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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 RFC 5191

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


     Protocol for Carrying Authentication for Network Access (PANA)
                        draft-ietf-pana-pana-02

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 23, 2004.

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



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   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 . . . . . . . . . . . . . . . . . . . . . . .   4
   2.     Terminology  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.     Protocol Overview  . . . . . . . . . . . . . . . . . . . .   6
   4.     Protocol Details . . . . . . . . . . . . . . . . . . . . .   8
   4.1    Common Processing Rules  . . . . . . . . . . . . . . . . .   8
   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



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   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








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1. Introduction

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

   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.











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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].






















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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 executed between the PaC and the PAA.

   The placement of the entities used in PANA largely depends on a
   certain architecture. The PAA may optionally interact with a AAA
   backend to authenticate the user (PaC). And in the case where the PAA
   and EP are co-located, the intercommunication may not require a
   separate protocol. 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 described in
   Section 4 of this document. PANA supports authentication of a PaC
   using various EAP methods. The EAP method used depends on the level
   of security required for 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 securing
   the data traffic [I-D.ietf-pana-ipsec].

   From a state machine aspect, PANA protocol consists of three phases



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   1.  Discovery and initial handshake phase

   2.  Authentication phase

   3.  Termination phase

   In the first phase, an IP address of PAA is discovered and a PANA
   session is established between PaC and PAA.  EAP 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.








































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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 the AVPs defined in
   this document is listed below:

   o  Cookie AVP: contains a random value that is 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 exchange (e.g. link-layer 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 pair of device
      identifier type and device identifier value.  Either a layer-2
      address or an IP address is 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 protocol execution
      results.

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

   o  Session-Lifetime AVP: contains the duration of authorized access.

   o  Failed-AVP: contains the offending AVP that caused a failure.

   o  NAP-Information AVP, ISP-Information AVP: contains the information
      on a NAP and 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



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   PAA.

4.1.3 Fragmentation

   PANA does not provide fragmentation of PANA messages. Instead, it
   relies on fragmentation provided by EAP methods and IP layer when
   needed.

4.1.4 Sequence Number and Retransmission

   PANA uses sequence numbers to provide ordered delivery of EAP
   messages. The design involves use of two sequence numbers to prevent
   some of the DoS attacks on the sequencing scheme.  Every PANA packet
   include one transmitted sequence number (tseq) and one received
   sequence number (rseq) in the PANA header.  See Appendix A for
   detailed explanation on why two sequence numbers are needed.

   The two sequence number fields have the same length of 32 bits and
   appear in PANA header.  tseq starts from initial sequence number
   (ISN) and is monotonically increased by 1. The serial number
   arithmetic defined in [RFC1982] is used for sequence number
   operation. The ISNs are exchanged between PaC and PAA during the
   discovery and initial handshake phase (see Section 4.2). The rules
   that govern the sequence numbers in other phases are described as
   follows.

   o  When a message is sent, a new sequence number is placed on the
      tseq field of message regardless of whether it is sent as a result
      of retransmission or not.  When a message is sent, rseq is copied
      from the tseq field of the last accepted message.

   o  When a message is received, it is considered valid in terms of
      sequence numbers if and only if (i) its tseq is greater than the
      tseq of the last accepted message and (ii) its rseq falls in the
      range between the tseq of the last acknowledged message + 1 and
      the tseq of the last transmitted message.

   PANA relies on EAP-layer retransmissions, or for 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 communicating peer are retransmitted based on timer at
   PANA-layer until a response is received (in which case the
   retransmission timer is stopped) or the number of retransmission
   reaches the maximum value (in which case the PANA session MUST be
   deleted immediately).  For PANA-layer retransmission, the
   retransmission timer SHOULD be calculated as described in [RFC2988]
   to provide congestion control.  See Section 10 for default timer and
   maximum retransmission count parameters.



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4.1.5 PANA Security Association

   A PANA SA is created as an attribute of a PANA session when EAP
   authentication succeeds with a creation of a Master Session Key (MSK)
   [I-D.ietf-eap-rfc2284bis].  A PANA SA is not created when the PANA
   authentication fails or no MSK is produced by any EAP authentication
   method. In the 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 PANA SA MUST be bound to the
   MSK derived from the first EAP authentication.  When a new MSK is
   derived as a result of EAP-based re-authentication, any key derived
   from the old MSK MUST be updated to a new one that is derived from
   the new MSK.

   The created PANA SA is deleted when the corresponding PANA session is
   deleted.  The lifetime of the PANA SA is the same 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 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



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         +  PANA_MAC_Key

   The PANA_MAC_Key is used 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 for HMAC-MD5 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 Message Authentication Code

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

   When a MAC AVP is included in a PANA message, the value field of the
   MAC AVP is calculated by using the PANA_MAC_Key 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 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 communication peer is bound to the
      PANA session, it matches the device identifier carried in MAC and/
      or IP header(s).

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

   o  The message payload contains a valid set of AVPs allowed for the
      message type and there is no missing AVP that needs to be included
      in the payload.




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   o  Each AVP is decoded correctly.

   o  When a 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 AVP is supported (this check is
      for both PaC and PAA) and is the requested one (this check is for
      PAA only) and the device identifier value contained in the AVP
      matches the value extracted from the lower-layer encapsulation
      header corresponding to the device identifier type contained in
      the AVP.  Note that 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 DoS attacks and an unprotected.  In addition, a
   non-acknowledged error notification message MAY be returned to the
   sender. See Section 4.1.8 for details.

4.1.8 Error Handling

   PANA-Error message MAY be sent by either PaC or PAA when a 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 cause of the error was a response message,
   the receiver of the PANA-Error message SHOULD NOT resend the same
   response until it receives the next request.

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

   When an error message is sent unprotected with MAC AVP and the
   lower-layer is insecure, the error message is treated as an
   informational message.  The receiver of such an error message MUST
   NOT change its state unless the error persists and the PANA session
   is not making any progress.

4.2 Discovery and Initial Handshake Phase

   When a PaC attaches to a network, and knows that it has to 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
   source address is set to the unspecified IP address if the PaC has
   not configured an address yet. PANA PAA discovery assumes that PaC



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   and PAA are one hop away from each other. If PaC knows the IP address
   of the PAA (some pre-configuration), it MAY unicast the PANA
   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 the implementations to deal with).

   There can be multiple PAAs on the link. The authentication and
   authorization result does not depend on which PAA is chosen by 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 are co-located, then an
   internal mechanism (e.g. API) between the EP module and the PAA
   module on the same host can prompt PAA to start PANA. In case they
   are separate, there needs to be an explicit message to prompt PAA.
   Upon detecting the need to authenticate a client, EP can send a
   PANA-PAA-Discover message to the PAA on behalf of the PaC. This
   message carries a device identifier of 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 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 header contains the initial
   sequence number.  The cookie is 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 described below.

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

   where <secret> is a randomly generated secret known only to the PAA,
   <secret-version> is an index used for choosing the secret for
   generating the cookie and '|' indicates concatenation.  The secret-



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   version should be changed frequently enough to prevent replay
   attacks. The secret key is locally known to the PAA only and valid
   for a certain time frame.

   PAA MAY enable NAP-ISP authentication separation by setting the
   S-flag of the message header of the PANA-Start-Request. Also, the
   PANA-Start-Request MAY contain zero or one NAP-Information AVP and
   zero or more ISP-Information AVPs to advertise the information on the
   NAP and/or ISPs.

   When a PaC receives the PANA-Start-Request message in response to the
   PANA-PAA-Discover message, it responds with a PANA-Start-Answer
   message if it wishes to enter the authentication phase.  The
   PANA-Start-Answer message contains the initial sequence numbers in
   the tseq and rseq fields of the PANA header, a copy of the received
   Cookie (if any) as the PANA payload.

   If the S-flag of the received PANA-Start-Request message is not set,
   PaC MUST NOT set the S-flag in the 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 the PANA-Start-Answer message.
   AAA routing will be based on the ISP choice if an ISP-Information AVP
   is specified in the PANA-Start-Answer message, otherwise it 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 case, PaC can also indicate its choice of ISP by including
   its ISP-Information AVP in the PANA-Start-Answer message.  AAA
   routing for NAP authentication will be based on the NAP.  AAA routing
   for ISP authentication will be based on the ISP choice if an
   ISP-Information AVP is specified in the PANA-Start-Answer message,
   otherwise it will be based on EAP identifier."

   When the PAA receives the PANA-Start-Answer message from the PaC, it
   verifies the cookie.  The cookie is considered as valid if the
   received cookie has the expected value.  If the computed cookie is
   valid, the protocol enters the authentication phase.  Otherwise, it
   MUST silently discard the received message.

   The PANA-Start-Request/Answer exchange is needed before entering
   authentication phase even when 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 message is retransmitted based on timer in the same
   manner as other messages retransmitted at PANA-layer.



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      PaC      PAA         Message
      ------------------------------------------------------
         ----->            PANA-PAA-Discover(0,0)
         <-----            PANA-Start-Request(x,0)[Cookie]
         ----->            PANA-Start-Answer(x,y)[Cookie]
                           (continued to authentication phase)


  Figure 2: Example Sequence for Discovery and Initial Handshake Phase


      PaC   EP      PAA    Message
      ------------------------------------------------------
       ---->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 Discovery and Initial Handshake Phase
                 when PANA-PAA-Discover is sent by PaC


4.3 Authentication Phase when PANA-PAA-Discover is sent by EP

   The main task in authentication phase is to carry EAP messages
   between PaC and PAA. All EAP messages except for EAP Success/Failure
   messages are carried in the PANA-Auth-Request/PANA-Auth-Answer
   messages.  When an EAP Success/Failure message is sent from a PAA,
   the message is carried in 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 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
   single PANA session, the PAA determines the execution order of NAP
   authentication and ISP authentication.  In this case, the PAA can
   indicate which EAP authentication is currently occurring by including
   a NAP-Information or an ISP-Information AVP of the corresponding EAP
   authentication in the first PANA-Auth-Request message sent to the
   PaC. In the case where the PaC agreed to perform separate
   authentications but did not specify its ISP choice in
   PANA-Start-Answer message, the PAA MUST include its NAP-Information
   AVP in PANA-Auth-Request message when it performs NAP authentication
   and MUST NOT include any service provider information AVP when it
   performs ISP authentication so that the PaC can always distinguish
   ISP authentication from NAP authentication.  The PAA SHOULD stop



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   including a NAP-Information or an ISP-Information AVP once it
   receives the first PANA-Auth-Answer message of the 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 another chance when an
   authentication method fails.  The NAP and ISP authentication are
   considered completely independent. Presence or success of one should
   not effect the other. Making an authentication decision based on the
   success or failure of each authentication is a network policy issue.
   PANA signals only the result of the immediately preceding EAP
   authentication method in PANA-Bind-Request messages.

   When an EAP method that is capable of deriving keys is used during
   the authentication phase and the keys are successfully derived the
   PANA-Bind-Request and PANA-Bind-Answer messages and all subsequent
   PANA messages MUST contain a MAC AVP.  The PANA-Bind-Request and the
   PANA-Bind-Answer message exchange is also used for binding device
   identifiers of the PaC and the PAA to the PANA SA. To achieve this,
   the PANA-Bind-Request and the PANA-Bind-Answer SHOULD contain a
   device identifier of the PAA and the PaC, respectively, in a
   Device-Id AVP.  The PaC MUST use the same type of device identifier
   as contained in the PANA-Bind-Request message.  The PANA-Bind-Request
   message 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 Protection-Capability AVP. When the information is preconfigured
   on the 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 specify how the PANA SA and the
   Protection-Capability AVP will be used to provide per-packet
   protection for data traffic.

   PANA-Bind-Request and PANA-Bind-Answer messages MUST be retransmitted
   based on 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)
                       [EAP{Success}, Device-Id, Lifetime, Protection-Cap., MAC]



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         ----->     PANA-Bind-Answer(y+3,x+3)
                       [Device-Id, Protection-Cap., MAC]

           Figure 4: Example Sequence in Authentication Phase


4.4 Re-authentication

   There are two types of re-authentication supported by PANA.

   The first type of re-authentication is based on EAP by entering an
   authentication phase.  In this case, some or all message exchanges
   for discovery and initial handshake phase MAY be omitted in the
   following way.  When a PaC wants to initiate EAP-based
   re-authentication, it sends a unicast PANA-PAA-Discovery message to
   the PAA.  This message MUST contain a Session-Id AVP which is used
   for identifying the PANA session on the PAA. If the PAA already has
   an established PANA session for the PaC with the matching identifier,
   it sends a PANA-Auth-Request message containing the same identifier
   to start an authentication phase.  If the PAA can not recognize the
   session identifier, it proceeds with regular authentication by
   sending back PANA-Start-Request.  When the PAA initiates EAP-based
   re-authentication, it sends a PANA-Auth-Request message containing
   the session identifier for the PaC to enter an authentication phase.
   PAA SHOULD initiate EAP authentication before the current session
   lifetime expires. In both cases, the tseq and rseq values are
   inherited 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 SHOULD be protected
   by adding a MAC AVP to each message.

   The second type of re-authentication is based on a single protected
   message exchange without entering the authentication phase.
   PANA-Reauth-Request and PANA-Reauth-Answer messages are used for this
   purpose.  If there is an established PANA SA, both the PaC and 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 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 the rate of performing re-authentication
   for both types of re-authentication.








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      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 second type
                           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 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 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 the Termination-Cause AVP.
   When there is an established PANA SA established between the PaC and
   the PAA, all messages exchanged during the termination phase MUST be
   protected with a MAC AVP.  When the sender of the PANA-
   Termination-Request receives a valid acknowledgment, all states
   maintained for 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 a Complete Message Sequence

   A complete PANA message sequence is illustrated in Figure 8. The
   example assumes the following scenario:



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   o  PaC multicasts PANA-PAA-Discover message

   o  The ISNs used by the PAA and the PaC are x and y, respectively.

   o  A single EAP sequence is used in authentication phase.

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

   o  The EAP authentication method derives keys. The PANA SA is
      established based on the unique and fresh session key provided by
      the EAP method.

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

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

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


      PaC      PAA  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]




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                 Figure 8: A Complete Message Sequence


4.7 Device ID Choice

   A PaC SHOULD configure 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 such as DHCP or stateless address autoconfiguration.
   Dynamic methods may or may not succeed depending on the local
   security policy.  In networks where clients have to be authorized
   before they are allowed to obtain an IP address, EPs will detect the
   associated activity and PANA 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 assumed that PAA knows the security mechanisms
   being provided or required on the access network (e.g., based on
   physical security, link-layer ciphers enabled before or after PANA,
   or IPsec). When IPsec-based mechanism [I-D.ietf-pana-ipsec] is the
   choice of access control, PAA SHOULD provide its IP address as device
   ID, and expect the PaC to provide its IP address in return.  In all
   other cases, link-layer addresses can be provided from both sides.

   When IPsec-based access control is used but the PaC is using an
   unspecified IP address in the authentication phase, the device 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. Eventually PaC MUST obtain an IP
   address, possibly by relying on the newly-created PANA session
   [I-D.tschofenig-pana-bootstrap-rfc3118], in order to gain full access
   to the network. PaC MUST update the device identifier registered on
   the PAA from unspecified to the valid IP address by initiating a
   PANA-Reauth-Request/PANA-Reauth-Answer exchange in which the IP
   address of the PaC is contained in the Device-Id AVP.

4.8 Session Lifetime

   The authentication phase determines the PANA session lifetime when
   the network access authorization succeeds. The Session-Lifetime AVP
   MAY be optionally included in the PANA-Bind-Request message to inform
   PaC about the 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 SHOULD be included after the
   final authentication.

   The lifetime is a non-negotiable parameter that 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.



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   PAA SHOULD initiate EAP authentication before the 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 disconnection before taking an action.

   The session lifetime parameter is not related to the transmission of
   PANA-Reauth-Request messages. These messages can be used for
   asynchronously verifying the liveness of the peer and enabling
   mobility optimizations. The decision to send PANA-Reauth-Request
   message is taken locally and does not require coordination between
   the peers.

4.9 Mobility Handling

   When a PaC wants to resume an ongoing PANA session after connecting
   to another link in the same access network, it MAY send the unexpired
   PANA session identifier in its PANA-Start-Answer message. In the
   absence of a 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 in the PANA-Start-Answer
   message, and it is configured to enable fast re-authentication, it
   SHOULD retrieve the PANA session attributes from the previous PAA of
   the PaC.  The mechanism required to determine the previous PAA of the
   PaC by relying on the PANA session identifier is outside the scope of
   PANA protocol. A possible solution is to embed the PAA identifier in
   the PANA session identifier. Furthermore, the mechanism required to
   retrieve the session attributes from the previous PAA is outside the
   scope of this protocol. Seamoby Context Transfer Protocol
   [I-D.ietf-seamoby-ctp] might be useful for this purpose.

   When the PAA is not configured to enable fast re-authentication, or
   can not retrieve the PANA session attributes, or the PANA session has
   already expired (i.e., session lifetime is zero), the PAA MUST send
   the PANA-Auth-Request message with the new session identifier and let
   the PANA exchange take its usual course. This action will engage EAP
   authentication and create a fresh PANA session from scratch.

   In case the new PAA retrieves the on-going PANA session attributes
   from the previous PAA, the PANA session continues with a PANA-Reauth
   exchange.  The MAC AVP contained in the PANA-Reauth messages MUST be
   generated and verified by using the retrieved PANA SA attributes.
   This exchange MUST also include Session-Id AVP that contains the
   newly assigned session identifier, and Device-Id AVP. A new PANA



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   session is 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 PANA exchanges on the new link. While MSK
   stays the same, a new PANA_MAC_Key is computed using the new
   parameters. Subsequent MAC-AVPs are processed using this new PANA SA.

4.10 Event Notification

   Upon detecting the need to authenticate a client, EP can send a
   trigger message to the PAA on behalf of the 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. 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 not physically secured,
   this message sent from EP to 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]
























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5. PANA Security Association Establishment

   When PANA 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 or service theft is not possible
   [I-D.ietf-pana-threats-eval].

   Anywhere else where there is no secure channel prior to PANA, the
   protocol needs to protect itself against such attacks. The device
   identifier that is used during the authentication needs to be
   verified at the end of the authentication to prevent service theft
   and DoS attacks. Additionally, a free loader should be prevented from
   spoofing data packets by using the device identifier of an already
   authorized legitimate client. Both of these requirements necessitate
   generation of a security association between the PaC and the PAA at
   the end of the authentication. This can only be done when the
   authentication method used can 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 EAP methods to provide a session key in
   order to establish a PANA security association. An example of such a
   method is EAP-TLS [RFC2716], whereas EAP-MD5 [RFC2284] is an example
   of a method that cannot create such keying material. The choice of
   EAP method becomes important, as already discussed in the next
   section.

   This keying material is already used within PANA during the final
   handshake. This handshake ensures that the device identifier that is
   bound to the PaC at the end of the authentication process 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. The other use of the keying material will be discussed in
   Section 7 and Section 8.
















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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
   eavesdropping and spoofing, therefore a stronger authentication
   method needs to be used to prevent attacks on the client and the
   network.

   The authentication method choice is a function of the underlying
   security of the network (e.g., physically secured, shared link,
   etc.). It is the responsibility of the user and the network operator
   to pick the right method for authentication. PANA carries EAP
   regardless of the EAP method used. It is outside the scope of PANA to
   mandate, recommend, or limit use of any authentication methods.  PANA
   cannot increase the strength of a weak authentication method to make
   it 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 does not
   concern itself with how they achieve protection for the weak methods
   (i.e., their EAP method payloads).



























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7. Filter Rule Installation

   PANA protocol provides client authentication and authorization
   functionality for securing network access. The other component of a
   complete solution is the access control which ensures that only
   authenticated and authorized clients can gain access to the network.
   PANA enables access control by identifying legitimate clients and
   generating filtering information for access control mechanisms.
   Getting this filtering information to the EPs (Enforcement Points)
   and performing filtering are outside the scope of PANA.

   Access control can be achieved by placing EPs in the network for
   policing the traffic flow. EPs should prevent data traffic 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 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 will (preferably)
   identify one of the existing protocols that can fit the requirements.
   Possible candidates include but not limited to COPS, SNMP, DIAMETER.
   This task is similar to what MIDCOM Working Group is trying to
   achieve, therefore some of the MIDCOM's output might be useful here.

   EPs' location in the network topology should be appropriate for
   performing access control functionality. The closest IP-capable
   access device to the client devices is the logical choice. PAA and
   EPs on an access network should be aware of each other as this is
   necessary for access control. Generally this can be achieved by
   manual configuration. Dynamic discovery is another possibility, but
   this is clearly outside the scope of PANA.

   Filtering rules generally include device identifiers for a client,
   and also cryptographic keying material when needed. Such keys are
   needed when attackers can eavesdrop and spoof on the device
   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.













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8. Data Traffic Protection

   Protecting data traffic of 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 underlying
   network is not physically secured. Encryption is needed when
   eavesdropping is a concern in the network.

   When the network is physically secured, or the link-layer ciphering
   is already enabled prior to PANA, data traffic protection is already
   in place. In other cases, enabling link-layer ciphering or network-
   layer ciphering might rely on PANA authentication. The user and
   network have to make sure an appropriate EAP method that can generate
   required keying materials is used. Once the keying material is
   available, it needs to be provided to the EP(s) for use 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 that a simple shared secret generated by an EAP
   method is not readily usable by IPsec for authentication and
   encryption of IP packets. Fresh and unique session key derived from
   the EAP method is still insufficient to produce an IPsec SA since
   both traffic selectors and other IPsec SA parameters are missing.
   The shared secret can be used in conjunction with a key management
   protocol like IKE [RFC2409] to 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 that can
   generate initial keying material.

   Using network-layer ciphers should be regarded as a substitute for
   link-layer ciphers when the latter is not available. IKE involves
   several message exchanges which can incur additional delay in getting
   basic IP connectivity for a mobile device. Such a latency is
   inevitable when there is no other alternative and this level of
   protection is required. Network-layer ciphering can also be used in
   addition to link-layer ciphering if the added benefits outweigh its
   cost to the user and the network.











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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 MUST be set to 1 to indicate PANA Version 1.

   Message Length

      The Message Length field is three octets and indicates the length
      of the PANA message including the header fields.

   Flags

      The Flags field is 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 message is a request. If cleared, the message is an
         answer.





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      S(eparate)

         When the S-flag is set in a PANA-Start-Request message it
         indicates that PAA is willing to offer separate EAP
         authentication for NAP and ISP.  When the S-flag is set in a
         PANA-Start-Answer message it indicates that PaC accepts on
         performing separate EAP authentication for NAP and ISP."

      r(eserved)

         these flag bits 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, and is used in order to
      communicate the message type with the message. The 24-bit address
      space is managed by IANA [ianaweb].  PANA uses its own address
      space for this field.

   Transmitted Sequence Number

      The Transmitted Sequence Number field contains the monotonically
      increasing 32 bit sequence number that the message sender
      increments every time a new PANA message is sent.

   Received Sequence Number

      The Received Sequence Number field contains the 32 bit transmitted
      sequence number that the message sender has last received from its
      peer.

   AVPs

      AVPs are a method of encapsulating information relevant to the
      PANA message.  See section Section 9.2 for more information on
      AVPs.


9.2 AVP Header

   Each AVP of type OctetString MUST be padded to align on a 32-bit
   boundary, while other AVP types align naturally. A number of
   zero-valued bytes are added to the end of the AVP Data field till a
   word boundary is reached. The length of the padding is not reflected
   in the AVP Length field [RFC3588].

   The fields in the AVP header MUST be sent in network byte order. The



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   format of 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 this 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 required.

      V(endor)

         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, and ignored by the receiver.




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   AVP Length

      The AVP Length field is three octets, and indicates the number of
      octets in this AVP including the AVP Code, AVP Length, AVP Flags,
      and the AVP data

   Vendor-Id

      The Vendor-Id field is present if the 'V' bit is set in the AVP
      Flags field. The optional four-octet Vendor-Id field contains the
      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 their privately managed AVP address
      space, guaranteeing 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 or more octets and contains information
      specific to the Attribute. The format and length of the Data field
      is determined by the AVP Code and 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               <------->



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                    Figure 9: PANA Message Overview

   Additionally the EP can 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 [RFC3588].  Note that PANA messages have a
   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 discover the address
   of PAA(s). Both sequence numbers in this message are set to zero (0).
   If the EP detects a new PaC and sends the PANA-PAA-Discover to the
   PAA, it 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 the PAA to the PaC. The PAA sets
   the transmission sequence number to an initial random value.  The
   received sequence number is 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 response to
   a PANA-Start-Request message.  The PANA_start message transmission
   sequence number field is copied to the received sequence number
   field.  The transmission sequence number is set to initial random



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   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 PAA to the 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 ISP-Information MUST NOT be included at the
   same time)"

9.3.6 PANA-Auth-Answer (PAN)

   PANA-Auth-Answer (PAN) is sent by the PaC to the PAA in response to 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 sent by the 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 >



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9.3.8 PANA-Bind-Answer (PBA)

   PANA-Bind-Answer (PBA) is sent by the PaC to the PAA in response to a
   PANA-Result-Request message.

         PANA-Bind-Answer ::= < PANA-Header: 4 >
                       < Session-Id >
                       < Device-Id >
                    *  [ AVP ]
                   0*1 < MAC >


9.3.9 PANA-Reauth-Request (PRAR)

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

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







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9.3.12 PANA-Termination-Answer (PTA)

   PANA-Termination-Answer (PTA) is sent either by the PaC or the PAA 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 used AVPs are defined in this document and some of them
   are defined in other documents like [RFC3588]. PANA proposes to use
   the same name space with the Diameter spec. For temporary allocation,
   PANA uses AVP type numbers starting from 1024.

9.4.1 MAC AVP

   The 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]. The AVP length varies depending on the
   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)



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   MAC

      The Message Authentication Code is encoded in network byte order.


9.4.2 Device-Id AVP

   The first octet (8 bits) of the 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) for L2_ADDRESS is expected to 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 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |           Data...                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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 [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



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   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 AVP (Code 1029) is of type of type Enumerated,
   and is used to indicate the reason why a session was terminated on
   the access device.  The AVP data is used as a collection of flags The
   following Termination-Cause AVP defined in [RFC3588] are used for
   PANA.

   LOGOUT                   1  (PaC -> PAA)

      The client initiated a disconnect

   ADMINISTRATIVE           4  (PAA -> Pac)

      The client was not granted access, or was disconnected, due to
      administrative reasons, such as the receipt of a
      Abort-Session-Request message.

   SESSION_TIMEOUT          8  (PAA -> PaC)

      The session has timed out, and service has been terminated.


9.4.7 Result-Code AVP

   The Result-Code AVP (AVP Code 1030) is of type Unsigned32 and
   indicates whether an EAP authentication was completed successfully or
   whether an error occurred.  Here are Result-Code AVP 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.



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   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 client could not be
      authorized.  This error could occur if the service requested is
      not permitted to the 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 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 the PANA header were either set to an
      invalid combination, or to a value that is inconsistent with the
      message type's definition.

   PANA_INVALID_AVP_BITS                   3009

      Error code from PAA to PaC or from PaC to PAA.  A message was
      received that included an AVP whose flag bits are set to an
      unrecognized value, or that is inconsistent with the 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 with this error



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      MUST contain one or more Failed-AVP AVP containing the 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.  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 Failed-AVP AVP.

   PANA_MISSING_AVP                        5005

      Error code from PAA to PaC or from PaC to PAA.  The message did
      not contain an AVP that is required by the message type
      definition.  If this value is sent in the Result-Code AVP, a
      Failed-AVP AVP SHOULD be included in the message.  The Failed-AVP
      AVP MUST contain an example of the missing AVP complete with the
      Vendor-Id if applicable.  The value field of the missing AVP
      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 PaC.  The PAA has detected AVPs in the
      message that contradicted each other, and is not willing to
      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 to PaC or from PaC to PAA.  A message was
      received with an AVP that MUST NOT be present.  The Failed-AVP AVP
      MUST be included and contain a copy of the offending AVP.




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   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 message definition.  The Failed-AVP AVP 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
      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 to PaC or from PaC to PAA.  This error is
      returned when a message is received with an invalid message
      length.


9.4.8 EAP-Payload AVP

   The EAP-Payload AVP (AVP Code 1031) is of type OctetString and is
   used to encapsulate the actual EAP packet that is being exchanged
   between the EAP peer and the EAP authenticator.

9.4.9 Session-Lifetime AVP

   The Session-Lifetime AVP (Code 1032) data is of type Unsigned32. It
   contains the number of seconds remaining before the 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 cases where a request is rejected or not
   fully processed due to erroneous information in a specific AVP.  The
   format of the Failed-AVP AVP is defined in [RFC3588].





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9.4.11 NAP-Information AVP

   The NAP-Information AVP (AVP Code: 1034) is of type Grouped, and
   contains zero or one Provider-Identifier AVP which carries the
   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 ::= < AVP Header: 1034 >
                    0*1 { Provider-Identifier }
                        { Provider-Name }
                     *  [ AVP ]


9.4.12 ISP-Information AVP

   The ISP-Information AVP (AVP Code: 1035) is of type Grouped, and
   contains zero or one Provider-Identifier AVP which carries the
   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 ::= < AVP Header: 1035 >
                    0*1 { Provider-Identifier }
                        { Provider-Name }
                     *  [ AVP ]


9.4.13 Provider-Identifier AVP

   The Provider-Identifier AVP (AVP Code: 1036) is of type Unsigned32,
   and contains an IANA assigned "SMI Network Management Private
   Enterprise Codes" [ianaweb] value, encoded in 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 provider.

9.5 AVP Occurrence Table

   The following tables lists the AVPs used in this document, and
   specifies in which PANA messages they MAY, or MAY NOT be present.

   The table uses the following symbols:

   0     The AVP MUST NOT be present in the message.






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   0+    Zero or more instances of the AVP MAY be present in the
         message.

   0-1   Zero or one instance of the AVP MAY be present in the message.
         It is considered an error if there are more than one instance
         of the AVP.

   1     One instance of the AVP MUST be present in the 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  |  0  |  0  | 0-1 |  0  |  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  |
      Session-Id          |  1   |  1   |  1  |  1  |  1  |
      Termination-Cause   |  0   |  0   |  1  |  0  |  0  |
      EAP-Payload         | 0-1  | 0-1  |  0  |  0  |  0  |
      MAC                 | 0-1  | 0-1  | 0-1 | 0-1 | 0-1 |
      Device-Id           |  1+  |  1+  |  0  |  0  |  0  |
      Cookie              |  0   |  0   |  0  |  0  |  0  |
      Protection-Cap.     |  0   |  0   |  0  |  0  |  0  |
      Session-Lifetime    |  0   |  0   |  0  |  0  |  0  |



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      Failed-AVP          |  0   |  0   |  0  |  0  |  1  |
      ISP-Information     |  0   |  0   |  0  |  0  |  0  |
      NAP-Information     |  0   |  0   |  0  |  0  |  0  |
      --------------------+------+------+-----+-----+-----+

                    Figure 10: AVP Occurrence Table













































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10. PANA Protocol Message Retransmissions

   The PANA protocol provides retransmissions for all the message
   exchanges except PANA-Auth-Request/Answer. PANA-Auth-Request messages
   carry EAP requests which are retransmitted by the EAP protocol
   entities when needed. The 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 PDI and PSA messages are always sent by the PaC.  PBR is sent by
   PAA.  The last two messages, PRAR and PTR are sent either by PaC or
   PAA.

   The rule is that the sender of the request message retransmits the
   request if the corresponding answer is not received in time.  Answer
   messages are sent as answers to the request messages, not based on a
   timer.  Exception to this rule is the PSA message.  Because of the
   stateless nature of the PAA in the beginning PaC provides
   retransmission also for the PSA message.  PANA-Error messages MUST
   not be 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
   message exchange terminates when either the 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 retransmission behavior is controlled and described by the
   following variables:

         RT     Retransmission timeout

         IRT    Initial retransmission time

         MRC    Maximum retransmission count

         MRT    Maximum retransmission time

         MRD    Maximum retransmission duration




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         RAND   Randomization factor

   With each message transmission or retransmission, the 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.

   Each of the 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
   cryptographically sound.  The algorithm SHOULD produce a different
   sequence of random numbers from each invocation.

   RT for the first message transmission is 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 value of RT (disregarding the
   randomization added by the use of RAND).  If MRT has a value of 0,
   there is no upper limit on the value of RT. Otherwise:

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

   MRC specifies an upper bound on the 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.




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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 sec   Initial PDI timeout.
           PDI_MRT         120 secs  Max PDI timeout value.
           PDI_MRC           0       Configurable.
           PDI_MRD           0       Configurable.

           REQ_IRT           1 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




























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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] 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] 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, a simple TTL
   check can prevent off-link attacks. Furthermore, additional filtering
   can be enabled on the EPs. An EP may be able to filter unauthorized
   PAA advertisements when they are received on the access side of the



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   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
   (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
   [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



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   [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
   object (MAC AVP) is defined which 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 used for this object
   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 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 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) 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 AAA-authorized
   session lifetime with an additional tolerance period. Unless PANA
   state is updated by executing another EAP authentication, PANA SA is
   removed when the current session expires. The lifetime of the PANA SA
   has to be bound to the AAA-authorized session lifetime with an
   additional tolerance period. Unless PANA state is updated by
   executing another EAP authentication, PANA SA is removed when the
   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
   [I-D.ietf-pppext-eap-ttls],PEAP [I-D.josefsson-pppext-eap-tls-eap] or



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   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]. Solving these
   problems is outside the scope of PANA. The compound authentication
   problem described in [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 [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 [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
   [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



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   established. As an example see Section 1 of
   [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 protection (for example IPsec
   [I-D.ietf-pana-ipsec]).

   As motivated in Section 6.4 of [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) 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. Operators are
   generally motivated to detect a disconnected end host as soon as
   possible in order to release resources (i.e., garbage collection).
   The PAA can remove per-session state information including installed
   security association, packet filters, etc.

   Different procedures can be used for disconnect indication. PANA
   cannot assume 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.

   A PANA session is associated with a session lifetime. The session is
   terminated unless it is refreshed by a new round of EAP
   authentication before it expires. Therefore, at the latest a
   disconnected client can be detected when its lifetime expires. A
   disconnect may also be detected earlier by using PANA
   reauthentication messages. A request message can be generated by
   either PaC or PAA at any time and the peer must respond with an
   answer message. A successful round-trip of this exchange is a simple
   verification that the peer is alive. This test can be engaged when
   there is a possibility that the peer might have disconnected (e.g.,
   after discontinuation of data traffic). Periodic use of this exchange



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   as a 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 abuse of 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.




































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12. Open Issues

   A list of open issues is maintained at [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.











































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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.













































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14. Acknowledgments

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















































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Normative References

   [I-D.ietf-pana-usage-scenarios]
              Ohba, Y., "Problem Statement and Usage Scenarios for
              PANA", draft-ietf-pana-usage-scenarios-06 (work in
              progress), April 2003.

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

   [I-D.ietf-pana-threats-eval]
              Parthasarathy, M., "PANA Threat Analysis and security
              requirements", draft-ietf-pana-threats-eval-04 (work in
              progress), May 2003.

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

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

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

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

   [I-D.ietf-pana-ipsec]
              Parthasarathy, M., "PANA 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.




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   [RFC2716]  Aboba, B. and 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),
              March 2003.

   [I-D.ietf-pppext-eap-ttls]
              Funk, P. and S. Blake-Wilson, "EAP Tunneled TLS
              Authentication Protocol (EAP-TTLS)",
              draft-ietf-pppext-eap-ttls-03 (work in progress), August
              2003.

   [I-D.tschofenig-eap-ikev2]
              Tschofenig, H. and D. Kroeselberg, "EAP IKEv2 Method
              (EAP-IKEv2)", draft-tschofenig-eap-ikev2-01 (work in
              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.
              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.



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   [I-D.walker-aaa-key-distribution]
              Housley, R., Walker, J. and N. Cam-Winget, "AAA 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 D. Simon, "EAP GSS Authentication Protocol",
              draft-aboba-pppext-eapgss-12 (work in progress), April
              2002.

   [RFC2478]  Baize, E. and D. Pinkas, "The Simple and Protected GSS-API
              Negotiation Mechanism", RFC 2478, December 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),
              August 2003.

























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Informative References

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

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

   [mitm]     Asokan, N., Niemi, V. 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.

   [802.11i]  Institute of Electrical and Electronics Engineers, "Draft
              supplement to 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 Electrical and Electronics Engineers,
              "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", IEEE Standard 802.11, 1997.























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URIs

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


Authors' Addresses

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

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


   Yoshihiro Ohba
   Toshiba America Information Systems, Inc.
   9740 Irvine Blvd.
   Irvine, CA  92619-1697
   USA

   Phone: +1 973 829 5174
   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: Hannes.Tschofenig@siemens.com







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   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











































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Appendix A. Adding sequence number to PANA for carrying EAP

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

   EAP [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 11: Undesirable scenario

   In Figure 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



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   comparison between the two approaches is provided. The method
   described in Appendix A.3.1 (i.e., the dual sequence number with
   orderly-delivery method) is suggested as the preferred method for
   PANA transport.

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 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.

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.










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        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 12: Example for Single sequence number with EAP retransmission

   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.)

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 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



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           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]



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

   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



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   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.

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.

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.






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   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]


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            |
         <--+                   (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]
                                (duplicate detected by PaC)
      15.------->   (y+6,x+8)   PANA-Bind-Answer




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   Figure 14: Example for Dual sequence number with orderly-delivery


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)



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      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 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 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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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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