    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.

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    RFC 5191                          PANA                          May 2008

    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

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          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].

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    RFC 5191                          PANA                          May 2008

       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.

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       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.).

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    RFC 5191                          PANA                          May 2008

       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.

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       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.

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       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.

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       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.

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    RFC 5191                          PANA                          May 2008

       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

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       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

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    RFC 5191                          PANA                          May 2008

       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.

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    RFC 5191                          PANA                          May 2008

       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.

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    RFC 5191                          PANA                          May 2008

    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.

    Forsberg, et al.            Standards Track                    [Page 14]

    RFC 5191                          PANA                          May 2008

    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

    Forsberg, et al.            Standards Track                    [Page 15]

    RFC 5191                          PANA                          May 2008

          *  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.

    Forsberg, et al.            Standards Track                    [Page 16]

    RFC 5191                          PANA                          May 2008

       - 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.

    Forsberg, et al.            Standards Track                    [Page 17]

    RFC 5191                          PANA                          May 2008

             +  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.

    Forsberg, et al.            Standards Track                    [Page 18]

    RFC 5191                          PANA                          May 2008

    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.

    Forsberg, et al.            Standards Track                    [Page 19]

    RFC 5191                          PANA                          May 2008

    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.

    Forsberg, et al.            Standards Track                    [Page 20]

    RFC 5191                          PANA                          May 2008

       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.

    Forsberg, et al.            Standards Track                    [Page 21]

    RFC 5191                          PANA                          May 2008

       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].

    Forsberg, et al.            Standards Track                    [Page 22]

    RFC 5191                          PANA                          May 2008

       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.

    Forsberg, et al.            Standards Track                    [Page 23]

    RFC 5191                          PANA                          May 2008

       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.

    Forsberg, et al.            Standards Track                    [Page 24]

    RFC 5191                          PANA                          May 2008

       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.

    Forsberg, et al.            Standards Track                    [Page 25]

    RFC 5191                          PANA                          May 2008

       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.

    Forsberg, et al.            Standards Track                    [Page 26]

    RFC 5191                          PANA                          May 2008

       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 ]

    Forsberg, et al.            Standards Track                    [Page 27]

    RFC 5191                          PANA                          May 2008

    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 >

    Forsberg, et al.            Standards Track                    [Page 28]

    RFC 5191                          PANA                          May 2008

    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.

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       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.

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    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.

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    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.

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    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

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       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.

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    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

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       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.

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    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].

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    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

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       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.

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       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.

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       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.

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       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.

    Forsberg, et al.            Standards Track                    [Page 42]

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       [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.

    Forsberg, et al.            Standards Track                    [Page 43]

    RFC 5191                          PANA                          May 2008

       [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.

    Forsberg, et al.            Standards Track                    [Page 44]

    RFC 5191                          PANA                          May 2008

    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

    Forsberg, et al.            Standards Track                    [Page 45]

    RFC 5191                          PANA                          May 2008

    Full Copyright Statement

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    Forsberg, et al.            Standards Track                    [Page 46]