PANA Working Group P. Jayaraman
Internet-Draft Net.Com
Expires: November 1, 2004 R. Lopez
Univ. of Murcia
Y. Ohba (Ed.)
Toshiba
M. Parthasarathy
Nokia
A. Yegin
Samsung
May 3, 2004
PANA Framework
draft-ietf-pana-framework-00
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on November 1, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
PANA design provides support for various types of deployments. Access
networks can differ based on the availability of lower-layer
security, placement of PANA entities, choice of client IP
configuration and authentication methods, etc. This I-D defines a
general framework for describing how these various deployment choices
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are handled by PANA and the access network architectures.
Additionally, two possible deployments are described in detail: using
PANA over DSL networks and WLAN networks.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Specification of Requirements . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. General PANA Framework . . . . . . . . . . . . . . . . . . 5
4. Environments . . . . . . . . . . . . . . . . . . . . . . . 9
5. IP Address Configuration . . . . . . . . . . . . . . . . . 11
6. Data Traffic Protection . . . . . . . . . . . . . . . . . 14
7. PAA-EP Protocol . . . . . . . . . . . . . . . . . . . . . 15
7.1 PAA and EP Locations . . . . . . . . . . . . . . . . . . . 15
7.1.1 Single PAA, Single EP, Co-located . . . . . . . . . . . . 16
7.1.2 Separate PAA and EP . . . . . . . . . . . . . . . . . . . 16
7.2 Notification of PaC Presence . . . . . . . . . . . . . . . 18
7.3 Filter Rule Installation . . . . . . . . . . . . . . . . . 18
8. Network Selection . . . . . . . . . . . . . . . . . . . . 19
9. Authentication Method Choice . . . . . . . . . . . . . . . 21
10. Example Cases . . . . . . . . . . . . . . . . . . . . . . 22
10.1 DSL Access Network . . . . . . . . . . . . . . . . . . . . 22
10.1.1 Bridging Mode . . . . . . . . . . . . . . . . . . . . . . 22
10.1.2 Address Translation (NAPT) Mode . . . . . . . . . . . . . 23
10.1.3 Router Mode . . . . . . . . . . . . . . . . . . . . . . . 23
10.1.4 PANA and Dynamic Internet Service Provider Selection . . . 24
10.2 Wireless LAN Example . . . . . . . . . . . . . . . . . . . 25
10.2.1 PANA with Bootstrapping IPsec . . . . . . . . . . . . . . 26
10.2.2 PANA with Bootstrapping WPA/IEEE 802.11i . . . . . . . . . 30
10.2.3 Capability Discovery . . . . . . . . . . . . . . . . . . . 34
11. Open Issue . . . . . . . . . . . . . . . . . . . . . . . . 35
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 36
Normative References . . . . . . . . . . . . . . . . . . . 37
Informative References . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 40
A. Other Possible Cases for PANA with Bootstrapping IPsec
in Wireless LAN . . . . . . . . . . . . . . . . . . . . . 41
A.1 IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
A.2 IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . 46
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1. Introduction
PANA design provides support for various types of deployments. Access
networks can differ based on the availability of lower-layer
security, placement of PANA entities, choice of client IP
configuration and authentication methods, etc.
PANA can be used in any access network regardless of the underlying
security. For example, the network might be physically secured, or
secured by means of cryptographic mechanisms after the successful
client-network authentication.
The PANA client, PANA authentication agent, authentication server,
and enforcement point are the relevant functional entities in this
design. PANA authentication agent and enforcement point(s) can be
placed on various elements in the access network (e.g., access point,
access router, dedicated host).
IP address configuration mechanisms vary as well. Static
configuration, DHCP, stateless address autoconfiguration are possible
mechanisms to choose from. If the client configures an IPsec tunnel
for enabling per-packet security, configuring IP addresses inside the
tunnel becomes relevant, for which there are additional choices such
as IKE.
This I-D defines a general framework for describing how these various
deployment choices are handled by PANA and the access network
architectures. Additionally, two possible deployments are described
in detail: using PANA over DSL networks and WLAN networks.
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
Pre-PANA address (PRPA)
This is the address configured before starting the PANA protocol
exchange.
Post-PANA address (POPA)
This is the address (optionally) configured after a successful
authentication.
IPsec Tunnel Inner Address (IPsec-TIA)
This is the address used as the inner address of an IPsec tunnel
mode SA. When IPsec protection is used, depending on the
deployment scenario used either a PRPA or POPA becomes the
IPsec-TIA.
IPsec Tunnel Outer Address (IPsec-TOA)
This is the address used as the outer address of an IPsec tunnel
mode SA. When IPsec protection is used, a PRPA becomes the
IPsec-TOA.
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3. General PANA Framework
PANA protocol is designed to facilitate authentication and
authorization of client hosts in access networks. PANA is an EAP
[I-D.ietf-eap-rfc2284bis] lower-layer that carries EAP authentication
methods encapsulated inside EAP between a client host and an agent in
the access network. While PANA enables the authentication process
between the two entities, it is only a part of an overall AAA and
access control framework. A AAA and access control framework using
PANA is comprised of four functional entities.
PANA Client (PaC):
The client implementation of the PANA protocol. This entity
resides on the client host that is requesting access to a local
area network. Example client hosts can be laptops, PDAs, cell
phones, desktops that are connected to a network via wired or
wireless networks. A PaC is responsible for requesting network
access and engaging in authentication process using the PANA
protocol.
PANA Authentication Agent (PAA):
The server implementation of the PANA protocol. A PAA is in
charge of interfacing with the PaCs for authenticating and
authorizing them for the network access service.
The PAA consults an authentication server in order to verify the
credentials and rights of a PaC. If the authentication server
resides on the same host as the PAA, an API is sufficient for this
interaction. When they are separated (a much more common case in
public access networks), a protocol needs to run between the two.
LDAP [RFC3377] and AAA protocols like RADIUS [RFC2865] and
Diameter [RFC3588] are commonly used for this purpose.
The PAA is also responsible for updating the access control state
(i.e., filters) depending on the creation and deletion of the
authorization state. The PAA communicates the updated state to
the enforcement points in the network. If the PAA and EP are
residing on the same host, an API is sufficient for this
communication. Otherwise, a protocol is required to carry the
authorized client attributes from the PAA to the EP. While not
prohibiting other protocols, currently SNMP [I-D.ietf-pana-snmp]
is suggested for this task.
The PAA resides on a node that is typically called a NAS (network
access server) in the local area network. PAA can be hosted on any
IP-enabled node on the same IP subnet as the PaC. For example on
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a BAS (broadband access server) in DSL networks, or PDSN in 3GPP2
networks.
Authentication Server (AS):
The server implementation that is in charge of verifying the
credentials of a PaC that is requesting the network access
service. The AS receives requests from the PAA on behalf of the
PaCs, and responds with the result of verification together with
the authorization parameters (e.g., allowed bandwidth, IP
configuration, etc). The AS might be hosted on the same host as
the PAA, on a dedicated host on the access network, or on a
central server somewhere on the Internet.
Enforcement Point (EP):
The access control implementation that is in charge of allowing
access to authorized clients while preventing access by others.
An EP learns the attributes of the authorized clients from the
PAA.
The EP uses simple or cryptographic filters to selectively allow
and discard data packets. These filters may be applied at the
link-layer or the IP-layer. When cryptographic access control is
used, a secure association protocol needs to run between the PaC
and EP. This protocol provides the cryptographic binding between
the communication channel and the authorization state. Examples of
secure association protocols include the 4-way handshake in IEEE
802.11i [802.11i], and IKE in IP-based access control. Link-layer
ciphering or IPsec [I-D.ietf-pana-ipsec] is used following the
secure association to enable per-packet integrity, authentication
and replay protection (and optionally confidentiality).
An EP must be located strategically in a local area network to
minimize the access of unauthorized clients to the network. For
example, the EP can be hosted on the switch that is directly
connected to the clients in a wired network. That way the EP can
drop unauthorized packets before they reach any other client host
or beyond the local area network.
Figure 1 illustrates these functional entities and the interfaces
(protocols, APIs) among them.
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RADIUS/
Diameter/
+-----+ PANA +-----+ LDAP/ API +-----+
| PaC |<----------------->| PAA |<---------------->| AS |
+-----+ +-----+ +-----+
^ ^
| |
| +-----+ |
IKE/ +-------->| EP |<--------+ SNMP/ API
4-way handshake +-----+
Figure 1: PANA Functional Model
Some of the entities may be co-located depending on the deployment
scenario. For example, the PAA and EP would be on the same node
(BAS) in DSL networks. In that case a simple API is sufficient
between the PAA and EP. In small enterprise deployments the PAA and
AS may be hosted on the same node (access router) that eliminates the
need for a protocol run between the two. The decision to co-locate
these entities or otherwise, and their precise location in the
network topology are deployment decisions.
Use of IKE or 4-way handshake protocols for secure association is
only required in the absence of any lower-layer security prior to
running PANA. Physically secured networks (e.g., DSL) or the
networks that are already cryptographically secured on the link-layer
prior to PANA run (e.g., cdma2000) do not require additional secure
association and per-packet ciphering. These networks can bind the
PANA authentication and authorization to the lower-layer secure
channel that is already available.
Figure 2 illustrates the signaling flow for authorizing a client for
network access.
PaC EP PAA AS
| | | |
IP address o | | |
config. | PANA | | AAA |
|<------------------------------>|<-------------->|
| | SNMP | |
(Optional) | |<-------------->| |
IP address o | | |
config. | Sec.Assoc. | | |
|<------------->| | |
| | | |
| Data traffic | | |
|<-----------------> | |
| | | |
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Figure 2: PANA Signaling Flow
The EP on the access network allows general data traffic from any
authorized PaC, whereas it allows only limited type of traffic (e.g.,
PANA, DHCP, router discovery) for the unauthorized PaCs. This
ensures that the newly attached clients have the minimum access
service to engage in PANA and get authorized for the unlimited
service.
The PaC MUST configure an IP address prior to running PANA. After the
successful PANA authentication, depending on the deployment scenario
PaC MAY need to re-configure its IP address or configure additional
IP address(es). The additional address configuration MAY be executed
as part of the secure association protocol run.
An initially unauthorized PaC starts the PANA authentication by
discovering the PAA on the access network, followed by the EAP
exchange over PANA. The PAA interfaces with the AS during this
process. Upon receiving the authentication and authorization result
from the AS, the PAA informs the PaC about the result of its network
access request.
If the PaC is authorized to gain the access to the network, the PAA
also sends the PaC-specific attributes (e.g., IP address,
cryptographic keys, etc.) to the EP by using SNMP. The EP uses this
information to alter its filters for allowing data traffic from and
to the PaC to pass through.
In case a cryptographic access control needs to be enabled after the
PANA authentication, a secure association protocol runs between the
PaC and the EP. The PaC should already have the input parameters to
this process as a result of the successful PANA exchange. Similarly,
the EP should have obtained them from the PAA via SNMP. Secure
association exchange produces the required security associations
between the PaC and the EP to enable per-packet protection.
Finally data traffic can start flowing from and to the newly
authorized PaC.
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4. Environments
The PANA protocol can be used on any network environment whether
there is a lower-layer secure channel prior to PANA, or one has to be
enabled upon successful PANA authentication. The secure channel
enabled by PANA may rely on link-layer ciphering or IP-layer
ciphering.
Two types of networks are:
a. Networks where a secure channel is already available prior to
running PANA
These are the networks where the lower-layer is already providing
protection against spoofing and eavesdropping (nevertheless the
client is still required to get authenticated and authorized for
the network access service).
One example is the DSL networks where the lower-layer security is
provided by physical means (a.1). Physical protection of the
network wiring ensures that practically there is only one client
that can send and receive IP packets on the link. Another example
is the cdma2000 networks where the lower-layer security is
provided by means of cryptographic protection (a.2). By the time
the client requests access to the network-layer services, it is
already authenticated and authorized for accessing the radio
channel, and link-layer ciphering is enabled.
The presence of a secure channel before PANA exchange eliminates
the need for executing a secure association protocol after PANA.
The PANA session can be bound to the communication channel it was
carried over. Also, the choice of EAP authentication method
depends on the presence of this security during PANA run. Use of
some authentication methods outside a secure channel is not
recommended (e.g., EAP-MD5).
b. Networks where a secure channel is created after running PANA
These are the networks where there is no lower-layer protection
prior to running PANA. A successful PANA authentication enables
generation of cryptographic keys that are used with a secure
association protocol to enable per-packet protection.
PANA authentication is run on an insecure channel that is
vulnerable to eavesdropping and spoofing. The choice of EAP
method must be resilient to the possible attacks associated with
such an environment. Furthermore, the EAP method must be able to
create cryptographic keys that will later be used by the secure
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association protocol.
Whether to use a link-layer per-packet security (b.1) or an
IP-layer one (b.2) is a deployment decision. This decision also
dictates the choice of the secure association protocol. If
link-layer protection is used, the protocol would be link
technology specific. If IP-layer protection is used, the secure
association protocol would be IKE and the per-packet security
would be provided by IPsec regardless of the link type.
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5. IP Address Configuration
PaC configures an IP address before the PANA protocol exchange
begins. This address is called a pre-PANA address (PRPA). After a
successful authentication, the client may have to configure a
post-PANA address (POPA) for communication with other nodes, if PRPA
is a local-use (e.g., link-local or private address) or a temporarily
allocated IP address. An operator might choose allocating a POPA
only after successful PANA authorization either to prevent waste of
premium IP resources until the client is authorized, or to enable
client identity based address assignment.
In case PaC is a IPv4-IPv6 dual-stack host, it may configure more
than one PRPA, at least one for each protocol. Nevertheless, the PaC
needs only one to run PANA which is executed once regardless of the
type and number of IP stacks. After successful PANA authentication,
similarly PaC may configure multiple POPAs.
There are different methods by which a PRPA can be configured.
1. In some deployments (e.g., DSL networks) the PaC may be statically
configured with an IP address. This address SHOULD be used as
PRPA.
2. In IPv4, most clients attempt to configure an address dynamically
using DHCP [RFC2131]. If they are unable to configure an address
using DHCP, they can configure a link-local address using
[I-D.ietf-zeroconf-ipv4-linklocal].
When the network access provider is able to run a DHCP server on
the access link, the client would configure the PRPA using DHCP.
This address may be from a private address pool [RFC1918]. Also,
the lease time on the address may vary. For example, a PRPA
configured solely for running PANA can have a short lease time.
PRPA may be used for local-use only (i.e., only for on-link
communication, such as for PANA and IPsec tunneling with EP), or
also for ultimate data communication.
In case there is no running DHCP server on the link, the client
would fall back to configuring a PRPA via zeroconfiguration
technique [I-D.ietf-zeroconf-ipv4-linklocal]. This yields a
long-term address that can only be used for on-link communication.
3. In IPv6, clients configure a link-local address [RFC2462] when
they initialize an interface. This address SHOULD be used as
PRPA.
When a PRPA is configured, the client starts the PANA protocol
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exchange. By that time, a dual-stack client might have configured
both an IPv4 address, and one or more IPv6 addresses as PRPAs. When
the client successfully authenticates to the network, it may be
required to configure POPAs for its subsequent data communication
with the other nodes.
If the client is already configured with a non-temporary address that
can be used with data communication, it is not required to configure
a POPA. Otherwise, PAA would indicate PaC the available POPA
configuration methods through the PANA-Bind-Request message. PaC can
choose one of the methods and execute accordingly.
1. If the network relies on physical or link-layer security, PaC can
configure a POPA using DHCP [RFC2131][RFC3315] or using IPv6
stateless auto-configuration [RFC2461]. If IPv4 is being used,
PRPA is likely to be a link-local or private address, or an
address with a short DHCP lease. An IPv4 PRPA SHOULD be
unconfigured when the POPA is configured to prevent IPv4 address
selection problem [I-D.ietf-zeroconf-ipv4-linklocal]. If IPv6 is
used, the link-local PRPA address SHOULD NOT be unconfigured
[RFC3484].
If the PaC is a dual-stack host, it can configure both IPv4 and
IPv6 type POPAs.
PRPA and the IP address of PAA are assumed to be on the same IP
subnet, hence the PaC and PAA can perform on-link communication as
required by PANA. When the PaC replaces its IPv4 PRPA with POPA,
this assumption may not hold true. In order to maintain the same
on-link communication, the PaC and PAA SHOULD create host routes
to each other upon PaC's IP address change. The PaC SHOULD create
a host route to the PAA, and the PAA SHOULD create a host route to
the PaC (POPA).
2. If the network uses IPsec for protecting the traffic on the link
subsequent to PANA authentication [I-D.ietf-pana-ipsec], PaC would
use the PRPA as the outer address of IPsec tunnel mode SA
(IPsec-TOA). PaC also needs to configure an inner address
(IPsec-TIA). There are different ways to configure IPsec-TIA
which are indicated in Pana-Bind-Request message.
When an IPv4 PRPA is configured, the same address may be used as
both IPsec-TOA and IPsec-TIA. In this case, a POPA is not
configured. Alternatively, an IPsec-TIA can be obtained via the
configuration method available within [RFC3456] for IPv4, and
[I-D.ietf-ipsec-ikev2] for both IPv4 and IPv6. This newly
configured address constitutes a POPA. Please refer to
[I-D.ietf-pana-ipsec] for more details.
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IKEv2 can enable configuration of both IPv4 and IPv6 TIAs for the
same IPsec tunnel mode SA. Therefore, IKEv2 is recommended for
handling dual-stack PaCs where single execution of PANA and IKE is
desired.
Although there are potentially a number of different ways to
configure a PRPA, and POPA when necessary, it should be noted that
the ultimate decision to use one or more of these in a deployment
depends on the operator. The decision is dictated by the operator's
choice of per-packet protection capability (physical and link-layer
vs network-layer), PRPA type (local and temporary vs global and
long-term), and POPA configuration mechanisms available in the
network.
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6. Data Traffic Protection
Protecting data traffic of authenticated and authorized client 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 a mechanism is outside the
scope of PANA protocol and is specified in [I-D.ietf-pana-ipsec].
PANA provides bootstrapping functionality for such a mechanism by
carrying EAP methods that can generate initial keying material.
Using network-layer ciphers should be regarded as a substitute for
link-layer ciphers when the latter is not available. 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. In
this case, PANA bootstraps only the network-layer ciphering and
link-layer is protected using any of the existing link-layer specific
methods.
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7. PAA-EP Protocol
The 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.
Access control can be achieved by placing EPs (Enforcement Points) in
the network for policing the traffic flow. EPs should prevent data
traffic from and to any unauthorized client unless it's either PANA
or one of the other allowed traffic types (e.g., ARP, IPv6 neighbor
discovery, DHCP, etc.).
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 identifies one of the existing protocols that can fit the
requirements. An assessment was made in the PANA Working Group and
SNMPv3 has been chosen as the mandatory PAA-EP protocol.
This section describes the possible models on the location of PAA and
EP, as well as the basic authorization information that needs to be
exchanged between PAA and EP. When PAA and EP are not co-located in
a single device, there are other issues such as dead or rebooted peer
detection and consideration for specific authorization and accounting
models. However, these issues are closely related to the PAA-EP
protocol solution and thus not discussed in this document. See
[I-D.ietf-pana-snmp] for further discussion.
7.1 PAA and EP Locations
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 left to implementations and outside the scope of this
document.
Since PANA allows the separation of EP and PAA, there are several
models depending on the number of EPs and PAAs and their locations.
This section describes all possible models on the placement of PAA(s)
and EP(s).
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7.1.1 Single PAA, Single EP, Co-located
This model corresponds to the legacy NAS model. Since the PAA and
the EP are co-located, the PAA-EP communication can be implemented
locally by using, e.g., IPC (Inter-Process Communication). The only
difference from the legacy NAS model is the case where there are
multiple co-located PAA/EP devices on the same IP link and the PAA/EP
devices are L2 switches or access points. In this case, for a PaC
that attaches to a given PAA/EP device, other PAA/EP devices should
not be visible to the PaC even if those devices are on the same IP
link. Otherwise, the PaC may result in finding a PAA that is not the
closest one to it during the PANA discovery and initial handshake
phase and performing PANA with the wrong PAA. To prevent this, each
PAA/EP device on an L2 switch or access point should not forward
multicast PANA discovery message sent by PaCs attached to it to other
devices.
7.1.2 Separate PAA and EP
When PAA is separated from EP, two cases are possible with regard to
whether PAA and EP are located in parallel or serial when viewed from
PaC, for each of models described in this section.
In the first case, PAA is located behind EP. The EP should be
configured to always pass through PANA messages and address
configuration protocol messages used for configuring an IP address
used for initial PANA messaging. This case can typically happen when
the EP is an L2 switch or an access point (the EP also has an IP
stack to communicate with PAA via a PAA-EP protocol).
+---+ +---+ +---+
|PaC|--------|EP |--------|PAA|
+---+ +---+\ +---+
\
+---- Internet
Figure 3: PAA and EP in Serial
In the other case, PAA is located in parallel to EP. Since the EP is
not on the communication path between PaC and PAA, the EP does not
have to configure to pass through PANA messages or address
configuration protocol messages in this case. This case can
typically happen when the EP is a router and the PAA is an
authentication gateway without IP routing functionality.
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+---+
+-----|PAA|
/ +---+
+---+/
|PaC|
+---+\
\ +---+
+-----|EP |---- Internet
+---+
Figure 4: PAA and EP in Parallel
In the remaining of this section, PaC is not shown in figures and the
figures cover both the serial and parallel models.
7.1.2.1 Single PAA, Single EP, Separated
The model benefits from separation of data traffic handling and AAA.
The EP does not need to have a AAA protocol implementation which
might be updated relatively more frequently than the per-packet
access enforcement implementation.
7.1.2.2 Single PAA, Multiple EPs
In this model, a single PAA controls multiple EPs. The PAA may be
separated from any EP or co-located with a particular EP. This model
might be useful where it is preferable to run a AAA protocol at a
single, manageable point. This model is particularly useful in an
access network that consists of a large number of access points on
which per-packet access enforcement is made. When a PaC is
authenticated to the PAA, the PAA should install access control
filters to each of the EPs under control of the PAA if the PAA cannot
tell which EP the PaC is attached to. Even if the PAA can tell which
EP the PaC is attached to, the PAA may install access control filters
to those EPs if the PaC is a mobile device that can roam among the
EPs. Such pre-installation of filters can reduce handoff latency.
If different access authorization policies are applied to different
EPs, different filter rules for a PaC may be installed on different
EPs.
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+---+
|EP |--+
+---+ \
\
+---+ +---+
|EP |----|PAA|
+---+ +---+
/
+---+ /
|EP |--+
+---+
Figure 5: An example model for a single PAA and multiple EPs
7.1.2.3 Multiple PAAs
The PANA protocol allows multiple PAAs to exist on the same IP link
and to be visible to PaCs on the link. PAAs may or may not be
co-located with EPs as long as authorization results do not depend on
whichever PAAs are chosen by a PaC [I-D.ietf-pana-pana].
7.2 Notification of PaC Presence
When PAA and EP are separated and PAA is configured to be the
initiator of the discovery and initial handshake phase of PANA, EP
has the responsibility to detect presence of a new PaC and notifies
the PAA(s) of the presence [I-D.ietf-pana-requirements]. Such a
presence notification is carried in a PAA-EP protocol message
[I-D.ietf-pana-snmp].
7.3 Filter Rule Installation
Filtering rules to be installed on EP generally include a device
identifier of PaC, and also cryptographic keying material (such as
keys, key pairs, and initialization values) when needed. The keying
material is needed when attackers can eavesdrop and spoof on the
device identifiers easily. Each keying material is uniquely
identified with a keying material name and has a lifetime for key
management purpose. The keying material is used with link-layer or
network-layer ciphering to provide additional protection. For issues
regarding data-origin authentication see Section 6. In addition to
the device identifier and keying material, other filter rules, such
as the IP filter rules specified in NAS-Filter-Rule AVPs carried in
Diameter EAP application [I-D.ietf-aaa-eap] may be installed on EP.
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8. Network Selection
The network selection problem statement is made in
[I-D.ietf-eap-netsel-problem]. The PANA protocol
[I-D.ietf-pana-pana] provides a way for networks to advertise which
ISPs are available and for PaC to choose one ISP from the advertised
information. When a PaC chooses an ISP in the PANA protocol
exchange, the ultimate destination of the AAA exchange is determined
based on the identity of the chosen service provider. It is also
possible that the PaC does not choose a specific ISP in the PANA
protocol exchange. In this case, both the ISP choice and the AAA
destination are determined based on the PaC's identity, where the
identity may be an NAI [RFC2486] or the physical port number or L2
address of the subscriber.
As described in [I-D.ietf-eap-netsel-problem], network selection is
not only related to AAA routing but also related to payload routing.
Once an ISP is chosen and the PaC is successfully authenticated and
authorized, PaC is assigned an address by the ISP whose IP prefix may
be different from that of the AR. This affects the routing of the
subsequent data traffic between AR and PaC. A suggested solution is
to add host route from AR to PaC's POPA address and host route from
PaC to AR.
Consider a typical DSL network where the AR, EP, and PAA are
co-located on a BAS (Broadband Access Server) in the access network
operated by a NAP (Network Access Provider). Figure 6 shows a
typical model for ISP selection.
<---- NAP ----><--------- ISP --------->
+---ISP1
/
+---+ +---------+/
|PaC|----|AR/EP/PAA|
+---+ +---------+\
BAS \
+---ISP2
Figure 6: A Network Selection Model
When network selection is made at L3 with the use of the PANA
protocol instead of L2-specific authentication mechanisms, the IP
link between PaC and PAA needs to exist prior to doing PANA (and
prior to network selection). In this model, the PRPA is either given
by NAP or a link-local address is auto-configured. After the
successful authentication with the ISP, PaC may acquire an address
(POPA) from the ISP. It also learns the address of the AR, e.g.,
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through DHCP, to be used as its default router. The address of the
AR may or may not be in the same IP subnet as that of the PaC's POPA.
If they don't share the same prefix, they SHOULD use host routes to
reach each other. Note that the physically secured DSL networks do
not require IPsec-based access control. Therefore the PaCs use one IP
address at a time where POPA replaces PRPA upon configuration.
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9. 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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10. Example Cases
10.1 DSL Access Network
In a DSL access network, PANA is seen applicable in the following
scenarios.
A typical DSL access consists of a NAS device at the DSL-access
provider and a DSL-modem (CPE) at the customer premises. The CPE
devices support multiple modes of operation and PANA is applicable in
each of these modes.
Host--+ +-------- ISP1
| DSL link |
+----- CPE ---------------- NAS ----+-------- ISP2
| (Bridge/NAPT/Router) |
Host--+ +-------- ISP3
<------- customer --> <------- NAP -----> <---- ISP --->
premise
Figure 7: DSL Model
The devices at the customer premises have been shown as "hosts" in
the above network.
DSL networks are protected by physical means. Eavesdropping and
spoofing attacks are prevented by keeping the unintended users
physically away from the network media. Therefore, generally
cryptographic protection of data traffic is not necessary.
Nevertheless, if enhanced security is deemed necessary for any
reason, IPsec-based access control can be enabled on DSL networks as
well by using the method described in [I-D.ietf-pana-ipsec].
10.1.1 Bridging Mode
In the bridging mode, the CPE acts as a simple layer-2 bridge. The
hosts at the customer premises will function as clients to obtain
addresses from the NAS device by using DHCP or PPPoE.
If PPPoE is used, authentication is typically performed using CHAP or
MS-CHAP.
PANA will be applicable when the hosts use DHCP to obtain IP address.
DHCP does not support authentication of the devices on either side of
the DSL access line. In the simplest method of address assignment,
the NAS will allocate the IP address to a host with a lease time
reasonably sufficient to complete a full PANA based authentication
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which will be triggered immediately after the address assignment. The
hosts will perform the PaC function and the NAS will perform the PAA,
EP and AR functions.
Host--+
(PaC) |
+----- CPE ---------------- NAS ------------- ISP
| (Bridge) (PAA,EP,AR)
Host--+
(PaC)
Figure 8: Bridge Mode
The DSL service provider's trunk network should not be accessible to
any host that has not successfully completed the PANA authentication
phase.
10.1.2 Address Translation (NAPT) Mode
In the NAPT mode, the CPE is configured with the authentication
parameters (i.e. username, password). In this case, the CPE acts as a
"client" of the NAS. If the CPE uses DHCP to obtain the IP address,
PANA will be necessary to authenticate the CPE and the NAS to each
other.
Host--+
|
+----- CPE ---------------- NAS ------------- ISP
| (NAPT, PaC) (PAA,EP,AR)
Host--+
Figure 9: NAPT Mode
The CPE in this case typically acts as a DHCP server for the devices
at the customer premises network. It applies NAPT mechanisms to
forward traffic between the customer premises network and the NAS.
If the CPE is configured with a static IP address and does not
perform DHCP, it will need to initiate a PANA authentication phase
before gaining access to the service provider's network.
10.1.3 Router Mode
In this case, the CPE acts as a full-fledged router for the customer
premises network. The CPE itself may obtain the IP address using
DHCP or be configured with static IP address. Once the CPE is
authenticated using PANA and is provided access to the service
provider's network, the NAS should begin exchanging routing updates
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with the CPE. All devices at the customer premises will then have
access to the service provider's network.
Host--+
|
+----- CPE ---------------- NAS ------------- ISP
| (Router, PaC) (PAA,EP,AR)
Host--+
Figure 10: Router Mode
As in the NAPT mode, it is possible that both ends of the DSL link
are configured with static IP addresses. PANA-based mutual
authentication of CPE and NAS is desirable before data-traffic is
exchanged between the customer premises network and the service
provider network.
10.1.4 PANA and Dynamic Internet Service Provider Selection
In some installations, a NAS device is shared by multiple service
providers. Each service provider configures the NAS with a certain IP
address space.
The devices at the customer premises network indicate their choice of
service provider and the NAS chooses the IP address from the
appropriate service provider's pool. In many cases, the address is
assigned not by the NAS but by the AAA server that is managed fully
by the service provider.
This simplifies the management of the DSL access network as it is not
always necessary to configure each DSL access line with the service
provider's identity. The service provider is chosen dynamically by
the CPE device. This is typically known as "dynamic Internet Service
Provider selection". The AAA function is usually overloaded to
perform dynamic ISP selection.
If the CPE device uses a PPP based protocol (PPP or PPPoE), the ISP
is chosen by mapping the username field of a CHAP response to a
provider.
If the CPE uses DHCP, the 'client-id' field of the DHCP-discover or
DHCP-request packet is mapped to the provider.
10.1.4.1 Selection as Part of the DHCP protocol or an Attribute of DSL
Access Line
The ISP selection, therefore the IP address pool, can be conveyed
based on the DHCP protocol exchange (as explained earlier), or by
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associating the DSL access line to the service provider before the
PANA authentication begins. When any of these schemes is used, the
IP address used during PANA authentication (PRPA) is the ultimate IP
address and it does not have to be changed upon successful
authorization.
10.1.4.2 Selection as Part of the PANA Authentication
The ISP selection of the client can be explicitly conveyed during the
PANA authentication. In that case, the client can be assigned a
temporary IP address (PRPA) prior to PANA authentication. This IP
address might be obtained via DHCP with a lease reasonably long to
complete PANA authentication, or via the zeroconf technique
[I-D.ietf-zeroconf-ipv4-linklocal]. In either case, successful PANA
authentication signalling prompts the client to obtain a new (long
term) IP address via DHCP. This new IP address (POPA) replaces the
previously allocated temporary IP address.
10.2 Wireless LAN Example
This section describes how PANA can be used on WLAN networks. In
most common WLAN deployments the IP addresses are dynamically
configured. Therefore this section does not cover the scenarios
where the IP address is statically configured. There are two models
depending on which layer security is bootstrapped from PANA
authentication, L2 or L3. When PANA authentication is used for
bootstrapping L3 security, L2 security is not necessarily to exist
even after PANA authentication. Instead, IPsec-based data traffic
protection is bootstrapped from PANA. The PAA can indicate the PaC
as to whether L2 or L3 protection is needed, by including a
Protection-Capability AVP in PANA-Bind-Request message. In both
cases, the most common deployment would be illustrated in Figure 11,
where EP is typically co-located with AP (access point) when PANA is
used for bootstrapping L2 security or with AR when PANA is used for
bootstrapping L3 security.
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+-----+
|AP/EP|----+
+-----+ |
|
+---+ +-----+ | +---------+
|PaC| |AP/EP|----+----|AR/PAA/EP|----- Internet
+---+ +-----+ | +---------+
|
+-----+ |
|AP/EP|----+
+-----+
Figure 11: PANA Wireless LAN Model
10.2.1 PANA with Bootstrapping IPsec
In this model, data traffic is protected by using IPsec tunnel mode
SA and an IP address is used as the device identifier of PaC (see
Section 5 for details). Some or all of AP, DHCPv4 Server (including
PRPA DHCPv4 Server and IPsec-TIA DHCPv4 Server), DHCPv6 Server, PAA
and EP may be co-located in a single device. EP is always co-located
with AR and may be co-located with PAA. When EP and PAA are not
co-located, PAA-EP protocol is used for communication between PAA and
EP.
Note that for all of the cases described in this section, PBR
(PANA-Bind-Request) and PBA (PANA-Bind-Answer) exchange in PANA
[I-D.ietf-pana-pana] should occur after installing the authorization
parameter to AR, so that IKE can be performed immediately after PANA
is successfully completed.
10.2.1.1 IPv4
Case A: IPsec-TIA obtained by using DHCPv4
In this case, the IPsec-TIA and IPsec-TOA are the same as the
PRPA, and all configuration information including the IP address
is obtained by using DHCPv4 [RFC2131]. No POPA is configured.
Case A is the simplest compared to other ones and might be used in
a network where IP address depletion attack on DHCP is not a
significant concern. The PRPA needs to be a routable address
unless NAT is performed on AR.
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PaC AP DHCPv4 Server PAA EP(AR)
| Link-layer | | | |
| association| | | |
|<---------->| | | |
| | | | |
| DHCPv4 | | |
|<-----------+------------>| | |
| | | | |
|PANA(Discovery and Initial Handshake phase |
| & PAR-PAN exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| | | |Authorization|
| | | |[IKE-PSK, |
| | | | PaC-DI, |
| | | | Session-Id] |
| | | |------------>|
| | | | |
|PANA(PBR-PBA exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| | IKE | |
|<-----------+---------------------------------------->|
| | | | |
| | | | |
Figure 12: An example case for configuring IPsec-TIA by using
DHCPv4
Case B: IPsec-TIA obtained by using IKE
In this case, the PRPA is obtained by using DHCPv4 and used as
IPsec-TOA. The POPA is obtained by using IKE (via a Configuration
Payload exchange or equivalent) and used as IPsec-TIA.
Case C: IPsec-TIA obtained by using RFC3456
Like Case B, the PRPA is obtained by using DHCPv4. The difference
is that the POPA (eventually used as IPsec-TIA) and other
configuration parameter are configured by running DHCPv4 over a
special IPsec tunnel mode SA [RFC3456]. Note that the PRPA DHCPv4
Server and IPsec-TIA DHCPv4 Server may be co-located on the same
node.
Note: this case may be used only when IKEv1 is used as the IPsec
key management protocol (IKEv2 does not seem to support RFC3456
equivalent case).
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PaC AP DHCPv4 Server PAA EP(AR)
| Link-layer | | | |
| association| | | |
|<---------->| | | |
| | | | |
| DHCPv4 | | |
|<-----------+------------>| | |
| | | | |
|PANA(Discovery and initial handshake phase |
| & PAR-PAN exchange in authentication phase) |
|<-----------+-------------------------->| |
| | | |
| | |Authorization|
| | |[IKE-PSK, |
| | | PaC-DI, |
| | | Session-Id] |
| | |------------>|
| | | |
|PANA(PBR-PBA exchange in authentication phase) |
|<-----------+-------------------------->| |
| | | |
| | IKE | |
| (with Configuration Payload exchange or equivalent) |
|<-----------+---------------------------------------->|
| | | |
| | | |
Figure 13: An example case for IPsec-TIA obtained by using IKE
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PRPA
PaC AP DHCPv4 Server PAA
| Link-layer | | |
| association| | |
|<---------->| | |
| | | |
| DHCPv4 | |
|<-----------+-------->| |
| | |
|PANA(Discovery and initial handshake phase
| & PAR-PAN exchange in authentication phase)
|<-----------+-------------------------->|
| | |
| | EP(AR) |
| | |Authorization|
| | |[IKE-PSK, |
| | | PaC-DI, |
| | | Session-Id] |
| | |<------------|
| | | |
|PANA(PBR-PBA exchange in authentication phase)
|<-----------+-------------------------->|
| | |
| IKEv1 phase I & II |
| (to create DHCP SA) |
|<-----------+------------>|
| | |
| DHCP over DHCP SA |
|<-----------+------------>|
| | |
| IKEv1 phase II |
| (to create IPsec SA for data traffic)
|<-----------+------------>|
Figure 14: An example case for configuring IPsec-TIA by using
RFC3456
10.2.1.2 IPv6
In the case of IPv6, the IPsec-TOA (PRPA) is the IPv6 link-local
address. IPsec-TIA (POPA) is obtained by using Configuration Payload
exchange of IKE version 2 (Note that there is no standard method for
configuring IPsec-TIA in IKEv1). Other configuration information may
be obtained in the same Configuration Payload exchange or may be
obtained by running an additional DHCPv6.
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PaC AP EP(AR) PAA
| Link-layer | | |
| association| | |
|<---------->| | |
| | | |
| | | |
|PANA(Discovery and Initial Handshake phase
| & PAR-PAN exchange in Authentication phase)
|<-----------+-------------------------->|
| | | |
| | | |
| | |Authorization|
| | |[IKE-PSK, |
| | | PaC-DI, |
| | | Session-Id] |
| | |<------------|
| | | |
|PANA(PBR-PBA exchange in authentication phase)
|<-----------+-------------------------->|
| | | |
| IKEv2 | |
|(w/Configuration Payload | |
| exchange to obtain IPsec-TIA) |
|<-----------+------------>| |
| | | |
Figure 15: An example sequence for configuring IPsec-TIA in IPv6
10.2.2 PANA with Bootstrapping WPA/IEEE 802.11i
In this model, PANA is used for authentication and authorization, and
L2 ciphering is used for access control, the latter is enabled by the
former. The L2 ciphering is based on using PSK (Pre-Shared Key) mode
of WPA (Wi-Fi Protected Access) [WPA] or IEEE 802.11i [802.11i],
which is derived from the EAP MSK as a result of successful PANA
authentication. In this document, the pre-shared key shared between
station and AP is referred to as PMK (Pair-wise Master Key). In this
model, MAC address is used as the device identifier in PANA.
A typical purpose of using this model is to reduce AP management cost
by allowing physical separation of RADIUS/Diameter client from access
points, where AP management can be a significant issue when deploying
a large number of access points.
By bootstrapping PSK mode of WPA and IEEE 802.11i from PANA it is
also possible to improve wireless LAN security by providing protected
disconnection procedure at L3.
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This model does not require any change in the current WPA and IEEE
802.11i specifications. This also means that PANA doesn't provide
any L2 security features beyond those already provided for in WPA and
IEEE 802.11i.
10.2.2.1 Separate PAA and AP
When PAA and AP are separated, two (virtual) APs are needed, one is
connected to an unauthenticated VLAN and the other to an
authenticated VLAN. The former and latter APs are referred to as
unauthenticated VLAN AP and authenticated VLAN AP, respectively. If
a PaC does not have a PMK with the authenticated VLAN AP, it runs
PANA on the unauthenticated VLAN to obtain the MAC address of the
authenticated VLAN AP and derive the PMK valid for the AP. Once the
PMK is obtained, the PaC associates with the authenticated VLAN AP
with performing 4-way handshake. It configures an (potentially new)
IP address and starts sending and receiving data traffic. Future
PANA exchanges are carried on the IEEE 802.1X Controlled Port of the
authenticated VLAN AP just like any other data traffic.
Separating PAA and AP may be used in a network where there is a large
number of APs in a single IP subnet and the network administrator
want to avoid setting up RADIUS client on each AP. Note that the
network administrator would still need to set up SNMPv3 security
association between each AP and PAA for secure PAA-EP communication,
however, in the environments where operator can rely on physical
layer security between PAA and EP, this might not be the case.
In a typical usage scenario, a single PAA co-located with DHCP server
is connected to both unauthenticated VLAN and authenticated VLAN and
that the unauthenticated VLAN AP and the authenticated VLAN AP are
co-located in a single physical AP, as shown in Figure 16. Note that
in an environment where virtual AP are not supported, physical APs
can be used instead of virtual APs.
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+------------------+
| Physical AP |
| +--------------+ |
| |Virtual AP1 | | Unauthenticated
| |(open-access) |---- VLAN \
| | | | \+-------+
+---+ | +--------------+ | |PAA/AR/|
|PaC| | | |DHCP |--- Internet
+---+ | +--------------+ | |Server |
| |Virtual AP2 | | /+-------+
| |(WPA PSK mode)|---- Authenticated /
| | | | VLAN
| +--------------+ |
| |
+------------------+
Figure 16: Separate PAA and AP with two virtual APs
When a PaC does not have a PMK with an authenticated VLAN AP, the
following procedure is taken:
1. The PaC associates with the unauthenticated VLAN AP.
2. The PaC configures a PRPA by using DHCP (in the case of IPv4) or
configures a link-local address (in the case of IPv6), and then
runs PANA by using the address.
3. Upon successful authentication, the PaC obtains a distinct PMK
for each authenticated VLAN AP controlled by the PAA.
4. The PaC associated with an authenticated VLAN AP, with performing
4-way handshake to establish a PTK (Pair-wise Transient Key)
between the PaC and AP, by using the PMK.
5. If the PaC is required to configure a new IP address (POPA) as
signaled by the PAA at the end of successful authentication, it
should configure POPA by using any method that the client
normally uses. If PRPA is an IPv4 address, it should be
unconfigured before POPA configuration.
Note that switching from one VLAN to another is a commonly used
technique in WPA (even without PANA) where the client that does not
have any valid credentials first accesses the certificate server via
https through the unauthenticated VLAN to perform a sign-in procedure
to obtain a certificate, and then switches to the authenticated VLAN
with the obtained certificate.
When the MSK is updated as a result of EAP re-authentication, a new
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PMK is derived for and transfered to each authenticated VLAN AP.
WPA/IEEE 802.11i 4-way handshake is performed between the PaC and its
currently associating authenticated VLAN AP to derive a new PTK.
10.2.2.2 Co-located PAA and AP
The IEEE 802.11 specification [802.11] allows Class 1 data frames to
be received in any state. Also, the latest version of IEEE 802.11i
[802.11i] optionally allows higher-layer data traffic that is
terminated between stations (including AP) are received and processed
on their IEEE 802.1X Uncontrolled Ports. This feature allows
processing IP-based traffic (such as ARP, IPv6 neighbor discovery,
DHCP, and PANA) on IEEE 802.1X Uncontrolled Port prior to client
authentication. (Note: WPA and its corresponding version of IEEE
802.11i draft do not explicitly define this operation, so it may be
safer not to use this co-located PAA and AP case in WPA).
Until the PaC is successfully authenticated, only a selected type of
IP traffic is allowed over the IEEE 802.1X Uncontrolled Port. Any
other IP traffic is dropped on the AP without forwarding to the DS
(Distribution System). Upon successful PANA authentication, the
traffic switches to the controlled port. Host configuration,
including obtaining an (potentially new) IP address, takes place on
this port. Usual DHCP-based, and also in the case of IPv6 stateless
autoconfiguration, mechanism is available to the PaC. After this
point, the rest of the IP traffic, including PANA exchanges, are
processed on the controlled port.
Since this case does not require virtual AP switching, the procedure
to bootstrap PSK mode becomes simpler compared to the separate PAA
and EP case, however, with a cost of configuring RADIUS/Diameter
client on each AP.
When a PaC does not have a PMK with an authenticated VLAN AP, the
following procedure is taken:
1. The PaC associates with the AP.
2. The PaC configures a PRPA by using DHCP (in the case of IPv4) or
configures a link-local address (in the case of IPv6), and then
runs PANA by using the address.
3. Upon successful authentication, the PaC obtains a PMK for each AP
controlled by the PAA.
4. The PaC performs 4-way handshake to establish a PTK (Pair-wise
Transient Key) between the PaC and AP, by using the PMK.
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5. The PaC obtains a POPA by using any method that the client
normally uses.
10.2.3 Capability Discovery
When a PaC is a mobile, there may be multiple APs available in its
vicinity. Each AP are connected to one of the following types of
access networks.
a) Free access network
There is no IEEE 802.1X or PANA authentication in this access
network.
b) PANA-secured network
There is PANA authentication in this access network.
c) IEEE 802.1X-secured network
There is IEEE 802.1X authentication in this access network.
Type (c) is distinguished from others by checking the capability
information advertised in IEEE 802.11 Beacon frames (IEEE 802.11i
defines RSN Information Element for this purpose). Types (a) and (b)
are not distinguishable until the PaC associates with the AP, get an
IP address, and engage in PANA discovery. The default PaC behavior
would be to act as if this is a free network and attempt DHCP. This
would be detected by the access network and trigger unsolicited PANA
discovery. A type (b) network would send a PANA-Start-Request to the
client and block general purpose data traffic. This helps the client
discover whether the network is type (a) or type (b). Or if the PaC
is pre-provisioned with the information that this is a PANA enabled
network, it can attempt PAA discovery immediately.
The PaC behavior after connecting to an AP of type (b) network is
described in Section 10.2, Section 10.2.1 and Section 10.2.2. Note
that in case of using PANA for bootstrapping WPA/IEEE 802.11i PSK
mode (see Section 10.2.2), PaC needs to know whether PAA and AP are
separated (see Section 10.2.2.1) or co-located (see Section 10.2.2.2)
due to PaC having to act differently in each mode. This is achieved
by checking the existence of an EP-Device-Id AVP in PANA-Bind-Request
message (if an EP-Device-Id AVP is included then PAA is not
co-located with AP).
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11. Open Issue
Certain combination of network environments and timing cases may
require further considerations.
If PaC changes access point right after a successful PANA
authorization but before POPA configuration, it might be confused
whether the new IP address configured via the new access point is the
POPA of the ongoing session or a PRPA of a new session. When the PRPA
and POPA types or configuration mechanisms are different this is not
a problem. One possible combination where such clues are not
available is when PaC moves from a Case A of Section 10.2.1.1
(IPsec-TIA obtained by using DHCPv4) network to a Case D of Appendix
A.1 (IPsec-TIA obtained by using RFC3118) network.
In another example, when PaC switches from one wired Ethernet hub to
another (without the use of bootstrapping IPsec) before configuring
the POPA. In this case, PaC may not able to know whether an obtained
address is the POPA in the same subnet or a PRPA in a new subnet.
For these cases, a mechanism to remove the ambiguity (PRPA vs. POPA)
may need to be defined.
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12. Acknowledgments
We would like to thank Bernard Aboba and Yacine El Mghazli for their
valuable comments.
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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.
[I-D.ietf-eap-rfc2284bis]
Blunk, L., "Extensible Authentication Protocol (EAP)",
draft-ietf-eap-rfc2284bis-09 (work in progress), February
2004.
[RFC3377] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[I-D.ietf-zeroconf-ipv4-linklocal]
Aboba, B., "Dynamic Configuration of Link-Local IPv4
Addresses", draft-ietf-zeroconf-ipv4-linklocal-14 (work in
progress), April 2004.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[I-D.ietf-ipsec-ikev2]
Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-13 (work in progress), March 2004.
[I-D.ietf-pana-snmp]
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Mghazli, Y., Ohba, Y. and J. Bournelle, "SNMP usage for
PAA-2-EP interface", draft-ietf-pana-snmp-00 (work in
progress), April 2004.
[I-D.ietf-pana-pana]
Forsberg, D., "Protocol for Carrying Authentication for
Network Access (PANA)", draft-ietf-pana-pana-03 (work in
progress), February 2004.
[I-D.ietf-pana-ipsec]
Parthasarathy, M., "PANA enabling IPsec based Access
Control", draft-ietf-pana-ipsec-02 (work in progress),
March 2004.
[I-D.ietf-eap-netsel-problem]
Arkko, J. and B. Aboba, "Network Discovery and Selection
Problem", draft-ietf-eap-netsel-problem-00 (work in
progress), January 2004.
[RFC2486] Aboba, B. and M. Beadles, "The Network Access Identifier",
RFC 2486, January 1999.
[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.yegin-eap-boot-rfc3118]
Yegin, A., Tschofenig, H. and D. Forsberg, "Bootstrapping
RFC3118 Delayed DHCP Authentication Using EAP-based
Network Access Authentication",
draft-yegin-eap-boot-rfc3118-00 (work in progress),
February 2004.
[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.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
[RFC3456] Patel, B., Aboba, B., Kelly, S. and V. Gupta, "Dynamic
Host Configuration Protocol (DHCPv4) Configuration of
IPsec Tunnel Mode", RFC 3456, January 2003.
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Informative References
[I-D.ietf-aaa-eap]
Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application",
draft-ietf-aaa-eap-05 (work in progress), April 2004.
[I-D.josefsson-pppext-eap-tls-eap]
Josefsson, S., Palekar, A., Simon, D. and G. Zorn,
"Protected EAP Protocol (PEAP)",
draft-josefsson-pppext-eap-tls-eap-07 (work in progress),
October 2003.
[I-D.ietf-pppext-eap-ttls]
Funk, P. and S. Blake-Wilson, "EAP Tunneled TLS
Authentication Protocol (EAP-TTLS)",
draft-ietf-pppext-eap-ttls-04 (work in progress), April
2004.
[I-D.tschofenig-eap-ikev2]
Tschofenig, H. and D. Kroeselberg, "EAP IKEv2 Method
(EAP-IKEv2)", draft-tschofenig-eap-ikev2-03 (work in
progress), February 2004.
[DSL] DSL Forum Architecture and Transport Working Group, "DSL
Forum TR-058 Multi-Service Architecture and Framework
Requirements", September 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/D10.0,
2004.
[802.11] Institute of Electrical and Electronics Engineers,
"Information technology - telecommunications and
information exchange between systems - local and
metropolitan area networks - specific requirements part
11: Wireless lan medium access control (mac) and physical
layer (phy) specifications", IEEE Standard 802.11,
1999(R2003).
[WPA] The Wi-Fi Alliance, "WPA (Wi-Fi Protected Access)", Wi-Fi
WPA v2.0, 2003.
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Authors' Addresses
Prakash Jayaraman
Network Equipment Technologies, Inc.
6900 Paseo Padre Parkway
Fremont, CA 94555
USA
Phone: +1 510 574 2305
EMail: prakash_jayaraman@net.com
Rafa Marin Lopez
University of Murcia
30071 Murcia
Spain
EMail: rafa@dif.um.es
Yoshihiro Ohba
Toshiba America Research, Inc.
1 Telcordia Drive
Piscateway, NJ 08854
USA
Phone: +1 732 699 5365
EMail: yohba@tari.toshiba.com
Mohan Parthasarathy
Nokia
313 Fairchild Drive
Mountain View, CA 94043
USA
Phone: +1 408 734 8820
EMail: mohanp@sbcglobal.net
Alper E. Yegin
Samsung Advanced Institute of Technology
75 West Plumeria Drive
San Jose, CA 95134
USA
Phone: +1 408 544 5656
EMail: alper.yegin@samsung.com
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Appendix A. Other Possible Cases for PANA with Bootstrapping IPsec in
Wireless LAN
This section describes other possible cases for PANA with
Bootstrapping IPsec in wireless LAN environments.
Appendix A.1 IPv4
Case D: IPsec-TIA obtained by using RFC3118
In this case, the POPA is configured and used as both IPsec-TIA
and IPsec-TOA. The IPsec-TIA is assigned by using RFC3118
(authenticated DHCP) [RFC3118] before running IKE. The DHCP-PSK
needed for authenticated DHCP is distributed from the PAA to the
POPA DHCPv4 server by using the method specified in
[I-D.yegin-eap-boot-rfc3118]. The PRPA is assigned by using
DHCPv4 and may be assigned with a short lease period in order to
provide some level of robustness against IP address depletion
attack. The IPsec-TIA is bound to an IPsec SA by using specifying
the IPsec-TIA as the SA Identification in IKEv1 phase II or IKEv2
CREATE_CHILD_SA exchange as specified in [I-D.ietf-pana-ipsec].
Once the IPsec-TIA is obtained, the PANA re-authentication based
on PRAR (PANA Re-Authentication Request) and PRAA (PANA
Re-Authentication Answer) exchange is performed with using the
obtained IPsec-TIA in order to inform PAA of the update of PaC-DI.
The IKE procedure should occur after the PRAR-PRAA exchange
procedure. The PaC unconfigures the PRPA immediately after the
IPsec-TIA is obtained.
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PRPA
PaC AP DHCPv4 Server PAA EP(AR)
| Link-layer | | | |
| association| | | |
|<---------->| | | |
| | | | |
| DHCPv4 | | |
|<-----------+--------->| | |
| | | | |
|PANA(Discovery and Initial Handshake phase |
| & PAR-PAN exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | |
| | | |
| | POPA | |
| | DHCPv4 Server |Authorization|
| | |Authorization|[IKE-PSK, |
| | |[DHCP-PSK, | PaC-DI, |
| | | Session-Id] | Session-Id] |
| | |<------------|------------>|
| | | | |
|PANA(PBR-PBA exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| Authenticated DHCPv4 | | |
| (RFC3118) | | |
|<-----------+------------>| | |
| | | | |
| PANA(PRAR-PRAA exchange using POPA as PaC-DI) |
|<-----------+-------------------------->| |
| | | | |
| | IKE | |
|<-----------+---------------------------------------->|
| | | | |
| | | | |
Figure 17: An example case for IPsec-TIA obtained by using RFC3118
Appendix A.2 IPv6
Case A: IPsec-TIA obtained by using DHCPv6
This case is similar to Case A in IPv4, except that a link-local
address is used as the PRPA and IPsec-TOA, and that the DHCPv6
procedure can occur at any time after link-layer association and
before IKE.
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This case is not recommended since there is an ambiguity on
whether IPv6 Neighbor Discovery for the POPA should run on the
physical interface or inside the IPsec tunnel or both.
PaC AP DHCPv6 Server PAA EP(AR)
| Link-layer | | | |
| association| | | |
|<---------->| | | |
| | | | |
| DHCPv6 | | |
|<-----------+------------>| | |
| | | | |
|PANA(Discovery and Initial Handshake phase |
| & PAR-PAN exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| | | |Authorization|
| | | |[IKE-PSK, |
| | | | PaC-DI, |
| | | | Session-Id] |
| | | |------------>|
| | | | |
|PANA(PBR-PBA exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| | IKE | |
|<-----------+---------------------------------------->|
| | | | |
| | | | |
Figure 18: An example case for IPsec-TIA obtained by using DHCPv6
Case B: IPsec-TIA obtained by using IPv6 stateless address
autoconfiguration
In this case, the IPsec-TOA (link-local address) and IPsec-TIA
(global address) are configured through IPv6 stateless address
autoconfiguration before running IKE. Other configuration
information can be obtained by using several methods including
authenticated DHCPv6, Configuration Payload exchange and DHCPv6
over IPsec SA.
This case is not recommended for the same reason as Case A of
IPv6.
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PaC AP PAA EP(AR)
| Link-layer | | |
| association| | |
|<---------->| | |
| | | |
| | | |
|PANA(Discovery and Initial Handshake phase |
| & PAR-PAN exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | |
| | |Authorization|
| | |[IKE-PSK, |
| | | PaC-DI, |
| | | Session-Id] |
| | |------------>|
| | | |
|PANA(PBR-PBA exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | |
| IPv6 stateless address autoconfiguration |
| (can occur at any time before Association and IKEv2) |
|<-----------+---------------------------------------->|
| | | |
| | IKEv2 | |
|<-----------+---------------------------------------->|
| | | |
Figure 19: An example sequence for IPsec-TIA obtained by using
IPv6 stateless address autoconfiguration
Case C: IPsec-TIA obtained by using authenticated DHCPv6
This case is similar to Case C of IPv4, except that a link-local
address is used as the PRPA, and that there is no need for
additional PRAR-PRAA exchange to update the PaC-DI.
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PaC AP DHCPv6 Server PAA EP(AR)
| Link-layer | | | |
| association| | | |
|<---------->| | | |
| | | | |
| | | | |
|PANA(Discovery and Initial Handshake phase |
| & PAR-PAN exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| | |Authorization|Authorization|
| | |[DHCP-PSK, |[IKE-PSK, |
| | | Session-Id] | PaC-DI, |
| | | | Session-Id] |
| | |<------------|------------>|
| | | | |
|PANA(PBR-PBA exchange in Authentication phase) |
|<-----------+-------------------------->| |
| | | | |
| Authenticated DHCPv6 | | |
|<-----------+------------>| | |
| | | | |
| PANA(PRAR-PRAA exchange using POPA as PaC-DI)
|<-----------+-------------------------->| |
| | | |Authorization|
| | | | [IKE-PSK, |
| | | | PaC-DI, |
| | | | Session-Id]|
| | | |------------>|
| | IKE | |
|<-----------+---------------------------------------->|
| | | | |
| | | | |
Figure 20: An example case for configuring IPsec-TIA by using
authenticated DHCPv6
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