Network Working Group P. Jayaraman

Network Working Group P. Jayaraman
Request for Comments: 5193 Net.Com
Category: Informational R. Lopez
Univ. of Murcia
Y. Ohba, Ed.
Toshiba
M. Parthasarathy
Nokia
A. Yegin
Samsung
May 2008

Protocol for Carrying Authentication for Network Access (PANA) Framework

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Abstract

This document defines the general Protocol for Carrying
Authentication for Network Access (PANA) framework functional
elements, high-level call flow, and deployment environments.

Table of Contents

1. Introduction ....................................................2
1.1. Specification of Requirements ..............................2
2. General PANA Framework ..........................................2
3. Call Flow .......................................................5
4. Environments ....................................................6
5. Security Considerations .........................................8
6. Acknowledgments .................................................8
7. References ......................................................8
7.1. Normative References .......................................8
7.2. Informative References .....................................9

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1. Introduction

PANA (Protocol for carrying Authentication for Network Access) is a
link-layer agnostic network access authentication protocol that runs
between a client that wants to gain access to the network and a
server on the network side. PANA defines a new Extensible
Authentication Protocol (EAP) [RFC3748] lower layer that uses IP
between the protocol end points.

The motivation to define such a protocol and the requirements are
described in [RFC4058]. Protocol details are documented in
[RFC5191]. Upon following a successful PANA authentication, per-
data-packet security can be achieved by using physical security,
link-layer ciphering, or IPsec [PANA-IPSEC]. The server
implementation of PANA may or may not be colocated with the entity
enforcing the per-packet access control function. When the server
for PANA and per-packet access control entities are separate, a
protocol (e.g., [ANCP-PROTO]) may be used to carry information
between the two nodes.

PANA is intended to 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. While it is mandatory for
a PANA deployment to implement behavior that ensures the integrity of
PANA messages when the EAP method produces MSK, it is not mandatory
to implement support for network security at the link-layer or
network-layer.

This document defines the general framework for describing how these
various PANA and other network access authentication elements
interact with each other, especially considering the two basic types
of deployment environments (see Section 4).

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].

2. General PANA Framework

PANA is designed to facilitate the authentication and authorization
of clients in access networks. PANA is an EAP [RFC3748] lower layer
that carries EAP authentication methods encapsulated inside EAP
between a client node and a server in the access network. While PANA

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enables the authentication process between the two entities, it is
only a part of an overall AAA (Authentication, Authorization and
Accounting) and access control framework. A AAA and access control
framework using PANA is comprised of four functional entities.

Figure 1 illustrates these functional entities and the interfaces
(protocols, APIs) among them.

RADIUS,
Diameter,
+-----+ PANA +-----+ LDAP, API, etc. +-----+
| PaC |<----------------->| PAA |<------------------->| AS |
+-----+ +-----+ +-----+
^ ^
| |
| +-----+ |
IKE, +-------->| EP |<--------+ ANCP, API, etc.
4-way handshake, +-----+
etc. .
.
.
v
Data traffic

Figure 1: PANA Functional Model

PANA Client (PaC):

The PaC is the client implementation of PANA. This entity resides
on the node that is requesting network access. PaCs can be end
hosts, such as laptops, PDAs, cell phones, desktop PCs, or routers
that are connected to a network via a wired or wireless interface.
A PaC is responsible for requesting network access and engaging in
the authentication process using PANA.

PANA Authentication Agent (PAA):

The PAA is the server implementation of PANA. 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 node 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.
AAA protocols like RADIUS [RFC2865] and Diameter [RFC3588] are
commonly used for this purpose.

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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 (EPs) in the network. If the PAA and EP
are residing on the same node, an API is sufficient for this
communication. Otherwise, a protocol is required to carry the
authorized client attributes from the PAA to the EP.

The PAA resides on a node that is typically called a NAS (network
access server) in the access network. For example, on a BRAS
(Broadband Remote Access Server) [DSL] in DSL networks, or PDSN
(Packet Data Serving Node) [3GPP2] in 3GPP2 networks. The PAA may
be one or more IP hops away from the PaCs.

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). This is the server that terminates the EAP
and the EAP methods. The AS might be hosted on the same node as
the PAA, on a dedicated node on the access network, or on a
central server somewhere in the Internet.

Enforcement Point (EP):

The access control implementation that is in charge of allowing
access (data traffic) of authorized clients while preventing
access by others. An EP learns the attributes of the authorized
clients from the PAA.

The EP uses non-cryptographic or cryptographic filters to
selectively allow and discard data packets. These filters may be
applied at the link layer or the IP layer [PANA-IPSEC]. When
cryptographic access control is used, a secure association
protocol [RFC3748] needs to run between the PaC and EP. After
completion of the secure association protocol, link- or network-
layer per-packet security (for example TKIP, IPsec ESP) is enabled
for integrity protection, data origin authentication, replay
protection, and optionally confidentiality protection.

An EP is located between the access network (the topology within
reach of any client) and the accessed network (the topology within
reach of only authorized clients). It must be located
strategically in a local area network to minimize the access of
unauthorized clients. It is recommended but not mandated that the

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EP be on the path between the PaC and the PAA for the
aforementioned reason. 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 node or nodes beyond the local area
network.

Some of the entities may be colocated depending on the deployment
scenario. For example, the PAA and EP would be on the same node
(BRAS) 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 colocate
these entities or otherwise, and their precise location in the
network topology, are deployment decisions that are out of the scope
of this document.

3. Call Flow

Figure 2 illustrates the signaling flow for authorizing a client for
network access.

PaC EP PAA AS
| | | |
IP address ->| | | |
config. | PANA | | AAA |
|<------------------------------>|<-------------->|
| | Provisioning | |
(Optional) | |<-------------->| |
IP address ->| | | |
reconfig. | Sec.Assoc. | | |
|<------------->| | |
| | | |
| Data traffic | | |
|<-----------------> | |
| | | |

Figure 2: PANA Signaling Flow

The EP on the access network allows general data traffic from any
authorized PaC, whereas it allows only a limited type of traffic
(e.g., PANA, DHCP, router discovery, etc.) 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 dynamically or statically configures an IP address prior to
running PANA. After the successful PANA authentication, depending on

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the deployment scenario, the PaC may need to re-configure its IP
address or configure additional IP address(es). For example, a
link-local IPv6 address may be used for PANA and the PaC may be
allowed to configure additional global IPv6 address(es) upon
successful authentication. Another example: A PaC may be limited to
using an IPv4 link-local address during PANA, and allowed to
reconfigure its interface with a non-link-local IPv4 address after
the authentication. General-purpose applications cannot use the
interface until PANA authentication succeeds and appropriate IP
address configuration takes place.

An initially unauthorized PaC starts PANA authentication by
discovering the PAA, followed by the EAP exchange over PANA. The PAA
interacts 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 access to the network, the PAA also
sends the PaC-specific attributes (e.g., IP address, cryptographic
keys, etc.) to the EP by using another protocol. The EP uses this
information to alter its filters to allow data traffic from and to
the PaC to pass through.

In case cryptographic access control needs to be enabled after PANA
authentication, a secure association protocol runs between the PaC
and the EP. Dynamic parameters required for that protocol (e.g.,
endpoint identity, shared secret) are derived from successful PANA
authentication; these parameters are used to authenticate the PaC to
the EP and vice-versa as part of creating the security association.
For example, see [PANA-IPSEC] for how it is done for IKE [RFC2409]
[RFC4306] based on using a key-generating EAP method for PANA between
the PaC and PAA. The secure association protocol exchange produces
the required security associations between the PaC and the EP to
enable cryptographic data traffic protection. Per-packet
cryptographic data traffic protection introduces additional per-
packet overhead but the overhead exists only between the PaC and EP
and will not affect communications beyond the EP.

Finally, filters that are installed at the EP allow general purpose
data traffic to flow between the PaC and the intranet/Internet.

4. Environments

PANA can be used on any network environment whether there is a
lower-layer secure channel between the PaC and the EP prior to PANA,
or one has to be enabled upon successful PANA authentication.

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With regard to network access authentication, two types of networks
need to be considered:

a. Networks where a secure channel is already available prior to
running PANA

This type of network is characterized by the existence of
protection against spoofing and eavesdropping. Nevertheless, user
authentication and authorization is required for network
connectivity.

a.1. One example is a DSL network where lower-layer security is
provided by a physical means. Physical protection of the
network wiring ensures that practically there is only one
client that can send and receive IP packets on the link.

a.2. Another example is a cdma2000 network where the lower-layer
security is provided by means of cryptographic protection.
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 the PANA exchange
eliminates the need for executing a secure association protocol
after PANA. The PANA session can be associated with the
communication channel it was carried over. Also, the choice of
EAP authentication method depends on the presence of this security
while PANA is running.

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. Successful PANA authentication enables the
generation of cryptographic keys that are used with a secure
association protocol to enable per-packet cryptographic
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
association protocol.

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Whether to use

b.1. link-layer per-packet security or

b.2. network-layer per-packet security

is a deployment decision and outside the scope of this document.
This decision also dictates the choice of the secure association
protocol. If link-layer protection is used, the protocol would be
link-layer specific. If IP-layer protection is used, the secure
association protocol would be IKE and the per-packet security
would be provided by IPsec AH/ESP regardless of the underlying
link-layer technology.

5. Security Considerations

Security is discussed throughout this document. For protocol-
specific security considerations, refer to [RFC4016] and [RFC5191].

6. Acknowledgments

We would like to thank Bernard Aboba, Yacine El Mghazli, Randy
Turner, Hannes Tschofenig, Lionel Morand, Mark Townsley, Jari Arkko,
Pekka Savola, Tom Yu, Joel Halpern, Lakshminath Dondeti, David Black,
and IEEE 802.11 Working Group for their valuable comments.

7. References

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and
H. Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, June 2004.

[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.

[RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.

[RFC4058] Yegin, A., Ed., Ohba, Y., Penno, R., Tsirtsis, G., and
C. Wang, "Protocol for Carrying Authentication for
Network Access (PANA) Requirements", RFC 4058, May 2005.

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[RFC5191] Forsberg, D., Ohba, Y., Ed., Patil, B., Tschofenig, H.,
and A. Yegin, "Protocol for Carrying Authentication for
Network Access (PANA)", RFC 5191, May 2008.

[DSL] DSL Forum Architecture and Transport Working Group, "DSL
Forum TR-059 DSL Evolution - Architecture Requirements
for the Support of QoS-Enabled IP Services", September
2003.

7.2. Informative References

[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.

[RFC4016] Parthasarathy, M., "Protocol for Carrying Authentication
and Network Access (PANA) Threat Analysis and Security
Requirements", RFC 4016, March 2005.

[ANCP-PROTO] Wadhwa, S., Moisand, J., Subramanian, S., Haag, T., and
N. Voigt, "Protocol for Access Node Control Mechanism in
Broadband Networks", Work in Progress, November 2007.

[PANA-IPSEC] Parthasarathy, M., "PANA Enabling IPsec based Access
Control", Work in Progress, July 2005.

[3GPP2] 3rd Generation Partnership Project 2, "cdma2000 Wireless
IP Network Standard", 3GPP2 P.S0001-B/v2.0, September
2004.

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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: [email protected]

Rafa Marin Lopez
University of Murcia
30100 Murcia
Spain

Phone: +34 968 398 501
EMail: [email protected]

Yoshihiro Ohba
Toshiba America Research, Inc.
1 Telcordia Drive
Piscateway, NJ 08854
USA

Phone: +1 732 699 5305
EMail: [email protected]

Mohan Parthasarathy
Nokia
313 Fairchild Drive
Mountain View, CA 94043
USA

Phone: +1 408 734 8820
EMail: [email protected]

Alper E. Yegin
Samsung
Istanbul,
Turkey

EMail: [email protected]

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