Network Working Group A. Yegin, Ed.
Internet-Draft Samsung AIT
Expires: December 9, 2004 Y. Ohba
Toshiba
R. Penno
Nortel Networks
G. Tsirtsis
Flarion
C. Wang
ARO/NCSU
June 10, 2004
Protocol for Carrying Authentication for Network Access (PANA)
Requirements
draft-ietf-pana-requirements-08.txt
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Copyright Notice
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Abstract
It is expected that future IP devices will have a variety of access
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technologies to gain network connectivity. Currently there are
access-specific mechanisms for providing client information to the
network for authentication and authorization purposes. In addition
to being limited to specific access media (e.g., 802.1X for IEEE 802
links), some of these protocols are limited to specific network
topologies (e.g., PPP for point-to-point links). The goal of this
document is to identify the requirements for a link-layer agnostic
protocol that allows a host and a network to authenticate each other
for network access. This protocol will run between a client's device
and an agent in the network where the agent might be a client of the
AAA infrastructure.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1 Authentication . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1 Authentication of Client . . . . . . . . . . . . . . . 6
4.1.2 Authorization, Accounting and Access Control . . . . . 7
4.1.3 Authentication Backend . . . . . . . . . . . . . . . . 8
4.1.4 Identifiers . . . . . . . . . . . . . . . . . . . . . 8
4.2 IP Address Assignment . . . . . . . . . . . . . . . . . . 9
4.3 EAP Lower Layer Requirements . . . . . . . . . . . . . . . 9
4.4 PAA-to-EP Protocol . . . . . . . . . . . . . . . . . . . . 9
4.5 Network . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.5.1 Multi-access . . . . . . . . . . . . . . . . . . . . . 10
4.5.2 Disconnect Indication . . . . . . . . . . . . . . . . 10
4.5.3 Location of PAA . . . . . . . . . . . . . . . . . . . 10
4.5.4 Secure Channel . . . . . . . . . . . . . . . . . . . . 11
4.6 Interaction with Other Protocols . . . . . . . . . . . . . 11
4.7 Performance . . . . . . . . . . . . . . . . . . . . . . . 11
4.8 Congestion Control . . . . . . . . . . . . . . . . . . . . 11
4.9 IP Version Independence . . . . . . . . . . . . . . . . . 12
4.10 Denial of Service Attacks . . . . . . . . . . . . . . . . 12
4.11 Client Identity Privacy . . . . . . . . . . . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1 Normative References . . . . . . . . . . . . . . . . . . . . 16
8.2 Informative References . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17
A. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 19
B. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . 24
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1. Introduction
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 parameters between the client and the access network.
See Appendix for the associated problem statement.
The protocol design will be limited to defining a messaging protocol
(i.e., a carrier) that will allow authentication payload to be
carried between the host/client and an agent/server in the access
network for authentication and authorization purposes regardless of
the AAA infrastructure that may (or may not) reside on the network.
As a network-layer protocol, it will be independent of the underlying
access technologies. It will also be applicable to any network
topology.
The intent is not to invent new security protocols and mechanisms but
to reuse existing mechanisms such as EAP [RFC2284]
[I-D.ietf-eap-rfc2284bis]. In particular, the requirements do not
mandate the need to define new authentication protocols (e.g.,
EAP-TLS [RFC2716]), key distribution or key agreement protocols, or
key derivation methods. The desired protocol can be viewed as the
front-end of the AAA protocol or any other protocol/mechanisms the
network is running at the background to authenticate its clients. It
will act as a carrier for an already defined security protocol or
mechanism.
As an example, the Mobile IP Working Group has already defined such a
carrier for Mobile IPv4 [RFC3344]. A Mobile IPv4 registration
request message is used as a carrier for authentication extensions
(MN-FA [RFC3344] or MN-AAA [RFC3012]) that allow a foreign agent to
authenticate mobile nodes before providing forwarding service. The
goal of PANA is similar in that it aims to define a network-layer
transport for authentication information; however, PANA will be
decoupled from mobility management and it will rely on other
specifications for the definition of authentication payloads.
This document defines the common terminology and identifies the
requirements of a protocol for PANA. These terminology and
requirements will be used to define and limit the scope of the work
to be done in this group.
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2. Requirements notation
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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3. Terminology
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.
PANA Client Identifier (PaCI)
The identifier that is presented by the PaC to the PAA for network
access authentication. A simple username and NAI [RFC2794] are
examples of PANA client identifiers.
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.
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.
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4. Requirements
4.1 Authentication
4.1.1 Authentication of Client
PANA MUST enable authentication of PaCs for network access. A PaC's
identity can be authenticated by verifying the credentials (e.g.,
identifier, authenticator) supplied by one of the users of the device
or the device itself. PANA MUST only grant network access service to
the device identified by the DI, rather than granting separate access
to multiple simultaneous users of the device. Once the network
access is granted to the device, the methods used by the device on
arbitrating which one of its users can access the network is outside
the scope of PANA.
PANA MUST NOT define new security protocols or mechanisms. Instead,
it MUST be defined as a "carrier" for such protocols. PANA MUST
identify which specific security protocol(s) or mechanism(s) it can
carry (the "payload"). EAP is a candidate protocol that satisfies
many of the requirements for authentication. PANA would be a carrier
protocol for EAP. If the PANA Working Group decides that extensions
to EAP are needed, it will define requirements for the EAP WG instead
of designing such extensions.
Providing authentication, integrity and replay protection for data
traffic after a successful PANA exchange is outside the scope of this
protocol. In networks where physical layer security is not present,
link-layer or network-layer ciphering (e.g., IPsec) can be used to
provide such security. These mechanisms require presence of
cryptographic keying material at PaC and EP. Although PANA does not
deal with key derivation or distribution, it enables this by the
virtue of carrying EAP and allowing appropriate EAP method selection.
Various EAP methods are capable of generating basic keying material.
The keying material produced by EAP methods cannot be directly used
with IPsec as it lacks the properties of an IPsec SA (security
association) which include secure cipher suite negotiation, mutual
proof of possession of keying material, freshness of transient
session keys, key naming, etc. These basic (initial) EAP keys can be
used with an IPsec key management protocol like IKE to generate the
required security associations. A separate protocol, called secure
association protocol, is required to generate IPsec SAs based on the
basic EAP keys. This protocol MUST be capable of enabling
IPsec-based access control on the EPs. IPsec SAs MUST enable
authentication, integrity and replay protection of data packets as
they are sent between the EP and PaC.
Providing a complete secure network access solution by also securing
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router discovery [RFC1256], neighbor discovery [RFC2461], and
address resolution protocols [RFC1982] is outside the scope as well.
Some access networks might require or allow their clients to get
authenticated and authorized by the NAP (network access provider) and
ISP before the clients gain network access. NAP is the owner of the
access network who provides physical and link-layer connectivity to
the clients. PANA MUST be capable of enabling two independent
authentication operations (i.e., execution of two separate EAP
methods) for the same client. Determining the authorization
parameters as a result of two separate authentications is an
operational issue and therefore it is outside the scope of PANA.
Both the PaC and the PAA MUST be able to perform mutual
authentication for network access. Providing only the capability of
a PAA authenticating the PaC is not sufficient. Mutual
authentication capability is required in some environments but not in
all of them. For example, clients might not need to authenticate the
access network when physical security is available (e.g., dial-up
networks).
PANA MUST be capable of carrying out both periodic and on-demand
re-authentication. Both the PaC and the PAA MUST be able to initiate
both the initial authentication and the re-authentication process.
Certain types of service theft are possible when the DI is not
protected during or after the PANA exchange
[I-D.ietf-pana-threats-eval]. PANA MUST have the capability to
exchange DI securely between the PAC and PAA where the network is
vulnerable to man-in-the-middle attacks. While PANA MUST provide
such a capability, its utility relies on the use of an authentication
method that can generate keys for cryptographic computations on PaC
and PAA.
4.1.2 Authorization, Accounting and Access Control
After a device is authenticated by using PANA, it MUST be authorized
for "network access." That is, the core requirement of PANA is to
verify the authorization of a PaC so that PaC's device may send and
receive any IP packets. It may also be possible to provide finer
granularity authorization, such as authorization for QoS or
individual services (e.g., http vs. ssh). However, while a backend
authorization infrastructure (e.g., Diameter) might provide such
indications to the PAA, explicit support for them is outside the
scope of PANA. For instance, PANA is not required to carry any
indication of which services are authorized for the authenticated
device.
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Providing access control functionality in the network is outside the
scope of PANA. Client access authentication SHOULD be followed by
access control to make sure only authenticated and authorized clients
can send and receive IP packets via the access network. Access
control can involve setting access control lists on the EPs.
Identification of clients that are authorized to access the network
is done by the PANA protocol exchange. If IPsec-based access control
is deployed in an access network, PaC and EPs should have the
required IPsec SA in place. Generating the IPsec SAs based on EAP
keys is outside the scope of PANA protocol. This transformation MUST
be handled by a separate secure association protocol (see section
4.1.1).
Carrying accounting data is outside the scope of PANA.
4.1.3 Authentication Backend
PANA protocol MUST NOT make any assumptions on the backend
authentication protocol or mechanisms. A PAA MAY interact with
backend AAA infrastructures such as RADIUS or Diameter, but it is not
a requirement. When the access network does not rely on an
IETF-defined AAA protocol (e.g., RADIUS, Diameter), it can still use
a proprietary backend system, or rely on the information locally
stored on the authentication agents.
The interaction between the PAA and the backend authentication
entities is outside the scope of PANA.
4.1.4 Identifiers
PANA SHOULD allow various types of identifiers to be used as the PaCI
(e.g., username, NAI, FQDN, etc.). This requirement generally relies
on the client identifiers supported by various EAP methods.
PANA SHOULD allow various types of identifiers to be used as the DI
(e.g., IP address, link-layer address, port number of a switch,
etc.).
A PAA MUST be able to create a binding between the PaCI and the
associated DI upon successful PANA exchange. This can be achieved by
PANA communicating the PaCI and DI to the PAA during the protocol
exchange. The DI can be carried either explicitly as part of the
PANA payload, or implicitly as the source of the PANA message, or
both. Multi-access networks also require use of a cryptographic
protection along with DI filtering to prevent unauthorized access
[I-D.ietf-pana-threats-eval]. The keying material required by the
cryptographic methods needs to be indexed by the DI. The binding
between DI and PaCI is used for access control and accounting in the
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network as described in section 4.1.2.
4.2 IP Address Assignment
Assigning an IP address to the client is outside the scope of PANA.
PaC MUST configure an IP address before running PANA.
4.3 EAP Lower Layer Requirements
The EAP protocol itself imposes various requirements on its transport
protocols. These requirements are based on the nature of the EAP
protocol, and they need to be satisfied for correct operation.
Please see [I-D.ietf-eap-rfc2284bis] for the generic transport
requirements that MUST be satisfied by PANA as well.
4.4 PAA-to-EP Protocol
PANA does not assume that the PAA is always co-located with the
EP(s). Network access enforcement can be provided by one or more
nodes on the same IP subnet as the client (e.g., multiple routers),
or on another subnet in the access domain (e.g., gateway to the
Internet, depending on the network architecture). When the PAA and
the EP(s) are separated, there needs to be another transport for
client provisioning. This transport is needed to create access
control lists to allow authenticated and authorized clients' traffic
through the EPs. PANA Working Group will preferably identify an
existing protocol solution that allows the PAA to deliver the
authorization information to one or more EPs when the PAA is
separated from EPs. Possible candidates include but are not limited
to COPS, SNMP, Diameter, etc. This task is similar to what the
MIDCOM Working Group is trying to achieve, therefore some of that
working group's output might be useful here.
It is assumed that the communication between PAA and EP(s) is secure.
The objective of using a PAA-to-EP protocol is to provide filtering
rules to EP(s) for allowing network access of a recently
authenticated and authorized PaC. The chosen protocol MUST be
capable of carrying DI and cryptographic keys for a given PaC from
PAA to EP. Depending on the PANA protocol design, support for either
of the pull model (i.e., EP initiating the PAA-to-EP protocol
exchange per PaC) or the push model (i.e., PAA initiating the
PAA-to-EP protocol exchange per PaC), or both may be required. For
example, if the design is such that the EP allows the PANA traffic to
pass through even for unauthenticated PaCs, the EP should also allow
and expect the PAA to send the filtering information at the end of a
successful PANA exchange without the EP ever sending a request.
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4.5 Network
4.5.1 Multi-access
PANA MUST support PaCs with multiple interfaces, and networks with
multiple routers on multi-access links. In other words, PANA MUST
NOT assume the PaC has only one network interface, or the access
network has only one first hop router, or the PaC is using a
point-to-point link.
4.5.2 Disconnect Indication
PANA MUST NOT assume that the link is connection-oriented. Links may
or may not provide disconnect indication. Such notification is
desirable in order for the PAA to cleanup resources when a client
moves away from the network (e.g., inform the enforcement points that
the client is no longer connected). PANA SHOULD have a mechanism to
provide disconnect indication. PANA MUST be capable of securing
disconnect messages in order to prevent malicious nodes from
leveraging this extension for DoS attacks.
This mechanism MUST allow the PAA to be notified about the departure
of a PaC from the network. This mechanism MUST also allow a PaC to
be notified about the discontinuation of the network access service.
Access discontinuation can happen due to various reasons such as
network systems going down, or a change in the access policy.
In case the clients cannot send explicit disconnect messages to the
PAA, PAA can still detect their departure by relying on periodic
authentication requests.
4.5.3 Location of PAA
The PAA and PaC MUST be exactly one IP hop away from each other.
That is, there must be no IP routers between the two. Note that this
does not mean they are on the same physical link. Bridging
techniques can place two nodes just exactly one IP hop away from each
other although they might be connected to separate physical links. A
PAA can be on the NAS (network access server) or WLAN access point or
first hop router. The use of PANA when the PAA is multiple IP hops
away from the PaC is outside the scope of PANA.
A PaC may or may not be pre-configured with the IP address of PAA.
Therefore the PANA protocol MUST define a dynamic discovery method.
Given that the PAA is one hop away from the PaC, there are a number
of discovery techniques that could be used (e.g., multicast or
anycast) by the PaC to find out the address of the PAA.
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4.5.4 Secure Channel
PANA MUST NOT assume presence of a secure channel between the PaC and
the PAA. PANA MUST be able to provide authentication especially in
networks which are not protected against eavesdropping and spoofing.
PANA MUST enable protection against replay attacks on both PaCs and
PAAs.
This requirement partially relies on the EAP protocol and the EAP
methods carried over PANA. Use of EAP methods that provide mutual
authentication and key derivation/distribution is essential for
satisfying this requirement. EAP does not make a secure channel
assumption, and supports various authentication methods that can be
used in such environments. Additionally, PANA MUST ensure its design
does not contain vulnerabilities that can be exploited when it is
used over insecure channels. PANA MAY provide a secure channel by
deploying a two-phase authentication. The first phase can be used
for creation of the secure channel, and the second phase is for
client and network authentication.
4.6 Interaction with Other Protocols
Mobility management is outside the scope of PANA. However, PANA MUST
be able to co-exist and MUST NOT unintentionally interfere with
various mobility management protocols, such as Mobile IPv4 [RFC3344],
Mobile IPv6 [I-D.ietf-mobileip-ipv6], fast handover protocols
[I-D.ietf-mipshop-fast-mipv6][I-D.ietf-mobileip-lowlatency-handoff],
and other standard protocols like IPv6 stateless address
auto-configuration [RFC2461] (including privacy extensions
[RFC3041]), and DHCP [RFC2131][RFC3315]. It MUST NOT make any
assumptions on the protocols or mechanisms used for IP address
configuration of the PaC.
4.7 Performance
PANA design SHOULD give consideration to efficient handling of the
authentication process. This is important for gaining network access
with minimum latency. As an example, a method like minimizing the
protocol signaling by creating local security associations can be
used for this purpose.
4.8 Congestion Control
PANA MUST provide congestion control for the protocol messaging.
Under certain conditions PaCs might unintentionally get synchronized
when sending their requests to the PAA (e.g., upon recovering from a
power outage on the access network). The network congestion
generated from such events can be avoided by using techniques like
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delayed initialization and exponential back off.
4.9 IP Version Independence
PANA MUST work with both IPv4 and IPv6.
4.10 Denial of Service Attacks
PANA MUST be robust against a class of DoS attacks such as blind
masquerade attacks through IP spoofing that would swamp the PAA,
causing it to spend resources and prevent network access by
legitimate clients.
4.11 Client Identity Privacy
Some clients might prefer hiding their identity from visited access
networks for privacy reasons. Providing identity protection for
clients is outside the scope of PANA. Note that some authentication
methods may already have this capability. Where necessary, identity
protection can be achieved by letting PANA carry such authentication
methods.
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5. IANA Considerations
This document has no actions for IANA.
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6. Security Considerations
This document identifies requirements for the PANA protocol design.
Due to the nature of this protocol most of the requirements are
security related. The actual protocol design is not specified in
this document. A thorough discussion on PANA security threats can be
found in PANA Threat Analysis and Security Requirements document
[I-D.ietf-pana-threats-eval]. Security threats identified in that
document are already included in this general PANA requirements
document.
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7. Acknowledgements
Authors would like to thank Bernard Aboba, Derek Atkins, Julien
Bournelle, Subir Das, Francis Dupont, Dan Forsberg, Pete McCann,
Lionel Morand, Thomas Narten, Mohan Parthasarathy, Basavaraj Patil,
Hesham Soliman, and the PANA Working Group members for their valuable
contributions to the discussions and preparation of this document.
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8. References
8.1 Normative References
[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2284] Blunk, L. and J. Vollbrecht, "PPP Extensible
Authentication Protocol (EAP)", RFC 2284, March 1998.
8.2 Informative References
[I-D.ietf-eap-rfc2284bis]
Blunk, L., "Extensible Authentication Protocol (EAP)",
draft-ietf-eap-rfc2284bis-09 (work in progress), February
2004.
[I-D.ietf-mipshop-fast-mipv6]
Koodli, R., "Fast Handovers for Mobile IPv6",
draft-ietf-mipshop-fast-mipv6-01 (work in progress),
February 2004.
[I-D.ietf-mobileip-ipv6]
Johnson, D., Perkins, C. and J. Arkko, "Mobility Support
in IPv6", draft-ietf-mobileip-ipv6-24 (work in progress),
July 2003.
[I-D.ietf-mobileip-lowlatency-handoff]
Malki, K., "Low latency Handoffs in Mobile IPv4",
draft-ietf-mobileip-lowlatency-handoffs-v4-09 (work in
progress), June 2004.
[IEEE-802.1X]
Institute of Electrical and Electronics Engineers, "Local
and Metropolitan Area Networks: Port-Based Network Access
Control", IEEE Standard 802.1X, September 2001.
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
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[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
August 1996.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access
Identifier Extension for IPv4", RFC 2794, March 2000.
[RFC3012] Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/
Response Extensions", RFC 3012, November 2000.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[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.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
Authors' Addresses
Alper E. Yegin (editor)
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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Yoshihiro Ohba
Toshiba America Research, Inc.
1 Telcordia Drive
Piscataway, NJ 08854
USA
Phone: +1 732 699 5305
EMail: yohba@tari.toshiba.com
Reinaldo Penno
Nortel Networks
600 Technology Park
Billerica, MA 01821
USA
Phone: +1 978 288 8011
EMail: rpenno@nortelnetworks.com
George Tsirtsis
Flarion
Bedminster One
135 Route 202/206 South
Bedminster, NJ 07921
USA
Phone: +44 20 88260073
EMail: G.Tsirtsis@Flarion.com, gtsirt@hotmail.com
Cliff Wang
ARO/NCSU
316 Riggsbee Farm
Morrisville, NC 27560
USA
Phone: +1 919 548 4207
EMail: cliffwangmail@yahoo.com
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Appendix A. Problem Statement
Access networks in most cases require some form of authentication in
order to prevent unauthorized usage. In the absence of physical
security (and sometimes in addition to it) a higher layer (L2+)
access authentication mechanism is needed. Depending on the
deployment scenarios, a number of features are expected from the
authentication mechanism. For example, support for various
authentication methods (e.g., MD5, TLS, SIM, etc.), network roaming,
network service provider discovery and selection, separate
authentication for access (L1+L2) service provider and ISP (L3), etc.
In the absence of a link-layer authentication mechanism that can
satisfy these needs, operators are forced to either use non-standard
ad-hoc solutions at layers above the link, insert additional shim
layers for authentication, or misuse some of the existing protocols
in ways that were not intended by design. PANA will be developed to
fill this gap by defining a standard network-layer access
authentication protocol. As a network-layer access authentication
protocol, PANA can be used over any link-layer that supports IP.
DSL networks are a specific example where PANA has the potential for
addressing some of the deployment scenarios therein. Some DSL
deployments do not use PPP as the access link-layer (IP is carried
over ATM and the subscriber device is either statically- or
DHCP-configured). The operators of these networks are either left
with using an application-layer web-based login (captive portal)
scheme for subscriber authentication, or providing a best-effort
service only as they cannot perform subscriber authentication
required for the differentiated services. The captive portal scheme
is a non-standard solution that has various limitations and security
flaws.
PPP-based authentication can provide some of the required
functionality. But using PPP only for authentication is not a good
choice, as it incurs additional messaging during the connection setup
and extra per-packet processing, and it forces the network topology
to a point-to-point model. Aside from resistance to incorporating
PPP into an architecture unless it is absolutely necessary, there is
even interest in the community to remove PPP from some of the
existing architectures and deployments (e.g., 3GPP2, DSL).
Using Mobile IPv4 authentication with a foreign agent instead of
proper network access authentication is an example of protocol
misuse. Registration Required flag allows a foreign agent to force
authentication even when the agent is not involved in any Mobile IPv4
signalling (co-located care-of address case), hence enabling the use
of a mobility-specific protocol for an unrelated functionality.
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PANA will carry EAP above IP in order to enable any authentication
method on any link-layer. EAP can already be carried by IEEE 802.1X
and PPP. IEEE 802.1X can only be used on unbridged IEEE 802 links,
hence it only applies to limited link types. Inserting PPP between
IP and a link-layer can be perceived as a way to enable EAP over that
particular link-layer, but using PPP for this reason has the
aforementioned drawbacks, hence not a good choice. While IEEE 802.1X
and PPP can continue to be used in their own domains, they do not
take away the need to have a protocol like PANA.
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Appendix B. Usage Scenarios
PANA will be applicable to various types of networks. Based on the
presence of lower-layer security prior to running PANA, the following
types cover all possibilities:
a) Physically secured networks (e.g., DSL networks). Although data
traffic is always carried over a physically secured link, the client
might need to be authenticated and authorized when accessing the IP
services.
b) Networks where L1-L2 is already cryptographically secured before
enabling IP (e.g., cdma2000 networks). Although the client is
authenticated on the radio link before enabling ciphering, it
additionally needs to get authenticated and authorized for accessing
the IP services.
c) No lower-layer security present before enabling IP. PANA is run
in an insecure network. PANA-based access authentication is used to
bootstrap cryptographic per-packet authentication and integrity
protection.
PANA is applicable to not only large-scale operator deployments with
full AAA infrastructure, but also to small disconnected deployments
like home networks and personal area networks.
Since PANA enables decoupling AAA from the link-layer procedures,
network access authentication does not have to take place during the
link establishment. This allows deferring client authentication
until the client attempts to access differentiated services (e.g.,
high bandwidth, unlimited access, etc.) in some deployments.
Additionally multiple simultaneous network access sessions over the
same link-layer connection can be realized as well.
Following scenarios capture the PANA usage model in different network
architectures with reference to its placement of logical elements
such as the PANA Client (PaC) and the PANA Authentication Agent (PAA)
with respect to the Enforcement Point (EP) and the Access Router
(AR). Five different scenarios are described in following
sub-sections. Note that PAA may or may not use AAA infrastructure to
verify the credentials of PaC to authorize network access.
Scenario 1: PAA co-located with EP but separated from AR
In this scenario (Figure 1), PAA is co-located with the enforcement
point on which access control is performed. This might be the case
where PAA is co-located with the L2 access device (e.g., an
IP-capable switch).
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PaC -----EP/PAA--+
|
+------ AR ----- (AAA)
|
PaC -----EP/PAA--+
Figure 1: PAA co-located with EP but separated from AR.
Scenario 2: PAA co-located with AR but separated from EP
In this scenario, PAA is not co-located with EPs but it is placed on
the AR. Although we have shown only one AR here there could be
multiple ARs, one of which is co-located with the PAA. Access
control parameters have to be distributed to the respective
enforcement points so that the corresponding device on which PaC is
authenticated can access to the network. A separate protocol is
needed between PAA and EP to carry access control parameters.
PaC ----- EP --+
|
+------ AR/PAA --- (AAA)
|
PaC ----- EP --+
Figure 2: PAA co-located with AR but separated from EP
Scenario 3: PAA co-located with EP and AR
In this scenario (Figure 3), PAA is co-located with the EP and AR on
which access control and routing are performed.
PaC ----- EP/PAA/AR--+
|
+-------(AAA)
|
PaC ----- EP/PAA/AR--+
Figure 3: PAA co-located with EP and AR.
Scenario 4: Separated PAA, EP, and AR
In this scenario, PAA is neither co-located with EPs nor with ARs.
It still resides on the same IP link as ARs. After the successful
authentication, access control parameters will be distributed to
respective enforcement points via a separate protocol and PANA does
not play any explicit role in this.
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PaC ----- EP -----+--- AR ---+
| |
PaC ----- EP --- -+ |
| |
PaC ----- EP -----+--- AR -- + ----(AAA)
|
+--- PAA
Figure 4: PAA, EP and AR separated.
Scenario 5: PAA separated from co-located EP and AR
In this scenario, EP and AR are co-located with each other bu
separated from PAA. PAA still resides on the same IP link as ARs.
After the successful authentication, access control parameters will
be distributed to respective enforcement points via a separate
protocol and PANA does not play any explicit role in this.
PaC --------------+--- AR/EP ---+
| |
PaC --------------+ |
| |
PaC --------------+--- AR/EP -- + ----(AAA)
|
+--- PAA
Figure 5: PAA separated from EP and AR.
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