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rfc:rfc5191

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.

Forsberg, et al. Standards Track [Page 1] 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

Forsberg, et al. Standards Track [Page 2] RFC 5191 PANA May 2008

    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].

Forsberg, et al. Standards Track [Page 3] 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.

Forsberg, et al. Standards Track [Page 4] RFC 5191 PANA May 2008

 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.).

Forsberg, et al. Standards Track [Page 5] 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.

Forsberg, et al. Standards Track [Page 6] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 7] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 8] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 9] 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

Forsberg, et al. Standards Track [Page 10] RFC 5191 PANA May 2008

 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

Forsberg, et al. Standards Track [Page 11] 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.

Forsberg, et al. Standards Track [Page 12] 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.

Forsberg, et al. Standards Track [Page 13] 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:
  1. 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.
  1. MSK is the master session key generated by the EAP method.
  1. "IETF PANA" is the ASCII code representation of the non-NULL

terminated string (excluding the double quotes around it).

  1. 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.
  1. 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

  1. 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.

Forsberg, et al. Standards Track [Page 29] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 30] RFC 5191 PANA May 2008

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.

Forsberg, et al. Standards Track [Page 31] RFC 5191 PANA May 2008

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.

Forsberg, et al. Standards Track [Page 32] RFC 5191 PANA May 2008

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

Forsberg, et al. Standards Track [Page 33] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 34] RFC 5191 PANA May 2008

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

Forsberg, et al. Standards Track [Page 35] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 36] RFC 5191 PANA May 2008

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].

Forsberg, et al. Standards Track [Page 37] RFC 5191 PANA May 2008

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

Forsberg, et al. Standards Track [Page 38] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 39] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 40] RFC 5191 PANA May 2008

 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.

Forsberg, et al. Standards Track [Page 41] RFC 5191 PANA May 2008

 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] RFC 5191 PANA May 2008

 [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

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
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 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
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 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
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Forsberg, et al. Standards Track [Page 46]

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