PANA Working Group                                           D. Forsberg
Internet-Draft                                                     Nokia
Expires: August 9, November 5, 2004                                  Y. Ohba (Ed.)
                                                                 Toshiba
                                                                B. Patil
                                                                   Nokia
                                                           H. Tschofenig
                                                                 Siemens
                                                                A. Yegin
                                                         DoCoMo USA Labs
                                                        February 9,
                                                                 Samsung
                                                             May 7, 2004

     Protocol for Carrying Authentication for Network Access (PANA)
                        draft-ietf-pana-pana-03
                        draft-ietf-pana-pana-04

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
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   This Internet-Draft will expire on August 9, November 5, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

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

Table of Contents

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   4   5
   1.1    Specification of Requirements  . . . . . . . . . . . . . .   4   5
   2.     Terminology  . . . . . . . . . . . . . . . . . . . . . . .   5   6
   3.     Protocol Overview  . . . . . . . . . . . . . . . . . . . .   7   8
   4.     Protocol Details . . . . . . . . . . . . . . . . . . . . .   9  10
   4.1    Common Processing Rules  . . . . . . . . . . . . . . . . .   9  10
   4.1.1  Payload Encoding . . . . . . . . . . . . . . . . . . . . .   9  10
   4.1.2  Transport Layer Protocol . . . . . . . . . . . . . . . . .  10  11
   4.1.3  Fragmentation  . . . . . . . . . . . . . . . . . . . . . .  10  11
   4.1.4  Sequence Number and Retransmission . . . . . . . . . . . .  10  11
   4.1.5  PANA Security Association  . . . . . . . . . . . . . . . .  11  12
   4.1.6  Message Authentication Code  . . . . . . . . . . . . . . .  12  14
   4.1.7  Message Validity Check . . . . . . . . . . . . . . . . . .  13  14
   4.1.8  Error Handling . . . . . . . . . . . . . . . . . . . . . .  14  15
   4.2    Discovery and Initial Handshake Phase  . . . . . . . . . .  14  16
   4.3    Authentication Phase . . . . . . . . . . . . . . . . . . .  17  19
   4.4    Re-authentication  . . . . . . . . . . . . . . . . . . . .  19  22
   4.5    Termination Phase  . . . . . . . . . . . . . . . . . . . .  20  23
   4.6    Illustration of a Complete Message Sequence  . . . . . . .  21  24
   4.7    Device ID Choice . . . . . . . . . . . . . . . . . . . . .  22  27
   4.8    Session Lifetime . . . . . . . . . . . . . . . . . . . . .  22  27
   4.9    Mobility Handling  . . . . . . . . . . . . . . . . . . . .  23  28
   4.10   Event Notification . . . . . . . . . . . . . . . . . . . .  24
   4.11   Support for Separate EP  . . . . . . . . . . . . . . . . .  24  30
   5.     PANA Security Association Establishment  . . . . . . . . .  25  31
   6.     Authentication Method Choice . . . . . . . . . . . . . . .  26
   7.     Filter Rule Installation . . . . . . . . . . . . . .     Message Formats  . . .  27
   8.     Data Traffic Protection . . . . . . . . . . . . . . . . .  28
   9.     Message Formats .  32
   6.1    IP and UDP Headers . . . . . . . . . . . . . . . . . . . .  29
   9.1  32
   6.2    PANA Header  . . . . . . . . . . . . . . . . . . . . . . .  29
   9.2  32
   6.3    AVP Header . . . . . . . . . . . . . . . . . . . . . . . .  30
   9.3  34
   6.4    PANA Messages  . . . . . . . . . . . . . . . . . . . . . .  32
   9.3.1  36
   6.4.1  Message Specifications . . . . . . . . . . . . . . . . . .  33
   9.3.2  36
   6.4.2  PANA-PAA-Discover (PDI)  . . . . . . . . . . . . . . . . .  33
   9.3.3  37
   6.4.3  PANA-Start-Request (PSR) . . . . . . . . . . . . . . . . .  33
   9.3.4  37
   6.4.4  PANA-Start-Answer (PSA)  . . . . . . . . . . . . . . . . .  33
   9.3.5  37
   6.4.5  PANA-Auth-Request (PAR)  . . . . . . . . . . . . . . . . .  34
   9.3.6  38
   6.4.6  PANA-Auth-Answer (PAN) . . . . . . . . . . . . . . . . . .  34
   9.3.7  38
   6.4.7  PANA-Bind-Request (PBR)  . . . . . . . . . . . . . . . . .  34
   9.3.8  38
   6.4.8  PANA-Bind-Answer (PBA) . . . . . . . . . . . . . . . . . .  35
   9.3.9  38
   6.4.9  PANA-Reauth-Request (PRAR) . . . . . . . . . . . . . . . .  35
   9.3.10  39
   6.4.10 PANA-Reauth-Answer (PRAA)  . . . . . . . . . . . . . . . .  35
   9.3.11  39
   6.4.11 PANA-Termination-Request (PTR) . . . . . . . . . . . . . .  35
   9.3.12  39
   6.4.12 PANA-Termination-Answer (PTA)  . . . . . . . . . . . . . .  36
   9.3.13  39
   6.4.13 PANA-Error (PER) . . . . . . . . . . . . . . . . . . . . .  36
   9.4  40
   6.4.14 PANA-FirstAuth-End-Request (PFER)  . . . . . . . . . . . .  40
   6.4.15 PANA-FirstAuth-End-Answer (PFEA) . . . . . . . . . . . . .  40
   6.5    AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . .  36
   9.4.1  40
   6.5.1  MAC AVP  . . . . . . . . . . . . . . . . . . . . . . . . .  36
   9.4.2  41
   6.5.2  Device-Id AVP  . . . . . . . . . . . . . . . . . . . . . .  37
   9.4.3  41
   6.5.3  Session-Id AVP . . . . . . . . . . . . . . . . . . . . . .  37
   9.4.4  41
   6.5.4  Cookie AVP . . . . . . . . . . . . . . . . . . . . . . . .  38
   9.4.5  42
   6.5.5  Protection-Capability AVP  . . . . . . . . . . . . . . . .  38
   9.4.6  42
   6.5.6  Termination-Cause AVP  . . . . . . . . . . . . . . . . . .  38
   9.4.7  42
   6.5.7  Result-Code AVP  . . . . . . . . . . . . . . . . . . . . .  38
   9.4.8  42
   6.5.8  EAP-Payload AVP  . . . . . . . . . . . . . . . . . . . . .  42
   9.4.9  46
   6.5.9  Session-Lifetime AVP . . . . . . . . . . . . . . . . . . .  42
   9.4.10  46
   6.5.10 Failed-AVP AVP . . . . . . . . . . . . . . . . . . . . . .  42
   9.4.11  46
   6.5.11 NAP-Information AVP  . . . . . . . . . . . . . . . . . . .  42
   9.4.12  46
   6.5.12 ISP-Information AVP  . . . . . . . . . . . . . . . . . . .  42
   9.4.13  47
   6.5.13 Provider-Identifier AVP  . . . . . . . . . . . . . . . . .  42
   9.4.14  47
   6.5.14 Provider-Name AVP  . . . . . . . . . . . . . . . . . . . .  43
   9.4.15  47
   6.5.15 EP-Device-Id AVP . . . . . . . . . . . . . . . . . . . . .  43
   9.4.16  47
   6.5.16 Key-Id AVP . . . . . . . . . . . . . . . . . . . . . . . .  43
   9.5  47
   6.5.17 Post-PANA-Address-Configuration (PPAC) AVP Occurrence Table . . . . . . . .  47
   6.5.18 Nonce AVP  . . . . . . . . . . .  43
   10.    PANA Protocol Message Retransmissions . . . . . . . . . .  45
   10.1   Transmission and Retransmission Parameters . . .  48
   6.6    AVP Occurrence Table . . . . .  47
   11.    Security Considerations . . . . . . . . . . . . . .  49
   7.     PANA Protocol Message Retransmissions  . . .  48
   12.    Open Issues . . . . . . .  51
   7.1    Transmission and Retransmission Parameters . . . . . . . .  53
   8.     IANA Considerations  . . . . . . . . . . . . . .  53
   13.    Change History . . . . .  54
   8.1    PANA UDP Port Number . . . . . . . . . . . . . . . . . . .  54
   14.    Acknowledgments
   8.2    PANA Multicast Address . . . . . . . . . . . . . . . . . .  54
   8.3    PANA Header  . . .  55
          Normative References . . . . . . . . . . . . . . . . . . .  56
          Informative References .  54
   8.3.1  Message Type . . . . . . . . . . . . . . . . .  57
          Authors' Addresses . . . . . .  54
   8.3.2  Flags  . . . . . . . . . . . . . .  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 . . . .  54
   8.4    AVP Header . . . . . . . . .  62
   A.2.1  Single sequence number with EAP retransmission method . .  62
   A.2.2  Single sequence number with PANA-layer retransmission
          method . . . . . . . . . . . . .  54
   8.4.1  AVP Code . . . . . . . . . . . . .  63
   A.3    Dual sequence number approach . . . . . . . . . . . .  54
   8.4.2  Flags  . .  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 . . . . . . . . . .  55
   8.4.3  Vendor Id  . . . . . . . . . . . . . .  69
          Intellectual Property and Copyright Statements . . . . . .  70

1. Introduction

   Providing secure network access service requires access control based
   on the authentication and authorization of the clients and the access
   networks.  Initial and subsequent client-to-network authentication
   provides parameters that are needed to police the traffic flow
   through the enforcement points.  A 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 work is identified as designing a link-layer agnostic
   transport for network access authentication methods. The Extensible
   Authentication Protocol (EAP) [I-D.ietf-eap-rfc2284bis] provides such
   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 are
   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
   [I-D.ietf-eap-rfc2284bis].

1.1 Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  The key
   words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
   "SHOULD NOT", "RECOMMENDED", "MAY", . . . .  55
   8.5    AVP Values . . . . . . . . . . . . . . . . . . . . . . . .  55
   8.5.1  MAC AVP Values . . . . . . . . . . . . . . . . . . . . . .  55
   8.5.2  Device-Id AVP Values . . . . . . . . . . . . . . . . . . .  55
   8.5.3  Protection-Capability AVP Values . . . . . . . . . . . . .  55
   8.5.4  Result-Code AVP Values . . . . . . . . . . . . . . . . . .  55
   8.5.5  Termination-Cause AVP Values . . . . . . . . . . . . . . .  55
   8.5.6  Provider-Identifier AVP Values . . . . . . . . . . . . . .  55
   8.5.7  Post-PANA-Address-Configuration AVP Values . . . . . . . .  55
   9.     Security Considerations  . . . . . . . . . . . . . . . . .  56
   10.    Open Issues and "OPTIONAL" in this document Change History . . . . . . . . . . . . . .  62
   11.    Acknowledgments  . . . . . . . . . . . . . . . . . . . . .  63
          Normative References . . . . . . . . . . . . . . . . . . .  64
          Informative References . . . . . . . . . . . . . . . . . .  66
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  69
          Intellectual Property and Copyright Statements . . . . . .  71

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 be interpreted as described in [RFC2119].

2. Terminology

   This section describes some terms introduced in this document:

   PANA Session:

      PANA session is defined as police the exchange of messages traffic flow
   through the enforcement points.  A protocol is needed to carry
   authentication methods between the
      PANA Client (PaC) client and the PANA Authentication Agent (PAA) to
      authenticate a user (PaC) access network.

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

   Scope of this work is considered identified as active until there is designing a disconnect
      indication by the PaC or the PAA terminates it.  A distinct link-layer agnostic
   transport for network access authentication methods. The Extensible
   Authentication Protocol (EAP) [I-D.ietf-eap-rfc2284bis] provides such
   authentication methods.  In other words, PANA
      session is associated with a pair will carry EAP which
   can carry various authentication methods.  By the virtue of device identifiers enabling
   transport of PaC and
      PAA.  For example, if the PaC has two interfaces connected to the
      same IP link with different IP addresses and IP address is used as
      a device identifier, a distinct PANA session will be created per
      interface if both interfaces addresses need to EAP above IP, any authentication method that can be authorized for
      network access.

   Session Identifier:

      This identifier
   carried as an EAP method is used made available to uniquely identify a PANA session on the
      PAA and PaC.  It is included in PANA messages to bind the message hence to any
   link-layer technology.  There is a specific PANA session.

   PANA Security Association:

      The representation clear division of the trust relation labor between the PaC
   PANA, EAP and the
      PAA that is created at the end of the authentication phase.  This
      security association includes the device identifier of the peer, EAP methods.

   Various environments and a shared key when available. usage models for PANA Client (PaC):

      The client side of are identified in the
   [I-D.ietf-pana-usage-scenarios] Internet-Draft.  Potential security
   threats for network-layer access authentication protocol that resides are
   discussed in [I-D.ietf-pana-threats-eval] draft.  These two drafts
   have been essential in defining the host device
      which is responsible for providing requirements
   [I-D.ietf-pana-requirements] on the credentials to prove its
      identity for network access authorization.

   Device Identifier (DI):

      The identifier used PANA protocol. Note that some of
   these requirements are imposed by the network as chosen payload, EAP
   [I-D.ietf-eap-rfc2284bis].

   There are components that are part of a handle to control and
      police the complete secure network access
   solution but are outside of a client.  Depending on the access
      technology, PANA protocol specification,
   including IP address configuration, authentication method choice,
   filter rule installation, data traffic protection and PAA-EP
   protocol.  These components are described in separate documents
   [I-D.ietf-pana-framework][I-D.ietf-pana-snmp].

1.1 Specification of Requirements

   In this identifier might contain any document, several words are used to signify the requirements
   of IP address,
      link-layer address, switch port number, etc. the specification.  These words are often capitalized.  The key
   words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
   "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
   are to be interpreted as described in [RFC2119].

2. Terminology

   This section describes some terms introduced in this document:

   PANA Session:

      PANA session is defined as the exchange of a connected
      device. messages between the
      PANA Client (PaC) and the PANA Authentication Agent (PAA):

      The access (PAA) to
      authenticate a user (PaC) for network side entity of access.  If the protocol whose
      responsibility
      authentication is to verify unsuccessful, the credentials provided by session is terminated.  The
      session is considered as active until there is a PANA
      client and grant network access service to disconnect
      indication by the device PaC or the PAA terminates it.  A distinct PANA
      session is associated with the client and identified by a DI.

   Enforcement Point (EP):

      A node on pair of device identifiers of PaC and
      PAA.  For example, if the access network where per-packet enforcement policies
      (i.e., filters) are applied on PaC has two interfaces connected to the inbound
      same IP link with different IP addresses and outbound traffic of
      client devices.  Information IP address is used as
      a device identifier, a distinct PANA session will be created per
      interface if both interfaces addresses need to be authorized for
      network access.

   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:

      A PANA security association is a relationship between the PaC and
      PAA, formed by the sharing of cryptographic keying material and
      associated context.  Security associations are duplex.  That is,
      one security association is needed to protect the bidirectional
      traffic between the PaC and the PAA.

   PANA Client (PaC):

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

   Device Identifier (DI):

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

   PANA Authentication Agent (PAA):

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

   Enforcement Point (EP):

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

   Network Access Provider (NAP):

      A service provider that provides physical and link-layer
      connectivity to an access network it manages.

   AAA-Key:

      A key derived by the EAP peer and EAP server and transported to
      the authenticator [I-D.ietf-eap-keying].

3. Protocol Overview

   The PANA protocol involves two functional entities namely the PaC and
   the PAA.  The protocol resides above the transport layer and the
   details are explained in Section 4.

   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).  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.  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

   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

   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.

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. (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  EP-Device-Id AVP: contains the device identifier of an EP.

   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.

   o  Key-Id AVP: contains a AAA-Key identifier.

4.1.2 Transport Layer Protocol

   PANA uses UDP as its transport layer

   o  PPAC AVP: Post-PANA-Address-Configuration AVP.  Conveys the list
      of IP address configuration methods available when sent by the
      PAA, and the chosen method when sent by the PaC.

   o  Nonce AVP: contains a randomly chosen value.

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.  PANA-PAA-Discover MAY be unicasted when the PaC MUST NOT use unspecified knows the
   IP address for communicating
   with of the 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 [1] 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 7 for default timer and
   maximum retransmission count parameters.

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 AAA-Key.  A PANA SA is
   not created when the PANA authentication fails or no AAA-Key is
   produced by any EAP authentication method.  In the case where two EAP
   authentications are performed in a sequence in a single PANA
   authentication,
   authentication phase, it is possible that two AAA-Keys are derived.
   If this happens, the PANA SA MUST be bound to the AAA-Key derived generated from the
   first EAP authentication. both AAA-Keys.
   When a new AAA-Key is derived as a result of EAP-based
   re-authentication, any key derived from the old AAA-Key MUST be
   updated to a new one that is derived from the new AAA-Key.  In order
   to distinguish the new AAA-Key from old ones, one Key-Id AVP MUST be
   carried in PANA-Bind-Request and PANA-Bind-Answer message messages or
   PANA-FirstAuth-End-Request and PANA-FirstAuth-End-Answer messages at
   the end of the EAP authentication phase which resulted in deriving a new
   AAA-Key.  The Key-Id AVP is of type Unsigned32 and MUST contain a
   value that uniquely identifies the AAA-Key within the PANA session.
   The PANA-Bind-Answer message (or the PANA-FirstAuth-End-Answer
   message) sent in response to a PANA-Bind-Request message (or a
   PANA-FirstAuth-End-Request message) with a Key-Id AVP MUST contain a
   Key-Id AVP with the same AAA-Key identifier carried in the request. PANA-Bind-Request
   PANA-Bind-Request, PANA-Bind-Answer, PANA-FirstAuth-End-Request and
   PANA-Bind-Answer
   PANA-FirstAuth-End-Answer messages with a Key-Id AVP MUST also carry
   a MAC AVP whose value is computed by using the new AAA-Key. PANA-MAC-Key
   derived from the new AAA-Key (or the new pair of AAA-Keys when the
   PANA_MAC_KEY is derived from two AAA-Keys).  Although the
   specification does not mandate a particular method for calculation of
   Key-Id AVP value, a simple method is to use monotonically increasing
   numbers.
   numbers."

   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

      *  List of device identifiers of EPs

      *  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:

         +  AAA-Key

         +  AAA-Key Identifier

         +  PANA_MAC_Key

   The PANA_MAC_Key is used to integrity protect PANA messages and messages.  When
   the PANA_MAC_Key is derived from the AAA-Key a single AAA-Key, it is computed in
   the following way:

      PANA_MAC_KEY = The first N bits of
                     HMAC_SHA1(AAA-Key, ISN_pac | ISN_paa | Session-ID)

   where the value of N depends on the integrity protection algorithm in
   use, i.e., N=160 for HMAC-SHA1.

   When the PANA_MAC_Key is derived from two AAA-Keys, it is computed in
   the following way:

      PANA_MAC_KEY = The first N bits of
                     HMAC_SHA1(AAA-Key1 | AAA-Key2, ISN_pac | ISN_paa |
                               Session-ID)

   where AAA-Key1 and AAA-Key2 are AAA-Keys for the first and second EAP
   authentication in a single PANA authentication phase, respectively.

   The length of AAA-Key AAA-Key, AAA-Key1 and AAA-Key2 MUST be N bits 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 = PANA_MAC_PRF(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.  PANA_MAC_PRF
   represents the pseudo random function corresponding to the MAC
   algorithm specified in the MAC AVP.  In this version of draft,
   PANA_MAC_PRF is HMAC-SHA1. The PaC and PAA MUST use the same
   algorithm to calculate a MAC AVP they originate and receive.  The
   algorithm is determined by the PAA when a PANA-Bind-Request with a
   MAC AVP is sent.  When the PaC does not support the MAC algorithm
   specified in the PANA-Bind-Request message, it MUST silently discard
   the message.  The PAA MUST NOT change the MAC algorithm throughout
   the continuation of the PANA session.

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  The IP Hop Limit (or TTL) field has a value of 255, i.e., the
      packet could not possibly have been forwarded by a router.

   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). header(s), or other auxiliary indetifier provided by the
      lower-layers (e.g., circuit ID).

   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.

   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
   well-known link local multicast address (TBD) and UDP port (TBD).
   PANA PAA discovery assumes that PaC 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.

   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 MAY also choose to start sending packets before getting
   authenticated.  In that case, the network should MAY detect this and send an
   unsolicited PANA-Start-Request message to PaC. PaC in addition to
   filtering the unauthorized traffic.  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  PAA-to-EP protocol MAY 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 used for this purpose.

   A PANA-Start-Request message MAY carry a Cookie AVP that contains a
   cookie.  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-
   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.

   Protection-Capability and Post-PANA-Address-Configuration AVPs MAY be
   optionally included in the PANA-Start-Request in order to indicate
   required and available capabilities for the network access.  These
   AVPs MAY be used by the PaC for assessing the capability match even
   before the authentication takes place.  But these AVPs are provided
   during the insecure discovery phase, there are certain security risks
   involved in using the provided information. See Section 9 for further
   discussion on this.

   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 MAY indicate its choice of ISP by
   including its an ISP-Information AVP in the PANA-Start-Answer message.
   When a AAA routing will backend is used, the identity of the destination AAA
   server or realm MUST be determined based on the ISP choice if an explicitly chosen
   ISP.  When the ISP-Information AVP is specified in not present, the PANA-Start-Answer message, otherwise it will be
   based access network
   MAY rely on the client identifier carried in the EAP identifier. authentication
   method to make this determination.

   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
   If the S-flag in the PANA-Start-Answer message.  AAA
   routing for NAP message is not set, only one
   authentication will be based on is performed and the NAP. processing occurs as described
   earlier.  If the S-flag in the PANA-Start-Answer message is set, the
   determination of the destination AAA routing server or realm for ISP
   authentication will be based on the ISP choice if an
   ISP-Information AVP is specified in performed as described earlier.  In addition, where
   backend AAA servers are used for NAP authentication, the PANA-Start-Answer message,
   otherwise it will be based on EAP identifier.  If NAP is
   considered the S-flag of ultimate AAA realm, and the
   received PANA-Start-Request message destination AAA server for
   this authentication is set and determined entirely by the S-flag of local configuration
   on the
   corresponding PANA-Start-Answer message is not set, only one EAP
   authentication occurs without distinction between NAP and ISP
   authentications.  In this case, access server hosting PAA (NAS).

   The PaC can still indicate its choice of choose an ISP by including its and contain an ISP-Information AVP in for the
   chosen ISP in a PANA-Start-Answer message even when there is no
   ISP-Information AVP contained in the PANA-Start-Request message.

   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.

   When a Cookie-AVP is carried in a PANA-Start-Request message, the
   initial

   Initial EAP Request MUST NOT MAY be optionally carried in by the
   PANA-Start-Request (as opposed to by a later PANA-Auth-Request)
   message in order for to reduce the number of round-trips.  This
   optimization SHOULD NOT be used if the PAA discovery is desired to be
   stateless.

   When a Cookie-AVP the S-flag is not carried set in a PANA-Start-Request message, the
   PAA does not need to be stateless.  In this case, the initial
   EAP Request message MAY MUST NOT be carried in the PANA-Start-Request message.
   (If the initial EAP Request were contained in the PANA-Start-Request
   message during the S-flag negotiation, the PaC cannot tell whether
   the EAP Request is for NAP authentication or ISP authentication.)

   If the initial EAP Request message is carried in the
   PANA-Start-Request message, an EAP Response message MUST be carried
   in the PANA-Start-Answer message returned to the PAA.

   In any case, PANA MUST NOT generate an EAP message on behalf of EAP
   peer or EAP (pass-through) authenticator.

   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 that carries a Cookie AVP is never
   retransmitted.  A PANA-Start-Request message that does not carry a
   Cookie AVP is retransmitted based on timer.  A PANA-Start-Answer
   message that carries a Cookie AVP is retransmitted based on timer in the same
   manner as other messages timer.  A
   PANA-Start-Answer message that does not carry a Cookie AVP is never
   retransmitted at PANA-layer. based on timer.

   It is possible that both PAA and PaC initiate the discovery and
   initial handshake procedure at the same time, i.e., the PAA sends a
   PANA-Start-Request message while the PaC sends a PANA-PAA-Discover
   message.  To resolve the race condition, the PAA SHOULD silently
   discard the PANA-PAA-Discover message received from the PaC after it
   has sent a PANA-Start-Request message with creating a state (i.e., no
   Cookie AVP included) for the PaC.  In this case PAA will retransmit
   PANA-Start-Request based on a timer, if PaC doesn't respond in time
   (message was lost for example).  If PAA had sent stateless
   PANA-Start-Request message (i.e., a Cookie AVP was included), then it
   SHOULD answer to the PANA-PAA-Discover message.

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

 Figure 2: Example Sequence for Discovery and Initial Handshake Phase
                 when PANA-PAA-Discover is sent by PaC

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

  Figure 3: Example Sequence for Discovery and Initial Handshake when
                    PANA-PAA-Discover
                 discovery is sent triggered by EP data traffic

4.3 Authentication Phase

   The main task in authentication phase is to carry EAP messages
   between PaC and PAA. All  EAP Request messages except for are carried in PANA-
   Auth-Request messages and optionally carried in PANA-Start-Request
   messages.  EAP Success/Failure Response messages are carried in the PANA-Auth-Request/PANA-Auth-Answer PANA-Auth-Answer
   messages and optionally carried in PANA-Start-Answer messages.  When
   an EAP Success/Failure message is sent from a PAA, the message is
   carried in the a PANA-Bind-Request (PBR) or PANA-FirstAuth-End-Request
   (PFER) message.  The PANA-
   Bind-Request PANA-FirstAuth-End-Reques message is acknowledged with a PANA-Bind-Answer.  It is
   possible to carry multiple MUST be used
   at the end of the first EAP sequences when the PaC and PAA have negotiated
   during the discovery and initial handshake phase to perform separate
   NAP and ISP authentications in a single PANA session. authentication phase.
   Otherwise, the PANA-Bind-Request message MUST be used.  The
   PANA-Bind-Request and PANA-FirstAuth-End-Request messages MUST be
   acknowledged with a PANA-Bind-Answer (PBA) and a
   PANA-FirstAuth-End-Answer (PFEA) messages, respectively.

   When the PaC and PAA have negotiated during the discovery and initial
   handshake phase to perform separate NAP and ISP authentications, the
   S-flag of PANA-Auth-Request and PANA-Auth-Answer messages MUST be
   set.  Otherwise, the S-flag MUST NOT be set.

   When separate NAP and ISP authentications in a
   single PANA session, are performed, 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 using N-flag in the first PANA-Auth-Request PANA
   message sent to the
   PaC. In the case where header.  When NAP authentication is performed, the PaC agreed to perform separate
   authentications but did not specify its N-flag
   MUST be set.  When ISP choice in
   PANA-Start-Answer message, authentication is performed, the PAA N-flag MUST include its NAP-Information
   AVP in PANA-Auth-Request message when it performs NAP authentication
   and
   NOT be set. The N-flag MUST NOT include any service provider information AVP be set when it
   performs S-flag is not set.

   When separate NAP and ISP authentications are performed, if the first
   EAP authentication so that has failed, the PaC PAA can always distinguish
   ISP choose not to perform the
   second EAP authentication from NAP authentication.  The PAA SHOULD stop
   including a NAP-Information or an ISP-Information AVP once it
   receives by clearing the S-flag of the
   PANA-FirstAuth-End-Request message.  In this case, the S-flag of the
   PANA-FirstAuth-End-Answer message sent by the PaC MUST be cleared.
   If the S-flag of the PANA-FirstAuth-End-Request message is set when
   the first PANA-Auth-Answer EAP authentication has failed, the PaC can choose not to
   perform the second EAP authentication by clearing the S-flag of the
   PANA-FirstAuth-End-Answer message.  If the first EAP authentication
   failed and the S-flag is not set in the PANA-FirstAuth-End-Answer
   message as a result of those operations, the current PANA session MUST be
   immediately deleted. Otherwise, the second EAP
   authentication. authentication MUST be
   performed.

   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 a network access authorization 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 derived, the
   PANA-FirstAuth-End-Request and PANA-FirstAuth-End-Answer and/or
   PANA-Bind-Request and PANA-Bind-Answer messages messages, and all subsequent
   PANA messages MUST contain a MAC AVP.  The PANA-Bind-Request

   When separate NAP and ISP authentications are performed and the
   PANA-Bind-Answer message exchange
   lower-layer is also used for binding device
   identifiers insecure, the two EAP methods MUST be capable of
   deriving keys.  In this case, if the PaC first EAP authentication is
   successful, the PANA-FirstAuth-End-Request and
   PANA-FirstAuth-End-Answer messages as well as PANA-Auth-Request and
   PANA-Auth-Answer messages in the PAA to second EAP authentication MUST be
   protected with the PANA SA. To achieve this, key derived from the AAA-Key for the first EAP
   authentication. The PANA-Bind-Request and the PANA-Bind-Answer SHOULD contain a
   device identifier of the PAA messages
   and the PaC, respectively, in a
   Device-Id AVP.  The PaC all subsequent PANA messages MUST use be protected either with the same type of device identifier
   as contained in
   AAA-Key for the PANA-Bind-Request message.  The PANA-Bind-Request
   message MAY also contain a Protection-Capability AVP to indicate first EAP authentication if
   link-layer or network-layer ciphering the first EAP
   authentication succeeds and the second EAP authentication fails, or
   with the AAA-Key for the second EAP authentication if the first EAP
   authentication fails and the second EAP authentication succeeds, or
   with the compound key derived from the two AAA-Keys, one for the
   first EAP authentication and the other from the second EAP
   authentication, if both the first and second EAP authentications
   succeed (see Section 4.1.5 for how the compound key is derived).

   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 when the identifiers are either IP or MAC addresses.  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.  Device identifier exchange that is protected by a
   MAC AVP prevents man-in-the-middle attacks.  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.

   Additionally, PANA-Bind-Request MUST include a
   Post-PANA-Address-Configuration AVP, which helps PAA to inform PaC
   about whether a new IP address MUST be configured and the available
   methods to do so.  PaC MUST include a PPAC AVP in order to indicate
   its choice of method when there is a match between the methods
   offered by the PAA and the methods available on the PaC.  When there
   is no match, a PPAC AVP MUST NOT be included and the Result-Code AVP
   MUST be set to PANA_PPAC_CAPABILITY_UNSUPPORTED in the
   PANA-Bind-Answer message.

   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] Section 4.1.4.

   EAP authentication can fail at a pass-through authenticator without
   sending an EAP-Failure message [I-D.ietf-eap-statemachine].  When
   this occurs, the PAA SHOULD send a PANA-Error message to the PaC with
   using PANA_UNABLE_TO_COMPLY result code.  The PaC SHOULD ignore the
   message unless it is secured by PANA or lower layer.  In any case, a
   more appropriate way is to rely on a timeout on the PaC.

   There is a case where EAP authentication succeeds with producing an
   EAP-Success message but network access authorization fails due to,
   e.g., authorization rejected by a AAA proxy or authorization locally
   rejected by a PAA. When this occurs, the PAA MUST send
   PANA-Bind-Request with a result code PANA_AUTHORIZATION_REJECTED.  If
   a AAA-Key is established between PaC and PAA by the time when the
   EAP-Success is generated by the EAP server (this is the case when the
   EAP method provides protected success indication), the this PANA-Bind
   message exchange MUST be protected with a MAC AVP and with carrying a
   Key-Id AVP.  The AAA-Key and the PANA session MUST be deleted after
   the PANA-Bind message exchange.

      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.,
                        PPAC, MAC]
         ----->     PANA-Bind-Answer(y+3,x+3)
                       [Device-Id, Protection-Cap.,     PANA-Bind-Answer(y+3,x+3)[Device-Id, PPAC, 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 MUST 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.  The PaC and the PAA can handle
   rate limitation on their own, they don't have to perform any
   coordination with each other. There is no negotiation of timers for
   this purpose.

      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
   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:

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

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

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

                 Figure 8: A Complete Message Sequence

4.7 Device ID Choice

   A PaC SHOULD configure an IP address before

   Another 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 message sequence is assumed that PAA knows the security mechanisms
   being provided or required on illustrated in Figure 9. The example
   assumes 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 following scenario:

   o  PaC multicasts PANA-PAA-Discover message

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

   o  PAA offers NAP and ISP separate authentication, as well as a
      choice of ISP from both sides.

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 "ISP1" and "ISP2".  PaC about accepts the valid lifetime of offer from
      PAA, with choosing "ISP1" as the PANA session. It MUST be ignored
   when included in other PANA messages. When there are multiple ISP.

   o  An EAP sequence for NAP authentication taking place, and an EAP sequence for ISP
      authentication is performed in this AVP SHOULD be included after order in authentication phase.

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

   o  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.
   PAA SHOULD initiate EAP authentication before methods derive keys.  Once the current session
   lifetime expires.

   PaC and PAA MAY optionally rely on lower-layer indications to
   expedite two EAP
      authenticatioins are successful, the detection of a disconnected peer. Availability and
   reliability of such indications depend on PANA_MAC_KEY is derived from
      the specific access
   technologies. two AAA-Keys.

   o  After PANA peer can use PANA-Reauth-Request message to verify
   the disconnection before taking an action.

   The session lifetime parameter SA is not related to the transmission of
   PANA-Reauth-Request messages. These established, all messages can be used for
   asynchronously verifying are integrity and
      replay protected with the liveness of MAC AVP.

   o  Re-authentication based on the peer and enabling
   mobility optimizations. The decision to send PANA-Reauth-Request
   message PANA-Reauth-Request/ PANA-Reauth-
      Answer exchange is taken locally performed.

   o  Re-authentication and does not require coordination between
   the peers.

   When separate EAP authentications termination phase are performed for ISP not shown.

      PaC      PAA  Message(tseq,rseq)[AVPs]
      -----------------------------------------------------
      // Discovery and initial handshake phase
         ----->    PANA-PAA-Discover (0,0)
         <-----     PANA-Start-Request (x,0)            // S-flag set
                    [Cookie, ISP-Information("ISP1"),
                     ISP-Information("ISP2"),
                     NAP-Information("MyNAP")]
         ----->     PANA-Start-Request-Answer (y,x)     // S-flag set
                    [Cookie, ISP-Information("ISP1")]   // PaC chooses "ISP1"

      // Authentication phase
         <-----     PANA-Auth-Request(x+1,y)[EAP]       // NAP in a
   single PANA session, it is possible that different authorization
   lifetime values are associated with the two authentications. In this
   case, the smaller authorization lifetime value MUST be used for
   calculating the PANA Session-Lifetime value. As a result, when
   EAP-based re-authentication occurs, both NAP authentication
                                                        // S- and ISP authentications
   will be performed in the same re-authentication procedure.

4.9 Mobility Handling

   When a PaC wants to resume an ongoing PANA session after connecting
   to another link N-flags set
         ----->     PANA-Auth-Answer(y+1,x+1)[EAP]      // S- and N-flags set
         <-----     PANA-Auth-Request(x+2,y+1)[EAP]     // S- and N-flags set
         ----->     PANA-Auth-Answer(y+2,x+2)[EAP]      // S- and N-flags set
         <-----     PANA-FirstAuth-End-Request(x+3,y+2) // S- and N-flags set
                      [EAP{Success}, Key-Id, MAC]
         ----->     PANA-FirstAuth-End-Answer(y+3,x+3)  // S- and N-flags set
                      [Key-Id, MAC]
         <-----     PANA-Auth-Request(x+3,y+4)[EAP, MAC]// ISP authentication
                                                        // S-flag set
         ----->     PANA-Auth-Answer(y+4,x+4)[EAP, MAC] // S-flag set
         <-----     PANA-Auth-Request(x+4,y+5)[EAP, MAC]// S-flag set
         ----->     PANA-Auth-Answer(y+5,x+5)[EAP, MAC] // S-flag set
         <-----     PANA-Bind-Request(x+5,y+6)          // S-flag set
                      [EAP{Success}, Device-Id, Key-Id,
                       Lifetime, Protection-Cap., PPAC, MAC]
         ----->     PANA-Bind-Answer(y+6,x+5)           // S-flag set
                      [Device-Id, Key-Id, PPAC, MAC]

     Figure 9: A Complete Message Sequence for NAP and ISP Separate
                            Authentications

4.7 Device ID Choice

   The device identifiers used in the same access network, it MAY send the unexpired context of PANA session can be an IP
   address, a MAC address, or an identifier that is not carried on data
   packets but has local significance in its PANA-Start-Answer message. In the
   absence of identifying a Session-Id AVP connected host
   (e.g., circuit ID).  The last type of identifiers are commonly used
   in this message, PAA MUST assume this physically secured point-to-point links where MAC addresses are
   not available.

   It is
   a fresh session and continue its normal execution.

   If assumed that PAA receives a session identifier in knows the PANA-Start-Answer
   message, link type 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 security
   mechanisms being provided or required to determine the previous PAA of on the
   PaC by relying access network (e.g.,
   based on physical security, link-layer ciphers enabled before or
   after PANA, or IPsec).  Based on that information, the PAA can decide
   what type of device ID will be used when running PANA session identifier with the
   client.  When IPsec-based mechanism [I-D.ietf-pana-ipsec] is outside the scope
   choice of
   PANA protocol. A possible solution is to embed the access control, PAA identifier in
   the PANA session identifier. Furthermore, SHOULD provide an IP address as device
   ID, and expect the mechanism required PaC to
   retrieve the session attributes from the previous PAA provide its IP address in return.  In case
   IPsec 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 not used, MAC addresses are used as device IDs when
   available.  If non-IPsec access control is enabled, and a MAC address
   is not configured to enable fast re-authentication, or
   can available, device ID exchange does not retrieve the occur within PANA.
   Instead, peers rely on lower-layers to provide locally-significant
   identifiers along with received PANA session attributes, or packets.

4.8 Session Lifetime

   The authentication phase determines the PANA session has
   already expired (i.e., session lifetime is zero), when
   the PAA MUST send network access authorization succeeds. The Session-Lifetime AVP
   MAY be optionally included in the PANA-Auth-Request PANA-Bind-Request message with to inform
   PaC about the new session identifier and let valid lifetime of the PANA exchange take its usual course. This action will engage session.  It MUST be ignored
   when included in other PANA messages.  When there are multiple 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 taking place, this AVP contained in SHOULD be included after the PANA-Reauth messages MUST
   final authentication.

   The lifetime is a non-negotiable parameter that can be
   generated and verified used by using PaC to
   manage PANA-related state.  PaC does not have to perform any actions
   when 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
   session is created upon successful completion of this exchange. This
   session inherits only lifetime expires, other than optionally purging local state.
   PAA SHOULD initiate EAP authentication before the current session lifetime, protection capability,
   lifetime expires.

   PaC and AAA-Key attributes from the previous session. Other attributes
   are generated based on the PANA exchanges PAA MAY optionally rely on lower-layer indications to
   expedite the new link. While
   AAA-Key stays the same, detection of a new PANA_MAC_Key is computed using disconnected peer. Availability and
   reliability of such indications depend on the new
   parameters. Subsequent MAC-AVPs are processed using this new specific access
   technologies.  PANA SA.

4.10 Event Notification

   Upon detecting the need to authenticate a client, EP peer can send a
   trigger use PANA-Reauth-Request message to
   verify the PAA on behalf of disconnection before taking an action.

   The session lifetime parameter is not related to the PaC. This can be one transmission of
   the
   PANA-Reauth-Request messages.  These 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 for
   asynchronously verifying the device identifier liveness of the PaC. So that, the PAA
   can peer and enabling
   mobility optimizations. The decision to send the unsolicited PANA-Start-Request PANA-Reauth-Request
   message directly to the
   PaC.  If the link is taken locally and does not require coordination between
   the EP peers.

   When separate EAP authentications are performed for ISP and PAA NAP in a
   single PANA session, it is not physically secured, possible that different authorization
   lifetime values are associated with the two authentications.  In this message sent from EP to PAA
   case, the smaller authorization lifetime value MUST be cryptographically protected
   (e.g., by using IPsec).

4.11 Support used for Separate EP
   calculating the PANA allows PAA Session-Lifetime value.  As a result, when
   EAP-based re-authentication occurs, both NAP and EP to ISP authentications
   will be separate entities.  In this case, if
   data traffic protection needs to performed in the same re-authentication procedure.

4.9 Mobility Handling

   A mobile PaC's AAA performance can be initiated after successful PANA
   authentication phase, PaC needs to know enhanced by deploying a
   context-transfer-based mechanism, where some session attributes are
   transferred from the device identifier of
   EP(s) so that it is able previous PAA to establish a security association with
   each EP the current one in order to protect data traffic.

   To this end, when
   avoid performing a Protection-Capability AVP with either
   L2_PROTECTION full EAP authentication (reactive approach).
   Additional mechanisms that are based on the proactive AAA state
   establishment at one or IPSEC_PROTECTION more candidate PAAs may be developed in the AVP payload
   future [I-D.irtf-aaaarch-handoff].  The details of a
   context-transfer-based mechanism is carried provided in this section.

   Upon changing its point of attachment, a
   PANA-Bind-Request message and if there is an EP PaC that has a different
   device wants to quickly
   resume its ongoing PANA session without running EAP MAY send its
   unexpired PANA session identifier than that of in its PANA-Start-Answer message.
   Along with the PAA, one or more EP-Device-Id Session-Id AVP, MAC and Nonce AVPs MUST also be carried included in the PANA-Bind-Request message.  In
   this case,
   if one EP has message.  Nonce AVP carries a randomly chosen value (PaC_Nonce),
   and MAC AVP is computed by using the same device identifier as PANA_MAC_Key shared between the PAA, an EP-Device-Id
   AVP
   PaC and its previous PAA that contains has an unexpired PANA session with the device identifier of
   PaC.  This action signals PaC's desire to perform the EP (i.e., mobility
   optimization.  In the PAA)
   MUST also be included absence of Session-Id AVP in the PANA-Bind-Request.

5. PANA Security Association Establishment

   When this message, PANA
   session takes its usual course (i.e., EAP-based authentication 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
   performed).

   If PAA receives a session identifier that is used during in the authentication needs PANA-Start-Answer
   message, and it is configured to be
   verified at the end of enable this optimization, it SHOULD
   retrieve the authentication to prevent service theft
   and DoS attacks. Additionally, a free loader should be prevented PANA session attributes 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 previous PAA.  Current
   PAA determines the PaC and identity of the previous PAA by looking at the end
   DiameterIdentity part of the authentication. This PANA session identifier.  The MAC AVP
   can only be done when verified by the
   authentication method used can generate cryptographic keys. Use previous PAA, therefore a copy of
   secret keys can prevent attacks which would otherwise the
   PANA message SHOULD be very easy provided 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 previous PAA.  The mechanism
   required to establish send a PANA security association. An example copy of such a
   method is EAP-TLS [RFC2716], whereas EAP-MD5
   [I-D.ietf-eap-rfc2284bis] the PANA-Start-Answer message from current
   PAA to the previous PAA, and retrieve the session attributes is an example of a method that cannot
   create such keying material. The choice of EAP method becomes
   important, as discussed in
   outside the next section.

   This keying material is already used within scope of PANA during the final
   handshake. This handshake ensures that protocol.  Seamoby Context Transfer
   Protocol [I-D.ietf-seamoby-ctp] might be useful for this purpose.

   When the device identifier that previous or current PAA is
   bound not configured to enable this
   optimization, the PaC at the end of the authentication process is current PAA can not
   coming from a man-in-the-middle, but from retrieve the legitimate PaC.
   Knowledge of PANA session
   attributes, or the same keying material on both PaC and PANA session has already expired (i.e., session
   lifetime is zero), the PAA helps
   prove this. The other use of MUST send the keying material will be discussed in
   Section 7 and Section 8.

6. Authentication Method Choice

   Authentication methods' capabilities and therefore applicability to
   various environments differ among them. Not all methods provide
   support for mutual authentication, key derivation or distribution,
   and DoS attack resiliency that are necessary for operating in
   insecure networks. Such networks might be susceptible to
   eavesdropping and spoofing, therefore PANA-Auth-Request message
   with a stronger authentication
   method needs to be used to prevent attacks on the client new session identifier and let the
   network.

   The PANA exchange take its
   usual course.  This action will engage EAP-based authentication method choice is and
   create a function of fresh PANA session from scratch.

   In case the underlying
   security of current PAA can retrieve the network (e.g., physically secured, shared link,
   etc.). It is on-going PANA session
   attributes from the responsibility previous PAA, the PANA session continues with a
   PANA-Bind exchange.

   As part of the user and context transfer, an intermediate AAA-Key material is
   provided by the network operator previous PAA to pick the right method for authentication. PANA carries EAP
   regardless current PAA.

      AAA-Key-int = The first N bits of
                    HMAC-SHA1(AAA-Key, DiameterIdentity | Session-ID)

   In case there are two AAA-Keys generated from a NAP-ISP
   authentication, the EAP method used. It AAA-Key-int computation is:

      AAA-Key-int = The first N bits of
                    HMAC-SHA1(AAA-Key1 | AAA-Key2, DiameterIdentity |
                              Session-ID)

   The value of N depends on the integrity protection algorithm in use,
   i.e., N=160 for HMAC-SHA1.  DiameterIdentity is outside the scope of PANA to
   mandate, recommend, or limit use identifier of any authentication methods.  PANA
   cannot increase the strength
   current PAA.  Session-ID is the identifier 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]). the PaC's PANA can carry these EAP encapsulating
   methods but it does not concern itself session
   with how they achieve
   protection for the weak methods (i.e., their EAP method payloads).

7. Filter Rule Installation

   PANA protocol provides client authentication and authorization
   functionality for securing network access. previous PAA.

   The other component of a
   complete solution current PAA and PaC compute the new AAA-Key by using the nonce
   values and the AAA-Key-int.  PAA_Nonce is the access control which ensures randomly chosen value
   that only
   authenticated and authorized clients can gain access to MUST be carried in a Nonce AVP in the network.
   PANA enables access control PANA-Bind-Request message.

      AAA-Key-new = The first N bits of
                    HMAC-SHA1(AAA-Key-int, PaC_nonce | PAA_nonce)

   New PANA_MAC_Key is computed based on the algorithm described in
   Section 4.1.5, by identifying legitimate clients and
   generating filtering information for access control mechanisms.
   Getting this filtering information to using the EPs (Enforcement Points) new AAA-Key and performing filtering are outside the scope of PANA.

   Access control can be achieved new Session-ID
   assigned by placing EPs in the network for
   policing current PAA.  The MAC AVP contained in the traffic flow. EPs should prevent data traffic from
   PANA-Bind-Request and
   to any unauthorized client unless it's PANA traffic. When a client PANA-Bind-Answer messages MUST be generated and
   verified by using the new PANA_MAC_Key.  The Session-ID AVP MUST
   include a new session identifier assigned by the current PAA.  A new
   PANA session is
   authenticated created upon successful completion of this exchange.

   Note that correct operation of this optimization relies on many
   factors, including applicability of authorization state from one
   network attachment to another.  [I-D.ietf-eap-keying] identifies this
   operation as "fast handoff" and authorized, provides deployment considerations.

   Operators are recommended to take those guidelines into account when
   using this optimization in their networks.

4.10 Support for Separate EP

   PANA allows PAA should notify EP(s) and ask for
   changing filtering rules EP to allow be separate entities.  In this case, if
   data traffic for a recently authorized
   client. There protection needs to be a protocol between PAA and initiated after successful PANA
   authentication phase, PaC needs to know the device identifier of
   EP(s) so that it is able to establish a security association with
   each EP to protect data traffic.

   To this end, when these
   entities are not co-located. PANA Working Group will not be defining a new protocol for Protection-Capability AVP with either
   L2_PROTECTION or IPSEC_PROTECTION in the AVP payload is carried in a
   PANA-Bind-Request message and if there is an EP that has a different
   device identifier than that of the PAA, one or more EP-Device-Id AVPs
   MUST also be carried in the PANA-Bind-Request message.  In this interaction. Instead, it will (preferably)
   identify case,
   if one of EP has the existing protocols same device identifier as the PAA, an EP-Device-Id
   AVP that can fit contains 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 device identifier of the MIDCOM's output might EP (i.e., the PAA)
   MUST also be useful here.

   EPs' location included in the network topology should PANA-Bind-Request.

   Aside from provisioning EP, the same PAA-to-EP protocol MAY be appropriate used
   for
   performing access control functionality. The closest IP-capable
   access device to triggering the client devices is the logical choice. PAA and
   EPs on upon detecting the need to authenticate a new
   client.

5. PANA Security Association Establishment

   When PANA is used over an access network should be aware of each other already established secure channel, such as this is
   necessary for access control. Generally this
   physically secured wires or ciphered link-layers, we can be achieved by
   manual configuration. Dynamic discovery reasonably
   assume that man-in-the-middle attack or service theft is another possibility, but
   this not possible
   [I-D.ietf-pana-threats-eval].

   Anywhere else where there 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 no secure channel prior to PANA, the
   protocol needs to protect itself against such attacks. The device
   identifiers easily. They are
   identifier that is used with link-layer or network-layer
   ciphering during the authentication needs to provide additional protection. For issues regarding
   data-origin be
   verified at the end of the authentication see Section 8.

8. Data Traffic Protection

   Protecting to prevent service theft
   and DoS attacks.  Additionally, a free loader should be prevented
   from spoofing data traffic packets by using the device identifier of authenticated and an
   already authorized clients from
   others is another component legitimate client.  Both of these requirements
   necessitate generation of providing a complete secure network
   access solution. Authentication, integrity security association between the PaC 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 PAA at the network.

   When end of the network is physically secured, or authentication.  This can only be done when
   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 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 authentication. The user relies on EAP and
   network have the EAP methods to make sure 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
   [I-D.ietf-eap-rfc2284bis] is an appropriate EAP example of a method that can generate
   required cannot
   create such keying materials is used. Once material. The choice of EAP method becomes
   important, as discussed in the next section.

   This 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 already used when data traffic
   protection within PANA during the final
   handshake.  This handshake ensures that the device identifier that is required but link-layer ciphering capability
   bound to the PaC at the end of the authentication process is not
   available. Note that
   coming from 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 man-in-the-middle, but from the EAP method is still insufficient to produce an IPsec SA since legitimate PaC.
   Knowledge of the same keying material on both traffic selectors PaC 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. PAA helps
   prove this.  The details other use of such mechanisms are outside the
   scope of this document and can be found in [I-D.ietf-pana-ipsec].

   Using network-layer ciphers should be regarded as a substitute for
   link-layer ciphers when the latter keying material is not available. IKE involves
   several discussed in
   [I-D.ietf-pana-framework].

6. Message Formats

   This section defines message exchanges which can incur additional delay formats for PANA protocol.

6.1 IP and header
   overhead in getting basic UDP Headers

   The Hop Limit (or TTL) field of the IP connectivity for a mobile device. Such header MUST be set to 255.
   When a
   latency is inevitable when there PANA-PAA-Discover message is no other alternative and this
   level multicast, IP destination address
   of protection the message is required. Network-layer ciphering can also set to a well-known link-local multicast address
   (TBD).  A PANA-PAA-Discover message MAY be
   used unicast in addition some cases as
   specified in Section 4.2. Any other PANA packet is unicasted between
   the PaC and the PAA.  The source and destination addresses SHOULD be
   set to link-layer ciphering if the added benefits
   outweigh its cost addresses on the interfaces from which the message will be
   sent and received, respectively.

   When the PANA packet is sent in response to a request, the user UDP source
   and destination ports of the network.

9. Message Formats

   This section defines message formats for response packet MUST be copied from the
   destination and source ports of the request packet, respectively.
   The destination port of an unsolicited PANA protocol.

9.1 packet MUST be set to an
   assigned value (TBD), and the source port MUST be set to a value
   chosen by the sender.

6.2 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 N r r|
      +-+-+-+-+-+-+-+-+

      R(equest)

         If set, the message is a request.  If cleared, the message is
         an answer.

      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
         authentications 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 authentications for NAP and ISP.

      r(eserved)

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

   Message Type

      The Message Type field S-flag is three octets, set in a PANA-Auth-Request/Answer,
         PANA-FirstAuth-End-Request/Answer and is used PANA-Bind-Request/Answer
         messages it indicates that separate authentications are being
         performed in order to
      communicate the message type with authentication phase.

      N(AP authentication)

         When the message. N-flag is set in a PANA-Auth-Request message, it
         indicates that PAA is performing NAP authentication.  When the
         N-flag is unset in a PANA-Auth-Request message, it indicates
         that PAA is performing ISP authentication.  The N-flag MUST NOT
         be set when S-flag is not set.

      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 6.3 for more information on
      AVPs.

9.2

6.3 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
   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.

   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

6.4 PANA Messages

   Figure 9 10 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-FirstAuth-End-Request  <--------
                 PANA-FirstAuth-End-Answer   -------->

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

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

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

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

                    Figure 9: 10: PANA Message Overview

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

9.3.1

6.4.1 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

6.4.2 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 >
                   0*1 < Session-Id >
                    *  [ AVP ]

9.3.3

6.4.3 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 ]
                       [ EAP-Payload ]
                       [ NAP-Information ]
                    *  [ ISP-Information ]
                       [ Protection-Capability]
                       [ PPAC ]
                    *  [ AVP ]

9.3.4

6.4.4 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
   value.

         PANA-Start-Answer ::= < PANA-Header: 2 [SEP] >
                       [ Session-Id ]
                       [ Cookie ]
                       [ Nonce ]
                       [ EAP-Payload ]
                       [ ISP-Information ]
                    *  [ AVP ]

9.3.5

6.4.5 PANA-Auth-Request (PAR)

   PANA-Auth-Request (PAR) is sent by the PAA to the PaC.

         PANA-Auth-Request ::= < PANA-Header: 3, REQ [SEP] [NAP] >
                       < 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

6.4.6 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 [SEP] [NAP] >
                       < Session-Id >
                       < EAP-Payload >
                    *  [ AVP ]
                   0*1 < MAC >

9.3.7

6.4.7 PANA-Bind-Request (PBR)

   PANA-Bind-Request (PBR) is sent by the PAA to the PaC.

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

9.3.8

6.4.8 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 [,SEP] [NAP] >
                       < Session-Id >
                       <
                       { Result-Code }
                       [ PPAC ]
                       [ Device-Id > ]
                       [ Key-Id ]
                    *  [ AVP ]
                   0*1 < MAC >

9.3.9

6.4.9 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

6.4.10 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

6.4.11 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 >

9.3.12

6.4.12 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

6.4.13 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

6.4.14 PANA-FirstAuth-End-Request (PFER)

   PANA-FirstAuth-End-Request (PFER) is sent by the PAA to the PaC.

         PANA-FirstAuth-End-Request ::= < PANA-Header: 8, REQ [SEP] [NAP] >
                       < Session-Id >
                       < Device-Id >
                       { EAP-Payload }
                       { Result-Code }
                       [ Key-Id ]
                    *  [ AVP ]
                   0*1 < MAC >

6.4.15 PANA-FirstAuth-End-Answer (PFEA)

   PANA-FirstAuth-End-Answer (PFEA) is sent by the PaC to the PAA in
   response to a PANA-FirstAuth-End-Request message.

         PANA-FirstAuth-End-Answer ::= < PANA-Header: 8, REQ [SEP] [NAP] >
                       < Session-Id >
                       < Device-Id >
                       [ Key-Id ]
                    *  [ AVP ]
                   0*1 < MAC >

6.5 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. [RFC3588].  For temporary allocation, PANA
   uses AVP type numbers starting from 1024.

9.4.1

6.5.1 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-SHA1 (20 bytes)

   MAC

      The Message Authentication Code is encoded in network byte order.

9.4.2

6.5.2 Device-Id AVP

   The first octet (8 bits) of the Device-Id AVP (Code 1025) AVP data
   contains the device type. Rest is of the AVP data payload contains the
   device data. Address type [RFC3588].  IPv4 and
   IPv6 addresses are encoded as specified in [RFC3588].  The content
   and format of data (including byte and bit ordering) for L2_ADDRESS link-layer
   addresses 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  Address families other than that are defined 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
   link-layer or IP addresses MUST NOT be used for this AVP.

6.5.3 Session-Id AVP (Code 1026) has an opaque data field, which is
   assigned by the PAA.

   All messages pertaining to a specific PANA
   Session session MUST include only one a
   Session-Id AVP and the same (Code 1026) which carries a PAA-assigned fix 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 PANA Session-Id AVP MAY use Diameter [RFC3588] message formatting. In
   this case has
   the same format as the Diameter Session-Id AVP code is 263.

9.4.4 [RFC3588].

6.5.4 Cookie AVP

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

9.4.5

6.5.5 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 indicates the cryptographic data protection capability indications.
   supported by the EPs.  Below is a list of specified data protection
   capabilities:

         0          UNKNOWN
         1          L2_PROTECTION
         2
         1          IPSEC_PROTECTION

9.4.6

6.5.6 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

6.5.7 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

6.5.7.1 Authentication Results Codes

   These result code values inform the PaC about the EAP authentication
   method success or failure. and
   authorization result.  The authentication result and authorization
   result can be different as described below, but only one result that
   corresponds to the one detected first is returned.

   PANA_SUCCESS                            2001

      The EAP method

      Both the authentication was successful (EAP-Success). and authorization processes are
      successful.

   PANA_AUTHENTICATION_REJECTED            4001

      The authentication process for failed.  When this error is returned,
      the client failed (EAP-Failure). authorization process also fails.

   PANA_AUTHORIZATION_REJECTED             5003

      A request was received for which the client could not be
      authorized.

      The authorization process failed.  This error could occur when
      authorization is rejected by a AAA proxy or rejected locally by a
      PAA, even if the service requested is
      not permitted to the client.

9.4.7.2 authentication procedure succeeds.

6.5.7.2 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
      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.

   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_UNABLE_TO_COMPLY                   5012

      This error is returned when a request is rejected for unspecified
      reasons.  For example, when an EAP authentication fails at an EAP
      pass-through authenticator without passing an EAP-Failure message
      to the PAA, a Result-Code AVP with this error code is carried in
      PANA-Bind-Request message without an EAP-Payload AVP.
      PANA-Error message.

   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.

   PANA_PROTECTION_CAPABILITY_UNSUPPORTED  5016

      Error code from PaC to PAA.  This error is returned when the PaC
      receives a PANA-Bind-Request is received with an
      Protection-Capability AVP and a valid MAC AVP but does not support
      the protection capability specified in the Protection-Capability
      AVP.

9.4.8

   PANA_PPAC_CAPABILITY_UNSUPPORTED  5017

      Error code from PaC to PAA.  This error is returned in a
      PANA-Bind-Answer message when there is no match between the list
      of PPAC methods offered by the PAA and the ones available on the
      PaC.

6.5.8 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

6.5.9 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

6.5.10 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].

9.4.11

6.5.11 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

6.5.12 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

6.5.13 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

6.5.14 Provider-Name AVP

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

9.4.15

6.5.15 EP-Device-Id AVP

   The EP-Device-Id AVP (AVP Code: 1038) contains the device identifier
   of an EP.  The payload format of the EP-Device-Id AVP is the same as
   that of the Device-Id AVP (see See section Section 9.4.2).

9.4.16 6.5.2).

6.5.16 Key-Id AVP

   The Key-Id AVP (AVP Code: 1039) is of type Integer32, and contains an
   AAA-Key identifier.  The AAA-Key identifier is assigned by PAA and
   MUST be unique within the PANA session.

9.5

6.5.17 Post-PANA-Address-Configuration (PPAC) 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 data field of PPAC AVP (Code 1040) is of type Unsigned32.  The
   AVP MUST NOT be present in the message.

   0+    Zero or more instances data is used to carry a set of flags which maps to various IP
   address configuration methods.  When sent by the AVP MAY be present in PAA, the
         message.

   0-1   Zero or AVP MUST
   have at least one instance of the AVP flags set, and MAY be present in the message.
         It is considered an error if there are have more than one instance
         of set.
   When sent by the AVP.

   1     One instance PaC, only one of the AVP flags MUST be present in the message.

   1+    At least one instance set.

   The format of the AVP MUST be present in the
         message.

                          +-----------------------------------------+
                          |        Message                          |
                          |          Type                           |
                          +-----+-----+-----+-----+-----+-----+-----+
      Attribute Name      | PSR | PSA | PAR | PAN | PBR | PBA | PDI |
      --------------------+-----+-----+-----+-----+-----+-----+-----+
      Result-Code         |  0  |  0  | data is as follows:

       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  |
      Session-Id          |  0  |  0  |  1  |  1  |  1  |  1  | 0-1 |
      Termination-Cause   |  0  |  0  |  0  |  0  |  0  | 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |N|D|A|T|I|                   Reserved                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   PPAC Flags

      N (No configuration)

         The PaC does not have to (if sent by PAA) or will not (if sent
         by PaC) configure a new IP address after PANA.

      D (DHCP)

         The PaC can (if sent by PAA) or will (if sent by PaC) use DHCP
         [RFC2131][RFC3315] to configure a new IP address after PANA.

      A (stateless autoconfiguration)

         The PaC can/will use stateless IPv6 address autoconfiguration
         [RFC2462] to configure a new IP address after PANA.

      T (DHCP with IPsec tunnel mode)

         The PaC can/will use [RFC3456] to configure a new IP address
         after PANA.

      I (IKEv2)

         The PaC can/will use [I-D.ietf-ipsec-ikev2] to configure a new
         IP address after PANA.

      Reserved

         These flag bits are reserved for future use, and MUST be set to
         zero, and ignored by the receiver.

   Unless the N-flag is set, the PaC MUST configure a new IP address
   using one of the methods indicated by the other flags.  Refer to
   [I-D.ietf-pana-framework] for a detailed discussion on when these
   methods can be used.

6.5.18 Nonce AVP

   The Nonce AVP (Code 1041) is of type OctetString.  The data contains
   a randomly generated value in opaque format. The data length MUST be
   between 8 and 256 bytes inclusive.

6.6 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  |
      EAP-Payload         | 0-1 |     The AVP MUST NOT be present in the message.

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

   0-1 |  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  |  1  |  0  |
      Session-Id          |  0  |
      MAC 0-1 |  1  |  1  |  1  |  1  | 0-1 |
      Termination-Cause   |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
      EAP-Payload         | 0-1 | 0-1 |  1  |  1  | 0-1 |  0  |  0  |
      MAC                 |  0  | 0-1 | 0-1 | 0-1 | 0-1 | 0-1 |  0  |
      Device-Id
      Nonce               |  0  | 0-1 |  0  |  0  | 0-1 |  0  |  1+  0  |  1+
      Device-Id           |  0  |  0  |  0  |  0  | 0-1 | 0-1 |  0  |
      Cookie              | 0-1 | 0-1 |  0  |  0  |  0  |  0  |  0  |
      Protection-Cap.     | 0-1 |  0  |  0  |  0  | 0-1 |  0  |  0  |
      PPAC                | 0-1 |  0  |  0  |  0  |  1  | 0-1 |  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  |  0  |
      NAP-Information     | 0-1 |  0  | 0-1  0  |  0  |  0  |  0  |  0  |
      EP-Device-Id        |  0  |  0  |  0  |  0  |  0+ |  0  |  0  |
      Key-Id              |  0  |  0  |  0  |  0  | 0-1 | 0-1 |  0  |
      --------------------+-----+-----+-----+-----+-----+-----+-----+

                          +-------------------------------+

                 Figure 11: AVP Occurrence Table (1/2)
                          +---------------------------------------------+
                          |      Message                                |
                          |       Type                                  |
                          +------+------+-----+-----+-----+
                          +------+------+-----+-----+-----+------+------+
      Attribute Name      | PRAR | PRAA | PTR | PTA | PER |
      --------------------+------+------+-----+-----+-----+ PFER | PFEA |
      --------------------+------+------+-----+-----+-----+------+------+
      Result-Code         |  0   |  0   |  0  |  0  |  1  |  1   |  0   |
      Session-Id          |  1   |  1   |  1  |  1  |  1  |  1   |  1   |
      Termination-Cause   |  0   |  0   |  1  |  0  |  0  |  0   |  0   |
      EAP-Payload         | 0-1  0   | 0-1  0   |  0  |  0  |  0  |  1   |  0   |
      MAC                 | 0-1  | 0-1  | 0-1 | 0-1 | 0-1 |
      Device-Id 0-1  |  1+ 0-1  |  1+
      Nonce               |  0   |  0   |  0  |
      Cookie  0  |  0  |  0   |  0   |
      Device-Id           | 0-1  | 0-1  |  0  |  0  |
      Protection-Cap.  0  |  0   |  0   |
      Cookie              |  0   |  0   |  0  |
      Session-Lifetime  0  |  0  |  0   |  0   |
      Protection-Cap.     |  0   |  0   |
      Failed-AVP  0  |  0  |  0  |  0   |  0   |  1
      PPAC                |
      ISP-Information  0   |  0   |  0  |  0  |  0  |  0   |
      NAP-Information  0   |
      Session-Lifetime    |  0   |  0   |  0  |  0  |  0  |
      EP-Device-Id  0   |  0   |
      Failed-AVP          |  0   |  0   |  0  |  0  |
      Key-Id  1  |  0   |  0   |
      ISP-Information     |  0   |  0   |  0  |
      --------------------+------+------+-----+-----+-----+

                    Figure 10: AVP Occurrence Table

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
         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.

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

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
   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). Security issues raised with
   this session key transport are described in [I-D.ietf-eap-keying].

   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 may be chosen by default in a future version of
   the PANA protocol specification. 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
   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) 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.

   f) 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.ietf-eap-keying]. This framework is also relevant for PANA in
   various ways. First, a  0  |  0  |  0   |  0   |
      NAP-Information     |  0   |  0   |  0  |  0  |  0  |  0   |  0   |
      EP-Device-Id        |  0   |  0   |  0  |  0  |  0  |  0   |  0   |
      Key-Id              |  0   |  0   |  0  |  0  |  0  | 0-1  | 0-1  |
      --------------------+------+------+-----+-----+-----+------+------+

                 Figure 12: AVP Occurrence Table (2/2)

7. PANA Protocol Message Retransmissions

   The PANA security association needs to be created.
   Additionally it might be necessary to trigger a protocol which allows
   link layer and network layer data protection to be established. As an
   example see Section 1 of [I-D.ietf-eap-keying] with [802.11i] and
   [802.11] as an example. Furthermore, a derived session key might help
   to create the pre-requisites provides retransmissions 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 all the establishment of a link layer or a network
   layer security association message
   exchanges except PANA-Auth-Request/Answer.  PANA-Auth-Request
   messages carry EAP requests which are outside retransmitted by the scope of PANA. EAP
   protocol entities when needed.  The
   interested reader should refer to the relevant working groups such as
   IPsec or Midcom.

   g) Liveness test

   Network access authentication messages that need PANA-level
   retransmissions are listed below:

         PANA-PAA-Discover (PDI)
         PANA-Start-Request (PSR)*
         PANA-Start-Answer (PSA)**
         PANA-Bind-Request (PBR)
         PANA-FirstAuth-End-Request (PFER)
         PANA-Reauth-Request (PRAR)
         PANA-Termination-Request (PTR)

         *)  PSR that carries a Cookie AVP is done for not retransmitted.
         **) PSA that does not carry a very specific purpose Cookie AVP is not retransmitted.

   The PDI and
   often charging procedures PSA messages are involved which allow restricting
   network resource usage based on some policies. In mobile environments
   it is always possible 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 an end host suddenly disconnects without
   transmitting a disconnect message. Operators the sender of the request message retransmits the
   request if the corresponding answer is not received in time.  Answer
   messages are generally motivated sent as answers to detect the request messages, not based on a disconnected end host as soon as possible in order
   timer.  Exception to
   release resources (i.e., garbage collection).  The this rule is the PSA message.  Because of the
   stateless nature of the PAA can remove
   per-session state information including installed security
   association, packet filters, etc.

   Different procedures can in the beginning PaC provides
   retransmission also for the PSA message.  PANA-Error messages MUST
   not be used retransmitted.  See Section 4.1.8 for disconnect indication. more details of PANA
   cannot assume link-layer disconnect indication. Hence
   error handling.

   PANA retransmission timers are based on the model used in DHCPv6
   [RFC3315].  Variables used here are also borrowed from this
   functionality has to be provided at
   specification.  PANA is a higher layer. With this version
   of request response like protocol.  The
   message exchange terminates when either the draft we suggest request sender
   successfully receives the appropriate answer, or when the message
   exchange is considered to have failed according to apply the soft-state principle found at
   other protocols (such as RSVP). Soft-state means that session state retransmission
   mechanism described below.

   The retransmission behavior is kept alive as long as refresh messages refresh controlled and described by the state.
   following variables:

         RT     Retransmission timeout

         IRT    Initial retransmission time

         MRC    Maximum retransmission count
         MRT    Maximum retransmission time

         MRD    Maximum retransmission duration

         RAND   Randomization factor

   With each message transmission or retransmission, the sender sets RT
   according to the rules given below.  If no
   new refresh messages are provided then RT expires before the state automatically times
   out message
   exchange terminates, the sender recomputes RT and resources are released. This process includes stopping
   accounting procedures.

   A PANA session retransmits the
   message.

   Each of the computations of a new RT include a randomization factor
   (RAND), which is associated a random number chosen with a session lifetime. uniform distribution
   between -0.1 and +0.1.  The session is
   terminated unless it randomization factor is refreshed by a new round included to
   minimize synchronization of EAP
   authentication before it expires. Therefore, at the latest messages.

   The algorithm for choosing a
   disconnected client can be detected when its lifetime expires. A
   disconnect may also random number does not need to be detected earlier by using PANA
   reauthentication messages. A request
   cryptographically sound.  The algorithm SHOULD produce a different
   sequence of random numbers from each invocation.

   RT for the first message can be generated by
   either PaC or PAA at any time and transmission is based on IRT:

         RT = IRT + RAND*IRT

   RT for each subsequent message transmission is based on the peer must respond with previous
   value of RT:

         RT = 2*RTprev + RAND*RTprev

   MRT specifies an
   answer message. A successful round-trip upper bound on the value of this exchange is a simple
   verification that RT (disregarding the peer is alive. This test can be engaged when
   randomization added by the use of RAND). If MRT has a value of 0,
   there is a possibility that no upper limit on the peer might have disconnected (e.g.,
   after discontinuation value of data traffic). Periodic use RT.  Otherwise:

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

   MRC specifies an upper bound on the number of this exchange
   as times a keep-alive requires additional care as it might result in
   congestion and hence false alarms. This exchange is cryptographically
   protected when PANA SA sender may
   retransmit a message.  Unless MRC is available in order to prevent threats
   associated with zero, the abuse of this functionality.

   h) Tear-Down message

   The PANA protocol supports exchange fails
   once the ability for both sender has transmitted the PaC and message MRC times.

   MRD specifies an upper bound on the PAA
   to transmit length of time a sender may
   retransmit a tear-down message. This  Unless MRD is zero, the message causes state removal, a
   stop of exchange fails
   once MRD seconds have elapsed since the accounting procedure client first transmitted the
   message.

   If both MRC and removes MRD are non-zero, 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.

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 -02 version of draft are: None.

   The remaining issues for -xx version exchange fails whenever
   either of draft are: 28, 52, 53, 54,
   55, 56, 57, 58 and 59.

13. Change History

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

   Issues incorporated the conditions specified in PANA-02 October 2003: 8, 17, 18, 19, 20, 21,
   22, 23, 24, 25, 26, 30, 31, 32 the previous two paragraphs are
   met.

   If both MRC and 33.

   Issues incorporated in PANA-03 February 2004: 2, 16, 34, 35, 36, 38,
   39, 40, 42, 43, 44, 50, 51 MRD are zero, the client continues to transmit the
   message until it receives a response.

7.1 Transmission and 60.

14. Acknowledgments

   We would like Retransmission Parameters

   This section presents a table of values used to thank all members 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 PANA working group first RT for
   their comments the PBR message is calculated using
   REQ_IRT as the IRT:

           RT = REQ_IRT + RAND*REQ_IRT

8. IANA Considerations

   This section provides guidance to this document.

Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to Indicate
              Requirement Levels", the
   Diameter protocol, in accordance with BCP 14, RFC 2119, March 1997.

   [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-07 (work 26 [IANA].  The following
   policies are used here with the meanings defined in progress), December
              2003.

   [RFC2716]  Aboba, B. and D. Simon, "PPP EAP TLS Authentication
              Protocol", RFC 2716, October 1999.

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

   [RFC2234]  Crocker, D. and P. Overell, "Augmented BNF BCP 26: "Private
   Use", "First Come First Served", "Expert Review", "Specification
   Required", "IETF Consensus", "Standards Action".

   This section explains the criteria to be used by the IANA for
   assignment of numbers within namespaces defined within this document.

   For registration requests where a Designated Expert should be
   consulted, the responsible IESG area director should appoint the
   Designated Expert.  For Designated Expert with Specification
   Required, the request is posted to the PANA WG mailing list (or, if
   it has been disbanded, a successor designated by the Area Director)
   for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

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

   [RFC2464]  Crawford, M., "Transmission review, and MUST include a pointer to a public
   specification.  Before a period of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. 30 days has passed, the Designated
   Expert will either approve or deny the registration request and
              M. Carney, "Dynamic Host Configuration Protocol for IPv6
              (DHCPv6)", RFC 3315, July 2003.

   [I-D.ietf-eap-keying]
              Aboba, B., "EAP Key Management Framework",
              draft-ietf-eap-keying-01 (work
   publish a notice of the decision to the PANA WG mailing list or its
   successor.  A denial notice must be justified by an explanation and,
   in progress), October 2003.

Informative References

   [I-D.ietf-pana-requirements]
              Yegin, A. and Y. Ohba, "Protocol the cases where it is possible, concrete suggestions on how the
   request can be modified so as to become acceptable.

8.1 PANA UDP Port Number

   TBD.

8.2 PANA Multicast Address

   TBD.

8.3 PANA Header

8.3.1 Message Type

   TBD.

8.3.2 Flags

   TBD.

8.4 AVP Header

8.4.1 AVP Code

   TBD.

8.4.2 Flags

   TBD.

8.4.3 Vendor Id

   TBD.

8.5 AVP Values

8.5.1 MAC AVP Values

   TBD.

8.5.2 Device-Id AVP Values

   TBD.

8.5.3 Protection-Capability AVP Values

   TBD.

8.5.4 Result-Code AVP Values

   TBD.

8.5.5 Termination-Cause AVP Values

   TBD.

8.5.6 Provider-Identifier AVP Values

   TBD.

8.5.7 Post-PANA-Address-Configuration AVP Values

   TBD.

9. Security Considerations

   The PANA protocol provides ordered delivery for Carrying
              Authentication 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 Network Access  (PANA)Requirements",
              draft-ietf-pana-requirements-07 (work in progress), June
              2003.

   [I-D.ietf-aaa-eap]
              Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application",
              draft-ietf-aaa-eap-03 (work in progress), October 2003.

   [I-D.puthenkulam-eap-binding]
              Puthenkulam, J., "The Compound Authentication Binding
              Problem", draft-puthenkulam-eap-binding-04 (work in
              progress), October 2003.

   [RFC2522]  Karn, P. the initial EAP message
   exchange.  Integrity protection can only be provided after the PANA
   SA has been established. Thus, PANA re-authentication, revocation and W. Simpson, "Photuris: Session-Key Management
              Protocol", RFC 2522, March 1999.

   [I-D.ietf-pana-usage-scenarios]
              Ohba, Y., "Problem Statement
   disconnect notifications can be authenticated, integrity and Usage Scenarios for
              PANA", draft-ietf-pana-usage-scenarios-06 (work replay
   protected.  In certain environments (e.g., on a shared link) the EAP
   method selection is an important issue.

   The PANA framework described in
              progress), April 2003.

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

   [I-D.ietf-pana-ipsec]
              Parthasarathy, M., "PANA enabling IPsec based Access
              Control", draft-ietf-pana-ipsec-01 (work 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 progress),
              January 2004.

   [I-D.ietf-seamoby-ctp]
              Loughney, J., "Context Transfer Protocol",
              draft-ietf-seamoby-ctp-08 (work the first message exchange.  Because of
   the architectural assumptions made in progress), January
              2004.

   [I-D.josefsson-pppext-eap-tls-eap]
              Josefsson, S., Palekar, A., Simon, D. and G. Zorn,
              "Protected 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 Protocol (PEAP)",
              draft-josefsson-pppext-eap-tls-eap-07 (work in progress),
              October 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-ikev2-02 (work in
              progress), October 2003.

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

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

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

   Since PAA and K. Nyberg, "Man-in-the-middle in
              tunnelled authentication",  In 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 Proceedings access
   side of the 11th
              International Workshop on Security Protocols, Cambridge,
              UK, April 2003.

   [802.11i]  Institute network where only PaCs are connected.

   In networks where lower-layers are not secured prior to running PANA,
   the capability discovery enabled through inclusion of Electrical
   Protection-Capability and Electronics Engineers, "Draft
              supplement Post-PANA-Address-Configuration AVPs in
   PANA-Start-Request message is susceptible 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/D7.0,
              2003.

   [802.11]   Institute spoofing.  Therefore,
   usage of Electrical and Electronics Engineers,
              "Information technology - telecommunications and
              information exchange between systems - local and
              metropolitan area these AVPs during the discovery phase in such insecure
   networks - specific requirements part
              11: Wireless lan medium access control (mac) and physical
              layer (phy) specifications", IEEE Standard 802.11,
              1999(R2003).

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
   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

Appendix A. Adding sequence is NOT RECOMMENDED.  The same AVPs are delivered via an
   integrity-protected PANA-Bind-Request upon successful authentication.

   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 PANA for carrying secure the EAP message exchange itself.  Hence an
   adversary can both eavesdrop the EAP

Appendix A.1 Why messages and is sequence number needed for PANA also able to carry EAP?
   inject arbitrary messages which might confuse both the EAP [I-D.ietf-eap-rfc2284bis] requires underlying transports 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
   provide ordered-delivery discard packets
   and packets have to be stored or forwarded to an AAA infrastructure
   some risk of messages.  If 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 underlying transport
   does not satisfy adversary to learn the ordering requirement, long-term password directly.
   Furthermore, if the following situation
   could happen:

        EAP Peer optional 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 Identity payload is used then it
   allows the adversary to unexpected ID]

                    Figure 11: Undesirable scenario

   In Figure 11, learn the second EAP Request message with Identifier=1
   arrives at identity of the PaC.  In such a
   case a privacy problem is prevalent.

   To prevent these threats, [I-D.ietf-pana-framework] suggests using
   proper EAP peer after methods for particular environments.  Depending on the third
   usage environment an EAP Request message with
   Identifier=2.  As a result, 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 peer accepts 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 second EAP
   Request as message authentication is finished a new EAP Request while it fresh and unique
   session key is just an old EAP Request that
   was already responded available to the PaC and the authentication might be totally messed
   up. PAA.  This problem occurs due to the fact assumes 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 method allows session key derivation and response
   message matching).  When EAP is running over PPP or IEEE 802 links,
   this is not that the generated
   session key has a problem, because those link-layers have good quality.  For further discussion about the ordering
   invariant characteristic.

   On
   importance of the other hand, session key generation refer to the PANA design has chosen UDP next subsection
   (d) about compound authentication.  The session key available for the
   PaC is established as its transport.
   Given that UDP does not provide ordered delivery part of packets the authentication and PANA
   does not assume any specific link-layer technology to carry EAP, PANA
   messages need to have a sequence number.

   In key exchange
   procedure of the following text we describe two possible approaches for
   sequence number handling selected EAP method.  The PAA obtains the session
   key via the AAA infrastructure (if used).  Security issues raised
   with this session key transport are described in PANA.
   [I-D.ietf-eap-keying].

   The first one makes use establishment of a
   single sequence number whereas the latter utilizes two. Finally a
   comparison between 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 two approaches is provided. The method
   described in Appendix A.3.1 (i.e., current version of the dual sequence number with
   orderly-delivery method) document an integrity
   object (MAC AVP) is suggested as the preferred method for
   PANA transport.

Appendix A.2 Single defined which supports data-origin
   authentication, replay protection based on sequence number approach

   This section discusses several methods numbers and
   integrity protection based on using a single
   sequence number for providing orderly keyed 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 digest.
   Confidentiality protection is monotonically increased by 1. not provided. The arithmetic defined
           in [RFC1982] is session keys used for sequence number operation.

   Rule 2: When a PAA sends an EAP message passed from EAP layer
   this object have to a
           PaC, a new sequence number is placed in be provided by the message,
           regardless of whether it is sent as a result EAP method.  For this version
   of a
           retransmission at the EAP layer or not.

   Note: It might be possible to define other mechanisms for sequence
   number handling if document it can be is assumed that a PAA detects EAP
   retransmissions.  However, such an assumption heavily depends on EAP
   implementation details no negotiation of algorithms and
   parameters takes place.  Instead HMAC-SHA1 is used by default.  A
   different algorithm may be chosen by default 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 future version of
   the sequence
           number PANA protocol specification.  The used algorithm is not greater than that indicated in
   the header of the last accepted message.

   Rule 5: When Integrity object.  To select the PAA receives a security
   association for signaling message from protection the PaC, it checks Session ID is
   conveyed.  The keyed message digest included in the
           sequence number and discards Integrity object
   will include all fields of the PANA signaling message if the sequence
           number does not match a pending request message.

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

 Figure 12: Example for Single sequence number with EAP retransmission

   This method is vulnerable to a blind DoS attack on including the
   sequence number since field of the PaC will accept quite a wide range packet.

   The protection of sequence
   numbers.  For example, if subsequent signaling messages prevents an attacker blindly sends a bogus message
   to a legitimate PaC with adversary
   from acting as a randomly chosen sequence number, it will
   be accepted by the PaC with 50% probability, and once this happens,
   all man-in-the-middle adversary, from injecting packets,
   from replaying messages sent and from modifying the communicating PAA will be discarded as
   long as they have a content of the
   exchanged packets.  This prevents subsequently described threats.

   If an entity (PAA or PaC) loses its state (especially the current
   sequence number smaller than number) then the accepted value.
   The problem of this method leads to a requirement for PaC entire PANA protocol has to have a
   narrow range be restarted.
   No re-synchronization procedure is provided.

   The lifetime of acceptable sequence numbers to make the blind DoS
   attack difficult. Note that the DoS attack cannot PANA SA has to be prevented if bound to the
   attacker AAA-authorized
   session lifetime with an additional tolerance period.  Unless PANA
   state is on updated by executing another EAP authentication, PANA SA is
   removed when the same IP link as PaC and able to eavesdrop current session expires.  The lifetime of the PANA
   conversation. However, the attacker needs
   SA has to put itself in
   promiscuous mode and thus spend more resources be bound 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 AAA-authorized session lifetime with PANA-layer retransmission
               method

   The next method an
   additional tolerance period.  Unless PANA state is still based on using a single sequence number but
   the PANA-layer takes updated by
   executing another EAP authentication, PANA SA is removed when the responsibility
   current session expires.

   d) Enabling weak legacy authentication methods in insecure networks
   Some of retransmission.  The
   method uses the following rules in addition authentication methods are not strong enough to the common rules
   described be used
   in Appendix A.2.

   Rule 3: Use PANA-layer retransmission for retransmitting both EAP insecure networks where attackers can easily eavesdrop and
           non-EAP messages (based 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 timer expiration). secure channel.  There are EAP layer
           retransmission is turned off. Retransmission based on timer
           occurs both on PaC and PAA side, but not on both sides
           simultaneously.  PAA 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
   EAP-IKEv2 [I-D.tschofenig-eap-ikev2].  PANA can carry these EAP
   tunneling methods which can carry the legacy methods.  PANA does retransmission at least not
   do anything special for this case.  The EAP tunneling method will
   have to produce keying material 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 PANA SA when needed.  There are
   certain MitM vulnerabilities with tunneling EAP methods [mitm].
   Solving these problems is outside the sequence number scope of PANA.  The compound
   authentication problem described in [I-D.puthenkulam-eap-binding] is equal
   likely to that be solved in EAP itself rather than in PANA.

   e) Device Identifier exchange

   As part of the last
           accepted message + 1.  If the sequence number is equal authorization procedure a Device Identifier has to
           that of be
   installed at the last accepted message, EP by the PAA.  The PaC retransmits the
           last transmitted message.  Otherwise, it silently discards provides the message.

   Rule 5: When Device
   Identifier information to the PAA receives a message from the PaC, it accepts secured with the
           message if PANA SA.  Section
   6.2.4 of [I-D.ietf-pana-threats-eval] describes a threat where an
   adversary modifies the sequence number is equal Device Identifier to that gain unauthorized access
   to the network.

   The installation of the last
           transmitted message.  If Device Identifier at the receiving sequence number EP (independently
   whether the EP is
           equal co-located with the PAA or not) has to that be
   accomplished in a secure manner.  These threats are, however, not
   part of the last transmitted message - 1, the PAA
           retransmits PANA protocol itself since the last transmitted message and discard protocol is not PANA
   specific.

   f) Triggering a data protection protocol

   Recent activities in the
           received message. Otherwise, EAP working group try to create a common
   framework for key derivation which is described in
   [I-D.ietf-eap-keying].  This framework is also relevant for PANA in
   various ways.  First, a PANA security association needs to be
   created.  Additionally it silently discards the
           message.

   Rule 6: The PaC retransmits the last transmitted EAP Response until might be necessary to trigger a
           new EAP Request message or protocol
   which allows link layer and network layer data protection to be
   established.  As an EAP Success/Failure message is
           received example see Section 1 of [I-D.ietf-eap-keying]
   with [802.11i] and accepted.

   Rule 7: PAA must keep [802.11] as an example.  Furthermore, a derived
   session key might help to create the copy pre-requisites for network-layer
   protection (for example IPsec [I-D.ietf-pana-ipsec]).

   As motivated in Section 6.4 of the last transmitted message and
           must [I-D.ietf-pana-threats-eval] it might
   be able necessary to retransmit it until establish either a valid message is
           received and accepted by the PAA link layer or a timer expires.  The
           timer is used if no new message will be sent from the PaC.

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

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

   This method has an advantage of eliminating EAP network layer retransmission
   by providing reliability at the PANA layer. Retransmission at
   protection to prevent certain thefts in certain scenarios.

   Threats specific to the EAP
   layer has establishment of 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 link layer or EAP Response message loss (in this case a network
   layer security association are outside the retransmission
   timer scope of PANA.  The
   interested reader should be calculated based on network characteristics) and (ii)
   long latency for EAP Response generation due refer to e.g., user input etc.
   (in this case the retransmission timer should be calculated based on
   user relevant working groups such as
   IPsec or application characteristics).  In general, the retransmission
   timer for case (ii) Midcom.

   g) Liveness test

   Network access authentication is longer than that done for case (i).  If case (i)
   happens while the retransmission timer is calculated a very specific purpose and
   often charging procedures are involved which allow restricting
   network resource usage based on user or
   application characteristics, then some policies.  In mobile
   environments it might frustrate is always possible that an end user
   since the completion 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 authentication procedure takes
   unnecessarily long.  If case (ii) happens while draft we suggest to apply the retransmission
   timer soft-state principle
   found at other protocols (such as RSVP).  Soft-state means that
   session state is calculated based on network characteristics (i.e., RTT), kept alive as long as refresh messages refresh the
   state.  If no new refresh messages are provided then unnecessarily traffic 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 generated
   terminated unless it is refreshed by retransmission.  Note that
   in this method a PaC still cannot distinguish case (i) and case (iii)
   the new round of EAP authenticator or a backend
   authentication server is taking 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 to generate and the peer must respond with an EAP Request.
   answer message.  A problem successful round-trip of this method exchange is a simple
   verification that it is based on the assumption peer is alive. This test can be engaged when
   there is a possibility that
   EAP authenticator does not send the peer might have disconnected (e.g.,
   after discontinuation of data traffic).  Periodic use of this
   exchange as a new EAP message until an EAP
   Response 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 outstanding EAP Request is received.  However, abuse of this
   assumption does not hold at least EAP Success/Failure functionality.

   h) Tear-Down message which
   does not need

   The PANA protocol supports the outstanding EAP Request 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 responded before
   sending protected to prevent an
   adversary from deleting state information and thereby causing denial
   of service attacks.

   i) Mobility optimization

   The mobility optimization described in Section 4.9 involves the EAP Success/Failure message.  This would require
   timer-based retransmission not only at PaC side but also at
   previous PAA side.
   Another problem occurs when providing a new EAP message overrides AAA-Key to the
   outstanding EAP Request, current PAA of the PaC cannot assume any more that PaC.
   There are security risks stemming from potential compromise of PAAs.
   Compromise of the
   sequence number current PAA does not yield compromise of the next message to
   previous PAA, as AAA-Key cannot be accepted is the last
   accepted message + 1.  So the PaC needs to accept computed from a range of sequence
   numbers, instead of compromised
   AAA-Key-new.  But a single sequence number. These two additional
   things would increase compromised previous PAA along with the complexity
   intercepted nonce values leads to the compromise of AAA-Key-new.
   Operators should be aware of this method.

Appendix A.3 Dual sequence number approach

   Based on the analysis potential risk of previous schemes, it is recognized that two
   sequence numbers are needed anyway, one for each direction.  Two
   different methods are proposed based on using this approach.  Both methods
   have
   optimization.  An operator can reduce 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 risk exposure by 1.  The arithmetic defined in
           [RFC1982] is used for sequence number operation.  It is
           assumed that forcing
   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 PaC to perform an EAP-based authentication immediately after the tseq field
   optimized PANA execution.

10. Open Issues and Change History

   A list of message.  Every transmitted
           message is given a new sequence number.

   Rule 3: When a message is sent from PaC or PAA, rseq open issues is copied from
           the tseq field maintained at [2].

   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.

   Issues incorporated in PANA-03 February 2004: 2, 16, 34, 35, 36, 38,
   39, 40, 42, 43, 44, 50, 51 and 60.

   Issues incorporated in PANA-04 May 2004: 28, 52, 53, 56, 57, 58, 59,
   61, 62, 63, 64, 65, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80 and 83.

11. Acknowledgments

   We would like to thank Jari Arkko, Mohan Parthasarathy, Julien
   Bournelle, Rafael Marin Lopez and all members 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 working
   group for their valuable comments to carry multiple EAP sequences this document.

Normative References

   [RFC2119]  Bradner, S., "Key words for use in a single PANA
   sequence, with using RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
              2131, March 1997.

   [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-09 (work in progress), February
              2004.

   [RFC2716]  Aboba, B. and D. Simon, "PPP EAP Success/Failure message as a delimiter TLS Authentication
              Protocol", RFC 2716, October 1999.

   [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.

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 2462, December 1998.

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

   [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.

   [RFC3456]  Patel, B., Aboba, B., Kelly, S. and V. Gupta, "Dynamic
              Host Configuration Protocol (DHCPv4) Configuration 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
              IPsec Tunnel Mode", RFC 3456, January 2003.

   [I-D.ietf-eap-keying]
              Aboba, B., "EAP Key Management Framework",
              draft-ietf-eap-keying-01 (work in progress), October 2003.

   [IANA]     Narten, T. and H. Alvestrand, "Guidelines for EAP messages.
   This method is referred to as orderly-delivery method.  The following
   rules are used Writing an
              IANA Considerations Section in addition to the common rules.

   Rule 5: Use the EAP-layer retransmission RFCs",  BCP 26, RFC 2434,
              October 1998.

Informative References

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

   [I-D.ietf-aaa-eap]
              Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application",
              draft-ietf-aaa-eap-05 (work in progress), April 2004.

   [I-D.puthenkulam-eap-binding]
              Puthenkulam, J., "The Compound Authentication Binding
              Problem", draft-puthenkulam-eap-binding-04 (work in
              progress), October 2003.

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

   [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.

   [I-D.ietf-pana-threats-eval]
              Parthasarathy, M., "PANA Threat Analysis and (ii) the rseq falls security
              requirements", draft-ietf-pana-threats-eval-04 (work in the range between the tseq of the
           last acknowledged message + 1
              progress), May 2003.

   [I-D.ietf-pana-ipsec]
              Parthasarathy, M., "PANA enabling IPsec based Access
              Control", draft-ietf-pana-ipsec-03 (work in progress), May
              2004.

   [I-D.ietf-pana-framework]
              Jayaraman, P., "PANA Framework",
              draft-ietf-pana-framework-00 (work in progress), May 2004.

   [I-D.ietf-pana-snmp]
              Mghazli, Y., Ohba, Y. and the tseq of the last
           transmitted message.  Otherwise, the received message is
           discarded.

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

   ^L                                 PANA                        June 2003

            |
         <--+                   (out of order. discarded)
      11.lost<---   (x+6,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
                                (retransmission timeout at PAA)
      12.<-------   (x+7,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
      13.--->lost   (y+5,x+7)   PANA-Bind-Answer
                                (retransmission timeout at PAA)
      14.<-------   (x+8,y+4)   PANA-Bind-Request[EAP Succ, ID=3]
                                (duplicate detected by PaC)
      15.------->   (y+6,x+8)   PANA-Bind-Answer
   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 J. Bournelle, "SNMP usage for all
   messages.  This method is referred to as reliable-delivery method.
   The following additional rules are applied
              PAA-2-EP interface", draft-ietf-pana-snmp-00 (work in addition
              progress), April 2004.

   [I-D.irtf-aaaarch-handoff]
              Arbaugh, W. and B. Aboba, "Experimental Handoff Extension
              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 RADIUS", draft-irtf-aaaarch-handoff-04 (work in
              progress), November 2003.

   [I-D.ietf-eap-statemachine]
              Vollbrecht, J., Eronen, P., Petroni, N. and Y. Ohba,
              "State Machines 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 Extensible Authentication Protocol
              (EAP) Peer and  Authenticator",
              draft-ietf-eap-statemachine-03 (work in progress), March
              2004.

   [I-D.ietf-seamoby-ctp]
              Loughney, J., "Context Transfer Protocol",
              draft-ietf-seamoby-ctp-08 (work in progress), January
              2004.

   [I-D.ietf-ipsec-ikev2]
              Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              draft-ietf-ipsec-ikev2-13 (work in progress), March 2004.

   [I-D.josefsson-pppext-eap-tls-eap]
              Josefsson, S., Palekar, A., Simon, D. and (ii) the rseq falls G. Zorn,
              "Protected EAP Protocol (PEAP)",
              draft-josefsson-pppext-eap-tls-eap-07 (work in the range between the tseq of the
           last acknowledged message progress),
              October 2003.

   [I-D.ietf-pppext-eap-ttls]
              Funk, P. and the tseq of the last
           transmitted message.  Otherwise, the received message is
           discarded.

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

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

   Figure 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 S. Blake-Wilson, "EAP Tunneled TLS
              Authentication Protocol (EAP-TTLS)",
              draft-ietf-pppext-eap-ttls-04 (work 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 progress), April
              2004.

   [I-D.tschofenig-eap-ikev2]
              Tschofenig, H. and D. Kroeselberg, "EAP IKEv2 Method
              (EAP-IKEv2)", draft-tschofenig-eap-ikev2-03 (work 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
              progress), February 2004.

   [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 communication delay that would occur if
   there is no reliability, as described
              Distributed Security Systems), pages 151-165, 1999.

   [mitm]     Asokan, N., Niemi, V. and K. Nyberg, "Man-in-the-middle in section Appendix A.2.2

Appendix A.4 Consensus

   Although it is recognizable that
              tunnelled authentication",  In the reliable-delivery method would
   be important in terms of improvement Proceedings of overall authentication
   latency, we believe that this is a performance problem the 11th
              International Workshop on Security Protocols, Cambridge,
              UK, April 2003.

   [802.11i]  Institute of EAP Electrical and not
   a problem of PANA.  It is agreed that solving the EAP problem is not
   the scope 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/D10.0,
              2004.

   [802.11]   Institute of PANA Electrical and simplicity is more important factor in the PANA
   design.

   As a consequence, the orderly-delivery method is chosen as the
   message transport 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,
              1999(R2003).

URIs

   [1]  <http://www.toshiba.com/tari/pana/sequence-number.txt>

   [2]  <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 Research, Inc.
   1 Telcordia Drive
   Piscataway, NJ  08854
   USA

   Phone: +1 732 699 5305
   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
   Alper E. Yegin
   Samsung Advanced Institute of PANA. Technology
   75 West Plumeria Drive
   San Jose, CA  95134
   USA

   Phone: +1 408 544 5656
   EMail: alper.yegin@samsung.com

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