PANA Working Group D. Forsberg
Internet-Draft Nokia
Intended status: Standards Track Y. Ohba (Ed.)
Expires: November 4, 2007 Toshiba
B. Patil
Nokia
H. Tschofenig
Siemens
A. Yegin
Samsung
May 3, 2007
Protocol for Carrying Authentication for Network Access (PANA)
draft-ietf-pana-pana-15
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Copyright Notice
Copyright (C) The IETF Trust (2007).
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Abstract
This document defines the Protocol for Carrying Authentication for
Network Access (PANA), a network-layer transport for Extensible
Authentication Protocol (EAP) to enable network access authentication
between clients and access networks. In EAP terms, PANA is a UDP-
based EAP lower layer that runs between the EAP peer and the EAP
authenticator.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Specification of Requirements . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Authentication and Authorization Phase . . . . . . . . . . 9
4.2. Access Phase . . . . . . . . . . . . . . . . . . . . . . . 12
4.3. Re-authentication Phase . . . . . . . . . . . . . . . . . 12
4.4. Termination Phase . . . . . . . . . . . . . . . . . . . . 14
5. Processing Rules . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Sequence Number and Retransmission . . . . . . . . . . . . 15
5.3. PANA Security Association . . . . . . . . . . . . . . . . 16
5.4. Message Authentication . . . . . . . . . . . . . . . . . . 18
5.5. Message Validity Check . . . . . . . . . . . . . . . . . . 18
5.6. PaC Updating its IP Address . . . . . . . . . . . . . . . 19
5.7. Session Lifetime . . . . . . . . . . . . . . . . . . . . . 20
6. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 21
6.1. IP and UDP Headers . . . . . . . . . . . . . . . . . . . . 21
6.2. PANA Message Header . . . . . . . . . . . . . . . . . . . 21
6.3. AVP Format . . . . . . . . . . . . . . . . . . . . . . . . 23
7. PANA Messages . . . . . . . . . . . . . . . . . . . . . . . . 26
7.1. PANA-Client-Initiation (PCI) . . . . . . . . . . . . . . . 28
7.2. PANA-Auth-Request (PAR) . . . . . . . . . . . . . . . . . 28
7.3. PANA-Auth-Answer (PAN) . . . . . . . . . . . . . . . . . . 29
7.4. PANA-Termination-Request (PTR) . . . . . . . . . . . . . . 29
7.5. PANA-Termination-Answer (PTA) . . . . . . . . . . . . . . 29
7.6. PANA-Notification-Request (PNR) . . . . . . . . . . . . . 29
7.7. PANA-Notification-Answer (PNA) . . . . . . . . . . . . . . 30
8. AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1. Algorithm AVP . . . . . . . . . . . . . . . . . . . . . . 31
8.2. AUTH AVP . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.3. EAP-Payload AVP . . . . . . . . . . . . . . . . . . . . . 32
8.4. Key-Id AVP . . . . . . . . . . . . . . . . . . . . . . . . 32
8.5. Nonce AVP . . . . . . . . . . . . . . . . . . . . . . . . 32
8.6. Result-Code AVP . . . . . . . . . . . . . . . . . . . . . 33
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8.7. Session-Lifetime AVP . . . . . . . . . . . . . . . . . . . 33
8.8. Termination-Cause AVP . . . . . . . . . . . . . . . . . . 33
9. Retransmission Timers . . . . . . . . . . . . . . . . . . . . 35
9.1. Transmission and Retransmission Parameters . . . . . . . . 36
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
10.1. PANA UDP Port Number . . . . . . . . . . . . . . . . . . . 37
10.2. PANA Message Header . . . . . . . . . . . . . . . . . . . 37
10.2.1. Version . . . . . . . . . . . . . . . . . . . . . . . 37
10.2.2. Message Type . . . . . . . . . . . . . . . . . . . . 37
10.2.3. Flags . . . . . . . . . . . . . . . . . . . . . . . . 38
10.3. AVP Header . . . . . . . . . . . . . . . . . . . . . . . . 38
10.3.1. AVP Code . . . . . . . . . . . . . . . . . . . . . . 38
10.3.2. Flags . . . . . . . . . . . . . . . . . . . . . . . . 39
10.4. AVP Values . . . . . . . . . . . . . . . . . . . . . . . . 39
10.4.1. Result-Code AVP Values . . . . . . . . . . . . . . . 39
10.4.2. Termination-Cause AVP Values . . . . . . . . . . . . 39
11. Security Considerations . . . . . . . . . . . . . . . . . . . 40
11.1. General Security Measures . . . . . . . . . . . . . . . . 40
11.2. Initial Exchange . . . . . . . . . . . . . . . . . . . . . 41
11.3. EAP Methods . . . . . . . . . . . . . . . . . . . . . . . 42
11.4. Cryptographic Keys . . . . . . . . . . . . . . . . . . . . 42
11.5. Per-packet Ciphering . . . . . . . . . . . . . . . . . . . 42
11.6. PAA-to-EP Communication . . . . . . . . . . . . . . . . . 43
11.7. Liveness Test . . . . . . . . . . . . . . . . . . . . . . 43
11.8. Early Termination of a Session . . . . . . . . . . . . . . 43
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 44
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
13.1. Normative References . . . . . . . . . . . . . . . . . . . 45
13.2. Informative References . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 47
Intellectual Property and Copyright Statements . . . . . . . . . . 49
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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 carries 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].
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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 is established between the PANA Client (PaC) and
the PANA Authentication Agent (PAA), and terminates as a result of
an authentication and authorization or liveness test failure, a
message delivery failure after retransmissions reach maximum
values, session lifetime expiration, an explicit termination
message or any event that causes discontinuation of the access
service. A fixed session identifier is maintained throughout a
session. A session cannot be shared across multiple network
interfaces.
Session Lifetime:
A duration that is associated with a PANA session. For an
established PANA session, the session lifetime is bound to the
lifetime of the current authorization given to the PaC. The
session lifetime can be extended by a new round of EAP
authentication before it expires. Until a PANA session is
established, the lifetime SHOULD be set to a value that allows the
PaC to detect a failed session in a reasonable amount of time.
Session Identifier:
This identifier is used to uniquely identify a PANA session on the
PaC and the PAA. It is included in PANA messages to bind the
message to a specific PANA session. This bidirectional identifier
is allocated by the PAA in the initial request message and freed
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when the session terminates. The session identifier is assigned
by the PAA and unique within the PAA.
PANA Security Association (PANA SA):
A PANA security association is formed between the PaC and the PAA
by sharing cryptographic keying material and associated context.
The formed duplex security association is used to protect the
bidirectional PANA signaling traffic between the PaC and PAA.
Enforcement Point (EP):
A node on the access network where per-packet enforcement policies
(i.e., filters) are applied on the inbound and outbound traffic of
access devices. The EP and the PAA may be 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.).
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].
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3. Protocol Overview
The PANA protocol is run between a client (PaC) and a server (PAA) in
order to perform authentication and authorization for the network
access service.
The protocol messaging consists of a series of requests and answers,
some of which may be initiated by either end. Each message can carry
zero or more AVPs within the payload. The main payload of PANA is
EAP which performs authentication. PANA helps the PaC and PAA
establish an EAP session.
PANA is a UDP-based protocol. It has its own retransmission
mechanism to reliably deliver messages.
PANA messages are sent between the PaC and PAA as part of a PANA
session. A PANA session consists of distinct phases:
o Authentication and authorization phase: This is the phase that
initiates a new PANA session and executes EAP between the PAA and
PaC. The PANA session can be initiated by both the PaC and the
PAA. The EAP payload (which 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 access device gains access to the network and can send and
receive IP traffic through the EP(s). At any time during this
phase, the PaC and PAA may optionally send PANA notification
messages to test liveness of the PANA session on the peer.
o Re-authentication phase: During the access phase, the PAA may, and
the PaC should, initiate re-authentication if they want to update
the PANA session lifetime before the PANA session lifetime
expires. EAP is carried by PANA to perform re-authentication.
This phase may be optionally triggered by both the PaC and the PAA
without any respect to the session lifetime. The re-
authentication phase is a sub-phase of the access phase. The
session moves to this sub-phase from the access phase when re-
authentication starts, and returns back there upon successful re-
authentication.
o Termination phase: The PaC or PAA may choose to discontinue the
access service at any time. An explicit disconnect message can be
sent by either end. If either the PaC or the PAA disconnects
without engaging in termination messaging, it is expected that
either the expiration of a finite session lifetime or failed
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liveness tests would clean up the session at the other end.
Cryptographic protection of messages between the PaC and PAA is
possible as soon as EAP in conjunction with the EAP method exports a
shared key. That shared key is used to create a PANA SA. The PANA
SA helps generate per-message authentication codes that provide
integrity protection and authentication.
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4. Protocol Details
The following sections explain in detail the various phases of a PANA
session.
4.1. Authentication and Authorization Phase
The main task of the authentication and authorization phase is to
establish a PANA session and carry EAP messages between the PaC and
the PAA. The PANA session can be initiated by either the PaC or the
PAA.
PaC-initiated Session:
When the PaC initiates a PANA session, it sends a
PANA-Client-Initiation message to the PAA. When the PaC is not
configured with an IP address of the PAA before initiating the
PANA session, DHCP [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 session but they
are outside the scope of this specification. The PAA that
receives the PANA-Client-Initiation message MUST respond to the
PaC with a PANA-Auth-Request message.
PAA-initiated Session:
When the PAA knows the IP address of the PaC, it MAY send an
unsolicited PANA-Auth-Request to the PaC. The details of how PAA
can learn the IP address of the PaC are outside the scope of this
specification.
A session identifier for the session is assigned by the PAA and
carried in the initial PANA-Auth-Request message. The same session
identifier MUST be carried in the subsequent messages exchanged
between the PAA and PaC throughout the session.
When the PaC receives the initial PANA-Auth-Request message from a
PAA, it responds with a PANA-Auth-Answer message, if it wishes to
continue the PANA session.
The initial PANA-Auth-Request and PANA-Auth-Answer messages MUST have
'S' (Start) bit set, regardless of whether the session is initiated
by the PaC or the PAA. Non-initial PANA-Auth-Request and
PANA-Auth-Answer messages as well as any other messages MUST NOT have
'S' bit set.
The PAA SHOULD limit the rate it processes incoming PANA-Client-
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Initiation messages to provide robustness against denial-of service
(DoS) attacks. Details of rate limiting are outside the scope of
this specification.
An Algorithm AVP MAY be included in the initial PANA-Auth-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 in the insecure initial request, there are certain security
risks involved in using the provided information. See Section 11 for
further discussion on this.
If the PAA wants to stay stateless in response to a
PANA-Client-Initiation message, it SHOULD NOT include an EAP-Payload
AVP in the initial PANA-Auth-Request message, and it SHOULD NOT re-
transmit the message on a timer. For this reason, the PaC MUST
retransmit the PANA-Client-Initiation message until it receives the
second PANA-Auth-Request message (not a retransmission of the initial
one) from the PAA.
It is possible that both the PAA and the PaC initiate the PANA
session at the same time, i.e., the PAA unsolicitedly sends the
initial PANA-Auth-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 the initial PANA-Auth-Request
message. The PAA uses the source IP address and the source port
number of the PANA-Client-Initiation message to identify the PaC
among multiple PANA-Client-Initiation messages sent from different
PaCs.
EAP messages are carried in PANA-Auth-Request messages.
PANA-Auth-Answer messages are simply used to acknowledge receipt of
the requests. As an optimization, a PANA-Auth-Answer message sent
from the PaC MAY include the EAP message. This optimization SHOULD
NOT be used when it takes time to generate the EAP message (due to,
e.g., intervention of human input), in which case returning an
PANA-Auth-Answer message without piggybacking an EAP message can
avoid unnecessary retransmission of the PANA-Auth-Request message.
A Nonce AVP MUST be included in the first PANA-Auth-Request and
PANA-Auth-Answer messages following the initial PANA-Auth-Request and
PANA-Auth-Answer messages (i.e. with 'S' (Start) bit set), and MUST
NOT be included in any other message, except during re-authentication
procedures (see Section 4.3).
The result of PANA authentication is carried in the last
PANA-Auth-Request message sent from the PAA to the PaC. This message
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carries the EAP authentication result and the result of PANA
authentication. The last PANA-Auth-Request message MUST be
acknowledged with a PANA-Auth-Answer message. The last
PANA-Auth-Request and PANA-Auth-Answer messages MUST have 'C'
(Complete) bit set, and any other message MUST NOT have 'C' bit set.
Figure 1 shows an example sequence in the authentication and
authorization phase for a PaC-initiated session.
PaC PAA Message(sequence number)[AVPs]
--------------------------------------------------------------------
-----> PANA-Client-Initiation(0)
<----- PANA-Auth-Request(x) // 'S' bit set
-----> PANA-Auth-Answer(x) // 'S' bit set
<----- PANA-Auth-Request(x+1)[Nonce, EAP-Payload]
-----> PANA-Auth-Answer(x+1)[Nonce] // No piggybacking EAP
-----> PANA-Auth-Request(y)[EAP-Payload]
<----- PANA-Auth-Answer(y)
<----- PANA-Auth-Request(x+2)[EAP-Payload]
-----> PANA-Auth-Answer(x+2)[EAP-Payload]
// Piggybacking EAP
<----- PANA-Auth-Request(x+3)[Result-Code, EAP-Payload,
Key-Id, Algorithm,
Session-Lifetime, AUTH]
// 'C' bit set
-----> PANA-Auth-Answer(x+3)[Key-Id, AUTH]
// 'C' bit set
Figure 1: Example sequence for the authentication and authorization
phase for a PaC-initiated session ("Piggybacking EAP" is the case in
which an EAP-Payload AVP is carried in PAN.)
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 last PANA-Auth-Request message with 'C'
(Complete) bit set 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 any PANA-Auth-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 silently terminate the session, expecting that a session
timeout on the PaC will clean up the state on the PaC.
There is a case where EAP authentication succeeds with producing an
EAP Success message but network access authorization fails due to,
e.g., authorization rejected by a AAA or authorization locally
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rejected by the PAA. When this occurs, the PAA MUST send the last
PANA-Auth-Request with a result code PANA_AUTHORIZATION_REJECTED. If
an MSK is available, the last PANA-Auth-Request and PANA-Auth-Answer
messages with 'C' (Complete) bit set MUST be protected with an AUTH
AVP and carry a Key-Id AVP. The last PANA-Auth-Request message MUST
also carry an Algorithm AVP if it is for the first derivation of keys
in the session. The PANA session MUST be terminated immediately
after the last PANA-Auth message exchange.
4.2. Access Phase
Once the authentication and authorization phase successfully
completes, the PaC gains access to the network and can send and
receive IP data traffic through the EP(s) and the PANA session enters
the access phase. In this phase, PANA-Notification-Request and
PANA-Notification-Answer messages with 'P' (Ping) bit set (ping
request and ping answer messages, respectively) can be used for
testing the liveness of the PANA session on the PANA peer. Both the
PaC and the PAA are allowed to send a ping request to the
communicating peer whenever they need to make sure the availability
of the session on the peer and expect the peer to return a ping
answer message. The ping request and answer messages MUST be
protected with an AUTH AVP when a PANA SA is available. A ping
request MUST NOT be sent in the authentication and authorization
phase, re-authentication phase and termination phase.
Implementations MUST limit the rate of performing this test. The PaC
and the PAA can handle rate limitation on their own, they do not have
to perform any coordination with each other. There is no negotiation
of timers for this purpose. Additionally, an implementation MAY
rate-limit processing the incoming ping requests. It should be noted
that if a PAA or PaC which considers its connectivity lost after a
relatively small number of unresponsive pings coupled with a peer
that is aggressively rate-limiting the ping request and answer
messages, false-positives could result. Therefore, a PAA or PaC
should not rely on frequent ping operation to quickly determine loss
of connectivity.
4.3. Re-authentication Phase
The PANA session in the access phase can enter the re-authentication
phase to extend the current session lifetime by re-executing EAP.
Once the re-authentication phase successfully completes, the session
re-enters the access phase. Otherwise, the session is terminated.
When the PaC initiates re-authentication, it sends a
PANA-Notification-Request message with 'A' bit set (a
re-authentication request message) to the PAA. This message MUST
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contain the session identifier assigned to the session being
re-authenticated. If the PAA already has an established PANA session
for the PaC with the matching session identifier, it MUST first
respond with a PANA-Notification-Answer message with 'A' bit set (a
re-authentication answer message), followed by a PANA-Auth-Request
message that starts a new EAP authentication. If the PAA cannot
identify the session, it MUST silently discard the message. The
first PANA-Auth-Request and PANA-Auth-Answer messages in the
re-authentication phase MUST have 'S' bit cleared and carry a Nonce
AVP.
The PaC may receive a PANA-Auth-Request before receiving the answer
to its outstanding re-authentication request message. This condition
can arise due to packet re-ordering or a race condition between the
PaC and PAA when they both attempt to engage in re-authentication.
The PaC MUST keep discarding the received PANA-Auth-Requests until it
receives the answer to its request.
When the PAA initiates re-authentication, it sends a
PANA-Auth-Request message containing the session identifier for the
PaC. The PAA MUST initiate EAP re-authentication before the current
session lifetime expires.
Re-authentication of an on-going PANA session MUST NOT reset the
sequence numbers.
For any re-authentication, if there is an established PANA SA, re-
authentication request and answer messages and subsequent
PANA-Auth-Request and PANA-Auth-Answer messages MUST be protected
with an AUTH AVP. The final PANA-Auth-Request and PANA-Auth-Answer
messages and any subsequent PANA message MUST be protected by using
the key generated from the latest EAP authentication.
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PaC PAA Message(sequence number)[AVPs]
------------------------------------------------------
-----> PANA-Notification-Request(q)[AUTH] // 'A' bit set
<----- PANA-Notification-Answer(q)[AUTH] // 'A' bit set
<----- PANA-Auth-Request(p)[EAP-Payload, Nonce, AUTH]
-----> PANA-Auth-Answer(p)[AUTH, Nonce]
-----> PANA-Auth-Request(q+1)[EAP-Payload, AUTH]
<----- PANA-Auth-Answer(q+1)[AUTH]
<----- PANA-Auth-Request(p+1)[EAP-Payload, AUTH]
-----> PANA-Auth-Answer(p+1)[EAP-Payload, AUTH]
<----- PANA-Auth-Request(p+2)[Result-Code, EAP-Payload,
Key-Id, Algorithm,
Session-Lifetime, AUTH]
// 'C' bit set
-----> PANA-Auth-Answer(p+2)[Key-Id, AUTH]// 'C' bit set
Figure 2: Example sequence for the re-authentication phase initiated
by PaC
4.4. Termination Phase
A procedure for explicitly terminating a PANA session can be
initiated either from the PaC (i.e., disconnect indication) or from
the PAA (i.e., session revocation). The PANA-Termination-Request and
PANA-Termination-Answer message exchanges are used for disconnect
indication and session revocation procedures.
The reason for termination is indicated in the Termination-Cause AVP.
When there is an established PANA SA between the PaC and the PAA, all
messages exchanged during the termination phase MUST be protected
with an AUTH AVP. When the sender of the PANA-Termination-Request
message receives a valid acknowledgment, all states maintained for
the PANA session MUST be terminated immediately.
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5. Processing Rules
5.1. Fragmentation
PANA does not provide fragmentation of PANA messages. Instead, it
relies on fragmentation provided by EAP methods and IP layer when
needed.
5.2. Sequence Number and Retransmission
PANA uses sequence numbers to provide ordered and reliable delivery
of messages.
The PaC and PAA maintain two sequence numbers: One is for setting the
sequence number of the next outgoing request, the other is for
matching the sequence number of the next incoming request. These
sequence numbers are 32-bit unsigned numbers. They are monotonically
incremented by 1 as new requests are generated and received, and
wrapped to zero on the next message after 2^32-1. Answers always
contain the same sequence number as the corresponding request.
Retransmissions reuse the sequence number contained in the original
packet.
The initial sequence numbers (ISN) are randomly picked by the PaC and
PAA as they send their very first request messages.
PANA-Client-Initiation message carries sequence number 0.
When a request message is received, it is considered valid in terms
of sequence numbers if and only if its sequence number matches the
expected value. This check does not apply to the
PANA-Client-Initiation message and the initial PANA-Auth-Request
message.
When an answer message is received, it is considered valid in terms
of sequence numbers if and only if its sequence number matches that
of the currently outstanding request. A peer can only have one
outstanding request at a time.
PANA request messages are retransmitted based on a timer until an
answer is received (in which case the retransmission timer is
stopped) or the number of retransmission reaches the maximum value
(in which case the PANA session MUST be terminated immediately).
The retransmission timers SHOULD be calculated as described in
Section 9 unless a given deployment chooses to use its own
retransmission timers optimized for the underlying link-layer
characteristics.
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Unless dropped due to rate limiting, the PaC and PAA MUST respond to
all duplicate request messages received. The last transmitted answer
MAY be cached in case it is not received by the peer 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
the EAP authentication method. When a new MSK is derived in the PANA
re-authentication phase, any key derived from the old MSK MUST be
updated to a new one that is derived from the new MSK. In order to
distinguish the new MSK from old ones, one Key-Id AVP MUST be carried
in the last PANA-Auth-Request and PANA-Auth-Answer messages with 'C'
(Complete) bit set at the end of the EAP authentication which
resulted in deriving a new MSK. The Key-Id AVP is of type Unsigned32
and MUST contain a value that uniquely identifies the MSK within the
PANA session. The last PANA-Auth-Answer message with 'C' (Complete)
bit set in response to the last PANA-Auth-Request message with 'C'
(Complete) bit set MUST contain a Key-Id AVP with the same MSK
identifier carried in the request. The last PANA-Auth-Request and
PANA-Auth-Answer messages with a Key-Id AVP MUST also carry an AUTH
AVP whose value is computed by using the new PANA_AUTH_KEY derived
from the new MSK. Although the specification does not mandate a
particular method for calculation of the Key-Id AVP value, a simple
method is to use monotonically increasing numbers.
The PANA session lifetime is bounded by the authorization lifetime
granted by the authentication server (same as the MSK lifetime). The
lifetime of the PANA SA (hence the PANA_AUTH_KEY) is the same as the
lifetime of the PANA session. The created PANA SA is deleted when
the corresponding PANA session is terminated.
PANA SA attributes as well as PANA session attributes are listed
below:
PANA Session attributes:
* Session Identifier
* IP address and UDP port number of the PaC.
* IP address and UDP port number of the PAA.
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* Sequence number for the next outgoing request
* Sequence number for the next incoming request
* Last transmitted message payload
* Retransmission interval
* Session lifetime
* PANA SA attributes
PANA SA attributes:
* Nonce generated by PaC (PaC_nonce)
* Nonce generated by PAA (PAA_nonce)
* MSK
* MSK Identifier
* PANA_AUTH_KEY
* Pseudo-random function
* Integrity algorithm
The PANA_AUTH_KEY is derived from the available MSK and it is used to
integrity protect PANA messages. The PANA_AUTH_KEY is computed in
the following way:
PANA_AUTH_KEY = prf+(MSK, 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 the last PANA-Auth-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 non-initial PANA-Auth-Answer and PANA-Auth-Request messages in
the authentication and authorization phase or the first
PANA-Auth-Answer and PANA-Auth-Request messages in the
re-authentication phase, respectively. Session_ID is the session
identifier of the session. Key_ID is the value of the Key-Id AVP.
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5.4. Message Authentication
A PANA message can contain an AUTH AVP for cryptographically
protecting the message.
When an AUTH AVP is included in a PANA message, the value field of
the AUTH AVP is calculated by using the PANA_AUTH_KEY in the
following way:
AUTH AVP value = PANA_AUTH_HASH(PANA_AUTH_KEY, PANA_PDU)
where PANA_PDU is the PANA message including the PANA header, with
the AUTH AVP value field first initialized to 0. PANA_AUTH_HASH
represents the integrity algorithm specified in the Algorithm AVP in
the last PANA-Auth-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 last
PANA-Auth-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 authentication and authorization phase and the
re-authentication phase:
+ PANA-Client-Initiation after completion of the initial
PANA-Auth-Request and PANA-Auth-Answer exchange.
+ Re-authentication request.
+ The last PANA-Auth-Request as well as ping request before
completion of the initial PANA-Auth-Request and
PANA-Auth-Answer exchange.
+ The initial PANA-Auth-Request after a PaC receives a valid
non-initial PANA-Auth-Request.
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+ PANA-Termination-Request.
* In the re-authentication phase:
+ PANA-Client-Initiation.
+ The initial PANA-Auth-Request.
* In the access phase:
+ PANA-Auth-Request.
+ PANA-Client-Initiation.
* In the termination phase:
+ PANA-Client-Initiation.
+ All requests but PANA-Termination-Request and ping request.
o The message payload contains a valid set of AVPs allowed for the
message type 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.
o When an Algorithm AVP is included, the algorithms indicated in the
AVP value is supported.
Invalid messages MUST be discarded in order to provide robustness
against DoS attacks.
5.6. PaC Updating its IP Address
A PaC's IP address used for PANA can change in certain situations,
e.g., when the PaC moves from one IP link to another within the same
PAA's realm. In order to maintain the PANA session, the PAA needs to
be notified about the change of PaC address.
After the PaC has changed its IP address used for PANA, it MUST send
any valid PANA message. If the message that carries the new PaC IP
address in the Source Address field of the IP header is valid, the
PAA MUST update the PANA session with the new PaC address. If there
is an established PANA SA, the message MUST be protected with an AUTH
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AVP.
5.7. Session Lifetime
The authentication and authorization phase determines the PANA
session lifetime and the lifetime is indicated to the PaC When the
network access authorization succeeds. For this purpose, when the
last PANA-Auth-Request message (i.e., with 'C' (Complete) bit set) in
authentication and authorization phase or re-authentication phase
carries a Result-Code AVP with a value of PANA_SUCCESS, a Session-
Lifetime AVP MUST also be carried in the message. A Session-Lifetime
AVP MUST be ignored when included in other PANA messages.
The lifetime is a non-negotiable parameter that can be used by the
PaC to manage PANA-related state. The PaC MUST initiate the re-
authentication phase before the current session lifetime expires if
it wants to extend the session.
The PaC and the PAA MAY use information obtained outside PANA (e.g.,
lower-layer indications) to expedite the detection of a disconnected
peer. Availability and reliability of such indications MAY depend on
a specific link-layer or network topology and are therefore only
hints. A PANA peer SHOULD use the ping request and answer exchange
to verify that a peer is, in fact, no longer alive, unless
information obtained outside PANA is being used to expedite the
detection of a disconnected peer.
The session lifetime parameter is not related to the transmission of
ping request messages. These messages can be used for asynchronously
verifying the liveness of the peer. The decision to send a ping
request message is taken locally and does not require coordination
between the peers.
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6. Message Format
This section defines message formats for PANA protocol.
6.1. IP and UDP Headers
Any PANA message is unicast between the PaC and the PAA.
For any PANA message sent from the peer that has initiated the PANA
session, the UDP source port is set to any number and the destination
port is set to the assigned PANA port number (to be assigned by
IANA). For any PANA message sent from the other peer, the source
port is set to the assigned PANA port number (to be assigned by IANA)
and the destination port is copied from the source port of the last
received message. In case both the PaC and PAA initiates the session
(i.e., PANA-Client-Initiation and unsolicited PANA-Auth-Request
messages cross each other), then the PaC is identified as the
initiator.
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.
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Message Length
The Message Length field is two octets and indicates the length of
the PANA message including the header fields.
Flags
The Flags field is two octets. The following bits are assigned:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R S C A P r r r r r r r r r r r|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R (Request)
If set, the message is a request. If cleared, the message is
an answer.
S (Start)
If set, the message is the first PANA-Auth-Request or PANA-
Auth-Answer in authentication and authorization phase. For
other messages, this bit MUST be cleared.
C (Complete)
If set, the message is the last PANA-Auth-Request or PANA-Auth-
Answer in authentication and authorization phase. For other
messages this bit MUST be cleared.
A (re-Authentication)
If set, the message is a PANA-Notification-Request or PANA-
Notification-Answer to initiate re-authentication. For other
messages this bit MUST be cleared.
P (Ping)
If set, the message is a PANA-Notification-Request or PANA-
Notification-Answer for liveness test. For other messages this
bit MUST be cleared.
r (reserved)
These flag bits are reserved for future use, and MUST be set to
zero, and ignored by the receiver.
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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.
6.3. AVP Format
Each AVP of type OctetString MUST be padded to align on a 32-bit
boundary, while other AVP types align naturally. A number of
zero-valued bytes are added to the end of the AVP Value field 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 are sent in network byte order. The AVP format
is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code | AVP Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Id (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value ...
+-+-+-+-+-+-+-+-+
AVP Code
The AVP Code, together with the optional Vendor ID field,
identifies 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 (Vendor)
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.
M (Mandatory)
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 considered as invalid.
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.
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r (reserved)
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 the Value field. The length of the AVP Code, AVP
Length, AVP Flags, Reserved and Vendor-Id fields are not counted
in the AVP Length value.
Reserved
This two-octet field is reserved for future use, 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.
Value
The Value field is zero or more octets and contains information
specific to the Attribute. The format of the Value field is
determined by the AVP Code and Vendor-Id fields. The length of
the Value field is determined by the AVP Length field.
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.
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7. PANA Messages
Each Request/Answer message pair is assigned a Sequence Number, and
the sub-type (i.e., request or answer) is identified via the 'R'
(Request) bit in the Message Flags field of the PANA message header.
Every PANA message MUST contain a message type in its header's
Message Type field, which is used to determine the action that is to
be taken for a particular message. Figure 3 lists all PANA messages
defined in this document:
Message-Name Abbrev. ID PaC<->PAA Ref.
----------------------------------------------------------
PANA-Client-Initiation PCI 1 --------> 7.1
PANA-Auth-Request PAR 2 <-------> 7.2
PANA-Auth-Answer PAN 2 <-------> 7.3
PANA-Termination-Request PTR 3 <-------> 7.4
PANA-Termination-Answer PTA 3 <-------> 7.5
PANA-Notification-Request PNR 4 <-------> 7.6
PANA-Notification-Answer PNA 4 <-------> 7.7
-----------------------------------------------------------
Figure 3: Table of PANA Messages
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
[r-bit] [s-bit] [c-bit] [a-bit] [p-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.
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s-bit = ", STA"
; If present, the 'S' bit in the Message
; Flags is set, indicating that the message
; is the initial PAR or PAN in authentication
; and authorization phase.
c-bit = ", COM"
; If present, the 'C' bit in the Message
; Flags is set, indicating that the message
; is the final PAR and PAN in authentication
; and authorization phase or re-authentication
; phase.
a-bit = ", REA"
; If present, the 'A' bit in the Message
; Flags is set, indicating that the message
; is a re-authentication request or answer.
p-bit = ", PIN"
; If present, the 'P' bit in the Message
; Flags is set, indicating that the message
; is a ping request or 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).
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; These braces cannot be used to express
; optional fixed rules (such as an optional
; AUTH at the end). To do this, the convention
; is '0*1fixed'.
min = 1*DIGIT
; The minimum number of times the element may
; be present. The default value is zero.
max = 1*DIGIT
; The maximum number of times the element may
; be present. The default value is infinity. A
; value of zero implies the AVP MUST NOT be
; present.
avp-spec = PANA-name
; The avp-spec has to be an AVP Name, defined
; in the base or extended PANA protocol
; specifications.
avp-name = avp-spec / "AVP"
; The string "AVP" stands for *any* arbitrary
; AVP Name, which does not conflict with the
; required or fixed position AVPs defined in
; the message definition.
7.1. PANA-Client-Initiation (PCI)
The PANA-Client-Initiation (PCI) message is used for PaC-initiated
session. The Sequence Number and Session Identifier fields in this
message MUST be set to zero (0).
PANA-Client-Initiation ::= < PANA-Header: 1 >
* [ AVP ]
7.2. PANA-Auth-Request (PAR)
The PANA-Auth-Request (PAR) message is either sent by the PAA or the
PaC.
The message MUST NOT have both 'S' and 'C' bits set.
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PANA-Auth-Request ::= < PANA-Header: 2, REQ[,STA][,COM] >
[ EAP-Payload ]
[ Algorithm ]
[ Nonce ]
[ Result-Code ]
[ Session-Lifetime ]
[ Key-Id ]
* [ AVP ]
0*1 < AUTH >
7.3. PANA-Auth-Answer (PAN)
The PANA-Auth-Answer (PAN) message is sent by either the PaC or the
PAA in response to a PANA-Auth-Request message.
The message MUST NOT have both 'S' and 'C' bits set.
PANA-Auth-Answer ::= < PANA-Header: 2 [,STA][,COM] >
[ Nonce ]
[ EAP-Payload ]
[ Key-Id ]
* [ AVP ]
0*1 < AUTH >
7.4. PANA-Termination-Request (PTR)
The PANA-Termination-Request (PTR) message is sent either by the PaC
or the PAA to terminate a PANA session.
PANA-Termination-Request ::= < PANA-Header: 3, REQ >
< Termination-Cause >
* [ AVP ]
0*1 < AUTH >
7.5. PANA-Termination-Answer (PTA)
The PANA-Termination-Answer (PTA) message is sent either by the PaC
or the PAA in response to PANA-Termination-Request.
PANA-Termination-Answer ::= < PANA-Header: 3 >
* [ AVP ]
0*1 < AUTH >
7.6. PANA-Notification-Request (PNR)
The PANA-Notification-Request (PNR) message is sent either by the PaC
or the PAA for signaling re-authentication and performing liveness
test.
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The message MUST have one of 'A' and 'P' bits exclusively set.
PANA-Notification-Request ::= < PANA-Header: 4, REQ[,REA][,PIN] >
* [ AVP ]
0*1 < AUTH >
7.7. PANA-Notification-Answer (PNA)
The PANA-Notification-Answer (PNA) message is sent by the PAA (PaC)
to the PaC (PAA) in response to a PANA-Notification-Request from the
PaC (PAA).
The message MUST have one of 'A' and 'P' bits exclusively set.
PANA-Notification-Answer ::= < PANA-Header: 4, REQ[,REA][,PIN] >
* [ AVP ]
0*1 < AUTH >
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8. AVPs in PANA
This document uses AVP Value Format such as 'OctetString' and
'Unsigned32' as defined in Section 4.2 of [RFC3588]. The definitions
of these data formats are not repeated in this document.
The following table lists the AVPs used in this document, and
specifies in which PANA messages they MAY, or MAY NOT be present.
The table uses the following symbols:
0 The AVP MUST NOT be present in the message.
0-1 Zero or one instance of the AVP MAY be present in the message.
It is considered an error if there are more than one instance
of the AVP.
1 One instance of the AVP MUST be present in the message.
+---------------------------+
| Message Type |
+---+---+---+---+---+---+---+
Attribute Name |PCI|PAR|PAN|PTR|PTA|PNR|PNA|
----------------------+---+---+---+---+---+---+---+
Algorithm | 0 |0-1| 0 | 0 | 0 | 0 | 0 |
AUTH | 0 |0-1|0-1|0-1|0-1|0-1|0-1|
EAP-Payload | 0 |0-1|0-1| 0 | 0 | 0 | 0 |
Key-Id | 0 |0-1|0-1| 0 | 0 | 0 | 0 |
Nonce | 0 |0-1|0-1| 0 | 0 | 0 | 0 |
Result-Code | 0 |0-1| 0 | 0 | 0 | 0 | 0 |
Session-Lifetime | 0 |0-1| 0 | 0 | 0 | 0 | 0 |
Termination-Cause | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
----------------------+---+---+---+---+---+---+---+
Figure 4: AVP Occurrence Table
8.1. 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.
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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. The AVP data is
of type OctetString.
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
authenticator. The AVP data is of type OctetString.
8.4. Key-Id AVP
The Key-Id AVP (AVP Code 4) is of type Integer32, and contains an MSK
identifier. The MSK identifier is assigned by PAA and MUST be unique
within the PANA session.
8.5. Nonce AVP
The Nonce AVP (AVP Code 5) carries a randomly chosen value that is
used in cryptographic key computations. The recommendations in
[RFC4086] apply with regard to generation of random values. The AVP
data is of type OctetString and it contains a randomly generated
value in opaque format. The data length MUST be between 8 and 256
octets inclusive.
The length of the nonces are determined based on the available
pseudo-random functions (PRFs) and the degree of trust placed into
the 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
case of HMAC-SHA1).
2. The PaC and the PAA each are not trusted with regard to the
computation of a random nonce (according to [RFC4086]). The
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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 maximum length of the nonce value in PANA Version 1
SHOULD be therefore 20 octets.
8.6. Result-Code AVP
The Result-Code AVP (AVP Code 6) is of type Unsigned32 and indicates
whether an EAP authentication was completed successfully. Result-
Code AVP values are described below.
PANA_SUCCESS 0
Both authentication and authorization processes are successful.
PANA_AUTHENTICATION_REJECTED 1
Authentication has failed. When 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.
8.7. Session-Lifetime AVP
The Session-Lifetime AVP (AVP Code 7) contains the number of seconds
remaining before the current session is considered expired. The AVP
data is of type Unsigned32.
8.8. Termination-Cause AVP
The Termination-Cause AVP (AVP Code 8) 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
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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.
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9. Retransmission Timers
The PANA protocol provides retransmissions for the
PANA-Client-Initiation message and all request messages.
PANA retransmission timers are based on the model used in DHCPv6
[RFC3315]. Variables used here are also borrowed from this
specification. PANA is a request/response-based protocol. The
message exchange terminates when the requester successfully receives
the answer or the message exchange is considered to have failed
according to the retransmission mechanism described below.
The retransmission behavior is controlled and described by the
following variables:
RT Retransmission timeout
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
value of RT:
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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 Max PCI retransmission attempts.
PCI_MRD 0 Max PCI retransmission duration.
REQ_IRT 1 sec Initial Request timeout.
REQ_MRT 30 secs Max Request timeout value.
REQ_MRC 10 Max Request retransmission attempts.
REQ_MRD 0 Max Request retransmission duration.
So for example the first RT for the PBR message is calculated using
REQ_IRT as the IRT:
RT = REQ_IRT + RAND*REQ_IRT
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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 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 1-4. See
Section 7.1 through Section 7.7 for the assignment of the namespace
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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'), 1 ('S'), 2 ('C'), 3 ('A') and 4
('P'). 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 8.8 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
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be encouraged instead.
10.3.2. Flags
There are 16 bits in the AVP Flags field of the AVP header, defined
in Section 6.3. This document assigns bit 0 ('V') and bit 1 ('M').
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 8.6 the Result-Code AVP (AVP Code 6) defines
the values 0-2.
All remaining values are available for assignment via IETF Consensus
[IANA].
10.4.2. Termination-Cause AVP Values
As defined in Section 8.8, the Termination-Cause AVP (AVP Code 8)
defines the values 1, 4 and 8.
All remaining values are available for assignment via IETF Consensus
[IANA].
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11. Security Considerations
The PANA protocol defines a UDP-based EAP encapsulation that runs
between two IP-enabled nodes. Various security threats that are
relevant to a protocol of this nature are outlined in [RFC4016].
Security considerations stemming from the use of EAP and EAP methods
are discussed in [RFC3748] [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
spoofing 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/or
a session identifier for a non-existing session) and any duplicate
answer are immediately discarded, and a duplicate request can trigger
transmission of the cached answer (i.e., no need to process the
request and generate a new answer).
The PANA framework defines EP which is ideally located on a network
device that can filter traffic from the PaCs before the traffic
enters the Internet/intranet. A set of filters can be used to
discard unauthorized packets, such as the initial PANA-Auth-Request
message that is received from the segment of the access network where
only the PaCs are supposed to be connected (i.e., preventing PAA
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impersonation).
The protocol also provides authentication and integrity protection to
PANA messages when the used EAP method can generate cryptographic
session keys. A PANA SA is generated based on the MSK exported by
the EAP method. This SA is used for generating an AUTH AVP to
protect the PANA message header and payload (including the complete
EAP message).
The cryptographic protection prevents an adversary from acting as a
man-in-the-middle, injecting messages, replaying messages and
modifying the content of the exchanged messages. Any packet that
fails to pass the AUTH verification is silently discarded. The
earliest this protection can be enabled is when the PANA-Auth-Request
message that signals a successful authentication (EAP Success) is
generated. Starting with these messages, any subsequent PANA message
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 grace period to that value.
Unless the PANA session is extended by executing another EAP
authentication, the PANA SA is removed when the current session
expires.
The ability to use cryptographic protection within PANA is determined
by the used EAP method, which is generally dictated by the deployment
environment. Insecure lower-layers necessitate use of key-generating
EAP methods. In networks where lower-layers are already secured,
cryptographic protection of PANA messages is not necessary.
11.2. Initial Exchange
The initial PANA-Auth-Request and PANA-Auth-Answer exchange is
vulnerable to spoofing attacks as these messages are not
authenticated and integrity protected. In order to prevent very
basic DoS attacks an adversary should not be able to cause state
creation by sending PANA-Client-Initiation messages to the PAA. This
protection is achieved by allowing the responder (PAA) to create as
little amount of state as possible in the initial message exchange.
However, it is difficult to prevent all spoofing attacks in the
initial message exchange entirely.
In networks where lower-layers are not secured prior to running PANA,
the capability discovery enabled through inclusion of an Algorithm
AVP in the initial PANA-Auth-Request message is susceptible to
spoofing leading to DoS attacks. Therefore, usage of this AVP during
the initial message exchange in such insecure networks is NOT
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RECOMMENDED. The same AVP is delivered with integrity protection via
the last PANA-Auth-Request message upon successful authentication.
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
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protocol is outside the scope of this document.
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
in access phase, expecting the peer to 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 ping request message if
a recent exchange has already confirmed that the peer is alive.
11.8. Early Termination of a Session
The PANA protocol supports the ability for both the PaC and the PAA
to transmit a tear-down message before the session lifetime expires.
This message causes state removal, a stop of the accounting procedure
and removes the installed per-PaC state on the EP(s). This message
is cryptographically protected when PANA SA is present.
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12. Acknowledgments
We would like to thank Mark Townsley, Jari Arkko, Mohan
Parthasarathy, Julien Bournelle, Rafael Marin Lopez, Pasi Eronen,
Randy Turner, Erik Nordmark, Lionel Morand, Avi Lior, Susan Thomson,
Giaretta Gerardo, Joseph Salowey, Sasikanth Bharadwaj, Spencer
Dawkins, Tom Yu, Bernard Aboba, Subir Das and all members of the PANA
working group for their valuable comments to this document.
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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-05 (work in progress),
December 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,
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"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-18 (work in
progress), February 2007.
[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.
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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
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Alper E. Yegin
Samsung Advanced Institute of Technology
Istanbul,
Turkey
Phone: +90 538 719 0181
Email: alper01.yegin@partner.samsung.com
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