

   The Result-Code AVP Length field (AVP Code 1030) is three octets, of type Unsigned32 and
   indicates the number
      of octets in this AVP including the AVP Code, AVP Length, whether an EAP authentication was completed successfully or
   whether an error occurred.  Here are Result-Code AVP
      Flags, values taken
   from [RFC3588] and adapted for PANA.

9.4.7.1 Authentication Results Codes

   These result code values inform the PaC about the EAP authentication
   method success or failure.

   PANA_SUCCESS                            2001

      The EAP method authentication was successful (EAP-Success).

   PANA_AUTHENTICATION_REJECTED            4001

      The authentication process for the client failed (EAP-Failure).

   PANA_AUTHORIZATION_REJECTED             5003

      A request was received for which the AVP data.

   Vendor-Id

      The Vendor-Id field is present client could not be
      authorized.  This error could occur if the 'V' bit service requested is set in
      not permitted to the AVP
      Flags field. The optional four-octet Vendor-Id field contains client.

9.4.7.2 Protocol Error Result Codes

   Protocol error result code values.

   PANA_MESSAGE_UNSUPPORTED                3001

      Error code from PAA to PaC or from PaC to PAA. Message type not
      recognized or supported.

   PANA_UNABLE_TO_DELIVER                  3002

      Error code from PAA to PaC.  PAA was unable to deliver the uniquely assigned id value, encoded EAP
      payload to the authentication server.

   PANA_INVALID_HDR_BITS                   3008

      Error code from PAA to PaC or from PaC to PAA.  A message was
      received whose bits in network byte order.
      Any vendor wishing the PANA header were either set to an
      invalid combination, or to implement a vendor-specific PANA AVP MUST
      use their own Vendor-Id along with their privately managed AVP
      address space, guaranteeing value that they will not collide with any
      other vendor's vendor-specific AVP(s), nor with future IETF
      applications.

   Data

      The Data field is zero inconsistent with the
      message type's definition.

   PANA_INVALID_AVP_BITS                   3009

      Error code from PAA to PaC or more octets and contains information
      specific from PaC to the Attribute. The format and length of the Data
      field PAA.  A message was
      received that included an AVP whose flag bits are set to an
      unrecognized value, or that is determined by inconsistent with the AVP Code and AVP Length fields.

9.3 PANA Messages

   Figure 9lists all PANA messages defined in this document
      Message       Direction: PaC---PAA
      ----------------------------------
      PANA-PAA-Discover        -------->

      PANA-Start-Request       <--------
      PANA-Start-Answer        -------->

      PANA-Auth-Request        <--------
      PANA-Auth-Answer         -------->

      PANA-Bind-Request        <--------
      PANA-Bind-Answer         -------->

      PANA-Reauth-Request      <------->
      PANA-Reauth-Answer       <------->

      PANA-Termination-Request <------->
      PANA-Termination-Answer  <------->

      PANA-Error               <------->

                      Figure 9: AVP's
      definition.

   PANA_AVP_UNSUPPORTED                    5001

      Error code from PAA to PaC or from PaC to PAA.  The received
      message contained an AVP that is not recognized or supported and
      was marked with the Mandatory bit.  A PANA Message Overview

   Additionally message with this error
      MUST contain one or more Failed-AVP AVP containing the EP can also send a PANA-PAA-Discover AVPs that
      caused the failure.

   PANA_UNKNOWN_SESSION_ID                 5002

      Error code from PAA to PaC or from PaC to PAA.  The message
      contained an unknown Session-Id.  PAA MUST NOT send this error
      result code value to PaC if PaC sent an unknown Session-Id in the
      PANA-Start-Answer message (session resumption).

   PANA_INVALID_AVP_VALUE                  5004

      Error code from PAA to PaC or from PaC to PAA.

9.3.1  Message specifications

   Every  The message
      contained an AVP with an invalid value in its data portion.  A
      PANA message indicating this error MUST include the offending AVPs
      within a corresponding ABNF
   [RFC2234] specification found in [DIAMETER].  Note that PANA
   messages have a different header format compared Failed-AVP AVP.

   PANA_MISSING_AVP                        5005

      Error code from PAA to Diameter.

   Example:

   message ::= < PANA-Header: <Message type>,
                               [REQ], [FIN]
                               * [ AVP ]

9.3.2 PANA-PAA-Discover (PDI) PaC or from PaC to PAA.  The PANA-PAA-Discover (PDI) message did
      not contain an AVP that is used to discover required by the address
   of PAA(s). Both sequence numbers in this message are set to zero
   (0). type
      definition.  If this value is sent in the EP detects Result-Code AVP, a new PaC and sends the PANA-PAA-Discover to
      Failed-AVP AVP SHOULD be included in the PAA, it message.  The Failed-AVP
      AVP MUST include contain an example of the Device-Id missing AVP complete with the
      Vendor-Id if applicable.  The value field of the PaC.

      PANA-PAA-Discover ::= < PANA-Header: 1 >
                 0*1 < Device-Id >
                  * [ missing AVP ]

9.3.3 PANA-Start-Request (PSR)

   PANA-Start-Request (PSR) is sent by
      should be of correct minimum length and contain zeroes.

   PANA_RESOURCES_EXCEEDED                 5006

      Error code from PAA to PaC.  A message was received that cannot be
      authorized because the client has already expended allowed
      resources.  An example of this error condition is a client that is
      restricted to one PANA session and attempts to establish a second
      session.

   PANA_CONTRADICTING_AVPS                 5007

      Error code from PAA to the PaC.  The PAA sets has detected AVPs in the transmission sequence number to an initial random value.  The
   received sequence number
      message that contradicted each other, and is set not willing to zero (0).

      PANA-Start-Request ::= < PANA-Header: 2, REQ >
                    [ Cookie ]
                  * [ AVP ]

9.3.4 PANA-Start-Answer (PSA)

   PANA-Start-Answer (PSA) is sent by the PaC
      provide service to the client. One or more Failed-AVP AVPs MUST be
      present, containing the AVPs that contradicted each other.

   PANA_AVP_NOT_ALLOWED                    5008

      Error code from PAA in response to
   a PANA-Start-Request message.  The PANA_start message transmission
   sequence number field is copied PaC or from PaC to the PAA.  A message was
      received sequence number
   field. with an AVP that MUST NOT be present.  The
   transmission sequence number is set to initial random value.

      PANA-Start-Answer ::= < PANA-Header: 3 >
                    [ Cookie ]
                  * [ Failed-AVP AVP ]

9.3.5 PANA-Auth-Request (PAR)

   PANA-Auth-Request (PAR) is sent by
      MUST be included and contain a copy of the offending AVP.

   PANA_AVP_OCCURS_TOO_MANY_TIMES          5009

      Error code from PAA to PaC or from PaC to PAA.  A message was
      received that included an AVP that appeared more often than
      permitted in the PaC.

      PANA-Auth-Request ::= < PANA-Header: 4, REQ >
                    < Session-Id >
                    < EAP-Payload >
                  * [ message definition.  The Failed-AVP AVP ]
                0*1 < MAC >

9.3.6 PANA-Auth-Answer (PAN)

   PANA-Auth-Answer (PAN) MUST be
      included and contain a copy of the first instance of the offending
      AVP that exceeded the maximum number of occurrences.

   PANA_UNSUPPORTED_VERSION                5011

      Error code from PAA to PaC or from PaC to PAA.  This error is
      returned when a message was received, whose version number is sent by the
      unsupported.

   PANA_INVALID_AVP_LENGTH                 5014

      Error code from PAA to PaC or from PaC to PAA.  The message
      contained an AVP with an invalid length. The PANA-Error message
      indicating this error MUST include the offending AVPs within a
      Failed-AVP AVP.

   PANA_INVALID_MESSAGE_LENGTH             5015

      Error code from PAA in response to PaC or from PaC to PAA.  This error is
      returned when a PANA-Auth-Request message.

      PANA-Auth-Answer ::= < PANA-Header: 5 >
                    < Session-Id >
                    < message is received with an invalid message
      length.

9.4.8 EAP-Payload >
                  * [ AVP ]
                0*1 < MAC >

9.3.7 PANA-Bind-Request (PBR)

   PANA-Bind-Request (PBR)

   The EAP-Payload AVP (AVP Code 1031) is sent by the PAA of type OctetString and is
   used to encapsulate the PaC.

      PANA-Bind-Request ::= < PANA-Header: 6, REQ, [FIN] >
                    < Session-Id >
                    < Device-Id >
                    { EAP-Payload }
                    { Result-Code }
                    [ Protection-Capability ]
                  * [ actual EAP packet that is being exchanged
   between the EAP peer and the EAP authenticator.

9.4.9 Session-Lifetime AVP ]
                0*1 < MAC >

9.3.8 PANA-Bind-Answer (PBA)

   PANA-Bind-Answer (PBA)

   The Session-Lifetime AVP (Code 1032) data is sent by of type Unsigned32. It
   contains the PaC to number of seconds remaining before the PAA current session
   is considered expired.

9.4.10 Failed-AVP AVP

   The Failed-AVP AVP (AVP Code 1033) is of type Grouped and provides
   debugging information in response to cases where a PANA-Result-Request message.

      PANA-Bind-Answer ::= < PANA-Header: 7, [FIN] >
                    < Session-Id >
                 < Device-Id >
                  * [ AVP ]
                0*1 < MAC >

9.3.9 PANA-Reauth-Request (PRAR)

   PANA-Reauth-Request (PRAR) request is either sent by the PaC rejected or not
   fully processed due to erroneous information in a specific AVP.  The
   format of the PAA.

      PANA-Reauth-Request ::= < PANA-Header: 8, REQ >
                    < Session-Id >
                 < Device-Id >
                  * [ Failed-AVP AVP ]
                0*1 < MAC >

9.3.10    PANA-Reauth-Answer (PRAA)

   PANA-Reauth-Answer (PRAA) is sent defined in response to a
   PANA-Reauth-Request.

      PANA-Reauth-Answer ::= < PANA-Header: 9 >
                    < Session-Id >
                    < Device-Id >
                  * [ [RFC3588].

9.4.11 NAP-Information AVP ]
                0*1 < MAC >

9.3.11    PANA-Termination-Request (PTR)

   PANA-Termination-Request (PTR)

   The NAP-Information AVP (AVP Code: 1034) is sent either by the PaC of type Grouped, and
   contains zero or one Provider-Identifier AVP which carries the PAA.

      PANA-Termination-Request
   identifier of the NAP and one Provider-Name AVP which carries the
   name of the NAP. Its Data field has the following ABNF grammar:

         NAP-Information ::= < PANA-Header: 10, REQ >
                   < Session-Id >
                   < Termination-Cause AVP Header: 1034 >
                    0*1 { Provider-Identifier }
                        { Provider-Name }
                     *  [ AVP ]
               0*1 < MAC >

9.3.12    PANA-Termination-Answer (PTA)

   PANA-Termination-Answer (PTA)

9.4.12 ISP-Information AVP

   The ISP-Information AVP (AVP Code: 1035) is sent either by the PaC of type Grouped, and
   contains zero or one Provider-Identifier AVP which carries the PAA
   in response to PANA-Termination-Request.

      PANA-Termination-Answer
   identifier of the ISP and one Provider-Name AVP which carries the
   name of the ISP.  Its Data field has the following ABNF grammar:

         ISP-Information ::= < PANA-Header: 11 >
                   < Session-Id AVP Header: 1035 >
                    0*1 { Provider-Identifier }
                        { Provider-Name }
                     *  [ AVP ]
               0*1 < MAC >

9.3.13    PANA-Error

   PANA-Error

9.4.13 Provider-Identifier AVP

   The Provider-Identifier AVP (AVP Code: 1036) is sent either by the PaC or the PAA.

   TBD

9.4 AVPs of type Unsigned32,
   and contains an IANA assigned "SMI Network Management Private
   Enterprise Codes" [ianaweb] value, encoded in PANA

   Some network byte order.

9.4.14 Provider-Name AVP

   The Provider-Name AVP (AVP Code: 1037) is of type UTF8String, and
   contains the UTF8-encoded name of the used provider.

9.5 AVP Occurrence Table

   The following tables lists the AVPs are defined used in this document document, and some of them
   are defined
   specifies in other documents like [DIAMETER]. PANA proposes to
   use the same name space with the Diameter spec. For temporary
   allocation, which PANA messages they MAY, or MAY NOT be present.

   The table uses AVP type numbers starting from 1024.

9.4.1 MAC AVP the following symbols:

   0     The first octet (8 bits) AVP MUST NOT be present in the message.

   0+    Zero or more instances of the MAC (Code 1024) AVP data contains MAY be present in the MAC algorithm type. Rest
         message.

   0-1   Zero or one instance of the AVP data payload contains the
   MAC encoded MAY be present in network byte order. The Algorithm 8 bit name space the message.
         It is managed by IANA [IANAWEB]. The considered an error if there are more than one instance
         of the AVP.

   1     One instance of the AVP length varies depending on MUST be present in the used algorithm. message.

   1+    At least one instance of the AVP MUST be present in the
         message.

                          +-----------------------------------------+
                          |        Message                          |
                          |          Type                           |
                          +-----+-----+-----+-----+-----+-----+-----+
      Attribute Name      | PSR | PSA | PAR | PAN | PBR | PBA | PDI |
      --------------------+-----+-----+-----+-----+-----+-----+-----+
      Result-Code         |  0  |  0  |  0  |  0  |  1  |  0  |  0  |
      Session-Id          |  0  |  0  |  1  |  1  |  1  |  1  |  0  |
      Termination-Cause   |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
      EAP-Payload         |  0  |  0  |  1  |  1  |  1  |  0  |  0  |
      MAC                 |  0  |  0  | 0-1 | 0-1 | 0-1 | 0-1 |  0  |
      Device-Id           |  0  |  0  |  0  |  0  |  1+ |  1+ | 0-1 |
      Cookie              | 0-1 | 0-1 |  0  |  0  |  0  |  0  |  0  |
      Protection-Cap.     |  0  |  0  |  0  |  0  | 0-1 |  0  |  0  |
      Session-Lifetime    |  0  |  0                   1                   2                   3  |  0 1 2 3 4 5 6 7 8 9  |  0 1 2 3 4 5 6 7 8 9  | 0-1 |  0 1 2 3 4 5 6 7 8 9  |  0  |
      Failed-AVP          |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
      ISP-Information     |  0+ | 0-1 | 0-1 |  0  |  0  |  0  |  0  |
      NAP-Information     | 0-1 |  0  | 0-1 |  0  |  0  |  0  |  0  |
      --------------------+-----+-----+-----+-----+-----+-----+-----+

                          +-------------------------------+
                          |      Message                  |
                          |       Type                    |
                          +------+------+-----+-----+-----+
      Attribute Name      | PRAR | PRAA | PTR | PTA | PER |
      --------------------+------+------+-----+-----+-----+
      Result-Code         |  0   |  0   |  0  |  0  |  1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |   Algorithm
      Session-Id          |           MAC...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Algorithm  1              HMAC-MD5 (16 bytes)
      2              HMAC-SHA1 (20 bytes)   |  1   |  1  |  1  |  1  |
      Termination-Cause   |  0   |  0   |  1  |  0  |  0  |
      EAP-Payload         | 0-1  | 0-1  |  0  |  0  |  0  |
      MAC

      The Message Authentication Code is encoded in network byte
      order.

9.4.2 Device-Id AVP

   The first octet (8 bits) of the                 | 0-1  | 0-1  | 0-1 | 0-1 | 0-1 |
      Device-Id (Code 1025) AVP data
   contains the device type. Rest of the AVP data payload contains
   the device data.  The content and format of data (including byte
   and bit ordering) is expected to be specified in specific
   documents.  For instance, [IPv6-ETHER].

         UNKNOWN           |  1+  |  1+  |  0  |  0  |  0  |
      Cookie              |  0   |  0   |  0  |  0  |  0  |
      Protection-Cap.     |  0   |  0   |  0
         IPV4_ADDRESS                      1
         IPV6_ADDRESS                      2
         L2_ADDRESS                        3

        For type 1 (IPv4 address), data size is 32 bits and for type 2
        (IPv6 address), data size is 128 bits.  |  0                   1                   2                   3  |  0 1 2 3 4 5 6 7 8 9  |
      Session-Lifetime    |  0 1 2 3 4 5 6 7 8 9   |  0 1 2 3 4 5 6 7 8 9   |  0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |     Type  0  |           Data...  0  |
      Failed-AVP          |  0   |  0   |  0  |  0  |  1  |
      ISP-Information     |  0   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9.4.3 Session-Id AVP

   Session-Id AVP (Code 1026) has an opaque data field, which is
   assigned by the PAA. All messages pertaining to a specific PANA
   Session MUST include only one Session-Id AVP and the same value
   MUST be used throughout the lifetime of a session.  When present,
   the Session-Id SHOULD appear immediately following the PANA header.

   The Session-Id MUST be globally and eternally unique, as it is
   meant to identify a PANA Session without reference to any
   other information, and may be needed to correlate historical
   authentication information with accounting information.

   The Session-Id AVP MAY use Diameter [DIAMETER] message
   formatting. In this case the AVP code is 263.

9.4.4 Cookie AVP

   The Cookie AVP (Code 1027) is of type OctetString. The data is
   opaque and the exact content is outside the scope of this protocol.

9.4.5 Protection-Capability AVP

   The Protection-Capability AVP (Code 1028) is of type Unsigned32.
   The AVP data is used as a collection of flags for different data
   protection capability indications.  Below is a list of specified
   data protection capabilities:  0          UNKNOWN
      1          L2_PROTECTION
      2          IPSEC_PROTECTION

9.4.6 Termination-Cause AVP

   The Termination-Cause   |  0  |  0  |  0  |
      NAP-Information     |  0   |  0   |  0  |  0  |  0  |
      --------------------+------+------+-----+-----+-----+

                    Figure 10: AVP is defined in [DIAMETER].

         LOGOUT                   1  (PaC -> PAA) Occurrence Table

10. PANA Protocol Message Retransmissions

   The user initiated a disconnect

         (SERVICE_NOT_PROVIDED     2  (PAA -> PaC))
            This value is used when the user disconnected
            prior to the receipt of the authorization answer
            message.

         BAD_ANSWER               3  (PaC -> PAA)
            This value indicates that PANA protocol provides retransmissions for all the authorization answer
            received message
   exchanges except PANA-Auth-Request/Answer. PANA-Auth-Request messages
   carry EAP requests which are retransmitted by the access device was not processed
            successfully.

         ADMINISTRATIVE           4  (PAA -> Pac) EAP protocol
   entities when needed. The user was not granted access, or was
            disconnected, due to administrative reasons,
            such as the receipt of a Abort-Session-Request
            message.

         (LINK_BROKEN              5) messages that need PANA-level
   retransmissions are listed below:

         PANA-PAA-Discover (PDI)
         PANA-Start-Answer (PSA)
         PANA-Bind-Request (PBR)
         PANA-Reauth-Request (PRAR)
         PANA-Termination-Request (PTR)

   The communication to PDI and PSA messages are always sent by the user was abruptly
            disconnected.

         AUTH_EXPIRED             6    (PAA -> PaC)
            The user's access was terminated since its
            authorized session time has expired.

         (USER_MOVED               7)  (PaC -> PAA)
            The user PaC.  PBR is receiving services from another
            access device. (See issue16).

         SESSION_TIMEOUT          8  (PAA -> PaC) sent by
   PAA.  The user's session has timed out, last two messages, PRAR and service
            has been terminated.

9.4.7 Result-Code AVP PTR are sent either by PaC or
   PAA.

   The Result-Code AVP rule is defined in [DIAMETER].

         SUCCESS                   2001
         COMMAND_UNSUPPORTED       3001
         UNABLE_TO_DELIVER         3002
         REALM_NOT_SERVED          3003
         TOO_BUSY                  3004
         INVALID_HDR_BITS          3008
         INVALID_AVP_BITS          3009
         AUTHENTICATION_REJECTED   4001
         AVP_UNSUPPORTED           5001
         UNKNOWN_SESSION_ID        5002
         AUTHORIZATION_REJECTED    5003
         INVALID_AVP_VALUE         5004
         MISSING_AVP               5005
         RESOURCES_EXCEEDED        5006
         AVP_OCCURS_TOO_MANY_TIMES 5009
         UNSUPPORTED_VERSION       5011
         INVALID_AVP_LENGTH        5014
         INVALID_MESSAGE_LENGTH    5015

9.4.8 EAP-Payload AVP

   The EAP-Payload AVP that the sender of the request message retransmits the
   request if the corresponding answer is defined not received in [DIAMETER-EAP].

9.5 AVP Occurrence Table

   The following tables lists time.  Answer
   messages are sent as answers to the AVPs used in request messages, not based on a
   timer.  Exception to this document, and
   specifies rule is the PSA message.  Because of the
   stateless nature of the PAA in which PANA the beginning PaC provides
   retransmission also for the PSA message.  PANA-Error messages they MAY, or MAY NOT MUST
   not be present. retransmitted.  See Section 4.1.8 for more details of PANA
   error handling.

   PANA retransmission timers are based on the model used in DHCPv6
   [RFC3315].  Variables used here are also borrowed from this
   specification.  PANA is a request response like protocol.  The table uses
   message exchange terminates when either the following symbols:

      0 request sender
   successfully receives the appropriate answer, or when the message
   exchange is considered to have failed according to the retransmission
   mechanism described below.

   The AVP MUST NOT be present in retransmission behavior is controlled and described by the message.
      0+    Zero
   following variables:

         RT     Retransmission timeout

         IRT    Initial retransmission time

         MRC    Maximum retransmission count

         MRT    Maximum retransmission time

         MRD    Maximum retransmission duration
         RAND   Randomization factor

   With each message transmission or more instances of retransmission, the AVP MAY be present in sender sets RT
   according to the rules given below.  If RT expires before the message
   exchange terminates, the sender recomputes RT and retransmits the
   message.
      0-1   Zero or one instance

   Each of the AVP MAY computations of a new RT include a randomization factor
   (RAND), which is a random number chosen with a uniform distribution
   between -0.1 and +0.1.  The randomization factor is included to
   minimize synchronization of messages.

   The algorithm for choosing a random number does not need to be present in
   cryptographically sound.  The algorithm SHOULD produce a different
   sequence of random numbers from each invocation.

   RT for the
            message. It first message transmission is considered an error if there are more than
            one instance based on IRT:

         RT = IRT + RAND*IRT

   RT for each subsequent message transmission is based on the previous
   value of RT:

         RT = 2*RTprev + RAND*RTprev

   MRT specifies an upper bound on the AVP.
      1     One instance value of RT (disregarding the AVP MUST be present in
   randomization added by the message.
      1+    At least one instance use of RAND).  If MRT has a value of 0,
   there is no upper limit on the AVP MUST be present in value of RT. Otherwise:

         if (RT > MRT)
            RT = MRT + RAND*MRT

   MRC specifies an upper bound on the
            message.

                       +-----------------------------------------+
                       |        Message                          |
                       |          Type                           |
                       +-----+-----+-----+-----+-----+-----+-----+
   Attribute Name      | PSR | PSA | PAR | PAN | PBR | PBA | PDI |
   --------------------+-----+-----+-----+-----+-----+-----+-----+
   Result-Code         |  0  |  0  |  0  |  0  |  1  |  0  |  0  |
   Session-Id          |  0  |  0  |  1  |  1  |  1  |  1  |  0  |
   Termination-Cause   |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
   EAP-Payload         |  0  |  0  |  1  |  1  |  1  |  0  |  0  |
   MAC                 |  0  |  0  | 0-1 | 0-1 | 0-1 | 0-1 |  0  |
   Device-Id           |  0  |  0  |  0  |  0  |  1+ |  1+ | 0-1 |
   Cookie              | 0-1 | 0-1 |  0  |  0  |  0  |  0  |  0  |
   Protection-Cap.     |  0  |  0  |  0  |  0  | 0-1 |  0  |  0  |
   --------------------+-----+-----+-----+-----+-----+-----+-----+

                       +-------------------------+
                       |      Message            |
                       |       Type              |
                       +------+------+-----+-----+
   Attribute Name      | PRAR | PRAA | PTR | PTA |
   --------------------+------+------+-----+-----+
   Result-Code         |  0   |  0   |  0  |  0  |
   Session-Id          |  1   |  1   |  1  | number of times a sender may
   retransmit a message.  Unless MRC is zero, the message exchange fails
   once the sender has transmitted the message MRC times.

   MRD specifies an upper bound on the length of time a sender may
   retransmit a message.  Unless MRD is zero, the message exchange fails
   once MRD seconds have elapsed since the client first transmitted the
   message.

   If both MRC and MRD are non-zero, the message exchange fails whenever
   either of the conditions specified in the previous two paragraphs are
   met.

   If both MRC and MRD are zero, the client continues to transmit the
   message until it receives a response.

10.1 Transmission and Retransmission Parameters

   This section presents a table of values used to describe the message
   retransmission behavior of request and PANA-Start-Answer messages
   marked with REQ_*. PANA-PAA-Discover message retransmission values
   are marked with PDI_*. The table shows default values.

           Parameter       Default   Description
           ------------------------------------------------
           PDI_IRT           1  |
   Termination-Cause   | sec   Initial PDI timeout.
           PDI_MRT         120 secs  Max PDI timeout value.
           PDI_MRC           0   |       Configurable.
           PDI_MRD           0   |       Configurable.

           REQ_IRT           1  |  0  |
   EAP-Payload         | 0-1  | 0-1  |  0  |  0  |
   MAC                 | 0-1  | 0-1  | 0-1 | 0-1 |
   Device-Id           |  1+  |  1+  |  0  |  0  |
   Cookie              |  0   |  0   |  0  |  0  |
   Protection-Cap.     |  0   |  0   |  0  |  0  |
   --------------------+------+------+-----+-----+

                      Figure 10: AVP Occurrence Table sec   Initial Request timeout.
           REQ_MRT          30 secs  Max Request timeout value.
           REQ_MRC          10       Max Request retry attempts.
           REQ_MRD           0       Configurable.

   So for example the first RT for the PBR message is calculated using
   REQ_IRT as the IRT:

           RT = REQ_IRT + RAND*REQ_IRT

11. Security Considerations

   The PANA protocol provides ordered delivery for EAP messages. If an
   EAP method that provides session keys is used, a PANA SA is created.
   The EAP Success/Failure message is one of the signaling messages
   which is integrity protected with this PANA SA.  The PANA protocol
   does not provide security protection for the initial EAP message
   exchange. Integrity protection can only be provided after the PANA SA
   has been established. Thus, PANA re-authentication, revocation and
   disconnect notifications can be authenticated, integrity and replay
   protected. In certain environments (e.g. on a shared link) the EAP
   method selection is an important issue.

   The PANA framework described in this document covers the discussion
   of different protocols which are of interest for a protocol between
   the PaC and the PAA (typically referred as the PANA protocol).

   The PANA itself consists of a sequence of steps which are executed to
   complete the network access authentication procedure. Some of these
   steps are optional.

   The following execution steps have been identified as being relevant
   for PANA. They security considerations will be discussed in detail
   subsequently.

   a) Discovery message exchange

   In general it is difficult to prevent a vulnerabilities of the
   discovery protocol since the initial discovery are unsecured. To
   prevent very basic attacks an adversary should not be able to cause
   state creation with discovery messages at the PAA. This is prevented
   by re-using a cookie concept (see [RFC2522]) [RFC2522] which allows the
   responder to be stateless in the first message exchange. Because of
   the architectural assumptions made in PANA (i.e. the PAA is the on
   the same link as the PaC) the return-routability concept does not
   provide additional protection. Hence it is difficult to prevent this
   threat entirely. Furthermore it is not possible to shift heavy
   cryptographic operations to the PaC at the first few messages since
   the computational effort depends on the EAP method. The usage of
   client-puzzles as introduced by [JB99] [jb99] is under investigation.

   Resistance against blind DoS attacks (i.e. attacks by off-path
   adversaries) is achieved with sequence numbers and cookies.

   Since PAA and PaC are supposed to be one IP hop away from each other, PANA messages away, a simple TTL
   check can prevent off-link attacks. Furthermore, additional filtering
   can be filtered whenever messages arrive at interfaces where enabled on the EPs. An EP may be able to filter unauthorized
   PAA advertisements when they are not expected. received on the access side of the
   network where only PaCs are connected.

   b) EAP over PANA message exchange

   The EAP derived session key is used to create a PANA security
   association. Since the execution of an EAP method might require a
   large number of roundtrips and no other session key is available it
   is not possible to secure the EAP message exchange itself. Hence an
   adversary can both eavesdrop the EAP messages and is also able to
   inject arbitrary messages which might confuse both the EAP peer on
   PaC and the EAP authenticator or authentication server on the PAA.
   The threats caused by this ability heavily depend on the EAP state
   machine. Since especially the PAA is not allowed to discard packets
   and packets have to be stored or forwarded to an AAA infrastructure
   some risk of DoS attacks exists.

   Eavesdropping EAP packets might cause problems when (a) the EAP
   method is weak and enables dictionary or replay attacks or even
   allows an adversary to learn the long-term password directly.
   Furthermore, if the optional EAP Identity payload is used then it
   allows the adversary to learn the identity of the PaC. In such a case
   a privacy problem is prevalent.

   To prevent these threats Section 6 suggests using proper EAP methods
   for particular environments. Depending on the usage environment an
   EAP authentication has to be used for example which supports user
   identity confidentiality, protection against dictionary attacks and
   session key establishment. It is therefore the responsibility of the
   network operators and end users to choose the proper EAP method.

   PANA does not protect the EAP method exchange, but provides ordered
   delivery with sequence numbers.  Sequence numbers and cookies provide
   resistance against blind DoS attacks.

   c) PANA SA establishment

   Once the EAP message authentication is finished a fresh and unique
   session key is available to the PaC and the PAA. This assumes that
   the EAP method allows session key derivation and that the generated
   session key has a good quality. For further discussion about the
   importance of the session key generation refer to the next subsection (c)
   (d) about compound authentication. The session key available for the
   PaC is established as part of the authentication and key exchange
   procedure of the selected EAP method. The PAA obtains the session key
   via the AAA infrastructure (if used). Draft
   [CFB02]
   [I-D.ietf-aaa-diameter-cms-sec] describes how a session key is
   securely carried (i.e. CMS protected) between AAA servers. Security
   issues raised with this session key transport are described in [WHC02].
   [I-D.walker-aaa-key-distribution].

   The establishment of a PANA SA is required in environments where no
   physical or link layer security is available. The PANA SA allows
   subsequently exchanged messages to experience cryptographic
   protection. For the current version of the document an Integrity integrity
   object (MAC AVP) is defined which is based on Diameter objects. The Integrity
   Object supports data-origin
   authentication, replay protection based on sequence numbers and
   integrity protection based on a keyed message digest. Confidentiality
   protection is not provided. The session keys (one for each direction) used for this object has
   have to be provided by the EAP method.  For this version of the
   document it is assumed that no negotiation of algorithms and
   parameters takes place. Instead HMAC-SHA1 is used per-default. by default. A
   different algorithm such as HMAC-MD5 might be used as an option. The
   used algorithm is indicated in the header of the Integrity object. To
   select the security association for signaling message protection the
   Session
   ID. ID is conveyed. The keyed message digest included in the
   Integrity object will include all fields of the PANA signaling
   message including the sequence number field of the packet.

   The protection of subsequent signaling messages prevents an adversary
   from acting as a man-in-the-middle adversary, from injecting packets,
   from replaying messages and from modifying the content of the
   exchanged packets. This prevents subsequently described threats.

   If an entity (PAA or PaC) looses loses its state (especially the current
   sequence number) then the entire PANA protocol has to be restarted.
   No re-synchronization procedure is provided.

   The lifetime of the PANA SA has to be bound to the refresh interval AAA-authorized
   session lifetime with an additional tolerance period. To provide fast re-
   authentication a separate security association (e.g. one stored at
   the local AAA server) should be used. By fast re-authentication we
   mean a new Unless PANA protocol execution which does not involve
   state is updated by executing another EAP authentication, PANA SA is
   removed when the entire
   AAA communication. current session expires. The ability lifetime of the PANA SA
   has to be bound to trigger such a protocol execution
   depends on the given AAA-authorized session lifetime with an
   additional tolerance period. Unless PANA state is updated by
   executing another EAP method and on the policy of authentication, PANA SA is removed when the local
   network requesting authentication.
   current session expires.

   d) Enabling weak legacy authentication methods in insecure networks

   Some of the authentication methods are not strong enough to be used
   in insecure networks where attackers can easily eavesdrop and spoof
   on the link. They may not be able to produce much needed keying
   material either. An example would be using EAP-MD5 over wireless
   links. Use of such legacy methods can be enabled by carrying them
   over a secure channel. There are EAP methods which are specifically
   designed for this purpose, such as EAP-TTLS [TTLS],PEAP [PEAP]
   [I-D.ietf-pppext-eap-ttls],PEAP [I-D.josefsson-pppext-eap-tls-eap] or
   EAP-IKEv2 [EAP-IKEv2]. [I-D.tschofenig-eap-ikev2]. PANA can carry these EAP
   tunneling methods which can carry the legacy methods. PANA does not
   do anything special for this case. The EAP tunneling method will have
   to produce keying material for PANA SA when needed. There are certain
   MitM vulnerabilities with tunneling EAP methods [MITM]. [mitm]. Solving these
   problems is outside the scope of PANA. The compound authentication
   problem described in [PL+03] [I-D.puthenkulam-eap-binding] is likely to be
   solved in EAP itself rather than in PANA.

   e) Preventing downgrading attacks

   EAP supports a number of different EAP methods for authentication and
   therefore it might be required to agree on a specific mechanism.  An
   unprotected negotiation mechanism is supported in EAP and a secure
   negotiation procedure for the GSS-API methods. The support of the
   GSS-API as an EAP method is described in [AS02]. [I-D.aboba-pppext-eapgss]. A
   protected negotiation is supported by the GSS-API with RFC 2478
   [RFC2478]. If desired, such a protection can also be offered by PANA
   by repeating the list of supported EAP methods protected with the
   PANA SA. This type of protection is similar to the protected
   negotiation described in [RFC3329].

   This issue requires further investigation especially since the EAP
   protocol is executed between different endpoints than the PANA
   protocol.

   f) Device Identifier exchange

   As part of the authorization procedure a Device Identifier has to be
   installed at the EP by the PAA. The PaC provides the Device
   Identifier information to the PAA secured with the PANA SA. Section
   6.2.4 of [THREATS] [I-D.ietf-pana-threats-eval] describes a threat where an
   adversary modifies the Device Identifier to gain unauthorized access
   to the network.

   The installation of the Device Identifier at the EP (independently
   whether the EP is co-located with the PAA or not) has to be
   accomplished in a secure manner. These threats are, however, not part
   of the PANA protocol itself since the protocol is not PANA specific.

   g) Triggering a data protection protocol

   Recent activities in the EAP working group try to create a common
   framework for key derivation which is described in [Ab02].
   [I-D.aboba-pppext-key-problem]. This framework is also relevant for
   PANA in various ways. First, a PANA security association needs to be
   created. Additionally it might be necessary to trigger a protocol
   which allows link layer and network layer data protection to be
   established. As an example see Section 1 of [Ab02]
   [I-D.aboba-pppext-key-problem] with [802.11i] and [802.11] as an
   example. Furthermore, a derived session key might help to create the
   pre-requisites for
   network layer network-layer protection (for example IPsec). IPsec
   [I-D.ietf-pana-ipsec]).

   As motivated in Section 6.4 of [THREATS] [I-D.ietf-pana-threats-eval] it might
   be necessary to establish either a link layer or a network layer
   protection to prevent certain thefts in certain scenarios.

   Threats specific to the establishment of a link layer or a network
   layer security association are outside the scope of PANA. The
   interested reader should refer to the relevant working groups such as
   IPsec or Midcom.

   h) Periodic refresh messages Liveness test

   Network access authentication is done for a very specific purpose and
   often charging procedures are involved which allow restricting
   network resource usage based on some policies. In mobility
   environments it is always possible that an end host suddenly
   disconnects without transmitting a disconnect message. If network
   access authentication as part of PANA is executed only at the
   beginning then an adversary can gain advantage of the installed
   packet filters to submit and receive data packets.

   Also for the network operator it might be desirable Operators are
   generally motivated to enforce a
   disconnect based on some external events (e.g. because of
   insufficient funds, etc.).

   An additional motivation for detecting detect a disconnected end host is
   the ability as soon as
   possible in order to release resources (i.e. (i.e., garbage collection).
   The PAA can remove per-session state information including installed
   security association, packet filters filters, etc.

   Different procedures can be used for disconnect indication. PANA
   cannot assume link layer link-layer disconnect indication. Hence this
   functionality has to be provided at a higher layer. With this version
   of the draft we suggest to apply the soft-state principle found at
   other protocols (such as RSVP). Soft-state means that session state
   is kept alive as long as refresh messages refresh the state. If no
   new refresh messages are provided then the state automatically times
   out and resources are released. This process
   includes stopping accounting procedures.

   Based on the different environments where PANA could be used it is
   difficult to fix a refresh interval. Hence a default refresh
   interval of 30 seconds is suggested. Additionally there is the
   possibility to negotiation this interval once the PANA security
   association is established. A policy at the PAA and the PaC would
   ensure that the refresh interval released. This process includes stopping
   accounting procedures.

   A PANA session is selected associated with a value which session lifetime. The session is
   either too high or too low. There
   terminated unless it is certainly refreshed by a tradeoff between
   the refresh interval and the bandwidth consumption. To reduce new round of EAP
   authentication before it expires. Therefore, at the
   bandwidth consumption latest a small
   disconnected client can be detected when its lifetime expires. A
   disconnect may also be detected earlier by using PANA
   reauthentication messages. A request message consisting only of a
   session identifier can be generated by
   either PaC or PAA at any time and the Integrity object peer must respond with an
   answer message. A successful round-trip of this exchange is used. The session
   identifier refers to the state a simple
   verification that has to be refreshed. Some
   environments do not need PANA refresh messages to detect orphan
   states. For these environments the refresh interval should peer is alive. This test can be set to
   zero which effectively disables engaged when
   there is a possibility that the usage peer might have disconnected (e.g.,
   after discontinuation of refresh messages. In
   case data traffic). Periodic use of IPsec protection this exchange
   as a dead-peer mechanism can be used to detect
   inactivity (see [HBR03]).

   Refresh messages are sent from the PaC keep-alive requires additional care as it might result in
   congestion and hence false alarms. This exchange is cryptographically
   protected when PANA SA is available in order to prevent threats
   associated with the PAA.

   From a security point abuse of view an adversary must not be able to
   inject, modify or replay refresh messages nor must he be able to
   change the refresh interval (e.g. setting it to zero) without
   detection. Hence these messages experience cryptographic protection. this functionality.

   i) Tear-Down message

   The PANA protocol supports the ability for both the PaC and the PAA
   to transmit a tear-down message. This message causes state removal, a
   stop of the accounting procedure and removes the installed packet
   filters.

   It is obvious that such a message must be protected to prevent an
   adversary from deleting state information and thereby causing denial
   of service attacks.

11

12. Open Issues

   A list of open issues is maintained at
   http://danforsberg.info:8080/pana-issues/.

12 [1].

   The remaining issues for -01 version of draft are: None.

   The remaining issues for -xx version of draft are: 2, 12, 16, 28, 29,
   34, 35, 36 and 37.

13. Change History

   Issues incorporated in PANA-01 June 2003: 1, 3, 10, 5, 6, 7 and 11.

   Issues incorporated in PANA-02 October 2003: 8, 17, 18, 19, 20, 21,
   22, 23, 24, 25, 26, 30, 31, 32 and 33.

14. Acknowledgments

   We would like to thank all members of the PANA working group for
   their comments to this document.

13

Normative References

   [802.11] I. S. 802.11-1997, "Information technology -
   telecommunications and information exchange between systems - local
   and metropolitan area networks - specific requirements part 11:
   Wireless lan medium access control (mac) and physical layer (phy)
   specifications," tech. rep., 1997.

   [RFC2522] P. Karn and W. Simpson, "Photuris: Session-key management
   protocol," RFC 2522, March 1999.

   [Ab02] B. Aboba and D. Simon: "EAP Keying Framework", Internet
   Draft, Internet Engineering Task Force, March, 2003,  Work in
   progress.

   [802.11i] I. D. 802.11i/D2, "Draft supplement to standard for
   telecommunications and information exchange between systems -
   lan/man specific requirements - part 11: Wireless medium access
   control (mac)

   [I-D.ietf-pana-usage-scenarios]
              Ohba, Y., "Problem Statement and physical layer (phy) specifications: Specification Usage Scenarios for enhanced security," tech. rep., 2001.

   [AS02] Aboba, B., Simon, D.: "EAP GSS Authentication Protocol",
   Internet Draft, Internet Engineering Task Force, April, 2002, Work
   in progress.

   [CFB02] P. Calhoun, S. Farrell, and W. Bulley: "Diameter CMS
   Security Application," Internet Draft, Internet Engineering Task
   Force, Mar. 2002,  Work
              PANA", draft-ietf-pana-usage-scenarios-06 (work in progress.
              progress), April 2003.

   [RFC2284]  Blunk, L. and J. Vollbrecht, "PPP Extensible
              Authentication Protocol (EAP)", RFC 2284, March 1998.

   [HBR03] G. Huang, S. Beaulieu, and D. Rochefort, "A traffic-based
   method of detecting dead ike peers", Internet Draft, Internet
   Engineering Task Force, 2003,  Work in progress.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
   (IKE)", RFC 2409, November 1998.

   [MITM] N. Asokan, V. Niemi, and K. Nyberg: "Man-in-the-middle in
   tunnelled authentication", In the Proceedings of the 11th
   International Workshop on Security Protocols, Cambridge, UK, April
   2003. To be published in the Springer-Verlag LNCS series.

   [PEAP] A. Palekar, D. Simon, G. Zorn

   [I-D.ietf-pana-threats-eval]
              Parthasarathy, M., "PANA Threat Analysis and S. Josefsson: "Protected
   EAP Protocol (PEAP)", Internet Draft, Internet Engineering Task
   Force, March 2003,  Work security
              requirements", draft-ietf-pana-threats-eval-04 (work in progress.

   [PL+03] J. Puthenkulam, V. Lortz, A. Palekar, D. Simon, and B.
   Aboba, "The compound authentication binding problem," internet
   draft, Internet Engineering Task Force,
              progress), May 2003.  Work in progress.

   [PY+02] R. Penno, A. Yegin, Y. Ohba, G. Tsirtsis, and C. Wang:
   "Protocol for Carrying Authentication for Network Access (PANA)
   Requirements and Terminology", Internet Draft, Internet Engineering
   Task Force,  June 2003, Work in progress.

   [RFC2284bis]   L. Blunk, J. Vollbrecht, B. Aboba, J. Carlson:
   "Extensible

   [I-D.ietf-pana-requirements]
              Yegin, A. and Y. Ohba, "Protocol for Carrying
              Authentication Protocol (EAP)", Internet Draft, Internet
   Engineering Task Force, January 2003, Work for Network Access  (PANA)Requirements",
              draft-ietf-pana-requirements-07 (work in progress. progress), June
              2003.

   [RFC1982]  Elz, R., R. and R. Bush, R.: "Serial Number Arithmetic", RFC 1982,
              August 1996.

   [RFC2478] E. Baize and D. Pinkas, "The simple and protected GSS-API
   negotiation mechanism," RFC 2478, Internet Engineering Task Force,
   Dec. 1998.

   [RFC2988] V.  Paxson, V. and M. Allman: Allman, "Computing TCP's Retransmission
              Timer", RFC 2988, November, November 2000.

   [RFC3329] J. Arkko,  V. Torvinen, G. Camarillo, A. Niemi, and T.
   Haukka: "Security Mechanism Agreement for the Session Initiation

   [I-D.ietf-eap-rfc2284bis]
              Blunk, L., "Extensible Authentication Protocol (SIP)", RFC 3329, January, (EAP)",
              draft-ietf-eap-rfc2284bis-06 (work in progress), September
              2003.

   [THREATS] M. Parthasarathy:

   [I-D.ietf-pana-ipsec]
              Parthasarathy, M., "PANA Threat Analysis enabling IPsec based Access
              Control", draft-ietf-pana-ipsec-00 (work in progress),
              October 2003.

   [I-D.tschofenig-pana-bootstrap-rfc3118]
              Tschofenig, H., "Bootstrapping RFC3118 Delayed
              authentication using PANA",
              draft-tschofenig-pana-bootstrap-rfc3118-00 (work in
              progress), June 2003.

   [I-D.ietf-seamoby-ctp]
              Loughney, J., "Context Transfer Protocol",
              draft-ietf-seamoby-ctp-04 (work in progress), October
              2003.

   [RFC2716]  Aboba, B. and security
   requirements", Internet Draft, Internet Engineering Task Force, May
   2003, Work D. Simon, "PPP EAP TLS Authentication
              Protocol", RFC 2716, October 1999.

   [I-D.josefsson-pppext-eap-tls-eap]
              Josefsson, S., Palekar, A., Simon, D. and G. Zorn,
              "Protected EAP Protocol (PEAP)",
              draft-josefsson-pppext-eap-tls-eap-06 (work in progress.

   [TTLS] progress),
              March 2003.

   [I-D.ietf-pppext-eap-ttls]
              Funk, P. Funk and S. Blake-Wilson: Blake-Wilson, "EAP tunneled Tunneled TLS authentication
   protocol (EAP-TTLS)," Internet Draft, Internet Engineering Task
   Force, November  2002.  Work in progress.

   [USAGE] Y. Ohba, S. Das, B. Patil, H. Soliman, A. Yegin, A.:
   "Problem Statement and Usage Scenarios for PANA", Internet Draft,
   Internet Engineering Task Force, April 2003, Work
              Authentication Protocol (EAP-TTLS)",
              draft-ietf-pppext-eap-ttls-03 (work in progress.

   [EAP-IKEv2] progress), August
              2003.

   [I-D.tschofenig-eap-ikev2]
              Tschofenig, H. Tschofenig and D. Kroeselberg: Kroeselberg, "EAP IKEv2 Method
              (EAP-IKEv2)", Internet Draft, Internet Engineering Task Force, June
   2003, Work draft-tschofenig-eap-ikev2-01 (work in progress.

   [WHC02]
              progress), July 2003.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, November 1998.

   [RFC2234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. Walker, R.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [I-D.ietf-aaa-eap]
              Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application",
              draft-ietf-aaa-eap-02 (work in progress), July 2003.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
              M. Carney, "Dynamic Host Configuration Protocol for IPv6
              (DHCPv6)", RFC 3315, July 2003.

   [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
              Protocol", RFC 2522, March 1999.

   [I-D.ietf-aaa-diameter-cms-sec]
              Calhoun, P., Farrell, S. and W. Bulley, "Diameter CMS
              Security Application", draft-ietf-aaa-diameter-cms-sec-04
              (work in progress), March 2002.

   [I-D.walker-aaa-key-distribution]
              Housley, R., Walker, J. and N. Cam-Winget: Cam-Winget, "AAA key
   distribution," Internet Draft, Internet Engineering Task Force, Apr.
   2002,  Expired.

   [DIAMETER-EAP] T. Hiller Key
              Distribution", draft-walker-aaa-key-distribution-00 (work
              in progress), April 2002.

   [I-D.puthenkulam-eap-binding]
              Puthenkulam, J., "The Compound Authentication Binding
              Problem", draft-puthenkulam-eap-binding-03 (work in
              progress), July 2003.

   [I-D.aboba-pppext-eapgss]
              Aboba, B. and G. Zorn: "Diameter Extensible D. Simon, "EAP GSS Authentication Protocol (EAP) Application", Internet Draft, Internet
   Engineering Task Force, March 2003, Work Protocol",
              draft-aboba-pppext-eapgss-12 (work in progress.

   [DIAMETER] P. Calhoun, J. Loughney, progress), April
              2002.

   [RFC2478]  Baize, E. Guttman, G. Zorn and J.
   Arkko: "Diameter Base Protocol", Internet Draft, Internet
   Engineering Task Force, D. Pinkas, "The Simple and Protected GSS-API
              Negotiation Mechanism", RFC 2478, December 2002, Work 1998.

   [RFC3329]  Arkko, J., Torvinen, V., Camarillo, G., Niemi, A. and T.
              Haukka, "Security Mechanism Agreement for the Session
              Initiation Protocol (SIP)", RFC 3329, January 2003.

   [I-D.aboba-pppext-key-problem]
              Aboba, B. and D. Simon, "EAP Key Management Framework",
              draft-aboba-pppext-key-problem-07 (work in progress.

   [IANAWEB] progress),
              August 2003.

Informative References

   [ianaweb]  IANA, "Number assignment", http://www.iana.org

   [CTP] J. Loughney, M. Nakhjiri, C. Perkins and R. Koodli:
   "Context Transfer Protocol", Internet Draft, Internet Engineering
   Task Force, June 2003, Work in progress.

   [JB99]  http://www.iana.org.

   [jb99]     Juels, A. Juels and J. Brainard: Brainard, "Client Puzzles: A
              Cryptographic Defense Against Connection Depletion
              Attacks", In S. Kent, editor,  Proceedings of NDSS '99 (Networks and
              Distributed Security Systems), pages 151-165, 1999.

Change History

   Changes from PANA-00 to PANA-01 June 2003

   - The names for the PANA messages have been changed. Hence it was
   necessary to reflect the new terminology

   [mitm]     Asokan, N., Niemi, V. and K. Nyberg, "Man-in-the-middle in other parts of
              tunnelled authentication",  In the
   draft.

   - New text has been added to Proceedings of the following sections:

     * Terminology
     * PANA Security Association
     * Message Authentication Code
     * Refresh Interval Negotiation
     * Mobility Handling
     * Event Notification
     * Message Formats

   - The details 11th
              International Workshop on message formats add more details Security Protocols, Cambridge,
              UK, April 2003.

   [802.11i]  Institute of Electrical and Electronics Engineers, "Draft
              supplement to several parts standard for telecommunications and
              information exchange between systems - lan/man specific
              requirements - part 11: Wireless medium access control
              (mac) and physical layer (phy) specifications:
              Specification for enhanced security", IEEE 802.11i/D6.0,
              2003.

   [802.11]   Institute of the draft. The AVP format is based on Diameter/ Electrical and Electronics Engineers,
              "Information technology - The open issue list has been replaced by a reference to the web
   page containing the open issues.

Author's telecommunications and
              information exchange between systems - local and
              metropolitan area networks - specific requirements part
              11: Wireless lan medium access control (mac) and physical
              layer (phy) specifications", IEEE Standard 802.11, 1997.

URIs

   [1]  <http://danforsberg.info:8080/pana-issues/>

Authors' Addresses

   Basavaraj Patil
   Nokia
   6000 Connection Dr.
   Irving, TX. 75039
   USA
   Phone:  +1 972-894-6709
   Email:  Basavaraj.Patil@nokia.com

   Dan Forsberg
   Nokia Research Center
   P.O. Box 407
   FIN-00045 NOKIA GROUP, GROUP
   Finland

   Phone: +358 50 4839470
   EMail: dan.forsberg@nokia.com

   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, Information Systems, Inc.
   P.O. Box 136
   Convent Station, NJ, 07961-0136
   9740 Irvine Blvd.
   Irvine, CA  92619-1697
   USA

   Phone: +1 973 829 5174
   Email:
   EMail: yohba@tari.toshiba.com

   Basavaraj Patil
   Nokia
   6000 Connection Dr.
   Irving, TX  75039
   USA

   Phone: +1 972-894-6709
   EMail: Basavaraj.Patil@nokia.com

   Hannes Tschofenig
   Siemens Corporate Technology
   Otto-Hahn-Ring 6
   81739 Munich
   Germany
   Email:

   EMail: Hannes.Tschofenig@siemens.com
   Alper E. Yegin
   DoCoMo USA Labs
   181 Metro Drive, Suite 300
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Appendix A. Adding sequence number to PANA for carrying EAP

   A.1.

Appendix A.1 Why is sequence number needed for PANA to carry EAP?

   EAP [RFC2284bis] [I-D.ietf-eap-rfc2284bis] requires underlying transports to
   provide ordered-delivery of messages.  If an underlying transport
   does not satisfy the ordering requirement, the following situation
   could happen:

        EAP Peer                 EAP Authenticator
      --------------------------------------------
      1. (got req 1)   <-------  Request ID=1
      2. Response ID=1 ---+
                          |      (timeout)
      3.                  | +--  Request ID=1
                          | |
                          +-|--> (got resp 1)
      4. (got req 2)   <----|--  Request ID=2
                            |
      5. Response ID=2 -----|--> (got resp 2)
                            |
      6. (got req 1)   <----+
      7. Response ID=1 --------> [discarded due to unexpected ID]

                    Figure A.1 11: Undesirable scenario

   In Figure A.1, 11, the second EAP Request message with Identifier=1
   arrives at the EAP peer after the third EAP Request message with
   Identifier=2.  As a result, the EAP peer accepts the second EAP
   Request as a new EAP Request while it is just an old EAP Request that
   was already responded and the authentication might be totally messed
   up.

   This problem occurs due to the fact that EAP doesn't recognize
   duplicate packets in the scope of one EAP protocol run, but only in
   the scope of current and previous packet (i.e., request and response
   message matching).  When EAP is running over PPP or IEEE 802 links,
   this is not a problem, because those link-layers have the ordering
   invariant characteristic.

   On the other hand, the PANA design has chosen UDP as its transport.
   Given that UDP does not provide ordered delivery of packets and PANA
   does not assume any specific link-layer technology to carry EAP, PANA
   messages need to have a sequence number.

   In the following text we describe two possible approaches for
   sequence number handling in PANA.  The first one makes use of a
   single sequence number whereas the latter utilizes two. Finally a
   comparison between the two approaches is provided. The method
   described in Section A.3.1. Appendix A.3.1 (i.e., the dual sequence number with
   orderly-delivery method) is suggested as the preferred method for
   PANA transport.

   A.2.

Appendix A.2 Single sequence number approach

   This section discusses several methods based on using a single
   sequence number for providing orderly message delivery.  Sequence
   number handling for all methods discussed in Section Appendix A.2 must comply
   to the following rules:

   Rule 1: The sequence number starts from initial sequence number (ISN)
           and is monotonically increased by 1.  The arithmetic defined
           in [RFC1982] is used for sequence number operation.

   Rule 2: When a PAA sends an EAP message passed from EAP layer to a
           PaC, a new sequence number is placed in the message,
           regardless of whether it is sent as a result of a
           retransmission at the EAP layer or not.

   Note: It might be possible to define other mechanisms for sequence
   number handling if it can be assumed that a PAA detects EAP
   retransmissions.  However, such an assumption heavily depends on EAP
   implementation details in particular on EAP APIs, thus it was decided
   not to use such an assumption.

   A.2.1.

Appendix A.2.1 Single sequence number with EAP retransmission method

   Again, the following rules must hold:

   Rule 3: Use EAP layer retransmission for retransmitting EAP messages
           (based on a timer expiration).

   Rule 4: When the PaC receives a message from the PAA, it checks the
           sequence number and discards the message if the sequence
           number is not greater than that of the last accepted message.

   Rule 5: When the PAA receives a message from the PaC, it checks the
           sequence number and discards the message if the sequence
           number does not match a pending request message.

        PaC    PAA Seq#  Message
      --------------------------------------------
      1. <-------  (x)   PANA-Auth-Request[EAP Req ID=1]
      2. ---+      (x)   PANA-Auth-Answer[EAP Res ID=1]
            |            (retransmission timeout at EAP-layer)
      3.    | +--  (x+1) PANA-Auth-Request[EAP Req ID=1]
            | |
            +-|-->       (discarded due to Rule 5)
              |          (retransmission timeout at EAP-layer)
      4. <----|--  (x+2) PANA-Auth-Request[EAP Req ID=1]
              |
      5. -----|--> (x+2) PANA-Auth-Answer[EAP Res ID=1]
              |
      6. <----+          (discarded due to Rule 4)
      7. <-------  (x+3) PANA-Auth-Request[EAP Req ID=2]
            .
            .

 Figure 1: 12: Example for Single sequence number with EAP retransmission
                                  method

   This method is vulnerable to a blind DoS attack on the sequence
   number since the PaC will accept quite a wide range of sequence
   numbers.  For example, if an attacker blindly sends a bogus message
   to a legitimate PaC with a randomly chosen sequence number, it will
   be accepted by the PaC with 50% probability, and once this happens,
   all messages sent from the communicating PAA will be discarded as
   long as they have a sequence number smaller than the accepted value.
   The problem of this method leads to a requirement for PaC to have a
   narrow range of acceptable sequence numbers to make the blind DoS
   attack difficult. Note that the DoS attack cannot be prevented if the
   attacker is on the same IP link as PaC and able to eavesdrop the PANA
   conversation. However, the attacker needs to put itself in
   promiscuous mode and thus spend more resources to eavesdrop and
   launch the attack (in other words, non-blind DoS attack is still
   possible as long as sequence numbers are unprotected.)

   A.2.2.

Appendix A.2.2 Single sequence number with PANA-layer retransmission
               method

   The next method is still based on using a single sequence number but
   the PANA-layer takes the responsibility of retransmission.  The
   method uses the following rules in addition to the common rules
   described in section Appendix A.2.

   Rule 3: Use PANA-layer retransmission for retransmitting both EAP and
           non-EAP messages (based on a timer expiration). EAP layer
           retransmission is turned off. Retransmission based on timer
           occurs both on PaC and PAA side, but not on both sides
           simultaneously.  PAA does retransmission at least for
           PANA_Termination and PANA_Reauth messages, otherwise PaC
           takes care of retransmission.

   Rule 4: When the PaC receives a message from the PAA, it accepts the
           message if the sequence number is equal to that of the last
           accepted message + 1.  If the sequence number is equal to
           that of the last accepted message, the PaC retransmits the
           last transmitted message.  Otherwise, it silently discards
           the message.

   Rule 5: When the PAA receives a message from the PaC, it accepts the
           message if the sequence number is equal to that of the last
           transmitted message.  If the receiving sequence number is
           equal to that of the last transmitted message - 1, the PAA
           retransmits the last transmitted message and discard the
           received message. Otherwise, it silently discards the
           message.

   Rule 6: The PaC retransmits the last transmitted EAP Response until a
           new EAP Request message or an EAP Success/Failure message is
           received and accepted.

   Rule 7: PAA must keep the copy of the last transmitted message and
           must be able to retransmit it until either a valid message is
           received and accepted by the PAA or a timer expires.  The
           timer is used if no new message will be sent from the PaC.

        PaC    PAA Seq#  Message
      --------------------------------------------
      1. <-------- (x)   PANA-Auth-Request[EAP Req ID=1]
      2. ---+      (x)   PANA-Auth-Answer[EAP Resp ID=1]
            |            (retransmission timeout at PaC)
      3. ---|----> (x)   PANA-Auth-Answer[EAP Resp ID=1]
      4.    | +--- (x+1) PANA-Auth-Request[EAP Req ID=2]
            | |
            +-|-->       (duplicate detected)
      5. <----|--- (x+1) PANA-Auth-Request[EAP Req ID=2]
              |
      6. -----|--> (x+1) PANA-Auth-Answer[EAP Resp ID=2]
              |
         <----|--- (x+2) PANA-Auth-Request[EAP Req ID=3]
      7. -----|--> (x+2) PANA-Auth-Answer[EAP Resp ID=3]
         <----+          (discarded by PaC)
                         (retransmission timeout at PaC)
      8. --------> (x+2) PANA-Auth-Answer[EAP Resp ID=3]
      9. lost<---- (x+3) PANA-Auth-Request[EAP Succ ID=3]
                         (retransmission timeout at PaC)
      10.---->lost (x+2) PANA-Auth-Answer[EAP Resp ID=3]
                         (retransmission timeout at PaC)
      11.--------> (x+2) PANA-Auth-Answer[EAP Resp ID=3]
      12.<-------- (x+3) PANA-Bind-Request[EAP Succ ID=3]
                         (retransmission timer stopped at PaC)
                         (deletion timeout at PAA)
                         (message (x+3) deleted at PAA)
      13.lost<---- (x+4) PANA-Termination-Request
                         (retransmission timeout at PAA)
      14.<-------- (x+4) PANA-Termination-Request
      15.---->lost (x+4) PANA-Termination-Answer
                         (retransmission timeout at PAA)
      16.<-------- (x+4) PANA-Termination-Request
      17.--------> (x+4) PANA-Termination-Answer
                         (retransmission timer stopped at PAA)

     Figure 2: 13: Example for Single sequence number with PANA-layer
                             retransmission method

   This method has an advantage of eliminating EAP layer retransmission
   by providing reliability at the PANA layer. Retransmission at the EAP
   layer has a problem with determining an appropriate retransmission
   timer value, which occurs when the lower-layer is unreliable.  In
   this case an EAP authenticator cannot distinguish between (i) EAP
   Request or EAP Response message loss (in this case the retransmission
   timer should be calculated based on network characteristics) and (ii)
   long latency for EAP Response generation due to e.g., user input etc.
   (in this case the retransmission timer should be calculated based on
   user or application characteristics).  In general, the retransmission
   timer for case (ii) is longer than that for case (i).  If case (i)
   happens while the retransmission timer is calculated based on user or
   application characteristics, then it might frustrate an end user
   since the completion of the authentication procedure takes
   unnecessarily long.  If case (ii) happens while the retransmission
   timer is calculated based on network characteristics (i.e., RTT),
   then unnecessarily traffic is generated by retransmission.  Note that
   in this method a PaC still cannot distinguish case (i) and case (iii)
   the EAP authenticator or a backend authentication server is taking
   time to generate an EAP Request.

   A problem of this method is that it is based on the assumption that
   EAP authenticator does not send a new EAP message until an EAP
   Response to the outstanding EAP Request is received.  However, this
   assumption does not hold at least EAP Success/Failure message which
   does not need the outstanding EAP Request to be responded before
   sending the EAP Success/Failure message.  This would require
   timer-based retransmission not only at PaC side but also at PAA side.
   Another problem occurs when a new EAP message overrides the
   outstanding EAP Request, the PaC cannot assume any more that the
   sequence number of the next message to be accepted is the last
   accepted message + 1.  So the PaC needs to accept a range of sequence
   numbers, instead of a single sequence number. These two additional
   things would increase the complexity of this method.

   A.3.

Appendix A.3 Dual sequence number approach

   Based on the analysis of previous schemes, it is recognized that two
   sequence numbers are needed anyway, one for each direction.  Two
   different methods are proposed based on this approach.  Both methods
   have the following rules in common.

   Rule 1: A PANA packet carries two sequence numbers: transmitted
           sequence number (tseq) and received sequence number (rseq).
           tseq starts from initial sequence number (ISN) and is
           monotonically increased by 1.  The arithmetic defined in
           [RFC1982] is used for sequence number operation.  It is
           assumed that the two sequence numbers have the same length
           for simplicity.

   Rule 2: When PAA or PAC sends a new message, a new sequence number is
           placed on the tseq field of message.  Every transmitted
           message is given a new sequence number.

   Rule 3: When a message is sent from PaC or PAA, rseq is copied from
           the tseq field of the last accepted message.

   Rule 4: For messages which experience a PANA layer retransmission,
           the retransmission timer is stopped when the message is
           acknowledged.

   It is possible to carry multiple EAP sequences in a single PANA
   sequence, with using EAP Success/Failure message as a delimiter of
   each EAP sequence.  In this case, EAP Success/Failure message needs
   to be reliably delivered.

   A.3.1.

Appendix A.3.1 Dual sequence number with orderly-delivery method

   This method relies on EAP layer retransmission for EAP messages.
   This method is referred to as orderly-delivery method.  The following
   rules are used in addition to the common rules.

   Rule 5: Use the EAP-layer retransmission for retransmitting EAP
           Requests (based on a timer expiration).  For other PANA layer
           messages that require a response from the peer, PANA layer
           has its own mechanism to retransmit the request until it gets
           a response or gives up.  A new tseq value is always used when
           sending any message even when it is retransmitted at PANA
           layer.

   Rule 6: When a message is received, it is accepted if (i) the tseq
           value is greater than the tseq of the last accepted message
           and (ii) the rseq falls in the range between the tseq of the
           last acknowledged message + 1 and the tseq of the last
           transmitted message.  Otherwise, the received message is
           discarded.

        PaC    PAA  (tseq,rseq) Message
      --------------------------------------------------
      1. <-------   (x,y)       PANA-Auth-Request[EAP Req, ID=1]
      2. ------->   (y+1,x)     PANA-Auth-Answer[EAP Resp, ID=1]
      3. <-------   (x+1,y+1)   PANA-Auth-Request[EAP Req, ID=2]
      4. --->lost   (y+2,x+1)   PANA-Auth-Answer[EAP Resp, ID=2]
                                (retransmission timeout at EAP layer)
      5. <-------   (x+2,y+1)   PANA-Auth-Request [EAP Req, ID=2]
      6. ------->   (y+3,x+2)   PANA-Auth-Answer[EAP Resp, ID=2]
      7. lost<---   (x+3,y+3)   PANA-Auth-Request[EAP Req, ID=3]
                                (retransmission timeout at EAP layer)
      8.    +----   (x+4,y+3)   PANA-Auth-Answer[EAP Req, ID=3]
            |                   (retransmission timeout at EAP layer)
      9. <--|----   (x+5,y+3)   PANA-Auth-Request[EAP Req, ID=3]
      10.---|--->   (y+4,x+5)   PANA-Auth-Answer[EAP Resp, ID=3]

   ^L                                 PANA                        June 2003

            |
         <--+                   (out of order. discarded)
      11.lost<---   (x+6,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
                                (retransmission timeout at PAA)
      12.<-------   (x+7,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
      13.--->lost   (y+5,x+7)   PANA-Bind-Answer
                                (retransmission timeout at PAA)
      14.<-------   (x+8,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
                             (dupicate
                                (duplicate detected by PaC)
      15.------->   (y+6,x+8)   PANA-Bind-Answer
   Figure 3: 14: Example for Dual sequence number with orderly-delivery
                                  method

   A.3.2.

Appendix A.3.2 Dual sequence number with reliable-delivery method

   This method relies solely on PANA layer retransmission for all
   messages.  This method is referred to as reliable-delivery method.
   The following additional rules are applied in addition to the common
   rules.

   Rule 5: Use the PANA layer retransmission for retransmitting all
           messages (based on a timer expiration).  EAP retransmission
           is turned off.

   Rule 6: Either an ACK message is used for acknowledgment or an
           acknowledgment can be piggybacked with data.  ACK messages
           are not retransmitted.  An ACK message is sent if no the
           acknowledgement cannot be piggybacked with a data within a
           given time frame W.

   Rule 7: When a message is received, it is accepted if (i) the tseq
           value is greater than the tseq of the last accepted message
           and (ii) the rseq falls in the range between the tseq of the
           last acknowledged message and the tseq of the last
           transmitted message.  Otherwise, the received message is
           discarded.

   Rule 8: When a duplicate message is received, the last transmitted
           message is retransmitted if the received message is not an
           ACK.  A message is considered as duplicate if its tseq value
           is equal to the tseq of the last accepted message.

        PaC    PAA  (tseq,rseq) Message
      --------------------------------------------------
      1. <-------   (x,y)       PANA-Auth-Request[EAP Req, ID=1]
                                (user input ongoing)
      2. ------->   (y+1,x)     PANA-Auth-Answer
                                (user input completed)
      3. ------->   (y+2,x)     PANA-Auth-Answer[EAP Resp, ID=1]
      4. <-------   (x+1,y+2)   PANA-Auth-Request [EAP Req, ID=2]
      5. --->lost   (y+3,x+1)   PANA-Auth-Answer[EAP Resp, ID=2]
                                (retransmission timeout at PAA)
      6. <-------   (x+1,y+2)   PANA-Auth-Request [EAP Req, ID=2]
                                (duplicate detected by PaC)
      7. ------->   (y+3,x+1)   PANA-Auth-Answer[EAP Resp, ID=2]
      8. lost<---   (x+2,y+3)   PANA-Auth-Request [EAP Req, ID=3]
                                (retransmission timeout at PaC)
      9. ------->   (y+3,x+1)   PANA-Auth-Answer[EAP Resp, ID=2]
                                (duplicate detected at PAA)
      10.<-------   (x+2,y+3)   PANA-Auth-Request [EAP Req, ID=3]
      11.---+       (y+4,x+2)   PANA-Auth-Answer[EAP Resp, ID=3]
            |                   (retransmission timeout at PAA)
      12.<--|----   (x+2,y+3)   PANA-Auth-Request [EAP Req, ID=3]
            |                   (duplicate detected at PaC)
      13.---|--->   (y+4,x+2)   PANA-Auth-Answer[EAP Resp, ID=3]
      14.<--|----   (x+3,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
      15.---|--->   (y+5,x+3)   PANA-Bind-Answer
            +--->               (out of order. discarded)

   Figure 4: 15: Example for Dual sequence number with reliable-delivery
                                 method

Appendix A.3.3 Comparison of the dual sequence number methods

   The orderly-delivery method is simpler than the reliable-delivery
   method in that the former does not allow sending a separate ACK while
   the latter does.

   In terms of authentication performance, the reliable-delivery method
   is better than the orderly-delivery method in that the former gives
   more detailed status of the link than the latter, e.g., an entity can
   know whether a request has reached the communicating peer without
   before receiving a response. The reliable-delivery can reduce
   retransmission traffic and communication delay that would occur if
   there is no reliability, as described in section A.2.2. Appendix A.2.2

Appendix A.4 Consensus

   Although it is recognizable that the reliable-delivery method would
   be important in terms of improvement of overall authentication
   latency, we believe that this is a performance problem of EAP and not
   a problem of PANA.  It is agreed that solving the EAP problem is not
   the scope of PANA and simplicity is more important factor in the PANA
   design.

   As a consequence, the orderly-delivery method is chosen as the
   message transport part of PANA.

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