PANA Working Group D. Forsberg
Internet-Draft Nokia
Intended status: Standards Track Y. Ohba (Ed.)
Expires: September 4, 2007 Toshiba
B. Patil
Nokia
H. Tschofenig
Siemens
A. Yegin
Samsung
March 3, 2007
Protocol for Carrying Authentication for Network Access (PANA)
draft-ietf-pana-pana-14
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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. 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 . . . . . . . . . . . . . . . . . 15
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. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 24
6.1. IP and UDP Headers . . . . . . . . . . . . . . . . . . . . 24
6.2. PANA Message Header . . . . . . . . . . . . . . . . . . . 24
6.3. AVP Format . . . . . . . . . . . . . . . . . . . . . . . . 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
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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. Early Termination of a Session . . . . . . . . . . . . . . 52
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 53
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 54
13.1. Normative References . . . . . . . . . . . . . . . . . . . 54
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13.2. Informative References . . . . . . . . . . . . . . . . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 56
Intellectual Property and Copyright Statements . . . . . . . . . . 58
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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 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].
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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 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.
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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].
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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 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.
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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 messages are
optional to use).
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.
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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.
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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 SHOULD limit the rate it processes incoming
PANA-Client-Initiation messages in order not to subject itself to
denial-of service attacks. Details of rate limiting are outside the
scope of this specification.
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 opposed 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.
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In order to prevent potential DoS attacks, the PAA SHOULD refrain
from 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. The PAA uses the source IP
address and the source port number of the PANA-Client-Initiation
message to identify the PaC in the handshake phase.
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 SHOULD 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
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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
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 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
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
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be deleted immediately after the PANA-Bind message exchange.
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. 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 PANA-Ping messages,
false-positives could result. Care should be taken when
rate-limiting PANA-Ping messages to periodically respond, and a PAA
or PaC should not rely on PANA-Ping messages to quickly determine
loss of connectivity.
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
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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
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 NOT reset the
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.
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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
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
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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: 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.
Unless dropped due to rate limiting, the PaC and PAA MUST respond to
all duplicate request messages received. The last transmitted answer
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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
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* 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
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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.
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+ 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
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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 PANA protocol 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
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does not change its PANA protocol state.
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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.
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.
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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 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.
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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:
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(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.
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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 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.
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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' 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
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[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
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; 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 ]
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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.
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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 >
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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).
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PANA-Update-Answer ::= < PANA-Header: 9 >
* [ 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 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.
+-------------------------------------------+
| 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)
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+-----------------------+
| 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
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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.
<Failed-AVP> ::= < 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
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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.
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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
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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.
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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.
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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 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
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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 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:
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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 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
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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'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.
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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].
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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 a PANA-Start-Request message
that is received from the segment of the access network where only
the PaCs are supposed to be connected.
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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.
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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.
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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. 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 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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Forsberg, et al. Expires September 4, 2007 [Page 58]
