PANA Working Group D. Forsberg Internet-Draft Nokia Intended status: Standards Track Y. Ohba (Ed.) Expires: June 9, 2007 Toshiba B. Patil Nokia H. Tschofenig Siemens A. Yegin Samsung December 6, 2006 Protocol for Carrying Authentication for Network Access (PANA) draft-ietf-pana-pana-13 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 9, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Forsberg, et al. Expires June 9, 2007 [Page 1] Internet-Draft PANA December 2006 Abstract This document defines the Protocol for Carrying Authentication for Network Access (PANA), a network-layer transport for Extensible Authentication Protocol (EAP) to enable network access authentication between clients and access networks. PANA protocol specification covers the client-to-network access authentication part of an overall secure network access framework, which additionally includes other protocols and mechanisms for service provisioning, access control as a result of initial authentication, and accounting. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Specification of Requirements . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 8 4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Transport Layer . . . . . . . . . . . . . . . . . . . . . 10 4.2. High-Level Attribute-Value Pair Description . . . . . . . 10 4.3. Handshake Phase . . . . . . . . . . . . . . . . . . . . . 10 4.4. Authentication and Authorization Phase . . . . . . . . . . 12 4.5. Access Phase . . . . . . . . . . . . . . . . . . . . . . . 14 4.6. Re-authentication Phase . . . . . . . . . . . . . . . . . 14 4.7. Termination Phase . . . . . . . . . . . . . . . . . . . . 16 5. Processing Rules . . . . . . . . . . . . . . . . . . . . . . . 17 5.1. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 17 5.2. Sequence Number and Retransmission . . . . . . . . . . . . 17 5.3. PANA Security Association . . . . . . . . . . . . . . . . 18 5.4. Message Authentication . . . . . . . . . . . . . . . . . . 19 5.5. Message Validity Check . . . . . . . . . . . . . . . . . . 20 5.6. PaC Updating its IP Address . . . . . . . . . . . . . . . 21 5.7. Session Lifetime . . . . . . . . . . . . . . . . . . . . . 21 5.8. Error Handling . . . . . . . . . . . . . . . . . . . . . . 22 6. Header Format . . . . . . . . . . . . . . . . . . . . . . . . 24 6.1. IP and UDP Headers . . . . . . . . . . . . . . . . . . . . 24 6.2. PANA Message Header . . . . . . . . . . . . . . . . . . . 24 6.3. AVP Header . . . . . . . . . . . . . . . . . . . . . . . . 26 7. PANA Messages . . . . . . . . . . . . . . . . . . . . . . . . 29 7.1. PANA-Client-Initiation (PCI) . . . . . . . . . . . . . . . 31 7.2. PANA-Start-Request (PSR) . . . . . . . . . . . . . . . . . 31 7.3. PANA-Start-Answer (PSA) . . . . . . . . . . . . . . . . . 31 7.4. PANA-Auth-Request (PAR) . . . . . . . . . . . . . . . . . 32 7.5. PANA-Auth-Answer (PAN) . . . . . . . . . . . . . . . . . . 32 7.6. PANA-Reauth-Request (PRR) . . . . . . . . . . . . . . . . 32 7.7. PANA-Reauth-Answer (PRA) . . . . . . . . . . . . . . . . . 32 7.8. PANA-Bind-Request (PBR) . . . . . . . . . . . . . . . . . 32 Forsberg, et al. Expires June 9, 2007 [Page 2] Internet-Draft PANA December 2006 7.9. PANA-Bind-Answer (PBA) . . . . . . . . . . . . . . . . . . 33 7.10. PANA-Ping-Request (PPR) . . . . . . . . . . . . . . . . . 33 7.11. PANA-Ping-Answer (PPA) . . . . . . . . . . . . . . . . . . 33 7.12. PANA-Termination-Request (PTR) . . . . . . . . . . . . . . 33 7.13. PANA-Termination-Answer (PTA) . . . . . . . . . . . . . . 34 7.14. PANA-Error-Request (PER) . . . . . . . . . . . . . . . . . 34 7.15. PANA-Error-Answer (PEA) . . . . . . . . . . . . . . . . . 34 7.16. PANA-Update-Request (PUR) . . . . . . . . . . . . . . . . 34 7.17. PANA-Update-Answer (PUA) . . . . . . . . . . . . . . . . . 34 8. AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . . . . 36 8.1. Algorithm AVP . . . . . . . . . . . . . . . . . . . . . . 37 8.2. AUTH AVP . . . . . . . . . . . . . . . . . . . . . . . . . 37 8.3. EAP-Payload AVP . . . . . . . . . . . . . . . . . . . . . 37 8.4. Failed-AVP AVP . . . . . . . . . . . . . . . . . . . . . . 38 8.5. Failed-Message-Header AVP . . . . . . . . . . . . . . . . 38 8.6. Key-Id AVP . . . . . . . . . . . . . . . . . . . . . . . . 38 8.7. Nonce AVP . . . . . . . . . . . . . . . . . . . . . . . . 38 8.8. Result-Code AVP . . . . . . . . . . . . . . . . . . . . . 39 8.8.1. Authentication Results Codes . . . . . . . . . . . . . 39 8.8.2. Protocol Error Result Codes . . . . . . . . . . . . . 39 8.9. Session-Lifetime AVP . . . . . . . . . . . . . . . . . . . 42 8.10. Termination-Cause AVP . . . . . . . . . . . . . . . . . . 42 9. Retransmission Timers . . . . . . . . . . . . . . . . . . . . 43 9.1. Transmission and Retransmission Parameters . . . . . . . . 44 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 10.1. PANA UDP Port Number . . . . . . . . . . . . . . . . . . . 46 10.2. PANA Message Header . . . . . . . . . . . . . . . . . . . 46 10.2.1. Version . . . . . . . . . . . . . . . . . . . . . . . 46 10.2.2. Message Type . . . . . . . . . . . . . . . . . . . . . 46 10.2.3. Flags . . . . . . . . . . . . . . . . . . . . . . . . 47 10.3. AVP Header . . . . . . . . . . . . . . . . . . . . . . . . 47 10.3.1. AVP Code . . . . . . . . . . . . . . . . . . . . . . . 47 10.3.2. Flags . . . . . . . . . . . . . . . . . . . . . . . . 48 10.4. AVP Values . . . . . . . . . . . . . . . . . . . . . . . . 48 10.4.1. Result-Code AVP Values . . . . . . . . . . . . . . . . 48 10.4.2. Termination-Cause AVP Values . . . . . . . . . . . . . 48 11. Security Considerations . . . . . . . . . . . . . . . . . . . 49 11.1. General Security Measures . . . . . . . . . . . . . . . . 49 11.2. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 50 11.3. EAP Methods . . . . . . . . . . . . . . . . . . . . . . . 51 11.4. Cryptographic Keys . . . . . . . . . . . . . . . . . . . . 51 11.5. Per-packet Ciphering . . . . . . . . . . . . . . . . . . . 51 11.6. PAA-to-EP Communication . . . . . . . . . . . . . . . . . 52 11.7. Liveness Test . . . . . . . . . . . . . . . . . . . . . . 52 11.8. IP Address Spoofing . . . . . . . . . . . . . . . . . . . 52 11.9. Early Termination of a Session . . . . . . . . . . . . . . 52 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 54 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Forsberg, et al. Expires June 9, 2007 [Page 3] Internet-Draft PANA December 2006 13.1. Normative References . . . . . . . . . . . . . . . . . . . 55 13.2. Informative References . . . . . . . . . . . . . . . . . . 55 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 57 Intellectual Property and Copyright Statements . . . . . . . . . . 59 Forsberg, et al. Expires June 9, 2007 [Page 4] Internet-Draft PANA December 2006 1. Introduction Providing secure network access service requires access control based on the authentication and authorization of the clients and the access networks. Client-to-network authentication provides parameters that are needed to police the traffic flow through the enforcement points. A protocol is needed to carry authentication methods between the client and the access network. Scope of this work is identified as designing a network layer transport for network access authentication methods. The Extensible Authentication Protocol (EAP) [RFC3748] provides such authentication methods. In other words, PANA will carry EAP which can carry various authentication methods. By the virtue of enabling transport of EAP above IP, any authentication method that can be carried as an EAP method is made available to PANA and hence to any link-layer technology. There is a clear division of labor between PANA (an EAP lower layer), EAP and EAP methods as described in [RFC3748]. Various environments and usage models for PANA are identified in Appendix A of [RFC4058]. Potential security threats for network-layer access authentication protocol are discussed in [RFC4016]. These have been essential in defining the requirements [RFC4058] on the PANA protocol. Note that some of these requirements are imposed by the chosen payload, EAP [RFC3748]. There are components that are part of a complete secure network access solution but are outside of the PANA protocol specification, including authentication method choice, data traffic protection, PAA-EP protocol, and PAA discovery. PANA authentication output is used for creating access control filters. These components are described in separate documents (see [I-D.ietf-pana-framework], [I-D.ietf-pana-snmp] and [I-D.ietf-dhc-paa-option]). The readers are recommended to read the PANA Framework document [I-D.ietf-pana-framework] prior to reading this protocol specification document. 1.1. Specification of Requirements In this document, several words are used to signify the requirements of the specification. These words are often capitalized. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Forsberg, et al. Expires June 9, 2007 [Page 5] Internet-Draft PANA December 2006 2. Terminology PANA Client (PaC): The client side of the protocol that resides in the access device (e.g., laptop, PDA, etc.). It is responsible for providing the credentials in order to prove its identity (authentication) for network access authorization. The PaC and the EAP peer are co-located in the same access device. PANA Authentication Agent (PAA): The protocol entity in the access network whose responsibility is to verify the credentials provided by a PANA client (PaC) and authorize network access to the access device. The PAA and the EAP authenticator (and optionally the EAP server) are co-located in the same node. Note the authentication and authorization procedure can, according to the EAP model, also be offloaded to the backend AAA infrastructure. PANA Session: A PANA session begins with the handshake between the PANA Client (PaC) and the PANA Authentication Agent (PAA), and terminates as a result of an authentication or liveness test failure, a message delivery failure after retransmissions reach maximum values, session lifetime expiration, or an explicit termination message. A fixed session identifier is maintained throughout a session. A session cannot be shared across multiple network interfaces. Session Lifetime: A duration that is associated with a PANA session. For an established PANA session, the session lifetime is bound to the lifetime of the current authorization given to the PaC. The session lifetime can be updated by a new round of EAP authentication before it expires. Session Identifier: This identifier is used to uniquely identify a PANA session on the PaC and the PAA. It is included in PANA messages to bind the message to a specific PANA session. This bidirectional identifier is allocated by the PAA in handshake phase and freed when the session terminates. The session identifier is assigned by the PAA and unique within the PAA during the lifetime of the session. Forsberg, et al. Expires June 9, 2007 [Page 6] Internet-Draft PANA December 2006 PANA Security Association (PANA SA): A PANA security association is formed between the PaC and the PAA by sharing cryptographic keying material and associated context. The formed duplex security association is used to protect the bidirectional PANA signaling traffic between the PaC and PAA. Enforcement Point (EP): A node on the access network where per-packet enforcement policies (i.e., filters) are applied on the inbound and outbound traffic of access devices. The EP and the PAA may be co-located. EPs should prevent data traffic from and to any unauthorized client unless it's either PANA or one of the other allowed traffic types (e.g., ARP, IPv6 neighbor discovery, DHCP, etc.). Detailed enforcement policies may be specified in deployment-specific PANA applicability documents. Master Session Key (MSK): A key derived by the EAP peer and the EAP server and transported to the EAP authenticator [RFC3748]. For additional terminology definitions see the PANA framework document [I-D.ietf-pana-framework]. Forsberg, et al. Expires June 9, 2007 [Page 7] Internet-Draft PANA December 2006 3. Protocol Overview The PANA protocol is run between a client (PaC) and a server (PAA) in order to perform authentication and authorization for the network access service. The protocol messaging consists of a series of request and responses, some of which may be initiated by either end. Each message can carry zero or more AVPs within the payload. The main payload of PANA is EAP which performs authentication. PANA helps the PaC and PAA establish an EAP session. PANA is a UDP-based protocol. It has its own retransmission mechanism to reliably deliver messages. PANA messages are sent between the PaC and PAA as part of a PANA session. A PANA session consists of distinct phases: o Handshake phase: This is the phase that initiates a new PANA session. The handshake phase can be triggered by both the PaC and the PAA. o Authentication and authorization phase: Immediately following the handshake phase is the EAP execution between the PAA and PaC. The EAP payload (which carry an EAP method inside) is what is used for authentication. The PAA conveys the result of authentication and authorization to the PaC at the end of this phase. o Access phase: After a successful authentication and authorization the host gains access to the network and can send and receive IP data traffic through the EP(s). At any time during this phase, the PaC and PAA may optionally send PANA ping messages to test liveness of the PANA session on the peer. o Re-authentication phase: During the access phase, the PAA must initiate re-authentication before the PANA session lifetime expires. EAP is carried by PANA to perform authentication. This phase may be optionally triggered by both the PaC and the PAA without any respect to the session lifetime. The session moves to this phase from the access phase, and returns back there upon successful re-authentication. o Termination phase: The PaC or PAA may choose to discontinue the access service at any time. An explicit disconnect message can be sent by either end. If either the PaC or the PAA disconnects without engaging in termination messaging, it is expected that either the expiration of a finite session lifetime or failed liveness tests would clean up the session at the other end. Forsberg, et al. Expires June 9, 2007 [Page 8] Internet-Draft PANA December 2006 PaC PAA Message ----------------------------------------------------- // Handshake phase -----> PANA-Client-Initiation <----- PANA-Start-Request -----> PANA-Start-Answer // Authentication and authorization phase <----- PANA-Auth-Request /* EAP Request */ -----> PANA-Auth-Answer -----> PANA-Auth-Request /* EAP Response */ <----- PANA-Auth-Answer <----- PANA-Bind-Request /* EAP Success */ -----> PANA-Bind-Answer // Access phase (IP data traffic allowed) <----- PANA-Ping-Request -----> PANA-Ping-Answer // Termination phase -----> PANA-Termination-Request <----- PANA-Termination-Answer Figure 1: Illustration of PANA messages in a session Note that depending on the environment and deployment the protocol flow depicted in Figure 1 can be abbreviated (An unsolicited PANA-Start-Request message can be sent without PANA-Client-Initiation, EAP responses can be piggybacked on the PANA-Auth-Answers, and PANA-Ping and PANA-Termination usage is optional). Cryptographic protection of messages between the PaC and PAA is possible as soon as EAP in conjunction with the EAP method exports a shared key. That shared key is used to create a PANA SA. The PANA SA helps generate per-message authentication codes that provide integrity protection and authentication. Throughout the lifetime of a session, various problems found with the incoming messages can generate a PANA error message sent in response. Forsberg, et al. Expires June 9, 2007 [Page 9] Internet-Draft PANA December 2006 4. Protocol Details The following sections explain in detail the various phases of a PANA session. 4.1. Transport Layer PANA uses UDP as its transport layer protocol. The UDP port number is To Be Assigned by IANA. All messages are always unicast. 4.2. High-Level Attribute-Value Pair Description The payload of any PANA message consists of zero or more AVPs (Attribute Value Pairs). The subsequent sections refer to these AVPs, therefore the list of AVPs are provided with a brief description before more extensive descriptions are included later in the document (see Section 8). o Algorithm AVP: contains a pseudo-random function and an integrity algorithm. o AUTH AVP: contains a Message Authentication Code that integrity protects the PANA message. o EAP AVP: contains an EAP PDU. o Failed-AVP: contains an offending AVP that caused a failure. o Failed-Message-Header AVP: contains the header of an offending message that caused a failure. o Key-Id AVP: contains an MSK identifier. o Nonce AVP: contains a randomly chosen value [RFC4086] that is used in cryptographic key computations. o Result-Code AVP: contains information about the protocol execution results. o Session-Lifetime AVP: contains the duration of authorized access. o Termination-Cause AVP: contains the reason of session termination. 4.3. Handshake Phase The handshake phase can be initiated by either the PaC or the PAA. Forsberg, et al. Expires June 9, 2007 [Page 10] Internet-Draft PANA December 2006 PaC-initiated Handshake: When the PaC initiates the handshake phase, it sends a PANA-Client-Initiation message to the PAA. When the PaC is not configured with an IP address of the PAA before initiating the handshake phase, DHCP [I-D.ietf-dhc-paa-option] is used as the default method for dynamically configuring the IP address of the PAA. Alternative methods for dynamically discovering the IP address of the PAA may be used for PaC-initiated handshake but they are outside the scope of this specification. The PAA that receives the PANA-Client-Initiation message MUST respond with a PANA-Start-Request message sent to the PaC. PAA-initiated Handshake: When the PAA knows the IP address of the PaC, it MAY send an unsolicited PANA-Start-Request to the PaC. The details of how PAA can learn the IP address of the PaC are outside the scope of this specification. A session identifier for the session is assigned by the PAA in the handshake phase and carried in the PANA-Start-Request message. The same session identifier MUST be carried in the subsequent messages exchanged between the PAA and PaC throughout the session. When the PaC receives a PANA-Start-Request message from a PAA, it responds with a PANA-Start-Answer message if it wishes to enter the authentication and authorization phase. The PAA MAY limit the rate it processes incoming PANA-Client-Initiation messages. An Algorithm AVP MAY be included in the PANA-Start-Request in order to indicate required and available capabilities for the network access. This AVP MAY be used by the PaC for assessing the capability match even before the authentication takes place. Since this AVP is provided during the insecure handshake phase, there are certain security risks involved in using the provided information. See Section 11 for further discussion on this. The initial EAP Request message MAY be carried by the PANA-Start-Request message (as oppose to by a later PANA-Auth-Request message) in order to reduce the number of round-trips. If the initial EAP Request message is carried in the PANA-Start-Request message, an EAP Response message MUST be carried in the PANA-Start-Answer message returned to the PAA. In order to prevent potential DoS attacks, the PAA MAY refrain from Forsberg, et al. Expires June 9, 2007 [Page 11] Internet-Draft PANA December 2006 timeout-based retransmission of the PANA-Start-Request message in response to a PaC-initiated handshake. For this reason, the PaC MUST retransmit the PANA-Client-Initiation message until it enters the authentication and authorization phase by receiving the first PANA-Auth-Request message from the PAA. It is possible that both the PAA and the PaC initiate the handshake procedure at the same time, i.e., the PAA sends a PANA-Start-Request message while the PaC sends a PANA-Client-Initiation message. To resolve the race condition, the PAA SHOULD silently discard the PANA-Client-Initiation message received from the PaC after it has sent a PANA-Start-Request message. Figure 2 shows an example sequence for PaC-initiated handshake. PaC PAA Message(sequence number)[AVPs] ------------------------------------------------------ -----> PANA-Client-Initiation(0) <----- PANA-Start-Request(x) -----> PANA-Start-Answer(x) (continued to the authentication and authorization phase) Figure 2: Example sequence for PaC-initiated handshake phase 4.4. Authentication and Authorization Phase The main task of the authentication and authorization phase is to carry EAP messages between the PaC and the PAA. EAP Request and Response messages are carried in PANA-Auth-Request messages. PANA-Auth-Answer messages are simply used to acknowledge receipt of the requests. As an optimization, a PANA-Auth-Answer message MAY include the EAP Response message. This optimization MAY not be used when it takes time to generate the EAP Response message (due to, e.g., intervention of human input), in which case returning an PANA-Auth-Answer message without piggybacking an EAP Response message can avoid unnecessary retransmission of the PANA-Auth-Request message. Another optimization allows optionally carrying the first EAP Request/Response message in PANA-Start-Request/Answer message as described in Section 4.3. A Nonce AVP MUST be included in the first PANA-Auth-Request and PANA-Auth-Answer messages. The result of PANA authentication is carried in a PANA-Bind-Request message sent from the PAA to the PaC. This message carries the EAP authentication result and the result of PANA authentication. The PANA-Bind-Request message MUST be acknowledged with a Forsberg, et al. Expires June 9, 2007 [Page 12] Internet-Draft PANA December 2006 PANA-Bind-Answer (PBA) message. Figure 3 shows an example sequence in the authentication and authorization phase. PaC PAA Message(sequence number)[AVPs] -------------------------------------------------------------------- (continued from the handshake phase) <----- PANA-Auth-Request(x+1)[Nonce, EAP{Request}] -----> PANA-Auth-Answer(x+1)[Nonce] // No piggybacking EAP Resp. -----> PANA-Auth-Request(y)[EAP{Response}] <----- PANA-Auth-Answer(y) <----- PANA-Auth-Request(x+2)[EAP{Request}] -----> PANA-Auth-Answer(x+2)[EAP{Response}] <----- PANA-Bind-Request(x+3)[Result-Code, EAP{Success}, Key-Id, Algorithm, Lifetime, AUTH] -----> PANA-Bind-Answer(x+3)[Key-Id, AUTH] Figure 3: Example sequence for the authentication and authorization phase When an EAP method that is capable of deriving keys is used during the authentication and authorization phase and the keys are successfully derived, the PANA message that carries the EAP Success message (i.e., a PANA-Bind-Request message) MUST contain a Key-Id AVP and an AUTH AVP, and an Algorithm AVP for the first derivation of keys in the session, and any subsequent message MUST contain an AUTH AVP. An Algorithm AVP MUST NOT be contained in a PANA-Bind-Request message after the first derivation of keys in the session. EAP authentication can fail at a pass-through authenticator without sending an EAP Failure message [RFC4137]. When this occurs, the PAA SHOULD send a PANA-Error-Request message to the PaC with using PANA_UNABLE_TO_COMPLY result code. The PaC MUST NOT change its state unless the error message is secured by PANA or lower-layer. In any case, a more appropriate way is to rely on a timeout on the PaC. There is a case where EAP authentication succeeds with producing an EAP Success message but network access authorization fails due to, e.g., authorization rejected by a AAA or authorization locally rejected by the PAA. When this occurs, the PAA MUST send a PANA-Bind-Request with a result code PANA_AUTHORIZATION_REJECTED. If an MSK is established between the PaC and the PAA by the time when the EAP Success message is generated by the EAP server (this is the case when the EAP method provides protected success indication), the PANA-Bind-Request and PANA-Bind-Answer messages MUST be protected with an AUTH AVP and carry a Key-Id AVP. The PANA-Bind-Request message MUST also carry an Algorithm AVP if it is for the first derivation of keys in the session. The MSK and the PANA session MUST be deleted immediately after the PANA-Bind message exchange. Forsberg, et al. Expires June 9, 2007 [Page 13] Internet-Draft PANA December 2006 4.5. Access Phase Once the authentication and authorization phase or the re-authentication phase successfully completes, the PaC gains access to the network and can send and receive IP data traffic through the EP(s) and the PANA session enters the access phase. In this phase, PANA-Ping-Request and PANA-Ping-Answer messages can be used for testing the liveness of the PANA session on the PANA peer. Both the PaC and the PAA are allowed to send a PANA-Ping-Request message to the communicating peer whenever they need to make sure the availability of the session on the peer and expect the peer to return a PANA-Ping-Answer message. Both PANA-Ping-Request and PANA-Ping-Answer messages MUST be protected with an AUTH AVP when a PANA SA is available. Implementations MUST limit the rate of performing this test. The PaC and the PAA can handle rate limitation on their own, they do not have to perform any coordination with each other. There is no negotiation of timers for this purpose. Additionally, an implementation MAY rate-limit processing the incoming PANA-Ping-Requests. Figure 4 and Figure 5 show liveness tests as they are initiated by the PaC and the PAA respectively. PaC PAA Message(sequence number)[AVPs] ------------------------------------------------------ -----> PANA-Ping-Request(q)[AUTH] <----- PANA-Ping-Answer(q)[AUTH] Figure 4: Example sequence for PaC-initiated liveness test PaC PAA Message(sequence number)[AVPs] ------------------------------------------------------ <----- PANA-Ping-Request(p)[AUTH] -----> PANA-Ping-Answer(p)[AUTH] Figure 5: Example sequence for PAA-initiated liveness test 4.6. Re-authentication Phase The PANA session in the access phase can enter the re-authentication phase to extend the current session lifetime by re-executing EAP. Once the re-authentication phase successfully completes, the session re-enters the access phase. Otherwise, the session is deleted. When the PaC wants to initiate re-authentication, it sends a Forsberg, et al. Expires June 9, 2007 [Page 14] Internet-Draft PANA December 2006 PANA-Reauth-Request message to the PAA. This message MUST contain the session identifier assigned to the session being re-authenticated. If the PAA already has an established PANA session for the PaC with the matching session identifier, it MUST first respond with a PANA-Reauth-Answer message, followed by a PANA-Auth-Request message that starts a new EAP authentication. If the PAA cannot identify the session, it MUST silently discard the message. A Nonce AVP MUST be included in the first PANA-Auth-Request and PANA-Auth-Answer messages in the re-authentication phase. The PaC may receive a PANA-Auth-Request before receiving the answer to its outstanding PANA-Reauth-Request. This condition can arise due to packet re-ordering or a race condition between the PaC and PAA when they both attempt to engage in re-authentication. The PaC MUST keep discarding the received PANA-Auth-Requests until it receives the answer to its request. When the PAA initiates re-authentication, it sends a PANA-Auth-Request message containing the session identifier for the PaC to enter the re-authentication phase. The PAA SHOULD initiate EAP re-authentication before the current session lifetime expires. Re-authentication of an on-going PANA session MUST maintain the existing sequence numbers. For any re-authentication, if there is an established PANA SA, PANA-Reauth-Request, PANA-Reauth-Answer, PANA-Auth-Request and PANA-Auth-Answer messages MUST be protected by adding an AUTH AVP to each message. PaC PAA Message(sequence number)[AVPs] ------------------------------------------------------ -----> PANA-Reauth-Request(q)[AUTH] <----- PANA-Reauth-Answer(q)[AUTH] <----- PANA-Auth-Request(p)[EAP{Request}, AUTH] -----> PANA-Auth-Answer(p)[AUTH] // No piggybacking EAP Resp. -----> PANA-Auth-Request(q+1)[EAP{Response}, AUTH] <----- PANA-Auth-Answer(q+1)[AUTH] // No piggybacking EAP Resp. <----- PANA-Auth-Request(p+1)[EAP{Request}, AUTH] -----> PANA-Auth-Answer(p+1)[EAP{Response}, AUTH] <----- PANA-Bind-Request(p+2)[Result-Code, EAP{Success}, Key-Id, Algorithm, Lifetime, AUTH] -----> PANA-Bind-Answer(p+2)[Key-Id, AUTH] Figure 6: Example sequence for the re-authentication phase initiated by PaC Forsberg, et al. Expires June 9, 2007 [Page 15] Internet-Draft PANA December 2006 4.7. Termination Phase A procedure for explicitly terminating a PANA session can be initiated either from the PaC (i.e., disconnect indication) or from the PAA (i.e., session revocation). The PANA-Termination-Request and PANA-Termination-Answer message exchanges are used for disconnect indication and session revocation procedures. The reason for termination is indicated in the Termination-Cause AVP. When there is an established PANA SA between the PaC and the PAA, all messages exchanged during the termination phase MUST be protected with an AUTH AVP. When the sender of the PANA-Termination-Request message receives a valid acknowledgment, all states maintained for the PANA session MUST be deleted immediately. PaC PAA Message(sequence number)[AVPs] ------------------------------------------------------ -----> PANA-Termination-Request(q)[AUTH] <----- PANA-Termination-Answer(q)[AUTH] Figure 7: Example sequence for the termination phase triggered by PaC Forsberg, et al. Expires June 9, 2007 [Page 16] Internet-Draft PANA December 2006 5. Processing Rules 5.1. Fragmentation PANA does not provide fragmentation of PANA messages. Instead, it relies on fragmentation provided by EAP methods and IP layer when needed. 5.2. Sequence Number and Retransmission PANA uses sequence numbers to provide ordered and reliable delivery of messages. The PaC and PAA maintain two sequence numbers: the next one to be used for a request it initiates and the next one it expects to see in a request from the other end. These sequence numbers are 32-bit unsigned numbers. They are monotonically incremented by 1 as new requests are generated and received, and wrapped to zero on the next message after 2^32-1. Answers always contain the same sequence number as the corresponding request. Retransmissions reuse the sequence number contained in the original packet. The initial sequence numbers (ISN) are randomly picked by the PaC and PAA as they send their very first request messages. PANA-Client-Initiation message carries sequence number 0. When a request message is received, it is considered valid in terms of sequence numbers if and only if its sequence number matches the expected value. This check does not apply to the PANA-Client-Initiation and PANA-Start-Request messages. When an answer message is received, it is considered valid in terms of sequence numbers if and only if its sequence number matches that of the currently outstanding request. A peer can only have one outstanding request at a time. PANA request messages are retransmitted based on a timer until a response is received (in which case the retransmission timer is stopped) or the number of retransmission reaches the maximum value (in which case the PANA session MUST be deleted immediately). The retransmission timers SHOULD be calculated as described in Section 9 unless a given deployment chooses to use its own retransmission timers optimized for the underlying link-layer characteristics. The PaC and PAA MUST respond to duplicate requests as long as the responding rate does not exceed a certain threshold value. The last Forsberg, et al. Expires June 9, 2007 [Page 17] Internet-Draft PANA December 2006 transmitted answer MAY be cached in case it is not received by the peer and that generates a retransmission of the last request. When available, the cached answer can be used instead of fully processing the retransmitted request and forming a new answer from scratch. 5.3. PANA Security Association A PANA SA is created as an attribute of a PANA session when EAP authentication succeeds with a creation of an MSK. A PANA SA is not created when the PANA authentication fails or no MSK is produced by any EAP authentication method. When a new MSK is derived in the PANA re-authentication phase, any key derived from the old MSK MUST be updated to a new one that is derived from the new MSK. In order to distinguish the new MSK from old ones, one Key-Id AVP MUST be carried in PANA-Bind-Request and PANA-Bind-Answer messages at the end of the EAP authentication which resulted in deriving a new MSK. The Key-Id AVP is of type Unsigned32 and MUST contain a value that uniquely identifies the MSK within the PANA session. The PANA-Bind-Answer message sent in response to a PANA-Bind-Request message with a Key-Id AVP MUST contain a Key-Id AVP with the same MSK identifier carried in the request. PANA-Bind-Request and PANA-Bind-Answer messages with a Key-Id AVP MUST also carry an AUTH AVP whose value is computed by using the new PANA_AUTH_KEY derived from the new MSK. Although the specification does not mandate a particular method for calculation of the Key-Id AVP value, a simple method is to use monotonically increasing numbers. The PANA session lifetime is bounded by the authorization lifetime granted by the authentication server (same as the MSK lifetime). The lifetime of the PANA SA (hence the PANA_AUTH_KEY) is the same as the lifetime of the PANA session. The created PANA SA is deleted when the corresponding PANA session is deleted. PANA SA attributes as well as PANA session attributes are listed below: PANA Session attributes: * Session Identifier * IP address and UDP port number of the PaC. * IP address and UDP port number of the PAA * Sequence number of the last transmitted request * Sequence number of the last received request Forsberg, et al. Expires June 9, 2007 [Page 18] Internet-Draft PANA December 2006 * Last transmitted message payload * Retransmission interval * Session lifetime * PANA SA attributes PANA SA attributes: * Nonce generated by PaC (PaC_nonce) * Nonce generated by PAA (PAA_nonce) * MSK * MSK Identifier * PANA_AUTH_KEY * Pseudo-random function * Integrity algorithm The PANA_AUTH_KEY is derived from the available MSK and it is used to integrity protect PANA messages. The PANA_AUTH_KEY is computed in the following way: PANA_AUTH_KEY = prf+(MSK, PaC_nonce|PAA_nonce|Session_ID|Key_ID) where the prf+ function is defined in IKEv2 [RFC4306]. The pseudo-random function to be used for the prf+ function is specified in the Algorithm AVP in a PANA-Bind-Request message. The length of PANA_AUTH_KEY depends on the integrity algorithm in use. See Section 5.4 for the detailed usage of the PANA_AUTH_KEY. PaC_nonce and PAA_nonce are values of the Nonce AVP carried in the first PANA-Auth-Answer and PANA-Auth-Request messages in the authentication and authorization phase or the re-authentication phase, respectively. Session_ID is the session identifier of the session. Key_ID is the value of the Key-ID AVP. 5.4. Message Authentication A PANA message can contain an AUTH AVP for cryptographically protecting the message. When an AUTH AVP is included in a PANA message, the value field of the AUTH AVP is calculated by using the PANA_AUTH_KEY in the Forsberg, et al. Expires June 9, 2007 [Page 19] Internet-Draft PANA December 2006 following way: AUTH AVP value = PANA_AUTH_HASH(PANA_AUTH_KEY, PANA_PDU) where PANA_PDU is the PANA message including the PANA header, with the AUTH AVP value field first initialized to 0. PANA_AUTH_HASH represents the integrity algorithm specified in the Algorithm AVP in a PANA-Bind-Request message. The PaC and PAA MUST use the same integrity algorithm to calculate an AUTH AVP they originate and receive. The algorithm is determined by the PAA. When the PaC does not support the integrity algorithm specified in the PANA-Bind-Request message, it MUST silently discard the message. 5.5. Message Validity Check When a PANA message is received, the message is considered to be invalid at least when one of the following conditions are not met: o Each field in the message header contains a valid value including sequence number, message length, message type, version number, flags, session identifier, etc. o The message type is one of the expected types in the current state. Specifically the following messages are unexpected and invalid: * In the handshake phase: + PANA-Termination-Request and PANA-Ping-Request. + PANA-Bind-Request. + PANA-Update-Request. + PANA-Reauth-Request. + PANA-Error-Request. * In the authentication and authorization phase and the re-authentication phase: + PANA-Client-Initiation. + PANA-Update-Request. + PANA-Start-Request after a PaC receives the first valid PANA-Auth-Request. Forsberg, et al. Expires June 9, 2007 [Page 20] Internet-Draft PANA December 2006 + PANA-Termination-Request before the PaC receives the first successful PANA-Bind-Request. * In the access phase: + PANA-Start-Request as well as a non-duplicate PANA-Bind-Request. + PANA-Client-Initiation. * In the termination phase: + PANA-Client-Initiation. + All requests but PANA-Termination-Request. o The message payload contains a valid set of AVPs allowed for the message type and there is no missing AVP that needs to be included in the payload and no AVP, which needs to be at a fixed position, is included in a position different from this fixed position. o Each AVP is decoded correctly. o When an AUTH AVP is included, the AVP value matches the hash value computed against the received message. Invalid messages MUST be discarded in order to provide robustness against DoS attacks. In addition, an error notification message MAY be returned to the sender. See Section 5.8 for details. 5.6. PaC Updating its IP Address A PaC's IP address used for PANA can change in certain situations, e.g., when the PaC moves from one IP link to another within the same PAA's realm. In order to maintain the PANA session, the PAA needs to be notified about the change of PaC address. After the PaC has changed its IP address used for PANA, it MUST send a PANA-Update-Request message to the PAA. The PAA MUST update the PANA session with the new PaC address carried in the Source Address field of the IP header and return a PANA-Update-Answer message. If there is an established PANA SA, both PANA-Update-Request and PANA-Update-Answer messages MUST be protected with an AUTH AVP. 5.7. Session Lifetime The authentication and authorization phase determines the PANA session lifetime when the network access authorization succeeds. The Forsberg, et al. Expires June 9, 2007 [Page 21] Internet-Draft PANA December 2006 Session-Lifetime AVP MAY be optionally included in the PANA-Bind-Request message to inform the PaC about the valid lifetime of the PANA session. It MUST be ignored when included in other PANA messages. When the Session-Lifetime AVP is not included in the PANA-Bind-Request message then the PaC has no knowledge about a PANA session limitation and must therefore conclude that the session is not limited. The lifetime is a non-negotiable parameter that can be used by the PaC to manage PANA-related state. The PaC does not have to perform any actions when the lifetime expires, other than purging local state. The PAA SHOULD initiate the PANA re-authentication phase before the current session lifetime expires. The PaC and the PAA MAY use information obtained outside PANA (e.g., lower-layer indications) to expedite the detection of a disconnected peer. Availability and reliability of such indications MAY depend on a specific link-layer or network topology and are therefore only hints. A PANA peer SHOULD use the PANA-Ping message exchange to verify that a peer is, in fact, no longer alive, unless information obtained outside PANA is being used to expedite the detection of a disconnected peer. The session lifetime parameter is not related to the transmission of PANA-Ping-Request messages. These messages can be used for asynchronously verifying the liveness of the peer. The decision to send a PANA-Ping-Request message is taken locally and does not require coordination between the peers. 5.8. Error Handling A PANA-Error-Request message MAY be sent by either the PaC or the PAA when a badly formed PANA message is received or in case of other errors. The receiver of this request MUST respond with a PANA-Error-Answer message. An adversary might craft erroneous PANA messages to launch a Denial of Service attack. Unless the PaC or the PAA performs a rate-limitation of the generated PANA-Error-Request messages it may be overburdened by responding to bogus messages. Note that a PANA-Error-Answer message that is sent in response to a PANA-Error-Request message does not require either the PaC or the PAA to create a state. If an error message is sent unprotected (i.e., without using an AUTH AVP) then the error message MUST be processed such that the receiver Forsberg, et al. Expires June 9, 2007 [Page 22] Internet-Draft PANA December 2006 does not change its state. Forsberg, et al. Expires June 9, 2007 [Page 23] Internet-Draft PANA December 2006 6. Header Format This section defines message formats for PANA protocol. 6.1. IP and UDP Headers Any PANA message is unicast between the PaC and the PAA. When the PANA message is sent in response to a request, the UDP source and destination ports of the response message MUST be copied from the destination and source ports of the request message, respectively. For other PANA messages, the source port MUST be set to a value chosen by the sender and the destination port MUST be set to the assigned PANA port (To Be Assigned by IANA). 6.2. PANA Message Header A summary of the PANA message header format is shown below. The fields are transmitted in network byte order. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Reserved | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Message Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVPs ... +-+-+-+-+-+-+-+-+-+-+-+-+- Version This Version field MUST be set to 1 to indicate PANA Version 1. Reserved This 8-bit field is reserved for future use, and MUST be set to zero, and ignored by the receiver. Forsberg, et al. Expires June 9, 2007 [Page 24] Internet-Draft PANA December 2006 Message Length The Message Length field is two octets and indicates the length of the PANA message including the header fields. Flags The Flags field is two octets. The following bits are assigned: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R r r r r r r r r r r r r r r r| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ R(equest) If set, the message is a request. If cleared, the message is an answer. r(eserved) These flag bits are reserved for future use, and MUST be set to zero, and ignored by the receiver. Message Type The Message Type field is two octets, and is used in order to communicate the message type with the message. The 16-bit address space is managed by IANA [ianaweb]. Session Identifier This field contains a 32 bit session identifier. Sequence Number This field contains contains a 32 bit sequence number. AVPs AVPs are a method of encapsulating information relevant to the PANA message. See section Section 6.3 for more information on AVPs. Forsberg, et al. Expires June 9, 2007 [Page 25] Internet-Draft PANA December 2006 6.3. AVP Header Each AVP of type OctetString MUST be padded to align on a 32-bit boundary, while other AVP types align naturally. A number of zero-valued bytes are added to the end of the AVP Data field till a word boundary is reached. The length of the padding is not reflected in the AVP Length field [RFC3588]. The fields in the AVP header are sent in network byte order. The format of the header is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Code | AVP Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Id (opt) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data ... +-+-+-+-+-+-+-+-+ AVP Code The AVP Code, together with the optional Vendor ID field, identifies attribute that follows. If the V-bit is not set, the Vendor ID is not present and the AVP Code refers to an IETF attribute. AVP Flags The AVP Flags field is two octets. The following bits are assigned: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V M r r r r r r r r r r r r r r| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ V(endor) The 'V' bit, known as the Vendor-Specific bit, indicates whether the optional Vendor-Id field is present in the AVP header. When set the AVP Code belongs to the specific vendor code address space. Forsberg, et al. Expires June 9, 2007 [Page 26] Internet-Draft PANA December 2006 M(andatory) The 'M' Bit, known as the Mandatory bit, indicates whether support of the AVP is required. If an AVP with the 'M' bit set is received by the PaC or PAA and either the AVP or its value is unrecognized, the message MUST be rejected and the receiver MUST send a PANA-Error-Request message. If the AVP was unrecognized the PANA-Error-Request message result code MUST be PANA_AVP_UNSUPPORTED. If the AVP value was unrecognized the PANA-Error-Request message result code MUST be PANA_INVALID_AVP_DATA. In either case the PANA-Error-Request message MUST carry a Failed-AVP AVP containing the offending mandatory AVP. AVPs with the 'M' bit cleared are informational only and a receiver that receives a message with such an AVP that is not recognized, or whose value is not recognized, MAY simply ignore the AVP. 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 two octets, and indicates the number of octets in this AVP including the AVP Code, AVP Length, AVP Flags, and the AVP data. Reserved This two-octet field is reserved for future use, and MUST be set to zero, and ignored by the receiver. Vendor-Id The Vendor-Id field is present if the 'V' bit is set in the AVP Flags field. The optional four-octet Vendor-Id field contains the IANA assigned "SMI Network Management Private Enterprise Codes" [ianaweb] value, encoded in network byte order. Any vendor wishing to implement a vendor-specific PANA AVP MUST use their own Vendor-Id along with their privately managed AVP address space, guaranteeing that they will not collide with any other vendor's vendor-specific AVP(s), nor with future IETF applications. Data The Data field is zero or more octets and contains information specific to the Attribute. The format and length of the Data Forsberg, et al. Expires June 9, 2007 [Page 27] Internet-Draft PANA December 2006 field is determined by the AVP Code and AVP Length fields. Unless otherwise noted, AVPs defined in this document will have the following default AVP Flags field settings: The 'M' bit MUST be set. The 'V' bit MUST NOT be set. Forsberg, et al. Expires June 9, 2007 [Page 28] Internet-Draft PANA December 2006 7. PANA Messages Each Request/Answer message pair is assigned a Sequence Number, and the sub-type (i.e., request or answer) is identified via the 'R' bit in the Message Flags field of the PANA message header. Every PANA message MUST contain a message ID in its header's Message Type field, which is used to determine the action that is to be taken for a particular message. Figure 8 lists all PANA messages defined in this document: Message-Name Abbrev. ID PaC<->PAA Ref. ---------------------------------------------------------- PANA-Client-Initiation PCI 1 --------> 7.1 PANA-Start-Request PSR 2 <-------- 7.2 PANA-Start-Answer PSA 2 --------> 7.3 PANA-Auth-Request PAR 3 <-------> 7.4 PANA-Auth-Answer PAN 3 <-------> 7.5 PANA-Reauth-Request PRR 4 --------> 7.6 PANA-Reauth-Answer PRA 4 <-------- 7.7 PANA-Bind-Request PBR 5 <-------- 7.8 PANA-Bind-Answer PBA 5 --------> 7.9 PANA-Ping-Request PPR 6 <-------> 7.10 PANA-Ping-Answer PPA 6 <-------> 7.11 PANA-Termination-Request PTR 7 <-------> 7.12 PANA-Termination-Answer PTA 7 <-------> 7.13 PANA-Error-Request PER 8 <-------> 7.14 PANA-Error-Answer PEA 8 <-------> 7.15 PANA-Update-Request PUR 9 <-------> 7.16 PANA-Update-Answer PUA 9 <-------> 7.17 ----------------------------------------------------------- Figure 8: Table of PANA Messages Every PANA message defined MUST include a corresponding ABNF [RFC2234] specification, which is used to define the AVPs that MUST or MAY be present. The following format is used in the definition: message-def = Message-Name "::=" PANA-message message-name = PANA-name PANA-name = ALPHA *(ALPHA / DIGIT / "-") PANA-message = header [ *fixed] [ *required] [ *optional] [ *fixed] header = "< PANA-Header: " Message-Type Forsberg, et al. Expires June 9, 2007 [Page 29] Internet-Draft PANA December 2006 [r-bit] ">" Message-Type = 1*DIGIT ; The Message Type assigned to the message r-bit = ", REQ" ; If present, the 'R' bit in the Message ; Flags is set, indicating that the message ; is a request, as opposed to an answer. fixed = [qual] "<" avp-spec ">" ; Defines the fixed position of an AVP. required = [qual] "{" avp-spec "}" ; The AVP MUST be present and can appear ; anywhere in the message. optional = [qual] "[" avp-name "]" ; The avp-name in the 'optional' rule cannot ; evaluate to any AVP Name which is included ; in a fixed or required rule. The AVP can ; appear anywhere in the message. qual = [min] "*" [max] ; See ABNF conventions, RFC 2234 Section 6.6. ; The absence of any qualifiers depends on whether ; it precedes a fixed, required, or optional ; rule. If a fixed or required rule has no ; qualifier, then exactly one such AVP MUST ; be present. If an optional rule has no ; qualifier, then 0 or 1 such AVP may be ; present. ; ; NOTE: "[" and "]" have a different meaning ; than in ABNF (see the optional rule, above). ; These braces cannot be used to express ; optional fixed rules (such as an optional ; AUTH at the end). To do this, the convention ; is '0*1fixed'. min = 1*DIGIT ; The minimum number of times the element may ; be present. The default value is zero. max = 1*DIGIT ; The maximum number of times the element may ; be present. The default value is infinity. A ; value of zero implies the AVP MUST NOT be Forsberg, et al. Expires June 9, 2007 [Page 30] Internet-Draft PANA December 2006 ; present. avp-spec = PANA-name ; The avp-spec has to be an AVP Name, defined ; in the base or extended PANA protocol ; specifications. avp-name = avp-spec / "AVP" ; The string "AVP" stands for *any* arbitrary ; AVP Name, which does not conflict with the ; required or fixed position AVPs defined in ; the message definition. Example-Request ::= < "PANA-Header: 9999999, REQ > { Result-Code } * [ AVP ] 0*1 < AUTH > 7.1. PANA-Client-Initiation (PCI) The PANA-Client-Initiation (PCI) message is used for PaC-initiated handshake. The Sequence Number and Session Identifier fields in this message MUST be set to zero (0). PANA-Client-Initiation ::= < PANA-Header: 1 > * [ AVP ] 7.2. PANA-Start-Request (PSR) The PANA-Start-Request (PSR) message is sent by the PAA to the PaC to start PANA authentication. The PAA sets the Sequence Number field to an initial random value and sets the Session Identifier field to a newly assigned value. PANA-Start-Request ::= < PANA-Header: 2, REQ > [ EAP-Payload ] [ Algorithm ] * [ AVP ] 7.3. PANA-Start-Answer (PSA) The PANA-Start-Answer (PSA) message is sent by the PaC to the PAA in response to a PANA-Start-Request message. This message completes the handshake to start PANA authentication. PANA-Start-Answer ::= < PANA-Header: 2 > [ EAP-Payload ] * [ AVP ] Forsberg, et al. Expires June 9, 2007 [Page 31] Internet-Draft PANA December 2006 7.4. PANA-Auth-Request (PAR) The PANA-Auth-Request (PAR) message is either sent by the PAA or the PaC. Its main task is to carry an EAP-Payload AVP. PANA-Auth-Request ::= < PANA-Header: 3, REQ > < EAP-Payload > [ Nonce ] * [ AVP ] 0*1 < AUTH > 7.5. PANA-Auth-Answer (PAN) The PANA-Auth-Answer (PAN) message is sent by either the PaC or the PAA in response to a PANA-Auth-Request message. It MAY carry an EAP-Payload AVP. PANA-Auth-Answer ::= < PANA-Header: 3 > [ Nonce ] [ EAP-Payload ] * [ AVP ] 0*1 < AUTH > 7.6. PANA-Reauth-Request (PRR) The PANA-Reauth-Request (PRR) message is sent by the PaC to the PAA to re-initiate EAP authentication. PANA-Reauth-Request ::= < PANA-Header: 4, REQ > * [ AVP ] 0*1 < AUTH > 7.7. PANA-Reauth-Answer (PRA) The PANA-Reauth-Answer (PRA) message is sent by the PAA to the PaC in response to a PANA-Reauth-Request message. PANA-Reauth-Answer ::= < PANA-Header: 4 > * [ AVP ] 0*1 < AUTH > 7.8. PANA-Bind-Request (PBR) The PANA-Bind-Request (PBR) message is sent by the PAA to the PaC to deliver the result of PANA authentication. Forsberg, et al. Expires June 9, 2007 [Page 32] Internet-Draft PANA December 2006 PANA-Bind-Request ::= < PANA-Header: 5, REQ > { Result-Code } [ EAP-Payload ] [ Session-Lifetime ] [ Key-Id ] [ Algorithm ] * [ AVP ] 0*1 < AUTH > 7.9. PANA-Bind-Answer (PBA) The PANA-Bind-Answer (PBA) message is sent by the PaC to the PAA in response to a PANA-Bind-Request message. PANA-Bind-Answer ::= < PANA-Header: 5 > [ Key-Id ] * [ AVP ] 0*1 < AUTH > 7.10. PANA-Ping-Request (PPR) The PANA-Ping-Request (PPR) message is either sent by the PaC or the PAA for performing liveness test. PANA-Ping-Request ::= < PANA-Header: 6, REQ > * [ AVP ] 0*1 < AUTH > 7.11. PANA-Ping-Answer (PPA) The PANA-Ping-Answer (PPA) message is sent in response to a PANA-Ping-Request. PANA-Ping-Answer ::= < PANA-Header: 6 > * [ AVP ] 0*1 < AUTH > 7.12. PANA-Termination-Request (PTR) The PANA-Termination-Request (PTR) message is sent either by the PaC or the PAA to terminate a PANA session. PANA-Termination-Request ::= < PANA-Header: 7, REQ > < Termination-Cause > * [ AVP ] 0*1 < AUTH > Forsberg, et al. Expires June 9, 2007 [Page 33] Internet-Draft PANA December 2006 7.13. PANA-Termination-Answer (PTA) The PANA-Termination-Answer (PTA) message is sent either by the PaC or the PAA in response to PANA-Termination-Request. PANA-Termination-Answer ::= < PANA-Header: 7 > * [ AVP ] 0*1 < AUTH > 7.14. PANA-Error-Request (PER) The PANA-Error-Request (PER) message is sent either by the PaC or the PAA to report an error with the last received PANA message. This message MUST contain one Failed-Message-Header AVP which carries the content of the PANA message header of the erroneous message. PANA-Error-Request ::= < PANA-Header: 8, REQ > < Result-Code > { Failed-Message-Header } * [ Failed-AVP ] * [ AVP ] 0*1 < AUTH > 7.15. PANA-Error-Answer (PEA) The PANA-Error-Answer (PEA) message is sent in response to a PANA-Error-Request. PANA-Error-Answer ::= < PANA-Header: 8 > * [ AVP ] 0*1 < AUTH > 7.16. PANA-Update-Request (PUR) The PANA-Update-Request (PUR) message is sent either by the PaC or the PAA to deliver attribute updates. In the scope of this specification only the IP address the PaC can be updated via this message. PANA-Update-Request ::= < PANA-Header: 9, REQ > * [ AVP ] 0*1 < AUTH > 7.17. PANA-Update-Answer (PUA) The PANA-Update-Answer (PUA) message is sent by the PAA (PaC) to the PaC (PAA) in response to a PANA-Update-Request from the PaC (PAA). Forsberg, et al. Expires June 9, 2007 [Page 34] Internet-Draft PANA December 2006 PANA-Update-Answer ::= < PANA-Header: 9 > * [ AVP ] 0*1 < AUTH > Forsberg, et al. Expires June 9, 2007 [Page 35] Internet-Draft PANA December 2006 8. AVPs in PANA This document uses AVP Data Format such as 'OctetString' and 'Unsigned32' as defined in Section 4.2 of [RFC3588]. The definitions of these data formats are not repeated in this document. The following tables lists the AVPs used in this document, and specifies in which PANA messages they MAY, or MAY NOT be present. The table uses the following symbols: 0 The AVP MUST NOT be present in the message. 0+ Zero or more instances of the AVP MAY be present in the message. 0-1 Zero or one instance of the AVP MAY be present in the message. It is considered an error if there are more than one instance of the AVP. 1 One instance of the AVP MUST be present in the message. 1+ At least one instance of the AVP MUST be present in the message. +-------------------------------------------+ | Message Type | +---+---+---+---+---+---+---+---+---+---+---+ Attribute Name |PCI|PSR|PSA|PAR|PAN|PRR|PRA|PBR|PBA|PPR|PPA| ----------------------+---+---+---+---+---+---+---+---+---+---+---+ Algorithm | 0 |0-1| 0 | 0 | 0 | 0 | 0 |0-1| 0 | 0 | 0 | AUTH | 0 | 0 | 0 |0-1|0-1|0-1|0-1|0-1|0-1|0-1|0-1| EAP-Payload | 0 |0-1|0-1| 1 |0-1| 0 | 0 |0-1| 0 | 0 | 0 | Failed-AVP | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | Failed-Message-Header | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | Key-Id | 0 | 0 | 0 | 0 | 0 | 0 | 0 |0-1|0-1| 0 | 0 | Nonce | 0 | 0 | 0 |0-1|0-1| 0 | 0 | 0 | 0 | 0 | 0 | Result-Code | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | Session-Lifetime | 0 | 0 | 0 | 0 | 0 | 0 | 0 |0-1| 0 | 0 | 0 | Termination-Cause | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ----------------------+---+---+---+---+---+---+---+---+---+---+---+ Figure 9: AVP Occurrence Table (1/2) Forsberg, et al. Expires June 9, 2007 [Page 36] Internet-Draft PANA December 2006 +-----------------------+ | Message Type | +---+---+---+---+---+---+ Attribute Name |PTR|PTA|PER|PEA|PUR|PUA| ----------------------+---+---+---+---+---+---+ Algorithm | 0 | 0 | 0 | 0 | 0 | 0 | AUTH |0-1|0-1|0-1|0-1|0-1|0-1| EAP-Payload | 0 | 0 | 0 | 0 | 0 | 0 | Failed-AVP | 0 | 0 | 0+| 0 | 0 | 0 | Failed-Message-Header | 0 | 0 | 1 | 0 | 0 | 0 | Key-Id | 0 | 0 | 0 | 0 | 0 | 0 | Nonce | 0 | 0 | 0 | 0 | 0 | 0 | Result-Code | 0 | 0 | 1 | 0 | 0 | 0 | Session-Lifetime | 0 | 0 | 0 | 0 | 0 | 0 | Termination-Cause | 1 | 0 | 0 | 0 | 0 | 0 | ----------------------+---+---+---+---+---+---+ Figure 10: AVP Occurrence Table (2/2) 8.1. Algorithm AVP The Algorithm AVP (AVP Code 1) is used for conveying the pseudo-random function to derive PANA_AUTH_KEY as well as the integrity algorithm to compute an AUTH AVP. The AVP data is of type Unsigned32. The first 16-bit of the AVP data contains an IKEv2 Transform ID of Transform Type 2 [RFC4306] corresponding to the key derivation function. The last 16-bit of the AVP data contains an IKEv2 Transform ID of Transform Type 3 [RFC4306] for the integrity algorithm. All PANA implementations MUST support PRF_HMAC_SHA1 (2) [RFC2104] for the key derivation algorithm and AUTH_HMAC_SHA1_160 (7) [RFC4595] corresponding to the integrity algorithm. 8.2. AUTH AVP The AUTH AVP (AVP Code 2) is used to integrity protect PANA messages. The AVP data payload contains the Message Authentication Code encoded in network byte order. The AVP length varies depending on the integrity algorithm specified in an Algorithm AVP. 8.3. EAP-Payload AVP The EAP-Payload AVP (AVP Code 3) is used for encapsulating the actual EAP message that is being exchanged between the EAP peer and the EAP Forsberg, et al. Expires June 9, 2007 [Page 37] Internet-Draft PANA December 2006 authenticator. The AVP data is of type OctetString. 8.4. Failed-AVP AVP The Failed-AVP AVP (AVP Code 4) provides debugging information in cases where a message is rejected or not fully processed due to erroneous information in a specific AVP. The AVP data is of type Grouped. The format of the Failed-AVP AVP using the ABNF grammar defined in [RFC3588] for Grouped AVP is as follows. ::= < AVP Header: 4 > 1* {AVP} In case of a failed grouped AVP, the Failed-AVP contains the whole grouped AVP. In case of a failed AVP inside a grouped AVP, the Failed-AVP contains the single offending AVP. 8.5. Failed-Message-Header AVP The Failed-Message-Header AVP (AVP Code 5) provides debugging information in cases where a message is rejected or not fully processed due to erroneous information in the message. The AVP data is of type OctetString. The AVP data contains the 16-octet header of the message that caused the error. 8.6. Key-Id AVP The Key-Id AVP (AVP Code 6) is of type Integer32, and contains an MSK identifier. The MSK identifier is assigned by PAA and MUST be unique within the PANA session. 8.7. Nonce AVP The Nonce AVP (AVP Code 7) carries a randomly chosen value that is used in cryptographic key computations. The recommendations in [RFC4086] apply with regard to generation of random values. The AVP data is of type OctetString and it contains a randomly generated value in opaque format. The data length MUST be between 8 and 256 octets inclusive. The length of the nonces are determined based on the available pseudo-random functions (PRFs) and the degree of trust placed into the two PaC and the PAA to compute random values. The length of the random value for the nonce is determined whether 1. The PaC and the PAA each are likely to be able to compute a random nonce (according to [RFC4086]). The length of the nonce has to be 1/2 the length of the PRF key (e.g., 10 octets in the Forsberg, et al. Expires June 9, 2007 [Page 38] Internet-Draft PANA December 2006 case of HMAC-SHA1). 2. The PaC and the PAA each are not trusted with regard to the computation a random nonce (according to [RFC4086]). The length of the nonce has to have the full length of the PRF key (e.g., 20 octets in the case of HMAC-SHA1). Furthermore, the strongest available PRF available for PANA has to be considered in this computation. Currently, only a single PRF (namely HMAC-SHA1) is available and therefore the maximum output length is 20 octets). The recommended maximum length of the nonce value is therefore currently 20 octets. 8.8. Result-Code AVP The Result-Code AVP (AVP Code 8) is of type Unsigned32 and indicates whether an EAP authentication was completed successfully or whether an error occurred. Result-Code AVP values are described in the subsequent sections. 8.8.1. Authentication Results Codes These result code values inform the PaC about the authentication and authorization result. The authentication result and authorization result can be different as described below, but only one result is returned to the PaC. These codes are used with PANA-Bind-Request message. PANA_SUCCESS 0 Both authentication and authorization processes are successful. PANA_AUTHENTICATION_REJECTED 1 Authentication has failed. When this error is returned, it is assumed that authorization is automatically failed. PANA_AUTHORIZATION_REJECTED 2 The authorization process has failed. This error could occur when authorization is rejected by a AAA server or rejected locally by a PAA, even if the authentication procedure has succeeded. 8.8.2. Protocol Error Result Codes These codes are used with PANA-Error-Request messages. Unless stated otherwise, they can be generated by both the PaC and the PAA. Forsberg, et al. Expires June 9, 2007 [Page 39] Internet-Draft PANA December 2006 PANA_MESSAGE_UNSUPPORTED 1001 Message type not recognized or supported. PANA_UNABLE_TO_DELIVER 1002 The PAA was unable to deliver the EAP payload to the authentication server. Only the PAA can generate this code. PANA_INVALID_HDR_BITS 1003 A message was received whose bits in the PANA message header were either set to an invalid combination, or to a value that is inconsistent with the message type definition. PANA_INVALID_AVP_FLAGS 1004 A message was received that included an AVP whose flag bits are set to an unrecognized value, or that is inconsistent with the AVP's definition. PANA_AVP_UNSUPPORTED 1005 The received message contained an AVP that is not recognized or supported and was marked with the Mandatory bit. A PANA message with this error MUST contain one or more Failed-AVP AVP containing the AVPs that caused the failure. PANA_INVALID_AVP_DATA 1006 The message contained an AVP with an invalid value in its data portion. A PANA message indicating this error MUST include the offending AVPs within a Failed-AVP AVP. PANA_MISSING_AVP 1007 The message did not contain an AVP that is required by the message type definition. If this value is sent in the Result-Code AVP, a Failed-AVP AVP SHOULD be included in the message. The Failed-AVP AVP MUST contain an example of the missing AVP complete with the Vendor-Id if applicable. The value field of the missing AVP should be of correct minimum length and contain zeroes. PANA_RESOURCES_EXCEEDED 1008 A message was received that cannot be authorized because the client has already expended allowed resources. An example of this error condition is a client that is restricted to one PANA session Forsberg, et al. Expires June 9, 2007 [Page 40] Internet-Draft PANA December 2006 and attempts to establish a second session. Only the PAA can generate this code. PANA_CONTRADICTING_AVPS 1009 The PAA has detected AVPs in the message that contradicted each other, and is not willing to provide service to the client. One or more Failed-AVP AVPs MUST be present, containing the AVPs that contradicted each other. Only the PAA can generate this code. PANA_AVP_NOT_ALLOWED 1010 A message was received with an AVP that MUST NOT be present. The Failed-AVP AVP MUST be included and contain a copy of the offending AVP. PANA_AVP_OCCURS_TOO_MANY_TIMES 1011 A message was received that included an AVP that appeared more often than permitted in the message definition. The Failed-AVP AVP MUST be included and contain a copy of the first instance of the offending AVP that exceeded the maximum number of occurrences. PANA_UNSUPPORTED_VERSION 1012 This error is returned when a message was received, whose version number is unsupported. PANA_UNABLE_TO_COMPLY 1013 This error is returned when a request is rejected for unspecified reasons. For example, when an EAP authentication fails at an EAP pass-through authenticator without passing an EAP Failure message to the PAA, a Result-Code AVP with this error code is carried in the PANA-Error-Request message. PANA_INVALID_AVP_LENGTH 1014 The message contained an AVP with an invalid length. The PANA-Error-Request message indicating this error MUST include the offending AVPs within a Failed-AVP AVP. PANA_INVALID_MESSAGE_LENGTH 1015 This error is returned when a message is received with an invalid message length. Forsberg, et al. Expires June 9, 2007 [Page 41] Internet-Draft PANA December 2006 8.9. Session-Lifetime AVP The Session-Lifetime AVP (AVP Code 9) contains the number of seconds remaining before the current session is considered expired. The AVP data is of type Unsigned32. 8.10. Termination-Cause AVP The Termination-Cause AVP (AVP Code 10) is used for indicating the reason why a session is terminated by the requester. The AVP data is of type Enumerated. The following Termination-Cause data values are used with PANA. LOGOUT 1 (PaC -> PAA) The client initiated a disconnect ADMINISTRATIVE 4 (PAA -> PaC) The client was not granted access, or was disconnected, due to administrative reasons. SESSION_TIMEOUT 8 (PAA -> PaC) The session has timed out, and service has been terminated. Forsberg, et al. Expires June 9, 2007 [Page 42] Internet-Draft PANA December 2006 9. Retransmission Timers The PANA protocol provides retransmissions for the PANA-Client-Initiation message and all request messages. PANA retransmission timers are based on the model used in DHCPv6 [RFC3315]. Variables used here are also borrowed from this specification. PANA is a request response like protocol. The message exchange terminates when the request sender successfully receives the appropriate answer, or when a protected PANA-Error-Request message for the request is received, or when the message exchange is considered to have failed according to the retransmission mechanism described below. The retransmission behavior is controlled and described by the following variables: RT Retransmission timeout IRT Initial retransmission time MRC Maximum retransmission count MRT Maximum retransmission time MRD Maximum retransmission duration RAND Randomization factor With each message transmission or retransmission, the sender sets RT according to the rules given below. If RT expires before the message exchange terminates, the sender recomputes RT and retransmits the message. Each of the computations of a new RT include a randomization factor (RAND), which is a random number chosen with a uniform distribution between -0.1 and +0.1. The randomization factor is included to minimize synchronization of messages. The algorithm for choosing a random number does not need to be cryptographically sound. The algorithm SHOULD produce a different sequence of random numbers from each invocation. RT for the first message transmission is based on IRT: RT = IRT + RAND*IRT RT for each subsequent message transmission is based on the previous Forsberg, et al. Expires June 9, 2007 [Page 43] Internet-Draft PANA December 2006 value of RT: RT = 2*RTprev + RAND*RTprev MRT specifies an upper bound on the value of RT (disregarding the randomization added by the use of RAND). If MRT has a value of 0, there is no upper limit on the value of RT. Otherwise: if (RT > MRT) RT = MRT + RAND*MRT MRC specifies an upper bound on the number of times a sender may retransmit a message. Unless MRC is zero, the message exchange fails once the sender has transmitted the message MRC times. MRD specifies an upper bound on the length of time a sender may retransmit a message. Unless MRD is zero, the message exchange fails once MRD seconds have elapsed since the client first transmitted the message. If both MRC and MRD are non-zero, the message exchange fails whenever either of the conditions specified in the previous two paragraphs are met. If both MRC and MRD are zero, the client continues to transmit the message until it receives a response. 9.1. Transmission and Retransmission Parameters This section presents a table of values used to describe the message retransmission behavior of PANA requests that are retransmitted (REQ_*) and PANA-Client-Initiation message (PCI_*). The table shows default values. Parameter Default Description ------------------------------------------------ PCI_IRT 1 sec Initial PCI timeout. PCI_MRT 120 secs Max PCI timeout value. PCI_MRC 0 Configurable. PCI_MRD 0 Configurable. REQ_IRT 1 sec Initial Request timeout. REQ_MRT 30 secs Max Request timeout value. REQ_MRC 10 Max Request retry attempts. REQ_MRD 0 Configurable. So for example the first RT for the PBR message is calculated using REQ_IRT as the IRT: Forsberg, et al. Expires June 9, 2007 [Page 44] Internet-Draft PANA December 2006 RT = REQ_IRT + RAND*REQ_IRT Forsberg, et al. Expires June 9, 2007 [Page 45] Internet-Draft PANA December 2006 10. IANA Considerations This section provides guidance to the Internet Assigned Numbers Authority (IANA) regarding registration of values related to the PANA protocol, in accordance with BCP 26 [IANA]. The following policies are used here with the meanings defined in BCP 26: "Private Use", "First Come First Served", "Expert Review", "Specification Required", "IETF Consensus", "Standards Action". This section explains the criteria to be used by the IANA for assignment of numbers within namespaces defined within this document. For registration requests where a Designated Expert should be consulted, the responsible IESG area director should appoint the Designated Expert. For Designated Expert with Specification Required, the request is posted to the PANA WG mailing list (or, if it has been disbanded, a successor designated by the Area Director) for comment and review, and MUST include a pointer to a public specification. Before a period of 30 days has passed, the Designated Expert will either approve or deny the registration request and publish a notice of the decision to the PANA WG mailing list or its successor. A denial notice must be justified by an explanation and, in the cases where it is possible, concrete suggestions on how the request can be modified so as to become acceptable. 10.1. PANA UDP Port Number PANA uses one well-known UDP port number (Section 4.1, Section 4.3 and Section 6.1), which needs to be assigned by the IANA. 10.2. PANA Message Header As defined in Section 6.2, the PANA message header contains two fields that requires IANA namespace management; the Version, Message Type and Flags fields. 10.2.1. Version The Version namespace is used to identify PANA versions. The Version values are assigned by Standards Action [IANA]. This document defines the Version 1. 10.2.2. Message Type The Message Type namespace is used to identify PANA messages. Values 0-65,519 are for permanent, standard message types, allocated by IETF Consensus [IANA]. This document defines the Message Types 1-9. See Section 7.1 through Section 7.17 for the assignment of the namespace Forsberg, et al. Expires June 9, 2007 [Page 46] Internet-Draft PANA December 2006 in this specification. The values 65,520 and 65,535 (hexadecimal values 0xfff0 - 0xffff) are reserved for experimental messages. As these codes are only for experimental and testing purposes, no guarantee is made for interoperability between the communicating PaC and PAA using experimental commands, as outlined in [IANA-EXP]. 10.2.3. Flags There are 16 bits in the Flags field of the PANA message header. This document assigns bit 0 ('R'equest). The remaining bits MUST only be assigned via a Standards Action [IANA]. 10.3. AVP Header As defined in Section 6.3, the AVP header contains three fields that requires IANA namespace management; the AVP Code, AVP Flags and Vendor-Id fields where only the AVP Code and AVP Flags create new namespaces. 10.3.1. AVP Code The 16-bit AVP Code namespace is used to identify attributes. There are multiple namespaces. Vendors can have their own AVP Codes namespace which will be identified by their Vendor-ID (also known as Enterprise-Number) and they control the assignments of their vendor-specific AVP codes within their own namespace. The absence of a Vendor-ID identifies the IETF IANA controlled AVP Codes namespace. The AVP Codes and sometimes also possible values in an AVP are controlled and maintained by IANA. AVP Code 0 is not used. This document defines the AVP Codes 1-10. See Section 8.1 through Section 8.10 for the assignment of the namespace in this specification. AVPs may be allocated following Designated Expert with Specification Required [IANA] or Standards Action. AVPs with 'M' bit set MUST be allocated by Standards Action. Note that PANA defines a mechanism for Vendor-Specific AVPs, where the Vendor-Id field in the AVP header is set to a non-zero value. Vendor-Specific AVPs codes are for Private Use and should be encouraged instead of allocation of global attribute types, for functions specific only to one vendor's implementation of PANA, where no interoperability is deemed useful. Where a Vendor-Specific AVP is implemented by more than one vendor, allocation of global AVPs should be encouraged instead. Forsberg, et al. Expires June 9, 2007 [Page 47] Internet-Draft PANA December 2006 10.3.2. Flags There are 16 bits in the AVP Flags field of the AVP header, defined in Section 6.3. This document assigns bit 0 ('V'endor Specific) and bit 1 ('M'andatory). The remaining bits should only be assigned via a Standards Action . 10.4. AVP Values Certain AVPs in PANA define a list of values with various meanings. For attributes other than those specified in this section, adding additional values to the list can be done on a First Come, First Served basis by IANA [IANA]. 10.4.1. Result-Code AVP Values As defined in Section 8.8.1 and Section 8.8.2 the Result-Code AVP (AVP Code 8) defines the values 0-3 and 1001-1015. All remaining values are available for assignment via IETF Consensus [IANA]. 10.4.2. Termination-Cause AVP Values As defined in Section 8.10, the Termination-Cause AVP (AVP Code 10) defines the values 1, 4 and 8. All remaining values are available for assignment via IETF Consensus [IANA]. Forsberg, et al. Expires June 9, 2007 [Page 48] Internet-Draft PANA December 2006 11. Security Considerations The PANA protocol defines a UDP-based EAP encapsulation that runs between two IP-enabled nodes on the same IP link. Various security threats that are relevant to a protocol of this nature are outlined in [RFC4016]. Security considerations stemming from the use of EAP and EAP methods are discussed in [RFC3748] [I-D.ietf-eap-keying]. This section provides a discussion on the security-related issues that are related to PANA framework and protocol design. An important element in assessing security of PANA design and deployment in a network is the presence of lower-layer (physical and link-layer) security. In the context of this document, lower-layers are said to be secure if they can prevent eavesdropping and spoofing of packets. Examples of such networks are physically-secured DSL networks and 3GPP2 networks with cryptographically-secured cdma2000 link-layer. In these examples, the lower-layer security is enabled even before running the first PANA-based authentication. In the absence of such a pre-established secure channel, one needs to be created in conjunction with PANA using a link-layer or network-layer cryptographic mechanism (e.g., IPsec). 11.1. General Security Measures PANA provides multiple mechanisms to secure a PANA session. PANA messages carry sequence numbers, which are monotonically incremented by 1 with every new request message. These numbers are randomly initialized at the beginning of the session, and verified against expected numbers upon receipt. A message whose sequence number is different than the expected one is silently discarded. In addition to accomplishing orderly delivery of EAP messages and duplicate elimination, this scheme also helps prevent an adversary spoof messages to disturb ongoing PANA and EAP sessions unless it can also eavesdrop to synchronize on the expected sequence number. Furthermore, impact of replay attacks is reduced as any stale message (i.e., a request or answer with an unexpected sequence number) and any duplicate answer are immediately discarded, and a duplicate request can trigger transmission of the cached answer (i.e., no need to process the request and generate a new answer). The PANA framework defines EP which is ideally located on a network device that can filter traffic from the PaCs before the traffic enters the Internet/intranet. A set of filters can be used to discard unauthorized packets, such as a PANA-Start-Request message that is received from the segment of the access network where only the PaCs are supposed to be connected. Forsberg, et al. Expires June 9, 2007 [Page 49] Internet-Draft PANA December 2006 The protocol also provides authentication and integrity protection to PANA messages when the used EAP method can generate cryptographic session keys. A PANA SA is generated based on the MSK exported by the EAP method. This SA is used for generating an AUTH AVP to protect the PANA message header and payload (including the complete EAP message). The cryptographic protection prevents an adversary from acting as a man-in-the-middle, injecting messages, replaying messages and modifying the content of the exchanged messages. Any packet that fails to pass the AUTH verification is silently discarded. The earliest this protection can be enabled is when the very first PANA-Bind-Request message that signals a successful authentication is generated. Starting with these messages, any subsequent PANA message until the session gets torn down can be cryptographically protected. The lifetime of the PANA SA is set to PANA session lifetime which is bounded by the authorization lifetime granted by the authentication server. An implementation MAY add a tolerance period to that value. Unless the PANA session is extended by executing another EAP authentication, the PANA SA is removed when the current session expires. The ability to use cryptographic protection within PANA is determined by the used EAP method, which is generally dictated by the deployment environment. Insecure lower-layers necessitate use of key-generating EAP methods. In networks where lower-layers are already secured, cryptographic protection of PANA messages is not necessary. 11.2. Handshake The handshake phase is vulnerable to spoofing attacks as these messages are not authenticated and integrity protected. In order to prevent very basic denial-of service attacks an adversary should not be able to cause state creation by sending PANA-Client-Initiation messages to the PAA. This protection is achieved by allowing the responder (PAA) to create as less amount of state as possible in the first round of message exchange. However, it is difficult to prevent all spoofing attacks in the handshake phase entirely. In networks where lower-layers are not secured prior to running PANA, the capability discovery enabled through inclusion of an Algorithm AVP in a PANA-Start-Request message is susceptible to spoofing leading to denial-of service attacks. Therefore, usage of this AVP during the handshake phase in such insecure networks is NOT RECOMMENDED. The same AVP is delivered via an integrity-protected PANA-Bind-Request upon successful authentication. Forsberg, et al. Expires June 9, 2007 [Page 50] Internet-Draft PANA December 2006 11.3. EAP Methods Eavesdropping EAP messages might cause problems when the EAP method is weak and enables dictionary or replay attacks or even allows an adversary to learn the long-term password directly. Furthermore, if the optional EAP Response/Identity payload is used then it allows the adversary to learn the identity of the PaC. In such a case a privacy problem is prevalent. To prevent these threats, [I-D.ietf-pana-framework] suggests using proper EAP methods for particular environments. Depending on the deployment environment an EAP authentication method which supports user identity confidentiality, protection against dictionary attacks and session key establishment must be used. It is therefore the responsibility of the network operators and users to choose a proper EAP method. 11.4. Cryptographic Keys When the EAP method exports an MSK, this key is used to produce a PANA SA with PANA_AUTH_KEY with a distinct key ID. The PANA_AUTH_KEY is unique to the PANA session, and takes PANA-based nonce values into computation to cryptographically separate itself from the MSK. The PANA_AUTH_KEY is solely used for authentication and integrity protection of the PANA messages within the designated session. The PANA SA lifetime is bounded by the MSK lifetime. Another execution of EAP method yields in a new MSK, and updates the PANA SA, PANA_AUTH_KEY and key ID. 11.5. Per-packet Ciphering Networks that are not secured at the lower-layers prior to running PANA can rely on enabling per-packet data traffic ciphering upon successful PANA SA establishment. The PANA framework allows generation of cryptographic keys from the PANA SA and use the keys with a secure association protocol to enable per-packet cryptographic protection such as link-layer or IPsec-based ciphering [I-D.ietf-pana-ipsec]. These mechanisms ultimately establish a cryptographic binding between the data traffic generated by and for a client and the authenticated identity of the client. Data traffic must be minimally data origin authenticated, replay and integrity protected, and optionally encrypted. How cryptographic keys are generated from the PANA SA and used with a secure association protocol is outside the scope of this document. Forsberg, et al. Expires June 9, 2007 [Page 51] Internet-Draft PANA December 2006 11.6. PAA-to-EP Communication The PANA framework allows separation of PAA from EP. SNMPv3 [I-D.ietf-pana-snmp] MAY be used between the PAA and EP for provisioning authorized PaC information on the EP. This exchange MUST be always physically or cryptographically protected for authentication, integrity and replay protection. 11.7. Liveness Test A PANA session is associated with a session lifetime. The session is terminated unless it is refreshed by a new round of EAP authentication before it expires. Therefore, at the latest a disconnected client can be detected when its session expires. A disconnect may also be detected earlier by using PANA ping messages. A request message can be generated by either PaC or PAA at any time and the peer must respond with an answer message. A successful round-trip of this exchange is a simple verification that the peer is alive. This test can be engaged when there is a possibility that the peer might have disconnected (e.g., after the discontinuation of data traffic for an extended period of time). Periodic use of this exchange as a keep-alive requires additional care as it might result in congestion and hence false alarms. This exchange is cryptographically protected when a PANA SA is available in order to prevent threats associated with the abuse of this functionality. Any valid PANA answer message received in response to a recently sent request message can be taken as an indication of peer's liveness. The PaC or PAA MAY forgo sending an explicit PANA-Ping-Request if a recent exchange has already confirmed that the peer is alive. 11.8. IP Address Spoofing PANA does not provide any means to prove ownership of the IP address presented by the PaC. Hence, an authorized PaC can launch a redirect attack by spoofing a victim's IP address. This problem and its solution are outside the scope of PANA. 11.9. Early Termination of a Session The PANA protocol supports the ability for both the PaC and the PAA to transmit a tear-down message before the session lifetime expires. This message causes state removal, a stop of the accounting procedure and removes the installed per-PaC state on the EP(s). This message Forsberg, et al. Expires June 9, 2007 [Page 52] Internet-Draft PANA December 2006 is cryptographically protected when PANA SA is present. Forsberg, et al. Expires June 9, 2007 [Page 53] Internet-Draft PANA December 2006 12. Acknowledgments We would like to thank Mark Townsley, Jari Arkko, Mohan Parthasarathy, Julien Bournelle, Rafael Marin Lopez, Pasi Eronen, Randy Turner, Erik Nordmark, Lionel Morand, Avi Lior, Susan Thomson, Giaretta Gerardo, Joseph Salowey, Sasikanth Bharadwaj, Spencer Dawkins, Tom Yu, Bernard Aboba and all members of the PANA working group for their valuable comments to this document. Forsberg, et al. Expires June 9, 2007 [Page 54] Internet-Draft PANA December 2006 13. References 13.1. Normative References [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, February 1997. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. [RFC4595] Maino, F. and D. Black, "Use of IKEv2 in the Fibre Channel Security Association Management Protocol", RFC 4595, July 2006. [I-D.ietf-dhc-paa-option] Morand, L., "DHCP options for PANA Authentication Agents", draft-ietf-dhc-paa-option-04 (work in progress), September 2006. [IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. 13.2. Informative References [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC4016] Parthasarathy, M., "Protocol for Carrying Authentication and Network Access (PANA) Threat Analysis and Security Requirements", RFC 4016, March 2005. [RFC4058] Yegin, A., Ohba, Y., Penno, R., Tsirtsis, G., and C. Wang, Forsberg, et al. Expires June 9, 2007 [Page 55] Internet-Draft PANA December 2006 "Protocol for Carrying Authentication for Network Access (PANA) Requirements", RFC 4058, May 2005. [RFC4137] Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba, "State Machines for Extensible Authentication Protocol (EAP) Peer and Authenticator", RFC 4137, August 2005. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [I-D.ietf-eap-keying] Aboba, B., "Extensible Authentication Protocol (EAP) Key Management Framework", draft-ietf-eap-keying-15 (work in progress), October 2006. [I-D.ietf-pana-ipsec] Parthasarathy, M., "PANA Enabling IPsec based Access Control", draft-ietf-pana-ipsec-07 (work in progress), July 2005. [I-D.ietf-pana-framework] Jayaraman, P., "Protocol for Carrying Authentication for Network Access (PANA) Framework", draft-ietf-pana-framework-07 (work in progress), August 2006. [I-D.ietf-pana-snmp] Mghazli, Y., "SNMP usage for PAA-EP interface", draft-ietf-pana-snmp-06 (work in progress), June 2006. [ianaweb] IANA, "Number assignment", http://www.iana.org. [IANA-EXP] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, January 2004. Forsberg, et al. Expires June 9, 2007 [Page 56] Internet-Draft PANA December 2006 Authors' Addresses Dan Forsberg Nokia Research Center P.O. Box 407 FIN-00045 NOKIA GROUP Finland Phone: +358 50 4839470 Email: dan.forsberg@nokia.com Yoshihiro Ohba Toshiba America Research, Inc. 1 Telcordia Drive Piscataway, NJ 08854 USA Phone: +1 732 699 5305 Email: yohba@tari.toshiba.com Basavaraj Patil Nokia 6000 Connection Dr. Irving, TX 75039 USA Phone: +1 972-894-6709 Email: Basavaraj.Patil@nokia.com Hannes Tschofenig Siemens Corporate Technology Otto-Hahn-Ring 6 81739 Munich Germany Email: Hannes.Tschofenig@siemens.com Forsberg, et al. Expires June 9, 2007 [Page 57] Internet-Draft PANA December 2006 Alper E. Yegin Samsung Advanced Institute of Technology Istanbul, Turkey Phone: +90 538 719 0181 Email: alper01.yegin@partner.samsung.com Forsberg, et al. Expires June 9, 2007 [Page 58] Internet-Draft PANA December 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). 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