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PANA Working Group                                           D. Forsberg
Internet-Draft                                                     Nokia
Expires: September 4, 2006                                 Y. Ohba (Ed.)
                                                                 Toshiba
                                                                B. Patil
                                                                   Nokia
                                                           H. Tschofenig
                                                                 Siemens
                                                                A. Yegin
                                                                 Samsung
                                                           March 3, 2006


     Protocol for Carrying Authentication for Network Access (PANA)
                        draft-ietf-pana-pana-11

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on September 4, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines the Protocol for Carrying Authentication for



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   Network Access (PANA), a link-layer agnostic transport for Extensible
   Authentication Protocol (EAP) to enable network access authentication
   between clients and access networks.  PANA protocol specification
   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 . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.   Specification of Requirements . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.   Transport Layer . . . . . . . . . . . . . . . . . . . . . 10
     4.2.   Payload Encoding  . . . . . . . . . . . . . . . . . . . . 10
     4.3.   Discovery and Handshake Phase . . . . . . . . . . . . . . 11
     4.4.   Authentication and Authorization Phase  . . . . . . . . . 15
     4.5.   Access Phase  . . . . . . . . . . . . . . . . . . . . . . 18
     4.6.   Re-authentication Phase . . . . . . . . . . . . . . . . . 19
     4.7.   Termination Phase . . . . . . . . . . . . . . . . . . . . 20
     4.8.   Separate NAP and ISP Authentication . . . . . . . . . . . 21
       4.8.1.  Negotiating Separate NAP and ISP Authentication  . . . 21
       4.8.2.  Execution of Separate NAP and ISP Authentication . . . 22
       4.8.3.  AAA-Key Calculation  . . . . . . . . . . . . . . . . . 23
   5.  Processing Rules . . . . . . . . . . . . . . . . . . . . . . . 24
     5.1.   Fragmentation . . . . . . . . . . . . . . . . . . . . . . 24
     5.2.   Sequence Number and Retransmission  . . . . . . . . . . . 24
     5.3.   PANA Security Association . . . . . . . . . . . . . . . . 25
     5.4.   Message Authentication  . . . . . . . . . . . . . . . . . 27
     5.5.   Message Validity Check  . . . . . . . . . . . . . . . . . 27
     5.6.   PaC-EP-Master-Key . . . . . . . . . . . . . . . . . . . . 29
     5.7.   Device ID Choice  . . . . . . . . . . . . . . . . . . . . 29
     5.8.   PaC Updating its IP Address . . . . . . . . . . . . . . . 30
     5.9.   Session Lifetime  . . . . . . . . . . . . . . . . . . . . 31
     5.10.  Network Selection . . . . . . . . . . . . . . . . . . . . 31
     5.11.  Error Handling  . . . . . . . . . . . . . . . . . . . . . 32
   6.  Header Format  . . . . . . . . . . . . . . . . . . . . . . . . 33
     6.1.   IP and UDP Headers  . . . . . . . . . . . . . . . . . . . 33
     6.2.   PANA Header . . . . . . . . . . . . . . . . . . . . . . . 33
     6.3.   AVP Header  . . . . . . . . . . . . . . . . . . . . . . . 35
   7.  PANA Messages  . . . . . . . . . . . . . . . . . . . . . . . . 39
     7.1.   PANA-PAA-Discover (PDI) . . . . . . . . . . . . . . . . . 41
     7.2.   PANA-Start-Request (PSR)  . . . . . . . . . . . . . . . . 42
     7.3.   PANA-Start-Answer (PSA) . . . . . . . . . . . . . . . . . 42
     7.4.   PANA-Auth-Request (PAR) . . . . . . . . . . . . . . . . . 42



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     7.5.   PANA-Auth-Answer (PAN)  . . . . . . . . . . . . . . . . . 43
     7.6.   PANA-Reauth-Request (PRAR)  . . . . . . . . . . . . . . . 43
     7.7.   PANA-Reauth-Answer (PRAA) . . . . . . . . . . . . . . . . 43
     7.8.   PANA-Bind-Request (PBR) . . . . . . . . . . . . . . . . . 43
     7.9.   PANA-Bind-Answer (PBA)  . . . . . . . . . . . . . . . . . 44
     7.10.  PANA-Ping-Request (PPR) . . . . . . . . . . . . . . . . . 44
     7.11.  PANA-Ping-Answer (PPA)  . . . . . . . . . . . . . . . . . 44
     7.12.  PANA-Termination-Request (PTR)  . . . . . . . . . . . . . 45
     7.13.  PANA-Termination-Answer (PTA) . . . . . . . . . . . . . . 45
     7.14.  PANA-Error-Request (PER)  . . . . . . . . . . . . . . . . 45
     7.15.  PANA-Error-Answer (PEA) . . . . . . . . . . . . . . . . . 45
     7.16.  PANA-FirstAuth-End-Request (PFER) . . . . . . . . . . . . 46
     7.17.  PANA-FirstAuth-End-Answer (PFEA)  . . . . . . . . . . . . 46
     7.18.  PANA-Update-Request (PUR) . . . . . . . . . . . . . . . . 46
     7.19.  PANA-Update-Answer (PUA)  . . . . . . . . . . . . . . . . 46
   8.  AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . . . . 48
     8.1.   Algorithm AVP . . . . . . . . . . . . . . . . . . . . . . 50
     8.2.   AUTH AVP  . . . . . . . . . . . . . . . . . . . . . . . . 50
     8.3.   Cookie AVP  . . . . . . . . . . . . . . . . . . . . . . . 51
     8.4.   Device-Id AVP . . . . . . . . . . . . . . . . . . . . . . 51
     8.5.   EAP-Payload AVP . . . . . . . . . . . . . . . . . . . . . 51
     8.6.   Failed-AVP AVP  . . . . . . . . . . . . . . . . . . . . . 51
     8.7.   ISP-Information AVP . . . . . . . . . . . . . . . . . . . 51
     8.8.   Key-Id AVP  . . . . . . . . . . . . . . . . . . . . . . . 52
     8.9.   NAP-Information AVP . . . . . . . . . . . . . . . . . . . 52
     8.10.  Nonce AVP . . . . . . . . . . . . . . . . . . . . . . . . 52
     8.11.  Notification AVP  . . . . . . . . . . . . . . . . . . . . 53
     8.12.  Post-PANA-Address-Configuration (PPAC) AVP  . . . . . . . 53
     8.13.  Protection-Capability AVP . . . . . . . . . . . . . . . . 55
     8.14.  Provider-Identifier AVP . . . . . . . . . . . . . . . . . 55
     8.15.  Provider-Name AVP . . . . . . . . . . . . . . . . . . . . 55
     8.16.  Result-Code AVP . . . . . . . . . . . . . . . . . . . . . 55
       8.16.1. Authentication Results Codes . . . . . . . . . . . . . 55
       8.16.2. Protocol Error Result Codes  . . . . . . . . . . . . . 56
     8.17.  Session-Id AVP  . . . . . . . . . . . . . . . . . . . . . 58
     8.18.  Session-Lifetime AVP  . . . . . . . . . . . . . . . . . . 59
     8.19.  Termination-Cause AVP . . . . . . . . . . . . . . . . . . 59
   9.  Retransmission Timers  . . . . . . . . . . . . . . . . . . . . 60
     9.1.   Transmission and Retransmission Parameters  . . . . . . . 61
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 63
     10.1.  PANA UDP Port Number  . . . . . . . . . . . . . . . . . . 63
     10.2.  PANA Multicast Address  . . . . . . . . . . . . . . . . . 63
     10.3.  PANA Header . . . . . . . . . . . . . . . . . . . . . . . 63
       10.3.1. Message Type . . . . . . . . . . . . . . . . . . . . . 63
       10.3.2. Flags  . . . . . . . . . . . . . . . . . . . . . . . . 64
     10.4.  AVP Header  . . . . . . . . . . . . . . . . . . . . . . . 64
       10.4.1. AVP Code . . . . . . . . . . . . . . . . . . . . . . . 64
       10.4.2. Flags  . . . . . . . . . . . . . . . . . . . . . . . . 65



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     10.5.  AVP Values  . . . . . . . . . . . . . . . . . . . . . . . 65
       10.5.1. Post-PANA-Address-Configuration AVP Values . . . . . . 65
       10.5.2. Protection-Capability AVP Values . . . . . . . . . . . 65
       10.5.3. Result-Code AVP Values . . . . . . . . . . . . . . . . 65
       10.5.4. Termination-Cause AVP Values . . . . . . . . . . . . . 65
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 67
     11.1.  General Security Measures . . . . . . . . . . . . . . . . 67
     11.2.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . 68
     11.3.  EAP Methods . . . . . . . . . . . . . . . . . . . . . . . 69
     11.4.  Separate NAP and ISP Authentication . . . . . . . . . . . 69
     11.5.  Cryptographic Keys  . . . . . . . . . . . . . . . . . . . 69
     11.6.  Per-packet Ciphering  . . . . . . . . . . . . . . . . . . 70
     11.7.  PAA-to-EP Communication . . . . . . . . . . . . . . . . . 70
     11.8.  Liveness Test . . . . . . . . . . . . . . . . . . . . . . 71
     11.9.  Updating PaC's IP Address . . . . . . . . . . . . . . . . 71
     11.10. Early Termination of a Session  . . . . . . . . . . . . . 71
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 72
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 73
     13.1.  Normative References  . . . . . . . . . . . . . . . . . . 73
     13.2.  Informative References  . . . . . . . . . . . . . . . . . 74
   Appendix A.  Example Sequence of Separate NAP and ISP
                Authentication  . . . . . . . . . . . . . . . . . . . 76
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 78
   Intellectual Property and Copyright Statements . . . . . . . . . . 80



























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1.  Introduction

   Providing secure network access service requires access control based
   on the authentication and authorization of the clients and the access
   networks.  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.  Appendix A of [RFC4058]
   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) [RFC3748] 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 (an EAP
   lower layer), EAP and EAP methods as described in [RFC3748].

   Various environments and usage models for PANA are identified in
   Appendix A of [RFC4058].  Potential security threats for network-
   layer access authentication protocol are discussed in [RFC4016].
   These have been essential in defining the requirements [RFC4058] on
   the PANA protocol.  Note that some of these requirements are imposed
   by the chosen payload, EAP [RFC3748].

   There are components that are part of a complete secure network
   access solution but are outside of the 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 (see
   [I-D.ietf-pana-framework] and [I-D.ietf-pana-snmp]).  The readers are
   recommended to go through the PANA Framework document [I-D.ietf-pana-
   framework] prior to reading this protocol specification document.

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", and "OPTIONAL" in this document
   are to be interpreted as described in [RFC2119].





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2.  Terminology

   PANA Client (PaC):

      The client side of the protocol that resides in the access device
      (e.g., laptop, PDA, etc.).  It is responsible for providing the
      credentials in order to prove its identity (authentication) for
      network access authorization.  The PaC and the EAP peer are co-
      located in the same access device.

   PANA Authentication Agent (PAA):

      The protocol entity in the access network whose responsibility is
      to verify the credentials provided by a PANA client (PaC) and
      authorize network access to the device associated with the client
      and identified by a Device Identifier (DI).  The PAA and the EAP
      authenticator (and optionally the EAP server) are co-located in
      the same node.  Note the authentication and authorization
      procedure can, according to the EAP model, be also offloaded to
      the backend AAA infrastructure.

   PANA Session:

      A PANA session begins with the handshake between the PANA Client
      (PaC) and the PANA Authentication Agent (PAA), and terminates as a
      result of an authentication or liveness test failure, a message
      delivery failure after retransmissions reach maximum values,
      session lifetime expiration, or an explicit termination message.
      A fixed session identifier is maintained throughout a session.  A
      session cannot be shared across multiple network interfaces.  Only
      one device identifier of the PaC is allowed to be bound to a PANA
      session for simplicity.

   Session Lifetime:

      A duration that is associated with a PANA session.  For an
      established PANA session, the session lifetime is bound to the
      lifetime of the current authorization given to the PaC.  The
      session lifetime can be updated by a new round of EAP
      authentication before it expires.

   Session Identifier:

      This identifier is used to uniquely identify a PANA session on the
      PAA and PaC.  It includes an identifier of the PAA, therefore it
      cannot be shared across multiple PAAs.  It is included in PANA
      messages to bind the message to a specific PANA session.  This
      bidirectional identifier is allocated by the PAA following the



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      handshake and freed when the session terminates.

   PANA Security Association (PANA SA):

      A PANA security association is formed between the PaC and the PAA
      by sharing cryptographic keying material and associated context.
      The formed duplex security association is used to protect the
      bidirectional PANA signaling traffic between the PaC and the PAA.

   Device Identifier (DI):

      The identifier used by the network as a handle to control and
      police the network access of a device.  Depending on the access
      technology, this identifier may contain an address that is carried
      in protocol headers (e.g., IP or link-layer address), or a locally
      significant identifier that is made available by the local
      protocol stack (e.g., circuit id, PPP interface id) of a connected
      device.

   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
      access devices.  Information such as the DI and (optionally)
      cryptographic keys are provided by the PAA per client for
      generating filters on the EP.  The EP and PAA may be co-located.

   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].

   For additional terminology definitions see the PANA framework
   document [I-D.ietf-pana-framework].












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3.  Protocol Overview

   The PANA protocol is run between a client (PaC) and a server (PAA) in
   order to perform authentication and authorization for the network
   access service.

   The protocol messaging consists of a series of request and responses,
   some of which may be initiated by either end.  Each message can carry
   zero or more AVPs within the payload.  The main payload of PANA is
   EAP which performs authentication.  PANA helps the PaC and PAA
   establish an EAP session.

   PANA is a UDP-based protocol.  It has its own retransmission
   mechanism to reliably deliver messages.

   PANA messages are sent between the PaC and PAA as part of a PANA
   session.  A PANA session consists of distinct phases:

   o  Discovery and handshake phase: This is the phase that initiates a
      new PANA session.  The PaC discovers the PAA(s) by either
      explicitly soliciting advertisements for them or receiving
      unsolicited advertisements.  The PaC's answer sent in response to
      an advertisement starts a new session.

   o  Authentication and authorization phase: Immediately following the
      discovery and handshake phase is the EAP execution between the PAA
      and PaC.  The EAP payload (which carry an EAP method inside) is
      what is used for authentication.  The PAA conveys the result of
      authentication and authorization to the PaC at the end of this
      phase.  This phase may involve execution of two EAP sessions back-
      to-back, one for the NAP and one for the ISP.

   o  Access phase: After a successful authentication and authorization
      the host gains access to the network and can send and receive IP
      data traffic through the EP(s).  At any time during this phase,
      the PaC and PAA may optionally send PANA ping messages to test
      liveness of the PANA session on the peer.

   o  Re-authentication phase: During the access phase, the PAA must
      initiate re-authentication before the PANA session lifetime
      expires.  EAP is carried by PANA to perform authentication.  This
      phase may be optionally triggered by both the PaC and the PAA
      without any respect to the session lifetime.  The session moves to
      this phase from the access phase, and returns back there upon
      successful re-authentication.

   o  Termination phase: The PaC or PAA may choose to discontinue the
      access service at any time.  An explicit disconnect message can be



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      sent by either end.  If either the PaC or the PAA disconnects
      without engaging in termination messaging, it is expected that
      either the expiration of a finite session lifetime or failed
      liveness tests would clean up the session at the other end.


     PaC  PAA    Message
   -----------------------------------------------------
   // Discovery and handshake phase
      ----->     PANA-PAA-Discover
      <-----     PANA-Start-Request
      ----->     PANA-Start-Answer

   // Authentication and authorization phase
      <-----     PANA-Auth-Request /* EAP Request */
      ----->     PANA-Auth-Answer
      ----->     PANA-Auth-Request /* EAP Response */
      <-----     PANA-Auth-Answer
      <-----     PANA-Bind-Request /* EAP Success */
      ----->     PANA-Bind-Answer

   // Access phase (IP data traffic allowed)
      <-----     PANA-Ping-Request
      ----->     PANA-Ping-Answer

   // Termination phase
      ----->     PANA-Termination-Request
      <-----     PANA-Termination-Answer

   Figure 1: Illustration of PANA messages in a session

   Note that depending on the environment and deployment the protocol
   flow depicted in Figure 1 can be abbreviated (An unsolicited PANA-
   Start-Request can be sent without a triggering PANA-PAA-Discover, EAP
   responses can be piggybacked on the PANA-Auth-Answers, and PANA-Ping
   and PANA-Termination usage is optional).

   Cryptographic protection of messages between the PaC and PAA is
   possible as soon as EAP in conjunction with the EAP method exports a
   shared key.  That shared key is used to create a PANA SA.  The PANA
   SA helps generate per-message authentication codes that provide
   integrity protection and authentication.

   Throughout the lifetime of a session, various problems found with the
   incoming messages can generate a PANA error message sent in response.






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4.  Protocol Details

   The following sections explain in detail the various phases of a PANA
   session.

4.1.  Transport Layer

   PANA uses UDP as its transport layer protocol.  The UDP port number
   is To Be Assigned by IANA.  All messages except for PANA-PAA-Discover
   are always unicast.  The PANA-PAA-Discover message MAY be unicast
   when the PaC knows the IP address of the PAA.

4.2.  Payload Encoding

   The payload of any PANA message consists of zero or more AVPs
   (Attribute Value Pairs).  The subsequent sections refer to these
   AVPs, therefore the list of AVPs are provided with a brief
   description before more extensive descriptions are included later in
   the document (see Section 8).

   o  Algorithm AVP: contains a pseudo-random function and an integrity
      algorithm.

   o  AUTH AVP: contains a Message Authentication Code that integrity
      protects the PANA message.

   o  Cookie AVP: contains a random value that is generated by the PAA
      according to [RFC4086] and used for making PAA discovery robust
      against blind resource consumption DoS attacks.

   o  Device-Id AVP: contains a device identifier (link-layer address or
      an IP address) of the PaC or an EP.

   o  EAP AVP: contains an EAP PDU.

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

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

   o  Protection-Capability AVP: contains the type of per-packet
      protection (link-layer vs. network-layer) when a cryptographic
      mechanism should be enabled after PANA authentication.

   o  NAP-Information AVP, ISP-Information AVP: contains the identifier
      of a NAP and an ISP, respectively.

   o  Nonce AVP: contains a randomly chosen value [RFC4086] that is used
      in cryptographic key computations.



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   o  Notification AVP: contains a displayable message.

   o  Provider-Identifier AVP: contains the identifier of a NAP or an
      ISP.

   o  PPAC AVP: Post-PANA-Address-Configuration AVP.  Used to indicate
      the available/chosen IP address configuration methods that can be
      used by the PaC after successful PANA authentication.

   o  Provider-Name AVP: contains a name of a NAP or an ISP.

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

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

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

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

4.3.  Discovery and Handshake Phase

   When the PaC knows the IP address of the PAA, it can send a unicast
   PANA-PAA-Discover message and initiate the PANA exchange.  In other
   cases, the PaC MUST rely on dynamic discovery methods, such as
   multicast-based and a traffic-driven discovery.

   Multicast-based Discovery:

      The PaCs and PAAs MUST implement multicast-based discovery where
      the PaC sends a PANA-PAA-Discover message to a well-known
      administratively scoped multicast address (To Be Assigned by IANA)
      and UDP port (To Be Assigned by IANA).

      The network administrator MUST configure the multicast scope such
      that the discovery messages can reach only the designated PAA(s).
      In case the PAA(s) is on the same link as the PaC, the
      administratively scoped multicast messages MUST not be forwarded
      by the routers.  Details of scope configuration are discussed in
      [RFC2365].

      The PAA(s) that receive the discovery message MUST respond with a
      unicast PANA-Start-Request message sent to the soliciting PaC.

   Traffic-driven Discovery:






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      Alternatively, the PaC MAY also choose to start sending data
      packets before getting authenticated.  The EP in an access network
      that implements PANA SHOULD drop such unauthorized packets upon
      receipt.  Additionally, the EP MAY also take this traffic as an
      indication of unauthorized PaC and notify the PAA.  The EP-to-PAA
      notification SHOULD be sent via [I-D.ietf-pana-snmp].  In
      response, the PAA SHOULD send an unsolicited PANA-Start-Request
      message to the PaC.  This is called traffic-driven PAA discovery
      (an alternative to the PaC explicitly soliciting for a PAA).
      Deployment of this alternate scheme is optional.

   Other Alternatives:

      The EP-to-PAA notification MAY also be generated in response to
      receiving a link-up event notification on the EP [I-D.ietf-dna-
      link-information].

      Alternative PAA discovery schemes may be designed (e.g., DHCP-
      based) but they are outside the scope of this specification.

   When the PaC receives a PANA-Start-Request message from a PAA, it
   responds with a PANA-Start-Answer message if it wishes to enter the
   authentication and authorization phase.

   There can be multiple PAAs in the access network and the PaC may
   receive multiple PANA-Start-Request messages from those PAAs.  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 first PANA-Start-Request message.

   A PANA-Start-Request message MAY carry a Cookie AVP that contains a
   random value generated by the PAA.  The random value is referred to
   as a cookie.  The cookie is used for preventing the PAA from resource
   consumption DoS attacks by blind attackers which bombard the PAA with
   PANA-PAA-Discover messages.  By relying on a cookie mechanism the PAA
   can avoid per-PaC state creation until after the PaC can produce the
   same cookie in its PANA-Start-Answer message.  In order to do that,
   the cookie MUST be 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 the PANA-Start-Answer message.  The PAA discovery
   that takes advantage of cookies is called "stateless PAA discovery".
   The exact algorithms and syntax used by the PAA to generate cookies
   does not affect interoperability and hence is not specified here.
   Additionally, the PAA MAY limit the rate it processes incoming PANA-
   PAA-Discover messages.

   When the PaC sends a PANA-Start-Answer message in response to a PANA-
   Start-Request containing a Cookie AVP, the answer MUST contain a



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   Cookie AVP with the cookie value copied from the request.

   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 matches the send cookie.  If the match is verified,
   the protocol enters the authentication and authorization phase.
   Otherwise, the PAA MUST silently discard the received message.

   The initial EAP Request message MAY be optionally carried by the
   PANA-Start-Request (as opposed to by a later PANA-Auth-Request)
   message in order to reduce the number of round-trips.  This
   optimization SHOULD NOT be used if the PAA discovery is desired to be
   stateless since transmission of an EAP Request message creates a
   state at EAP layer.  See [RFC4137] for more information on the EAP
   state machine and the allocation of state information in the
   respective protocol steps.

   A Protection-Capability AVP, an Algorithm AVP and a Post-PANA-
   Address-Configuration (PPAC) AVP MAY be 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.
   Since these AVPs are provided during the insecure discovery and
   handshake phase, there are certain security risks involved in using
   the provided information.  See Section 11 for further discussion on
   this.

   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.

   The PANA-Start-Request/Answer exchange is needed before entering the
   authentication and authorization phase even when the PaC is pre-
   configured with the IP address of the PAA and the PANA-PAA-Discover
   message is unicast.

   A Nonce AVP MUST be included in the first PANA-Auth-Request and PANA-
   Auth-Answer messages in the authentication and authorization phase
   when stateless PAA discovery is used, and in PANA-Start-Request and
   PANA-Start-Answer messages in this phase otherwise.

   A PANA-Start-Request message in stateless PAA discovery MUST NOT be
   retransmitted as this voids the statelessness on the PAA.  Instead,
   the PaC MUST retransmit the PANA-PAA-Discover message until it
   receives a PANA-Start-Request message, and retransmit the PANA-Start-
   Answer message until it receives a PANA-Auth-Request message.  The
   PaC can determine whether the PAA is using stateless PAA discovery by
   looking at the L-flag in the PANA header.  The PANA-Start-Request



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   message MUST be retransmitted instead of the PANA-Start-Answer
   message when stateful PAA discovery is used (L-flag is not set).

   It is possible that both the PAA and the PaC initiate the discovery
   and 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.,
   L-flag is not set) for the PaC.  In this case the PAA will retransmit
   the PANA-Start-Request message based on a timer, if the PaC doesn't
   respond in time (the message was lost for example).  If the PAA had
   sent a PANA-Start-Request message without creating a state for the
   PaC (i.e., L-flag is set), then it SHOULD answer to the PANA-PAA-
   Discover message.

   Figure 2 shows an example sequence for the discovery and handshake
   phase when a PANA-PAA-Discover message is sent by the PaC.  Figure 3
   shows an example sequence for the discovery and handshake phase with
   traffic-driven PAA discovery.

      PaC      PAA         Message(sequence number)[AVPs]
      ------------------------------------------------------
         ----->            PANA-PAA-Discover(0)
         <-----            PANA-Start-Request(x)[Cookie]
         ----->            PANA-Start-Answer(x)[Cookie]
                           (continued to the authentication and
                            authorization phase)

   Figure 2: Example sequence for the discovery and handshake phase when
   PANA-PAA-Discover is sent by the PaC


      PaC   EP      PAA    Message(sequence number)[AVPs]
      ------------------------------------------------------
       ---->o              (Data packet arrival or L2 trigger)
             ------>       PAA-to-EP protocol, or another mechanism
       <------------       PANA-Start-Request(x)[Cookie]
       ------------>       PANA-Start-Answer(x)[Cookie]
                           (continued to the authentication and
                            authorization phase)

   Figure 3: Example sequence for the discovery and handshake phase with
   traffic-driven PAA discovery







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4.4.  Authentication and Authorization Phase

   The main task of the authentication and authorization phase is to
   carry EAP messages between the PaC and the PAA.  EAP Request and
   Response messages are carried in PANA-Auth-Request messages.  PANA-
   Auth-Answer messages are simply used to acknowledge receipt of the
   requests.  As an optimization, a PANA-Auth-Answer message MAY include
   the EAP Response message.  This optimization MAY not be used when it
   takes time to generate the EAP Response message (due to, e.g.,
   intervention of human input), in which case returning an EAP-Auth-
   Answer message without piggybacking an EAP Response message can avoid
   unnecessary retransmission of the PANA-Auth-Request message.  Another
   optimization allows optionally carrying the first EAP Request/
   Response message in PANA-Start-Request/Answer message as described in
   Section 4.3.

   When stateless PAA discovery was performed in the discovery and
   handshake phase, a Nonce AVP MUST be included in the first PANA-Auth-
   Request and PANA-Auth-Answer messages.

   PANA allows execution of two separate authentication methods, one
   with NAP and one with ISP under the same PANA session.  This optional
   feature may be offered by the PAA and accepted by the PaC.  When
   performed separately, the result of the first EAP authentication is
   signaled via PANA-FirstAuth-End-Request and PANA-FirstAuth-End-Answer
   message exchange which delineates the first method execution from the
   next.  See Section 4.8 for a detailed discussion on separate NAP and
   ISP authentication.

   The result of PANA authentication is carried in a PANA-Bind-Request
   message sent from the PAA to the PaC.  This message carries the final
   EAP authentication result (whether it is the second EAP
   authentication result of NAP and ISP separate authentication, or the
   sole EAP authentication result) and the result of PANA
   authentication.  The PANA-Bind-Request message MUST be acknowledged
   with a PANA-Bind-Answer (PBA) message.  Figure 4 shows an example
   sequence in the authentication and authorization phase (no separate
   authentication).













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   PaC      PAA  Message(sequence number)[AVPs]
   --------------------------------------------------------------------
                 (continued from the discovery and handshake phase)
      <-----     PANA-Auth-Request(x+1)
                    [Session-Id, Nonce, EAP{Request}]
      ----->     PANA-Auth-Answer(x+1) // No piggybacking EAP Response
                    [Session-Id, Nonce]
      ----->     PANA-Auth-Request(y)
                    [Session-Id, EAP{Response}]
      <-----     PANA-Auth-Answer(y)
                    [Session-Id]
      <-----     PANA-Auth-Request(x+2)
                    [Session-Id, EAP{Request}]
      ----->     PANA-Auth-Answer(x+2) // Piggybacking EAP Response
                    [Session-Id, EAP{Response}]
      <-----     PANA-Bind-Request(x+3)
                    [Session-Id, Result-Code, EAP{Success}, Device-Id,
                     Key-Id, Algorithm,
                     Lifetime, Protection-Cap., PPAC, AUTH]
      ----->     PANA-Bind-Answer(x+3)
                    [Session-Id, Device-Id, Key-Id, PPAC, AUTH]

   Figure 4: Example sequence for the authentication and authorization
   phase

   When an EAP method that is capable of deriving keys is used during
   the authentication and authorization phase and the keys are
   successfully derived, the PANA message that carries the EAP Success
   message (i.e., a PANA-FirstAuth-End-Request or a PANA-Bind-Request
   message) MUST contain a Key-Id AVP and an AUTH AVP, and an Algorithm
   AVP for the first derivation of keys in the session, and any
   subsequent message MUST contain an AUTH AVP.  An Algorithm AVP MUST
   NOT be contained in a PANA-FirstAuth-End-Request or a PANA-Bind-
   Request message after the first derivation of keys in the session.

   The PANA-Bind-Request and the PANA-Bind-Answer message exchange is
   also used for binding device identifiers of the PaC and EP(s) to the
   PANA SA.  To achieve this, if a Protection-Capability AVP is included
   in the PANA-Bind-Request message, the message MUST contain the device
   identifier in a Device-Id AVP for each EP.  Otherwise, if a
   Protection-Capability AVP is not included in the PANA-Bind-Request
   message, the message MUST contain the device identifier in a
   Device-Id AVP for each EP when a link-layer or IP address is used as
   the device identifier of the PaC.  The PANA-Bind-Answer message MUST
   contain the PaC's device identifier in a Device-Id AVP when it is
   already presented with that of EP(s) in the request with using the
   same type of device identifier as contained in the request.  If the
   PANA-Bind-Answer message sent from the PaC does not contain a



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   Device-Id AVP with the same device identifier type contained in the
   request, the PAA sends a PANA-Error-Request message with a
   PANA_MISSING_AVP result code, and wait for a PANA-Error-Answer
   message to terminate the session.

   The PANA-Bind-Request message with a PANA_SUCCESS result code MUST
   also contain a Protection-Capability AVP if link-layer or network-
   layer ciphering is enabled after the authentication and authorization
   phase.  The PANA-Bind-Request message MAY also contain a Protection-
   Capability AVP to indicate if link-layer or network-layer ciphering
   should be enabled after the authentication and authorization phase.
   No link-layer or network-layer specific information is included in
   the Protection-Capability AVP.  It is assumed that the 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.  When the PaC does not support the protection capability
   indicated in the Protection-Capability AVP, the PaC MUST send a PANA-
   Error-Request message with a PANA_PROTECTION_CAPABILITY_UNSUPPORTED
   result code and terminate the PANA session.

   Additionally, the PANA-Bind-Request message with a PANA_SUCCESS
   result code MUST include a Post-PANA-Address-Configuration (PPAC)
   AVP, which helps the PAA to inform the PaC about whether a new IP
   address MUST be configured and the available methods to do so.  In
   this case, the PaC MUST include a PPAC AVP in the PANA-Bind-Answer
   message 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, the PaC MUST send a
   PANA-Error-Request message with a PANA_PPAC_CAPABILITY_UNSUPPORTED
   result code and terminate the PANA session.

   EAP authentication can fail at a pass-through authenticator without
   sending an EAP Failure message [RFC4137].  When this occurs, the PAA
   SHOULD send a PANA-Error-Request message to the PaC with using
   PANA_UNABLE_TO_COMPLY result code.  The PaC MUST NOT change its state
   unless the error message 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 or authorization locally
   rejected by the PAA.  When this occurs, the PAA MUST send a PANA-
   Bind-Request with a result code PANA_AUTHORIZATION_REJECTED.  If a
   AAA-Key is established between the PaC and the PAA by the time when
   the EAP Success message is generated by the EAP server (this is the
   case when the EAP method provides protected success indication), the
   PANA-Bind-Request and PANA-Bind-Answer messages MUST be protected



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   with an AUTH AVP and carry a Key-Id AVP.  The PANA-Bind-Request
   message MUST also carry an Algorithm AVP if it is for the first
   derivation of keys in the session.  The AAA-Key and the PANA session
   MUST be deleted immediately after the PANA-Bind message exchange.

4.5.  Access Phase

   Once the authentication and authorization phase or the re-
   authentication phase successfully completes, the PaC gains access to
   the network and can send and receive IP data traffic through the
   EP(s) and the PANA session enters the access phase.  In this phase,
   PANA-Ping-Request and PANA-Ping-Answer messages can be used for
   testing the liveness of the PANA session on the PANA peer.  Both the
   PaC and the PAA are allowed to send a PANA-Ping-Request message to
   the communicating peer whenever they need to make sure the
   availability of the session on the peer and expect the peer to return
   a PANA-Ping-Answer message.  Both PANA-Ping-Request and PANA-Ping-
   Answer messages MUST be protected with an AUTH AVP when a PANA SA is
   available.

   Implementations MUST limit the rate of performing this test.  The PaC
   and the PAA can handle rate limitation on their own, they do not have
   to perform any coordination with each other.  There is no negotiation
   of timers for this purpose.  Additionally, an implementation MAY
   rate-limit processing the incoming PANA-Ping-Requests.

   Figure 5 and Figure 6 show liveness tests as they are initiated by
   the PaC and the PAA respectively.

   PaC      PAA     Message(sequence number)[AVPs]
   ------------------------------------------------------
      ----->        PANA-Ping-Request(q)[Session-Id, AUTH]
      <-----        PANA-Ping-Answer(q)[Session-Id, AUTH]


   Figure 5: Example sequence for PaC-initiated liveness test


   PaC      PAA     Message(sequence number)[AVPs]
   ------------------------------------------------------
      <-----        PANA-Ping-Request(p)[Session-Id, AUTH]
      ----->        PANA-Ping-Answer(p)[Session-Id, AUTH]

   Figure 6: Example sequence for PAA-initiated liveness test







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4.6.  Re-authentication Phase

   The PANA session in the access phase can enter the re-authentication
   phase to extend the current session lifetime by re-executing EAP.
   Once the re-authentication phase successfully completes, the session
   re-enters the access phase.  Otherwise, the session is deleted.

   When the PaC wants to initiate re-authentication, it sends a PANA-
   Reauth-Request 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 session identifier, it MUST first respond with a
   PANA-Reauth-Answer message, followed by a PANA-Auth-Request that
   starts a new EAP authentication.  If the PAA cannot identify the
   session, it MAY respond with a PANA-Error-Request message with a
   result code PANA_UNKNOWN_SESSION_ID.  Transmission of this error
   request is made optional in case this behavior is leveraged for a DoS
   attack on the PAA.

   The PaC may receive a PANA-Auth-Request before receiving the answer
   to its outstanding PANA-Reauth-Request.  This condition can arise due
   to packet re-ordering or a race condition between the PaC and PAA
   when they both attempt to engage in re-authentication.  The PaC MUST
   keep discarding the received PANA-Auth-Requests until it receives the
   answer to its request.

   When the PAA initiates re-authentication, it sends a PANA-Auth-
   Request message containing the session identifier for the PaC to
   enter the re-authentication phase.  The PAA SHOULD initiate EAP re-
   authentication before the current session lifetime expires.

   Re-authentication of an on-going PANA session MUST maintain the
   existing sequence numbers.

   For any re-authentication, if there is an established PANA SA, PANA-
   Auth-Request and PANA-Auth-Answer messages MUST be protected by
   adding a MAC AVP to each message.  Any subsequent EAP authentication
   MUST be performed with the same ISP and NAP that was selected during
   the discovery and handshake phase.  The value of the S-flag
   ("separate authentication" flag, see Section 4.8.1) of the PANA
   messages exchanged in the re-authentication phase MUST be inherited
   from the previous authentication and authorization phase or re-
   authentication phase.








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   PaC      PAA  Message(sequence number)[AVPs]
   ------------------------------------------------------
      ----->     PANA-Reauth-Request(q)
                    [Session-Id, AUTH]
      <-----     PANA-Reauth-Answer(q)
                    [Session-Id, AUTH]
      <-----     PANA-Auth-Request(p)
                    [Session-Id, EAP{Request}, AUTH]
      ----->     PANA-Auth-Answer(p)   // No piggybacking EAP Response
                    [Session-Id, AUTH]
      ----->     PANA-Auth-Request(q+1)
                    [Session-Id, EAP{Response}, AUTH]
      <-----     PANA-Auth-Answer(q+1) // No piggybacking EAP Response
                    [Session-Id, AUTH]
      <-----     PANA-Auth-Request(p+1)
                    [Session-Id, EAP{Request}, AUTH]
      ----->     PANA-Auth-Answer(p+1) // Piggybacking EAP Response
                    [Session-Id, EAP{Response}, AUTH]
      <-----     PANA-Bind-Request(p+2)
                    [Session-Id, Result-Code, EAP{Success},
                     Device-Id, Key-Id, Algorithm,
                     Lifetime, Protection-Cap., PPAC, AUTH]
      ----->     PANA-Bind-Answer(p+2)
                    [Session-Id, Device-Id, Key-Id, PPAC, AUTH]

   Figure 7: Example sequence for the re-authentication phase initiated
   by PaC

4.7.  Termination Phase

   A procedure for explicitly terminating a PANA session can be
   initiated either from the PaC (i.e., disconnect indication) or from
   the PAA (i.e., session revocation).  The PANA-Termination-Request and
   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 between the PaC and the PAA, all
   messages exchanged during the termination phase MUST be protected
   with an AUTH AVP.  When the sender of the PANA-Termination-Request
   message receives a valid acknowledgment, all states maintained for
   the PANA session MUST be deleted immediately.









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   PaC      PAA     Message(sequence number)[AVPs]
   ------------------------------------------------------
      ----->        PANA-Termination-Request(q)[Session-Id, AUTH]
      <-----        PANA-Termination-Answer(q)[Session-Id, AUTH]

   Figure 8: Example sequence for the termination phase triggered by PaC

4.8.  Separate NAP and ISP Authentication

   PANA allows running at most two EAP sessions in sequence in the
   authentication and authorization phase to support separate NAP and
   ISP authentication as described in this section.  A typical network
   access authentication includes execution of one EAP method with the
   ISP.  This separation allows the PaC to perform an additional
   authentication method for receiving differentiated services from the
   NAP.

   Currently, running multiple EAP sessions in sequence in the
   authentication and authorization phase is designed only for separate
   NAP and ISP authentication.  It is not for running arbitrary number
   of EAP sessions in sequence, or giving the PaC another chance to try
   another EAP authentication method within an integrated NAP and ISP
   authentication when an EAP authentication method fails.

   Within separate NAP and ISP authentication, the NAP authentication
   and the ISP authentication are considered completely independent.
   Presence or success of one should not effect the other.  Making a
   network access authorization decision based on the success or failure
   of each authentication is a network policy issue.

4.8.1.  Negotiating Separate NAP and ISP Authentication

   When the PaC and PAA negotiates in the discovery and handshake phase
   to perform separate NAP and ISP authentication, the PaC and the PAA
   operate in the following way in addition to the behavior defined in
   Section 4.3

   In the discovery and handshake phase, the PAA MAY advertise
   availability of separate NAP and ISP authentication ([I-D.ietf-pana-
   framework]) by setting the S-flag on the PANA header of the PANA-
   Start-Request message.

   If the S-flag of the received PANA-Start-Request message is set, the
   PaC can indicate its desire to perform separate NAP and ISP
   authentication by setting the S-flag in the PANA-Start-Answer
   message.  If the S-flag of the received PANA-Start-Request message is
   not set, the PaC MUST NOT set the S-flag in the PANA-Start-Answer
   message sent back to the PAA.



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   If the S-flag in the PANA-Start-Answer message is not set, only one
   authentication is performed (ISP-only) and the processing occurs as
   described in Section 4.3.

   When the S-flag is set in a PANA-Start-Request message, the initial
   EAP Request message MUST NOT be carried in the PANA-Start-Request
   message.  (If the initial EAP Request message were contained in the
   PANA-Start-Request message during the S-flag negotiation, the PaC
   cannot tell whether the EAP Request message is for NAP authentication
   or ISP authentication.)

4.8.2.  Execution of Separate NAP and ISP Authentication

   When the PaC and PAA have negotiated in the discovery and handshake
   phase to perform separate NAP and ISP authentication, the PaC and the
   PAA operate in the following way in addition to the behavior defined
   in Section 4.4

   o  The S-flag of PANA-Auth-Request and PANA-Auth-Answer messages MUST
      be set.

   o  An EAP Success/Failure message is carried in a PANA-FirstAuth-End-
      Request (PFER) message as well as a PANA-Bind-Request (PBR)
      message.  The PANA-FirstAuth-End-Request message MUST be used at
      the end of the first EAP authentication and the PANA-Bind-Request
      MUST be used for the second EAP authentication.  The PANA-
      FirstAuth-End-Request messages MUST be acknowledged with a PANA-
      FirstAuth-End-Answer (PFEA) message.

   o  If the first EAP authentication has failed, the PAA can choose not
      to perform the second EAP authentication 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 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
      PANA session MUST be immediately deleted.  Otherwise, the second
      EAP authentication MUST be performed.

   o  The PAA determines the execution order of NAP authentication and
      ISP authentication.  In this case, the PAA can indicate which
      authentication (NAP authentication or ISP authentication) is
      currently occurring by using N-flag in the PANA message header.
      When NAP authentication is being performed, the N-flag MUST be
      set.  When ISP authentication is being performed, the N-flag MUST



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      NOT be set.  The N-flag MUST NOT be set when S-flag is not set.

   When the PaC and PAA have negotiated in the discovery and handshake
   phase to perform separate NAP and ISP authentication, and the lower-
   layer is insecure, the two EAP authentication methods used in the
   separate authentication MUST be capable of deriving keys (AAA-Key).

4.8.3.  AAA-Key Calculation

   When the PaC and PAA have negotiated in the discovery and handshake
   phase to perform separate NAP and ISP authentication, if the lower-
   layer is insecure, the two EAP authentication methods used in the
   separate authentication MUST be capable of deriving keys.  In this
   case, if the 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 second EAP
   authentication MUST be protected with the key derived from the AAA-
   Key for the first EAP authentication.  The PANA-Bind-Request and
   PANA-Bind-Answer messages and all subsequent PANA messages exchanged
   in the access phase, re-authentication phase and termination phase
   MUST be protected either with the AAA-Key for the first EAP
   authentication if 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 AAA-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 authentication succeed.  See Section 5.3 for how to
   derive the AAA-Key.






















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5.  Processing Rules

5.1.  Fragmentation

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

5.2.  Sequence Number and Retransmission

   PANA uses sequence numbers to provide ordered and reliable delivery
   of messages.

   The PaC and PAA maintain two sequence numbers: the next one to be
   used for a request it initiates and the next one it expects to see in
   a request from the other end.  These sequence numbers are 32-bit
   unsigned numbers.  They are monotonically incremented by 1 as new
   requests are generated and received, and wrapped to zero on the next
   message after 2^32-1.  Answers always contain the same sequence
   number as the corresponding request.  Retransmissions reuse the
   sequence number contained in the original packet.

   The initial sequence numbers (ISN) are randomly picked by the PaC and
   PAA as they send their very first request messages.  PANA-PAA-
   Discover message carries sequence number 0.

   When a request message is received, it is considered valid in terms
   of sequence numbers if and only if its sequence number matches the
   expected value.  This check does not apply to the PANA-PAA-Discover,
   PANA-Start-Request messages.

   When an answer message is received, it is considered valid in terms
   of sequence numbers if and only if its sequence number matches that
   of the currently outstanding request.  A peer can only have one
   outstanding request at a time.

   PANA messages are retransmitted based on a timer 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).

   The retransmission timers SHOULD be calculated as described in
   [RFC2988] to provide congestion control.  See Section 9 for default
   timer and maximum retransmission count parameters.

   The PaC and PAA MUST respond to duplicate requests as long as the
   responding rate does not exceed a certain threshold value.  The last
   transmitted answer MAY be cached in case it is not received by the



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   peer and that generates a retransmission of the last request.  When
   available, the cached answer can be used instead of fully processing
   the retransmitted request and forming a new answer from scratch.

   PANA MUST NOT generate EAP message duplication.  EAP payload of a
   retransmitted PANA message MUST NOT be passed to the EAP layer.

5.3.  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
   sessions are performed in sequence in the PANA authentication and
   authorization phase, it is possible that two AAA-Keys are derived.
   If this happens, the PANA SA MUST be generated from both AAA-Keys.
   When a new AAA-Key is derived in the PANA re-authentication phase,
   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 messages or PANA-FirstAuth-End-
   Request and PANA-FirstAuth-End-Answer messages at the end of the EAP
   authentication 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-Answer, PANA-FirstAuth-End-Request and PANA-FirstAuth-End-Answer
   messages with a Key-Id AVP MUST also carry an AUTH AVP whose value is
   computed by using the new PANA_AUTH_KEY derived from the new AAA-Key
   (or the new pair of AAA-Keys when the PANA_AUTH_KEY is derived from
   two AAA-Keys).  Although the specification does not mandate a
   particular method for calculation of the Key-Id AVP value, a simple
   method is to use monotonically increasing numbers.

   The PANA session lifetime is bounded by the authorization lifetime
   granted by the authentication server (same as the AAA-Key lifetime).
   The lifetime of the PANA SA (hence the PANA_AUTH_KEY) is the same as
   the lifetime of the PANA session.  The created PANA SA is deleted
   when the corresponding PANA session is deleted.

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






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   PANA Session attributes:

      *  Session-Id

      *  Device-Id of PaC

      *  IP address and UDP port number of the PaC.

      *  IP address of PAA

      *  List of device identifiers of EPs

      *  Sequence number of the last transmitted request

      *  Sequence number of the last received request

      *  Last transmitted message payload

      *  Retransmission interval

      *  Session lifetime

      *  Protection-Capability

      *  PANA SA attributes

   PANA SA attributes:

      *  Nonce generated by PaC (PaC_nonce)

      *  Nonce generated by PAA (PAA_nonce)

      *  AAA-Key

      *  AAA-Key Identifier

      *  PANA_AUTH_KEY

      *  Pseudo-random function

      *  Integrity algorithm

   The PANA_AUTH_KEY is derived from the available AAA-Key(s) and it is
   used to integrity protect PANA messages.  If there is only one AAA-
   Key available, e.g., due to ISP-only authentication, or with one
   failed and one successful separate NAP and ISP authentication (see
   Section 4.8), the PANA_AUTH_KEY computation is based on that single
   key.  Otherwise, two AAA-Keys available to PANA can be combined in



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   following way ('|' indicates concatenation):

      AAA-Key = AAA-Key1 | AAA-Key2

   The PANA_AUTH_KEY is computed in the following way:

   PANA_AUTH_KEY = prf+(AAA-Key, PaC_nonce | PAA_nonce | Session-ID)

   where the prf+ function is defined in IKEv2 [RFC4306].  The pseudo-
   random function to be used for the prf+ function is specified in the
   Algorithm AVP in a PANA-FirstAuth-End-Request or a PANA-Bind-Request
   message.  The length of PANA_AUTH_KEY depends on the integrity
   algorithm in use.  See Section 5.4 for the detailed usage of the
   PANA_AUTH_KEY.

5.4.  Message Authentication

   A PANA message can contain an AUTH AVP for cryptographically
   protecting the message.

   When an AUTH AVP is included in a PANA message, the value field of
   the AUTH AVP is calculated by using the PANA_AUTH_KEY in the
   following way:

      AUTH AVP value = PANA_AUTH_HASH(PANA_AUTH_KEY, PANA_PDU)

   where PANA_PDU is the PANA message including the PANA header, with
   the AUTH AVP value field first initialized to 0.  PANA_AUTH_HASH
   represents the integrity algorithm specified in the Algorithm AVP in
   a PANA-Bind-Request message.  The PaC and PAA MUST use the same
   integrity algorithm to calculate an AUTH AVP they originate and
   receive.  The algorithm is determined by the PAA.  When the PaC does
   not support the integrity algorithm specified in the PANA-Bind-
   Request message, it MUST silently discard the message.

5.5.  Message Validity Check

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

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

   o  The message type is one of the expected types in the current
      state.  Specifically the following messages are unexpected and
      invalid:




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      *  In the discovery and handshake phase:

         +  PANA-Termination-Request and PANA-Ping-Request.

         +  PANA-Bind-Request.

         +  PANA-Update-Request.

         +  PANA-Reauth-Request.

         +  PANA-Error-Request.

      *  In the authentication and authorization phase and the re-
         authentication phase:

         +  PANA-PAA-Discover.

         +  PANA-Update-Request.

         +  PANA-Start-Request after a PaC receives the first valid
            PANA-Auth-Request.

         +  PANA-Termination-Request before the PaC receives the first
            successful PANA-Bind-Request.

      *  In the access phase:

         +  PANA-Start-Request as well as a non-duplicate PANA-Bind-
            Request.

         +  PANA-PAA-Discover.

      *  In the termination phase:

         +  PANA-PAA-Discover.

         +  All requests but PANA-Termination-Request.

   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 and no AVP, which needs to be at a fixed position,
      is included in a position different from this fixed position.

   o  Each AVP is decoded correctly.

   o  When an AUTH AVP is included, the AVP value matches the hash value
      computed against the received message.




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   o  When a Device-Id AVP is included, the AVP is valid if the device
      identifier type contained in the AVP is supported (check performed
      by both the PaC and the PAA) and is the requested one (check
      performed by the PAA only).  Note that a Device-Id AVP carries the
      device identifier of the PaC in messages from the PaC to the PAA
      and the device identifier(s) of the EP(s) in messages from the PAA
      to the PaC.

   Invalid messages MUST be discarded in order to provide robustness
   against DoS attacks.  In addition, an error notification message MAY
   be returned to the sender.  See Section 5.11 for details.

5.6.  PaC-EP-Master-Key

   As described in Section 4.4, use of a cryptographic filtering
   mechanism is indicated by inclusion of a Protection-Capability AVP in
   the PANA-Bind-Request message in the authentication and authorization
   phase.  In this case, a PaC-EP-Master-Key is derived from the AAA-Key
   for each EP and used by a secure association protocol for
   bootstrapping link-layer or IPsec ciphering between the PaC and EP.
   The PaC-EP-Master-Key derivation algorithm is defined as follows.

   PaC-EP-Master-Key = The first 64 octets of
                       prf+(AAA-Key, "PaC-EP master key" |
                            Session ID | Key-ID | EP-Device-Id)

   The prf+ function is defined in IKEv2 [RFC4306].  The pseudo-random
   function used for the prf+ function is specified in the Algorithm AVP
   carried in a PANA-FirstAuth-End-Request or a PANA-Bind-Request
   message.

   EP-Device-Id is the Data field of the Device-Id AVP for the
   corresponding EP.

5.7.  Device ID Choice

   The device identifier used in the context of PANA can be an IP
   address, a MAC address, or an identifier that may not be carried in
   data packets but has local significance in identifying a connected
   device (e.g., circuit id, PPP interface id).  The last type of
   identifiers are commonly used in point-to-point links where MAC
   addresses are not available and lower-layers are already physically
   or cryptographically secured.

   It is assumed that the PAA knows the link type and the security
   mechanisms being provided or required on the access network (based on
   configuration of the network administrator).  For example, one
   network administrator might want to use IPsec for securing the



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   network access while another one (for a different network) might rely
   on physical security.

   When IPsec-based security [I-D.ietf-pana-ipsec] is the choice of
   access control, the PAA MUST provide IP address(es) as EP(s)' device
   ID, and expect the PaC to provide its IP address in return.
   Similarly, IP addresses are used when the EP(s) is not on the same IP
   subnet as the PaC is.

   In other cases, MAC addresses are used as device identifiers when
   they are available.

   If non-IPsec access control is enabled, and a MAC address is not
   available, locally-significant identifiers (e.g., as a circuit id)
   MUST be used as device id.  Note that these identifiers are not
   exchanged within PANA messages.  Instead, peers rely on lower-layers
   to provide them along with received PANA messages.

5.8.  PaC Updating its IP Address

   A PaC's IP address can change in certain situations.  For example,
   the PANA framework [I-D.ietf-pana-framework] describes a case in
   which a PaC replaces a pre-PANA address (PRPA) with a post-PANA
   address (POPA).  In another situation a PaC may change its IP address
   used for PANA when it moves from one IP link to another within the
   same PAA's realm.  In order to maintain the PANA session, the PAA
   needs to be notified about the change of PaC address.

   If the device identifier of the PaC is the IP address, it is also
   subject to the same change.  The PAA needs to be notified about the
   change of device identifier as well so that the PAA can update the
   EP(s).  If IPsec is used between the PaC and the EPs, an IKE or
   MOBIKE [I-D.ietf-mobike-protocol] run is needed following such a
   change.

   After the PaC has changed its IP address, it MUST send a PANA-Update-
   Request message to the PAA.  If the PaC has also changed its device
   identifier, the PANA-Update-Request message MUST include a Device-Id
   AVP containing the new device identifier.  The PAA MUST update the
   PANA session with the new PaC address carried in the Source Address
   field of the IP header and the new device identifier carried in the
   Device-Id AVP, and return a PANA-Update-Answer message.  The PANA-
   Update-Answer message MUST contain one or more Device-Id AVPs for the
   EPs if the set of EPs serving the PaC has also changed.  If there is
   an established PANA SA, both PANA-Update-Request and PANA-Update-
   Answer messages MUST be protected with an AUTH AVP.





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5.9.  Session Lifetime

   The authentication and authorization 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 the PaC about the valid lifetime of the
   PANA session.  It MUST be ignored when included in other PANA
   messages.

   When the Session-Lifetime AVP is not included in the PANA-Bind-
   Request message then the PaC has no knowledge about a PANA session
   limitation and must therefore conclude that the session is not
   limited.

   The lifetime is a non-negotiable parameter that can be used by the
   PaC to manage PANA-related state.  The PaC does not have to perform
   any actions when the lifetime expires, other than purging local
   state.  The PAA SHOULD initiate the PANA re-authentication phase
   before the current session lifetime expires.

   The PaC and the PAA MAY use information obtained outside PANA (e.g.,
   lower-layer indications) to expedite the detection of a disconnected
   peer.  Availability and reliability of such indications MAY depend on
   a specific link layer or network topology and are therefore only
   hints.  A PANA peer SHOULD use the PANA-Ping message exchange to
   verify the liveness of a peer before taking an action.

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

   When separate ISP and NAP authentication is performed, it is possible
   that different authorization lifetime values are associated with the
   two EAP authentication sessions.  In this case, the smaller
   authorization lifetime value MUST be used for calculating the PANA
   Session-Lifetime value.  As a result, both NAP and ISP authentication
   will be performed in the re-authentication phase.

5.10.  Network Selection

   The PANA discovery and handshake phase allows the PaC to learn
   identity of the NAP and a list of ISPs that are available through the
   NAP.  The PaC can not only learn the ISPs but also convey the
   selected ISP explicitly during the handshake phase.  The PAA is
   assumed to be pre-configured with the information of ISPs that are
   served by the NAP.



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   A PANA-Start-Request message sent from the PAA MAY contain zero or
   one NAP-Information AVP, and zero or more ISP-Information AVPs.  The
   PaC MAY indicate its choice of ISP by including an ISP-Information
   AVP in the PANA-Start-Answer message.  The PaC MAY convey its ISP
   even when there is no ISP-Information AVP contained in the PANA-
   Start-Request message.  The PaC can do that when it is pre-configured
   with ISP information.

   In the absence of an ISP explicitly selected and conveyed by the PaC,
   ISP selection is typically performed based on the client identifier
   (e.g., using the realm portion of an NAI carried in EAP method).  A
   backend AAA protocol (e.g., RADIUS) will run between the AAA client
   on the PAA and a AAA server in the selected ISP domain.

   The PANA-based ISP selection mechanism dictates the next-hop AAA
   proxy on the PAA.  If the NAP requires all AAA traffic to go through
   its local AAA proxy, it may have to rely on a mechanism to relay the
   selected ISP information from PAA (AAA client) to the local AAA
   proxy.  The local AAA proxy can forward the AAA traffic to the
   selected ISP domain upon processing.  Further details, including how
   the AAA client relays AAA routing information to the AAA proxy, are
   outside the scope of PANA.

   An alternative ISP discovery mechanism is outlined in [RFC4284] which
   suggests advertising ISP information in-band with the ongoing EAP
   method execution.  Deployments using the PANA's built-in ISP
   discovery mechanism need not use the other mechanism.

5.11.  Error Handling

   A PANA-Error-Request message MAY be sent by either the PaC or the PAA
   when a badly formed PANA message is received or in case of other
   errors.  The receiver of this request MUST respond with a PANA-Error-
   Answer message.

   An adversary might craft erroneous PANA messages to launch a Denial
   of Service attack.  Unless the PaC or the PAA performs a rate-
   limitation of the generated PANA-Error-Request messages it may be
   overburdened by responding to bogus messages.  Note that a PANA-
   Error-Answer message that is sent in response to a PANA-Error-Request
   message does not require either the PaC or the PAA to create state.

   If an error message is sent unprotected (i.e., without using an AUTH
   AVP) and the lower-layer is insecure then the error message MUST be
   processed such that the receiver does not change its state.






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6.  Header Format

   This section defines message formats for PANA protocol.

6.1.  IP and UDP Headers

   When a PANA-PAA-Discover message is multicast, IP destination address
   of the message is set to a well-known administratively scoped
   multicast address (To Be Assigned by IANA).  A PANA-PAA-Discover
   message MAY be unicast in some cases as specified in Section 4.3.
   Any other PANA message is unicast between the PaC and the PAA.  The
   source and destination addresses SHOULD be set to the addresses on
   the interfaces from which the message will be sent and received,
   respectively.

   When the PANA message is sent in response to a request, the UDP
   source and destination ports of the response message MUST be copied
   from the destination and source ports of the request message,
   respectively.

   The source port of an unsolicited PANA message MUST be set to a value
   chosen by the sender.  The destination port MUST be set to the peer's
   port number if it has already been discovered via earlier PANA
   exchanges, set to the assigned PANA port (To Be Assigned by IANA)
   otherwise.

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    |   Reserved    |        Message Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Flags              |         Message Type          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Sequence Number                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  AVPs ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-








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   Version

      This Version field MUST be set to 1 to indicate PANA Version 1.

   Reserved

      This 8-bit field is reserved for future use, and MUST be set to
      zero, and ignored by the receiver.

   Message Length

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

   Flags

      The Flags field is two octets.  The following bits are assigned:

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R S N L r r r r r r r r r r 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 NAP and ISP
         authentication.  When the S-flag is set in a PANA-Start-Answer
         message it indicates that the PaC accepts on performing
         separate NAP and ISP authentication.  The PaC may also respond
         with the S-flag not set which implies the PaC has chosen to
         authenticate with the ISP only.  When the S-flag is set in a
         PANA-Auth-Request/Answer, PANA-FirstAuth-End-Request/Answer and
         PANA-Bind-Request/Answer messages it indicates that separate
         NAP and ISP authentication is being performed in the
         authentication and authorization phase.  For other cases,
         S-flag MUST NOT be set.

      N(AP authentication)






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         When the N-flag is set in a PANA-Auth-Request, a PANA-
         FirstAuth-End-Request or a PANA-Bind-Request message, it
         indicates that the current EAP authentication is for NAP
         authentication.  When the N-flag is unset in a PANA-Auth-
         Request, a PANA-FirstAuth-End-Request or a PANA-Bind-Request
         message, it indicates that the current EAP authentication is
         for ISP authentication.  The PaC MUST copy the value of the
         flag in its answer from the last received request of the PAA.
         The value of the flag on an answer MUST be copied from the
         request.  The N-flag MUST NOT be set when S-flag is not set.

      L(stateLess discovery)

         When the L-flag is set in a PANA-Start-Request message it
         indicates that the PAA is performing stateless discovery.
         Cookie AVP MUST be included in both the PANA-Start-Request and
         the PANA-Start-Answer messages when performing stateless
         discovery.

      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 two octets, and is used in order to
      communicate the message type with the message.  The 16-bit address
      space is managed by IANA [ianaweb].  PANA uses its own address
      space for this field.

   Sequence Number

      The Sequence Number field contains a 32 bit value.

   AVPs

      AVPs are a method of encapsulating information relevant to the
      PANA message.  See section Section 6.3 for more information on
      AVPs.

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].



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   The fields in the AVP header are 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           |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         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 two octets.  The following bits are
      assigned:

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V M r r r r r r r r r r r r r r|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      M(andatory)

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

         If an AVP with the 'M' bit set is received by the PaC or PAA
         and either the AVP or its value is unrecognized, the message
         MUST be rejected and the receiver MUST send a PANA-Error-
         Request message.  If the AVP was unrecognized the PANA-Error-
         Request message result code MUST be PANA_AVP_UNSUPPORTED.  If
         the AVP value was unrecognized the PANA-Error-Request message
         result code MUST be PANA_INVALID_AVP_DATA.  In either case the
         PANA-Error-Request message MUST carry a Failed-AVP AVP
         containing the offending mandatory AVP.




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         AVPs with the 'M' bit cleared are informational only and a
         receiver that receives a message with such an AVP that is not
         recognized, or whose value is not recognized, MAY simply ignore
         the AVP.

      V(endor)

         The 'V' bit, known as the Vendor-Specific bit, indicates
         whether the optional Vendor-Id field is present in the AVP
         header.  When set the AVP Code belongs to the specific vendor
         code address space.

      r(eserved)

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

      Unless otherwise noted, AVPs defined in this document will have
      the following default AVP Flags field settings: The 'M' bit MUST
      be set.  The 'V' bit MUST NOT be set.

   AVP Length

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

   Reserved

      This two-octet field is reserved for future use, and MUST be set
      to zero, and ignored by the receiver.

   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
      IANA assigned "SMI Network Management Private Enterprise Codes"
      [ianaweb] 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







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      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.
















































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7.  PANA Messages

   Each Request/Answer message pair is assigned a Sequence Number, and
   the sub-type (i.e., request or answer) is identified via the 'R' bit
   in the Message Flags field of the PANA header.

   Every PANA message MUST contain a message ID in its header's
   Message-Id field, which is used to determine the action that is to be
   taken for a particular message.  Figure 9 lists all PANA messages
   defined in this document:

   Message-Name              Abbrev. ID PaC<->PAA  Ref.
   ----------------------------------------------------------
   PANA-PAA-Discover          PDI    1  -------->  7.1
   PANA-Start-Request         PSR    2  <--------  7.2
   PANA-Start-Answer          PSA    2  -------->  7.3
   PANA-Auth-Request          PAR    3  <------->  7.4
   PANA-Auth-Answer           PAN    3  <------->  7.5
   PANA-Reauth-Request        PRAR   4  -------->  7.6
   PANA-Reauth-Answer         PRAA   4  <--------  7.7
   PANA-Bind-Request          PBR    5  <--------  7.8
   PANA-Bind-Answer           PBA    5  -------->  7.9
   PANA-Ping-Request          PPR    6  <------->  7.10
   PANA-Ping-Answer           PPA    6  <------->  7.11
   PANA-Termination-Request   PTR    7  <------->  7.12
   PANA-Termination-Answer    PTA    7  <------->  7.13
   PANA-Error-Request         PER    8  <------->  7.14
   PANA-Error-Answer          PEA    8  <------->  7.15
   PANA-FirstAuth-End-Request PFER   9  <--------  7.16
   PANA-FirstAuth-End-Answer  PFEA   9  -------->  7.17
   PANA-Update-Request        PUR    10 <------->  7.18
   PANA-Update-Answer         PUA    10 <------->  7.19
   -----------------------------------------------------------

   Figure 9: Table of PANA Messages

   Every PANA message defined MUST include a corresponding ABNF
   [RFC2234] specification, which is used to define the AVPs that MUST
   or MAY be present.  The following format is used in the definition:

   message-def      = Message-Name "::=" PANA-message

   message-name     = PANA-name

   PANA-name        = ALPHA *(ALPHA / DIGIT / "-")

   PANA-message     = header  [ *fixed] [ *required] [ *optional]
                      [ *fixed]



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   header           = "< PANA-Header: " Message-Id
                      [r-bit] [s-bit] [n-bit] ">"

   Message-Id       = 1*DIGIT
                      ; The message code assigned to the message

   r-bit            = ", REQ"
                      ; If present, the 'R' bit in the Message
                      ; Flags is set, indicating that the message
                      ; is a request, as opposed to an answer.

   s-bit            = ", SEP"
                      ; If present, the 'S' bit in the Message
                      ; Flags is set, indicating support for
                      ; separate NAP and ISP authentication.

   n-bit            = ", NAP"
                      ; If present, the 'N' bit in the Message
                      ; Flags is set, indicating that current
                      ; EAP authentication is for NAP authentication.

   l-bit            = ", SLS"
                      ; If present, the 'L' bit in the Message
                      ; Flags is set, indicating PAA is performing
                      ; stateless discovery

   fixed            = [qual] "<" avp-spec ">"
                      ; Defines the fixed position of an AVP

   required         = [qual] "{" avp-spec "}"
                      ; The AVP MUST be present and can appear
                      ; anywhere in the message.

   optional         = [qual] "[" avp-name "]"
                      ; The avp-name in the 'optional' rule cannot
                      ; evaluate to any AVP Name which is included
                      ; in a fixed or required rule.  The AVP can
                      ; appear anywhere in the message.

   qual             = [min] "*" [max]
                      ; See ABNF conventions, RFC 2234 Section 6.6.
                      ; The absence of any qualifiers depends on whether
                      ; it precedes a fixed, required, or optional
                      ; rule.  If a fixed or required rule has no
                      ; qualifier, then exactly one such AVP MUST
                      ; be present.  If an optional rule has no
                      ; qualifier, then 0 or 1 such AVP may be
                      ; present.



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                      ;
                      ; NOTE:  "[" and "]" have a different meaning
                      ; than in ABNF (see the optional rule, above).
                      ; These braces cannot be used to express
                      ; optional fixed rules (such as an optional
                      ; AUTH at the end).  To do this, the convention
                      ; is '0*1fixed'.

   min              = 1*DIGIT
                      ; The minimum number of times the element may
                      ; be present.  The default value is zero.

   max              = 1*DIGIT
                      ; The maximum number of times the element may
                      ; be present.  The default value is infinity.  A
                      ; value of zero implies the AVP MUST NOT be
                      ; present.

   avp-spec         = PANA-name
                      ; The avp-spec has to be an AVP Name, defined
                      ; in the base or extended PANA protocol
                      ; specifications.

   avp-name         = avp-spec / "AVP"
                      ; The string "AVP" stands for *any* arbitrary
                      ; AVP Name, which does not conflict with the
                      ; required or fixed position AVPs defined in
                      ; the message definition.

   Example-Request ::= < "PANA-Header: 9999999, REQ >
                       < Session-Id >
                       { Result-Code }
                    *  [ AVP ]
                   0*1 < AUTH >

7.1.  PANA-PAA-Discover (PDI)

   The PANA-PAA-Discover (PDI) message is used to discover the address
   of PAA(s).  The sequence number in this message is always set to zero
   (0).

   PANA-PAA-Discover ::= < PANA-Header: 1 >
                       [ Notification ]
                    *  [ AVP ]







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7.2.  PANA-Start-Request (PSR)

   The PANA-Start-Request (PSR) message is sent by the PAA to the PaC to
   advertise availability of the PAA and start PANA authentication.  The
   PAA sets the sequence number to an initial random value.

   PANA-Start-Request ::= < PANA-Header: 2, REQ [,SEP] [,SLS] >
                       [ Nonce ]
                       [ Cookie ]
                       [ EAP-Payload ]
                       [ NAP-Information ]
                    *  [ ISP-Information ]
                       [ Protection-Capability]
                       [ Algorithm ]
                       [ PPAC ]
                       [ Notification ]
                    *  [ AVP ]

7.3.  PANA-Start-Answer (PSA)

   The PANA-Start-Answer (PSA) message is sent by the PaC to the PAA in
   response to a PANA-Start-Request message.  This message completes the
   handshake to start PANA authentication.

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

7.4.  PANA-Auth-Request (PAR)

   The PANA-Auth-Request (PAR) message is either sent by the PAA or the
   PaC.  Its main task is to carry an EAP-Payload AVP.

   PANA-Auth-Request ::= < PANA-Header: 3, REQ [,SEP] [,NAP] >
                       < Session-Id >
                       < EAP-Payload >
                       [ Nonce ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >







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7.5.  PANA-Auth-Answer (PAN)

   THe PANA-Auth-Answer (PAN) message is sent by either the PaC or the
   PAA in response to a PANA-Auth-Request message.  It MAY carry an EAP-
   Payload AVP.

   PANA-Auth-Answer ::= < PANA-Header: 3 [,SEP] [,NAP] >
                       < Session-Id >
                       [ Nonce ]
                       [ EAP-Payload ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.6.  PANA-Reauth-Request (PRAR)

   The PANA-Reauth-Request (PRAR) message is sent by the PaC to the PAA
   to re-initiate EAP authentication.

   PANA-Reauth-Request ::= < PANA-Header: 4, REQ >
                       < Session-Id >
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.7.  PANA-Reauth-Answer (PRAA)

   The PANA-Reauth-Answer (PRAA) message is sent by the PAA to the PaC
   in response to a PANA-Reauth-Request message.

   PANA-Reauth-Answer ::= < PANA-Header: 4 >
                       < Session-Id >
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.8.  PANA-Bind-Request (PBR)

   The PANA-Bind-Request (PBR) message is sent by the PAA to the PaC to
   deliver the result of PANA authentication.











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   PANA-Bind-Request ::= < PANA-Header: 5, REQ [,SEP] [,NAP] >
                       < Session-Id >
                       { Result-Code }
                       [ PPAC ]
                       [ EAP-Payload ]
                       [ Session-Lifetime ]
                       [ Protection-Capability ]
                       [ Key-Id ]
                       [ Algorithm ]
                    *  [ Device-Id ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.9.  PANA-Bind-Answer (PBA)

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

   PANA-Bind-Answer ::= < PANA-Header: 5 [,SEP] [,NAP] >
                       < Session-Id >
                       [ PPAC ]
                       [ Device-Id ]
                       [ Key-Id ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.10.  PANA-Ping-Request (PPR)

   The PANA-Ping-Request (PPR) message is either sent by the PaC or the
   PAA for performing liveness test.

   PANA-Ping-Request ::= < PANA-Header: 6, REQ >
                       < Session-Id >
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.11.  PANA-Ping-Answer (PPA)

   The PANA-Ping-Answer (PPA) message is sent in response to a PANA-
   Ping-Request.

   PANA-Ping-Answer ::= < PANA-Header: 6 >
                       < Session-Id >
                       [ Notification ]
                    *  [ AVP ]



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                   0*1 < AUTH >

7.12.  PANA-Termination-Request (PTR)

   The PANA-Termination-Request (PTR) message is sent either by the PaC
   or the PAA to terminate a PANA session.

   PANA-Termination-Request ::= < PANA-Header: 7, REQ >
                       < Session-Id >
                       < Termination-Cause >
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.13.  PANA-Termination-Answer (PTA)

   The PANA-Termination-Answer (PTA) message is sent either by the PaC
   or the PAA in response to PANA-Termination-Request.

   PANA-Termination-Answer ::= < PANA-Header: 7 >
                       < Session-Id >
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.14.  PANA-Error-Request (PER)

   The PANA-Error-Request (PER) message is sent either by the PaC or the
   PAA to report an error with the last received PANA message.

   PANA-Error-Request ::= < PANA-Header: 8, REQ >
                        < Session-Id >
                        < Result-Code >
                     *  [ Failed-AVP ]
                        [ Notification ]
                     *  [ AVP ]
                    0*1 < AUTH >

7.15.  PANA-Error-Answer (PEA)

   The PANA-Error-Answer (PEA) message is sent in response to a PANA-
   Error-Request.

   PANA-Error-Answer ::= < PANA-Header: 8 >
                        < Session-Id >
                        [ Notification ]
                     *  [ AVP ]
                    0*1 < AUTH >



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7.16.  PANA-FirstAuth-End-Request (PFER)

   The PANA-FirstAuth-End-Request (PFER) message is sent by the PAA to
   the PaC to signal the result of the first EAP authentication method
   when separate NAP and ISP authentication is performed.

   PANA-FirstAuth-End-Request ::= < PANA-Header: 9, REQ [,SEP] [,NAP] >
                       < Session-Id >
                       { Result-Code }
                       [ EAP-Payload ]
                       [ Key-Id ]
                       [ Algorithm ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.17.  PANA-FirstAuth-End-Answer (PFEA)

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

   PANA-FirstAuth-End-Answer ::= < PANA-Header: 9, REQ [,SEP] [,NAP] >
                       < Session-Id >
                       [ Key-Id ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.18.  PANA-Update-Request (PUR)

   The PANA-Update-Request (PUR) message is sent either by the PaC or
   the PAA to deliver attribute updates and notifications.  In the scope
   of this specification only the IP address and device identifer of the
   PaC can be updated via this message.

   PANA-Update-Request ::= < PANA-Header: 10, REQ >
                       < Session-Id >
                       [ Device-Id ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >

7.19.  PANA-Update-Answer (PUA)

   The PANA-Update-Answer (PUA) message is sent by the PAA (PaC) to the
   PaC (PAA) in response to a PANA-Update-Request from the PaC (PAA).





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   PANA-Update-Answer ::= < PANA-Header: 10 >
                       < Session-Id >
                    *  [ Device-Id ]
                       [ Notification ]
                    *  [ AVP ]
                   0*1 < AUTH >













































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8.  AVPs in PANA

   PANA defines several AVPs that are specific to the protocol.  A
   number of others AVPs are reused.  These are specified in other
   documents such as [RFC3588].

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

   The table uses the following symbols:

   0     The AVP MUST NOT be present in the message.

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

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

   1     One instance of the AVP MUST be present in the message.

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



























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                         +---------------------------------------------+
                         |                  Message                    |
                         |                   Type                      |
                         +---+---+---+---+---+----+----+---+---+---+---+
   Attribute Name        |PDI|PSR|PSA|PAR|PAN|PRAR|PRAA|PBR|PBA|PPR|PPA|
   ----------------------+---+---+---+---+---+----+----+---+---+---+---+
   Algorithm             | 0 |0-1| 0 | 0 | 0 | 0  | 0  |0-1| 0 | 0 | 0 |
   AUTH                  | 0 | 0 | 0 |0-1|0-1|0-1 |0-1 |0-1|0-1|0-1|0-1|
   Cookie                | 0 |0-1|0-1| 0 | 0 | 0  | 0  | 0 | 0 | 0 | 0 |
   Device-Id             | 0 | 0 | 0 | 0 | 0 | 0  | 0  | 0+|0-1| 0 | 0 |
   EAP-Payload           | 0 |0-1|0-1| 1 |0-1| 0  | 0  |0-1| 0 | 0 | 0 |
   Failed-AVP            | 0 | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 | 0 | 0 |
   ISP-Information       | 0 | 0+|0-1| 0 | 0 | 0  | 0  | 0 | 0 | 0 | 0 |
   Key-Id                | 0 | 0 | 0 | 0 | 0 | 0  | 0  |0-1|0-1| 0 | 0 |
   NAP-Information       | 0 |0-1| 0 | 0 | 0 | 0  | 0  | 0 | 0 | 0 | 0 |
   Nonce                 | 0 |0-1|0-1|0-1|0-1| 0  | 0  | 0 | 0 | 0 | 0 |
   Notification          |0-1|0-1|0-1|0-1|0-1|0-1 |0-1 |0-1|0-1|0-1|0-1|
   PPAC                  | 0 |0-1| 0 | 0 | 0 | 0  | 0  |0-1|0-1| 0 | 0 |
   Protection-Capability | 0 |0-1| 0 | 0 | 0 | 0  | 0  |0-1| 0 | 0 | 0 |
   Result-Code           | 0 | 0 | 0 | 0 | 0 | 0  | 0  | 1 | 0 | 0 | 0 |
   Session-Id            | 0 | 0 | 0 | 1 | 1 | 1  | 1  | 1 | 1 | 1 | 1 |
   Session-Lifetime      | 0 | 0 | 0 | 0 | 0 | 0  | 0  |0-1| 0 | 0 | 0 |
   Termination-Cause     | 0 | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 | 0 | 0 |
   ----------------------+---+---+---+---+---+----+----+---+---+---+---+

   Figure 10: AVP Occurrence Table (1/2)

























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                         +---------------------------------+
                         |              Message            |
                         |               Type              |
                         +---+---+---+---+----+----+---+---+
   Attribute Name        |PTR|PTA|PER|PEA|PFER|PFEA|PUR|PUA|
   ----------------------+---+---+---+---+----+----+---+---+
   Algorithm             | 0 | 0 | 0 | 0 |0-1 | 0  | 0 | 0 |
   AUTH                  |0-1|0-1|0-1|0-1|0-1 |0-1 |0-1|0-1|
   Cookie                | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Device-Id             | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   EAP-Payload           | 0 | 0 | 0 | 0 |0-1 | 0  | 0 | 0 |
   Failed-AVP            | 0 | 0 | 0+| 0 | 0  | 0  | 0 | 0 |
   ISP-Information       | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Key-Id                | 0 | 0 | 0 | 0 |0-1 |0-1 | 0 | 0 |
   NAP-Information       | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Nonce                 | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Notification          |0-1|0-1|0-1|0-1|0-1 |0-1 |0-1|0-1|
   PPAC                  | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Protection-Capability | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Result-Code           | 0 | 0 | 1 | 0 | 1  | 0  | 0 | 0 |
   Session-Id            | 1 | 1 | 1 | 1 | 1  | 1  | 1 | 1 |
   Session-Lifetime      | 0 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   Termination-Cause     | 1 | 0 | 0 | 0 | 0  | 0  | 0 | 0 |
   ----------------------+---+---+---+---+----+----+---+---+

   Figure 11: AVP Occurrence Table (2/2)

8.1.  Algorithm AVP

   The Algorithm AVP (AVP Code 1) is used for conveying the pseudo-
   random function to derive PANA_AUTH_KEY and PaC-EP-Master-Key as well
   as the integrity algorithm to compute an AUTH AVP.  The AVP data is
   of type Unsigned32.

   The first 16-bit of the AVP data contains an IKEv2 Transform ID of
   Transform Type 2 [RFC4306] corresponding to the key derivation
   function.

   The last 16-bit of the AVP data contains an IKEv2 Transform ID of
   Transform Type 3 [RFC4306] for the integrity algorithm.

   All PANA implementations MUST support PRF_HMAC_SHA1 (2) [RFC2104] for
   the key derivation algorithm and AUTH_HMAC_SHA1_160 (7) [ianaweb]
   corresponding to the integrity algorithm.

8.2.  AUTH AVP

   The AUTH AVP (AVP Code 2) is used to integrity protect PANA messages.



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   The AVP data payload contains the Message Authentication Code encoded
   in network byte order.  The AVP length varies depending on the
   integrity algorithm specified in an Algorithm AVP.

8.3.  Cookie AVP

   The Cookie AVP (AVP Code 3) is used for carrying a random value
   generated by the PAA according to [RFC4086].  The AVP data is of type
   OctetString.  The random value is referred to as a cookie and used
   for making PAA discovery robust against blind resource consumption
   DoS attacks.  The exact algorithms and syntax used by the PAA to
   generate a cookie does not affect interoperability and not specified
   in this document.  An example cookie generation algorithm is shown in
   Section 4.3.

8.4.  Device-Id AVP

   The Device-Id AVP (AVP Code 4) is used for carrying device
   identifiers of PaC and EP(s).  The AVP data is of 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 link-layer addresses is expected to be specified in
   specific documents that describe how IP operates over different link-
   layers.  For instance, [RFC2464].  Address families other than that
   are defined for link-layer or IP addresses MUST NOT be used for this
   AVP.

8.5.  EAP-Payload AVP

   The EAP-Payload AVP (AVP Code 5) is used for encapsulating the actual
   EAP message that is being exchanged between the EAP peer and the EAP
   authenticator.  The AVP data is of type OctetString.

8.6.  Failed-AVP AVP

   The Failed-AVP AVP (AVP Code 6) provides debugging information in
   cases where a request is rejected or not fully processed due to
   erroneous information in a specific AVP.  The AVP data is of type
   Grouped.  The format of the Failed-AVP AVP is defined in [RFC3588].
   In case of a failed grouped AVP, the Failed-AVP contains the whole
   grouped AVP.  In case of a failed AVP inside a grouped AVP, the
   Failed-AVP contains the single offending AVP.

8.7.  ISP-Information AVP

   The ISP-Information AVP (AVP Code 7) 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.  The AVP data is



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   of type Grouped, and it has the following ABNF grammar:

   ISP-Information ::= < AVP Header: 7 >
                    0*1 { Provider-Identifier }
                        { Provider-Name }
                     *  [ AVP ]

8.8.  Key-Id AVP

   The Key-Id AVP (AVP Code 8) 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.

8.9.  NAP-Information AVP

   The NAP-Information AVP (AVP Code 9) 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.  The AVP data is
   of type Grouped, and it has the following ABNF grammar:

   NAP-Information ::= < AVP Header: 9 >
                    0*1 { Provider-Identifier }
                        { Provider-Name }
                     *  [ AVP ]

8.10.  Nonce AVP

   The Nonce AVP (AVP Code 10) carries a randomly chosen value that is
   used in cryptographic key computations.  The recommendations in
   [RFC4086] apply with regard to generation of random values.  The AVP
   data is of type OctetString and it contains a randomly generated
   value in opaque format.  The data length MUST be between 8 and 256
   octets inclusive.

   The length of the nonces are determined based on the available
   pseudo-random functions (PRFs) and the degree of trust placed into
   the two PaC and the PAA to compute random values.  The length of the
   random value for the nonce is determined whether

   1.  The PaC and the PAA each are likely to be able to compute a
       random nonce (according to [RFC4086]).  The length of the nonce
       has to be 1/2 the length of the PRF key (e.g., 10 octets in the
       case of HMAC-SHA1).

   2.  The PaC and the PAA each are not trusted with regard to the
       computation a random nonce (according to [RFC4086]).  The length
       of the nonce has to have the full length of the PRF key (e.g., 20
       octets in the case of HMAC-SHA1).



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   Furthermore, the strongest available PRF available for PANA has to be
   considered in this computation.  Currently, only a single PRF (namely
   HMAC-SHA1) is available and therefore the maximum output length is 20
   octets).  The recommended maximum length of the nonce value is
   therefore currently 20 octets.

8.11.  Notification AVP

   The Notification AVP (AVP Code 11) is optionally used to convey a
   displayable message sent by either the PaC or the PAA.  It can be
   included in any message, whether it is a request or answer.  In case
   a notification needs to be sent but there is no outgoing PANA message
   to deliver this AVP, a PANA-Update-Request that only carries a
   Notification AVP SHOULD be generated.

   The 'M' bit in the AVP header of this AVP MUST NOT be set.

   Receipt this AVP does not change PANA state.

   AVP data is of type OctetString and it contains the following fields
   in the listed order:

   Language Tag Length

      This field contains the length of the Language Tag in octets.  The
      length of this field is 2 octets.

   Language Tag

      This field contains the language tag defined in [I-D.ietf-ltru-
      registry] to indicate the language used for Displayable String.
      The length of this data is determined by the Language Tag Length
      field.

   Displayable String

      This field contains UTF-8 encoded ISO 10646 characters [RFC2279]
      using the language indicated by the Language Tag. The length of
      this data is determined by the AVP Length field and the Language
      Tag Length field.  This data MUST NOT be null terminated.

8.12.  Post-PANA-Address-Configuration (PPAC) AVP

   The PPAC AVP (AVP Code 12) is used for conveying the available types
   of post-PANA IP address configuration mechanisms when sent by the
   PAA, and the chosen one when sent by the PaC.  Each possible
   mechanisms is represented by a flag.  The AVP data is of type
   Unsigned32.



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   The format of the AVP 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 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |N|F|S|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.

      F (DHCPv4)

         The PaC can (if sent by PAA) or will (if sent by PaC) use
         DHCPv4 [RFC2131] to configure a new IPv4 address after PANA.

      S (DHCPv6)

         The PaC can (if sent by PAA) or will (if sent by PaC) use
         DHCPv6 [RFC3315] to configure a new IPv4 address after PANA.

      A (stateless autoconfiguration)

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

      T (DHCPv4 with IPsec tunnel mode)

         The PaC can/will use [RFC3456] to configure a new IPv4 address
         after PANA.

      I (IKEv2)

         The PaC can/will use [RFC4306] to configure (a) new IPv4 and/or
         IPv6 address(es) after PANA.

      Reserved

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

   The PAA MUST set either the N-flag, or one or more of the other
   flags.  If the N-flag is set, the PaC MUST only set its N-flag in its
   response.  If the N-flag is not set by the PAA, that means the PaC



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   MUST configure POPA(s) using the method(s) indicated by the flags.
   If IPsec-based access control is not used, the F-flag, S-flag or
   A-flag MUST be set by the PAA, and the PaC MUST echo the same flag(s)
   in its response.  Refer to [I-D.ietf-pana-framework] for a detailed
   discussion on when these methods can be used.

8.13.  Protection-Capability AVP

   The Protection-Capability AVP (AVP Code 13) indicates the
   cryptographic data protection capability supported and required by
   the EPs.  The AVP data is of type Unsigned32.  Below is a list of
   valid data values and associated protection capabilities:

      0          L2_PROTECTION
      1          IPSEC_PROTECTION

8.14.  Provider-Identifier AVP

   The Provider-Identifier AVP (AVP Code 14) is of type Unsigned32, and
   contains an IANA assigned "SMI Network Management Private Enterprise
   Codes" [ianaweb] value, encoded in network byte order.

8.15.  Provider-Name AVP

   The Provider-Name AVP (AVP Code 15) is of type UTF8String, and
   contains the UTF8-encoded name of the provider.

8.16.  Result-Code AVP

   The Result-Code AVP (AVP Code 16) 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.

8.16.1.  Authentication Results Codes

   These result code values inform the PaC about the authentication and
   authorization result.  The authentication result and authorization
   result can be different as described below, but only one result is
   returned to the PaC.  These codes are used with PANA-Bind-Request and
   PANA-FirstAuth-End-Request messages.

   PANA_SUCCESS                            2001

      Both authentication and authorization processes are successful.






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   PANA_AUTHENTICATION_REJECTED            4001

      Authentication has failed.  When this error is returned, it is
      assumed that authorization is automatically failed.

   PANA_AUTHORIZATION_REJECTED             5003

      The authorization process has failed.  This error could occur when
      authorization is rejected by a AAA server or rejected locally by a
      PAA, even if the authentication procedure has succeeded.

8.16.2.  Protocol Error Result Codes

   These codes are used with PANA-Error-Request messages.  Unless stated
   otherwise, they can be generated by both the PaC and the PAA.

   PANA_MESSAGE_UNSUPPORTED                3001

      Message type not recognized or supported.

   PANA_UNABLE_TO_DELIVER                  3002

      The PAA was unable to deliver the EAP payload to the
      authentication server.  Only the PAA can generate this code.

   PANA_INVALID_HDR_BITS                   3008

      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 definition.

   PANA_INVALID_AVP_FLAGS                   3009

      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

      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






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      The message contained an unknown Session-Id.  A PANA message
      indicating this error MUST include the unknown Session-Id AVP
      within a Failed-AVP AVP.

   PANA_INVALID_AVP_DATA                   5004

      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

      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

      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.  Only the PAA can
      generate this code.

   PANA_CONTRADICTING_AVPS                 5007

      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.  Only the PAA can generate this code.

   PANA_AVP_NOT_ALLOWED                    5008

      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

      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.





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   PANA_UNSUPPORTED_VERSION                5011

      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
      the PANA-Error-Request message.

   PANA_INVALID_AVP_LENGTH                 5014

      The message contained an AVP with an invalid length.  The PANA-
      Error-Request message indicating this error MUST include the
      offending AVPs within a Failed-AVP AVP.

   PANA_INVALID_MESSAGE_LENGTH             5015

      This error is returned when a message is received with an invalid
      message length.

   PANA_PROTECTION_CAPABILITY_UNSUPPORTED  5016

      This error is returned when the PaC receives a PANA-Bind-Request
      message with a Protection-Capability AVP and a valid AUTH AVP but
      does not support the protection capability specified in the
      Protection-Capability AVP.  Only the PaC can generate this code.

   PANA_PPAC_CAPABILITY_UNSUPPORTED  5017

      This error is returned when there is no match between the list of
      PPAC methods offered by the PAA and the ones available on the PaC.
      Only the PaC can generate this code.

8.17.  Session-Id AVP

   All messages pertaining to a specific PANA session MUST include a
   Session-Id AVP (AVP Code 17) which carries a PAA-assigned fixed
   session identifier value throughout the lifetime of a session.  When
   present, the Session-Id AVP MUST 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



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   information with accounting information.  The PANA Session-Id AVP has
   the same format as the Diameter Session-Id AVP [RFC3588].

8.18.  Session-Lifetime AVP

   The Session-Lifetime AVP (AVP Code 18) contains the number of seconds
   remaining before the current session is considered expired.  The AVP
   data is of type Unsigned32.

8.19.  Termination-Cause AVP

   The Termination-Cause AVP (AVP Code 19) is used for indicating the
   reason why a session is terminated by the requester.  The AVP data is
   of type Enumerated.  The following Termination-Cause data values are
   used with 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.

   SESSION_TIMEOUT          8  (PAA -> PaC)

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























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9.  Retransmission Timers

   The PANA protocol provides retransmissions for the PANA-PAA-Discover
   message and all request messages, with the exception that the PANA-
   Start-Answer message is retransmitted instead of the PANA-Start-
   Request message in stateless PAA discovery.

   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




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   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.

9.1.  Transmission and Retransmission Parameters

   This section presents a table of values used to describe the message
   retransmission behavior of PANA requests and answers that are
   retransmitted (REQ_*) and PANA-PAA-Discover message (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



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   REQ_IRT as the IRT:

           RT = REQ_IRT + RAND*REQ_IRT
















































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10.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to the PANA
   protocol, in accordance with BCP 26 [IANA].  The following policies
   are used here with the meanings defined in 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 comment and review, and MUST include a pointer to a public
   specification.  Before a period of 30 days has passed, the Designated
   Expert will either approve or deny the registration request and
   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 the cases where it is possible, concrete suggestions on how the
   request can be modified so as to become acceptable.

10.1.  PANA UDP Port Number

   PANA uses one well-known UDP port number (Section 4.1, Section 4.3
   and Section 6.1), which needs to be assigned by the IANA.

10.2.  PANA Multicast Address

   PANA uses one well-known administratively scoped IPv4 multicast
   address, and one well-known administratively scoped IPv6 multicast
   address (Section 4.3 and Section 6.1), which need to be assigned by
   the IANA.

10.3.  PANA Header

   As defined in Section 6.2, the PANA header contains two fields that
   requires IANA namespace management; the Message Type and Flags field.

10.3.1.  Message Type

   The Message Type namespace is used to identify PANA messages.  Values
   0-65,533 are for permanent, standard message types, allocated by IETF
   Consensus [IANA].  This document defines the Message Types 1-10.  See
   Section 7.1 through Section 7.19 for the assignment of the namespace



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   in this specification.

   The values 65,534 and 65,535 (hexadecimal values 0xfffe - 0xffff) are
   reserved for experimental messages.  As these codes are only for
   experimental and testing purposes, no guarantee is made for
   interoperability between the communicating PaC and PAA using
   experimental commands, as outlined in [IANA-EXP].

10.3.2.  Flags

   There are 16 bits in the Flags field of the PANA header.  This
   document assigns bit 0 ('R'equest), bit 1 ('S'eparate) and bit 2
   ('N'AP Authentication).  The remaining bits MUST only be assigned via
   a Standards Action [IANA].

10.4.  AVP Header

   As defined in Section 6.3, the AVP header contains three fields that
   requires IANA namespace management; the AVP Code, AVP Flags and
   Vendor-Id fields where only the AVP Code and AVP Flags create new
   namespaces.

10.4.1.  AVP Code

   The AVP Code namespace is used to identify attributes.  There are
   multiple namespaces.  Vendors can have their own AVP Codes namespace
   which will be identified by their Vendor-ID (also known as
   Enterprise-Number) and they control the assignments of their vendor-
   specific AVP codes within their own namespace.  The absence of a
   Vendor-ID or a Vendor-ID value of zero (0) identifies the IETF IANA
   controlled AVP Codes namespace.  The AVP Codes and sometimes also
   possible values in an AVP are controlled and maintained by IANA.

   AVP Code 0 is not used.  This document defines the AVP Codes 1-19.
   See Section 8.1 through Section 8.19 for the assignment of the
   namespace in this specification.

   AVPs may be allocated following Designated Expert with Specification
   Required [IANA].  Release of blocks of AVPs (more than 3 at a time
   for a given purpose) should require IETF Consensus.

   Note that PANA defines a mechanism for Vendor-Specific AVPs, where
   the Vendor-Id field in the AVP header is set to a non-zero value.
   Vendor-Specific AVPs codes are for Private Use and should be
   encouraged instead of allocation of global attribute types, for
   functions specific only to one vendor's implementation of PANA, where
   no interoperability is deemed useful.  Where a Vendor-Specific AVP is
   implemented by more than one vendor, allocation of global AVPs should



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   be encouraged instead.

10.4.2.  Flags

   There are 16 bits in the AVP Flags field of the AVP header, defined
   in Section 6.3.  This document assigns bit 0 ('V'endor Specific) and
   bit 1 ('M'andatory).  The remaining bits should only be assigned via
   a Standards Action .

10.5.  AVP Values

   Certain AVPs in PANA define a list of values with various meanings.
   For attributes other than those specified in this section, adding
   additional values to the list can be done on a First Come, First
   Served basis by IANA [IANA].

10.5.1.  Post-PANA-Address-Configuration AVP Values

   As defined in Section 8.12, the Post-PANA-Address-Configuration AVP
   (AVP Code 12) defines the bits 0 ('N': no configuration), 1 ('F':
   DHCPv4), 2 ('S': DHCPv6), 3 ('A' stateless autoconfiguration), 4
   ('T': DHCPv4 with IPsec tunnel mode) and 5 ('I': IKEv2).

   All remaining values are available for assignment via a Standards
   Action [IANA].

10.5.2.  Protection-Capability AVP Values

   As defined in Section 8.13, the Protection-Capability AVP (AVP Code
   13) defines the values 0 and 1.

   All remaining values are available for assignment via a Standards
   Action [IANA].

10.5.3.  Result-Code AVP Values

   As defined in Section 8.16.1 and Section 8.16.2 the Result-Code AVP
   (AVP Code 16) defines the values 2001, 3001-3002, 3008-3009, 4001,
   5001-5009 and 5011-5017.

   All remaining values are available for assignment via IETF Consensus
   [IANA].

10.5.4.  Termination-Cause AVP Values

   As defined in Section 8.19, the Termination-Cause AVP (AVP Code 19)
   defines the values 1, 4 and 8.




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   All remaining values are available for assignment via IETF Consensus
   [IANA].

















































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11.  Security Considerations

   The PANA protocol defines a UDP-based EAP encapsulation that runs
   between two IP-enabled nodes on the same IP link.  Various security
   threats that are relevant to a protocol of this nature are outlined
   in [RFC4016].  Security considerations stemming from the use of EAP
   and EAP methods are discussed in [RFC3748] [I-D.ietf-eap-keying].
   This section provides a discussion on the security-related issues
   that are related to PANA framework and protocol design.

   An important element in assessing security of PANA design and
   deployment in a network is the presence of lower-layer (physical and
   link-layer) security.  In the context of this document, lower-layers
   are said to be secure if they can prevent eavesdropping and spoofing
   of packets.  Examples of such networks are physically-secured DSL
   networks and 3GPP2 networks with cryptographically-secured cdma2000
   link-layer.  In these examples, the lower-layer security is enabled
   even before running the first PANA-based authentication.  In the
   absence of such a pre-established secure channel, one needs to be
   created in conjunction with PANA using a link-layer or network-layer
   cryptographic mechanism (e.g., IPsec).

11.1.  General Security Measures

   PANA provides multiple mechanisms to secure a PANA session.

   PANA messages carry sequence numbers, which are monotonically
   incremented by 1 with every new request message.  These numbers are
   randomly initialized at the beginning of the session, and verified
   against expected numbers upon receipt.  A message whose sequence
   number is different than the expected one is silently discarded.  In
   addition to accomplishing orderly delivery of EAP messages and
   duplicate elimination, this scheme also helps prevent an adversary
   spoof messages to disturb ongoing PANA and EAP sessions unless it can
   also eavesdrop to synchronize on the expected sequence number.
   Furthermore, impact of replay attacks is reduced as any stale message
   (i.e., a request or answer with an unexpected sequence number) and
   any duplicate answer are immediately discarded, and a duplicate
   request can trigger transmission of the cached answer (i.e., no need
   to process the request and generate a new answer).

   The PANA framework defines EP which is ideally located on a network
   device that can filter traffic from the PaCs before the traffic
   enters the Internet/intranet.  A set of filters can be used to
   discard unauthorized packets, such as a PANA-Start-Request message
   that is received from the segment of the access network where only
   the PaCs are supposed to be connected.




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   The protocol also provides authentication and integrity protection to
   PANA messages when the used EAP method can generate cryptographic
   session keys.  A PANA SA is generated based on the AAA-Key exported
   by the EAP method.  This SA is used for generating an AUTH AVP to
   protect the PANA header and payload (including the complete EAP
   message).

   The cryptographic protection prevents an adversary from acting as a
   man-in-the-middle, injecting messages, replaying messages and
   modifying the content of the exchanged messages.  Any packet that
   fails to pass the AUTH verification is silently discarded.  The
   earliest this protection can be enabled is when the very first PANA-
   Bind-Request or PANA-FirstAuth-End-Request message that signals a
   successful authentication is generated.  Starting with these
   messages, any subsequent PANA message until the session gets torn
   down can be cryptographically protected.

   The PANA SA enables authenticated and integrity protected exchange of
   the device ID information between the PaC and PAA.  This ensures
   there were no man-in-the-middle during the PANA authentication.

   The lifetime of the PANA SA is set to PANA session lifetime which is
   bounded by the authorization lifetime granted by the authentication
   server.  An implementation MAY add a tolerance period to that value.
   Unless the PANA session is extended by executing another EAP
   authentication, the PANA SA is removed when the current session
   expires.

   The ability to use cryptographic protection within PANA is determined
   by the used EAP method, which is generally dictated by the deployment
   environment.  Insecure lower-layers necessitate use of key-generating
   EAP methods.  In networks where lower-layers are already secured,
   cryptographic protection of PANA messages is not necessary.

11.2.  Discovery

   The discovery and handshake phase is vulnerable to spoofing attacks
   as these messages are not authenticated and integrity protected.  In
   order to prevent very basic denial-of service attacks an adversary
   should not be able to cause state creation by sending discovery
   messages to the PAA.  This protection is achieved by using a cookie-
   based scheme (similar to [RFC2522] which allows the responder (PAA)
   to be stateless in the first round of message exchange.  However, it
   is difficult to prevent all spoofing attacks in the discovery and
   handshake phase entirely.

   In networks where lower-layers are not secured prior to running PANA,
   the capability discovery enabled through inclusion of Protection-



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   Capability and Post-PANA-Address-Configuration AVPs in a PANA-Start-
   Request message is susceptible to spoofing leading to denial-of
   service attacks.  Therefore, usage of these AVPs during the discovery
   and handshake phase in such insecure networks is NOT RECOMMENDED.
   The same AVPs are delivered via an integrity-protected PANA-Bind-
   Request upon successful authentication.

11.3.  EAP Methods

   Eavesdropping EAP messages might cause problems when 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 Response/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, [I-D.ietf-pana-framework] suggests using
   proper EAP methods for particular environments.  Depending on the
   deployment environment an EAP authentication method which supports
   user identity confidentiality, protection against dictionary attacks
   and session key establishment must be used.  It is therefore the
   responsibility of the network operators and users to choose a proper
   EAP method.

11.4.  Separate NAP and ISP Authentication

   The PANA design allows running two separate EAP sessions for the same
   PaC in the authentication and authorization phase: one with the NAP,
   and one with the ISP.  The process of arriving at the resultant
   authorization, which is a combination of the individual
   authorizations obtained from respective service providers, is outside
   the scope of this protocol.  In the absence of lower-layer security,
   both authentications MUST be able to generate a AAA-Key, leading to
   generation of a PANA SA.  The resultant PANA SA cryptographically
   binds the two AAA-Keys together, hence it prevents man-in-the-middle
   attacks.

11.5.  Cryptographic Keys

   When the EAP method exports a AAA-Key, this key is used to produce a
   PANA SA with PANA_AUTH_KEY with a distinct key ID.  The PANA_AUTH_KEY
   is unique to the PANA session, and takes PANA-based nonce values into
   computation to cryptographically separate itself from the AAA-Key.

   The PANA_AUTH_KEY is solely used for authentication and integrity
   protection of the PANA messages within the designated session.

   Two AAA-Keys may be generated as a result of separate NAP and ISP



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   authentication.  In that case, the AAA-Key used with the PANA SA is
   the combination of both keys.

   The PANA SA lifetime is bounded by the AAA-Key lifetime.  Another
   execution of EAP method yields in a new AAA-Key, and updates the PANA
   SA, PANA_AUTH_KEY and key ID.

   When link-layer or network-layer ciphering [I-D.ietf-pana-ipsec] is
   enabled as a result of successful PANA authentication, a PaC-EP-
   Master-Key is generated for each EP from the AAA-Key, session
   identifier, key identifier, and the EP device identifier.  The PaC-
   EP-Master-Key derivation algorithm defined in Section 5.6 ensures
   cryptographic independency among different PaC-EP-Master-Keys.

   The lifetime of PaC-EP master key is bounded by the lifetime of the
   PANA SA.  This key may be used with a secure association protocol
   [RFC4306] to produce further cipher-specific and transient keys.

11.6.  Per-packet Ciphering

   Networks that are not secured at the lower-layers prior to running
   PANA can rely on enabling per-packet data traffic ciphering upon
   successful PANA session establishment.  The PANA framework allows
   generation of a PaC-EP master key from AAA-Key for using with a per-
   packet protection mechanism, such as link-layer or IPsec-based
   ciphering [I-D.ietf-pana-ipsec].  In case the master key is not
   readily useful to the ciphering mechanism, an additional secure
   association protocol [RFC4306] may be needed to produce the required
   keying material.  These mechanisms ultimately establish a
   cryptographic binding between the data traffic generated by and for a
   client and the authenticated identity of the client.  Data traffic
   must be minimally data origin authenticated, replay and integrity
   protected, and optionally encrypted.

11.7.  PAA-to-EP Communication

   The PANA framework allows separation of PAA from EP(s).  SNMPv3
   [I-D.ietf-pana-snmp] is used between the PAA and EP for provisioning
   authorized PaC information on the EP.  This exchange MUST be always
   physically or cryptographically protected for authentication,
   integrity and replay protection.  It MUST also be privacy-protected
   when PaC-EP master key for per-packet ciphering is transmitted to the
   EP.

   The PaC-EP master key MUST be unique to the PaC and EP pair.  The
   session identifier and the device identifier of the EP are taken into
   computation for achieving this effect [I-D.ietf-pana-ipsec].
   Compromise of an EP does not automatically lead to compromise of



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   another EP or the PAA.

11.8.  Liveness Test

   A PANA session is associated with a session lifetime.  The session is
   terminated unless it is refreshed by a new round of EAP
   authentication before it expires.  Therefore, at the latest a
   disconnected client can be detected when its session expires.  A
   disconnect may also be detected earlier by using PANA ping messages.
   A request message can be generated by either PaC or PAA at any time
   and the peer must respond with an answer message.  A successful
   round-trip of this exchange is a simple verification that the peer is
   alive.

   This test can be engaged when there is a possibility that the peer
   might have disconnected (e.g., after the discontinuation of data
   traffic for an extended period of time).  Periodic use of this
   exchange as a keep-alive requires additional care as it might result
   in congestion and hence false alarms.

   This exchange is cryptographically protected when a PANA SA is
   available in order to prevent threats associated with the abuse of
   this functionality.

   Any valid PANA answer message received in response to a recently sent
   request message can be taken as an indication of peer's liveness.
   The PaC or PAA MAY forgo sending an explicit PANA-Ping-Request if a
   recent exchange has already confirmed that the peer is alive.

11.9.  Updating PaC's IP Address

   There is no way to prove the ownership of the IP address presented by
   the PaC.  Hence an authorized PaC can launch a redirect attack by
   spoofing a victim's IP address.

11.10.  Early Termination of a Session

   The PANA protocol supports the ability for both the PaC and the PAA
   to transmit a tear-down message before the session lifetime expires.
   This message causes state removal, a stop of the accounting procedure
   and removes the installed per-PaC state on the EP(s).  This message
   is cryptographically protected when PANA SA is present.









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12.  Acknowledgments

   We would like to thank Jari Arkko, Mohan Parthasarathy, Julien
   Bournelle, Rafael Marin Lopez, Pasi Eronen, Randy Turner, Erik
   Nordmark, Lionel Morand, Avi Lior, Susan Thomson, Giaretta Gerardo,
   Joseph Salowey, Sasikanth Bharadwaj and all members of the PANA
   working group for their valuable comments to this document.












































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13.  References

13.1.  Normative References

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

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

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

   [RFC2279]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 2279, January 1998.

   [RFC2365]  Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
              RFC 2365, July 1998.

   [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.

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

   [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
              IPsec Tunnel Mode", RFC 3456, January 2003.

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

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)",
              RFC 3748, June 2004.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [I-D.ietf-ltru-registry]
              Phillips, A. and M. Davis, "Tags for Identifying



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              Languages", draft-ietf-ltru-registry-14 (work in
              progress), October 2005.

   [IANA]     Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs",  BCP 26, RFC 2434,
              October 1998.

13.2.  Informative References

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

   [RFC4016]  Parthasarathy, M., "Protocol for Carrying Authentication
              and Network Access (PANA) Threat Analysis and Security
              Requirements", RFC 4016, March 2005.

   [RFC4058]  Yegin, A., Ohba, Y., Penno, R., Tsirtsis, G., and C. Wang,
              "Protocol for Carrying Authentication for Network Access
              (PANA) Requirements", RFC 4058, May 2005.

   [RFC4137]  Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba,
              "State Machines for Extensible Authentication Protocol
              (EAP) Peer and Authenticator", RFC 4137, August 2005.

   [RFC4284]  Adrangi, F., Lortz, V., Bari, F., and P. Eronen, "Identity
              Selection Hints for the Extensible Authentication Protocol
              (EAP)", RFC 4284, January 2006.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [I-D.ietf-eap-keying]
              Aboba, B., "Extensible Authentication Protocol (EAP) Key
              Management Framework", draft-ietf-eap-keying-09 (work in
              progress), January 2006.

   [I-D.ietf-pana-ipsec]
              Parthasarathy, M., "PANA Enabling IPsec based Access
              Control", draft-ietf-pana-ipsec-07 (work in progress),
              July 2005.

   [I-D.ietf-pana-framework]
              Jayaraman, P., "PANA Framework",
              draft-ietf-pana-framework-05 (work in progress),
              July 2005.

   [I-D.ietf-pana-snmp]
              Mghazli, Y., "SNMP usage for PAA-EP interface",



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              draft-ietf-pana-snmp-05 (work in progress), January 2006.

   [I-D.ietf-mobike-protocol]
              Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", draft-ietf-mobike-protocol-08 (work in
              progress), February 2006.

   [I-D.ietf-dna-link-information]
              Yegin, A., "Link-layer Event Notifications for Detecting
              Network Attachments", draft-ietf-dna-link-information-03
              (work in progress), October 2005.

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

   [IANA-EXP]
              Narten, T., "Assigning Experimental and Testing Numbers
              Considered Useful",  BCP 82, RFC 3692, January 2004.


































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Appendix A.  Example Sequence of Separate NAP and ISP Authentication

   A PANA message sequence with separate NAP and ISP authentication is
   illustrated in Figure 12.  The example assumes the following
   scenario:

   o  The PaC initiates the discovery and handshake phase.

   o  The PAA offers separate NAP and ISP authentication, as well as a
      choice of ISP from "ISP1" and "ISP2".  The PaC accepts the offer
      from PAA, with choosing "ISP1" as the ISP.

   o  NAP authentication and ISP authentication is performed in this
      order in the authentication and authorization phase.

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

   o  After a PANA SA is established, all messages are integrity and
      replay protected with AUTH AVPs.

   o  The access, re-authentication and termination phases are not
      shown.




























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

   // Authentication and authorization phase
      <-----     PANA-Auth-Request(x+1)    // NAP authentication.
                    [Session-Id, Nonce,    // (S,N)-flags set
                     EAP{Request}]         // for all messages during
                                           // NAP authentication.
      ----->     PANA-Auth-Answer(x+1)[Session-Id, Nonce]
      ----->     PANA-Auth-Request(y)[Session-Id, EAP{Response}]
      <-----     PANA-Auth-Answer(y)[Session-Id]
      <-----     PANA-Auth-Request(x+2)[Session-Id, EAP{Request}]
      ----->     PANA-Auth-Answer(x+2)[Session-Id, EAP{Response}]
      <-----     PANA-FirstAuth-End-Request(x+3)
                    [Session-Id, EAP{Success}, Key-Id, Algorithm, AUTH]
      ----->     PANA-FirstAuth-End-Answer(x+3)
                    [Session-Id, Key-Id, AUTH]
      <-----     PANA-Auth-Request(x+4)     // ISP authentication.
                    [Session-Id, EAP{Request}, AUTH]  // Only S-flag set
                                            // for all messages during
                                            // ISP authentication.
      ----->     PANA-Auth-Answer(x+4)[Session-Id, AUTH]
      ----->     PANA-Auth-Request(y+1)[Session-Id, EAP{Response}, AUTH]
      <-----     PANA-Auth-Answer(y+1)[Session-Id, AUTH]
      <-----     PANA-Auth-Request(x+5)[Session-Id, EAP{Request}, AUTH]
      ----->     PANA-Auth-Answer(x+5)[Session-Id, EAP{Response}, AUTH]
      <-----     PANA-Bind-Request(x+6)
                    [Session-Id, Result-Code, EAP{Success}, Device-Id,
                     Key-Id, Lifetime, Protection-Cap., PPAC, AUTH]
      ----->     PANA-Bind-Answer(x+6)[Session-Id, Device-Id, Key-Id,
                     PPAC, AUTH]

   Figure 12: A Complete Message Sequence for Separate NAP and ISP
   Authentication







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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












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   Alper E. Yegin
   Samsung Advanced Institute of Technology
   Istanbul,
   Turkey

   Phone: +90 538 719 0181
   Email: alper01.yegin@partner.samsung.com












































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