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RFC 5191 - Protocol for Carrying Authentication for Network Acce


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Network Working Group                                        D. Forsberg
Request for Comments: 5191                                         Nokia
Category: Standards Track                                   Y. Ohba, Ed.
                                                                 Toshiba
                                                                B. Patil
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                                A. Yegin
                                                                 Samsung
                                                                May 2008

     Protocol for Carrying Authentication for Network Access (PANA)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document defines the Protocol for Carrying Authentication for
   Network Access (PANA), a network-layer transport for Extensible
   Authentication Protocol (EAP) to enable network access authentication
   between clients and access networks.  In EAP terms, PANA is a
   UDP-based EAP lower layer that runs between the EAP peer and the EAP
   authenticator.

Table of Contents

   1. Introduction ....................................................3
      1.1. Specification of Requirements ..............................4
   2. Terminology .....................................................4
   3. Protocol Overview ...............................................6
   4. Protocol Details ................................................7
      4.1. Authentication and Authorization Phase .....................7
      4.2. Access Phase ..............................................11
      4.3. Re-Authentication Phase ...................................11
      4.4. Termination Phase .........................................13
   5. Processing Rules ...............................................13
      5.1. Fragmentation .............................................13
      5.2. Sequence Number and Retransmission ........................14
      5.3. PANA Security Association .................................15
      5.4. Message Authentication ....................................17
      5.5. Message Validity Check ....................................17
      5.6. PaC Updating Its IP Address ...............................19
      5.7. Session Lifetime ..........................................19
   6. Message Format .................................................20
      6.1. IP and UDP Headers ........................................20
      6.2. PANA Message Header .......................................20
      6.3. AVP Format ................................................22
   7. PANA Messages ..................................................24
      7.1. PANA-Client-Initiation (PCI) ..............................27
      7.2. PANA-Auth-Request (PAR) ...................................28
      7.3. PANA-Auth-Answer (PAN) ....................................28
      7.4. PANA-Termination-Request (PTR) ............................28
      7.5. PANA-Termination-Answer (PTA) .............................29
      7.6. PANA-Notification-Request (PNR) ...........................29
      7.7. PANA-Notification-Answer (PNA) ............................29
   8. AVPs in PANA ...................................................29
      8.1. AUTH AVP ..................................................30
      8.2. EAP-Payload AVP ...........................................30
      8.3. Integrity-Algorithm AVP ...................................31
      8.4. Key-Id AVP ................................................31
      8.5. Nonce AVP .................................................31
      8.6. PRF-Algorithm AVP .........................................32
      8.7. Result-Code AVP ...........................................32
      8.8. Session-Lifetime AVP ......................................32
      8.9. Termination-Cause AVP .....................................33
   9. Retransmission Timers ..........................................33
      9.1. Transmission and Retransmission Parameters ................35
   10. IANA Considerations ...........................................35
      10.1. PANA UDP Port Number .....................................36
      10.2. PANA Message Header ......................................36
           10.2.1. Message Type ......................................36
           10.2.2. Flags .............................................36

      10.3. AVP Header ...............................................36
           10.3.1. AVP Code ..........................................37
           10.3.2. Flags .............................................37
      10.4. AVP Values ...............................................37
           10.4.1. Result-Code AVP Values ............................37
           10.4.2. Termination-Cause AVP Values ......................38
   11. Security Considerations .......................................38
      11.1. General Security Measures ................................38
      11.2. Initial Exchange .........................................40
      11.3. EAP Methods ..............................................40
      11.4. Cryptographic Keys .......................................40
      11.5. Per-Packet Ciphering .....................................41
      11.6. PAA-to-EP Communication ..................................41
      11.7. Liveness Test ............................................41
      11.8. Early Termination of a Session ...........................42
   12. Acknowledgments ...............................................42
   13. References ....................................................42
      13.1. Normative References .....................................42
      13.2. Informative References ...................................43

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.

   The scope of this work is identified as designing a network-layer
   transport for network access authentication methods.  The Extensible
   Authentication Protocol (EAP) [RFC3748] provides such authentication
   methods.  In other words, PANA carries EAP, which can carry various
   authentication methods.  By the virtue of enabling the 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] of 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 PANA Authentication Agent (PAA) discovery, authentication
   method choice, PANA Authentication Agent-Enforcement Point (PAA-EP)
   protocol, access control filter creation, and data traffic
   protection.  These components are described in separate documents
   (see [RFC5193] and [RFC5192]).

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].

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
      colocated in the same access device.

   PANA Authentication Agent (PAA):

      The protocol entity in the access network whose responsibility it
      is to verify the credentials provided by a PANA client (PaC) and
      authorize network access to the access device.  The PAA and the
      EAP authenticator (and optionally the EAP server) are colocated in
      the same node.  Note the authentication and authorization
      procedure can, according to the EAP model, also be offloaded to
      the back end Authentication, Authorization, and Accounting (AAA)
      infrastructure.

   PANA Session:

      A PANA session is established between the PANA Client (PaC) and
      the PANA Authentication Agent (PAA), and it terminates as a result
      of an authentication and authorization or liveness test failure, a
      message delivery failure after retransmissions reach maximum
      values, session lifetime expiration, an explicit termination
      message or any event that causes discontinuation of the access
      service.  A fixed session identifier is maintained throughout a
      session.  A session cannot be shared across multiple network
      interfaces.

   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 extended by a new round of EAP
      authentication before it expires.  Until a PANA session is
      established, the lifetime SHOULD be set to a value that allows the
      PaC to detect a failed session in a reasonable amount of time.

   Session Identifier:

      This identifier is used to uniquely identify a PANA session on the
      PaC and the PAA.  It is included in PANA messages to bind the
      message to a specific PANA session.  This bidirectional identifier
      is allocated by the PAA in the initial request message and freed
      when the session terminates.  The session identifier is assigned
      by the PAA and is unique within the PAA.

   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 PAA.

   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.  The EP and the PAA may be colocated.  EPs should
      prevent data traffic from and to any unauthorized client, unless
      that data traffic is either PANA or one of the other allowed
      traffic types (e.g., Address Resolution Protocol (ARP), IPv6
      neighbor discovery, DHCP, etc.).

   Master Session Key (MSK):

      A key derived by the EAP peer and the EAP server and transported
      to the EAP authenticator [RFC3748].

   For additional terminology definitions, see the PANA framework
   document [RFC5193].

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 requests and answers,
   some of which may be initiated by either end.  Each message can carry
   zero or more AVPs (Attribute-Value Pairs) 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  Authentication and authorization phase: This is the phase that
      initiates a new PANA session and executes EAP between the PAA and
      PaC.  The PANA session can be initiated by both the PaC and the
      PAA.  The EAP payload (which carries 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.

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

   o  Re-authentication phase: During the access phase, the PAA may, and
      the PaC should, initiate re-authentication if they want to update
      the PANA session lifetime before the PANA session lifetime
      expires.  EAP is carried by PANA to perform re-authentication.
      This phase may be optionally triggered by both the PaC and the PAA
      without any respect to the session lifetime.  The
      re-authentication phase is a sub-phase of the access phase.  The
      session moves to this sub-phase from the access phase when
      re-authentication starts, 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
      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.

   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.

4.  Protocol Details

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

4.1.  Authentication and Authorization Phase

   The main task of the authentication and authorization phase is to
   establish a PANA session and carry EAP messages between the PaC and
   the PAA.  The PANA session can be initiated by either the PaC or the
   PAA.

   PaC-initiated Session:

      When the PaC initiates a PANA session, it sends a
      PANA-Client-Initiation message to the PAA.  When the PaC is not
      configured with an IP address of the PAA before initiating the
      PANA session, DHCP [RFC5192] is used as the default method for
      dynamically configuring the IP address of the PAA.  Alternative
      methods for dynamically discovering the IP address of the PAA may
      be used for PaC-initiated sessions, but they are outside the scope
      of this specification.  The PAA that receives the
      PANA-Client-Initiation message MUST respond to the PaC with a
      PANA-Auth-Request message.

   PAA-initiated Session:

      When the PAA knows the IP address of the PaC, it MAY send an
      unsolicited PANA-Auth-Request to the PaC.  The details of how PAA
      can learn the IP address of the PaC are outside the scope of this
      specification.

   A session identifier for the session is assigned by the PAA and
   carried in the initial PANA-Auth-Request message.  The same session
   identifier MUST be carried in the subsequent messages exchanged
   between the PAA and PaC throughout the session.

   When the PaC receives the initial PANA-Auth-Request message from a
   PAA, it responds with a PANA-Auth-Answer message, if it wishes to
   continue the PANA session.  Otherwise, it silently discards the
   PANA-Auth-Request message.

   The initial PANA-Auth-Request and PANA-Auth-Answer messages MUST have
   the 'S' (Start) bit set, regardless of whether the session is
   initiated by the PaC or the PAA.  Non-initial PANA-Auth-Request and
   PANA-Auth-Answer messages as well as any other messages MUST NOT have
   the 'S' (Start) bit set.

   It is recommended that the PAA limit the rate at which it processes
   incoming PANA-Client-Initiation messages to provide robustness
   against denial of service (DoS) attacks.  The details of rate
   limiting are outside the scope of this specification.

   If a PANA SA needs to be established with use of a key-generating EAP
   method, the Pseudo-Random Function (PRF) and integrity algorithms to
   be used for PANA_AUTH_KEY derivation (see Section 5.3) and AUTH AVP
   calculation (see Section 5.4) are negotiated as follows: the PAA
   sends the initial PANA-Auth-Request carrying one or more
   PRF-Algorithm AVPs and one or more Integrity-Algorithm AVPs for the
   PRF and integrity algorithms supported by it, respectively.  The PaC
   then selects one PRF algorithm and one integrity algorithm from these
   AVPs carried in the initial PANA-Auth-Request, and it responds with
   the initial PANA-Auth-Answer carrying one PRF-Algorithm AVP and one
   Integrity-Algorithm AVP for the selected algorithms.  The negotiation
   is protected after the MSK is available, as described in Section 5.3.

   If the PAA wants to stay stateless in response to a
   PANA-Client-Initiation message, it doesn't include an EAP-Payload AVP
   in the initial PANA-Auth-Request message, and it should not
   retransmit the message on a timer.  For this reason, the PaC MUST
   retransmit the PANA-Client-Initiation message until it receives the
   second PANA-Auth-Request message (not a retransmission of the initial
   one) from the PAA.

   It is possible that both the PAA and the PaC initiate the PANA
   session at the same time, i.e., the PAA sends the initial PANA-Auth-
   Request message without solicitation while the PaC sends a
   PANA-Client-Initiation message.  To resolve the race condition, the
   PAA MUST silently discard the PANA-Client-Initiation message received
   from the PaC after it has sent the initial PANA-Auth-Request message.
   The PAA uses the source IP address and the source port number of the
   PANA-Client-Initiation message to identify the PaC among multiple
   PANA-Client-Initiation messages sent from different PaCs.

   EAP 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 sent
   from the PaC MAY include the EAP message.  This optimization SHOULD
   NOT be used when it takes time to generate the EAP message (due to,
   e.g., intervention of human input), in which case returning an
   PANA-Auth-Answer message without piggybacking an EAP message can
   avoid unnecessary retransmission of the PANA-Auth-Request message.

   A Nonce AVP MUST be included in the first PANA-Auth-Request and
   PANA-Auth-Answer messages following the initial PANA-Auth-Request and
   PANA-Auth-Answer messages (i.e., with the 'S' (Start) bit set), and
   MUST NOT be included in any other message, except during
   re-authentication procedures (see Section 4.3).

   The result of PANA authentication is carried in the last
   PANA-Auth-Request message sent from the PAA to the PaC.  This message
   carries the EAP authentication result and the result of PANA
   authentication.  The last PANA-Auth-Request message MUST be
   acknowledged with a PANA-Auth-Answer message.  The last
   PANA-Auth-Request and PANA-Auth-Answer messages MUST have the 'C'
   (Complete) bit set, and any other message MUST NOT have the 'C'
   (Complete) bit set.  Figure 1 shows an example sequence in the
   authentication and authorization phase for a PaC-initiated session.

   PaC      PAA  Message(sequence number)[AVPs]
   ---------------------------------------------------------------------
      ----->     PANA-Client-Initiation(0)
      <-----     PANA-Auth-Request(x)[PRF-Algorithm,Integrity-Algorithm]
                                              // The 'S' (Start) bit set
      ----->     PANA-Auth-Answer(x)[PRF-Algorithm, Integrity-Algorithm]
                                              // The 'S' (Start) bit set
      <-----     PANA-Auth-Request(x+1)[Nonce, EAP-Payload]
      ----->     PANA-Auth-Answer(x+1)[Nonce] // No piggybacking EAP
      ----->     PANA-Auth-Request(y)[EAP-Payload]
      <-----     PANA-Auth-Answer(y)
      <-----     PANA-Auth-Request(x+2)[EAP-Payload]
      ----->     PANA-Auth-Answer(x+2)[EAP-Payload]
                                            // Piggybacking EAP
      <-----     PANA-Auth-Request(x+3)[Result-Code, EAP-Payload,
                                        Key-Id, Session-Lifetime, AUTH]
                                           // The 'C' (Complete) bit set
      ----->     PANA-Auth-Answer(x+3)[Key-Id, AUTH]
                                           // The 'C' (Complete) bit set

   Figure 1: Example sequence for the authentication and authorization
             phase for a PaC-initiated session ("Piggybacking EAP" is
             the case in which an EAP-Payload AVP is carried in PAN)

   If a PANA SA needs to be established with use of a key-generating EAP
   method and an MSK is successfully generated, the last
   PANA-Auth-Request message with the 'C' (Complete) bit set MUST
   contain a Key-Id AVP and an AUTH AVP for the first derivation of keys
   in the session, and any subsequent message MUST contain an AUTH AVP.

   EAP authentication can fail at a pass-through authenticator without
   sending an EAP Failure message [RFC4137].  When this occurs, the PAA
   SHOULD silently terminate the session, expecting that a session
   timeout on the PaC will clean up the state 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 server or authorization locally
   rejected by the PAA.  When this occurs, the PAA MUST send the last
   PANA-Auth-Request with a result code PANA_AUTHORIZATION_REJECTED.  If
   an MSK is available, the last PANA-Auth-Request and PANA-Auth-Answer
   messages with the 'C' (Complete) bit set MUST be protected with an
   AUTH AVP and carry a Key-Id AVP.  The PANA session MUST be terminated
   immediately after the last PANA-Auth message exchange.

   For reasons described in Section 3 of [RFC5193], the PaC may need to
   reconfigure the IP address after a successful authentication and
   authorization phase to obtain an IP address that is usable for

   exchanging data traffic through EP.  In this case, the PAA sets the
   'I' (IP Reconfiguration) bit of PANA-Auth-Request messages in the
   authentication and authorization phase to indicate to the PaC the
   need for IP address reconfiguration.  How IP address reconfiguration
   is performed is outside the scope of this document.

4.2.  Access Phase

   Once the authentication and authorization 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-Notification-Request
   and PANA-Notification-Answer messages with the 'P' (Ping) bit set
   (ping request and ping answer messages, respectively) 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 ping request to the
   communicating peer whenever they need to ensure the availability of
   the session on the peer, and they expect the peer to return a ping
   answer message.  The ping request and answer messages MUST be
   protected with an AUTH AVP when a PANA SA is available.  A ping
   request MUST NOT be sent in the authentication and authorization
   phase, re-authentication phase, and termination phase.

   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 ping requests.  It should be noted that
   if a PAA or PaC that considers its connectivity lost after a
   relatively small number of unresponsive pings is coupled with a peer
   that is aggressively rate limiting the ping request and answer
   messages, then false-positives could result.  Therefore, a PAA or PaC
   should not rely on frequent ping operation to quickly determine loss
   of connectivity.

4.3.  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 terminated.

   When the PaC initiates re-authentication, it sends a
   PANA-Notification-Request message with the 'A' (re-Authentication)
   bit set (a re-authentication request message) to the PAA.  This
   message MUST contain the session identifier assigned to the session
   being re-authenticated.  If the PAA already has an established PANA
   session for the PaC with the matching session identifier, it MUST

   first respond with a PANA-Notification-Answer message with the 'A'
   (re-Authentication) bit set (a re-authentication answer message),
   followed by a PANA-Auth-Request message that starts a new EAP
   authentication.  If the PAA cannot identify the session, it MUST
   silently discard the message.  The first PANA-Auth-Request and
   PANA-Auth-Answer messages in the re-authentication phase MUST have
   the 'S' (Start) bit cleared and carry a Nonce AVP.

   The PaC may receive a PANA-Auth-Request before receiving the answer
   to its outstanding re-authentication request message.  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.  The PAA MUST initiate EAP re-authentication before the current
   session lifetime expires.

   Re-authentication of an ongoing PANA session MUST NOT reset the
   sequence numbers.

   For any re-authentication, if there is an established PANA SA,
   re-authentication request and answer messages and subsequent
   PANA-Auth-Request and PANA-Auth-Answer messages MUST be protected
   with an AUTH AVP.  The final PANA-Auth-Request and PANA-Auth-Answer
   messages and any subsequent PANA message MUST be protected by using
   the key generated from the latest EAP authentication.

   PaC      PAA  Message(sequence number)[AVPs]
   ---------------------------------------------------------------------
      ----->     PANA-Notification-Request(q)[AUTH]
                               // The 'A' (re-Authentication) bit set
      <-----     PANA-Notification-Answer(q)[AUTH]
                               // The 'A' (re-Authentication) bit set
      <-----     PANA-Auth-Request(p)[EAP-Payload, Nonce, AUTH]
      ----->     PANA-Auth-Answer(p)[AUTH, Nonce]
      ----->     PANA-Auth-Request(q+1)[EAP-Payload, AUTH]
      <-----     PANA-Auth-Answer(q+1)[AUTH]
      <-----     PANA-Auth-Request(p+1)[EAP-Payload, AUTH]
      ----->     PANA-Auth-Answer(p+1)[EAP-Payload, AUTH]
      <-----     PANA-Auth-Request(p+2)[Result-Code, EAP-Payload,
                                        Key-Id, Session-Lifetime, AUTH]
                                        // The 'C' (Complete) bit set
      ----->     PANA-Auth-Answer(p+2)[Key-Id, AUTH]
                                        // The 'C' (Complete) bit set

   Figure 2: Example sequence for the re-authentication phase initiated
             by PaC

4.4.  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 terminated immediately.

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: one is for setting the
   sequence number of the next outgoing request; the other is for
   matching the sequence number of the next incoming request.  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-Client-Initiation 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-Client-Initiation message and the initial PANA-Auth-Request
   message.

   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 request messages are retransmitted based on a timer until an
   answer 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 terminated immediately).

   The retransmission timers SHOULD be calculated as described in
   Section 9, unless a given deployment chooses to use its own
   retransmission timers optimized for the underlying link-layer
   characteristics.

   Unless dropped due to rate limiting, the PaC and PAA MUST respond to
   all duplicate request messages received.  The last transmitted answer
   MAY be cached in case it is not received by the peer, which 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.

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 an MSK.  A PANA SA is not
   created when the PANA authentication fails or no MSK is produced by
   the EAP authentication method.  When a new MSK is derived in the PANA
   re-authentication phase, any key derived from the old MSK MUST be
   updated to a new one that is derived from the new MSK.  In order to
   distinguish the new MSK from old ones, one Key-Id AVP MUST be carried
   in the last PANA-Auth-Request and PANA-Auth-Answer messages with the
   'C' (Complete) bit set at the end of the EAP authentication, which
   resulted in deriving a new MSK.  The Key-Id AVP is of type Unsigned32
   and MUST contain a value that uniquely identifies the MSK within the
   PANA session.  The last PANA-Auth-Answer message with the 'C'
   (Complete) bit set in response to the last PANA-Auth-Request message
   with the 'C' (Complete) bit set MUST contain a Key-Id AVP with the
   same MSK identifier carried in the request.  The last
   PANA-Auth-Request and PANA-Auth-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 MSK.  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 MSK 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 terminated.

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

   PANA Session attributes:

      *  Session Identifier

      *  IP address and UDP port number of the PaC

      *  IP address and UDP port number of the PAA

      *  Sequence number for the next outgoing request

      *  Sequence number for the next incoming request

      *  Last transmitted message payload

      *  Retransmission interval

      *  Session lifetime

      *  PANA SA attributes

   PANA SA attributes:

      *  Nonce generated by PaC (PaC_nonce)

      *  Nonce generated by PAA (PAA_nonce)

      *  MSK

      *  MSK Identifier

      *  PANA_AUTH_KEY

      *  Pseudo-random function

      *  Integrity algorithm

   The PANA_AUTH_KEY is derived from the available MSK, and it is used
   to integrity protect PANA messages.  The PANA_AUTH_KEY is computed in
   the following way:

   PANA_AUTH_KEY = prf+(MSK, "IETF PANA"|I_PAR|I_PAN|
             PaC_nonce|PAA_nonce|Key_ID)

   where:

   - The prf+ function is defined in IKEv2 [RFC4306].  The pseudo-random
     function to be used for the prf+ function is negotiated using
     PRF-Algorithm AVP in the initial PANA-Auth-Request and
     PANA-Auth-Answer exchange with 'S' (Start) bit set.

   - MSK is the master session key generated by the EAP method.

   - "IETF PANA" is the ASCII code representation of the non-NULL
     terminated string (excluding the double quotes around it).

   - I_PAR and I_PAN are the initial PANA-Auth-Request and
     PANA-Auth-Answer messages (the PANA header and the following PANA
     AVPs) with 'S' (Start) bit set, respectively.

   - PaC_nonce and PAA_nonce are values of the Nonce AVP carried in the
     first non-initial PANA-Auth-Answer and PANA-Auth-Request messages
     in the authentication and authorization phase or the first
     PANA-Auth-Answer and PANA-Auth-Request messages in the
     re-authentication phase, respectively.

   - Key_ID is the value of the Key-Id AVP.

   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 negotiated using
   Integrity-Algorithm AVP in the initial PANA-Auth-Request and
   PANA-Auth-Answer exchange with 'S' (Start) bit set.  The PaC and PAA
   MUST use the same integrity algorithm to calculate an AUTH AVP they
   originate and receive.

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, flags, session
      identifier, etc.

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

      *  In the authentication and authorization phase:

         +  PANA-Client-Initiation after completion of the initial
            PANA-Auth-Request and PANA-Auth-Answer exchange with 'S'
            (Start) bit set.

         +  Re-authentication request.

         +  Ping request.

         +  The last PANA-Auth-Request with 'C' (Complete) bit set
            before completion of the initial PANA-Auth-Request and
            PANA-Auth-Answer exchange with 'S' (Start) bit set.

         +  The initial PANA-Auth-Request with 'S' (Start) bit set after
            a PaC receives a valid non-initial PANA-Auth-Request with
            'S' (Start) bit cleared.

         +  PANA-Termination-Request.

      *  In the re-authentication phase:

         +  PANA-Client-Initiation.

         +  The initial PANA-Auth-Request.

      *  In the access phase:

         +  PANA-Auth-Request.

         +  PANA-Client-Initiation.

      *  In the termination phase:

         +  PANA-Client-Initiation.

         +  All requests but PANA-Termination-Request and ping request.

   o  The message payload contains a valid set of AVPs allowed for the
      message type.  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 recognized and decoded correctly.

   o  Once the PANA authentication succeeds in using a key-generating
      EAP method, the PANA-Auth-Request message that carries the EAP
      Success and any subsequent message in that session contains an
      AUTH AVP.  The AVP value matches the hash value computed against
      the received message.

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

5.6.  PaC Updating Its IP Address

   A PaC's IP address used for PANA can change in certain situations,
   e.g., when IP address reconfiguration is needed for the PaC to obtain
   an IP address after successful PANA authentication (see Section 3 of
   [RFC5193]) or when the PaC 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.

   After the PaC has changed its IP address used for PANA, it MUST send
   any valid PANA message.  If the message that carries the new PaC IP
   address in the Source Address field of the IP header is valid, the
   PAA MUST update the PANA session with the new PaC address.  If there
   is an established PANA SA, the message MUST be protected with an AUTH
   AVP.

5.7.  Session Lifetime

   The authentication and authorization phase determines the PANA
   session lifetime, and the lifetime is indicated to the PaC when the
   network access authorization succeeds.  For this purpose, when the
   last PANA-Auth-Request message (i.e., with the 'C' (Complete) bit
   set) in authentication and authorization phase or re-authentication
   phase carries a Result-Code AVP with a value of PANA_SUCCESS, a
   Session-Lifetime AVP MUST also be carried in the message.  A
   Session-Lifetime AVP MUST be ignored when included in other PANA
   messages.

   The lifetime is a non-negotiable parameter that can be used by the
   PaC to manage PANA-related state.  The PaC MUST initiate the
   re-authentication phase before the current session lifetime expires,
   if it wants to extend the session.

   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 ping request and answer exchange
   to verify that a peer is, in fact, no longer alive, unless
   information obtained outside PANA is being used to expedite the
   detection of a disconnected peer.

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

6.  Message Format

   This section defines message formats for PANA protocol.

6.1.  IP and UDP Headers

   Any PANA message is unicast between the PaC and the PAA.

   For any PANA message sent from the peer that has initiated the PANA
   session, the UDP source port is set to any number on which the peer
   can receive incoming PANA messages, and the destination port is set
   to the assigned PANA port number (716).  For any PANA message sent
   from the other peer, the source port is set to the assigned PANA port
   number (716), and the destination port is copied from the source port
   of the last received message.  In case both the PaC and PAA initiate
   the session (i.e., PANA-Client-Initiation and unsolicited PANA-Auth-
   Request messages cross each other), then the PaC is identified as the
   initiator.  All PANA peers MUST listen on the assigned PANA port
   number (716).

6.2.  PANA Message Header

   A summary of the PANA message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Reserved            |        Message Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Flags             |         Message Type          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Session Identifier                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  AVPs ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

   Reserved

      This 16-bit field is reserved for future use.  It 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 C A P I r r r r r r r r r r|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   R (Request)

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

   S (Start)

      If set, the message is the first PANA-Auth-Request or
      PANA-Auth-Answer in authentication and authorization phase.  For
      other messages, this bit MUST be cleared.

   C (Complete)

      If set, the message is the last PANA-Auth-Request or
      PANA-Auth-Answer in authentication and authorization phase.  For
      other messages, this bit MUST be cleared.

   A (re-Authentication)

      If set, the message is a PANA-Notification-Request or
      PANA-Notification-Answer to initiate re-authentication.  For other
      messages, this bit MUST be cleared.

   P (Ping)

      If set, the message is a PANA-Notification-Request or
      PANA-Notification-Answer for liveness test.  For other messages,
      this bit MUST be cleared.

   I (IP Reconfiguration)

      If set, it indicates that the PaC is required to perform IP
      address reconfiguration after successful authentication and
      authorization phase to configure an IP address that is usable for
      exchanging data traffic across EP.  This bit is set by the PAA
      only for PANA-Auth-Request messages in the authentication and
      authorization phase.  For other messages, this bit MUST be
      cleared.

   r (reserved)

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

   Message Type

      The Message Type field is two octets, and it is used in order to
      communicate the message type with the message.  Message Type
      allocation is managed by IANA [IANAWEB].

   Session Identifier

      This field contains a 32-bit session identifier.

   Sequence Number

      This field contains a 32-bit sequence number.

   AVPs

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

6.3.  AVP Format

   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 Value field until a
   word boundary is reached.  The length of the padding is not reflected
   in the AVP Length field [RFC3588].

   The fields in the AVP are sent in network byte order.  The AVP format
   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)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Value ...
   +-+-+-+-+-+-+-+-+

   AVP Code

      The AVP Code, together with the optional Vendor-Id field,
      identifies an attribute that follows.  If the V-bit is not set,
      then the Vendor-Id is not present and the AVP Code refers to an
      IETF attribute.

   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 r r r r r r r r r r r r r r r|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   V (Vendor)

      The 'V' (Vendor) 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.  All AVPs
      defined in this document MUST have the 'V' (Vendor) bit cleared.

   r (reserved)

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

   AVP Length

      The AVP Length field is two octets, and indicates the number of
      octets in the Value field.  The length of the AVP Code, AVP
      Length, AVP Flags, Reserved and Vendor-Id fields are not counted
      in the AVP Length value.

   Reserved

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

   Vendor-Id

      The Vendor-Id field is present if the 'V' (Vendor) 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.

   Value

      The Value field is zero or more octets and contains information
      specific to the Attribute.  The format of the Value field is
      determined by the AVP Code and Vendor-Id fields.  The length of
      the Value field is determined by the AVP Length field.

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'
   (Request) bit in the Message Flags field of the PANA message header.

   Every PANA message MUST contain a message type in its header's
   Message Type field, which is used to determine the action that is to
   be taken for a particular message.  Figure 3 lists all PANA messages
   defined in this document:

   Message Name              Abbrev. Message  PaC<->PAA  Ref.
                                     Type
   ---------------------------------------------------------------------
   PANA-Client-Initiation     PCI    1        -------->  7.1
   PANA-Auth-Request          PAR    2        <------->  7.2
   PANA-Auth-Answer           PAN    2        <------->  7.3
   PANA-Termination-Request   PTR    3        <------->  7.4
   PANA-Termination-Answer    PTA    3        <------->  7.5
   PANA-Notification-Request  PNR    4        <------->  7.6
   PANA-Notification-Answer   PNA    4        <------->  7.7
   ---------------------------------------------------------------------

   Figure 3: Table of PANA Messages

   The language used for PANA message definitions (i.e., AVPs valid for
   that PANA message type), in Section 7.1 through Section 7.7, is
   defined using ABNF [RFC5234] as follows:

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

   Message-Name     = PANA-name

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

   PANA-message     = header LWSP *fixed LWSP *required
                             LWSP *optional LWSP *fixed

   header           = "<" LWSP "PANA-Header:" LWSP Message-Type
                      [r-bit] [s-bit] [c-bit] [a-bit] [p-bit] [i-bit]
                      LWSP ">"

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

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

   s-bit            = ",STA"
                      ; If present, the 'S' (Start) bit in the Message
                      ; Flags is set, indicating that the message
                      ; is the initial PAR or PAN in authentication
                      ; and authorization phase.

   c-bit            = ",COM"
                      ; If present, the 'C' bit in the Message
                      ; Flags is set, indicating that the message
                      ; is the final PAR and PAN in authentication
                      ; and authorization phase or re-authentication
                      ; phase.

   a-bit            = ",REA"
                      ; If present, the 'A' (re-Authentication) bit
                      ; in the Message Flags is set, indicating that
                      ; the message is a re-authentication request or
                      ; answer.

   p-bit            = ",PIN"
                      ; If present, the 'P' (Ping) bit in the Message
                      ; Flags is set, indicating that the message
                      ; is a ping request or answer.

   i-bit            = ",IPR"
                      ; If present, the 'I' (IP Reconfiguration) bit
                      ; in the Message Flags is set, indicating that
                      ; the PaC requires IP address reconfiguration
                      ; after successful authentication and
                      ; authorization phase.

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

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

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

   qual             = [min] "*" [max]
                      ; See ABNF conventions, RFC 5234 Section 3.6.
                      ; 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.
                      ;
                      ; 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.

7.1.  PANA-Client-Initiation (PCI)

   The PANA-Client-Initiation (PCI) message is used for PaC-initiated
   session.  The Sequence Number and Session Identifier fields in this
   message MUST be set to zero (0).

   PANA-Client-Initiation ::= < PANA-Header: 1 >
                      *[ AVP ]

7.2.  PANA-Auth-Request (PAR)

   The PANA-Auth-Request (PAR) message is either sent by the PAA or the
   PaC.

   The message MUST NOT have both the 'S' (Start) and 'C' (Complete)
   bits set.

   PANA-Auth-Request ::= < PANA-Header: 2,REQ[,STA][,COM][,IPR] >
                       [ EAP-Payload ]
                       [ Nonce ]
                      *[ PRF-Algorithm ]
                      *[ Integrity-Algorithm ]
                       [ Result-Code ]
                       [ Session-Lifetime ]
                       [ Key-Id ]
                      *[ AVP ]
                    0*1< AUTH >

7.3.  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.

   The message MUST NOT have both the 'S' (Start) and 'C' (Complete)
   bits set.

   PANA-Auth-Answer ::= < PANA-Header: 2[,STA][,COM] >
                       [ Nonce ]
                       [ PRF-Algorithm ]
                       [ Integrity-Algorithm ]
                       [ EAP-Payload ]
                       [ Key-Id ]
                      *[ AVP ]
                    0*1< AUTH >

7.4.  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: 3,REQ >
                       < Termination-Cause >
                      *[ AVP ]
                    0*1< AUTH >

7.5.  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: 3 >
                      *[ AVP ]
                    0*1< AUTH >

7.6.  PANA-Notification-Request (PNR)

   The PANA-Notification-Request (PNR) message is used for signaling
   re-authentication and performing liveness test.  See Section 4.3 and
   Section 4.2 for details on re-authentication and liveness test,
   respectively.

   The message MUST have one of the 'A' (re-Authentication) and 'P'
   (Ping) bits exclusively set.

   PANA-Notification-Request ::= < PANA-Header: 4,REQ[,REA][,PIN] >
                      *[ AVP ]
                    0*1< AUTH >

7.7.  PANA-Notification-Answer (PNA)

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

   The message MUST have one of the 'A' (re-Authentication) and 'P'
   (Ping) bits exclusively set.

   PANA-Notification-Answer ::= < PANA-Header: 4[,REA][,PIN] >
                      *[ AVP ]
                    0*1< AUTH >

8.  AVPs in PANA

   This document uses AVP Value Format such as 'OctetString' and
   'Unsigned32' as defined in Section 4.2 of [RFC3588].  The definitions
   of these data formats are not repeated in this document.

   The following table 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.

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

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

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

                         +---------------------------+
                         |        Message Type       |
                         +---+---+---+---+---+---+---+
   Attribute Name        |PCI|PAR|PAN|PTR|PTA|PNR|PNA|
   ----------------------+---+---+---+---+---+---+---+
   AUTH                  | 0 |0-1|0-1|0-1|0-1|0-1|0-1|
   EAP-Payload           | 0 |0-1|0-1| 0 | 0 | 0 | 0 |
   Integrity-Algorithm   | 0 |0+ |0-1| 0 | 0 | 0 | 0 |
   Key-Id                | 0 |0-1|0-1| 0 | 0 | 0 | 0 |
   Nonce                 | 0 |0-1|0-1| 0 | 0 | 0 | 0 |
   PRF-Algorithm         | 0 |0+ |0-1| 0 | 0 | 0 | 0 |
   Result-Code           | 0 |0-1| 0 | 0 | 0 | 0 | 0 |
   Session-Lifetime      | 0 |0-1| 0 | 0 | 0 | 0 | 0 |
   Termination-Cause     | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
   ----------------------+---+---+---+---+---+---+---+

   Figure 4: AVP Occurrence Table

8.1.  AUTH AVP

   The AUTH AVP (AVP Code 1) is used to integrity protect PANA messages.
   The AVP data payload contains the Message Authentication Code encoded
   in network byte order.  The AVP length varies depending on the
   integrity algorithm used.  The AVP data is of type OctetString.

8.2.  EAP-Payload AVP

   The EAP-Payload AVP (AVP Code 2) 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.

8.3.  Integrity-Algorithm AVP

   The Integrity-Algorithm AVP (AVP Code 3) is used for conveying the
   integrity algorithm to compute an AUTH AVP.  The AVP data is of type
   Unsigned32.  The AVP data contains an Internet Key Exchange Protocol
   version 2 (IKEv2) Transform ID of Transform Type 3 [RFC4306] for the
   integrity algorithm.  All PANA implementations MUST support
   AUTH_HMAC_SHA1_160 (7) [RFC4595].

8.4.  Key-Id AVP

   The Key-Id AVP (AVP Code 4) is of type Integer32 and contains an MSK
   identifier.  The MSK identifier is assigned by PAA and MUST be unique
   within the PANA session.

8.5.  Nonce AVP

   The Nonce AVP (AVP Code 5) 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 PaC and the PAA to compute random values.  The length of the
   random value for the nonce is determined in one of two ways,
   depending on 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 of 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).

   Furthermore, the strongest available PRF 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.  Therefore, the maximum length of the nonce value SHOULD be
   20 octets.

8.6.  PRF-Algorithm AVP

   The PRF-Algorithm AVP (AVP Code 6) is used for conveying the
   pseudo-random function to derive PANA_AUTH_KEY.  The AVP data is of
   type Unsigned32.  The AVP data contains an IKEv2 Transform ID of
   Transform Type 2 [RFC4306].  All PANA implementations MUST support
   PRF_HMAC_SHA1 (2) [RFC2104].

8.7.  Result-Code AVP

   The Result-Code AVP (AVP Code 7) is of type Unsigned32 and indicates
   whether an EAP authentication was completed successfully.
   Result-Code AVP values are described below.

   PANA_SUCCESS                               0

      Both authentication and authorization processes are successful.

   PANA_AUTHENTICATION_REJECTED               1

      Authentication has failed.  When authentication fails,
      authorization is also considered to have failed.

   PANA_AUTHORIZATION_REJECTED                2

      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.

8.8.  Session-Lifetime AVP

   The Session-Lifetime AVP (AVP Code 8) contains the number of seconds
   remaining before the current session is considered expired.  The AVP
   data is of type Unsigned32.

8.9.  Termination-Cause AVP

   The Termination-Cause AVP (AVP Code 9) 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.

9.  Retransmission Timers

   The PANA protocol provides retransmissions for the
   PANA-Client-Initiation message and all request messages.

   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-based protocol.  The
   message exchange terminates when the requester successfully receives
   the answer, or 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 from the previous (re)transmission

      IRT    Base value for RT for the initial retransmission

      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 the 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 retransmission is based on IRT:

         RT = IRT + RAND*IRT

   RT for each subsequent message retransmission 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 (REQ_*) and PANA-Client-
   Initiation message (PCI_*).  The table shows default values.

   Parameter       Default   Description
   ---------------------------------------------------------------------
   PCI_IRT           1 sec   Initial PCI timeout.
   PCI_MRT         120 secs  Max PCI timeout value.
   PCI_MRC           0       Max PCI retransmission attempts.
   PCI_MRD           0       Max PCI retransmission duration.

   REQ_IRT           1 sec   Initial Request timeout.
   REQ_MRT          30 secs  Max Request timeout value.
   REQ_MRC          10       Max Request retransmission attempts.
   REQ_MRD           0       Max Request retransmission duration.

   So, for example, the first RT for the PANA-Auth-Request (PAR) message
   is calculated using REQ_IRT as the IRT:

         RT = REQ_IRT + RAND*REQ_IRT

10.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding the 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", and "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.

   IANA has created a registry for PANA.

10.1.  PANA UDP Port Number

   PANA uses one well-known UDP port number (see Section 6.1), which has
   been assigned by the IANA (716).

10.2.  PANA Message Header

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

10.2.1.  Message Type

   The Message Type namespace is used to identify PANA messages.
   Message Type 0 is not used and is not assigned by IANA.  The range of
   values 1 - 65,519 are for permanent, standard message types,
   allocated by IETF Consensus [IANA].  This document defines the range
   of values 1 - 4.  The same Message Type is used for both the request
   and the answer messages, except for type 1.  The Request bit
   distinguishes requests from answers.  See Section 7 for the
   assignment of the namespace in this specification.

   The range of values 65,520 - 65,535 (hexadecimal values 0xfff0 -
   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].

10.2.2.  Flags

   There are 16 bits in the Flags field of the PANA message header.
   This document assigns bit 0 ('R'), 1 ('S'), 2 ('C'), 3 ('A'), 4
   ('P'), and 5 ('I') in Section 6.2.  The remaining bits MUST only be
   assigned via a Standards Action [IANA].

10.3.  AVP Header

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

10.3.1.  AVP Code

   The 16-bit 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 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 and is not assigned by IANA.  This document
   defines the AVP Codes 1-9.  See Section 8.1 through Section 8.9 for
   the assignment of the namespace in this specification.

   AVPs may be allocated following Designated Expert Review with
   Specification Required [IANA] or Standards Action.

   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 AVP 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
   be encouraged instead.

10.3.2.  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').  The remaining
   bits should only be assigned via a Standards Action .

10.4.  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].

10.4.1.  Result-Code AVP Values

   As defined in Section 8.7, the Result-Code AVP (AVP Code 7) defines
   the values 0-2.

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

10.4.2.  Termination-Cause AVP Values

   As defined in Section 8.9, the Termination-Cause AVP (AVP Code 9)
   defines the values 1, 4, and 8.

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

11.  Security Considerations

   The PANA protocol defines a UDP-based EAP encapsulation that runs
   between two IP-enabled nodes.  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] [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 the security of PANA design and
   deployment in a network is the presence of lower-layer security.  In
   the context of this document, lower layers are said to be secure if
   the environment provides adequate protection against spoofing and
   confidentiality based on its operational needs.  For example, DSL and
   cdma2000 networks' lower-layer security is enabled even before
   running the first PANA-based authentication.  In the absence of such
   a preestablished secure channel prior to running PANA, one can be
   created after the successful PANA authentication 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 they are
   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 from spoofing messages to disturb ongoing PANA and EAP
   sessions unless it can also eavesdrop to synchronize with 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/or a session identifier for a
   non-existing session) 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 the initial PANA-Auth-Request
   message that is received from the segment of the access network,
   where only the PaCs are supposed to be connected (i.e., preventing
   PAA impersonation).

   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 MSK exported by
   the EAP method.  This SA is used for generating an AUTH AVP to
   protect the PANA message 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 PANA-Auth-Request
   message that signals a successful authentication (EAP Success) is
   generated.  Starting with these messages, any subsequent PANA message
   can be cryptographically protected until the session gets torn down.

   The lifetime of the PANA SA is set to the PANA session lifetime,
   which is bounded by the authorization lifetime granted by the
   authentication server.  An implementation MAY add a grace 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 the use of
   key-generating EAP methods.  In networks where lower layers are
   already secured, cryptographic protection of PANA messages is not
   necessary.

11.2.  Initial Exchange

   The initial PANA-Auth-Request and PANA-Auth-Answer exchange is
   vulnerable to spoofing attacks as these messages are not
   authenticated and integrity protected.  In order to prevent very
   basic DoS attacks, an adversary should not be able to cause state
   creation by sending PANA-Client-Initiation messages to the PAA.  This
   protection is achieved by allowing the responder (PAA) to create as
   little state as possible in the initial message exchange.  However,
   it is difficult to prevent all spoofing attacks in the initial
   message exchange entirely.

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, [RFC5193] suggests using proper EAP methods
   for particular environments.  Depending on the deployment
   environment, an EAP authentication method that 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.  Cryptographic Keys

   When the EAP method exports an MSK, 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 it takes PANA-based nonce values
   into computation to cryptographically separate itself from the MSK.

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

   The PANA SA lifetime is bounded by the MSK lifetime.  Another
   execution of the EAP method yields a new MSK, and it updates the PANA
   SA, PANA_AUTH_KEY, and key ID.

11.5.  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 SA establishment.  The PANA framework allows
   generation of cryptographic keys from the PANA SA and uses the keys
   with a secure association protocol to enable per-packet cryptographic
   protection, such as link-layer or IPsec-based ciphering [PANA-IPSEC].
   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 can be data origin
   authenticated, replay and integrity protected, and optionally
   encrypted using the cryptographic keys.  How these keys are generated
   from the PANA SA and used with a secure association protocol is
   outside the scope of this document.

11.6.  PAA-to-EP Communication

   The PANA framework allows separation of PAA from EP.  The protocol
   exchange between the PAA and EP for provisioning authorized PaC
   information on the EP must be protected for authentication,
   integrity, and replay protection.

11.7.  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, the latest a
   disconnected client can be detected is 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
   in access phase with the expectation that the peer responds 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 a peer's liveness.
   The PaC or PAA MAY forgo sending an explicit ping request message if
   a recent exchange has already confirmed that the peer is alive.

11.8.  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.

12.  Acknowledgments

   We would like to thank Mark Townsley, 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, Spencer
   Dawkins, Tom Yu, Bernard Aboba, Subir Das, John Vollbrecht, Prakash
   Jayaraman, and all members of the PANA working group for their
   valuable comments on this document.

13.  References

13.1.  Normative References

   [RFC2104]     Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
                 Keyed-Hashing for Message Authentication", RFC 2104,
                 February 1997.

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

   [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, Ed., "Extensible Authentication Protocol
                 (EAP)", RFC 3748, June 2004.

   [RFC4086]     Eastlake, D., 3rd, Schiller, J., and S. Crocker,
                 "Randomness Requirements for Security", BCP 106, RFC
                 4086, June 2005.

   [RFC5234]     Crocker, D., Ed., and P. Overell, "Augmented BNF for
                 Syntax Specifications: ABNF", STD 68, RFC 5234, January
                 2008.

   [RFC5192]     Morand, L., Yegin A., Kumar S., and S. Madanapalli,
                 "DHCP Options for Protocol for Carrying Authentication
                 for Network Access (PANA) Authentication Agents", RFC
                 5192, May 2008.

   [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

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

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

   [RFC4058]     Yegin, A., Ed., 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.

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

   [RFC4595]     Maino, F. and D. Black, "Use of IKEv2 in the Fibre
                 Channel Security Association Management Protocol", RFC
                 4595, July 2006.

   [RFC5193]     Jayaraman, P., Lopez R., Ohba Y., Ed., Parthasarathy,
                 M., and A. Yegin, "Protocol for Carrying Authentication
                 for Network Access (PANA) Framework", RFC 5193, May
                 2008.

   [EAP-KEYING]  Aboba, B., Simon D., and P. Eronen, "Extensible
                 Authentication Protocol (EAP) Key Management
                 Framework", Work in Progress, November 2007.

   [PANA-IPSEC]  Parthasarathy, M., "PANA Enabling IPsec based Access
                 Control", Work in progress, July 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.

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 Siemens Networks
   6000 Connection Drive
   Irving, TX  75039
   USA

   EMail: basavaraj.patil@nsn.com

   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6 Espoo 02600
   Finland

   Phone: +358 (50) 4871445
   EMail: Hannes.Tschofenig@nsn.com
   URI: http://www.tschofenig.priv.at

   Alper E. Yegin
   Samsung
   Istanbul, Turkey

   EMail: a.yegin@partner.samsung.com

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