PANA Working Group                                                   
   Internet Draft                                           D. Forsberg 
                                                                   Nokia 
                                                                 Y. Ohba 
                                                                 Toshiba 
                                                                B. Patil 
                                                                   Nokia 
                                                           H. Tschofenig 
                                                                 Siemens 
                                                                A. Yegin 
                                                         DoCoMo USA Labs 
   Document: draft-ietf-pana-pana-01.txt                                
   Expires: December 2003                                     June 2003 
    
    
      Protocol for Carrying Authentication for Network Access (PANA) 
                       <draft-ietf-pana-pana-01.txt> 
    
    
Status of this Memo 
 
    
   This document is an Internet-Draft and is subject to all provisions  
   of Section 10 of RFC2026.  
    
   Internet-Drafts are working documents of the Internet Engineering  
   Task Force (IETF), its areas, and its working groups. Note that  
   other groups may also distribute working documents as Internet- 
   Drafts.  
    
   Internet-Drafts are draft documents valid for a maximum of six  
   months and may be updated, replaced, or obsoleted by other documents  
   at any time. It is inappropriate to use Internet-Drafts as reference  
   material or to cite them other than as "work in progress."  
    
   The list of current Internet-Drafts can be accessed at  
   http://www.ietf.org/1id-abstracts.html  
    
   The list of Internet-Draft Shadow Directories can be accessed at  
   http://www.ietf.org/shadow.html 










 
 
Tschofenig et al.      Expires - December 2003               [Page 1] 
                                 PANA                        June 2003 
 
 
Abstract 
    
   This document defines the Protocol for Carrying Authentication for 
   Network Access (PANA), a link-layer agnostic transport for 
   Extensible Authentication Protocol (EAP) to enable network access 
   authentication between clients and access networks. PANA can carry 
   any authentication method that can be specified as an EAP method, 
   and can be used on any link that can carry IP. PANA covers the 
   client-to-network access authentication part of an overall secure 
   network access framework, which additionally includes other 
   protocols and mechanisms for service provisioning, access control as 
   a result of initial authentication, and accounting. 
 
Table of Contents 
    
   1  Introduction..................................................3 
   2  Terminology...................................................4 
   3  Protocol Overview.............................................5 
   4  Protocol Details..............................................6 
      4.1  Common Processing Rules.................................6 
      4.2  Discovery and Initial Handshake Phase..................10 
      4.3  Authentication Phase...................................12 
      4.4  Re-authentication......................................14 
      4.5  Termination Phase......................................16 
      4.6  Illustration of a Complete Message Sequence............16 
      4.7  Device ID choice.......................................18 
      4.8  Refresh Interval Negotiation...........................18 
      4.9  Mobility Handling......................................19 
      4.10   Event Notification...................................19 
      4.11   PaC Implications.....................................20 
      4.12   PAA Implications.....................................20 
   5  PANA Security Association Establishment......................20 
   6  Authentication Method Choice.................................21 
   7  Filter Rule Installation.....................................21 
   8  Data Traffic Protection......................................22 
   9  Message Formats..............................................23 
      9.1  PANA Header............................................23 
      9.2  AVP Header.............................................24 
      9.3  PANA Messages..........................................26 
      9.4  AVPs in PANA...........................................29 
      9.5  AVP Occurrence Table...................................32 
   10   Security Considerations...................................33 
   11   Open Issues...............................................39 
   12   Acknowledgments...........................................39 
   13   References................................................39 
   Change History..................................................42 
   Appendix A.  Adding sequence number to PANA for carrying EAP....43 
   Full Copyright Statement........................................52 
    
 
 
Tschofenig et al.      Expires - December 2003               [Page 2] 
                                 PANA                        June 2003 
 
 
1  Introduction 
    
   Providing secure network access service requires access control 
   based on the authentication and authorization of the clients and the 
   access networks. Initial and subsequent client-to-network 
   authentication provides parameters that are needed to police the 
   traffic flow through the enforcement points. A protocol is needed to 
   carry authentication methods between the client and the access 
   network. IETF PANA Working Group has been chartered with the goal 
   of designing a network-layer access authentication protocol. 
    
   Link-layer authentication mechanisms are used as enablers of secure 
   network access. A higher-layer authentication is deemed necessary 
   when link-layer authentication mechanisms are either not available 
   for lack of technology or deployment difficulties, or not able to 
   meet the overall requirements, or when multi-layer (e.g., link-layer 
   and network-layer) authentication is needed. Currently there is no 
   standard network-layer solution for authenticating clients for 
   network access. In the absence of such a solution, some inadequate 
   standards-based solutions are deployed or non-standard ad-hoc 
   solutions are invented. [USAGE] describes the problem statement in 
   detail. 
    
   Scope of this working group is identified as designing a link-layer 
   agnostic transport for network access authentication methods. PANA 
   Working Group has identified EAP [RFC2284] as the payload for this 
   protocol and carrier for authentication methods. In other words, 
   PANA will carry EAP which can carry various authentication methods. 
   By the virtue of enabling transport of EAP above IP, any 
   authentication method that can be carried as an EAP method is 
   made available to PANA and hence to any link-layer technology. There 
   is a clear division of labor between PANA, EAP and EAP methods. 
   Defining new authentication methods, or deriving/distributing keys 
   is outside the scope of PANA. Providing a secure channel that 
   protects EAP and EAP methods against eavesdropping and spoofing is 
   not an objective of the PANA design. 
    
   While PANA is a fundamental part of a complete secure network access 
   solution, its responsibility is limited to authentication and 
   authorization of the client and the network. Providing access 
   control is outside the scope of PANA. A separate provisioning 
   protocol is needed for passing filtering  information to access 
   control nodes in the network. Additionally, mechanisms to provide 
   data traffic protection in terms of authentication, integrity and 
   replay protection, and encryption are outside the scope as well. 
    
   Various environments and usage models for PANA are identified in the 
   [USAGE] Internet-Draft. Potential security threats for network-layer 
   access authentication protocol is discussed in [THREATS] draft. 
 
 
Tschofenig et al.      Expires - December 2003               [Page 3] 
                                 PANA                        June 2003 
 
 
   These two drafts have been essential in defining the requirements 
   [PY+02] on the PANA protocol. Note that some of these requirements 
   are imposed by the chosen payload, EAP [RFC2284]. 
    
   This Internet-Draft makes an attempt for defining the PANA protocol 
   based on the other drafts discussed above. Special care has been 
   given to ensure the currently stated scope is observed and to keep 
   the protocol as simple as possible. The current state of this draft 
   is not complete, but it should be regarded as a work in progress. 
   The authors made effort to capture the common understanding 
   developed within the working group as much as possible. The design 
   choices being made in this draft should not be considered as cast in 
   stone. 
    
2  Terminology 
    
   This section describes some terms introduced in this document:  
 
   PANA Session: 
         
        PANA session is defined as the exchange of messages between the 
        PANA Client (PaC) and the PANA Authentication Agent (PAA) to 
        authenticate a user (PaC) for network access. If the 
        authentication is unsuccessful, the session is terminated. The 
        session is considered as active until there is a disconnect 
        indication by the PaC or the PAA terminates it.  
    
   Session Identifier: 
       
        This identifier is used to uniquely identify a PANA session on 
        the PAA and PaC. It is included in PANA messages to bind the 
        message to a specific PANA session. 
 
   PANA Disconnect Indication: 
      
        PANA session termination with explicit notification from a PaC 
        sent to the PAA. The PDI also includes the session identifier. 
    
   PANA Session Revocation: 
    
        PANA session termination with explicit notification sent from 
        the PAA to the PaC. The PSR includes the session identifier. 
    
   PANA Security Association: 
    
        The representation of the trust relation between the PaC and 
        the PAA that is created at the end of the authentication phase 
        (PH2). This security association includes the device identifier 
        of the peer, and a shared key when available. 
 
 
Tschofenig et al.      Expires - December 2003               [Page 4] 
                                 PANA                        June 2003 
 
 
         
         
   The definition of the terms PANA Client (PaC), PANA Authentication 
   Agent (PAA), Enforcement Point (EP) and Device Identifier (DI) can 
   be found in [PY+02]. 
    
3  Protocol Overview 
    
   The PANA protocol involves two functional entities namely the PaC 
   and the PAA. The EP, mentioned in the context with PANA, is a 
   logical entity. There is, however, the option that the EP is not 
   physically co-located with the PAA. In case that the PAA and the EP 
   are co-located only an API is required instead of a separate 
   protocol. In the case where the PAA is separated from the EP, a 
   separate protocol will be used between the PAA and the EP for 
   managing access control. The protocol and messaging between the PAA 
   and EP for access authorization is outside the scope of this draft 
   and will be dealt separately. 
    
   The PANA protocol (PaC<->PAA) resides above the transport layer and 
   the details are explained in Section 4.2. Although this document 
   describes the interaction with a number of entities and with other 
   protocol which enable network access authentication; the PANA 
   protocol itself is executed between the PaC and the PAA. 
    
   The protocol has three primary functions: 
    
   1. The PaC discovering the address of the PAA 
   2. The transport of EAP payloads between the PaC and the PAA 
   3. Access authorization by the PAA to the EP [Note that this aspect 
   is outside the scope of the PANA protocol.] 
    
   The placement of the entities used in PANA largely depend on a 
   certain architecture. The PAA may optionally interact with a AAA 
   backend to authenticate the user (PaC). And in the case where the 
   PAA and EP are co-located, step 3 mentioned above may not require a 
   separate protocol. Figure 1 illustrates the interactions in a 
   simplified manner:  
    
        PaC                   EP            PAA           AAA 
        ---                   ---           ---           --- 
    
          PAA Discovery 
        <---------------------o-----------------> (1) 
      |               PANA_REQUEST 
      | ----------------------------------------> 
      |                          AAA interaction 
      |(2)                                      -----------> 
      |                                         <----------- 
 
 
Tschofenig et al.      Expires - December 2003               [Page 5] 
                                 PANA                        June 2003 
 
 
      |         PANA_RESPONSE 
      | <--------------------------------------- 
      | 
                                Authorization 
                              <-----------------  (3) 
    
                          Figure 1: PANA Protocol 
    
   The details of each of these aspects of the protocol are described 
   in section 4 of this document. PANA supports authentication of a PaC 
   using various EAP methods. The EAP method used depends on the level 
   of security required for the EAP messaging itself. PANA does not 
   secure the data traffic itself. However, EAP methods that enable key 
   exchange may allow other protocols to be bootstrapped for securing 
   the data traffic.   
    
   From a state machine aspect, PANA protocol consists of three phases 
    
   1. Discovery and initial handshake phase 
   2. Authentication phase 
   3. Termination phase 
       
   In the first phase, an IP address of PAA is discovered and a PANA 
   session is established between PaC and PAA.  EAP messages are 
   exchanged and a PANA SA is established in the second phase. The 
   established PANA session as well as a PANA SA is deleted in the 
   third phase. 
    
4  Protocol Details 
    
4.1 Common Processing Rules 
    
4.1.1 Payload Encoding 
    
   The payload of any PANA message consists of zero or more AVPs 
   (Attribute Value Pairs).  A brief description of the AVPs defined in 
   this document is listed below: 
    
   - Cookie AVP: contains a random value that is used for making 
     initial handshake robust against blind resource consumption DoS 
     attacks. 
    
   - Protection-Cap. AVP: contains information which protection should 
   be initiated after the PANA exchange (e.g. link-layer or network 
   layer protection). 
   - Device-Id AVP: contains a device identifier of the sender of the 
     message. A device identifier is represented as a pair of device 
     identifier type and device identifier value.  Either a layer-2 
     address or an IP address is used for the device identifier value. 
 
 
Tschofenig et al.      Expires - December 2003               [Page 6] 
                                 PANA                        June 2003 
 
 
    
   - EAP AVP: contains an EAP PDU. 
    
   - MAC AVP: contains a Message Authentication Code that protects a 
     PANA message PDU. 
    
   - Termination-Cause AVP: contains the reason of session termination. 
    
   - Result-Code AVP: contains information about the protocol execution 
   results.  
    
   - Session-Id AVP: contains the session identifier value.  
    
    
4.1.2 Transport Layer Protocol 
    
   PANA uses UDP as its transport layer protocol.  The UDP port number 
   is TBD.  All messages except for PANA-PAA-Discover are always 
   unicast.  PaC MAY use unspecified IP address for communicating with 
   PAA.   
    
4.1.3 Fragmentation 
    
   PANA does not provide fragmentation of PANA messages.  Instead, it 
   relies on fragmentation provided by EAP methods and IP layer when 
   needed. 
    
4.1.4 Sequence Number and Retransmission 
    
   PANA uses sequence numbers to provide ordered delivery of EAP 
   messages. The design involves use of two sequence numbers to prevent 
   some of the DoS attacks on the sequencing scheme.  Every PANA packet 
   include one transmitted sequence number (tseq) and one received 
   sequence number (rseq) in the PANA header.  See Appendix for 
   detailed explanation on why two sequence numbers are needed. 
    
   The two sequence number fields have the same length of N (TBD: 
   possibly 32) bits and appear in PANA header.  tseq starts from 
   initial sequence number (ISN) and is monotonically increased by 1.  
   The serial number arithmetic defined in [RFC1982] is used for 
   sequence number operation.  The ISNs are exchanged between PaC and 
   PAA during the discovery and initial handshake phase (see section 
   "Discovery and Initial Handshake Phase").  The rules that govern the 
   sequence numbers in other phases are described as follows. 
    
   o When a message is sent, a new sequence number is placed on the 
   tseq field of message regardless of whether it is sent as a result 
   of retransmission or not.  When a message is sent, rseq is copied 
   from the tseq field of the last accepted message. 
 
 
Tschofenig et al.      Expires - December 2003               [Page 7] 
                                 PANA                        June 2003 
 
 
    
   o When a message is received, it is considered as valid in terms of 
   sequence numbers if and only if (i) its tseq is greater than the  
   tseq of the last accepted message and (ii) its rseq falls in the 
   range between the tseq of the last acknowledged message + 1 and the 
   tseq of the last transmitted message. 
    
   PANA relies on EAP-layer retransmission for retransmitting EAP 
   Request based on timer.  Other PANA layer messages that require a 
   response from the communicating peer are retransmitted based on 
   timer at PANA-layer until a response is received (in which case the 
   retransmission timer is stopped) or the number of retransmission 
   reaches the maximum value (in which case the PANA session MUST be 
   deleted immediately).  For PANA-layer retransmission, the 
   retransmission timer SHOULD be calculated as described in [RFC2988] 
   to provide congestion control (TBD: default timer and maximum 
   retransmission count suggestions). 
    
4.1.5 PANA Security Association 
    
   A PANA SA is created as an attribute of a PANA session when EAP 
   authentication succeeds with a creation of a Master Session Key 
   (MSK) [RFC2284bis].  A PANA SA is not created when the PANA 
   authentication fails or no MSK is produced by any EAP authentication 
   method. In the case where two EAP authentications are performed in a 
   sequence in a single PANA authentication, it is possible that two 
   MSKs are derived. If this happens, the PANA SA MUST be bound to the 
   MSK derived from the first EAP authentication.  When a new MSK is 
   derived as a result of EAP-based re-authentication, any key derived 
   from the old MSK MUST be updated to a new one that is derived from 
   the new MSK. 
    
   The created PANA SA is deleted when the corresponding PANA session 
   is deleted.  The lifetime of the PANA SA is the same as the lifetime 
   of the PANA session for simplicity. 
    
   PANA SA attributes as well as PANA session attributes are listed 
   below: 
    
    PANA Session attributes: 
      - Session-Id 
      - Device-Id of PaC 
      - Device-Id of PAA 
      - Initial tseq of PaC (ISN_pac) 
      - Initial tseq of PAA (ISN_paa) 
      - Last transmitted tseq value 
      - Last received rseq value 
      - Last transmitted message payload 
      - Retransmission interval 
 
 
Tschofenig et al.      Expires - December 2003               [Page 8] 
                                 PANA                        June 2003 
 
 
      - Session lifetime 
      - Protection-Capability 
      - PANA SA attributes: 
          + MSK 
          + PANA_MAC_Key 
    
   The PANA_MAC_Key is used to integrity protect PANA messages and 
   derived from the MSK in the following way: 
    
      PANA_MAC_KEY = The first N-bit of 
                     HMAC_SHA1(MSK, ISN_pac | ISN_paa | Session-ID) 
   where the value of N depends on the integrity protection  algorithm 
   in use, i.e., N=128 for HMAC-MD5 and N=160 for HMAC-SHA1. 
    
   The length of MSK MUST be N-bit or longer.  See section 4.1.6 for 
   the detailed usage of the PANA_MAC_Key. 
 
4.1.6 Message Authentication Code 
    
   A PANA message can contain a MAC (Message Authentication Code) AVP 
   for cryptographically protecting the message. 
    
   When a MAC AVP is included in a PANA message, the value field of the 
   MAC AVP is calculated by using the PANA_MAC_Key in the following 
   way: 
    
     MAC AVP value = HMAC_SHA1(PANA_MAC_Key, PANA_PDU) 
    
   where PANA_PDU is the PANA message including the PANA header, with 
   the MAC AVP value field first initialized to 0.  
    
4.1.7 Message Validity Check 
    
   When a PANA message is received, the message is considered to be 
   invalid at least when one of the following conditions are not met: 
    
   o Each field in the message header contains a valid value including 
   sequence number, message length, message type, version number, 
   flags, etc. 
    
   o When a device identifier of the communication peer is bound to the 
   PANA session, it matches the device identifier carried in MAC and/or 
   IP header(s). 
    
   o The message type is one of the expected types in the current 
   state. 
    
   o The message payload contains a valid set of AVPs allowed for the 

 
 
Tschofenig et al.      Expires - December 2003               [Page 9] 
                                 PANA                        June 2003 
 
 
   message type and there is no missing AVP that needs to be included 
   in the payload. 
    
   o Each AVP is decoded correctly. 
    
   o When a MAC AVP is included, the AVP value matches the MAC value 
   computed against the received message. 
    
   o When a Device-Id AVP is included, the AVP is valid if the device 
   identifier type contained in the AVP matches the expected one (this 
   check is for PAA only) and the device identifier value contained in 
   the AVP matches the value extracted from the lower-layer 
   encapsulation header corresponding to the device identifier type 
   contained in the AVP. 
    
   Invalid messages MUST be discarded in order to provide robustness 
   against DoS attacks and an unprotected.  (TBD: in addition, a 
   non-acknowledged error notification message MAY be returned to the 
   sender.) 
    
4.2 Discovery and Initial Handshake Phase 
    
   When a PaC attaches to a network, and knows that it has to discover 
   PAA for PANA, it can send a PANA-PAA-Discover message to a well-
   known link local multicast address (TBD) and UDP port (TBD). The 
   source address is set to the unspecified IP address if the PaC has 
   not configured an address yet. PANA PAA discovery assumes that PaC 
   and PAA are one hop away from each other. If PaC knows the IP 
   address of the PAA (some pre-configuration), it can unicast the PANA 
   discovery message to that address. PAA answers to the PANA-PAA-
   Discover message with a PANA-Start-Request message. 
    
   When the PAA receives such a request, or upon receiving some lower 
   layer indications of a new PaC, PAA can unicast a PANA-Start-Request 
   message. The destination address may be unspecified IP address, but 
   the L2 destination would be a unicast address (something for the 
   implementations to deal with).  
    
   There can be multiple PAAs on the link. The result does not depend 
   on which PAA PaC chooses. By default PaC chooses the PAA that sent 
   the first response. 
    
   PaC may also choose to start sending packets before getting 
   authenticated. In that case, the network should detect this and send 
   an unsolicited PANA-Start-Request message to PaC. EP is the node 
   that can detect such activity. If EP and PAA are co-located, then an 
   internal mechanism (e.g. API) between the EP module and the PAA 
   module on the same host can prompt PAA to start PANA. In case they 
   are separate, there needs to an explicit message to prompt PAA. Upon 
 
 
Tschofenig et al.      Expires - December 2003              [Page 10] 
                                 PANA                        June 2003 
 
 
   detecting the need to authenticate a client, EP can send a PANA-PAA-
   Discover message to the PAA on behalf of the PaC.  This message 
   carries a device identifier of the PaC in a Device-ID AVP. So that, 
   the PAA can send the unsolicited PANA-Start-Request message directly 
   to the PaC.  If the link between the EP and PAA is not secure, the 
   PANA-PAA-Discover message sent from the EP to the PAA MUST be 
   protected by using.  
    
   A PANA-Start-Request message contains a cookie carried in a Cookie 
   AVP in the payload, respectively.  The rseq field of the header is 
   set to zero (0).  The tseq field of the header contains the initial 
   sequence number.  The cookie is used for preventing the PAA from 
   resource consumption DoS attacks by blind attackers.  The cookie is 
   computed in such a way as not to require any saved per-session state 
   to recognize its valid cookie when a particular message sent by the 
   PaC in response to the PANA-Start-Request message arrives.  The 
   exact algorithms and syntax used for generating cookies does not 
   affect interoperability and hence is not specified here.  An example 
   algorithm is described below. 
    
    
   Cookie = 
     <secret-version> | HMAC_SHA1( <Device-Id of PaC> | <secret> ) 
    
   where <secret> is a randomly generated secret known only to  the 
   PAA, <secret-version> is an index used for choosing the secret for 
   generating the cookie and '|' indicates concatenation.  The secret-
   version should be changed frequently enough to prevent replay 
   attacks. The secret key is locally known to the PAA only and valid 
   for a certain time frame. 
 
   When a PaC receives the PANA-Start-Request message in response to 
   the PANA-PAA-Discover message, it responds with a PANA-Start-Answer 
   message. The PANA-Start-Answer message contains the initial sequence 
   numbers in the tseq and rseq fields of the PANA header, a copy of 
   the received Cookie as the PANA payload. 
    
   When the PAA receives the PANA-Start-Request message from the PaC, 
   it verifies the cookie.  The cookie is considered as valid if the 
   received cookie has the expected value.  If the computed cookie is 
   valid, the protocol enters the authentication phase.  Otherwise, it 
   MUST silently discard the received message. 
     
   The PANA-Start-Request/Answer exchange is needed before entering 
   authentication phase even when the PaC is pre-configured with PAAs 
   IP address and the PANA-PAA-Discover message is unicast. 
    


 
 
Tschofenig et al.      Expires - December 2003              [Page 11] 
                                 PANA                        June 2003 
 
 
   A PANA-Start-Request message is never retransmitted. A PANA-Start-
   Answer message is retransmitted based on timer in the same manner as 
   other messages retransmitted at PANA-layer. 
    
    
   PaC      PAA         Message 
   ------------------------------------------------------ 
      ----->            PANA-PAA-Discover(0,0) 
      <-----            PANA-Start-Request(x,0)[Cookie] 
      ----->            PANA-Start-Answer(x,y)[ Cookie] 
                        (continued to authentication phase) 
    
                 (PANA-PAA-Discover sent by PaC) 
   Figure 2: Example Sequence for Discovery and Initial Handshake Phase 
    
    
   PaC   EP      PAA    Message 
   ------------------------------------------------------ 
    ---->o              (Data packet arrival or L2 trigger) 
          ------>       PANA-PAA-Discover(0,0)[Device-Id] 
    <------------       PANA-Start-Request(x,0)[ Cookie] 
    ------------>       PANA-Start-Answer(y,x)[ Cookie] 
                        (continued to authentication phase) 
    
                 (PANA-PAA-Discover sent by EP) 
   Figure 3: Example Sequence for Discovery and Initial Handshake Phase 
 
4.3 Authentication Phase 
    
   The main task in authentication phase is to carry EAP messages 
   between PaC and PAA. All EAP messages except for EAP Success/Failure 
   messages are carried in the PANA-Auth-Request/PANA-Auth-Answer 
   messages.  When an EAP Success/Failure message is sent from a PAA, 
   the message is carried in the PANA-Bind-Request message.  The PANA-
   Bind-Request message is acknowledged with a PANA-Bind-Answer.  It is 
   possible to carry multiple EAP sequences in a single PANA sequence.  
    
   A single PANA session can enable more than one EAP authentication. 
   This is used to satisfy the separate NAP and ISP authentications 
   scenario.  Each EAP authentication is delineated from the subsequent 
   one.  The F-flag in the PANA header indicates if this was the final 
   authentication from sender's perspective.  If the PAA enables two 
   separate authentication, it should not set the F-flag in after the 
   first EAP method.  This indicates PAA's willingness to offer another 
   authentication method for NAP-ISP separation.  PaC can respond with 
   the F-flag unset, indicating PaC's willingness to go through a 
   second authentication method.  The PaC can optionally decline by 
   setting the F-flag, and this concludes the PANA authentication.  If 
   the PAA does not offer two levels of authentication, then it sets 
 
 
Tschofenig et al.      Expires - December 2003              [Page 12] 
                                 PANA                        June 2003 
 
 
   the F-flag even at the end of first EAP exchange.  In that case the 
   PaC has no other option but to set the F-flag to mark the end of 
   PANA authentication. 
    
   Currently, use of multiple EAP methods in PANA is designed only for 
   NAP-ISP authentication separation.  It is not for arbitrary EAP 
   method sequencing, or giving the PaC another chance when an 
   authentication method fails.  The NAP and ISP authentication are 
   considered completely independent.  Presence or success of one 
   should not effect the other. Making a decision based on the success 
   or failure of each authentication is a network policy issue.  PANA 
   signals only the result of the immediately preceding EAP 
   authentication method. 
    
   When an EAP method that is capable of deriving keys is used during 
   the authentication phase and the keys are successfully derived all 
   subsequent PANA messages MUST contain a MAC AVP.  The PANA-Bind-
   Request and the PANA-Bind-Answer message exchange is also used for 
   binding device identifiers of the PaC and the PAA to the PANA SA.  
   To achieve this, the PANA-Bind-Request and the PANA-Bind-Answer 
   SHOULD contain a device identifier of the PAA and the PaC, 
   respectively, in a Device-Id AVP.  The PaC MUST use the same type of 
   device identifier as contained in the PANA-Bind-Request message.   
   The PANA-Bind-Request message MAY also contain a Protection-Capability 
   AVP to indicate if link-layer or network-layer ciphering should be 
   initiated after PANA.  No link layer or network layer specific 
   information is included in the Protection-Capability AVP. When the 
   information is preconfigured on the PaC and the PAA this AVP can be 
   omitted. It is assumed that at least PAA is aware of the security 
   capabilities of the access network. The PANA protocol does not 
   specify how the PANA SA and the Protection-Capability AVP will be 
   used to provide per-packet protection for data traffic. 
    
   PANA-Bind-Request and PANA-Bind-Answer messages MUST be 
   retransmitted based on the retransmission rule described in Appendix 
   A. 
    












 
 
Tschofenig et al.      Expires - December 2003              [Page 13] 
                                 PANA                        June 2003 
 
 
    
   PaC      PAA  Message(tseq,rseq)[AVPs] 
   ------------------------------------------------- 
                 (continued from discovery and initial handshake phase) 
      <-----     PANA-Auth-Request(x+1,y)[EAP{Request}] 
      ----->     PANA-Auth-Answer(y+1,x+1)[EAP{Response}] 
        . 
        . 
      <-----     PANA-Auth-Request (x+2,y+1)[EAP{Request}] 
      ----->     PANA-Auth-Answer (y+2,x+2)[EAP{Response}] 
      <-----     PANA-Bind-Request(x+3,y+2)                // F-flag 
   set 
                   [EAP{Success}, Device-Id, Protection-Cap., MAC]  
      ----->     PANA-Bind-Answer(y+3,x+3) 
                   [Device-Id, Protection-Cap., MAC]  // F-flag set 
    
            Figure 4: Example Sequence in Authentication Phase 
    
4.4 Re-authentication 
    
   There are two types of re-authentication supported by PANA.   
    
   The first type of re-authentication is based on EAP by entering an 
   authentication phase.  In this case, some or all message exchanges 
   for discovery and initial handshake phase MAY be omitted in the 
   following way.  When a PaC initiates EAP-based re-authentication, it 
   sends a PANA-PAA-Discovery message to the PAA.  If the PAA already 
   has an established PANA session for the PaC with a device identifier 
   that matches the one extracted from the MAC header and/or IP header 
   of the PANA-PAA-Discover message, it sends a PANA-Auth-Request 
   message with the session identifier for that PANA session to start 
   an authentication phase.  When the PAA initiates EAP-based re-
   authentication, it sends a PANA-Auth-Request message with the 
   session identifier for the PaC to enter an authentication phase.  In 
   both cases, the tseq and rseq values are inheritated from the 
   previous (re-)authentication.  For any EAP-based re-authentication, 
   if there is an established PANA SA, PANA-Auth-Request and PANA-Auth-
   Answer messages MAY be protected by adding a MAC AVP to each 
   message. 
    
   The second type of re-authentication is based on a single protected 
   message exchange without entering the authentication phase. 
   PANA-Reauth-Request and PANA-Reauth-Answer messages are used for 
   this purpose.  If there is an established PANA SA, both the PaC and 
   the PAA are allowed to send a PANA-Reauth-Request message to the 
   communicating peer whenever it needs to make sure the availability 
   of the PANA SA on the peer and expect the peer to return a PANA-
   Reauth-Answer message.  Both PANA-Reauth-Request/ PANA-Reauth-Answer 
   messages MUST be protected with a MAC AVP. 
 
 
Tschofenig et al.      Expires - December 2003              [Page 14] 
                                 PANA                        June 2003 
 
 
    
   Implementations MUST limit the rate of performing re-authentication 
   for both types of re-authentication. 
    













































 
 
Tschofenig et al.      Expires - December 2003              [Page 15] 
                                 PANA                        June 2003 
 
 
    
   PaC      PAA     Message(tseq,rseq)[AVPs] 
   ------------------------------------------------------ 
      ----->        PANA-Reauth-Request(q,p)[MAC] 
      <-----        PANA-Reauth-Answer(p+1,q)[MAC] 
    
   Figure 5: Example Sequence for PaC-initiated Re-authentication 
    
    
    
   PaC      PAA     Message(tseq,rseq)[AVPs] 
   ------------------------------------------------------ 
      <-----        PANA-Reauth-Request(p,q)[MAC] 
      ----->        PANA-Reauth-Answer(q+1,p)[MAC] 
    
   Figure 6: Example Sequence for PAA-initiated Re-authentication 
    
4.5 Termination Phase 
    
   A procedure for explicitly terminating a PANA session can be 
   initiated either from PaC (i.e., disconnect indication) or from PAA 
   (i.e., session revocation).  The PANA-Termination-Request  and the 
   PANA-Termination-Answer message exchanges are used for 
   disconnect indication and session revocation procedures.  
    
   The reason for termination is indicated in the Termination-Cause 
   AVP. When there is an established PANA SA established between the 
   PaC and the PAA, all messages exchanged during the termination phase 
   MUST be protected with a MAC AVP.  When the sender of the PANA-
   Termination-Request  receives a valid acknowledgment, all states 
   maintained for the PANA session MUST be deleted immediately. 
    
    
   PaC      PAA     Message(tseq,rseq)[AVPs] 
   ------------------------------------------------------ 
      ----->        PANA-Termination-Request(q,p)[MAC] 
      <-----        PANA-Termination-Answer(p+1,q)[MAC] 
    
   Figure 7: Example Sequence for Session Termination 
    
    
4.6 Illustration of a Complete Message Sequence 
    
   A complete PANA message sequence is illustrated in Figure 8.  The 
   example assumes the following scenario: 
    
   - PaC multicasts PANA-PAA-Discover message 
    
   - The ISNs used by the PAA and the PaC are x and y, respectively. 
 
 
Tschofenig et al.      Expires - December 2003              [Page 16] 
                                 PANA                        June 2003 
 
 
    
   - A single EAP sequence is used in authentication phase. 
    
   - An EAP authentication method with a single round trip is used in 
   the EAP sequence. 
    
   - The EAP authentication method derives keys. The PANA SA is 
   established based on the unique and fresh session key provided by 
   the EAP method. 
    
   - After PANA SA is established, all messages are integrity and 
   replay protected with the MAC AVP. 
    
   - Re-authentication based on the PANA-Reauth-Request/ PANA-Reauth-
   Answer exchange is performed. 
    
   - The PANA session is terminated as a result of the PANA-
   Termination-Request indication from the PaC. 
    
    
   PaC      PAA  Message(tseq,rseq)[AVPs] 
   ----------------------------------------------------- 
   // Discovery and initial handshake phase 
      ----->     PANA-PAA-Discover (0,0) 
      <-----     PANA-Start-Request (x,0)[Cookie] 
      ----->     PANA-Start-Request-Answer (y,x)[Cookie] 
    
   // Authentication phase 
      <-----     PANA-Auth-Request(x+1,y)[EAP] 
      ----->     PANA-Auth-Answer(y+1,x+1)[EAP] 
      <-----     PANA-Auth-Request(x+2,y+1)[EAP] 
      ----->     PANA-Auth-Answer(y+2,x+2)[EAP] 
      <-----     PANA-Bind-Request(x+3,y+2)        // F-flag set 
                   [EAP, Device-Id, Data-Protection, MAC]  
    
      ----->     PANA-Bind-Answer(y+3,x+3)         // F-flag set 
                   [Device-Id, Data-Protection, MAC]  
    
   // Re-authentication 
      <-----     PANA-Reauth-Request (x+4,y+3)[MAC] 
      ----->     PANA-Reauth-Answer (y+4,x+4)[MAC] 
    
   // Termination phase 
      ----->     PANA-Termination-Request(y+5,x+4)[MAC] 
      <-----     PANA-Termination-Answer (x+5,y+5)[MAC] 
    
                   Figure 8: A Complete Message Sequence 
    

 
 
Tschofenig et al.      Expires - December 2003              [Page 17] 
                                 PANA                        June 2003 
 
 
4.7 Device ID choice 
    
   PaC has to pick a device identifier to provide for PANA exchanges.  
   In this version of the specification, device ID is considered to be 
   fixed.  Future versions might enable changing it during a PANA 
   session. 
    
   A PaC will configure an IP address before PANA if it can. It might 
   either have a pre-configured IP address, or have to obtain one via 
   dynamic methods such as DHCP or stateless address autoconfiguration. 
   Dynamic methods may or may not succeed depending on the local 
   security policy.  In networks where the PaCs need to use PANA prior 
   to address configuration, EPs will detect the PaCs attempt to get IP 
   address and help PAA to initiate authentication. 
    
   Either an IP address or link-layer address should be used as device 
   DI at any time.  The only case an IP address should be used as 
   device ID is when IPsec will be used for protecting data traffic 
   after initial authentication.  Any other time a link-layer address 
   can be used by both PAA and PaC as device ID. It is assumed that PAA 
   knows the security mechanisms being provided or required on the 
   access network (e.g., physical security, link-layer ciphers prior to 
   PANA, link-layer ciphers enabled after PANA, IPsec).  When IPsec is 
   the choice of data ciphering, PAA should provide its IP address as 
   device ID, and expect the PaC to provide its IP address if it has 
   one.  In all other cases, link-layer addresses can be provided from 
   both sides.  
    
   When IPsec ciphering is used but the PaC uses an unspecified IP 
   address in the authentication phase, it MUST use its MAC address for 
   the device identifier until the PaC is configured with a specified 
   IP address that is used for IPsec ciphering. Once such a specified 
   IP address is configured, the PaC MUST update the device identifier 
   registered on the PAA from the MAC address to the IP address by 
   initiating a PANA-Reauth-Request/PANA-Reauth-Answer exchange in 
   which the IP address of the PaC is contained in the Device-Id AVP 
   contained in the PANA-Reauth-Request message sent from the PaC. 
    
4.8 Refresh Interval Negotiation 
    
   The authentication phase also determines the PANA session lifetime 
   when authorization succeeds. The Session-Lifetime AVP (to be 
   defined, Code XXX) is used to determine the valid lifetime of PANA 
   session. This AVP MUST NOT be included in any message other than the 
   PANA-Bind-Request and PANA-Bind-Anser message. It MUST be ignored 
   when received in other messages or the authorization result is a 
   failure. 
    

 
 
Tschofenig et al.      Expires - December 2003              [Page 18] 
                                 PANA                        June 2003 
 
 
   This AVP carries the maximum session lifetime offered by the network 
   when included in the PANA-Bind-Request sent by the PAA. If it is 
   omitted, or contains the value 0xFFFFFFFF, this means the session 
   lifetime is infinity. This AVP carries the requested session 
   lifetime when it is sent by the PaC. If requested session lifetime 
   is greater than the offered lifetime, then it is ignored and the 
   offered lifetime becomes the session lifetime. The requested 
   lifetime becomes the session lifetime if it is less than or equal to 
   the offered lifetime. The PaC MUST perform a PANA authentication (by 
   sending a PANA-Auth-Request andnot a PANA-Reauth-Request) before the 
   session lifetime expires. Failure to do so yields in PaC losing 
   network access. 
 
4.9 Mobility Handling 
 
   If PaC wants to resume an ongoing PANA session after connecting to 
   another link in the same access network, it can send the unexpired 
   PANA session id in its PANA-Start-Request message. In the absence of 
   session id AVP in this message, PAA can assume this is a fresh 
   session and assigns a new session ID in the first PANA-Auth-Request 
   message. 
    
   If PAA receives a session id in the PANA-Start-Request message, and 
   it is configured to enable fast re-authentication, it SHOULD 
   retrieve the PANA SA from the previous PAA of the PaC. Determining 
   the previous PAA of the PaC by using the PANA session id is outside 
   the scope of this protocol. A possible solution is to embed thePAA 
   identifier into the message. Furthermore, the mechanism required to 
   retrieve the PANA SA from the previous PAA is outside the scope of 
   PANA protocol. Seamoby Context Transfer Protocol [CTP] might be 
   useful here. 
    
   If the PAA is not configured to enable fast re-authentication, or 
   can not retrieve the PANA SA, or the PANA SA has expired, the PAA 
   MUST send the PANA-Start-Request message with a new session id and 
   let the PANA exchange take its usual course. Otherwise, PAA MUST 
   continue the PANA session with a PANA_Reauth exchange (rather than 
   PANA_Auth exchange which, in most of the times, means full 
   authentication). Device ID AVPs MUST be included in this exchange to 
   bind the new DIs to the PANA SA. 
    
   TBD: This is a proposal and requires further thoughts.  
    
4.10 Event Notification 
    
   Upon detecting the need to authenticate a client, EP can send a 
   trigger message to the PAA on behalf of the PaC. This can be one of 
   the messages provided by the PAA-to-EP protocol, or, in the absence 
   of such a facility, PANA-PAA_Discover can be used as well. This 
 
 
Tschofenig et al.      Expires - December 2003              [Page 19] 
                                 PANA                        June 2003 
 
 
   message MUST carry the device identifier of the PaC. So that, the 
   PAA can send the unsolicited PANA-Start-Request  message directly to 
   the PaC.  If the link between the EP and PAA is not physically 
   secured, this message sent from EP to PAA MUST be cryptographically 
   protected (e.g., by using IPsec). 
 
4.11 PaC Implications 
    
   - PaC state machine. [TBD] 
    
4.12 PAA Implications 
    
   - PAA state machine. [TBD] 
    
5  PANA Security Association Establishment 
    
   When PANA is used over an already established secure channel, such 
   as physically secured wires or ciphered link-layers, we can 
   reasonably assume that man-in-the-middle attack or service theft is 
   not possible [THREATS]. 
    
   Anywhere else where there is no secure channel prior to PANA, the 
   protocol needs to protect itself against such attacks. The device 
   identifier that is used during the authentication needs to be 
   verified at the end of the authentication to prevent service theft 
   and DoS attacks. Additionally, a free loader should be prevented 
   from spoofing data packets by using the device identifier of an 
   already authorized legitimate client. Both of these requirements 
   necessitate generation of a security association between the 
   PaC and the PAA at the end of the authentication. This can only be 
   done when the authentication method used can generate cryptographic 
   keys. Use of secret keys can prevent attacks which would otherwise 
   be very easy to launch by eavesdropping on and spoofing traffic over 
   an insecure link. 
    
   PANA relies on EAP and the EAP methods to provide a session key in 
   order to establish a PANA security association. An example of such a 
   method is EAP-TLS [EAPTLS], whereas EAP-MD5 [RFC2284] is an example 
   of a method that cannot create such keying material. The choice of 
   EAP method becomes important, as already discussed in the next 
   section. 
    
   This keying material is already used within PANA during the final 
   handshake. This handshake ensures that the device identifier that is 
   bound to the PaC at the end of the authentication process is not 
   coming from a man-in-the-middle, but from the legitimate PaC. 
   Knowledge of the same keying material on both PaC and the PAA helps 
   prove this. The other use of the keying material will be discussed 
   in sections 7 and 8. 
 
 
Tschofenig et al.      Expires - December 2003              [Page 20] 
                                 PANA                        June 2003 
 
 
    
6  Authentication Method Choice 
    
   Authentication methods' capabilities and therefore applicability to 
   various environments differ among them. Not all methods provide 
   support for mutual authentication, key derivation or distribution, 
   and DoS attack resiliency that are necessary for operating in 
   insecure networks. Such networks might be susceptible to 
   eavesdropping and spoofing, therefore a stronger authentication 
   method needs to be used to prevent attacks on the client and 
   the network.  
    
   The authentication method choice is a function of the underlying 
   security of the network (e.g., physically secured, shared link, 
   etc.). It is the responsibility of the user and the network operator 
   to pick the right method for authentication. PANA carries EAP 
   regardless of the EAP method used. It is outside the scope of PANA 
   to mandate, recommend, or limit use of any authentication methods. 
   PANA cannot increase the strength of a weak authentication method to 
   make it suitable for an insecure environment. There are some EAP-
   based approaches to achieve this goal (see [PEAP],[TTLS],[EAP-
   IKEv2]). PANA can carry these EAP encapsulating methods but it does 
   not concern itself with how they achieve protection for the weak 
   methods (i.e., their EAP method payloads). 
    
7  Filter Rule Installation 
    
   PANA protocol provides client authentication and authorization 
   functionality for securing network access. The other component of a 
   complete solution is the access control which ensures that only 
   authenticated and authorized clients can gain access to the network. 
   PANA enables access control by identifying legitimate clients and 
   generating filtering information for access control mechanisms. 
   Getting this filtering information to the EPs (Enforcement Points) 
   and performing filtering are outside the scope of PANA. 
    
   Access control can be achieved by placing EPs in the network for 
   policing the traffic flow. EPs should prevent data traffic from and 
   to any unauthorized client unless it's PANA traffic. When a client 
   is authenticated and authorized, PAA should notify EP(s) and ask for 
   changing filtering rules to allow traffic for a recently authorized 
   client. There needs to be a protocol between PAA and EP(s) when 
   these entities are not co-located. PANA Working Group will not be 
   defining a new protocol for this interaction. Instead, it will 
   (preferably) identify one of the existing protocols that can fit the 
   requirements. Possible candidates include but not limited to COPS, 
   SNMP, DIAMETER. This task is similar to what MIDCOM Working Group is 
   trying to achieve, therefore some of the MIDCOM's output might be 
   useful here.     
 
 
Tschofenig et al.      Expires - December 2003              [Page 21] 
                                 PANA                        June 2003 
 
 
    
   EPs location in the network topology should be appropriate for 
   performing access control functionality. The closest IP-capable 
   access device to the client devices is the logical choice. PAA and 
   EPs on an access network should be aware of each other as this is 
   necessary for access control. Generally this can be achieved by 
   manual configuration. Dynamic discovery is another possibility, but 
   this is clearly outside the scope of PANA. 
    
   Filtering rules generally include device identifiers for a client, 
   and also cryptographic keying material when needed. Such keys are 
   needed when attackers can eavesdrop and spoof on the device 
   identifiers easily. They are used with link-layer or network-layer 
   ciphering to provide additional protection. For issues regarding 
   data-origin authentication see Section 8. 
    
8  Data Traffic Protection 
    
   Protecting data traffic of authenticated and authorized clients from 
   others is another component of providing a complete secure network 
   access solution. Authentication, integrity and replay protection of 
   data packets are needed to prevent spoofing when the underlying 
   network is not physically secured. Encryption is needed when 
   eavesdropping is a concern in the network. 
    
   When the network is physically secured, or the link-layer ciphering 
   is already enabled prior to PANA, data traffic protection is already 
   in place. In other cases, enabling link-layer ciphering or network-
   layer ciphering might rely on PANA authentication. The user and 
   network have to make sure an appropriate EAP method that can 
   generate required keying materials is used. Once the keying material 
   is available, it needs to be provided to the EP(s) for use with 
   ciphering. 
    
   Network-layer ciphering, i.e., IPsec, can be used when data traffic 
   protection is required but link-layer ciphering capability is not 
   available. Note that a simple shared secret generated by an EAP 
   method is not readily usable by IPsec for authentication and 
   encryption of IP packets. Fresh and unique session key derived from 
   the EAP method is still insufficient to produce an IPsec SA since 
   both traffic selectors and other IPsec SA parameters are missing. 
   The shared secret can be used in conjunction with a key management 
   protocol like IKE [RFC2409] to turn a simple shared secret into the 
   required IPsec SA. The details of this mechanism is outside the 
   scope of PANA protocol, and it can be outlined in a separate 
   Internet-Draft. PANA provides bootstrapping functionality for such a 
   mechanism by carrying EAP methods that can generate initial keying 
   material. 
    
 
 
Tschofenig et al.      Expires - December 2003              [Page 22] 
                                 PANA                        June 2003 
 
 
   Using network-layer ciphers should be regarded as a substitute for 
   link-layer ciphers when the latter is not available. IKE involves 
   several message exchanges which can incur additional delay in 
   getting basic IP connectivity for a mobile device. Such a latency is 
   inevitable when there is no other alternative and this level of 
   protection is required. Network-layer ciphering can also be used in 
   addition to link-layer ciphering if the added benefits outweigh its 
   cost to the user and the network. 
    
9  Message Formats 
    
   This section defines message formats for PANA protocol.   
    
9.1 PANA Header 
 
   A summary of the PANA header format is shown below.  The fields are 
   transmitted in network byte order. 
 
       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |    Version    |                 Message Length                | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |    Flags      |                 Message Type                  | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |                 Transmitted Sequence Number                   | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |                 Received Sequence Number                      | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |  AVPs ... 
      +-+-+-+-+-+-+-+-+-+-+-+-+- 
    
   Version 
    
     This Version field MUST be set to 1 to indicate PANA Version 1. 
    
   Message Length 
    
     The Message Length field is three octets and indicates the 
     length of the PANA message including the header fields. 
    
   Flags 
    
     The Flags field is eight bits.  The following bits are assigned: 
    
     0 1 2 3 4 5 6 7 
    +-+-+-+-+-+-+-+-+ 
    |R r r r F r r r| 
    +-+-+-+-+-+-+-+-+ 
 
 
Tschofenig et al.      Expires - December 2003              [Page 23] 
                                 PANA                        June 2003 
 
 
    
       R(equest)    
    
                   - If set, the message is a request. If cleared, 
                     the message is an answer. 
    
       F(inish)     
                   - F-flag in the PANA header indicates if this  was 
                     the final authentication from sender's 
                     perspective.  If PAA enables two separate 
                     authentication, it should not set F-flag in the 
                     PANA-Bind-Request message after the first EAP  
                     method. 
    
       r(eserved)   
    
                   - these flag bits are reserved for future use, 
                     and MUST be set to zero, and ignored by the 
                     receiver. 
    
    
   Message Type 
    
     The Message Type field is three octets, and is used in order to 
     communicate the message type with the message.  The 24-bit 
     address space is managed by IANA [IANAWEB]. 
    
   Transmitted Sequence Number 
    
     The Transmitted Sequence Number field contains the monotonically 
     increasing 32 bit sequence number that the message sender 
     increments every time a new packet is sent. 
    
   Received Sequence Number 
    
     The Received Sequence Number field contains the 32 bit 
     transmitted sequence number that the peer has last received. 
    
   AVPs 
    
     AVPs are a method of encapsulating information relevant to the 
     PANA message.  See section 9.2 for more information on AVPs. 
    
 
9.2 AVP Header 
 
       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 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 
 
Tschofenig et al.      Expires - December 2003              [Page 24] 
                                 PANA                        June 2003 
 
 
      |                           AVP Code                            | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |   AVP Flags   |                  AVP Length                   | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |                         Vendor-Id (opt)                       | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |    Data ... 
      +-+-+-+-+-+-+-+-+ 
    
    
   AVP Code 
    
      The AVP Code, combined with the Vendor-Id field, identifies the 
      attribute uniquely. AVP numbers are allocated by IANA [IANAWEB]. 
    
   AVP Flags 
    
      The AVP Flags field is eight bits.  The following bits are 
      assigned: 
    
       0 1 2 3 4 5 6 7 
      +-+-+-+-+-+-+-+-+ 
      |V M r r r r r r| 
      +-+-+-+-+-+-+-+-+ 
    
         M(andatory)  
    
                   - The 'M' Bit, known as the Mandatory bit, 
                     indicates whether support of the AVP is 
                     required. 
    
         V(endor)     
    
                   - The 'V' bit, known as the Vendor-Specific bit, 
                     indicates whether the optional Vendor-Id field 
                     is present in the AVP header. 
    
         r(eserved)   
    
                   - these flag bits are reserved for future use, 
                     and MUST be set to zero, and ignored by the 
                     receiver. 
    
   AVP Length 
    
      The AVP Length field is three octets, and indicates the number 
      of octets in this AVP including the AVP Code, AVP Length, AVP 
      Flags, and the AVP data. 
    
 
 
Tschofenig et al.      Expires - December 2003              [Page 25] 
                                 PANA                        June 2003 
 
 
   Vendor-Id 
    
      The Vendor-Id field is present if the 'V' bit is set in the AVP 
      Flags field. The optional four-octet Vendor-Id field contains 
      the uniquely assigned id value, encoded in network byte order. 
      Any vendor wishing to implement a vendor-specific PANA AVP MUST 
      use their own Vendor-Id along with their privately managed AVP 
      address space, guaranteeing that they will not collide with any 
      other vendor's vendor-specific AVP(s), nor with future IETF 
      applications. 
    
   Data 
    
      The Data field is zero or more octets and contains information 
      specific to the Attribute. The format and length of the Data 
      field is determined by the AVP Code and AVP Length fields. 
    
 
9.3 PANA Messages 
 
   Figure 9lists all PANA messages defined in this document  
      Message       Direction: PaC---PAA 
      ---------------------------------- 
      PANA-PAA-Discover        -------->   
    
      PANA-Start-Request       <-------- 
      PANA-Start-Answer        --------> 
    
      PANA-Auth-Request        <-------- 
      PANA-Auth-Answer         --------> 
    
      PANA-Bind-Request        <-------- 
      PANA-Bind-Answer         --------> 
    
      PANA-Reauth-Request      <-------> 
      PANA-Reauth-Answer       <-------> 
    
      PANA-Termination-Request <-------> 
      PANA-Termination-Answer  <-------> 
    
      PANA-Error               <-------> 
    
                      Figure 9: PANA Message Overview 
 
   Additionally the EP can also send a PANA-PAA-Discover message to the 
   PAA. 
 
 

 
 
Tschofenig et al.      Expires - December 2003              [Page 26] 
                                 PANA                        June 2003 
 
 
9.3.1  Message specifications 
 
   Every PANA message MUST include a corresponding ABNF 
   [RFC2234] specification found in [DIAMETER].  Note that PANA 
   messages have a different header format compared to Diameter. 
 
   Example: 
    
   message ::= < PANA-Header: <Message type>,  
                               [REQ], [FIN]  
                               * [ AVP ] 
 
9.3.2 PANA-PAA-Discover (PDI) 
 
   The PANA-PAA-Discover (PDI) message is used to discover the address 
   of PAA(s). Both sequence numbers in this message are set to zero 
   (0). If the EP detects a new PaC and sends the PANA-PAA-Discover to 
   the PAA, it MUST include the Device-Id of the PaC. 
    
      PANA-PAA-Discover ::= < PANA-Header: 1 > 
                 0*1 < Device-Id >   
                  * [ AVP ] 
 
9.3.3 PANA-Start-Request (PSR) 
 
   PANA-Start-Request (PSR) is sent by the PAA to the PaC. The PAA sets 
   the transmission sequence number to an initial random value.  The 
   received sequence number is set to zero (0). 
    
      PANA-Start-Request ::= < PANA-Header: 2, REQ > 
                    [ Cookie ] 
                  * [ AVP ] 
 
9.3.4 PANA-Start-Answer (PSA) 
 
   PANA-Start-Answer (PSA) is sent by the PaC to the PAA in response to 
   a PANA-Start-Request message.  The PANA_start message transmission 
   sequence number field is copied to the received sequence number 
   field.  The 
   transmission sequence number is set to initial random value. 
    
      PANA-Start-Answer ::= < PANA-Header: 3 > 
                    [ Cookie ] 
                  * [ AVP ] 
 
9.3.5 PANA-Auth-Request (PAR) 
 
   PANA-Auth-Request (PAR) is sent by the PAA to the PaC. 
    
 
 
Tschofenig et al.      Expires - December 2003              [Page 27] 
                                 PANA                        June 2003 
 
 
      PANA-Auth-Request ::= < PANA-Header: 4, REQ > 
                    < Session-Id > 
                    < EAP-Payload > 
                  * [ AVP ] 
                0*1 < MAC > 
 
9.3.6 PANA-Auth-Answer (PAN) 
    
   PANA-Auth-Answer (PAN) is sent by the PaC to the PAA in response to 
   a PANA-Auth-Request message. 
    
      PANA-Auth-Answer ::= < PANA-Header: 5 > 
                    < Session-Id > 
                    < EAP-Payload > 
                  * [ AVP ] 
                0*1 < MAC > 
 
9.3.7 PANA-Bind-Request (PBR) 
    
   PANA-Bind-Request (PBR) is sent by the PAA to the PaC. 
    
      PANA-Bind-Request ::= < PANA-Header: 6, REQ, [FIN] > 
                    < Session-Id > 
                    < Device-Id > 
                    { EAP-Payload } 
                    { Result-Code } 
                    [ Protection-Capability ] 
                  * [ AVP ] 
                0*1 < MAC > 
 
9.3.8 PANA-Bind-Answer (PBA) 
 
   PANA-Bind-Answer (PBA) is sent by the PaC to the PAA in response to 
   a PANA-Result-Request message. 
    
      PANA-Bind-Answer ::= < PANA-Header: 7, [FIN] > 
                    < Session-Id > 
                 < Device-Id > 
                  * [ AVP ] 
                0*1 < MAC > 
 
9.3.9 PANA-Reauth-Request (PRAR) 
 
   PANA-Reauth-Request (PRAR) is either sent by the PaC or the PAA. 
    
      PANA-Reauth-Request ::= < PANA-Header: 8, REQ > 
                    < Session-Id > 
                 < Device-Id > 
                  * [ AVP ] 
 
 
Tschofenig et al.      Expires - December 2003              [Page 28] 
                                 PANA                        June 2003 
 
 
                0*1 < MAC > 
 
9.3.10    PANA-Reauth-Answer (PRAA) 
 
   PANA-Reauth-Answer (PRAA) is sent in response to a 
   PANA-Reauth-Request. 
    
      PANA-Reauth-Answer ::= < PANA-Header: 9 > 
                    < Session-Id > 
                    < Device-Id > 
                  * [ AVP ] 
                0*1 < MAC > 
    
9.3.11    PANA-Termination-Request (PTR) 
    
   PANA-Termination-Request (PTR) is sent either by the PaC or the PAA. 
    
      PANA-Termination-Request ::= < PANA-Header: 10, REQ > 
                   < Session-Id > 
                   < Termination-Cause > 
                 * [ AVP ] 
               0*1 < MAC > 
 
9.3.12    PANA-Termination-Answer (PTA) 
    
   PANA-Termination-Answer (PTA) is sent either by the PaC or the PAA 
   in response to PANA-Termination-Request. 
    
      PANA-Termination-Answer ::= < PANA-Header: 11 > 
                   < Session-Id > 
                 * [ AVP ] 
               0*1 < MAC > 
 
9.3.13    PANA-Error  
 
   PANA-Error is sent either by the PaC or the PAA.  
    
   TBD 
 
9.4 AVPs in PANA 
 
   Some of the used AVPs are defined in this document and some of them 
   are defined in other documents like [DIAMETER]. PANA proposes to 
   use the same name space with the Diameter spec. For temporary 
   allocation, PANA uses AVP type numbers starting from 1024. 
 
9.4.1 MAC AVP 
 
   The first octet (8 bits) of the MAC (Code 1024) AVP data contains 
 
 
Tschofenig et al.      Expires - December 2003              [Page 29] 
                                 PANA                        June 2003 
 
 
   the MAC algorithm type. Rest of the AVP data payload contains the 
   MAC encoded in network byte order. The Algorithm 8 bit name space 
   is managed by IANA [IANAWEB]. The AVP length varies depending on 
   the used algorithm. 
       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |   Algorithm   |           MAC...                                  
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   Algorithm       
    
      1              HMAC-MD5 (16 bytes) 
      2              HMAC-SHA1 (20 bytes) 
    
   MAC 
    
      The Message Authentication Code is encoded in network byte 
      order. 
 
9.4.2 Device-Id AVP 
 
   The first octet (8 bits) of the Device-Id (Code 1025) AVP data 
   contains the device type. Rest of the AVP data payload contains 
   the device data.  The content and format of data (including byte 
   and bit ordering) is expected to be specified in specific 
   documents.  For instance, [IPv6-ETHER]. 
    
         UNKNOWN                           0 
         IPV4_ADDRESS                      1 
         IPV6_ADDRESS                      2 
         L2_ADDRESS                        3 
    
        For type 1 (IPv4 address), data size is 32 bits and for type 2 
        (IPv6 address), data size is 128 bits. 
    
       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |     Type      |           Data...                             |     
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 
9.4.3 Session-Id AVP 
    
   Session-Id AVP (Code 1026) has an opaque data field, which is 
   assigned by the PAA. All messages pertaining to a specific PANA 
   Session MUST include only one Session-Id AVP and the same value 
   MUST be used throughout the lifetime of a session.  When present, 
 
 
Tschofenig et al.      Expires - December 2003              [Page 30] 
                                 PANA                        June 2003 
 
 
   the Session-Id SHOULD appear immediately following the PANA header. 
    
   The Session-Id MUST be globally and eternally unique, as it is 
   meant to identify a PANA Session without reference to any 
   other information, and may be needed to correlate historical 
   authentication information with accounting information. 
    
   The Session-Id AVP MAY use Diameter [DIAMETER] message 
   formatting. In this case the AVP code is 263.  
 
9.4.4 Cookie AVP 
    
   The Cookie AVP (Code 1027) is of type OctetString. The data is 
   opaque and the exact content is outside the scope of this protocol. 
 
9.4.5 Protection-Capability AVP 
    
   The Protection-Capability AVP (Code 1028) is of type Unsigned32. 
   The AVP data is used as a collection of flags for different data 
   protection capability indications.  Below is a list of specified 
   data protection capabilities: 
    
      0          UNKNOWN 
      1          L2_PROTECTION 
      2          IPSEC_PROTECTION 
    
9.4.6 Termination-Cause AVP 
 
   The Termination-Cause AVP is defined in [DIAMETER]. 
    
         LOGOUT                   1  (PaC -> PAA) 
            The user initiated a disconnect 
    
         (SERVICE_NOT_PROVIDED     2  (PAA -> PaC)) 
            This value is used when the user disconnected  
            prior to the receipt of the authorization answer 
            message. 
    
         BAD_ANSWER               3  (PaC -> PAA) 
            This value indicates that the authorization answer 
            received by the access device was not processed 
            successfully. 
    
         ADMINISTRATIVE           4  (PAA -> Pac) 
            The user was not granted access, or was  
            disconnected, due to administrative reasons,  
            such as the receipt of a Abort-Session-Request 
            message. 
    
 
 
Tschofenig et al.      Expires - December 2003              [Page 31] 
                                 PANA                        June 2003 
 
 
         (LINK_BROKEN              5) 
            The communication to the user was abruptly  
            disconnected. 
    
         AUTH_EXPIRED             6    (PAA -> PaC) 
            The user's access was terminated since its  
            authorized session time has expired. 
    
         (USER_MOVED               7)  (PaC -> PAA) 
            The user is receiving services from another  
            access device. (See issue16). 
    
         SESSION_TIMEOUT          8  (PAA -> PaC) 
            The user's session has timed out, and service  
            has been terminated. 
    
9.4.7 Result-Code AVP 
 
   The Result-Code AVP is defined in [DIAMETER]. 
    
         SUCCESS                   2001 
         COMMAND_UNSUPPORTED       3001 
         UNABLE_TO_DELIVER         3002 
         REALM_NOT_SERVED          3003 
         TOO_BUSY                  3004 
         INVALID_HDR_BITS          3008 
         INVALID_AVP_BITS          3009 
         AUTHENTICATION_REJECTED   4001 
         AVP_UNSUPPORTED           5001 
         UNKNOWN_SESSION_ID        5002 
         AUTHORIZATION_REJECTED    5003 
         INVALID_AVP_VALUE         5004 
         MISSING_AVP               5005 
         RESOURCES_EXCEEDED        5006 
         AVP_OCCURS_TOO_MANY_TIMES 5009 
         UNSUPPORTED_VERSION       5011 
         INVALID_AVP_LENGTH        5014 
         INVALID_MESSAGE_LENGTH    5015 
 
9.4.8 EAP-Payload AVP 
 
   The EAP-Payload AVP is defined in [DIAMETER-EAP]. 
 
9.5 AVP Occurrence Table 
    
   The following tables lists the AVPs used in this document, and 
   specifies in which PANA messages they MAY, or MAY NOT be present. 
    
   The table uses the following symbols: 
 
 
Tschofenig et al.      Expires - December 2003              [Page 32] 
                                 PANA                        June 2003 
 
 
    
      0     The AVP MUST NOT be present in the message. 
      0+    Zero or more instances of the AVP MAY be present in the 
            message. 
      0-1   Zero or one instance of the AVP MAY be present in the 
            message. It is considered an error if there are more than 
            one instance of the AVP. 
      1     One instance of the AVP MUST be present in the message. 
      1+    At least one instance of the AVP MUST be present in the 
            message. 
    
                       +-----------------------------------------+ 
                       |        Message                          | 
                       |          Type                           | 
                       +-----+-----+-----+-----+-----+-----+-----+ 
   Attribute Name      | PSR | PSA | PAR | PAN | PBR | PBA | PDI |  
   --------------------+-----+-----+-----+-----+-----+-----+-----+ 
   Result-Code         |  0  |  0  |  0  |  0  |  1  |  0  |  0  | 
   Session-Id          |  0  |  0  |  1  |  1  |  1  |  1  |  0  | 
   Termination-Cause   |  0  |  0  |  0  |  0  |  0  |  0  |  0  | 
   EAP-Payload         |  0  |  0  |  1  |  1  |  1  |  0  |  0  |  
   MAC                 |  0  |  0  | 0-1 | 0-1 | 0-1 | 0-1 |  0  | 
   Device-Id           |  0  |  0  |  0  |  0  |  1+ |  1+ | 0-1 | 
   Cookie              | 0-1 | 0-1 |  0  |  0  |  0  |  0  |  0  | 
   Protection-Cap.     |  0  |  0  |  0  |  0  | 0-1 |  0  |  0  | 
   --------------------+-----+-----+-----+-----+-----+-----+-----+ 
    
    
                       +-------------------------+ 
                       |      Message            | 
                       |       Type              | 
                       +------+------+-----+-----+ 
   Attribute Name      | PRAR | PRAA | PTR | PTA |  
   --------------------+------+------+-----+-----+ 
   Result-Code         |  0   |  0   |  0  |  0  |  
   Session-Id          |  1   |  1   |  1  |  1  | 
   Termination-Cause   |  0   |  0   |  1  |  0  | 
   EAP-Payload         | 0-1  | 0-1  |  0  |  0  | 
   MAC                 | 0-1  | 0-1  | 0-1 | 0-1 | 
   Device-Id           |  1+  |  1+  |  0  |  0  | 
   Cookie              |  0   |  0   |  0  |  0  | 
   Protection-Cap.     |  0   |  0   |  0  |  0  | 
   --------------------+------+------+-----+-----+ 
    
                      Figure 10: AVP Occurrence Table 
    
10 Security Considerations 
    

 
 
Tschofenig et al.      Expires - December 2003              [Page 33] 
                                 PANA                        June 2003 
 
 
   The PANA protocol provides ordered delivery for EAP messages.  If an 
   EAP method that provides session keys is used, a PANA SA is created. 
   The EAP Success/Failure message is one of the signaling messages 
   which is integrity protected with this PANA SA.  The PANA protocol 
   does not provide security protection for the initial EAP message 
   exchange. Integrity protection can only be provided after the PANA 
   SA has been established.  Thus, PANA re-authentication, revocation 
   and disconnect notifications can be authenticated, integrity and 
   replay protected. In certain environments (e.g. on a shared link) 
   the EAP method selection is an important issue.  
    
   The PANA framework described in this document covers the discussion 
   of different protocols which are of interest for a protocol between 
   the PaC and the PAA (typically referred as the PANA protocol).  
    
   The PANA itself consists of a sequence of steps which are executed 
   to complete the network access authentication procedure. Some of 
   these steps are optional.  
    
   The following execution steps have been identified as being relevant 
   for PANA. They security considerations will be discussed in detail 
   subsequently.  
    
   a) Discovery message exchange  
    
   In general it is difficult to prevent a vulnerabilities of the 
   discovery protocol since the initial discovery are unsecured. To 
   prevent very basic attacks an adversary should not be able to cause 
   state creation with discovery messages at the PAA. This is prevented 
   by re-using a cookie concept (see [RFC2522]) which allows the 
   responder to be stateless in the first message exchange. Because of 
   the architectural assumptions  made in PANA (i.e. the PAA is the on 
   the same link as the PaC) the return-routability concept does not 
   provide additional protection. Hence it is difficult to prevent this 
   threat entirely. Furthermore it is not possible to shift heavy 
   cryptographic operations to the PaC at the first few messages since 
   the computational effort depends on the EAP method. The usage of 
   client-puzzles as introduced by [JB99] is under investigation.  
    
   Resistance against blind DoS attacks (i.e. attacks by off-path 
   adversaries) is achieved with sequence numbers and cookies.  
    
   Since PAA and PaC are one IP hop away from each other, PANA messages 
   can be filtered whenever messages arrive at interfaces where they 
   are not expected.  
    
   b) EAP over PANA message exchange  
    

 
 
Tschofenig et al.      Expires - December 2003              [Page 34] 
                                 PANA                        June 2003 
 
 
   The EAP derived session key is used to create a PANA security 
   association. Since the execution of an EAP method might require a 
   large number of roundtrips and no other session key is available it 
   is not possible to secure the EAP message exchange itself. Hence an 
   adversary can both eavesdrop the EAP messages and is also able to 
   inject arbitrary messages which might confuse both the PaC and the 
   PAA. The threats caused by this ability heavily depend on the EAP 
   state machine. Since especially the PAA is not allowed to discard 
   packets and packets have to be stored or forwarded to an AAA 
   infrastructure some risk of DoS attacks exists.  
    
   Eavesdropping EAP packets might cause problems when (a) the EAP 
   method is weak and enables dictionary or replay attacks or even 
   allows an adversary to learn the long-term password directly. 
   Furthermore, if the optional EAP Identity payload is used then it 
   allows the adversary to learn the identity of the PaC. In such a 
   case a privacy problem is prevalent.  
    
   To prevent these threats Section 6 suggests using proper EAP methods 
   for particular environments. Depending on the usage environment an 
   EAP authentication has to be used for example which supports user 
   identity confidentiality, protection against dictionary attacks and 
   session key establishment. It is therefore the responsibility of the 
   network operators and end users to choose the proper EAP method.  
    
   PANA does not protect the EAP method exchange, but provides ordered 
   delivery with sequence numbers.  Sequence numbers and cookies 
   provide resistance against blind DoS attacks. 
    
   c) PANA SA establishment  
    
   Once the EAP message authentication is finished a fresh and unique 
   session key is available to the PaC and the PAA. This assumes that 
   the EAP method allows session key derivation and that the generated 
   session key has a good quality. For further discussion about the 
   importance of the session key generation refer to the next 
   subsection (c) about compound authentication. The session key 
   available for the PaC is established as part of the authentication 
   and key exchange procedure of the selected EAP method. The PAA 
   obtains the session key via the AAA infrastructure (if used). Draft 
   [CFB02] describes how a session key is securely carried (i.e. CMS 
   protected) between AAA servers. Security issues raised with this 
   session key transport are described in [WHC02].  
    
   The establishment of a PANA SA is required in environments where no 
   physical or link layer security is available. The PANA SA allows 
   subsequently exchanged messages to experience cryptographic 
   protection. For the current version of the document an Integrity 
   object is defined which is based on Diameter objects. The Integrity 
 
 
Tschofenig et al.      Expires - December 2003              [Page 35] 
                                 PANA                        June 2003 
 
 
   Object supports data-origin authentication, replay protection based 
   on sequence numbers and integrity protection based on a keyed 
   message digest. Confidentiality protection is not provided. The 
   session keys (one for each direction) used for this object has to be 
   provided by the EAP method. For this version of the document it is 
   assumed that no negotiation of algorithms and parameters takes 
   place. Instead HMAC-SHA1 is used per-default. A different algorithm 
   such as HMAC-MD5 might be used as an option. The used algorithm is 
   indicated in the header of the Integrity object. To select the 
   security association for signaling message protection the Session 
   ID. The keyed message digest included in the Integrity object will 
   include all fields of the PANA signaling message including the 
   sequence number field of the packet.  
    
   The protection of subsequent signaling messages prevents an 
   adversary from acting as a man-in-the-middle adversary, from 
   injecting packets, from replaying messages and from modifying the 
   content of the exchanged packets. This prevents subsequently 
   described threats. 
    
   If an entity (PAA or PaC) looses its state (especially the current 
   sequence number) then the entire PANA protocol has to be restarted. 
   No re-synchronization procedure is provided.  
    
   The lifetime of the PANA SA has to be bound to the refresh interval 
   with an additional tolerance period. To provide fast re-
   authentication a separate security association (e.g. one stored at 
   the local AAA server) should be used. By fast re-authentication we 
   mean a new PANA protocol execution which does not involve the entire 
   AAA communication. The ability to trigger such a protocol execution 
   depends on the given EAP method and on the policy of the local 
   network requesting authentication.  
    
   d) Enabling weak legacy authentication methods in insecure networks 
    
   Some of the authentication methods are not strong enough to be used 
   in insecure networks where attackers can easily eavesdrop and spoof 
   on the link. They may not be able to produce much needed keying 
   material either. An example would be using EAP-MD5 over wireless 
   links. Use of such legacy methods can be enabled by carrying them 
   over a secure channel. There are EAP methods which are specifically 
   designed for this purpose, such as EAP-TTLS [TTLS],PEAP [PEAP] or 
   EAP-IKEv2 [EAP-IKEv2]. PANA can carry these EAP tunneling methods 
   which can carry the legacy methods. PANA does not do anything 
   special for this case. The EAP tunneling method will have to produce 
   keying material for PANA SA when needed. There are certain MitM 
   vulnerabilities with tunneling EAP methods [MITM]. Solving these 
   problems is outside the scope of PANA. The compound authentication 

 
 
Tschofenig et al.      Expires - December 2003              [Page 36] 
                                 PANA                        June 2003 
 
 
   problem described in [PL+03] is likely to be solved in EAP itself 
   rather than in PANA.  
 
   e) Preventing downgrading attacks 
    
   EAP supports a number of different EAP methods for authentication 
   and therefore it might be required to agree on a specific mechanism. 
   An unprotected negotiation mechanism is supported in EAP and a 
   secure negotiation procedure for the GSS-API methods. The support of 
   the GSS-API as an EAP method is described in [AS02]. A protected 
   negotiation is supported by the GSS-API with RFC 2478 [RFC2478]. If 
   desired, such a protection can also be offered by PANA by repeating 
   the list of supported EAP methods protected with the PANA SA. This 
   type of protection is similar to the protected negotiation described 
   in [RFC3329].  
    
   This issue requires further investigation especially since the EAP 
   protocol is executed between different endpoints than the PANA 
   protocol.  
    
   f) Device Identifier exchange 
    
   As part of the authorization procedure a Device Identifier has to be 
   installed at the EP by the PAA. The PaC provides the Device 
   Identifier information to the PAA secured with the PANA SA. Section 
   6.2.4 of [THREATS] describes a threat where an adversary modifies 
   the Device Identifier to gain unauthorized access to the network.  
    
   The installation of the Device Identifier at the EP (independently 
   whether the EP is co-located with the PAA or not) has to be 
   accomplished in a secure manner. These threats are, however, not 
   part of the PANA protocol itself since the protocol is not PANA 
   specific.  
    
   g) Triggering a data protection protocol 
    
   Recent activities in the EAP working group try to create a common 
   framework for key derivation which is described in [Ab02]. This 
   framework is also relevant for PANA in various ways. First, a PANA 
   security association needs to be created. Additionally it might be 
   necessary to trigger a protocol which allows link layer and network 
   layer data protection to be established. As an example see Section 1 
   of [Ab02] with [802.11i] and [802.11] as an example. Furthermore, a 
   derived session key might help to create the pre-requisites for 
   network layer protection (for example IPsec).  
    
   As motivated in Section 6.4 of [THREATS] it might be necessary to 
   establish either a link layer or a network layer protection to 
   prevent certain thefts in certain scenarios.  
 
 
Tschofenig et al.      Expires - December 2003              [Page 37] 
                                 PANA                        June 2003 
 
 
    
   Threats specific to the establishment of a link layer or a network 
   layer security association are outside the scope of PANA. The 
   interested reader should refer to the relevant working groups such 
   as IPsec or Midcom.  
    
   h) Periodic refresh messages 
    
   Network access authentication is done for a very specific purpose 
   and often charging procedures are involved which allow restricting 
   network resource usage based on some policies. In mobility 
   environments it is always possible that an end host suddenly 
   disconnects without transmitting a disconnect message. If network 
   access authentication as part of PANA is executed only at the 
   beginning then an adversary can gain advantage of the installed 
   packet filters to submit and receive data packets.  
    
   Also for the network operator it might be desirable to enforce a 
   disconnect based on some external events (e.g. because of 
   insufficient funds, etc.).  
    
   An additional motivation for detecting a disconnected end host is 
   the ability to release resources (i.e. garbage collection). The PAA 
   can remove per-session state information including installed 
   security association, packet filters etc.  
    
   Different procedures can be used for disconnect indication. PANA 
   cannot assume link layer disconnect indication. Hence this 
   functionality has to be provided at a higher layer. With this 
   version of the draft we suggest to apply the soft-state principle 
   found at other protocols (such as RSVP). Soft-state means that 
   session state is kept alive as long as refresh messages refresh the 
   state. If no new refresh messages are provided then the state 
   automatically times out and resources are released. This process 
   includes stopping accounting procedures.  
    
   Based on the different environments where PANA could be used it is 
   difficult to fix a refresh interval. Hence a default refresh 
   interval of 30 seconds is suggested. Additionally there is the 
   possibility to negotiation this interval once the PANA security 
   association is established. A policy at the PAA and the PaC would 
   ensure that the refresh interval is selected with a value which is 
   either too high or too low. There is certainly a tradeoff between 
   the refresh interval and the bandwidth consumption. To reduce the 
   bandwidth consumption a small PANA message consisting only of a 
   session identifier and the Integrity object is used. The session 
   identifier refers to the state that has to be refreshed. Some 
   environments do not need PANA refresh messages to detect orphan 
   states. For these environments the refresh interval should be set to 
 
 
Tschofenig et al.      Expires - December 2003              [Page 38] 
                                 PANA                        June 2003 
 
 
   zero which effectively disables the usage of refresh messages. In 
   case of IPsec protection a dead-peer mechanism can be used to detect 
   inactivity (see [HBR03]). 
    
   Refresh messages are sent from the PaC to the PAA.  
    
   From a security point of view an adversary must not be able to 
   inject, modify or replay refresh messages nor must he be able to 
   change the refresh interval (e.g. setting it to zero) without 
   detection. Hence these messages experience cryptographic protection. 
    
   i) Tear-Down message 
    
   The PANA protocol supports the ability for both the PaC and the PAA 
   to transmit a tear-down message. This message causes state removal, 
   a stop of the accounting procedure and removes the installed packet 
   filters.  
    
   It is obvious that such a message must be protected to prevent an 
   adversary from deleting state information and thereby causing denial 
   of service attacks.  
    
11 Open Issues 
    
   A list of open issues is maintained at  
   http://danforsberg.info:8080/pana-issues/.  
    
12 Acknowledgments 
    
   We would like to thank all members of the PANA working group for 
   their comments to this document.  
    
13 References 
    
   [802.11] I. S. 802.11-1997, "Information technology - 
   telecommunications and information exchange between systems - local 
   and metropolitan area networks - specific requirements part 11: 
   Wireless lan medium access control (mac) and physical layer (phy) 
   specifications," tech. rep., 1997. 
    
   [RFC2522] P. Karn and W. Simpson, "Photuris: Session-key management 
   protocol," RFC 2522, March 1999. 
 
   [Ab02] B. Aboba and D. Simon: "EAP Keying Framework", Internet 
   Draft, Internet Engineering Task Force, March, 2003,  Work in 
   progress. 
    
   [802.11i] I. D. 802.11i/D2, "Draft supplement to standard for 
   telecommunications and information exchange between systems - 
 
 
Tschofenig et al.      Expires - December 2003              [Page 39] 
                                 PANA                        June 2003 
 
 
   lan/man specific requirements - part 11: Wireless medium access 
   control (mac) and physical layer (phy) specifications: Specification 
   for enhanced security," tech. rep., 2001. 
    
   [AS02] Aboba, B., Simon, D.: "EAP GSS Authentication Protocol", 
   Internet Draft, Internet Engineering Task Force, April, 2002, Work 
   in progress. 
    
   [CFB02] P. Calhoun, S. Farrell, and W. Bulley: "Diameter CMS 
   Security Application," Internet Draft, Internet Engineering Task 
   Force, Mar. 2002,  Work in progress. 
    
   [RFC2284] Blunk, L. and J. Vollbrecht, "PPP Extensible 
   Authentication Protocol (EAP)", RFC 2284, March 1998. 
 
   [HBR03] G. Huang, S. Beaulieu, and D. Rochefort, "A traffic-based 
   method of detecting dead ike peers", Internet Draft, Internet 
   Engineering Task Force, 2003,  Work in progress. 
    
   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange 
   (IKE)", RFC 2409, November 1998. 
 
   [MITM] N. Asokan, V. Niemi, and K. Nyberg: "Man-in-the-middle in 
   tunnelled authentication", In the Proceedings of the 11th 
   International Workshop on Security Protocols, Cambridge, UK, April 
   2003. To be published in the Springer-Verlag LNCS series. 
 
   [PEAP] A. Palekar, D. Simon, G. Zorn and S. Josefsson: "Protected 
   EAP Protocol (PEAP)", Internet Draft, Internet Engineering Task 
   Force, March 2003,  Work in progress. 
 
   [PL+03] J. Puthenkulam, V. Lortz, A. Palekar, D. Simon, and B. 
   Aboba, "The compound authentication binding problem," internet 
   draft, Internet Engineering Task Force, 2003.  Work in progress. 
 
   [PY+02] R. Penno, A. Yegin, Y. Ohba, G. Tsirtsis, and C. Wang: 
   "Protocol for Carrying Authentication for Network Access (PANA) 
   Requirements and Terminology", Internet Draft, Internet Engineering 
   Task Force,  June 2003, Work in progress. 
 
   [RFC2284bis]   L. Blunk, J. Vollbrecht, B. Aboba, J. Carlson: 
   "Extensible Authentication Protocol (EAP)", Internet Draft, Internet 
   Engineering Task Force, January 2003, Work in progress.  
    
   [RFC1982] Elz, R., Bush, R.: "Serial Number Arithmetic", RFC 1982, 
   August 1996.  
 
   [RFC2478] E. Baize and D. Pinkas, "The simple and protected GSS-API 

 
 
Tschofenig et al.      Expires - December 2003              [Page 40] 
                                 PANA                        June 2003 
 
 
   negotiation mechanism," RFC 2478, Internet Engineering Task Force, 
   Dec. 1998. 
    
   [RFC2988] V. Paxson,  and M. Allman: "Computing TCP's Retransmission 
   Timer", RFC 2988, November, 2000.  
    
   [RFC3329] J. Arkko,  V. Torvinen, G. Camarillo, A. Niemi, and T. 
   Haukka: "Security Mechanism Agreement for the Session Initiation 
   Protocol (SIP)", RFC 3329, January, 2003.  
 
   [THREATS] M. Parthasarathy: "PANA Threat Analysis and security 
   requirements", Internet Draft, Internet Engineering Task Force, May 
   2003, Work in progress. 
    
   [TTLS] P. Funk and S. Blake-Wilson: "EAP tunneled TLS authentication 
   protocol (EAP-TTLS)," Internet Draft, Internet Engineering Task 
   Force, November  2002.  Work in progress. 
    
   [USAGE] Y. Ohba, S. Das, B. Patil, H. Soliman, A. Yegin, A.: 
   "Problem Statement and Usage Scenarios for PANA", Internet Draft, 
   Internet Engineering Task Force, April 2003, Work in progress. 
    
   [EAP-IKEv2] H. Tschofenig and D. Kroeselberg: "EAP IKEv2 Method 
   (EAP-IKEv2)", Internet Draft, Internet Engineering Task Force, June 
   2003, Work in progress.  
    
   [WHC02] J. Walker, R. Housley, and N. Cam-Winget: "AAA key 
   distribution," Internet Draft, Internet Engineering Task Force, Apr. 
   2002,  Expired. 
    
   [DIAMETER-EAP] T. Hiller and G. Zorn: "Diameter Extensible 
   Authentication Protocol (EAP) Application", Internet Draft, Internet 
   Engineering Task Force, March 2003, Work in progress. 
    
   [DIAMETER] P. Calhoun, J. Loughney, E. Guttman, G. Zorn and J. 
   Arkko: "Diameter Base Protocol", Internet Draft, Internet 
   Engineering Task Force,  December 2002, Work in progress. 
    
   [IANAWEB] IANA, "Number assignment", http://www.iana.org  
    
   [CTP] J. Loughney, M. Nakhjiri, C. Perkins and R. Koodli: 
   "Context Transfer Protocol", Internet Draft, Internet Engineering 
   Task Force, June 2003, Work in progress. 
    
   [JB99]   A. Juels and J. Brainard: "Client Puzzles: A Cryptographic 
   Defense Against Connection Depletion Attacks", In S. Kent, editor, 
   Proceedings of NDSS '99 (Networks and Distributed Security 
   Systems), pages 151-165, 1999. 
 
 
 
Tschofenig et al.      Expires - December 2003              [Page 41] 
                                 PANA                        June 2003 
 
 
Change History 
 
   Changes from PANA-00 to PANA-01 June 2003 
    
   - The names for the PANA messages have been changed. Hence it was 
   necessary to reflect the new terminology in other parts of the 
   draft.  
    
   - New text has been added to the following sections:  
    
     * Terminology 
     * PANA Security Association 
     * Message Authentication Code 
     * Refresh Interval Negotiation 
     * Mobility Handling 
     * Event Notification 
     * Message Formats      
    
   - The details on message formats add more details to several parts 
   of the draft. The AVP format is based on Diameter/  
    
   - The open issue list has been replaced by a reference to the web 
   page containing the open issues.  
    
Author's Addresses 
    
   Basavaraj Patil 
   Nokia 
   6000 Connection Dr. 
   Irving, TX. 75039 
   USA 
   Phone:  +1 972-894-6709 
   Email:  Basavaraj.Patil@nokia.com 
    
   Dan Forsberg  
   Nokia Research Center 
   P.O. Box 407 
   FIN-00045 NOKIA GROUP, Finland 
    
   Phone: +358 50 4839470 
   EMail: dan.forsberg@nokia.com 
    
    
   Alper E. Yegin  
   DoCoMo USA Labs  
   181 Metro Drive, Suite 300  
   San Jose, CA, 95110  
   USA  
   Phone: +1 408 451 4743  
 
 
Tschofenig et al.      Expires - December 2003              [Page 42] 
                                 PANA                        June 2003 
 
 
   Email: alper@docomolabs-usa.com  
    
    
   Yoshihiro Ohba  
   Toshiba America Research, Inc.  
   P.O. Box 136  
   Convent Station, NJ, 07961-0136  
   USA  
   Phone: +1 973 829 5174  
   Email: yohba@tari.toshiba.com  
    
   Hannes Tschofenig  
   Siemens Corporate Technology 
   Otto-Hahn-Ring 6 
   81739 Munich 
   Germany 
   Email: Hannes.Tschofenig@siemens.com 
 
Appendix A.  Adding sequence number to PANA for carrying EAP 
    
   A.1. Why is sequence number needed for PANA to carry EAP? 
    
   EAP [RFC2284bis] requires underlying transports to provide 
   ordered-delivery of messages.  If an underlying transport does not 
   satisfy the ordering requirement, the following situation could 
   happen: 
    
     EAP Peer                 EAP Authenticator 
   -------------------------------------------- 
   1. (got req 1)   <-------  Request ID=1  
   2. Response ID=1 ---+ 
                       |      (timeout) 
   3.                  | +--  Request ID=1 
                       | | 
                       +-|--> (got resp 1) 
   4. (got req 2)   <----|--  Request ID=2  
                         | 
   5. Response ID=2 -----|--> (got resp 2) 
                         | 
   6. (got req 1)   <----+ 
   7. Response ID=1 --------> [discarded due to unexpected ID] 
    
       Figure A.1  Undesirable scenario 
 
   In Figure A.1, the second EAP Request message with Identifier=1 
   arrives at the EAP peer after the third EAP Request message with 
   Identifier=2.  As a result, the EAP peer accepts the second EAP 


 
 
Tschofenig et al.      Expires - December 2003              [Page 43] 
                                 PANA                        June 2003 
 
 
   Request as a new EAP Request while it is just an old EAP Request 
   that was already responded and the authentication might be totally 
   messed up. 
    
   This problem occurs due to the fact that EAP doesn't recognize 
   duplicate packets in the scope of one EAP protocol run, but only in 
   the scope of current and previous packet (i.e., request and response 
   message matching).  When EAP is running over PPP or IEEE 802 links, 
   this is not a problem, because those link-layers have the ordering 
   invariant characteristic. 
    
   On the other hand, the PANA design has chosen UDP as its transport. 
   Given that UDP does not provide ordered delivery of packets and PANA 
   does not assume any specific link-layer technology to carry EAP, 
   PANA messages need to have a sequence number. 
    
   In the following text we describe two possible approaches for 
   sequence number handling in PANA.  The first one makes use of a 
   single sequence number whereas the latter utilizes two.  Finally a 
   comparison between the two approaches is provided.  The method 
   described in Section A.3.1. (i.e., the dual sequence number with 
   orderly-delivery method) is suggested as the preferred method for 
   PANA transport. 
    
   A.2. Single sequence number approach 
    
   This section discusses several methods based on using a single 
   sequence number for providing orderly message delivery.  Sequence 
   number handling for all methods discussed in Section A.2 must comply 
   to the following rules: 
    
   Rule 1: The sequence number starts from initial sequence number 
   (ISN) 
           and is monotonically increased by 1.  The arithmetic defined 
           in [RFC1982] is used for sequence number operation. 
    
   Rule 2: When a PAA sends an EAP message passed from EAP layer to a 
           PaC, a new sequence number is placed in the message, 
           regardless of whether it is sent as a result of a 
           retransmission at the EAP layer or not. 
    
   Note: It might be possible to define other mechanisms for sequence 
   number handling if it can be assumed that a PAA detects EAP 
   retransmissions.  However, such an assumption heavily depends on EAP 
   implementation details in particular on EAP APIs, thus it was 
   decided not to use such an assumption. 
    
    
   A.2.1. Single sequence number with EAP retransmission method 
 
 
Tschofenig et al.      Expires - December 2003              [Page 44] 
                                 PANA                        June 2003 
 
 
    
   Again, the following rules must hold:  
    
   Rule 3: Use EAP layer retransmission for retransmitting EAP messages 
           (based on a timer expiration). 
    
   Rule 4: When the PaC receives a message from the PAA, it checks the 
           sequence number and discards the message if the sequence 
           number is not greater than that of the last accepted 
   message. 
    
   Rule 5: When the PAA receives a message from the PaC, it checks the 
           sequence number and discards the message if the sequence 
           number does not match a pending request message. 
    
     PaC    PAA Seq#  Message 
   -------------------------------------------- 
   1. <-------  (x)   PANA-Auth-Request[EAP Req ID=1] 
   2. ---+      (x)   PANA-Auth-Answer[EAP Res ID=1] 
         |            (retransmission timeout at EAP-layer) 
   3.    | +--  (x+1) PANA-Auth-Request[EAP Req ID=1] 
         | | 
         +-|-->       (discarded due to Rule 5) 
           |          (retransmission timeout at EAP-layer) 
   4. <----|--  (x+2) PANA-Auth-Request[EAP Req ID=1] 
           | 
   5. -----|--> (x+2) PANA-Auth-Answer[EAP Res ID=1] 
           | 
   6. <----+          (discarded due to Rule 4) 
   7. <-------  (x+3) PANA-Auth-Request[EAP Req ID=2] 
         . 
         . 
    
   Figure 1: Example for Single sequence number with EAP retransmission 
                                  method 
    
   This method is vulnerable to a blind DoS attack on the sequence 
   number since the PaC will accept quite a wide range of sequence 
   numbers.  For example, if an attacker blindly sends a bogus message 
   to a legitimate PaC with a randomly chosen sequence number, it will 
   be accepted by the PaC with 50% probability, and once this happens, 
   all messages sent from the communicating PAA will be discarded as 
   long as they have a sequence number smaller than the accepted value.  
   The problem of this method leads to a requirement for PaC to have a 
   narrow range of acceptable sequence numbers to make the blind DoS 
   attack difficult. Note that the DoS attack cannot be prevented if 
   the attacker is on the same IP link as PaC and able to eavesdrop the 
   PANA conversation. However, the attacker needs to put itself in 
   promiscuous mode and thus spend more resources to eavesdrop and 
 
 
Tschofenig et al.      Expires - December 2003              [Page 45] 
                                 PANA                        June 2003 
 
 
   launch the attack (in other words, non-blind DoS attack is still 
   possible as long as sequence numbers are unprotected.) 
    
    
   A.2.2. Single sequence number with PANA-layer retransmission method 
    
   The next method is still based on using a single sequence number but 
   the PANA-layer takes the responsibility of retransmission.  The 
   method uses the following rules in addition to the common rules 
   described in section A.2. 
    
   Rule 3: Use PANA-layer retransmission for retransmitting both EAP 
   and 
           non-EAP messages (based on a timer expiration).  EAP layer 
           retransmission is turned off. Retransmission based on timer 
           occurs both on PaC and PAA side, but not on both sides 
           simultaneously.  PAA does retransmission at least for 
           PANA_Termination and PANA_Reauth messages, otherwise PaC 
           takes care of retransmission. 
    
   Rule 4: When the PaC receives a message from the PAA, it accepts the 
           message if the sequence number is equal to that of the last 
           accepted message + 1.  If the sequence number is equal to 
           that of the last accepted message, the PaC retransmits the 
           last transmitted message.  Otherwise, it silently discards 
           the message. 
    
   Rule 5: When the PAA receives a message from the PaC, it accepts the 
           message if the sequence number is equal to that of the last 
           transmitted message.  If the receiving sequence number is 
           equal to that of the last transmitted message - 1, the PAA 
           retransmits the last transmitted message and discard the 
           received message. Otherwise, it silently discards the  
           message. 
    
   Rule 6: The PaC retransmits the last transmitted EAP Response until 
           a new EAP Request message or an EAP Success/Failure message 
           is received and accepted. 
    
   Rule 7: PAA must keep the copy of the last transmitted message and 
           must be able to retransmit it until either a valid message 
           is received and accepted by the PAA or a timer expires.  The 
           timer is used if no new message will be sent from the PaC. 
    





 
 
Tschofenig et al.      Expires - December 2003              [Page 46] 
                                 PANA                        June 2003 
 
 
    
     PaC    PAA Seq#  Message 
   -------------------------------------------- 
   1. <-------- (x)   PANA-Auth-Request[EAP Req ID=1] 
   2. ---+      (x)   PANA-Auth-Answer[EAP Resp ID=1] 
         |            (retransmission timeout at PaC) 
   3. ---|----> (x)   PANA-Auth-Answer[EAP Resp ID=1] 
   4.    | +--- (x+1) PANA-Auth-Request[EAP Req ID=2] 
         | | 
         +-|-->       (duplicate detected) 
   5. <----|--- (x+1) PANA-Auth-Request[EAP Req ID=2]  
           | 
   6. -----|--> (x+1) PANA-Auth-Answer[EAP Resp ID=2] 
           | 
      <----|--- (x+2) PANA-Auth-Request[EAP Req ID=3]  
   7. -----|--> (x+2) PANA-Auth-Answer[EAP Resp ID=3] 
      <----+          (discarded by PaC) 
                      (retransmission timeout at PaC) 
   8. --------> (x+2) PANA-Auth-Answer[EAP Resp ID=3] 
   9. lost<---- (x+3) PANA-Auth-Request[EAP Succ ID=3] 
                      (retransmission timeout at PaC) 
   10.---->lost (x+2) PANA-Auth-Answer[EAP Resp ID=3] 
                      (retransmission timeout at PaC) 
   11.--------> (x+2) PANA-Auth-Answer[EAP Resp ID=3] 
   12.<-------- (x+3) PANA-Bind-Request[EAP Succ ID=3] 
                      (retransmission timer stopped at PaC) 
                      (deletion timeout at PAA) 
                      (message (x+3) deleted at PAA) 
   13.lost<---- (x+4) PANA-Termination-Request 
                      (retransmission timeout at PAA) 
   14.<-------- (x+4) PANA-Termination-Request 
   15.---->lost (x+4) PANA-Termination-Answer 
                      (retransmission timeout at PAA) 
   16.<-------- (x+4) PANA-Termination-Request 
   17.--------> (x+4) PANA-Termination-Answer 
                      (retransmission timer stopped at PAA) 
    
       Figure 2: Example for Single sequence number with PANA-layer 
                           retransmission method 
    
   This method has an advantage of eliminating EAP layer retransmission 
   by providing reliability at the PANA layer.  Retransmission at the 
   EAP layer has a problem with determining an appropriate 
   retransmission timer value, which occurs when the lower-layer is 
   unreliable.  In this case an EAP authenticator cannot distinguish 
   between (i) EAP Request or EAP Response message loss (in this case 
   the retransmission timer should be calculated based on network 
   characteristics) and (ii) long latency for EAP Response generation 
   due to e.g., user input etc. (in this case the retransmission timer 
 
 
Tschofenig et al.      Expires - December 2003              [Page 47] 
                                 PANA                        June 2003 
 
 
   should be calculated based on user or application characteristics).  
   In general, the retransmission timer for case (ii) is longer than 
   that for case (i).  If case (i) happens while the retransmission 
   timer is calculated based on user or application characteristics, 
   then it might frustrate an end user since the completion of the 
   authentication procedure takes unnecessarily long.  If case (ii) 
   happens while the retransmission timer is calculated based on 
   network characteristics (i.e., RTT), then unnecessarily traffic is 
   generated by retransmission.  Note that in this method a PaC still 
   cannot distinguish case (i) and case (iii) the EAP authenticator or 
   a backend authentication server is taking time to generate an EAP 
   Request. 
    
   A problem of this method is that it is based on the assumption that 
   EAP authenticator does not send a new EAP message until an EAP 
   Response to the outstanding EAP Request is received.  However, this 
   assumption does not hold at least EAP Success/Failure message which 
   does not need the outstanding EAP Request to be responded before 
   sending the EAP Success/Failure message.  This would require 
   timer-based retransmission not only at PaC side but also at PAA 
   side. 
   Another problem occurs when a new EAP message overrides the 
   outstanding EAP Request, the PaC cannot assume any more that the 
   sequence number of the next message to be accepted is the last 
   accepted message + 1.  So the PaC needs to accept a range of 
   sequence numbers, instead of a single sequence number. These two 
   additional things would increase the complexity of this method. 
    
   A.3.  Dual sequence number approach 
    
   Based on the analysis of previous schemes, it is recognized that two 
   sequence numbers are needed anyway, one for each direction.  Two 
   different methods are proposed based on this approach.  Both methods 
   have the following rules in common. 
    
    
   Rule 1: A PANA packet carries two sequence numbers: transmitted 
           sequence number (tseq) and received sequence number (rseq). 
           tseq starts from initial sequence number (ISN) and is 
           monotonically increased by 1.  The arithmetic defined in 
           [RFC1982] is used for sequence number operation.  It is 
           assumed that the two sequence numbers have the same length 
           for simplicity. 
    
   Rule 2: When PAA or PAC sends a new message, a new sequence number 
           is placed on the tseq field of message.  Every transmitted 
           message is given a new sequence number. 
    
   Rule 3: When a message is sent from PaC or PAA, rseq is copied from 
 
 
Tschofenig et al.      Expires - December 2003              [Page 48] 
                                 PANA                        June 2003 
 
 
           the tseq field of the last accepted message. 
    
   Rule 4: For messages which experience a PANA layer retransmission, 
           the retransmission timer is stopped when the message is 
           acknowledged. 
    
   It is possible to carry multiple EAP sequences in a single PANA 
   sequence, with using EAP Success/Failure message as a delimiter of 
   each EAP sequence.  In this case, EAP Success/Failure message needs 
   to be reliably delivered. 
    
    
   A.3.1.  Dual sequence number with orderly-delivery method 
    
   This method relies on EAP layer retransmission for EAP messages.  
   This method is referred to as orderly-delivery method.  The 
   following rules are used in addition to the common rules. 
    
   Rule 5: Use the EAP-layer retransmission for retransmitting EAP 
           Requests (based on a timer expiration).  For other PANA 
           layer messages that require a response from the peer, PANA 
           layer has its own mechanism to retransmit the request until 
           it gets a response or gives up.  A new tseq value is always 
           used when sending any message even when it is retransmitted 
           at PANA layer. 
    
   Rule 6: When a message is received, it is accepted if (i) the tseq 
           value is greater than the tseq of the last accepted message 
           and (ii) the rseq falls in the range between the tseq of the 
           last acknowledged message + 1 and the tseq of the last 
           transmitted message.  Otherwise, the received message is 
           discarded. 
    
    
     PaC    PAA  (tseq,rseq) Message 
   -------------------------------------------------- 
   1. <-------   (x,y)       PANA-Auth-Request[EAP Req, ID=1] 
   2. ------->   (y+1,x)     PANA-Auth-Answer[EAP Resp, ID=1]  
   3. <-------   (x+1,y+1)   PANA-Auth-Request[EAP Req, ID=2] 
   4. --->lost   (y+2,x+1)   PANA-Auth-Answer[EAP Resp, ID=2] 
                             (retransmission timeout at EAP layer) 
   5. <-------   (x+2,y+1)   PANA-Auth-Request [EAP Req, ID=2] 
   6. ------->   (y+3,x+2)   PANA-Auth-Answer[EAP Resp, ID=2] 
   7. lost<---   (x+3,y+3)   PANA-Auth-Request[EAP Req, ID=3] 
                             (retransmission timeout at EAP layer) 
   8.    +----   (x+4,y+3)   PANA-Auth-Answer[EAP Req, ID=3] 
         |                   (retransmission timeout at EAP layer) 
   9. <--|----   (x+5,y+3)   PANA-Auth-Request[EAP Req, ID=3] 
   10.---|--->   (y+4,x+5)   PANA-Auth-Answer[EAP Resp, ID=3] 
 
 
Tschofenig et al.      Expires - December 2003              [Page 49] 
                                 PANA                        June 2003 
 
 
         | 
      <--+                   (out of order. discarded) 
   11.lost<---   (x+6,y+4)   PANA-Bind-Request[EAP Succ, ID=3] 
                             (retransmission timeout at PAA) 
   12.<-------   (x+7,y+4)   PANA-Bind-Request[EAP Succ, ID=3] 
   13.--->lost   (y+5,x+7)   PANA-Bind-Answer 
                             (retransmission timeout at PAA) 
   14.<-------   (x+8,y+4)   PANA-Bind-Request[EAP Succ, ID=3] 
                             (dupicate detected by PaC) 
   15.------->   (y+6,x+8)   PANA-Bind-Answer 
    
     Figure 3: Example for Dual sequence number with orderly-delivery 
                                  method 
    
   A.3.2.  Dual sequence number with reliable-delivery method 
    
   This method relies solely on PANA layer retransmission for all 
   messages.  This method is referred to as reliable-delivery method. 
   The following additional rules are applied in addition to the common 
   rules. 
    
    
   Rule 5: Use the PANA layer retransmission for retransmitting all 
           messages (based on a timer expiration).  EAP retransmission 
           is turned off. 
    
   Rule 6: Either an ACK message is used for acknowledgment or an 
           acknowledgment can be piggybacked with data.  ACK messages 
           are not retransmitted.  An ACK message is sent if no the 
           acknowledgement cannot be piggybacked with a data within a 
           given time frame W. 
    
   Rule 7: When a message is received, it is accepted if (i) the tseq 
           value is greater than the tseq of the last accepted message 
           and (ii) the rseq falls in the range between the tseq of the 
           last acknowledged message and the tseq of the last 
           transmitted message.  Otherwise, the received message is 
           discarded.   
    
   Rule 8: When a duplicate message is received, the last transmitted 
           message is retransmitted if the received message is not an 
           ACK.  A message is considered as duplicate if its tseq value 
           is equal to the tseq of the last accepted message. 
    
    




 
 
Tschofenig et al.      Expires - December 2003              [Page 50] 
                                 PANA                        June 2003 
 
 
     PaC    PAA  (tseq,rseq) Message 
   -------------------------------------------------- 
   1. <-------   (x,y)       PANA-Auth-Request[EAP Req, ID=1] 
                             (user input ongoing) 
   2. ------->   (y+1,x)     PANA-Auth-Answer 
                             (user input completed) 
   3. ------->   (y+2,x)     PANA-Auth-Answer[EAP Resp, ID=1]  
   4. <-------   (x+1,y+2)   PANA-Auth-Request [EAP Req, ID=2] 
   5. --->lost   (y+3,x+1)   PANA-Auth-Answer[EAP Resp, ID=2] 
                             (retransmission timeout at PAA) 
   6. <-------   (x+1,y+2)   PANA-Auth-Request [EAP Req, ID=2] 
                             (duplicate detected by PaC) 
   7. ------->   (y+3,x+1)   PANA-Auth-Answer[EAP Resp, ID=2] 
   8. lost<---   (x+2,y+3)   PANA-Auth-Request [EAP Req, ID=3] 
                             (retransmission timeout at PaC) 
   9. ------->   (y+3,x+1)   PANA-Auth-Answer[EAP Resp, ID=2] 
                             (duplicate detected at PAA) 
   10.<-------   (x+2,y+3)   PANA-Auth-Request [EAP Req, ID=3] 
   11.---+       (y+4,x+2)   PANA-Auth-Answer[EAP Resp, ID=3] 
         |                   (retransmission timeout at PAA) 
   12.<--|----   (x+2,y+3)   PANA-Auth-Request [EAP Req, ID=3] 
         |                   (duplicate detected at PaC) 
   13.---|--->   (y+4,x+2)   PANA-Auth-Answer[EAP Resp, ID=3] 
   14.<--|----   (x+3,y+4)   PANA-Bind-Request[EAP Succ, ID=3] 
   15.---|--->   (y+5,x+3)   PANA-Bind-Answer 
         +--->               (out of order. discarded) 
    
     Figure 4: Example for Dual sequence number with reliable-delivery 
                                  method 
    
    
   A.3.3  Comparison of the dual sequence number methods 
    
   The orderly-delivery method is simpler than the reliable-delivery 
   method in that the former does not allow sending a separate ACK 
   while the latter does. 
    
   In terms of authentication performance, the reliable-delivery method 
   is better than the orderly-delivery method in that the former gives 
   more detailed status of the link than the latter, e.g., an entity 
   can know whether a request has reached the communicating peer 
   without before receiving a response.  The reliable-delivery can 
   reduce retransmission traffic and communication delay that would 
   occur if there is no reliability, as described in section A.2.2. 
    
    
   A.4  Consensus 
    

 
 
Tschofenig et al.      Expires - December 2003              [Page 51] 
                                 PANA                        June 2003 
 
 
   Although it is recognizable that the reliable-delivery method would 
   be important in terms of improvement of overall authentication 
   latency, we believe that this is a performance problem of EAP and 
   not a problem of PANA.  It is agreed that solving the EAP problem is 
   not the scope of PANA and simplicity is more important factor in the 
   PANA design. 
    
   As a consequence, the orderly-delivery method is chosen as the 
   message transport part of PANA. 
 
 
Full Copyright Statement 
 
   Copyright (C) The Internet Society (2003). All Rights Reserved. 
    
   This document and translations of it may be copied and furnished to 
   others, and derivative works that comment on or otherwise explain it 
   or assist in its implementation may be prepared, copied, published 
   and distributed, in whole or in part, without restriction of any 
   kind, provided that the above copyright notice and this paragraph 
   are included on all such copies and derivative works. However, this 
   document itself may not be modified in any way, such as by removing 
   the copyright notice or references to the Internet Society or other 
   Internet organizations, except as needed for the purpose of 
   developing Internet standards in which case the procedures for 
   copyrights defined in the Internet Standards process must be 
   followed, or as required to translate it into languages other than 
   English. 
    
   The limited permissions granted above are perpetual and will not be 
   revoked by the Internet Society or its successors or assignees. 
    
   This document and the information contained herein is provided on an 
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 
 
 
Acknowledgement 
    
   Funding for the RFC Editor function is currently provided by the 
   Internet Society. 
 
 



 
 
Tschofenig et al.      Expires - December 2003              [Page 52]