PANA Working Group D. Forsberg
Internet-Draft Nokia
Expires: November 5, 2004 Y. Ohba (Ed.)
Toshiba
B. Patil
Nokia
H. Tschofenig
Siemens
A. Yegin
Samsung
May 7, 2004
Protocol for Carrying Authentication for Network Access (PANA)
draft-ietf-pana-pana-04
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines the Protocol for Carrying Authentication for
Network Access (PANA), a link-layer agnostic transport for Extensible
Authentication Protocol (EAP) to enable network access authentication
between clients and access networks. PANA can carry any
authentication method that can be specified as an EAP method, and can
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be used on any link that can carry IP. PANA covers the
client-to-network access authentication part of an overall secure
network access framework, which additionally includes other protocols
and mechanisms for service provisioning, access control as a result
of initial authentication, and accounting.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Specification of Requirements . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . 8
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . 10
4.1 Common Processing Rules . . . . . . . . . . . . . . . . . 10
4.1.1 Payload Encoding . . . . . . . . . . . . . . . . . . . . . 10
4.1.2 Transport Layer Protocol . . . . . . . . . . . . . . . . . 11
4.1.3 Fragmentation . . . . . . . . . . . . . . . . . . . . . . 11
4.1.4 Sequence Number and Retransmission . . . . . . . . . . . . 11
4.1.5 PANA Security Association . . . . . . . . . . . . . . . . 12
4.1.6 Message Authentication Code . . . . . . . . . . . . . . . 14
4.1.7 Message Validity Check . . . . . . . . . . . . . . . . . . 14
4.1.8 Error Handling . . . . . . . . . . . . . . . . . . . . . . 15
4.2 Discovery and Initial Handshake Phase . . . . . . . . . . 16
4.3 Authentication Phase . . . . . . . . . . . . . . . . . . . 19
4.4 Re-authentication . . . . . . . . . . . . . . . . . . . . 22
4.5 Termination Phase . . . . . . . . . . . . . . . . . . . . 23
4.6 Illustration of a Complete Message Sequence . . . . . . . 24
4.7 Device ID Choice . . . . . . . . . . . . . . . . . . . . . 27
4.8 Session Lifetime . . . . . . . . . . . . . . . . . . . . . 27
4.9 Mobility Handling . . . . . . . . . . . . . . . . . . . . 28
4.10 Support for Separate EP . . . . . . . . . . . . . . . . . 30
5. PANA Security Association Establishment . . . . . . . . . 31
6. Message Formats . . . . . . . . . . . . . . . . . . . . . 32
6.1 IP and UDP Headers . . . . . . . . . . . . . . . . . . . . 32
6.2 PANA Header . . . . . . . . . . . . . . . . . . . . . . . 32
6.3 AVP Header . . . . . . . . . . . . . . . . . . . . . . . . 34
6.4 PANA Messages . . . . . . . . . . . . . . . . . . . . . . 36
6.4.1 Message Specifications . . . . . . . . . . . . . . . . . . 36
6.4.2 PANA-PAA-Discover (PDI) . . . . . . . . . . . . . . . . . 37
6.4.3 PANA-Start-Request (PSR) . . . . . . . . . . . . . . . . . 37
6.4.4 PANA-Start-Answer (PSA) . . . . . . . . . . . . . . . . . 37
6.4.5 PANA-Auth-Request (PAR) . . . . . . . . . . . . . . . . . 38
6.4.6 PANA-Auth-Answer (PAN) . . . . . . . . . . . . . . . . . . 38
6.4.7 PANA-Bind-Request (PBR) . . . . . . . . . . . . . . . . . 38
6.4.8 PANA-Bind-Answer (PBA) . . . . . . . . . . . . . . . . . . 38
6.4.9 PANA-Reauth-Request (PRAR) . . . . . . . . . . . . . . . . 39
6.4.10 PANA-Reauth-Answer (PRAA) . . . . . . . . . . . . . . . . 39
6.4.11 PANA-Termination-Request (PTR) . . . . . . . . . . . . . . 39
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6.4.12 PANA-Termination-Answer (PTA) . . . . . . . . . . . . . . 39
6.4.13 PANA-Error (PER) . . . . . . . . . . . . . . . . . . . . . 40
6.4.14 PANA-FirstAuth-End-Request (PFER) . . . . . . . . . . . . 40
6.4.15 PANA-FirstAuth-End-Answer (PFEA) . . . . . . . . . . . . . 40
6.5 AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . . 40
6.5.1 MAC AVP . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.5.2 Device-Id AVP . . . . . . . . . . . . . . . . . . . . . . 41
6.5.3 Session-Id AVP . . . . . . . . . . . . . . . . . . . . . . 41
6.5.4 Cookie AVP . . . . . . . . . . . . . . . . . . . . . . . . 42
6.5.5 Protection-Capability AVP . . . . . . . . . . . . . . . . 42
6.5.6 Termination-Cause AVP . . . . . . . . . . . . . . . . . . 42
6.5.7 Result-Code AVP . . . . . . . . . . . . . . . . . . . . . 42
6.5.8 EAP-Payload AVP . . . . . . . . . . . . . . . . . . . . . 46
6.5.9 Session-Lifetime AVP . . . . . . . . . . . . . . . . . . . 46
6.5.10 Failed-AVP AVP . . . . . . . . . . . . . . . . . . . . . . 46
6.5.11 NAP-Information AVP . . . . . . . . . . . . . . . . . . . 46
6.5.12 ISP-Information AVP . . . . . . . . . . . . . . . . . . . 47
6.5.13 Provider-Identifier AVP . . . . . . . . . . . . . . . . . 47
6.5.14 Provider-Name AVP . . . . . . . . . . . . . . . . . . . . 47
6.5.15 EP-Device-Id AVP . . . . . . . . . . . . . . . . . . . . . 47
6.5.16 Key-Id AVP . . . . . . . . . . . . . . . . . . . . . . . . 47
6.5.17 Post-PANA-Address-Configuration (PPAC) AVP . . . . . . . . 47
6.5.18 Nonce AVP . . . . . . . . . . . . . . . . . . . . . . . . 48
6.6 AVP Occurrence Table . . . . . . . . . . . . . . . . . . . 49
7. PANA Protocol Message Retransmissions . . . . . . . . . . 51
7.1 Transmission and Retransmission Parameters . . . . . . . . 53
8. IANA Considerations . . . . . . . . . . . . . . . . . . . 54
8.1 PANA UDP Port Number . . . . . . . . . . . . . . . . . . . 54
8.2 PANA Multicast Address . . . . . . . . . . . . . . . . . . 54
8.3 PANA Header . . . . . . . . . . . . . . . . . . . . . . . 54
8.3.1 Message Type . . . . . . . . . . . . . . . . . . . . . . . 54
8.3.2 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.4 AVP Header . . . . . . . . . . . . . . . . . . . . . . . . 54
8.4.1 AVP Code . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.4.2 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 55
8.4.3 Vendor Id . . . . . . . . . . . . . . . . . . . . . . . . 55
8.5 AVP Values . . . . . . . . . . . . . . . . . . . . . . . . 55
8.5.1 MAC AVP Values . . . . . . . . . . . . . . . . . . . . . . 55
8.5.2 Device-Id AVP Values . . . . . . . . . . . . . . . . . . . 55
8.5.3 Protection-Capability AVP Values . . . . . . . . . . . . . 55
8.5.4 Result-Code AVP Values . . . . . . . . . . . . . . . . . . 55
8.5.5 Termination-Cause AVP Values . . . . . . . . . . . . . . . 55
8.5.6 Provider-Identifier AVP Values . . . . . . . . . . . . . . 55
8.5.7 Post-PANA-Address-Configuration AVP Values . . . . . . . . 55
9. Security Considerations . . . . . . . . . . . . . . . . . 56
10. Open Issues and Change History . . . . . . . . . . . . . . 62
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 63
Normative References . . . . . . . . . . . . . . . . . . . 64
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Informative References . . . . . . . . . . . . . . . . . . 66
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 69
Intellectual Property and Copyright Statements . . . . . . 71
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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. Initial and subsequent client-to-network authentication
provides parameters that are needed to police the traffic flow
through the enforcement points. A protocol is needed to carry
authentication methods between the client and the access network.
Currently there is no standard network-layer solution for
authenticating clients for network access.
[I-D.ietf-pana-usage-scenarios] describes the problem statement that
led to the development of PANA.
Scope of this work is identified as designing a link-layer agnostic
transport for network access authentication methods. The Extensible
Authentication Protocol (EAP) [I-D.ietf-eap-rfc2284bis] 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, EAP and EAP methods.
Various environments and usage models for PANA are identified in the
[I-D.ietf-pana-usage-scenarios] Internet-Draft. Potential security
threats for network-layer access authentication protocol are
discussed in [I-D.ietf-pana-threats-eval] draft. These two drafts
have been essential in defining the requirements
[I-D.ietf-pana-requirements] on the PANA protocol. Note that some of
these requirements are imposed by the chosen payload, EAP
[I-D.ietf-eap-rfc2284bis].
There are components that are part of a complete secure network
solution but are outside of the PANA protocol specification,
including IP address configuration, authentication method choice,
filter rule installation, data traffic protection and PAA-EP
protocol. These components are described in separate documents
[I-D.ietf-pana-framework][I-D.ietf-pana-snmp].
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
This section describes some terms introduced in this document:
PANA Session:
PANA session is defined as the exchange of messages between the
PANA Client (PaC) and the PANA Authentication Agent (PAA) to
authenticate a user (PaC) for network access. If the
authentication is unsuccessful, the session is terminated. The
session is considered as active until there is a disconnect
indication by the PaC or the PAA terminates it. A distinct PANA
session is associated with a pair of device identifiers of PaC and
PAA. For example, if the PaC has two interfaces connected to the
same IP link with different IP addresses and IP address is used as
a device identifier, a distinct PANA session will be created per
interface if both interfaces addresses need to be authorized for
network access.
Session Identifier:
This identifier is used to uniquely identify a PANA session on the
PAA and PaC. It is included in PANA messages to bind the message
to a specific PANA session.
PANA Security Association:
A PANA security association is a relationship between the PaC and
PAA, formed by the sharing of cryptographic keying material and
associated context. Security associations are duplex. That is,
one security association is needed to protect the bidirectional
traffic between the PaC and the PAA.
PANA Client (PaC):
The client side of the protocol that resides in the host device
which is responsible for providing the credentials to prove its
identity for network access authorization.
Device Identifier (DI):
The identifier used by the network as a handle to control and
police the network access of a client. Depending on the access
technology, this identifier might contain any of IP address,
link-layer address, switch port number, etc. of a connected
device.
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PANA Authentication Agent (PAA):
The access network side entity of the protocol whose
responsibility is to verify the credentials provided by a PANA
client and grant network access service to the device associated
with the client and identified by a DI.
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
client devices. Information such as DI and (optionally)
cryptographic keys are provided by PAA per client for constructing
filters on the EP.
Network Access Provider (NAP):
A service provider that provides physical and link-layer
connectivity to an access network it manages.
AAA-Key:
A key derived by the EAP peer and EAP server and transported to
the authenticator [I-D.ietf-eap-keying].
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3. Protocol Overview
The PANA protocol involves two functional entities namely the PaC and
the PAA. The protocol resides above the transport layer and the
details are explained in Section 4.
The placement of the entities used in PANA largely depends on a
certain architecture. The PAA may optionally interact with a AAA
backend to authenticate the user (PaC). The EP, mentioned in the
context with PANA, is a logical entity. There is, however, the option
that the EP is not physically co-located with the PAA. In case that
the PAA and the EP are co-located only an API is required for
intercommunication instead of a separate protocol. In the case where
the PAA is separated from the EP, a separate protocol will be used
between the PAA and the EP for managing access control. The protocol
and messaging between the PAA and EP for access authorization is
outside the scope of this draft and will be dealt separately. Figure
1 illustrates the interactions in a simplified manner:
PaC EP PAA AAA
--- --- --- ---
PAA Discovery
<---------------------o------------> (1)
PANA Authentication AAA interaction
<----------------------------------><------------> (2)
Authorization
<------------- (3)
Figure 1: PANA Framework
PANA supports authentication of a PaC using various EAP methods. The
EAP method used depends on the level of security required for the EAP
messaging itself. PANA does not secure the data traffic itself.
However, EAP methods that enable key exchange may allow other
protocols to be bootstrapped for securing the data traffic
[I-D.ietf-pana-ipsec].
From a state machine aspect, PANA protocol consists of three phases
1. Discovery and initial handshake phase
2. Authentication phase
3. Termination phase
In the first phase, an IP address of PAA is discovered and a PANA
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session is established between PaC and PAA. EAP messages are
exchanged and a PANA SA is established in the second phase. The
established PANA session as well as a PANA SA is deleted in the third
phase.
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4. Protocol Details
4.1 Common Processing Rules
4.1.1 Payload Encoding
The payload of any PANA message consists of zero or more AVPs
(Attribute Value Pairs). A brief description of the AVPs defined in
this document is listed below:
o Cookie AVP: contains a random value that is used for making
initial handshake robust against blind resource consumption DoS
attacks.
o Protection-Capability AVP: contains information which protection
should be initiated after the PANA exchange (e.g., link-layer or
network layer protection).
o Device-Id AVP: contains a device identifier of the sender of the
message. A device identifier is represented as a pair of device
identifier type and device identifier value. Either a layer-2
address or an IP address is used for the device identifier value.
o EP-Device-Id AVP: contains the device identifier of an EP.
o EAP AVP: contains an EAP PDU.
o MAC AVP: contains a Message Authentication Code that protects a
PANA message PDU.
o Termination-Cause AVP: contains the reason of session termination.
o Result-Code AVP: contains information about the protocol execution
results.
o Session-Id AVP: contains the session identifier value.
o Session-Lifetime AVP: contains the duration of authorized access.
o Failed-AVP: contains the offending AVP that caused a failure.
o NAP-Information AVP, ISP-Information AVP: contains the information
on a NAP and an ISP, respectively.
o Key-Id AVP: contains a AAA-Key identifier.
o PPAC AVP: Post-PANA-Address-Configuration AVP. Conveys the list
of IP address configuration methods available when sent by the
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PAA, and the chosen method when sent by the PaC.
o Nonce AVP: contains a randomly chosen value.
4.1.2 Transport Layer Protocol
PANA uses UDP as its transport layer protocol. The UDP port number
is TBD. All messages except for PANA-PAA-Discover are always
unicast. PANA-PAA-Discover MAY be unicasted when the PaC knows the
IP address of the PAA.
4.1.3 Fragmentation
PANA does not provide fragmentation of PANA messages. Instead, it
relies on fragmentation provided by EAP methods and IP layer when
needed.
4.1.4 Sequence Number and Retransmission
PANA uses sequence numbers to provide ordered delivery of EAP
messages. The design involves use of two sequence numbers to prevent
some of the DoS attacks on the sequencing scheme. Every PANA packet
include one transmitted sequence number (tseq) and one received
sequence number (rseq) in the PANA header. See [1] for detailed
explanation on why two sequence numbers are needed.
The two sequence number fields have the same length of 32 bits and
appear in PANA header. tseq starts from initial sequence number
(ISN) and is monotonically increased by 1. The serial number
arithmetic defined in [RFC1982] is used for sequence number
operation. The ISNs are exchanged between PaC and PAA during the
discovery and initial handshake phase (see Section 4.2). The rules
that govern the sequence numbers in other phases are described as
follows.
o When a message is sent, a new sequence number is placed on the
tseq field of message regardless of whether it is sent as a result
of retransmission or not. When a message is sent, rseq is copied
from the tseq field of the last accepted message.
o When a message is received, it is considered valid in terms of
sequence numbers if and only if (i) its tseq is greater than the
tseq of the last accepted message and (ii) its rseq falls in the
range between the tseq of the last acknowledged message + 1 and
the tseq of the last transmitted message.
PANA relies on EAP-layer retransmissions, or for example NAS
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functionality [I-D.ietf-aaa-eap], for retransmitting EAP Requests
based on timer. Other PANA layer messages that require a response
from the communicating peer are retransmitted based on timer at
PANA-layer until a response is received (in which case the
retransmission timer is stopped) or the number of retransmission
reaches the maximum value (in which case the PANA session MUST be
deleted immediately). For PANA-layer retransmission, the
retransmission timer SHOULD be calculated as described in [RFC2988]
to provide congestion control. See Section 7 for default timer and
maximum retransmission count parameters.
4.1.5 PANA Security Association
A PANA SA is created as an attribute of a PANA session when EAP
authentication succeeds with a creation of a AAA-Key. A PANA SA is
not created when the PANA authentication fails or no AAA-Key is
produced by any EAP authentication method. In the case where two EAP
authentications are performed in sequence in a single PANA
authentication phase, it is possible that two AAA-Keys are derived.
If this happens, the PANA SA MUST be generated from both AAA-Keys.
When a new AAA-Key is derived as a result of EAP-based
re-authentication, any key derived from the old AAA-Key MUST be
updated to a new one that is derived from the new AAA-Key. In order
to distinguish the new AAA-Key from old ones, one Key-Id AVP MUST be
carried in PANA-Bind-Request and PANA-Bind-Answer messages or
PANA-FirstAuth-End-Request and PANA-FirstAuth-End-Answer messages at
the end of the EAP authentication which resulted in deriving a new
AAA-Key. The Key-Id AVP is of type Unsigned32 and MUST contain a
value that uniquely identifies the AAA-Key within the PANA session.
The PANA-Bind-Answer message (or the PANA-FirstAuth-End-Answer
message) sent in response to a PANA-Bind-Request message (or a
PANA-FirstAuth-End-Request message) with a Key-Id AVP MUST contain a
Key-Id AVP with the same AAA-Key identifier carried in the request.
PANA-Bind-Request, PANA-Bind-Answer, PANA-FirstAuth-End-Request and
PANA-FirstAuth-End-Answer messages with a Key-Id AVP MUST also carry
a MAC AVP whose value is computed by using the new PANA-MAC-Key
derived from the new AAA-Key (or the new pair of AAA-Keys when the
PANA_MAC_KEY is derived from two AAA-Keys). Although the
specification does not mandate a particular method for calculation of
Key-Id AVP value, a simple method is to use monotonically increasing
numbers."
The created PANA SA is deleted when the corresponding PANA session is
deleted. The lifetime of the PANA SA is the same as the lifetime of
the PANA session for simplicity.
PANA SA attributes as well as PANA session attributes are listed
below:
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PANA Session attributes:
* Session-Id
* Device-Id of PaC
* Device-Id of PAA
* List of device identifiers of EPs
* Initial tseq of PaC (ISN_pac)
* Initial tseq of PAA (ISN_paa)
* Last transmitted tseq value
* Last received rseq value
* Last transmitted message payload
* Retransmission interval
* Session lifetime
* Protection-Capability
* PANA SA attributes:
+ AAA-Key
+ AAA-Key Identifier
+ PANA_MAC_Key
The PANA_MAC_Key is used to integrity protect PANA messages. When
the PANA_MAC_Key is derived from a single AAA-Key, it is computed in
the following way:
PANA_MAC_KEY = The first N bits of
HMAC_SHA1(AAA-Key, ISN_pac | ISN_paa | Session-ID)
where the value of N depends on the integrity protection algorithm in
use, i.e., N=160 for HMAC-SHA1.
When the PANA_MAC_Key is derived from two AAA-Keys, it is computed in
the following way:
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PANA_MAC_KEY = The first N bits of
HMAC_SHA1(AAA-Key1 | AAA-Key2, ISN_pac | ISN_paa |
Session-ID)
where AAA-Key1 and AAA-Key2 are AAA-Keys for the first and second EAP
authentication in a single PANA authentication phase, respectively.
The length of AAA-Key, AAA-Key1 and AAA-Key2 MUST be N bits or
longer. See Section 4.1.6 for the detailed usage of the
PANA_MAC_Key.
4.1.6 Message Authentication Code
A PANA message can contain a MAC (Message Authentication Code) AVP
for cryptographically protecting the message.
When a MAC AVP is included in a PANA message, the value field of the
MAC AVP is calculated by using the PANA_MAC_Key in the following way:
MAC AVP value = PANA_MAC_PRF(PANA_MAC_Key, PANA_PDU)
where PANA_PDU is the PANA message including the PANA header, with
the MAC AVP value field first initialized to 0. PANA_MAC_PRF
represents the pseudo random function corresponding to the MAC
algorithm specified in the MAC AVP. In this version of draft,
PANA_MAC_PRF is HMAC-SHA1. The PaC and PAA MUST use the same
algorithm to calculate a MAC AVP they originate and receive. The
algorithm is determined by the PAA when a PANA-Bind-Request with a
MAC AVP is sent. When the PaC does not support the MAC algorithm
specified in the PANA-Bind-Request message, it MUST silently discard
the message. The PAA MUST NOT change the MAC algorithm throughout
the continuation of the PANA session.
4.1.7 Message Validity Check
When a PANA message is received, the message is considered to be
invalid at least when one of the following conditions are not met:
o The IP Hop Limit (or TTL) field has a value of 255, i.e., the
packet could not possibly have been forwarded by a router.
o Each field in the message header contains a valid value including
sequence number, message length, message type, version number,
flags, etc.
o When a device identifier of the communication peer is bound to the
PANA session, it matches the device identifier carried in MAC and/
or IP header(s), or other auxiliary indetifier provided by the
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lower-layers (e.g., circuit ID).
o The message type is one of the expected types in the current
state.
o The message payload contains a valid set of AVPs allowed for the
message type and there is no missing AVP that needs to be included
in the payload.
o Each AVP is decoded correctly.
o When a MAC AVP is included, the AVP value matches the MAC value
computed against the received message.
o When a Device-Id AVP is included, the AVP is valid if the device
identifier type contained in the AVP is supported (this check is
for both PaC and PAA) and is the requested one (this check is for
PAA only) and the device identifier value contained in the AVP
matches the value extracted from the lower-layer encapsulation
header corresponding to the device identifier type contained in
the AVP. Note that a Device-Id AVP carries the PaC's device
identifier in messages from PaC to PAA and PAA's device identifier
in messages from PAA to PaC.
Invalid messages MUST be discarded in order to provide robustness
against DoS attacks and an unprotected. In addition, a
non-acknowledged error notification message MAY be returned to the
sender. See Section 4.1.8 for details.
4.1.8 Error Handling
PANA-Error message MAY be sent by either PaC or PAA when a badly
formed PANA message is received or in case of other errors. If the
cause of this error message was a request message (e.g.,
PANA-PAA-Discover or *-Request), then the request MAY be
retransmitted immediately without waiting for its retransmission
timer to go off. If the cause of the error was a response message,
the receiver of the PANA-Error message SHOULD NOT resend the same
response until it receives the next request.
To defend against DoS attacks a timer MAY be used. One (1) error
notification is sent to each different sender each N seconds. N is a
configurable parameter.
When an error message is sent unprotected with MAC AVP and the
lower-layer is insecure, the error message is treated as an
informational message. The receiver of such an error message MUST
NOT change its state unless the error persists and the PANA session
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is not making any progress.
4.2 Discovery and Initial Handshake Phase
When a PaC attaches to a network, and knows that it has to discover
PAA for PANA, it SHOULD send a PANA-PAA-Discover message to a
well-known link local multicast address (TBD) and UDP port (TBD).
PANA PAA discovery assumes that PaC and PAA are one hop away from
each other. If PaC knows the IP address of the PAA (some
pre-configuration), it MAY unicast the PANA discovery message to that
address. PAA SHOULD answer to the PANA-PAA-Discover message with a
PANA-Start-Request message.
When the PAA receives such a request, or upon receiving some lower
layer indications of a new PaC, PAA SHOULD unicast a
PANA-Start-Request message.
There can be multiple PAAs on the link. The authentication and
authorization result does not depend on which PAA is chosen by the
PaC. By default the PaC MAY choose the PAA that sent the first
response.
PaC MAY also choose to start sending packets before getting
authenticated. In that case, the network MAY detect this and send an
unsolicited PANA-Start-Request message to PaC in addition to
filtering the unauthorized traffic. EP is the node that can detect
such activity. PAA-to-EP protocol MAY be used for this purpose.
A PANA-Start-Request message MAY carry a Cookie AVP that contains a
cookie. The rseq field of the header is set to zero (0). The tseq
field of the header contains the initial sequence number. The cookie
is used for preventing the PAA from resource consumption DoS attacks
by blind attackers. The cookie is computed in such a way that it does
not require any per-session state maintenance on the PAA in order to
verify the cookie returned in a PANA-Start-Answer message. The exact
algorithms and syntax used for generating cookies does not affect
interoperability and hence is not specified here. An example
algorithm is described below.
Cookie =
<secret-version> | HMAC_SHA1( <Device-Id of PaC> | <secret> )
where <secret> is a randomly generated secret known only to the PAA,
<secret-version> is an index used for choosing the secret for
generating the cookie and '|' indicates concatenation. The secret-
version should be changed frequently enough to prevent replay
attacks. The secret key is locally known to the PAA only and valid
for a certain time frame.
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Protection-Capability and Post-PANA-Address-Configuration AVPs MAY be
optionally included in the PANA-Start-Request in order to indicate
required and available capabilities for the network access. These
AVPs MAY be used by the PaC for assessing the capability match even
before the authentication takes place. But these AVPs are provided
during the insecure discovery phase, there are certain security risks
involved in using the provided information. See Section 9 for further
discussion on this.
PAA MAY enable NAP-ISP authentication separation by setting the
S-flag of the message header of the PANA-Start-Request. Also, the
PANA-Start-Request MAY contain zero or one NAP-Information AVP and
zero or more ISP-Information AVPs to advertise the information on the
NAP and/or ISPs.
When a PaC receives the PANA-Start-Request message in response to the
PANA-PAA-Discover message, it responds with a PANA-Start-Answer
message if it wishes to enter the authentication phase. The
PANA-Start-Answer message contains the initial sequence numbers in
the tseq and rseq fields of the PANA header, a copy of the received
Cookie (if any) as the PANA payload.
If the S-flag of the received PANA-Start-Request message is not set,
PaC MUST NOT set the S-flag in the PANA-Start-Answer message sent
back to the PAA. In this case, PaC MAY indicate its choice of ISP by
including an ISP-Information AVP in the PANA-Start-Answer message.
When a AAA backend is used, the identity of the destination AAA
server or realm MUST be determined based on the explicitly chosen
ISP. When the ISP-Information AVP is not present, the access network
MAY rely on the client identifier carried in the EAP authentication
method to make this determination.
If the S-flag of the received PANA-Start-Request message is set, PaC
can indicate its desire to perform separate EAP authentication for
NAP and ISP by setting the S-flag in the PANA-Start-Answer message.
If the S-flag in the PANA-Start-Answer message is not set, only one
authentication is performed and the processing occurs as described
earlier. If the S-flag in the PANA-Start-Answer message is set, the
determination of the destination AAA server or realm for ISP
authentication is performed as described earlier. In addition, where
backend AAA servers are used for NAP authentication, the NAP is
considered the ultimate AAA realm, and the destination AAA server for
this authentication is determined entirely by the local configuration
on the access server hosting PAA (NAS).
The PaC can choose an ISP and contain an ISP-Information AVP for the
chosen ISP in a PANA-Start-Answer message even when there is no
ISP-Information AVP contained in the PANA-Start-Request message.
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When the PAA receives the PANA-Start-Answer message from the PaC, it
verifies the cookie. The cookie is considered as valid if the
received cookie has the expected value. If the computed cookie is
valid, the protocol enters the authentication phase. Otherwise, it
MUST silently discard the received message.
Initial EAP Request MAY be optionally carried by the
PANA-Start-Request (as opposed to by a later PANA-Auth-Request)
message in order to reduce the number of round-trips. This
optimization SHOULD NOT be used if the PAA discovery is desired to be
stateless.
When the S-flag is set in a PANA-Start-Request message, the initial
EAP Request MUST NOT be carried in the PANA-Start-Request message.
(If the initial EAP Request were contained in the PANA-Start-Request
message during the S-flag negotiation, the PaC cannot tell whether
the EAP Request is for NAP authentication or ISP authentication.)
If the initial EAP Request message is carried in the
PANA-Start-Request message, an EAP Response message MUST be carried
in the PANA-Start-Answer message returned to the PAA.
In any case, PANA MUST NOT generate an EAP message on behalf of EAP
peer or EAP (pass-through) authenticator.
The PANA-Start-Request/Answer exchange is needed before entering
authentication phase even when the PaC is pre-configured with PAAs IP
address and the PANA-PAA-Discover message is unicast.
A PANA-Start-Request message that carries a Cookie AVP is never
retransmitted. A PANA-Start-Request message that does not carry a
Cookie AVP is retransmitted based on timer. A PANA-Start-Answer
message that carries a Cookie AVP is retransmitted based on timer. A
PANA-Start-Answer message that does not carry a Cookie AVP is never
retransmitted based on timer.
It is possible that both PAA and PaC initiate the discovery and
initial handshake procedure at the same time, i.e., the PAA sends a
PANA-Start-Request message while the PaC sends a PANA-PAA-Discover
message. To resolve the race condition, the PAA SHOULD silently
discard the PANA-PAA-Discover message received from the PaC after it
has sent a PANA-Start-Request message with creating a state (i.e., no
Cookie AVP included) for the PaC. In this case PAA will retransmit
PANA-Start-Request based on a timer, if PaC doesn't respond in time
(message was lost for example). If PAA had sent stateless
PANA-Start-Request message (i.e., a Cookie AVP was included), then it
SHOULD answer to the PANA-PAA-Discover message.
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PaC PAA Message
------------------------------------------------------
-----> PANA-PAA-Discover(0,0)
<----- PANA-Start-Request(x,0)[Cookie]
-----> PANA-Start-Answer(y,x)[Cookie]
(continued to authentication phase)
Figure 2: Example Sequence for Discovery and Initial Handshake Phase
when PANA-PAA-Discover is sent by PaC
PaC EP PAA Message
------------------------------------------------------
---->o (Data packet arrival or L2 trigger)
------> PAA-to-EP protocol, or another mechanism
<------------ PANA-Start-Request(x,0)[Cookie]
------------> PANA-Start-Answer(y,x)[Cookie]
(continued to authentication phase)
Figure 3: Example Sequence for Discovery and Initial Handshake when
discovery is triggered by data traffic
4.3 Authentication Phase
The main task in authentication phase is to carry EAP messages
between PaC and PAA. EAP Request messages are carried in PANA-
Auth-Request messages and optionally carried in PANA-Start-Request
messages. EAP Response messages are carried in PANA-Auth-Answer
messages and optionally carried in PANA-Start-Answer messages. When
an EAP Success/Failure message is sent from a PAA, the message is
carried in a PANA-Bind-Request (PBR) or PANA-FirstAuth-End-Request
(PFER) message. The PANA-FirstAuth-End-Reques message MUST be used
at the end of the first EAP when the PaC and PAA have negotiated
during the discovery and initial handshake phase to perform separate
NAP and ISP authentications in a single PANA authentication phase.
Otherwise, the PANA-Bind-Request message MUST be used. The
PANA-Bind-Request and PANA-FirstAuth-End-Request messages MUST be
acknowledged with a PANA-Bind-Answer (PBA) and a
PANA-FirstAuth-End-Answer (PFEA) messages, respectively.
When the PaC and PAA have negotiated during the discovery and initial
handshake phase to perform separate NAP and ISP authentications, the
S-flag of PANA-Auth-Request and PANA-Auth-Answer messages MUST be
set. Otherwise, the S-flag MUST NOT be set.
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When separate NAP and ISP authentications are performed, the PAA
determines the execution order of NAP authentication and ISP
authentication. In this case, the PAA can indicate which EAP
authentication is currently occurring by using N-flag in the PANA
message header. When NAP authentication is performed, the N-flag
MUST be set. When ISP authentication is performed, the N-flag MUST
NOT be set. The N-flag MUST NOT be set when S-flag is not set.
When separate NAP and ISP authentications are performed, if the first
EAP authentication has failed, the PAA can choose not to perform the
second EAP authentication by clearing the S-flag of the
PANA-FirstAuth-End-Request message. In this case, the S-flag of the
PANA-FirstAuth-End-Answer message sent by the PaC MUST be cleared.
If the S-flag of the PANA-FirstAuth-End-Request message is set when
the first EAP authentication has failed, the PaC can choose not to
perform the second EAP authentication by clearing the S-flag of the
PANA-FirstAuth-End-Answer message. If the first EAP authentication
failed and the S-flag is not set in the PANA-FirstAuth-End-Answer
message as a result of those operations, the PANA session MUST be
immediately deleted. Otherwise, the second EAP authentication MUST be
performed.
Currently, use of multiple EAP methods in PANA is designed only for
NAP-ISP authentication separation. It is not for arbitrary EAP
method sequencing, or giving the PaC another chance when an
authentication method fails. The NAP and ISP authentication are
considered completely independent. Presence or success of one should
not effect the other. Making a network access authorization decision
based on the success or failure of each authentication is a network
policy issue.
When an EAP method that is capable of deriving keys is used during
the authentication phase and the keys are successfully derived, the
PANA-FirstAuth-End-Request and PANA-FirstAuth-End-Answer and/or
PANA-Bind-Request and PANA-Bind-Answer messages, and all subsequent
PANA messages MUST contain a MAC AVP.
When separate NAP and ISP authentications are performed and the
lower-layer is insecure, the two EAP methods MUST be capable of
deriving keys. In this case, if the first EAP authentication is
successful, the PANA-FirstAuth-End-Request and
PANA-FirstAuth-End-Answer messages as well as PANA-Auth-Request and
PANA-Auth-Answer messages in the second EAP authentication MUST be
protected with the key derived from the AAA-Key for the first EAP
authentication. The PANA-Bind-Request and PANA-Bind-Answer messages
and all subsequent PANA messages MUST be protected either with the
AAA-Key for the first EAP authentication if the first EAP
authentication succeeds and the second EAP authentication fails, or
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with the AAA-Key for the second EAP authentication if the first EAP
authentication fails and the second EAP authentication succeeds, or
with the compound key derived from the two AAA-Keys, one for the
first EAP authentication and the other from the second EAP
authentication, if both the first and second EAP authentications
succeed (see Section 4.1.5 for how the compound key is derived).
The PANA-Bind-Request and the PANA-Bind-Answer message exchange is
also used for binding device identifiers of the PaC and the PAA to
the PANA SA when the identifiers are either IP or MAC addresses. To
achieve this, the PANA-Bind-Request and the PANA-Bind-Answer SHOULD
contain a device identifier of the PAA and the PaC, respectively, in
a Device-Id AVP. Device identifier exchange that is protected by a
MAC AVP prevents man-in-the-middle attacks. The PaC MUST use the
same type of device identifier as contained in the PANA-Bind-Request
message. The PANA-Bind-Request message MAY also contain a
Protection-Capability AVP to indicate if link-layer or network-layer
ciphering should be initiated after PANA. No link layer or network
layer specific information is included in the Protection-Capability
AVP. When the information is preconfigured on the PaC and the PAA
this AVP can be omitted. It is assumed that at least PAA is aware of
the security capabilities of the access network. The PANA protocol
does not specify how the PANA SA and the Protection-Capability AVP
will be used to provide per-packet protection for data traffic.
Additionally, PANA-Bind-Request MUST include a
Post-PANA-Address-Configuration AVP, which helps PAA to inform PaC
about whether a new IP address MUST be configured and the available
methods to do so. PaC MUST include a PPAC AVP in order to indicate
its choice of method when there is a match between the methods
offered by the PAA and the methods available on the PaC. When there
is no match, a PPAC AVP MUST NOT be included and the Result-Code AVP
MUST be set to PANA_PPAC_CAPABILITY_UNSUPPORTED in the
PANA-Bind-Answer message.
PANA-Bind-Request and PANA-Bind-Answer messages MUST be retransmitted
based on the retransmission rule described in Section 4.1.4.
EAP authentication can fail at a pass-through authenticator without
sending an EAP-Failure message [I-D.ietf-eap-statemachine]. When
this occurs, the PAA SHOULD send a PANA-Error message to the PaC with
using PANA_UNABLE_TO_COMPLY result code. The PaC SHOULD ignore the
message unless it is secured by PANA or lower layer. In any case, a
more appropriate way is to rely on a timeout on the PaC.
There is a case where EAP authentication succeeds with producing an
EAP-Success message but network access authorization fails due to,
e.g., authorization rejected by a AAA proxy or authorization locally
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rejected by a PAA. When this occurs, the PAA MUST send
PANA-Bind-Request with a result code PANA_AUTHORIZATION_REJECTED. If
a AAA-Key is established between PaC and PAA by the time when the
EAP-Success is generated by the EAP server (this is the case when the
EAP method provides protected success indication), the this PANA-Bind
message exchange MUST be protected with a MAC AVP and with carrying a
Key-Id AVP. The AAA-Key and the PANA session MUST be deleted after
the PANA-Bind message exchange.
PaC PAA Message(tseq,rseq)[AVPs]
-------------------------------------------------
(continued from discovery and initial handshake phase)
<----- PANA-Auth-Request(x+1,y)[EAP{Request}]
-----> PANA-Auth-Answer(y+1,x+1)[EAP{Response}]
.
.
<----- PANA-Auth-Request (x+2,y+1)[EAP{Request}]
-----> PANA-Auth-Answer (y+2,x+2)[EAP{Response}]
<----- PANA-Bind-Request(x+3,y+2)
[EAP{Success}, Device-Id, Lifetime, Protection-Cap.,
PPAC, MAC]
-----> PANA-Bind-Answer(y+3,x+3)[Device-Id, PPAC, MAC]
Figure 4: Example Sequence in Authentication Phase
4.4 Re-authentication
There are two types of re-authentication supported by PANA.
The first type of re-authentication is based on EAP by entering an
authentication phase. In this case, some or all message exchanges
for discovery and initial handshake phase MAY be omitted in the
following way. When a PaC wants to initiate EAP-based
re-authentication, it sends a unicast PANA-PAA-Discovery message to
the PAA. This message MUST contain a Session-Id AVP which is used
for identifying the PANA session on the PAA. If the PAA already has
an established PANA session for the PaC with the matching identifier,
it sends a PANA-Auth-Request message containing the same identifier
to start an authentication phase. If the PAA can not recognize the
session identifier, it proceeds with regular authentication by
sending back PANA-Start-Request. When the PAA initiates EAP-based
re-authentication, it sends a PANA-Auth-Request message containing
the session identifier for the PaC to enter an authentication phase.
PAA SHOULD initiate EAP authentication before the current session
lifetime expires. In both cases, the tseq and rseq values are
inherited from the previous (re-)authentication. For any EAP-based
re-authentication, if there is an established PANA SA,
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PANA-Auth-Request and PANA-Auth-Answer messages MUST be protected by
adding a MAC AVP to each message.
The second type of re-authentication is based on a single protected
message exchange without entering the authentication phase.
PANA-Reauth-Request and PANA-Reauth-Answer messages are used for this
purpose. If there is an established PANA SA, both the PaC and the
PAA are allowed to send a PANA-Reauth-Request message to the
communicating peer whenever it needs to make sure the availability of
the PANA SA on the peer and expect the peer to return a PANA-
Reauth-Answer message. Both PANA-Reauth-Request/ PANA-Reauth-Answer
messages MUST be protected with a MAC AVP.
Implementations MUST limit the rate of performing re-authentication
for both types of re-authentication. The PaC and the PAA can handle
rate limitation on their own, they don't have to perform any
coordination with each other. There is no negotiation of timers for
this purpose.
PaC PAA Message(tseq,rseq)[AVPs]
------------------------------------------------------
-----> PANA-Reauth-Request(q,p)[MAC]
<----- PANA-Reauth-Answer(p+1,q)[MAC]
Figure 5: Example Sequence for PaC-initiated second type
Re-authentication
PaC PAA Message(tseq,rseq)[AVPs]
------------------------------------------------------
<----- PANA-Reauth-Request(p,q)[MAC]
-----> PANA-Reauth-Answer(q+1,p)[MAC]
Figure 6: Example Sequence for PAA-initiated second type
Re-authentication
4.5 Termination Phase
A procedure for explicitly terminating a PANA session can be
initiated either from PaC (i.e., disconnect indication) or from PAA
(i.e., session revocation). The PANA-Termination-Request and the
PANA-Termination-Answer message exchanges are used for disconnect
indication and session revocation procedures.
The reason for termination is indicated in the Termination-Cause AVP.
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When there is an established PANA SA established between the PaC and
the PAA, all messages exchanged during the termination phase MUST be
protected with a MAC AVP. When the sender of the
PANA-Termination-Request receives a valid acknowledgment, all states
maintained for the PANA session MUST be deleted immediately.
PaC PAA Message(tseq,rseq)[AVPs]
------------------------------------------------------
-----> PANA-Termination-Request(q,p)[MAC]
<----- PANA-Termination-Answer(p+1,q)[MAC]
Figure 7: Example Sequence for Session Termination
4.6 Illustration of a Complete Message Sequence
A complete PANA message sequence is illustrated in Figure 8. The
example assumes the following scenario:
o PaC multicasts PANA-PAA-Discover message
o The ISNs used by the PAA and the PaC are x and y, respectively.
o A single EAP sequence is used in authentication phase.
o An EAP authentication method with a single round trip is used in
the EAP sequence.
o The EAP authentication method derives keys. The PANA SA is
established based on the unique and fresh session key provided by
the EAP method.
o After PANA SA is established, all messages are integrity and
replay protected with the MAC AVP.
o Re-authentication based on the PANA-Reauth-Request/ PANA-Reauth-
Answer exchange is performed.
o The PANA session is terminated as a result of the PANA-
Termination-Request indication from the PaC.
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PaC PAA Message(tseq,rseq)[AVPs]
-----------------------------------------------------
// Discovery and initial handshake phase
-----> PANA-PAA-Discover (0,0)
<----- PANA-Start-Request (x,0)[Cookie]
-----> PANA-Start-Request-Answer (y,x)[Cookie]
// Authentication phase
<----- PANA-Auth-Request(x+1,y)[EAP]
-----> PANA-Auth-Answer(y+1,x+1)[EAP]
<----- PANA-Auth-Request(x+2,y+1)[EAP]
-----> PANA-Auth-Answer(y+2,x+2)[EAP]
<----- PANA-Bind-Request(x+3,y+2)
[EAP{Success}, Device-Id, Lifetime, Protection-Cap., MAC]
-----> PANA-Bind-Answer(y+3,x+3)[Device-Id, MAC]
// Re-authentication
<----- PANA-Reauth-Request (x+4,y+3)[MAC]
-----> PANA-Reauth-Answer (y+4,x+4)[MAC]
// Termination phase
-----> PANA-Termination-Request(y+5,x+4)[MAC]
<----- PANA-Termination-Answer (x+5,y+5)[MAC]
Figure 8: A Complete Message Sequence
Another PANA message sequence is illustrated in Figure 9. The example
assumes the following scenario:
o PaC multicasts PANA-PAA-Discover message
o The ISNs used by the PAA and the PaC are x and y, respectively.
o PAA offers NAP and ISP separate authentication, as well as a
choice of ISP from "ISP1" and "ISP2". PaC accepts the offer from
PAA, with choosing "ISP1" as the ISP.
o An EAP sequence for NAP authentication and an EAP sequence for ISP
authentication is performed in this order in authentication phase.
o An EAP authentication method with a single round trip is used in
the EAP sequence.
o The EAP authentication methods derive keys. Once the two EAP
authenticatioins are successful, the PANA_MAC_KEY is derived from
the two AAA-Keys.
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o After PANA SA is established, all messages are integrity and
replay protected with the MAC AVP.
o Re-authentication based on the PANA-Reauth-Request/ PANA-Reauth-
Answer exchange is performed.
o Re-authentication and termination phase are not shown.
PaC PAA Message(tseq,rseq)[AVPs]
-----------------------------------------------------
// Discovery and initial handshake phase
-----> PANA-PAA-Discover (0,0)
<----- PANA-Start-Request (x,0) // S-flag set
[Cookie, ISP-Information("ISP1"),
ISP-Information("ISP2"),
NAP-Information("MyNAP")]
-----> PANA-Start-Request-Answer (y,x) // S-flag set
[Cookie, ISP-Information("ISP1")] // PaC chooses "ISP1"
// Authentication phase
<----- PANA-Auth-Request(x+1,y)[EAP] // NAP authentication
// S- and N-flags set
-----> PANA-Auth-Answer(y+1,x+1)[EAP] // S- and N-flags set
<----- PANA-Auth-Request(x+2,y+1)[EAP] // S- and N-flags set
-----> PANA-Auth-Answer(y+2,x+2)[EAP] // S- and N-flags set
<----- PANA-FirstAuth-End-Request(x+3,y+2) // S- and N-flags set
[EAP{Success}, Key-Id, MAC]
-----> PANA-FirstAuth-End-Answer(y+3,x+3) // S- and N-flags set
[Key-Id, MAC]
<----- PANA-Auth-Request(x+3,y+4)[EAP, MAC]// ISP authentication
// S-flag set
-----> PANA-Auth-Answer(y+4,x+4)[EAP, MAC] // S-flag set
<----- PANA-Auth-Request(x+4,y+5)[EAP, MAC]// S-flag set
-----> PANA-Auth-Answer(y+5,x+5)[EAP, MAC] // S-flag set
<----- PANA-Bind-Request(x+5,y+6) // S-flag set
[EAP{Success}, Device-Id, Key-Id,
Lifetime, Protection-Cap., PPAC, MAC]
-----> PANA-Bind-Answer(y+6,x+5) // S-flag set
[Device-Id, Key-Id, PPAC, MAC]
Figure 9: A Complete Message Sequence for NAP and ISP Separate
Authentications
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4.7 Device ID Choice
The device identifiers used in the context of PANA can be an IP
address, a MAC address, or an identifier that is not carried on data
packets but has local significance in identifying a connected host
(e.g., circuit ID). The last type of identifiers are commonly used
in physically secured point-to-point links where MAC addresses are
not available.
It is assumed that PAA knows the link type and the security
mechanisms being provided or required on the access network (e.g.,
based on physical security, link-layer ciphers enabled before or
after PANA, or IPsec). Based on that information, the PAA can decide
what type of device ID will be used when running PANA with the
client. When IPsec-based mechanism [I-D.ietf-pana-ipsec] is the
choice of access control, PAA SHOULD provide an IP address as device
ID, and expect the PaC to provide its IP address in return. In case
IPsec is not used, MAC addresses are used as device IDs when
available. If non-IPsec access control is enabled, and a MAC address
is not available, device ID exchange does not occur within PANA.
Instead, peers rely on lower-layers to provide locally-significant
identifiers along with received PANA packets.
4.8 Session Lifetime
The authentication phase determines the PANA session lifetime when
the network access authorization succeeds. The Session-Lifetime AVP
MAY be optionally included in the PANA-Bind-Request message to inform
PaC about the valid lifetime of the PANA session. It MUST be ignored
when included in other PANA messages. When there are multiple EAP
authentication taking place, this AVP SHOULD be included after the
final authentication.
The lifetime is a non-negotiable parameter that can be used by PaC to
manage PANA-related state. PaC does not have to perform any actions
when the lifetime expires, other than optionally purging local state.
PAA SHOULD initiate EAP authentication before the current session
lifetime expires.
PaC and PAA MAY optionally rely on lower-layer indications to
expedite the detection of a disconnected peer. Availability and
reliability of such indications depend on the specific access
technologies. PANA peer can use PANA-Reauth-Request message to
verify the disconnection before taking an action.
The session lifetime parameter is not related to the transmission of
PANA-Reauth-Request messages. These messages can be used for
asynchronously verifying the liveness of the peer and enabling
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mobility optimizations. The decision to send PANA-Reauth-Request
message is taken locally and does not require coordination between
the peers.
When separate EAP authentications are performed for ISP and NAP in a
single PANA session, it is possible that different authorization
lifetime values are associated with the two authentications. In this
case, the smaller authorization lifetime value MUST be used for
calculating the PANA Session-Lifetime value. As a result, when
EAP-based re-authentication occurs, both NAP and ISP authentications
will be performed in the same re-authentication procedure.
4.9 Mobility Handling
A mobile PaC's AAA performance can be enhanced by deploying a
context-transfer-based mechanism, where some session attributes are
transferred from the previous PAA to the current one in order to
avoid performing a full EAP authentication (reactive approach).
Additional mechanisms that are based on the proactive AAA state
establishment at one or more candidate PAAs may be developed in the
future [I-D.irtf-aaaarch-handoff]. The details of a
context-transfer-based mechanism is provided in this section.
Upon changing its point of attachment, a PaC that wants to quickly
resume its ongoing PANA session without running EAP MAY send its
unexpired PANA session identifier in its PANA-Start-Answer message.
Along with the Session-Id AVP, MAC and Nonce AVPs MUST be included in
this message. Nonce AVP carries a randomly chosen value (PaC_Nonce),
and MAC AVP is computed by using the PANA_MAC_Key shared between the
PaC and its previous PAA that has an unexpired PANA session with the
PaC. This action signals PaC's desire to perform the mobility
optimization. In the absence of Session-Id AVP in this message, PANA
session takes its usual course (i.e., EAP-based authentication is
performed).
If PAA receives a session identifier in the PANA-Start-Answer
message, and it is configured to enable this optimization, it SHOULD
retrieve the PANA session attributes from the previous PAA. Current
PAA determines the identity of the previous PAA by looking at the
DiameterIdentity part of the PANA session identifier. The MAC AVP
can only be verified by the previous PAA, therefore a copy of the
PANA message SHOULD be provided to the previous PAA. The mechanism
required to send a copy of the PANA-Start-Answer message from current
PAA to the previous PAA, and retrieve the session attributes is
outside the scope of PANA protocol. Seamoby Context Transfer
Protocol [I-D.ietf-seamoby-ctp] might be useful for this purpose.
When the previous or current PAA is not configured to enable this
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optimization, the current PAA can not retrieve the PANA session
attributes, or the PANA session has already expired (i.e., session
lifetime is zero), the PAA MUST send the PANA-Auth-Request message
with a new session identifier and let the PANA exchange take its
usual course. This action will engage EAP-based authentication and
create a fresh PANA session from scratch.
In case the current PAA can retrieve the on-going PANA session
attributes from the previous PAA, the PANA session continues with a
PANA-Bind exchange.
As part of the context transfer, an intermediate AAA-Key material is
provided by the previous PAA to the current PAA.
AAA-Key-int = The first N bits of
HMAC-SHA1(AAA-Key, DiameterIdentity | Session-ID)
In case there are two AAA-Keys generated from a NAP-ISP
authentication, the AAA-Key-int computation is:
AAA-Key-int = The first N bits of
HMAC-SHA1(AAA-Key1 | AAA-Key2, DiameterIdentity |
Session-ID)
The value of N depends on the integrity protection algorithm in use,
i.e., N=160 for HMAC-SHA1. DiameterIdentity is the identifier of the
current PAA. Session-ID is the identifier of the PaC's PANA session
with the previous PAA.
The current PAA and PaC compute the new AAA-Key by using the nonce
values and the AAA-Key-int. PAA_Nonce is the randomly chosen value
that MUST be carried in a Nonce AVP in the PANA-Bind-Request message.
AAA-Key-new = The first N bits of
HMAC-SHA1(AAA-Key-int, PaC_nonce | PAA_nonce)
New PANA_MAC_Key is computed based on the algorithm described in
Section 4.1.5, by using the new AAA-Key and the new Session-ID
assigned by the current PAA. The MAC AVP contained in the
PANA-Bind-Request and PANA-Bind-Answer messages MUST be generated and
verified by using the new PANA_MAC_Key. The Session-ID AVP MUST
include a new session identifier assigned by the current PAA. A new
PANA session is created upon successful completion of this exchange.
Note that correct operation of this optimization relies on many
factors, including applicability of authorization state from one
network attachment to another. [I-D.ietf-eap-keying] identifies this
operation as "fast handoff" and provides deployment considerations.
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Operators are recommended to take those guidelines into account when
using this optimization in their networks.
4.10 Support for Separate EP
PANA allows PAA and EP to be separate entities. In this case, if
data traffic protection needs to be initiated after successful PANA
authentication phase, PaC needs to know the device identifier of
EP(s) so that it is able to establish a security association with
each EP to protect data traffic.
To this end, when a Protection-Capability AVP with either
L2_PROTECTION or IPSEC_PROTECTION in the AVP payload is carried in a
PANA-Bind-Request message and if there is an EP that has a different
device identifier than that of the PAA, one or more EP-Device-Id AVPs
MUST also be carried in the PANA-Bind-Request message. In this case,
if one EP has the same device identifier as the PAA, an EP-Device-Id
AVP that contains the device identifier of the EP (i.e., the PAA)
MUST also be included in the PANA-Bind-Request.
Aside from provisioning EP, the same PAA-to-EP protocol MAY be used
for triggering the PAA upon detecting the need to authenticate a new
client.
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5. PANA Security Association Establishment
When PANA is used over an already established secure channel, such as
physically secured wires or ciphered link-layers, we can reasonably
assume that man-in-the-middle attack or service theft is not possible
[I-D.ietf-pana-threats-eval].
Anywhere else where there is no secure channel prior to PANA, the
protocol needs to protect itself against such attacks. The device
identifier that is used during the authentication needs to be
verified at the end of the authentication to prevent service theft
and DoS attacks. Additionally, a free loader should be prevented
from spoofing data packets by using the device identifier of an
already authorized legitimate client. Both of these requirements
necessitate generation of a security association between the PaC and
the PAA at the end of the authentication. This can only be done when
the authentication method used can generate cryptographic keys. Use
of secret keys can prevent attacks which would otherwise be very easy
to launch by eavesdropping on and spoofing traffic over an insecure
link.
PANA relies on EAP and the EAP methods to provide a session key in
order to establish a PANA security association. An example of such a
method is EAP-TLS [RFC2716], whereas EAP-MD5
[I-D.ietf-eap-rfc2284bis] is an example of a method that cannot
create such keying material. The choice of EAP method becomes
important, as discussed in the next section.
This keying material is already used within PANA during the final
handshake. This handshake ensures that the device identifier that is
bound to the PaC at the end of the authentication process is not
coming from a man-in-the-middle, but from the legitimate PaC.
Knowledge of the same keying material on both PaC and the PAA helps
prove this. The other use of the keying material is discussed in
[I-D.ietf-pana-framework].
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6. Message Formats
This section defines message formats for PANA protocol.
6.1 IP and UDP Headers
The Hop Limit (or TTL) field of the IP header MUST be set to 255.
When a PANA-PAA-Discover message is multicast, IP destination address
of the message is set to a well-known link-local multicast address
(TBD). A PANA-PAA-Discover message MAY be unicast in some cases as
specified in Section 4.2. Any other PANA packet is unicasted between
the PaC and the PAA. The source and destination addresses SHOULD be
set to the addresses on the interfaces from which the message will be
sent and received, respectively.
When the PANA packet is sent in response to a request, the UDP source
and destination ports of the response packet MUST be copied from the
destination and source ports of the request packet, respectively.
The destination port of an unsolicited PANA packet MUST be set to an
assigned value (TBD), and the source port MUST be set to a value
chosen by the sender.
6.2 PANA Header
A summary of the PANA header format is shown below. The fields are
transmitted in network byte order.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmitted Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Received Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVPs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
Version
This Version field MUST be set to 1 to indicate PANA Version 1.
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Message Length
The Message Length field is three octets and indicates the length
of the PANA message including the header fields.
Flags
The Flags field is eight bits. The following bits are assigned:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R r r r S N r r|
+-+-+-+-+-+-+-+-+
R(equest)
If set, the message is a request. If cleared, the message is
an answer.
S(eparate)
When the S-flag is set in a PANA-Start-Request message it
indicates that PAA is willing to offer separate EAP
authentications for NAP and ISP. When the S-flag is set in a
PANA-Start-Answer message it indicates that PaC accepts on
performing separate EAP authentications for NAP and ISP. When
the S-flag is set in a PANA-Auth-Request/Answer,
PANA-FirstAuth-End-Request/Answer and PANA-Bind-Request/Answer
messages it indicates that separate authentications are being
performed in the authentication phase.
N(AP authentication)
When the N-flag is set in a PANA-Auth-Request message, it
indicates that PAA is performing NAP authentication. When the
N-flag is unset in a PANA-Auth-Request message, it indicates
that PAA is performing ISP authentication. The N-flag MUST NOT
be set when S-flag is not set.
r(eserved)
these flag bits are reserved for future use, and MUST be set to
zero, and ignored by the receiver.
Message Type
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The Message Type field is three octets, and is used in order to
communicate the message type with the message. The 24-bit address
space is managed by IANA [ianaweb]. PANA uses its own address
space for this field.
Transmitted Sequence Number
The Transmitted Sequence Number field contains the monotonically
increasing 32 bit sequence number that the message sender
increments every time a new PANA message is sent.
Received Sequence Number
The Received Sequence Number field contains the 32 bit transmitted
sequence number that the message sender has last received from its
peer.
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 Header
Each AVP of type OctetString MUST be padded to align on a 32-bit
boundary, while other AVP types align naturally. A number of
zero-valued bytes are added to the end of the AVP Data field till a
word boundary is reached. The length of the padding is not reflected
in the AVP Length field [RFC3588].
The fields in the AVP header MUST be sent in network byte order. The
format of the header is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Flags | AVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Id (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
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AVP Code
The AVP Code, combined with the Vendor-Id field, identifies the
attribute uniquely. AVP numbers are allocated by IANA [ianaweb].
PANA uses its own address space for this field although some of
the AVP formats are borrowed from Diameter protocol [RFC3588].
AVP Flags
The AVP Flags field is eight bits. The following bits are
assigned:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V M r r r r r r|
+-+-+-+-+-+-+-+-+
M(andatory)
The 'M' Bit, known as the Mandatory bit, indicates whether
support of the AVP is required.
V(endor)
The 'V' bit, known as the Vendor-Specific bit, indicates
whether the optional Vendor-Id field is present in the AVP
header.
r(eserved)
these flag bits are reserved for future use, and MUST be set to
zero, and ignored by the receiver.
AVP Length
The AVP Length field is three octets, and indicates the number of
octets in this AVP including the AVP Code, AVP Length, AVP Flags,
and the AVP data
Vendor-Id
The Vendor-Id field is present if the 'V' bit is set in the AVP
Flags field. The optional four-octet Vendor-Id field contains the
uniquely assigned id value, encoded in network byte order. Any
vendor wishing to implement a vendor-specific PANA AVP MUST use
their own Vendor-Id along with their privately managed AVP address
space, guaranteeing that they will not collide with any other
vendor's vendor-specific AVP(s), nor with future IETF
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applications.
Data
The Data field is zero or more octets and contains information
specific to the Attribute. The format and length of the Data
field is determined by the AVP Code and AVP Length fields.
6.4 PANA Messages
Figure 10 lists all PANA messages defined in this document
Message Direction: PaC---PAA
----------------------------------------
PANA-PAA-Discover -------->
PANA-Start-Request <--------
PANA-Start-Answer -------->
PANA-Auth-Request <--------
PANA-Auth-Answer -------->
PANA-FirstAuth-End-Request <--------
PANA-FirstAuth-End-Answer -------->
PANA-Bind-Request <--------
PANA-Bind-Answer -------->
PANA-Reauth-Request <------->
PANA-Reauth-Answer <------->
PANA-Termination-Request <------->
PANA-Termination-Answer <------->
PANA-Error <------->
Figure 10: PANA Message Overview
6.4.1 Message Specifications
Every PANA message MUST include a corresponding ABNF [RFC2234]
specification found in [RFC3588]. Note that PANA messages have a
different header format compared to Diameter.
Example:
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message ::= < PANA-Header: <Message type>, [REQ] [SEP] >
* [ AVP ]
6.4.2 PANA-PAA-Discover (PDI)
The PANA-PAA-Discover (PDI) message is used to discover the address
of PAA(s). Both sequence numbers in this message are set to zero
(0).
PANA-PAA-Discover ::= < PANA-Header: 1 >
0*1 < Session-Id >
* [ AVP ]
6.4.3 PANA-Start-Request (PSR)
PANA-Start-Request (PSR) is sent by the PAA to the PaC. The PAA sets
the transmission sequence number to an initial random value. The
received sequence number is set to zero (0).
PANA-Start-Request ::= < PANA-Header: 2, REQ [SEP] >
[ Cookie ]
[ EAP-Payload ]
[ NAP-Information ]
* [ ISP-Information ]
[ Protection-Capability]
[ PPAC ]
* [ AVP ]
6.4.4 PANA-Start-Answer (PSA)
PANA-Start-Answer (PSA) is sent by the PaC to the PAA in response to
a PANA-Start-Request message. The PANA_start message transmission
sequence number field is copied to the received sequence number
field. The transmission sequence number is set to initial random
value.
PANA-Start-Answer ::= < PANA-Header: 2 [SEP] >
[ Session-Id ]
[ Cookie ]
[ Nonce ]
[ EAP-Payload ]
[ ISP-Information ]
* [ AVP ]
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6.4.5 PANA-Auth-Request (PAR)
PANA-Auth-Request (PAR) is sent by the PAA to the PaC.
PANA-Auth-Request ::= < PANA-Header: 3, REQ [SEP] [NAP] >
< Session-Id >
< EAP-Payload >
* [ AVP ]
0*1 < MAC >
(Both NAP-Information and ISP-Information MUST NOT be included at the
same time)
6.4.6 PANA-Auth-Answer (PAN)
PANA-Auth-Answer (PAN) is sent by the PaC to the PAA in response to a
PANA-Auth-Request message.
PANA-Auth-Answer ::= < PANA-Header: 3 [SEP] [NAP] >
< Session-Id >
< EAP-Payload >
* [ AVP ]
0*1 < MAC >
6.4.7 PANA-Bind-Request (PBR)
PANA-Bind-Request (PBR) is sent by the PAA to the PaC.
PANA-Bind-Request ::= < PANA-Header: 4, REQ [SEP] [NAP] >
< Session-Id >
{ Result-Code }
{ PPAC }
[ EAP-Payload ]
[ Device-Id ]
[ Session-Lifetime ]
[ Protection-Capability ]
[ Key-Id ]
[ Nonce ]
* [ EP-Device-Id ]
* [ AVP ]
0*1 < MAC >
6.4.8 PANA-Bind-Answer (PBA)
PANA-Bind-Answer (PBA) is sent by the PaC to the PAA in response to a
PANA-Result-Request message.
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PANA-Bind-Answer ::= < PANA-Header: 4 [,SEP] [NAP] >
< Session-Id >
{ Result-Code }
[ PPAC ]
[ Device-Id ]
[ Key-Id ]
* [ AVP ]
0*1 < MAC >
6.4.9 PANA-Reauth-Request (PRAR)
PANA-Reauth-Request (PRAR) is either sent by the PaC or the PAA.
PANA-Reauth-Request ::= < PANA-Header: 5, REQ >
< Session-Id >
[ Device-Id ]
* [ AVP ]
0*1 < MAC >
6.4.10 PANA-Reauth-Answer (PRAA)
PANA-Reauth-Answer (PRAA) is sent in response to a
PANA-Reauth-Request.
PANA-Reauth-Answer ::= < PANA-Header: 5 >
< Session-Id >
[ Device-Id ]
* [ AVP ]
0*1 < MAC >
6.4.11 PANA-Termination-Request (PTR)
PANA-Termination-Request (PTR) is sent either by the PaC or the PAA.
PANA-Termination-Request ::= < PANA-Header: 6, REQ >
< Session-Id >
< Termination-Cause >
* [ AVP ]
0*1 < MAC >
6.4.12 PANA-Termination-Answer (PTA)
PANA-Termination-Answer (PTA) is sent either by the PaC or the PAA in
response to PANA-Termination-Request.
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PANA-Termination-Answer ::= < PANA-Header: 6 >
< Session-Id >
* [ AVP ]
0*1 < MAC >
6.4.13 PANA-Error (PER)
PANA-Error is sent either by the PaC or the PAA.
PANA-Error ::= < PANA-Header: 7 >
< Session-Id >
< Result-Code >
{ Failed-AVP }
* [ AVP ]
0*1 < MAC >
6.4.14 PANA-FirstAuth-End-Request (PFER)
PANA-FirstAuth-End-Request (PFER) is sent by the PAA to the PaC.
PANA-FirstAuth-End-Request ::= < PANA-Header: 8, REQ [SEP] [NAP] >
< Session-Id >
< Device-Id >
{ EAP-Payload }
{ Result-Code }
[ Key-Id ]
* [ AVP ]
0*1 < MAC >
6.4.15 PANA-FirstAuth-End-Answer (PFEA)
PANA-FirstAuth-End-Answer (PFEA) is sent by the PaC to the PAA in
response to a PANA-FirstAuth-End-Request message.
PANA-FirstAuth-End-Answer ::= < PANA-Header: 8, REQ [SEP] [NAP] >
< Session-Id >
< Device-Id >
[ Key-Id ]
* [ AVP ]
0*1 < MAC >
6.5 AVPs in PANA
Some of the used AVPs are defined in this document and some of them
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are defined in other documents like [RFC3588]. PANA proposes to use
the same name space with [RFC3588]. For temporary allocation, PANA
uses AVP type numbers starting from 1024.
6.5.1 MAC AVP
The first octet (8 bits) of the MAC (Code 1024) AVP data contains the
MAC algorithm type. Rest of the AVP data payload contains the MAC
encoded in network byte order. The Algorithm 8 bit name space is
managed by IANA [ianaweb]. The AVP length varies depending on the
used algorithm.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm | MAC...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Algorithm
1 HMAC-SHA1 (20 bytes)
MAC
The Message Authentication Code is encoded in network byte order.
6.5.2 Device-Id AVP
The Device-Id AVP (Code 1025) is of Address type [RFC3588]. IPv4 and
IPv6 addresses are encoded as specified in [RFC3588]. The content
and format of data (including byte and bit ordering) for link-layer
addresses is expected to be specified in specific documents that
describe how IP operates over different link-layers. For instance,
[RFC2464]. Address families other than that are defined for
link-layer or IP addresses MUST NOT be used for this AVP.
6.5.3 Session-Id AVP
All messages pertaining to a specific PANA session MUST include a
Session-Id AVP (Code 1026) which carries a PAA-assigned fix value
throughout the lifetime of a session. When present, the Session-Id
SHOULD appear immediately following the PANA header.
The Session-Id MUST be globally and eternally unique, as it is meant
to identify a PANA Session without reference to any other
information, and may be needed to correlate historical authentication
information with accounting information. The PANA Session-Id AVP has
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the same format as the Diameter Session-Id AVP [RFC3588].
6.5.4 Cookie AVP
The Cookie AVP (Code 1027) is of type OctetString. The data is
opaque and the exact content is outside the scope of this protocol.
6.5.5 Protection-Capability AVP
The Protection-Capability AVP (Code 1028) is of type Unsigned32. The
AVP data indicates the cryptographic data protection capability
supported by the EPs. Below is a list of specified data protection
capabilities:
0 L2_PROTECTION
1 IPSEC_PROTECTION
6.5.6 Termination-Cause AVP
The Termination-Cause AVP (Code 1029) is of type of type Enumerated,
and is used to indicate the reason why a session was terminated on
the access device. The AVP data is used as a collection of flags The
following Termination-Cause AVP defined in [RFC3588] are used for
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, such as the receipt of a
Abort-Session-Request message.
SESSION_TIMEOUT 8 (PAA -> PaC)
The session has timed out, and service has been terminated.
6.5.7 Result-Code AVP
The Result-Code AVP (AVP Code 1030) is of type Unsigned32 and
indicates whether an EAP authentication was completed successfully or
whether an error occurred. Here are Result-Code AVP values taken from
[RFC3588] and adapted for PANA.
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6.5.7.1 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 that
corresponds to the one detected first is returned.
PANA_SUCCESS 2001
Both the authentication and authorization processes are
successful.
PANA_AUTHENTICATION_REJECTED 4001
The authentication process failed. When this error is returned,
the authorization process also fails.
PANA_AUTHORIZATION_REJECTED 5003
The authorization process failed. This error could occur when
authorization is rejected by a AAA proxy or rejected locally by a
PAA, even if the authentication procedure succeeds.
6.5.7.2 Protocol Error Result Codes
Protocol error result code values.
PANA_MESSAGE_UNSUPPORTED 3001
Error code from PAA to PaC or from PaC to PAA. Message type not
recognized or supported.
PANA_UNABLE_TO_DELIVER 3002
Error code from PAA to PaC. PAA was unable to deliver the EAP
payload to the authentication server.
PANA_INVALID_HDR_BITS 3008
Error code from PAA to PaC or from PaC to PAA. A message was
received whose bits in the PANA header were either set to an
invalid combination, or to a value that is inconsistent with the
message type's definition.
PANA_INVALID_AVP_BITS 3009
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Error code from PAA to PaC or from PaC to PAA. 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 5001
Error code from PAA to PaC or from PaC to PAA. 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_UNKNOWN_SESSION_ID 5002
Error code from PAA to PaC or from PaC to PAA. The message
contained an unknown Session-Id. PAA MUST NOT send this error
result code value to PaC if PaC sent an unknown Session-Id in the
PANA-Start-Answer message (session resumption).
PANA_INVALID_AVP_VALUE 5004
Error code from PAA to PaC or from PaC to PAA. 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 5005
Error code from PAA to PaC or from PaC to PAA. 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 5006
Error code from PAA to PaC. 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 and attempts to establish a second
session.
PANA_CONTRADICTING_AVPS 5007
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Error code from PAA to PaC. 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.
PANA_AVP_NOT_ALLOWED 5008
Error code from PAA to PaC or from PaC to PAA. 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 5009
Error code from PAA to PaC or from PaC to PAA. 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 5011
Error code from PAA to PaC or from PaC to PAA. This error is
returned when a message was received, whose version number is
unsupported.
PANA_UNABLE_TO_COMPLY 5012
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
PANA-Error message.
PANA_INVALID_AVP_LENGTH 5014
Error code from PAA to PaC or from PaC to PAA. The message
contained an AVP with an invalid length. The PANA-Error message
indicating this error MUST include the offending AVPs within a
Failed-AVP AVP.
PANA_INVALID_MESSAGE_LENGTH 5015
Error code from PAA to PaC or from PaC to PAA. This error is
returned when a message is received with an invalid message
length.
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PANA_PROTECTION_CAPABILITY_UNSUPPORTED 5016
Error code from PaC to PAA. This error is returned when the PaC
receives a PANA-Bind-Request is received with an
Protection-Capability AVP and a valid MAC AVP but does not support
the protection capability specified in the Protection-Capability
AVP.
PANA_PPAC_CAPABILITY_UNSUPPORTED 5017
Error code from PaC to PAA. This error is returned in a
PANA-Bind-Answer message when there is no match between the list
of PPAC methods offered by the PAA and the ones available on the
PaC.
6.5.8 EAP-Payload AVP
The EAP-Payload AVP (AVP Code 1031) is of type OctetString and is
used to encapsulate the actual EAP packet that is being exchanged
between the EAP peer and the EAP authenticator.
6.5.9 Session-Lifetime AVP
The Session-Lifetime AVP (Code 1032) data is of type Unsigned32. It
contains the number of seconds remaining before the current session
is considered expired.
6.5.10 Failed-AVP AVP
The Failed-AVP AVP (AVP Code 1033) is of type Grouped and provides
debugging information in cases where a request is rejected or not
fully processed due to erroneous information in a specific AVP. The
format of the Failed-AVP AVP is defined in [RFC3588].
6.5.11 NAP-Information AVP
The NAP-Information AVP (AVP Code: 1034) is of type Grouped, and
contains zero or one Provider-Identifier AVP which carries the
identifier of the NAP and one Provider-Name AVP which carries the
name of the NAP. Its Data field has the following ABNF grammar:
NAP-Information ::= < AVP Header: 1034 >
0*1 { Provider-Identifier }
{ Provider-Name }
* [ AVP ]
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6.5.12 ISP-Information AVP
The ISP-Information AVP (AVP Code: 1035) is of type Grouped, and
contains zero or one Provider-Identifier AVP which carries the
identifier of the ISP and one Provider-Name AVP which carries the
name of the ISP. Its Data field has the following ABNF grammar:
ISP-Information ::= < AVP Header: 1035 >
0*1 { Provider-Identifier }
{ Provider-Name }
* [ AVP ]
6.5.13 Provider-Identifier AVP
The Provider-Identifier AVP (AVP Code: 1036) is of type Unsigned32,
and contains an IANA assigned "SMI Network Management Private
Enterprise Codes" [ianaweb] value, encoded in network byte order.
6.5.14 Provider-Name AVP
The Provider-Name AVP (AVP Code: 1037) is of type UTF8String, and
contains the UTF8-encoded name of the provider.
6.5.15 EP-Device-Id AVP
The EP-Device-Id AVP (AVP Code: 1038) contains the device identifier
of an EP. The payload format of the EP-Device-Id AVP is the same as
that of the Device-Id AVP (see See section Section 6.5.2).
6.5.16 Key-Id AVP
The Key-Id AVP (AVP Code: 1039) is of type Integer32, and contains an
AAA-Key identifier. The AAA-Key identifier is assigned by PAA and
MUST be unique within the PANA session.
6.5.17 Post-PANA-Address-Configuration (PPAC) AVP
The data field of PPAC AVP (Code 1040) is of type Unsigned32. The
AVP data is used to carry a set of flags which maps to various IP
address configuration methods. When sent by the PAA, the AVP MUST
have at least one of the flags set, and MAY have more than one set.
When sent by the PaC, only one of the flags MUST be set.
The format of the AVP data is as follows:
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|D|A|T|I| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PPAC Flags
N (No configuration)
The PaC does not have to (if sent by PAA) or will not (if sent
by PaC) configure a new IP address after PANA.
D (DHCP)
The PaC can (if sent by PAA) or will (if sent by PaC) use DHCP
[RFC2131][RFC3315] to configure a new IP address after PANA.
A (stateless autoconfiguration)
The PaC can/will use stateless IPv6 address autoconfiguration
[RFC2462] to configure a new IP address after PANA.
T (DHCP with IPsec tunnel mode)
The PaC can/will use [RFC3456] to configure a new IP address
after PANA.
I (IKEv2)
The PaC can/will use [I-D.ietf-ipsec-ikev2] to configure a new
IP address after PANA.
Reserved
These flag bits are reserved for future use, and MUST be set to
zero, and ignored by the receiver.
Unless the N-flag is set, the PaC MUST configure a new IP address
using one of the methods indicated by the other flags. Refer to
[I-D.ietf-pana-framework] for a detailed discussion on when these
methods can be used.
6.5.18 Nonce AVP
The Nonce AVP (Code 1041) is of type OctetString. The data contains
a randomly generated value in opaque format. The data length MUST be
between 8 and 256 bytes inclusive.
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6.6 AVP Occurrence Table
The following tables lists the AVPs used in this document, and
specifies in which PANA messages they MAY, or MAY NOT be present.
The table uses the following symbols:
0 The AVP MUST NOT be present in the message.
0+ Zero or more instances of the AVP MAY be present in the
message.
0-1 Zero or one instance of the AVP MAY be present in the message.
It is considered an error if there are more than one instance
of the AVP.
1 One instance of the AVP MUST be present in the message.
1+ At least one instance of the AVP MUST be present in the
message.
+-----------------------------------------+
| Message |
| Type |
+-----+-----+-----+-----+-----+-----+-----+
Attribute Name | PSR | PSA | PAR | PAN | PBR | PBA | PDI |
--------------------+-----+-----+-----+-----+-----+-----+-----+
Result-Code | 0 | 0 | 0 | 0 | 1 | 1 | 0 |
Session-Id | 0 | 0-1 | 1 | 1 | 1 | 1 | 0-1 |
Termination-Cause | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
EAP-Payload | 0-1 | 0-1 | 1 | 1 | 0-1 | 0 | 0 |
MAC | 0 | 0-1 | 0-1 | 0-1 | 0-1 | 0-1 | 0 |
Nonce | 0 | 0-1 | 0 | 0 | 0-1 | 0 | 0 |
Device-Id | 0 | 0 | 0 | 0 | 0-1 | 0-1 | 0 |
Cookie | 0-1 | 0-1 | 0 | 0 | 0 | 0 | 0 |
Protection-Cap. | 0-1 | 0 | 0 | 0 | 0-1 | 0 | 0 |
PPAC | 0-1 | 0 | 0 | 0 | 1 | 0-1 | 0 |
Session-Lifetime | 0 | 0 | 0 | 0 | 0-1 | 0 | 0 |
Failed-AVP | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
ISP-Information | 0+ | 0-1 | 0 | 0 | 0 | 0 | 0 |
NAP-Information | 0-1 | 0 | 0 | 0 | 0 | 0 | 0 |
EP-Device-Id | 0 | 0 | 0 | 0 | 0+ | 0 | 0 |
Key-Id | 0 | 0 | 0 | 0 | 0-1 | 0-1 | 0 |
--------------------+-----+-----+-----+-----+-----+-----+-----+
Figure 11: AVP Occurrence Table (1/2)
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+---------------------------------------------+
| Message |
| Type |
+------+------+-----+-----+-----+------+------+
Attribute Name | PRAR | PRAA | PTR | PTA | PER | PFER | PFEA |
--------------------+------+------+-----+-----+-----+------+------+
Result-Code | 0 | 0 | 0 | 0 | 1 | 1 | 0 |
Session-Id | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
Termination-Cause | 0 | 0 | 1 | 0 | 0 | 0 | 0 |
EAP-Payload | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
MAC | 0-1 | 0-1 | 0-1 | 0-1 | 0-1 | 0-1 | 0-1 |
Nonce | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Device-Id | 0-1 | 0-1 | 0 | 0 | 0 | 0 | 0 |
Cookie | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Protection-Cap. | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
PPAC | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Session-Lifetime | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Failed-AVP | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
ISP-Information | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
NAP-Information | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
EP-Device-Id | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Key-Id | 0 | 0 | 0 | 0 | 0 | 0-1 | 0-1 |
--------------------+------+------+-----+-----+-----+------+------+
Figure 12: AVP Occurrence Table (2/2)
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7. PANA Protocol Message Retransmissions
The PANA protocol provides retransmissions for all the message
exchanges except PANA-Auth-Request/Answer. PANA-Auth-Request
messages carry EAP requests which are retransmitted by the EAP
protocol entities when needed. The messages that need PANA-level
retransmissions are listed below:
PANA-PAA-Discover (PDI)
PANA-Start-Request (PSR)*
PANA-Start-Answer (PSA)**
PANA-Bind-Request (PBR)
PANA-FirstAuth-End-Request (PFER)
PANA-Reauth-Request (PRAR)
PANA-Termination-Request (PTR)
*) PSR that carries a Cookie AVP is not retransmitted.
**) PSA that does not carry a Cookie AVP is not retransmitted.
The PDI and PSA messages are always sent by the PaC. PBR is sent by
PAA. The last two messages, PRAR and PTR are sent either by PaC or
PAA.
The rule is that the sender of the request message retransmits the
request if the corresponding answer is not received in time. Answer
messages are sent as answers to the request messages, not based on a
timer. Exception to this rule is the PSA message. Because of the
stateless nature of the PAA in the beginning PaC provides
retransmission also for the PSA message. PANA-Error messages MUST
not be retransmitted. See Section 4.1.8 for more details of PANA
error handling.
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 either the request sender
successfully receives the appropriate answer, 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
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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:
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.
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If both MRC and MRD are zero, the client continues to transmit the
message until it receives a response.
7.1 Transmission and Retransmission Parameters
This section presents a table of values used to describe the message
retransmission behavior of request and PANA-Start-Answer messages
marked with REQ_*. PANA-PAA-Discover message retransmission values
are marked with PDI_*. The table shows default values.
Parameter Default Description
------------------------------------------------
PDI_IRT 1 sec Initial PDI timeout.
PDI_MRT 120 secs Max PDI timeout value.
PDI_MRC 0 Configurable.
PDI_MRD 0 Configurable.
REQ_IRT 1 sec Initial Request timeout.
REQ_MRT 30 secs Max Request timeout value.
REQ_MRC 10 Max Request retry attempts.
REQ_MRD 0 Configurable.
So for example the first RT for the PBR message is calculated using
REQ_IRT as the IRT:
RT = REQ_IRT + RAND*REQ_IRT
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8. IANA Considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the
Diameter 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.
8.1 PANA UDP Port Number
TBD.
8.2 PANA Multicast Address
TBD.
8.3 PANA Header
8.3.1 Message Type
TBD.
8.3.2 Flags
TBD.
8.4 AVP Header
8.4.1 AVP Code
TBD.
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8.4.2 Flags
TBD.
8.4.3 Vendor Id
TBD.
8.5 AVP Values
8.5.1 MAC AVP Values
TBD.
8.5.2 Device-Id AVP Values
TBD.
8.5.3 Protection-Capability AVP Values
TBD.
8.5.4 Result-Code AVP Values
TBD.
8.5.5 Termination-Cause AVP Values
TBD.
8.5.6 Provider-Identifier AVP Values
TBD.
8.5.7 Post-PANA-Address-Configuration AVP Values
TBD.
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9. Security Considerations
The PANA protocol provides ordered delivery for EAP messages. If an
EAP method that provides session keys is used, a PANA SA is created.
The EAP Success/Failure message is one of the signaling messages
which is integrity protected with this PANA SA. The PANA protocol
does not provide security protection for the initial EAP message
exchange. Integrity protection can only be provided after the PANA
SA has been established. Thus, PANA re-authentication, revocation and
disconnect notifications can be authenticated, integrity and replay
protected. In certain environments (e.g., on a shared link) the EAP
method selection is an important issue.
The PANA framework described in this document covers the discussion
of different protocols which are of interest for a protocol between
the PaC and the PAA (typically referred as the PANA protocol).
The PANA itself consists of a sequence of steps which are executed to
complete the network access authentication procedure. Some of these
steps are optional.
The following execution steps have been identified as being relevant
for PANA. They security considerations will be discussed in detail
subsequently.
a) Discovery message exchange
In general it is difficult to prevent a vulnerabilities of the
discovery protocol since the initial discovery are unsecured. To
prevent very basic attacks an adversary should not be able to cause
state creation with discovery messages at the PAA. This is prevented
by re-using a cookie concept (see [RFC2522] which allows the
responder to be stateless in the first message exchange. Because of
the architectural assumptions made in PANA (i.e., the PAA is the on
the same link as the PaC) the return-routability concept does not
provide additional protection. Hence it is difficult to prevent this
threat entirely. Furthermore it is not possible to shift heavy
cryptographic operations to the PaC at the first few messages since
the computational effort depends on the EAP method. The usage of
client-puzzles as introduced by [jb99] is under investigation.
Resistance against blind DoS attacks (i.e., attacks by off-path
adversaries) is achieved with sequence numbers and cookies.
Since PAA and PaC are supposed to be one IP hop away, a simple TTL
check can prevent off-link attacks. Furthermore, additional
filtering can be enabled on the EPs. An EP may be able to filter
unauthorized PAA advertisements when they are received on the access
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side of the network where only PaCs are connected.
In networks where lower-layers are not secured prior to running PANA,
the capability discovery enabled through inclusion of
Protection-Capability and Post-PANA-Address-Configuration AVPs in
PANA-Start-Request message is susceptible to spoofing. Therefore,
usage of these AVPs during the discovery phase in such insecure
networks is NOT RECOMMENDED. The same AVPs are delivered via an
integrity-protected PANA-Bind-Request upon successful authentication.
b) EAP over PANA message exchange
The EAP derived session key is used to create a PANA security
association. Since the execution of an EAP method might require a
large number of roundtrips and no other session key is available it
is not possible to secure the EAP message exchange itself. Hence an
adversary can both eavesdrop the EAP messages and is also able to
inject arbitrary messages which might confuse both the EAP peer on
PaC and the EAP authenticator or authentication server on the PAA.
The threats caused by this ability heavily depend on the EAP state
machine. Since especially the PAA is not allowed to discard packets
and packets have to be stored or forwarded to an AAA infrastructure
some risk of DoS attacks exists.
Eavesdropping EAP packets might cause problems when (a) the EAP
method is weak and enables dictionary or replay attacks or even
allows an adversary to learn the long-term password directly.
Furthermore, if the optional EAP Identity payload is used then it
allows the adversary to learn the identity of the PaC. In such a
case a privacy problem is prevalent.
To prevent these threats, [I-D.ietf-pana-framework] suggests using
proper EAP methods for particular environments. Depending on the
usage environment an EAP authentication has to be used for example
which supports user identity confidentiality, protection against
dictionary attacks and session key establishment. It is therefore
the responsibility of the network operators and end users to choose
the proper EAP method.
PANA does not protect the EAP method exchange, but provides ordered
delivery with sequence numbers. Sequence numbers and cookies provide
resistance against blind DoS attacks.
c) PANA SA establishment
Once the EAP message authentication is finished a fresh and unique
session key is available to the PaC and the PAA. This assumes that
the EAP method allows session key derivation and that the generated
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session key has a good quality. For further discussion about the
importance of the session key generation refer to the next subsection
(d) about compound authentication. The session key available for the
PaC is established as part of the authentication and key exchange
procedure of the selected EAP method. The PAA obtains the session
key via the AAA infrastructure (if used). Security issues raised
with this session key transport are described in
[I-D.ietf-eap-keying].
The establishment of a PANA SA is required in environments where no
physical or link layer security is available. The PANA SA allows
subsequently exchanged messages to experience cryptographic
protection. For the current version of the document an integrity
object (MAC AVP) is defined which supports data-origin
authentication, replay protection based on sequence numbers and
integrity protection based on a keyed message digest.
Confidentiality protection is not provided. The session keys used for
this object have to be provided by the EAP method. For this version
of the document it is assumed that no negotiation of algorithms and
parameters takes place. Instead HMAC-SHA1 is used by default. A
different algorithm may be chosen by default in a future version of
the PANA protocol specification. The used algorithm is indicated in
the header of the Integrity object. To select the security
association for signaling message protection the Session ID is
conveyed. The keyed message digest included in the Integrity object
will include all fields of the PANA signaling message including the
sequence number field of the packet.
The protection of subsequent signaling messages prevents an adversary
from acting as a man-in-the-middle adversary, from injecting packets,
from replaying messages and from modifying the content of the
exchanged packets. This prevents subsequently described threats.
If an entity (PAA or PaC) loses its state (especially the current
sequence number) then the entire PANA protocol has to be restarted.
No re-synchronization procedure is provided.
The lifetime of the PANA SA has to be bound to the AAA-authorized
session lifetime with an additional tolerance period. Unless PANA
state is updated by executing another EAP authentication, PANA SA is
removed when the current session expires. The lifetime of the PANA
SA has to be bound to the AAA-authorized session lifetime with an
additional tolerance period. Unless PANA state is updated by
executing another EAP authentication, PANA SA is removed when the
current session expires.
d) Enabling weak legacy authentication methods in insecure networks
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Some of the authentication methods are not strong enough to be used
in insecure networks where attackers can easily eavesdrop and spoof
on the link. They may not be able to produce much needed keying
material either. An example would be using EAP-MD5 over wireless
links. Use of such legacy methods can be enabled by carrying them
over a secure channel. There are EAP methods which are specifically
designed for this purpose, such as EAP-TTLS
[I-D.ietf-pppext-eap-ttls],PEAP [I-D.josefsson-pppext-eap-tls-eap] or
EAP-IKEv2 [I-D.tschofenig-eap-ikev2]. PANA can carry these EAP
tunneling methods which can carry the legacy methods. PANA does not
do anything special for this case. The EAP tunneling method will
have to produce keying material for PANA SA when needed. There are
certain MitM vulnerabilities with tunneling EAP methods [mitm].
Solving these problems is outside the scope of PANA. The compound
authentication problem described in [I-D.puthenkulam-eap-binding] is
likely to be solved in EAP itself rather than in PANA.
e) Device Identifier exchange
As part of the authorization procedure a Device Identifier has to be
installed at the EP by the PAA. The PaC provides the Device
Identifier information to the PAA secured with the PANA SA. Section
6.2.4 of [I-D.ietf-pana-threats-eval] describes a threat where an
adversary modifies the Device Identifier to gain unauthorized access
to the network.
The installation of the Device Identifier at the EP (independently
whether the EP is co-located with the PAA or not) has to be
accomplished in a secure manner. These threats are, however, not
part of the PANA protocol itself since the protocol is not PANA
specific.
f) Triggering a data protection protocol
Recent activities in the EAP working group try to create a common
framework for key derivation which is described in
[I-D.ietf-eap-keying]. This framework is also relevant for PANA in
various ways. First, a PANA security association needs to be
created. Additionally it might be necessary to trigger a protocol
which allows link layer and network layer data protection to be
established. As an example see Section 1 of [I-D.ietf-eap-keying]
with [802.11i] and [802.11] as an example. Furthermore, a derived
session key might help to create the pre-requisites for network-layer
protection (for example IPsec [I-D.ietf-pana-ipsec]).
As motivated in Section 6.4 of [I-D.ietf-pana-threats-eval] it might
be necessary to establish either a link layer or a network layer
protection to prevent certain thefts in certain scenarios.
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Threats specific to the establishment of a link layer or a network
layer security association are outside the scope of PANA. The
interested reader should refer to the relevant working groups such as
IPsec or Midcom.
g) Liveness test
Network access authentication is done for a very specific purpose and
often charging procedures are involved which allow restricting
network resource usage based on some policies. In mobile
environments it is always possible that an end host suddenly
disconnects without transmitting a disconnect message. Operators are
generally motivated to detect a disconnected end host as soon as
possible in order to release resources (i.e., garbage collection).
The PAA can remove per-session state information including installed
security association, packet filters, etc.
Different procedures can be used for disconnect indication. PANA
cannot assume link-layer disconnect indication. Hence this
functionality has to be provided at a higher layer. With this
version of the draft we suggest to apply the soft-state principle
found at other protocols (such as RSVP). Soft-state means that
session state is kept alive as long as refresh messages refresh the
state. If no new refresh messages are provided then the state
automatically times out and resources are released. This process
includes stopping accounting procedures.
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 lifetime expires. A
disconnect may also be detected earlier by using PANA
reauthentication 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 discontinuation of data traffic). 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 PANA SA is available in order to
prevent threats associated with the abuse of this functionality.
h) Tear-Down message
The PANA protocol supports the ability for both the PaC and the PAA
to transmit a tear-down message. This message causes state removal,
a stop of the accounting procedure and removes the installed packet
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filters.
It is obvious that such a message must be protected to prevent an
adversary from deleting state information and thereby causing denial
of service attacks.
i) Mobility optimization
The mobility optimization described in Section 4.9 involves the
previous PAA providing a AAA-Key to the current PAA of the PaC.
There are security risks stemming from potential compromise of PAAs.
Compromise of the current PAA does not yield compromise of the
previous PAA, as AAA-Key cannot be computed from a compromised
AAA-Key-new. But a compromised previous PAA along with the
intercepted nonce values leads to the compromise of AAA-Key-new.
Operators should be aware of the potential risk of using this
optimization. An operator can reduce the risk exposure by forcing
the PaC to perform an EAP-based authentication immediately after the
optimized PANA execution.
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10. Open Issues and Change History
A list of open issues is maintained at [2].
Issues incorporated in PANA-01 June 2003: 1, 3, 10, 5, 6, 7 and 11.
Issues incorporated in PANA-02 October 2003: 8, 17, 18, 19, 20, 21,
22, 23, 24, 25, 26, 30, 31, 32 and 33.
Issues incorporated in PANA-03 February 2004: 2, 16, 34, 35, 36, 38,
39, 40, 42, 43, 44, 50, 51 and 60.
Issues incorporated in PANA-04 May 2004: 28, 52, 53, 56, 57, 58, 59,
61, 62, 63, 64, 65, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80 and 83.
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11. Acknowledgments
We would like to thank Jari Arkko, Mohan Parthasarathy, Julien
Bournelle, Rafael Marin Lopez and all members of the PANA working
group for their valuable comments to this document.
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Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
August 1996.
[RFC2988] Paxson, V. and M. Allman, "Computing TCP's Retransmission
Timer", RFC 2988, November 2000.
[I-D.ietf-eap-rfc2284bis]
Blunk, L., "Extensible Authentication Protocol (EAP)",
draft-ietf-eap-rfc2284bis-09 (work in progress), February
2004.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[RFC2234] Crocker, D. 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.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998.
[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.
[RFC3456] Patel, B., Aboba, B., Kelly, S. and V. Gupta, "Dynamic
Host Configuration Protocol (DHCPv4) Configuration of
IPsec Tunnel Mode", RFC 3456, January 2003.
[I-D.ietf-eap-keying]
Aboba, B., "EAP Key Management Framework",
draft-ietf-eap-keying-01 (work in progress), October 2003.
[IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
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October 1998.
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Informative References
[I-D.ietf-pana-requirements]
Yegin, A. and Y. Ohba, "Protocol for Carrying
Authentication for Network Access (PANA)Requirements",
draft-ietf-pana-requirements-07 (work in progress), June
2003.
[I-D.ietf-aaa-eap]
Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application",
draft-ietf-aaa-eap-05 (work in progress), April 2004.
[I-D.puthenkulam-eap-binding]
Puthenkulam, J., "The Compound Authentication Binding
Problem", draft-puthenkulam-eap-binding-04 (work in
progress), October 2003.
[RFC2522] Karn, P. and W. Simpson, "Photuris: Session-Key Management
Protocol", RFC 2522, March 1999.
[I-D.ietf-pana-usage-scenarios]
Ohba, Y., "Problem Statement and Usage Scenarios for
PANA", draft-ietf-pana-usage-scenarios-06 (work in
progress), April 2003.
[I-D.ietf-pana-threats-eval]
Parthasarathy, M., "PANA Threat Analysis and security
requirements", draft-ietf-pana-threats-eval-04 (work in
progress), May 2003.
[I-D.ietf-pana-ipsec]
Parthasarathy, M., "PANA enabling IPsec based Access
Control", draft-ietf-pana-ipsec-03 (work in progress), May
2004.
[I-D.ietf-pana-framework]
Jayaraman, P., "PANA Framework",
draft-ietf-pana-framework-00 (work in progress), May 2004.
[I-D.ietf-pana-snmp]
Mghazli, Y., Ohba, Y. and J. Bournelle, "SNMP usage for
PAA-2-EP interface", draft-ietf-pana-snmp-00 (work in
progress), April 2004.
[I-D.irtf-aaaarch-handoff]
Arbaugh, W. and B. Aboba, "Experimental Handoff Extension
to RADIUS", draft-irtf-aaaarch-handoff-04 (work in
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progress), November 2003.
[I-D.ietf-eap-statemachine]
Vollbrecht, J., Eronen, P., Petroni, N. and Y. Ohba,
"State Machines for Extensible Authentication Protocol
(EAP) Peer and Authenticator",
draft-ietf-eap-statemachine-03 (work in progress), March
2004.
[I-D.ietf-seamoby-ctp]
Loughney, J., "Context Transfer Protocol",
draft-ietf-seamoby-ctp-08 (work in progress), January
2004.
[I-D.ietf-ipsec-ikev2]
Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-13 (work in progress), March 2004.
[I-D.josefsson-pppext-eap-tls-eap]
Josefsson, S., Palekar, A., Simon, D. and G. Zorn,
"Protected EAP Protocol (PEAP)",
draft-josefsson-pppext-eap-tls-eap-07 (work in progress),
October 2003.
[I-D.ietf-pppext-eap-ttls]
Funk, P. and S. Blake-Wilson, "EAP Tunneled TLS
Authentication Protocol (EAP-TTLS)",
draft-ietf-pppext-eap-ttls-04 (work in progress), April
2004.
[I-D.tschofenig-eap-ikev2]
Tschofenig, H. and D. Kroeselberg, "EAP IKEv2 Method
(EAP-IKEv2)", draft-tschofenig-eap-ikev2-03 (work in
progress), February 2004.
[ianaweb] IANA, "Number assignment", http://www.iana.org.
[jb99] Juels, A. and J. Brainard, "Client Puzzles: A
Cryptographic Defense Against Connection Depletion
Attacks", Proceedings of NDSS '99 (Networks and
Distributed Security Systems), pages 151-165, 1999.
[mitm] Asokan, N., Niemi, V. and K. Nyberg, "Man-in-the-middle in
tunnelled authentication", In the Proceedings of the 11th
International Workshop on Security Protocols, Cambridge,
UK, April 2003.
[802.11i] Institute of Electrical and Electronics Engineers, "Draft
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supplement to standard for telecommunications and
information exchange between systems - lan/man specific
requirements - part 11: Wireless medium access control
(mac) and physical layer (phy) specifications:
Specification for enhanced security", IEEE 802.11i/D10.0,
2004.
[802.11] Institute of Electrical and Electronics Engineers,
"Information technology - telecommunications and
information exchange between systems - local and
metropolitan area networks - specific requirements part
11: Wireless lan medium access control (mac) and physical
layer (phy) specifications", IEEE Standard 802.11,
1999(R2003).
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URIs
[1] <http://www.toshiba.com/tari/pana/sequence-number.txt>
[2] <http://danforsberg.info:8080/pana-issues/>
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
75 West Plumeria Drive
San Jose, CA 95134
USA
Phone: +1 408 544 5656
EMail: alper.yegin@samsung.com
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