PANA Working Group D. Forsberg
Internet-Draft Nokia
Expires: August 9, 2004 Y. Ohba
Toshiba
B. Patil
Nokia
H. Tschofenig
Siemens
A. Yegin
DoCoMo USA Labs
February 9, 2004
Protocol for Carrying Authentication for Network Access (PANA)
draft-ietf-pana-pana-03
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 9, 2004.
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 . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Specification of Requirements . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . 9
4.1 Common Processing Rules . . . . . . . . . . . . . . . . . 9
4.1.1 Payload Encoding . . . . . . . . . . . . . . . . . . . . . 9
4.1.2 Transport Layer Protocol . . . . . . . . . . . . . . . . . 10
4.1.3 Fragmentation . . . . . . . . . . . . . . . . . . . . . . 10
4.1.4 Sequence Number and Retransmission . . . . . . . . . . . . 10
4.1.5 PANA Security Association . . . . . . . . . . . . . . . . 11
4.1.6 Message Authentication Code . . . . . . . . . . . . . . . 12
4.1.7 Message Validity Check . . . . . . . . . . . . . . . . . . 13
4.1.8 Error Handling . . . . . . . . . . . . . . . . . . . . . . 14
4.2 Discovery and Initial Handshake Phase . . . . . . . . . . 14
4.3 Authentication Phase . . . . . . . . . . . . . . . . . . . 17
4.4 Re-authentication . . . . . . . . . . . . . . . . . . . . 19
4.5 Termination Phase . . . . . . . . . . . . . . . . . . . . 20
4.6 Illustration of a Complete Message Sequence . . . . . . . 21
4.7 Device ID Choice . . . . . . . . . . . . . . . . . . . . . 22
4.8 Session Lifetime . . . . . . . . . . . . . . . . . . . . . 22
4.9 Mobility Handling . . . . . . . . . . . . . . . . . . . . 23
4.10 Event Notification . . . . . . . . . . . . . . . . . . . . 24
4.11 Support for Separate EP . . . . . . . . . . . . . . . . . 24
5. PANA Security Association Establishment . . . . . . . . . 25
6. Authentication Method Choice . . . . . . . . . . . . . . . 26
7. Filter Rule Installation . . . . . . . . . . . . . . . . . 27
8. Data Traffic Protection . . . . . . . . . . . . . . . . . 28
9. Message Formats . . . . . . . . . . . . . . . . . . . . . 29
9.1 PANA Header . . . . . . . . . . . . . . . . . . . . . . . 29
9.2 AVP Header . . . . . . . . . . . . . . . . . . . . . . . . 30
9.3 PANA Messages . . . . . . . . . . . . . . . . . . . . . . 32
9.3.1 Message Specifications . . . . . . . . . . . . . . . . . . 33
9.3.2 PANA-PAA-Discover (PDI) . . . . . . . . . . . . . . . . . 33
9.3.3 PANA-Start-Request (PSR) . . . . . . . . . . . . . . . . . 33
9.3.4 PANA-Start-Answer (PSA) . . . . . . . . . . . . . . . . . 33
9.3.5 PANA-Auth-Request (PAR) . . . . . . . . . . . . . . . . . 34
9.3.6 PANA-Auth-Answer (PAN) . . . . . . . . . . . . . . . . . . 34
9.3.7 PANA-Bind-Request (PBR) . . . . . . . . . . . . . . . . . 34
9.3.8 PANA-Bind-Answer (PBA) . . . . . . . . . . . . . . . . . . 35
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9.3.9 PANA-Reauth-Request (PRAR) . . . . . . . . . . . . . . . . 35
9.3.10 PANA-Reauth-Answer (PRAA) . . . . . . . . . . . . . . . . 35
9.3.11 PANA-Termination-Request (PTR) . . . . . . . . . . . . . . 35
9.3.12 PANA-Termination-Answer (PTA) . . . . . . . . . . . . . . 36
9.3.13 PANA-Error (PER) . . . . . . . . . . . . . . . . . . . . . 36
9.4 AVPs in PANA . . . . . . . . . . . . . . . . . . . . . . . 36
9.4.1 MAC AVP . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.4.2 Device-Id AVP . . . . . . . . . . . . . . . . . . . . . . 37
9.4.3 Session-Id AVP . . . . . . . . . . . . . . . . . . . . . . 37
9.4.4 Cookie AVP . . . . . . . . . . . . . . . . . . . . . . . . 38
9.4.5 Protection-Capability AVP . . . . . . . . . . . . . . . . 38
9.4.6 Termination-Cause AVP . . . . . . . . . . . . . . . . . . 38
9.4.7 Result-Code AVP . . . . . . . . . . . . . . . . . . . . . 38
9.4.8 EAP-Payload AVP . . . . . . . . . . . . . . . . . . . . . 42
9.4.9 Session-Lifetime AVP . . . . . . . . . . . . . . . . . . . 42
9.4.10 Failed-AVP AVP . . . . . . . . . . . . . . . . . . . . . . 42
9.4.11 NAP-Information AVP . . . . . . . . . . . . . . . . . . . 42
9.4.12 ISP-Information AVP . . . . . . . . . . . . . . . . . . . 42
9.4.13 Provider-Identifier AVP . . . . . . . . . . . . . . . . . 42
9.4.14 Provider-Name AVP . . . . . . . . . . . . . . . . . . . . 43
9.4.15 EP-Device-Id AVP . . . . . . . . . . . . . . . . . . . . . 43
9.4.16 Key-Id AVP . . . . . . . . . . . . . . . . . . . . . . . . 43
9.5 AVP Occurrence Table . . . . . . . . . . . . . . . . . . . 43
10. PANA Protocol Message Retransmissions . . . . . . . . . . 45
10.1 Transmission and Retransmission Parameters . . . . . . . . 47
11. Security Considerations . . . . . . . . . . . . . . . . . 48
12. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 53
13. Change History . . . . . . . . . . . . . . . . . . . . . . 54
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 55
Normative References . . . . . . . . . . . . . . . . . . . 56
Informative References . . . . . . . . . . . . . . . . . . 57
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 59
A. Adding sequence number to PANA for carrying EAP . . . . . 61
A.1 Why is sequence number needed for PANA to carry EAP? . . . 61
A.2 Single sequence number approach . . . . . . . . . . . . . 62
A.2.1 Single sequence number with EAP retransmission method . . 62
A.2.2 Single sequence number with PANA-layer retransmission
method . . . . . . . . . . . . . . . . . . . . . . . . . . 63
A.3 Dual sequence number approach . . . . . . . . . . . . . . 66
A.3.1 Dual sequence number with orderly-delivery method . . . . 66
A.3.2 Dual sequence number with reliable-delivery method . . . . 68
A.3.3 Comparison of the dual sequence number methods . . . . . . 69
A.4 Consensus . . . . . . . . . . . . . . . . . . . . . . . . 69
Intellectual Property and Copyright Statements . . . . . . 70
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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].
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:
The representation of the trust relation between the PaC and the
PAA that is created at the end of the authentication phase. This
security association includes the device identifier of the peer,
and a shared key when available.
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.
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4.1.2 Transport Layer Protocol
PANA uses UDP as its transport layer protocol. The UDP port number
is TBD. All messages except for PANA-PAA-Discover are always
unicast. PaC MUST NOT use unspecified IP address for communicating
with PAA.
4.1.3 Fragmentation
PANA does not provide fragmentation of PANA messages. Instead, it
relies on fragmentation provided by EAP methods and IP layer when
needed.
4.1.4 Sequence Number and Retransmission
PANA uses sequence numbers to provide ordered delivery of EAP
messages. The design involves use of two sequence numbers to prevent
some of the DoS attacks on the sequencing scheme. Every PANA packet
include one transmitted sequence number (tseq) and one received
sequence number (rseq) in the PANA header. See Appendix A 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
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
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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 10 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 a sequence in a single PANA
authentication, it is possible that two AAA-Keys are derived. If this
happens, the PANA SA MUST be bound to the AAA-Key derived from the
first EAP authentication. 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 message at
the end of the authentication phase 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 sent in response to a PANA-Bind-Request
with a Key-Id AVP MUST contain a Key-Id AVP with the same AAA-Key
identifier carried in the request. PANA-Bind-Request and
PANA-Bind-Answer messages with a Key-Id AVP MUST also carry a MAC AVP
whose value is computed by using the new AAA-Key. 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:
PANA Session attributes:
* Session-Id
* Device-Id of PaC
* Device-Id of PAA
* List of device identifiers of EPs
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* 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 and
derived from the AAA-Key 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.
The length of AAA-Key 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
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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 Each field in the message header contains a valid value including
sequence number, message length, message type, version number,
flags, etc.
o When a device identifier of the communication peer is bound to the
PANA session, it matches the device identifier carried in MAC and/
or IP header(s).
o The message type is one of the expected types in the current
state.
o The message payload contains a valid set of AVPs allowed for the
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
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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
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 that sent
the first response.
PaC may also choose to start sending packets before getting
authenticated. In that case, the network should detect this and send
an unsolicited PANA-Start-Request message to PaC. EP is the node that
can detect such activity. If EP and PAA are co-located, then an
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internal mechanism (e.g. API) between the EP module and the PAA
module on the same host can prompt PAA to start PANA. In case they
are separate, there needs to be an explicit message to prompt PAA.
Upon detecting the need to authenticate a client, EP can send a
PANA-PAA-Discover message to the PAA on behalf of the PaC. This
message carries a device identifier of the PaC in a Device-ID AVP. So
that, the PAA can send the unsolicited PANA-Start-Request message
directly to the PaC. If the link between the EP and PAA is not
secure, the PANA-PAA-Discover message sent from the EP to the PAA
MUST be protected by using, e.g., IPsec.
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.
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 can indicate its choice of ISP by
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including its ISP-Information AVP in the PANA-Start-Answer message.
AAA routing will be based on the ISP choice if an ISP-Information AVP
is specified in the PANA-Start-Answer message, otherwise it will be
based on EAP identifier.
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.
In this case, PaC can also indicate its choice of ISP by including
its ISP-Information AVP in the PANA-Start-Answer message. AAA
routing for NAP authentication will be based on the NAP. AAA routing
for ISP authentication will be based on the ISP choice if an
ISP-Information AVP is specified in the PANA-Start-Answer message,
otherwise it will be based on EAP identifier. If the S-flag of the
received PANA-Start-Request message is set and the S-flag of the
corresponding PANA-Start-Answer message is not set, only one EAP
authentication occurs without distinction between NAP and ISP
authentications. In this case, PaC can still indicate its choice of
ISP by including its ISP-Information AVP in the PANA-Start-Answer
message.
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.
When a Cookie-AVP is carried in a PANA-Start-Request message, the
initial EAP Request MUST NOT be carried in the PANA-Start-Request
message in order for the PAA to be stateless.
When a Cookie-AVP is not carried in a PANA-Start-Request message, the
PAA does not need to be stateless. In this case, the initial EAP
Request message MAY be carried in the PANA-Start-Request message.
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 is never retransmitted. A
PANA-Start-Answer message is retransmitted based on timer in the same
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manner as other messages retransmitted at PANA-layer.
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 for the
PaC.
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)
------> PANA-PAA-Discover(0,0)[Device-Id]
<------------ 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
PANA-PAA-Discover is sent by EP
4.3 Authentication Phase
The main task in authentication phase is to carry EAP messages
between PaC and PAA. All EAP messages except for EAP Success/Failure
messages are carried in the PANA-Auth-Request/PANA-Auth-Answer
messages. When an EAP Success/Failure message is sent from a PAA,
the message is carried in the PANA-Bind-Request message. The PANA-
Bind-Request message is acknowledged with a PANA-Bind-Answer. It is
possible to carry multiple EAP sequences in a single PANA session.
When PaC and PAA negotiated during the discovery and initial
handshake phase to perform separate NAP and ISP authentications in a
single PANA session, the PAA determines the execution order of NAP
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authentication and ISP authentication. In this case, the PAA can
indicate which EAP authentication is currently occurring by including
a NAP-Information or an ISP-Information AVP of the corresponding EAP
authentication in the first PANA-Auth-Request message sent to the
PaC. In the case where the PaC agreed to perform separate
authentications but did not specify its ISP choice in
PANA-Start-Answer message, the PAA MUST include its NAP-Information
AVP in PANA-Auth-Request message when it performs NAP authentication
and MUST NOT include any service provider information AVP when it
performs ISP authentication so that the PaC can always distinguish
ISP authentication from NAP authentication. The PAA SHOULD stop
including a NAP-Information or an ISP-Information AVP once it
receives the first PANA-Auth-Answer message of the current EAP
authentication.
Currently, use of multiple EAP methods in PANA is designed only for
NAP-ISP authentication separation. It is not for arbitrary EAP
method sequencing, or giving the PaC another chance when an
authentication method fails. The NAP and ISP authentication are
considered completely independent. Presence or success of one should
not effect the other. Making an authentication decision based on the
success or failure of each authentication is a network policy issue.
PANA signals only the result of the immediately preceding EAP
authentication method in PANA-Bind-Request messages.
When an EAP method that is capable of deriving keys is used during
the authentication phase and the keys are successfully derived the
PANA-Bind-Request and PANA-Bind-Answer messages and all subsequent
PANA messages MUST contain a MAC AVP. The PANA-Bind-Request and the
PANA-Bind-Answer message exchange is also used for binding device
identifiers of the PaC and the PAA to the PANA SA. To achieve this,
the PANA-Bind-Request and the PANA-Bind-Answer SHOULD contain a
device identifier of the PAA and the PaC, respectively, in a
Device-Id AVP. The PaC MUST use the same type of device identifier
as contained in the PANA-Bind-Request message. The PANA-Bind-Request
message MAY also contain a Protection-Capability AVP to indicate if
link-layer or network-layer ciphering should be initiated after PANA.
No link layer or network layer specific information is included in
the Protection-Capability AVP. When the information is preconfigured
on the PaC and the PAA this AVP can be omitted. It is assumed that at
least PAA is aware of the security capabilities of the access
network. The PANA protocol does not specify how the PANA SA and the
Protection-Capability AVP will be used to provide per-packet
protection for data traffic.
PANA-Bind-Request and PANA-Bind-Answer messages MUST be retransmitted
based on the retransmission rule described in Appendix A.
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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., MAC]
-----> PANA-Bind-Answer(y+3,x+3)
[Device-Id, Protection-Cap., 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,
PANA-Auth-Request and PANA-Auth-Answer messages SHOULD 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
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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.
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.
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]
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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.
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, Protection-Cap., MAC]
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// 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
4.7 Device ID Choice
A PaC SHOULD configure an IP address before PANA if it can. It might
either have a pre-configured IP address, or have to obtain one via
dynamic methods such as DHCP or stateless address autoconfiguration.
Dynamic methods may or may not succeed depending on the local
security policy. In networks where clients have to be authorized
before they are allowed to obtain an IP address, EPs will detect the
associated activity and PANA protocol will be engaged before the
clients can configure a valid IP address.
Either an IP address or a link-layer address SHOULD be used as device
ID at any time. It is assumed that PAA knows 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). When IPsec-based mechanism [I-D.ietf-pana-ipsec] is the
choice of access control, PAA SHOULD provide its IP address as device
ID, and expect the PaC to provide its IP address in return. In all
other cases, link-layer addresses can be provided from both sides.
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.
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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
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
When a PaC wants to resume an ongoing PANA session after connecting
to another link in the same access network, it MAY send the unexpired
PANA session identifier in its PANA-Start-Answer message. In the
absence of a Session-Id AVP in this message, PAA MUST assume this is
a fresh session and continue its normal execution.
If PAA receives a session identifier in the PANA-Start-Answer
message, and it is configured to enable fast re-authentication, it
SHOULD retrieve the PANA session attributes from the previous PAA of
the PaC. The mechanism required to determine the previous PAA of the
PaC by relying on the PANA session identifier is outside the scope of
PANA protocol. A possible solution is to embed the PAA identifier in
the PANA session identifier. Furthermore, the mechanism required to
retrieve the session attributes from the previous PAA is outside the
scope of this protocol. Seamoby Context Transfer Protocol
[I-D.ietf-seamoby-ctp] might be useful for this purpose.
When the PAA is not configured to enable fast re-authentication, or
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 the new session identifier and let
the PANA exchange take its usual course. This action will engage EAP
authentication and create a fresh PANA session from scratch.
In case the new PAA retrieves the on-going PANA session attributes
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from the previous PAA, the PANA session continues with a PANA-Reauth
exchange. The MAC AVP contained in the PANA-Reauth messages MUST be
generated and verified by using the retrieved PANA SA attributes.
This exchange MUST also include Session-Id AVP that contains the
newly assigned session identifier, and Device-Id AVP. A new PANA
session is created upon successful completion of this exchange. This
session inherits only the session lifetime, protection capability,
and AAA-Key attributes from the previous session. Other attributes
are generated based on the PANA exchanges on the new link. While
AAA-Key stays the same, a new PANA_MAC_Key is computed using the new
parameters. Subsequent MAC-AVPs are processed using this new PANA SA.
4.10 Event Notification
Upon detecting the need to authenticate a client, EP can send a
trigger message to the PAA on behalf of the PaC. This can be one of
the messages provided by the PAA-to-EP protocol, or, in the absence
of such a facility, PANA-PAA_Discover can be used as well. This
message MUST carry the device identifier of the PaC. So that, the PAA
can send the unsolicited PANA-Start-Request message directly to the
PaC. If the link between the EP and PAA is not physically secured,
this message sent from EP to PAA MUST be cryptographically protected
(e.g., by using IPsec).
4.11 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.
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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 will be discussed in
Section 7 and Section 8.
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6. Authentication Method Choice
Authentication methods' capabilities and therefore applicability to
various environments differ among them. Not all methods provide
support for mutual authentication, key derivation or distribution,
and DoS attack resiliency that are necessary for operating in
insecure networks. Such networks might be susceptible to
eavesdropping and spoofing, therefore a stronger authentication
method needs to be used to prevent attacks on the client and the
network.
The authentication method choice is a function of the underlying
security of the network (e.g., physically secured, shared link,
etc.). It is the responsibility of the user and the network operator
to pick the right method for authentication. PANA carries EAP
regardless of the EAP method used. It is outside the scope of PANA to
mandate, recommend, or limit use of any authentication methods. PANA
cannot increase the strength of a weak authentication method to make
it suitable for an insecure environment. There are some EAP- based
approaches to achieve this goal (see
[I-D.josefsson-pppext-eap-tls-eap],[I-D.ietf-pppext-eap-ttls],
[I-D.tschofenig-eap-ikev2]). PANA can carry these EAP encapsulating
methods but it does not concern itself with how they achieve
protection for the weak methods (i.e., their EAP method payloads).
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7. Filter Rule Installation
PANA protocol provides client authentication and authorization
functionality for securing network access. The other component of a
complete solution is the access control which ensures that only
authenticated and authorized clients can gain access to the network.
PANA enables access control by identifying legitimate clients and
generating filtering information for access control mechanisms.
Getting this filtering information to the EPs (Enforcement Points)
and performing filtering are outside the scope of PANA.
Access control can be achieved by placing EPs in the network for
policing the traffic flow. EPs should prevent data traffic from and
to any unauthorized client unless it's PANA traffic. When a client is
authenticated and authorized, PAA should notify EP(s) and ask for
changing filtering rules to allow traffic for a recently authorized
client. There needs to be a protocol between PAA and EP(s) when these
entities are not co-located. PANA Working Group will not be defining
a new protocol for this interaction. Instead, it will (preferably)
identify one of the existing protocols that can fit the requirements.
Possible candidates include but not limited to COPS, SNMP, DIAMETER.
This task is similar to what MIDCOM Working Group is trying to
achieve, therefore some of the MIDCOM's output might be useful here.
EPs' location in the network topology should be appropriate for
performing access control functionality. The closest IP-capable
access device to the client devices is the logical choice. PAA and
EPs on an access network should be aware of each other as this is
necessary for access control. Generally this can be achieved by
manual configuration. Dynamic discovery is another possibility, but
this is clearly outside the scope of PANA.
Filtering rules generally include device identifiers for a client,
and also cryptographic keying material when needed. Such keys are
needed when attackers can eavesdrop and spoof on the device
identifiers easily. They are used with link-layer or network-layer
ciphering to provide additional protection. For issues regarding
data-origin authentication see Section 8.
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8. Data Traffic Protection
Protecting data traffic of authenticated and authorized clients from
others is another component of providing a complete secure network
access solution. Authentication, integrity and replay protection of
data packets are needed to prevent spoofing when the underlying
network is not physically secured. Encryption is needed when
eavesdropping is a concern in the network.
When the network is physically secured, or the link-layer ciphering
is already enabled prior to PANA, data traffic protection is already
in place. In other cases, enabling link-layer ciphering or network-
layer ciphering might rely on PANA authentication. The user and
network have to make sure an appropriate EAP method that can generate
required keying materials is used. Once the keying material is
available, it needs to be provided to the EP(s) for use with
ciphering.
Network-layer ciphering, i.e., IPsec, can be used when data traffic
protection is required but link-layer ciphering capability is not
available. Note that a simple shared secret generated by an EAP
method is not readily usable by IPsec for authentication and
encryption of IP packets. Fresh and unique session key derived from
the EAP method is still insufficient to produce an IPsec SA since
both traffic selectors and other IPsec SA parameters are missing.
The shared secret can be used in conjunction with a key management
protocol like IKE [RFC2409] to turn a simple shared secret into the
required IPsec SA. The details of such mechanisms are outside the
scope of this document and can be found in [I-D.ietf-pana-ipsec].
Using network-layer ciphers should be regarded as a substitute for
link-layer ciphers when the latter is not available. IKE involves
several message exchanges which can incur additional delay and header
overhead in getting basic IP connectivity for a mobile device. Such a
latency is inevitable when there is no other alternative and this
level of protection is required. Network-layer ciphering can also be
used in addition to link-layer ciphering if the added benefits
outweigh its cost to the user and the network.
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9. Message Formats
This section defines message formats for PANA protocol.
9.1 PANA Header
A summary of the PANA header format is shown below. The fields are
transmitted in network byte order.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmitted Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Received Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVPs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
Version
This Version field MUST be set to 1 to indicate PANA Version 1.
Message Length
The Message Length field is three octets and indicates the length
of the PANA message including the header fields.
Flags
The Flags field is eight bits. The following bits are assigned:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R r r r S r r r|
+-+-+-+-+-+-+-+-+
R(equest)
If set, the message is a request. If cleared, the message is an
answer.
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S(eparate)
When the S-flag is set in a PANA-Start-Request message it
indicates that PAA is willing to offer separate EAP
authentication 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 authentication for NAP and ISP.
r(eserved)
these flag bits are reserved for future use, and MUST be set to
zero, and ignored by the receiver.
Message Type
The Message Type field is three octets, and is used in order to
communicate the message type with the message. The 24-bit address
space is managed by IANA [ianaweb]. 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 9.2 for more information on
AVPs.
9.2 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
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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 ...
+-+-+-+-+-+-+-+-+
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.
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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
applications.
Data
The Data field is zero or more octets and contains information
specific to the Attribute. The format and length of the Data field
is determined by the AVP Code and AVP Length fields.
9.3 PANA Messages
Figure 9 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-Bind-Request <--------
PANA-Bind-Answer -------->
PANA-Reauth-Request <------->
PANA-Reauth-Answer <------->
PANA-Termination-Request <------->
PANA-Termination-Answer <------->
PANA-Error <------->
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Figure 9: PANA Message Overview
Additionally the EP can also send a PANA-PAA-Discover message to the
PAA.
9.3.1 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:
message ::= < PANA-Header: <Message type>, [REQ] [SEP] >
* [ AVP ]
9.3.2 PANA-PAA-Discover (PDI)
The PANA-PAA-Discover (PDI) message is used to discover the address
of PAA(s). Both sequence numbers in this message are set to zero (0).
If the EP detects a new PaC and sends the PANA-PAA-Discover to the
PAA, it MUST include the Device-Id of the PaC.
PANA-PAA-Discover ::= < PANA-Header: 1 >
0*1 < Device-Id >
0*1 < Session-Id >
* [ AVP ]
9.3.3 PANA-Start-Request (PSR)
PANA-Start-Request (PSR) is sent by the PAA to the PaC. The PAA sets
the transmission sequence number to an initial random value. The
received sequence number is set to zero (0).
PANA-Start-Request ::= < PANA-Header: 2, REQ [SEP] >
[ Cookie ]
[ EAP-Payload ]
[ NAP-Information ]
* [ ISP-Information ]
* [ AVP ]
9.3.4 PANA-Start-Answer (PSA)
PANA-Start-Answer (PSA) is sent by the PaC to the PAA in response to
a PANA-Start-Request message. The PANA_start message transmission
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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] >
[ Cookie ]
[ EAP-Payload ]
[ ISP-Information ]
* [ AVP ]
9.3.5 PANA-Auth-Request (PAR)
PANA-Auth-Request (PAR) is sent by the PAA to the PaC.
PANA-Auth-Request ::= < PANA-Header: 3, REQ >
< Session-Id >
< EAP-Payload >
0*1 [ NAP-Information ]
0*1 [ ISP-Information ]
* [ AVP ]
0*1 < MAC >
(Both NAP-Information and ISP-Information MUST NOT be included at the
same time)
9.3.6 PANA-Auth-Answer (PAN)
PANA-Auth-Answer (PAN) is sent by the PaC to the PAA in response to a
PANA-Auth-Request message.
PANA-Auth-Answer ::= < PANA-Header: 3 >
< Session-Id >
< EAP-Payload >
* [ AVP ]
0*1 < MAC >
9.3.7 PANA-Bind-Request (PBR)
PANA-Bind-Request (PBR) is sent by the PAA to the PaC.
PANA-Bind-Request ::= < PANA-Header: 4, REQ >
< Session-Id >
< Device-Id >
{ EAP-Payload }
{ Result-Code }
[ Session-Lifetime ]
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[ Protection-Capability ]
[ Key-Id ]
* [ EP-Device-Id ]
* [ AVP ]
0*1 < MAC >
9.3.8 PANA-Bind-Answer (PBA)
PANA-Bind-Answer (PBA) is sent by the PaC to the PAA in response to a
PANA-Result-Request message.
PANA-Bind-Answer ::= < PANA-Header: 4 >
< Session-Id >
< Device-Id >
[ Key-Id ]
* [ AVP ]
0*1 < MAC >
9.3.9 PANA-Reauth-Request (PRAR)
PANA-Reauth-Request (PRAR) is either sent by the PaC or the PAA.
PANA-Reauth-Request ::= < PANA-Header: 5, REQ >
< Session-Id >
< Device-Id >
* [ AVP ]
0*1 < MAC >
9.3.10 PANA-Reauth-Answer (PRAA)
PANA-Reauth-Answer (PRAA) is sent in response to a
PANA-Reauth-Request.
PANA-Reauth-Answer ::= < PANA-Header: 5 >
< Session-Id >
< Device-Id >
* [ AVP ]
0*1 < MAC >
9.3.11 PANA-Termination-Request (PTR)
PANA-Termination-Request (PTR) is sent either by the PaC or the PAA.
PANA-Termination-Request ::= < PANA-Header: 6, REQ >
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< Session-Id >
< Termination-Cause >
* [ AVP ]
0*1 < MAC >
9.3.12 PANA-Termination-Answer (PTA)
PANA-Termination-Answer (PTA) is sent either by the PaC or the PAA in
response to PANA-Termination-Request.
PANA-Termination-Answer ::= < PANA-Header: 6 >
< Session-Id >
* [ AVP ]
0*1 < MAC >
9.3.13 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 >
9.4 AVPs in PANA
Some of the used AVPs are defined in this document and some of them
are defined in other documents like [RFC3588]. PANA proposes to use
the same name space with the Diameter spec. For temporary allocation,
PANA uses AVP type numbers starting from 1024.
9.4.1 MAC AVP
The first octet (8 bits) of the MAC (Code 1024) AVP data contains 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...
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Algorithm
1 HMAC-SHA1 (20 bytes)
MAC
The Message Authentication Code is encoded in network byte order.
9.4.2 Device-Id AVP
The first octet (8 bits) of the Device-Id (Code 1025) AVP data
contains the device type. Rest of the AVP data payload contains the
device data. The content and format of data (including byte and bit
ordering) for L2_ADDRESS is expected to be specified in specific
documents that describe how IP operates over different link-layers.
For instance, [RFC2464].
RESERVED 0
IPV4_ADDRESS 1
IPV6_ADDRESS 2
L2_ADDRESS 3
For type 1 (IPv4 address), data size is 32 bits and for type 2 (IPv6
address), data size is 128 bits.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Data... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9.4.3 Session-Id AVP
Session-Id AVP (Code 1026) has an opaque data field, which is
assigned by the PAA. All messages pertaining to a specific PANA
Session MUST include only one Session-Id AVP and the same value MUST
be used throughout the lifetime of a session. When present, 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.
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The Session-Id AVP MAY use Diameter [RFC3588] message formatting. In
this case the AVP code is 263.
9.4.4 Cookie AVP
The Cookie AVP (Code 1027) is of type OctetString. The data is opaque
and the exact content is outside the scope of this protocol.
9.4.5 Protection-Capability AVP
The Protection-Capability AVP (Code 1028) is of type Unsigned32. The
AVP data is used as a collection of flags for different data
protection capability indications. Below is a list of specified data
protection capabilities:
0 UNKNOWN
1 L2_PROTECTION
2 IPSEC_PROTECTION
9.4.6 Termination-Cause AVP
The Termination-Cause AVP (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.
9.4.7 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
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from [RFC3588] and adapted for PANA.
9.4.7.1 Authentication Results Codes
These result code values inform the PaC about the EAP authentication
method success or failure.
PANA_SUCCESS 2001
The EAP method authentication was successful (EAP-Success).
PANA_AUTHENTICATION_REJECTED 4001
The authentication process for the client failed (EAP-Failure).
PANA_AUTHORIZATION_REJECTED 5003
A request was received for which the client could not be
authorized. This error could occur if the service requested is
not permitted to the client.
9.4.7.2 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
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
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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
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.
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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-Bind-Request message without an EAP-Payload AVP.
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.
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.
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9.4.8 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.
9.4.9 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.
9.4.10 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].
9.4.11 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 ]
9.4.12 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 ]
9.4.13 Provider-Identifier AVP
The Provider-Identifier AVP (AVP Code: 1036) is of type Unsigned32,
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and contains an IANA assigned "SMI Network Management Private
Enterprise Codes" [ianaweb] value, encoded in network byte order.
9.4.14 Provider-Name AVP
The Provider-Name AVP (AVP Code: 1037) is of type UTF8String, and
contains the UTF8-encoded name of the provider.
9.4.15 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 9.4.2).
9.4.16 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.
9.5 AVP Occurrence Table
The following tables lists the AVPs used in this document, and
specifies in which PANA messages they MAY, or MAY NOT be present.
The table uses the following symbols:
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 |
--------------------+-----+-----+-----+-----+-----+-----+-----+
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Result-Code | 0 | 0 | 0 | 0 | 1 | 0 | 0 |
Session-Id | 0 | 0 | 1 | 1 | 1 | 1 | 0-1 |
Termination-Cause | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
EAP-Payload | 0-1 | 0-1 | 1 | 1 | 1 | 0 | 0 |
MAC | 0 | 0 | 0-1 | 0-1 | 0-1 | 0-1 | 0 |
Device-Id | 0 | 0 | 0 | 0 | 1+ | 1+ | 0-1 |
Cookie | 0-1 | 0-1 | 0 | 0 | 0 | 0 | 0 |
Protection-Cap. | 0 | 0 | 0 | 0 | 0-1 | 0 | 0 |
Session-Lifetime | 0 | 0 | 0 | 0 | 0-1 | 0 | 0 |
Failed-AVP | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
ISP-Information | 0+ | 0-1 | 0-1 | 0 | 0 | 0 | 0 |
NAP-Information | 0-1 | 0 | 0-1 | 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 |
--------------------+-----+-----+-----+-----+-----+-----+-----+
+-------------------------------+
| Message |
| Type |
+------+------+-----+-----+-----+
Attribute Name | PRAR | PRAA | PTR | PTA | PER |
--------------------+------+------+-----+-----+-----+
Result-Code | 0 | 0 | 0 | 0 | 1 |
Session-Id | 1 | 1 | 1 | 1 | 1 |
Termination-Cause | 0 | 0 | 1 | 0 | 0 |
EAP-Payload | 0-1 | 0-1 | 0 | 0 | 0 |
MAC | 0-1 | 0-1 | 0-1 | 0-1 | 0-1 |
Device-Id | 1+ | 1+ | 0 | 0 | 0 |
Cookie | 0 | 0 | 0 | 0 | 0 |
Protection-Cap. | 0 | 0 | 0 | 0 | 0 |
Session-Lifetime | 0 | 0 | 0 | 0 | 0 |
Failed-AVP | 0 | 0 | 0 | 0 | 1 |
ISP-Information | 0 | 0 | 0 | 0 | 0 |
NAP-Information | 0 | 0 | 0 | 0 | 0 |
EP-Device-Id | 0 | 0 | 0 | 0 | 0 |
Key-Id | 0 | 0 | 0 | 0 | 0 |
--------------------+------+------+-----+-----+-----+
Figure 10: AVP Occurrence Table
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10. 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-Answer (PSA)
PANA-Bind-Request (PBR)
PANA-Reauth-Request (PRAR)
PANA-Termination-Request (PTR)
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
MRT Maximum retransmission time
MRD Maximum retransmission duration
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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.
If both MRC and MRD are zero, the client continues to transmit the
message until it receives a response.
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10.1 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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11. 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 side of the
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network where only PaCs are connected.
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 Section 6 suggests using proper EAP methods
for particular environments. Depending on the usage environment an
EAP authentication has to be used for example which supports user
identity confidentiality, protection against dictionary attacks and
session key establishment. It is therefore the responsibility of the
network operators and end users to choose the proper EAP method.
PANA does not protect the EAP method exchange, but provides ordered
delivery with sequence numbers. Sequence numbers and cookies provide
resistance against blind DoS attacks.
c) PANA SA establishment
Once the EAP message authentication is finished a fresh and unique
session key is available to the PaC and the PAA. This assumes that
the EAP method allows session key derivation and that the generated
session key has a good quality. For further discussion about the
importance of the session key generation refer to the next subsection
(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
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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
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
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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.
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
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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
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.
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12. Open Issues
A list of open issues is maintained at [1].
The remaining issues for -01 version of draft are: None.
The remaining issues for -02 version of draft are: None.
The remaining issues for -xx version of draft are: 28, 52, 53, 54,
55, 56, 57, 58 and 59.
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13. Change History
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.
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14. Acknowledgments
We would like to thank all members of the PANA working group for
their 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.
[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-07 (work in progress), December
2003.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[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.
[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.
[I-D.ietf-eap-keying]
Aboba, B., "EAP Key Management Framework",
draft-ietf-eap-keying-01 (work in progress), October 2003.
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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-03 (work in progress), October 2003.
[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-01 (work in progress),
January 2004.
[I-D.ietf-seamoby-ctp]
Loughney, J., "Context Transfer Protocol",
draft-ietf-seamoby-ctp-08 (work in progress), January
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]
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Funk, P. and S. Blake-Wilson, "EAP Tunneled TLS
Authentication Protocol (EAP-TTLS)",
draft-ietf-pppext-eap-ttls-03 (work in progress), August
2003.
[I-D.tschofenig-eap-ikev2]
Tschofenig, H. and D. Kroeselberg, "EAP IKEv2 Method
(EAP-IKEv2)", draft-tschofenig-eap-ikev2-02 (work in
progress), October 2003.
[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
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/D7.0,
2003.
[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://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 Information Systems, Inc.
9740 Irvine Blvd.
Irvine, CA 92619-1697
USA
Phone: +1 973 829 5174
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
DoCoMo USA Labs
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4743
EMail: alper@docomolabs-usa.com
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Appendix A. Adding sequence number to PANA for carrying EAP
Appendix A.1 Why is sequence number needed for PANA to carry EAP?
EAP [I-D.ietf-eap-rfc2284bis] requires underlying transports to
provide ordered-delivery of messages. If an underlying transport
does not satisfy the ordering requirement, the following situation
could happen:
EAP Peer EAP Authenticator
--------------------------------------------
1. (got req 1) <------- Request ID=1
2. Response ID=1 ---+
| (timeout)
3. | +-- Request ID=1
| |
+-|--> (got resp 1)
4. (got req 2) <----|-- Request ID=2
|
5. Response ID=2 -----|--> (got resp 2)
|
6. (got req 1) <----+
7. Response ID=1 --------> [discarded due to unexpected ID]
Figure 11: Undesirable scenario
In Figure 11, the second EAP Request message with Identifier=1
arrives at the EAP peer after the third EAP Request message with
Identifier=2. As a result, the EAP peer accepts the second EAP
Request as a new EAP Request while it is just an old EAP Request that
was already responded and the authentication might be totally messed
up.
This problem occurs due to the fact that EAP doesn't recognize
duplicate packets in the scope of one EAP protocol run, but only in
the scope of current and previous packet (i.e., request and response
message matching). When EAP is running over PPP or IEEE 802 links,
this is not a problem, because those link-layers have the ordering
invariant characteristic.
On the other hand, the PANA design has chosen UDP as its transport.
Given that UDP does not provide ordered delivery of packets and PANA
does not assume any specific link-layer technology to carry EAP, PANA
messages need to have a sequence number.
In the following text we describe two possible approaches for
sequence number handling in PANA. The first one makes use of a
single sequence number whereas the latter utilizes two. Finally a
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comparison between the two approaches is provided. The method
described in Appendix A.3.1 (i.e., the dual sequence number with
orderly-delivery method) is suggested as the preferred method for
PANA transport.
Appendix A.2 Single sequence number approach
This section discusses several methods based on using a single
sequence number for providing orderly message delivery. Sequence
number handling for all methods discussed in Appendix A.2 must comply
to the following rules:
Rule 1: The sequence number starts from initial sequence number (ISN)
and is monotonically increased by 1. The arithmetic defined
in [RFC1982] is used for sequence number operation.
Rule 2: When a PAA sends an EAP message passed from EAP layer to a
PaC, a new sequence number is placed in the message,
regardless of whether it is sent as a result of a
retransmission at the EAP layer or not.
Note: It might be possible to define other mechanisms for sequence
number handling if it can be assumed that a PAA detects EAP
retransmissions. However, such an assumption heavily depends on EAP
implementation details in particular on EAP APIs, thus it was decided
not to use such an assumption.
Appendix A.2.1 Single sequence number with EAP retransmission method
Again, the following rules must hold:
Rule 3: Use EAP layer retransmission for retransmitting EAP messages
(based on a timer expiration).
Rule 4: When the PaC receives a message from the PAA, it checks the
sequence number and discards the message if the sequence
number is not greater than that of the last accepted message.
Rule 5: When the PAA receives a message from the PaC, it checks the
sequence number and discards the message if the sequence
number does not match a pending request message.
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PaC PAA Seq# Message
--------------------------------------------
1. <------- (x) PANA-Auth-Request[EAP Req ID=1]
2. ---+ (x) PANA-Auth-Answer[EAP Res ID=1]
| (retransmission timeout at EAP-layer)
3. | +-- (x+1) PANA-Auth-Request[EAP Req ID=1]
| |
+-|--> (discarded due to Rule 5)
| (retransmission timeout at EAP-layer)
4. <----|-- (x+2) PANA-Auth-Request[EAP Req ID=1]
|
5. -----|--> (x+2) PANA-Auth-Answer[EAP Res ID=1]
|
6. <----+ (discarded due to Rule 4)
7. <------- (x+3) PANA-Auth-Request[EAP Req ID=2]
.
.
Figure 12: Example for Single sequence number with EAP retransmission
This method is vulnerable to a blind DoS attack on the sequence
number since the PaC will accept quite a wide range of sequence
numbers. For example, if an attacker blindly sends a bogus message
to a legitimate PaC with a randomly chosen sequence number, it will
be accepted by the PaC with 50% probability, and once this happens,
all messages sent from the communicating PAA will be discarded as
long as they have a sequence number smaller than the accepted value.
The problem of this method leads to a requirement for PaC to have a
narrow range of acceptable sequence numbers to make the blind DoS
attack difficult. Note that the DoS attack cannot be prevented if the
attacker is on the same IP link as PaC and able to eavesdrop the PANA
conversation. However, the attacker needs to put itself in
promiscuous mode and thus spend more resources to eavesdrop and
launch the attack (in other words, non-blind DoS attack is still
possible as long as sequence numbers are unprotected.)
Appendix A.2.2 Single sequence number with PANA-layer retransmission
method
The next method is still based on using a single sequence number but
the PANA-layer takes the responsibility of retransmission. The
method uses the following rules in addition to the common rules
described in Appendix A.2.
Rule 3: Use PANA-layer retransmission for retransmitting both EAP and
non-EAP messages (based on a timer expiration). EAP layer
retransmission is turned off. Retransmission based on timer
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occurs both on PaC and PAA side, but not on both sides
simultaneously. PAA does retransmission at least for
PANA_Termination and PANA_Reauth messages, otherwise PaC
takes care of retransmission.
Rule 4: When the PaC receives a message from the PAA, it accepts the
message if the sequence number is equal to that of the last
accepted message + 1. If the sequence number is equal to
that of the last accepted message, the PaC retransmits the
last transmitted message. Otherwise, it silently discards
the message.
Rule 5: When the PAA receives a message from the PaC, it accepts the
message if the sequence number is equal to that of the last
transmitted message. If the receiving sequence number is
equal to that of the last transmitted message - 1, the PAA
retransmits the last transmitted message and discard the
received message. Otherwise, it silently discards the
message.
Rule 6: The PaC retransmits the last transmitted EAP Response until a
new EAP Request message or an EAP Success/Failure message is
received and accepted.
Rule 7: PAA must keep the copy of the last transmitted message and
must be able to retransmit it until either a valid message is
received and accepted by the PAA or a timer expires. The
timer is used if no new message will be sent from the PaC.
PaC PAA Seq# Message
--------------------------------------------
1. <-------- (x) PANA-Auth-Request[EAP Req ID=1]
2. ---+ (x) PANA-Auth-Answer[EAP Resp ID=1]
| (retransmission timeout at PaC)
3. ---|----> (x) PANA-Auth-Answer[EAP Resp ID=1]
4. | +--- (x+1) PANA-Auth-Request[EAP Req ID=2]
| |
+-|--> (duplicate detected)
5. <----|--- (x+1) PANA-Auth-Request[EAP Req ID=2]
|
6. -----|--> (x+1) PANA-Auth-Answer[EAP Resp ID=2]
|
<----|--- (x+2) PANA-Auth-Request[EAP Req ID=3]
7. -----|--> (x+2) PANA-Auth-Answer[EAP Resp ID=3]
<----+ (discarded by PaC)
(retransmission timeout at PaC)
8. --------> (x+2) PANA-Auth-Answer[EAP Resp ID=3]
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9. lost<---- (x+3) PANA-Auth-Request[EAP Succ ID=3]
(retransmission timeout at PaC)
10.---->lost (x+2) PANA-Auth-Answer[EAP Resp ID=3]
(retransmission timeout at PaC)
11.--------> (x+2) PANA-Auth-Answer[EAP Resp ID=3]
12.<-------- (x+3) PANA-Bind-Request[EAP Succ ID=3]
(retransmission timer stopped at PaC)
(deletion timeout at PAA)
(message (x+3) deleted at PAA)
13.lost<---- (x+4) PANA-Termination-Request
(retransmission timeout at PAA)
14.<-------- (x+4) PANA-Termination-Request
15.---->lost (x+4) PANA-Termination-Answer
(retransmission timeout at PAA)
16.<-------- (x+4) PANA-Termination-Request
17.--------> (x+4) PANA-Termination-Answer
(retransmission timer stopped at PAA)
Figure 13: Example for Single sequence number with PANA-layer
retransmission
This method has an advantage of eliminating EAP layer retransmission
by providing reliability at the PANA layer. Retransmission at the EAP
layer has a problem with determining an appropriate retransmission
timer value, which occurs when the lower-layer is unreliable. In
this case an EAP authenticator cannot distinguish between (i) EAP
Request or EAP Response message loss (in this case the retransmission
timer should be calculated based on network characteristics) and (ii)
long latency for EAP Response generation due to e.g., user input etc.
(in this case the retransmission timer should be calculated based on
user or application characteristics). In general, the retransmission
timer for case (ii) is longer than that for case (i). If case (i)
happens while the retransmission timer is calculated based on user or
application characteristics, then it might frustrate an end user
since the completion of the authentication procedure takes
unnecessarily long. If case (ii) happens while the retransmission
timer is calculated based on network characteristics (i.e., RTT),
then unnecessarily traffic is generated by retransmission. Note that
in this method a PaC still cannot distinguish case (i) and case (iii)
the EAP authenticator or a backend authentication server is taking
time to generate an EAP Request.
A problem of this method is that it is based on the assumption that
EAP authenticator does not send a new EAP message until an EAP
Response to the outstanding EAP Request is received. However, this
assumption does not hold at least EAP Success/Failure message which
does not need the outstanding EAP Request to be responded before
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sending the EAP Success/Failure message. This would require
timer-based retransmission not only at PaC side but also at PAA side.
Another problem occurs when a new EAP message overrides the
outstanding EAP Request, the PaC cannot assume any more that the
sequence number of the next message to be accepted is the last
accepted message + 1. So the PaC needs to accept a range of sequence
numbers, instead of a single sequence number. These two additional
things would increase the complexity of this method.
Appendix A.3 Dual sequence number approach
Based on the analysis of previous schemes, it is recognized that two
sequence numbers are needed anyway, one for each direction. Two
different methods are proposed based on this approach. Both methods
have the following rules in common.
Rule 1: A PANA packet carries two sequence numbers: transmitted
sequence number (tseq) and received sequence number (rseq).
tseq starts from initial sequence number (ISN) and is
monotonically increased by 1. The arithmetic defined in
[RFC1982] is used for sequence number operation. It is
assumed that the two sequence numbers have the same length
for simplicity.
Rule 2: When PAA or PAC sends a new message, a new sequence number is
placed on the tseq field of message. Every transmitted
message is given a new sequence number.
Rule 3: When a message is sent from PaC or PAA, rseq is copied from
the tseq field of the last accepted message.
Rule 4: For messages which experience a PANA layer retransmission,
the retransmission timer is stopped when the message is
acknowledged.
It is possible to carry multiple EAP sequences in a single PANA
sequence, with using EAP Success/Failure message as a delimiter of
each EAP sequence. In this case, EAP Success/Failure message needs
to be reliably delivered.
Appendix A.3.1 Dual sequence number with orderly-delivery method
This method relies on EAP layer retransmission for EAP messages.
This method is referred to as orderly-delivery method. The following
rules are used in addition to the common rules.
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Rule 5: Use the EAP-layer retransmission for retransmitting EAP
Requests (based on a timer expiration). For other PANA layer
messages that require a response from the peer, PANA layer
has its own mechanism to retransmit the request until it gets
a response or gives up. A new tseq value is always used when
sending any message even when it is retransmitted at PANA
layer.
Rule 6: When a message is received, it is accepted if (i) the tseq
value is greater than the tseq of the last accepted message
and (ii) the rseq falls in the range between the tseq of the
last acknowledged message + 1 and the tseq of the last
transmitted message. Otherwise, the received message is
discarded.
PaC PAA (tseq,rseq) Message
--------------------------------------------------
1. <------- (x,y) PANA-Auth-Request[EAP Req, ID=1]
2. -------> (y+1,x) PANA-Auth-Answer[EAP Resp, ID=1]
3. <------- (x+1,y+1) PANA-Auth-Request[EAP Req, ID=2]
4. --->lost (y+2,x+1) PANA-Auth-Answer[EAP Resp, ID=2]
(retransmission timeout at EAP layer)
5. <------- (x+2,y+1) PANA-Auth-Request [EAP Req, ID=2]
6. -------> (y+3,x+2) PANA-Auth-Answer[EAP Resp, ID=2]
7. lost<--- (x+3,y+3) PANA-Auth-Request[EAP Req, ID=3]
(retransmission timeout at EAP layer)
8. +---- (x+4,y+3) PANA-Auth-Answer[EAP Req, ID=3]
| (retransmission timeout at EAP layer)
9. <--|---- (x+5,y+3) PANA-Auth-Request[EAP Req, ID=3]
10.---|---> (y+4,x+5) PANA-Auth-Answer[EAP Resp, ID=3]
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|
<--+ (out of order. discarded)
11.lost<--- (x+6,y+4) PANA-Bind-Request[EAP Succ, ID=3]
(retransmission timeout at PAA)
12.<------- (x+7,y+4) PANA-Bind-Request[EAP Succ, ID=3]
13.--->lost (y+5,x+7) PANA-Bind-Answer
(retransmission timeout at PAA)
14.<------- (x+8,y+4) PANA-Bind-Request[EAP Succ, ID=3]
(duplicate detected by PaC)
15.-------> (y+6,x+8) PANA-Bind-Answer
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Figure 14: Example for Dual sequence number with orderly-delivery
Appendix A.3.2 Dual sequence number with reliable-delivery method
This method relies solely on PANA layer retransmission for all
messages. This method is referred to as reliable-delivery method.
The following additional rules are applied in addition to the common
rules.
Rule 5: Use the PANA layer retransmission for retransmitting all
messages (based on a timer expiration). EAP retransmission
is turned off.
Rule 6: Either an ACK message is used for acknowledgment or an
acknowledgment can be piggybacked with data. ACK messages
are not retransmitted. An ACK message is sent if no the
acknowledgement cannot be piggybacked with a data within a
given time frame W.
Rule 7: When a message is received, it is accepted if (i) the tseq
value is greater than the tseq of the last accepted message
and (ii) the rseq falls in the range between the tseq of the
last acknowledged message and the tseq of the last
transmitted message. Otherwise, the received message is
discarded.
Rule 8: When a duplicate message is received, the last transmitted
message is retransmitted if the received message is not an
ACK. A message is considered as duplicate if its tseq value
is equal to the tseq of the last accepted message.
PaC PAA (tseq,rseq) Message
--------------------------------------------------
1. <------- (x,y) PANA-Auth-Request[EAP Req, ID=1]
(user input ongoing)
2. -------> (y+1,x) PANA-Auth-Answer
(user input completed)
3. -------> (y+2,x) PANA-Auth-Answer[EAP Resp, ID=1]
4. <------- (x+1,y+2) PANA-Auth-Request [EAP Req, ID=2]
5. --->lost (y+3,x+1) PANA-Auth-Answer[EAP Resp, ID=2]
(retransmission timeout at PAA)
6. <------- (x+1,y+2) PANA-Auth-Request [EAP Req, ID=2]
(duplicate detected by PaC)
7. -------> (y+3,x+1) PANA-Auth-Answer[EAP Resp, ID=2]
8. lost<--- (x+2,y+3) PANA-Auth-Request [EAP Req, ID=3]
(retransmission timeout at PaC)
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9. -------> (y+3,x+1) PANA-Auth-Answer[EAP Resp, ID=2]
(duplicate detected at PAA)
10.<------- (x+2,y+3) PANA-Auth-Request [EAP Req, ID=3]
11.---+ (y+4,x+2) PANA-Auth-Answer[EAP Resp, ID=3]
| (retransmission timeout at PAA)
12.<--|---- (x+2,y+3) PANA-Auth-Request [EAP Req, ID=3]
| (duplicate detected at PaC)
13.---|---> (y+4,x+2) PANA-Auth-Answer[EAP Resp, ID=3]
14.<--|---- (x+3,y+4) PANA-Bind-Request[EAP Succ, ID=3]
15.---|---> (y+5,x+3) PANA-Bind-Answer
+---> (out of order. discarded)
Figure 15: Example for Dual sequence number with reliable-delivery
method
Appendix A.3.3 Comparison of the dual sequence number methods
The orderly-delivery method is simpler than the reliable-delivery
method in that the former does not allow sending a separate ACK while
the latter does.
In terms of authentication performance, the reliable-delivery method
is better than the orderly-delivery method in that the former gives
more detailed status of the link than the latter, e.g., an entity can
know whether a request has reached the communicating peer without
before receiving a response. The reliable-delivery can reduce
retransmission traffic and communication delay that would occur if
there is no reliability, as described in section Appendix A.2.2
Appendix A.4 Consensus
Although it is recognizable that the reliable-delivery method would
be important in terms of improvement of overall authentication
latency, we believe that this is a performance problem of EAP and not
a problem of PANA. It is agreed that solving the EAP problem is not
the scope of PANA and simplicity is more important factor in the PANA
design.
As a consequence, the orderly-delivery method is chosen as the
message transport part of PANA.
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