MIP6 Working Group G. Giaretta
Internet Draft I. Guardini
Expires: Ocotber 29 2005 E. Demaria
TILab
J. Bournelle
GET/INT
R. Lopez
Univ. of Murcia
April 2005
Goals for AAA-HA interface
draft-ietf-mip6-aaa-ha-goals-00.txt
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Abstract
In commercial deployments Mobile IPv6 can be a service offered by a
Mobility Services Provider (MSP). In this case all protocol
operations may need to be explicitely authorized and traced. A
convenient approach to do that is to define an interface between the
Home Agent (HA) and the AAA infrastructure of the MSP, which stores
user's credentials and service profiles. The availability of this
interface can be useful also to enable dynamic Mobile IPv6
bootstrapping on both the mobile node and the designated HA.
Internet-Draft AAA-HA interface goals September 2004
This document describes various scenarios where an interface between
the HA and the AAA infrastructure of the MSP is required.
Furthermore, a list of design goals for this interface is provided.
Conventions used in this document
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 RFC-2119 [1].
Table of Contents
1. Introduction................................................3
2. Motivation..................................................4
3. Basic security model........................................5
4. Bootstrapping scenarios.....................................6
4.1 Scenario 1...............................................6
4.2 Scenario 2...............................................6
4.3 Scenario 3...............................................7
4.4 Scenario 4...............................................8
5. Goals for the AAA-HA interface..............................9
5.1 General goals............................................9
5.2 Service Authorization....................................9
5.3 Accounting..............................................10
5.4 Mobile Node Authentication..............................10
5.5 Provisioning of configuration parameters................10
6. Mapping between goals and scenarios........................11
7. IANA Considerations........................................12
8. Security Considerations....................................13
9. Acknowledgment.............................................14
10. References.................................................15
10.1 Normative References..................................15
10.2 Informative References................................15
AuthorsÆ Addresses..............................................16
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1. Introduction
Mobile IPv6 [2] was originally designed as a standalone protocol to
handle terminal mobility relying on a centralized and pre-configured
Home Agent (HA). Nonetheless, if Mobile IPv6 is a service offered by
a Mobility Services Provider (MSP), all protocol operations may need
to be explicitely authorized and traced (e.g. for accounting
purposes). A convenient approach to achieve this result is to define
an interface between the AAA infrastructure of the MSP and the HA.
Such an interface may be useful also in some Mobile IPv6 dynamic
bootstrapping scenarios [3].
This document describes various scenarios for which an interface
between the HA and the AAA infrastructure of the MSP is useful.
Furthermore, a list of goals for such an interface is provided.
No assumptions are made on the protocol used to implement the
interface. An obvious choice may be the employment of a AAA protocol
such as RADIUS or Diameter. Nonetheless, for some scenarios, other
non AAA protocols such as SNMPv3 [5] or COPS-PR [6] may satisfy all
the goals described herewith.
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2. Motivation
Mobile IPv6 specification [2] requires that Mobile Nodes (MNs) are
provisioned with a set of configuration parameters, namely the Home
Address and the Home Agent Address, in order to accomplish a home
registration. Moreover MNs and Home Agents (HAs) must share the
cryptographic material needed to protect Mobile IPv6 signaling (e.g.
shared keys or certificates to setup an IPsec security association).
The simplest option is to statically provision all the necessary
configuration data on MNs and HAs. This solution raises obvious
scalability issues especially in a large network with a lot of users
(e.g. a mobile operator network). For this reason the dynamic Mobile
IPv6 bootstrapping problem is currently under study [3].
In case Mobile IPv6 is a service offered by a Mobility Service
Provider (MSP) all protocol operations (e.g. home registrations) may
need to be explicitely authorized and monitored (e.g. for accounting
purposes). This can be accomplished relying on the AAA
infrastructure of the MSP, that stores users' service profiles and
credentials.
The deployment of this service model requires the availability of an
interface between the AAA infrastructure and the HA, that can be
seen as the Network Access Server (NAS) for Mobile IPv6. The core
capabilities that should be supported by this interface include
Mobile IPv6 service authorization and maintenance (e.g. asynchronous
service termination) as well as the exchange of accounting data.
This is the basic set of features needed in any Mobile IPv6
bootstrapping scenario (i.e. static or dynamic).
Moreover, whenever static provisioning is not feasible, the AAA
infrastructure of the MSP can be used as the central element to
build a dynamic Mobile IPv6 bootstrapping solution. In this case the
AAA infrastructure can be exploited also to send to the designated
HA the needed configuration parameters (e.g. keying material) as
well as to assist the HA with mobile node authentication.
There is therefore space for the definition of a general AAA-HA
communication interface capable to support the basic features
described above (e.g. authorization and accounting) as well as the
extended capabilities (e.g. transfer of configuration data) needed
to enable various dynamic Mobile IPv6 bootstrapping scenarios.
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3. Basic security model
The basic security model behind this draft assumes that the mobile
node shares a pre-configured trust relationship with the AAA server
of the MSP (AAAH), as stated in [3]. Furthermore the HA is expected
to share a trust relationship with the AAAH server (see Figure 1).
MN AAAH HA
^ ^ ^ ^
| | | |
+----------------+ +---------------+
trust relationship trust relationship
Figure 1 - Basic Model
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4. Bootstrapping scenarios
This section describes some bootstrapping scenarios in which a
communication between the AAA infrastructure of the Mobility Service
Provider and the Home Agent is needed. These scenarios include both
dynamic (Scenario 1 and Scenario 2) and static (Scenario 3 and
Scenario 4) bootstrapping.
4.1 Scenario 1
In this scenario, depicted in Figure 2, the MN discovers the Home
Agent address (e.g. by means of a new DNS SRV record or DHCP) and
performs an IKEv2 [4] exchange with the HA to setup the IPsec SA
needed to protect mobility signaling. Eventually, during this
handshake, the MN can also obtain a valid Home Address from the HA.
The MN is not expected to share a pre-configured trust relationship
with the HA, nor to share a secret with it. For this reason, peer
authentication in IKEv2 can be performed through an EAP exchange.
The HA, behaving as an EAP authenticator operating in pass-through
mode, forwards this EAP exchange to the AAAH server, that can
authenticate the MN and authorize the Mobile IPv6 service.
Therefore, in this case an interface between the HA and the AAAH
server is needed at least for authentication and authorization
purposes.
MN AAAH HA
<---------- IKEv2(EAP) -------->
<--------->
AAA-HA protocol
Figure 2 - Dynamic MIPv6 bootstrapping through IKEv2 and EAP
4.2 Scenario 2
In this scenario Mobile IPv6 bootstrapping is performed during
network access authentication (it is assumed that the access
provider and the MSP are the same entity, i.e. Integrated ASP [3])
and the AAA server of the MSP (AAAH) controls the whole
bootstrapping procedure interacting with both the mobile node and
the designated HA.
The AAAH server and the MN can exploit AAA routing to exchange
configuration data. Possible approaches to implement this
communication are the following:
- if network access authentication is carried out using EAP, it is
possible to piggyback Mobile IPv6 configuration parameters (e.g.
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Home Agent address, Home Address) within the EAP exchange [7]. See
Figure 3;
- alternatively, Mobile IPv6 parameters can be transferred to the
Network Access Server (NAS) by means of RADIUS or Diameter AVPs
[8] and then forwarded to the MN through other means (e.g. L2-
specific extensions, DHCP [9]). See Figure 4 for an example.
In both cases, the AAAH server must communicate with the designated
HA to select a suitable Home Address for the MN and to deliver to
the HA the necessary configuration parameters (e.g. pre-shared key
for IKE bootstrapping). Therefore in this scenario an interface
between the AAAH server and the HA must be defined for parameter
exchange as well as authentication and Mobile IPv6 service
authorization.
MN AAAH HA
<------------------------> <-------->
Piggybacking of MIPv6 AAA-HA protocol
data within EAP
Figure 3 - MIPv6 bootstrapping with piggybacking within EAP
MN NAS AAAH HA
<----------> <---------> <-------->
L2-specific MIPv6 AAA-HA protocol
extensions RADIUS AVPs
Figure 4 - MIPv6 bootstrapping with RADIUS AVPs
4.3 Scenario 3
In this scenario the MN is statically provisioned with the data
needed to bootstrap Mobile IPv6 service (i.e. Home Agent Address,
Home Address and a shared secret with the HA). For example, the MN
can be configured with a pre-shared key to dynamically establish an
IPsec Security Association with the HA using IKE.
However, in general the static configuration of these parameters and
the authentication performed through the pre-shared key may not be
sufficient to conclude that the MN is authorized for MIPv6 service.
For example, the MSP might want to prevent the usage of MIPv6 if the
the credit of the MN is going to exhaust. Moreover, there might be
the need for the MSP to enforce more complex dynamic authorization
policies based on time of day and/or visited location.
This implies that during the IKE exchange the HA must communicate
with the AAAH server in order to explicitly authorize MIPv6 service
for that particular MN. See Figure 5.
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MN AAAH HA
<-------------- IKE ------------>
<----------->
AAA-HA protocol
Figure 5 - Mobile IPv6 authorization with static boostrapping
4.4 Scenario 4
In this scenario, the IPsec SA between MN and HA is statically and
manually configured, thus the MN does not need to perform an IKE
exchange with the HA. The MN activates MIPv6 service, sending a
Binding Update message to the HA in order to update its location.
The presence of the IPsec SA between MN and HA is enough in order to
authenticate the binding management messages. However, it is not
enough to authorize MIPv6 service; thus, as soon as it receives a
Binding Update, the HA must explicitly authorize MIPv6 service
interacting with the AAAH server (Figure 6). For this purpose, an
interface between the HA and the AAAH is needed at least for
authorization purposes.
If deemed necessary, the explicit authorization of Binding Updates
based on the handshake depicted in Figure 5 can be used also in the
bootstrapping scenarios described in the previous sections. It may
be useful to enforce dynamic authorization policies, such as those
based on the MN's location.
MN AAAH HA
------------ BU ------------>
<----------->
AAA-HA protocol
<----------- BA -------------
Figure 6 - Binding Update Authorization
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5. Goals for the AAA-HA interface
The motivations and scenarios illustrated in previous sections raise
the need to define an interface between the AAAH server and the HA.
The following sections list a set of goals for this interface.
5.1 General goals
G1.1 The AAAH server and the HA must be able to authenticate each
other (mutual authentication) in order to prevent the
installation of unauthorized state on the HA.
G1.2 The AAA-HA interface must provide integrity protection in
order to prevent any alteration of exchanged data (e.g. Mobile
IPv6 configuration parameters).
G1.3 The AAA-HA interface must provide replay protection.
G1.4 The AAA-HA interface should provide confidentiality since it
may be used to transfer security parameters (e.g. IKE pre-
shared key).
G1.5 The AAA-HA interface should support inactive peer detection.
This functionality can be used by the AAAH server to maintain
a list of active HAs (e.g. useful for HA selection).
5.2 Service Authorization
G2.1 The AAA-HA interface should allow the use of Network Access
Identifier (NAI) to identify the mobile node.
G2.2 The HA should be able to query the AAAH server to verify
Mobile IPv6 service authorization for the mobile node.
G2.3 The AAAH server should be able to enforce explicit operational
limitations and authorization restrictions on the HA (e.g.
packet filters, QoS parameters).
G2.4 The AAAH server should be able to send an authorization
lifetime to the HA to limit Mobile IPv6 session duration for
the MN.
G2.5 The HA should be able to request to the AAAH server an
extension of the authorization lifetime granted to the MN.
G2.6 The AAAH server should be able to force the HA to terminate an
active Mobile IPv6 session for authorization policy reasons
(e.g. credit exhaustion).
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G2.7 The AAAH server should be able to retreive the Mobile IPv6
state associated to a specific MN from the correspondent HA.
This may be useful to periodically verify the Mobile IPv6
service status.
5.3 Accounting
G3.1 The AAA-HA interface must support the transfer of accounting
records needed for service control and charging. These include
(but may not be limited to): time of binding cache entry
creation and deletion, octets sent and received by the mobile
node in Bi-directional Tunneling, etc.
5.4 Mobile Node Authentication
G4.1 The AAA-HA interface should support MN authentication (and re-
authentication) with the HA working as NAS and the AAAH server
working as back-end authentication server.
G4.2 The AAA-HA interface should support at least pass-through EAP
authentication with the HA working as EAP authenticator
operating in pass-through mode and the AAAH server working as
back-end authentication server.
5.5 Provisioning of configuration parameters
G5.1 The AAAH server should be able to poll the designated HA for
the allocation of a Home Address to the MN. Optionally, the
AAAH server can provide a set of hints for the construction of
the Home Address (e.g. a preferred Home Address or a preferred
Interface Identifier).
G5.2 The HA should be able to communicate to the AAAH server the
Home Address allocated to the MN.
G5.3 The AAAH server should be able to send to the HA the security
data needed to setup the IPsec SA between the MN and the HA.
Possible security data are the authentication method and the
cryptographic material to be used for IKE bootstrapping.
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6. Mapping between goals and scenarios
The table below shows which goals, among those listed in section 5,
are strictly (X) or optionally (O) required for each of the
scenarios discussed in section 4.
Section +---------------------------------------+
Defined Goals | Scen. 1 | Scen. 2 | Scen. 3 | Scen. 4 |
-------------------+---------|---------|---------|---------|
G1.1 | X | X | X | X |
G1.2 | X | X | X | X |
5.1 G1.3 | X | X | X | X |
G1.4 | O | X | O | O |
G1.5 | X | X | X | X |
-------------------|---------|---------|---------|---------|
G2.1 | X | X | O | O |
G2.2 | X | X | X | X |
G2.3 | X | X | X | X |
5.2 G2.4 | X | X | X | X |
G2.5 | X | X | X | X |
G2.6 | X | X | X | X |
G2.7 | X | X | X | X |
-------------------|---------|---------|---------|---------|
5.3 G3.1 | X | X | X | X |
-------------------|---------|---------|---------|---------|
5.4 G4.1 | X | | | |
G4.2 | X | | | |
-------------------|---------|---------|---------|---------|
G5.1 | | X | | |
5.5 G5.2 | | X | | |
G5.3 | | X | | |
-------------------+---------+---------+---------+---------+
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7. IANA Considerations
No new message formats or services are defined in this document.
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8. Security Considerations
As stated in section 5.1 the AAA-HA interface must provide mutual
authentication, integrity and replay protection. Furthermore, if
security parameters (e.g. IKE pre-shared key) are transferred
through this interface, confidentiality support is also required.
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9. Acknowledgment
The authors would like to thank James Kempf, Alper Yegin, Vijay
Devarapalli, Basavaraj Patil, Gopal Dommety and Hannes Tschofenig
for their comments and feedback.
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10. References
10.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
10.2 Informative References
[3] Patel, A. et al. "Problem Statement for bootstrapping Mobile IPv6",
draft-ietf-mip6-bootstrap-ps-02 (work in progress), March 2005.
[4] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-17 (work in progress), September 2004.
[5] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction and
Applicability Statements for Internet-Standard Management
Framework", RFC 3410, December 2002.
[6] K. Chan, D. Durham, S. Gai, S. Herzog, K. McCloghrie, F.
Reichmeyer, J. Seligson, A. Smith, R. Yavatkar, "COPS Usage for
Policy Provisioning,", RFC 3084, March 2001.
[7] Giaretta, G., Guardini, I., Demaria, E., Bournelle, J., Laurent-
Maknavicius, M., "MIPv6 Authorization and Configuration based on
EAP", draft-giaretta-mip6-authorization-eap-02 (work in progress),
September 2004.
[8] Chowdhury, K. and Lior, A., "RADIUS Attributes for Mobile IPv6
bootstrapping", draft-chowdhury-mip6-bootstrap-radius-01 (work in
progress), October 2004.
[9] Jang, H. J. and Yegin, A., "DHCP Option for Home Agent Discovery in
MIPv6", draft-jang-dhc-haopt-01 (work in progress), April 2005.
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AuthorsÆ Addresses
Gerardo Giaretta
Telecom Italia Lab
via G. Reiss Romoli, 274
10148 TORINO
Italy
Phone: +39 011 2286904
Email: gerardo.giaretta@tilab.com
Ivano Guardini
Telecom Italia Lab
via G. Reiss Romoli, 274
10148 TORINO
Italy
Phone: +39 011 2285424
Email: ivano.guardini@tilab.com
Elena Demaria
Telecom Italia Lab
via G. Reiss Romoli, 274
10148 TORINO
Italy
Phone: +39 011 2285403
Email: elena.demaria@tilab.com
Julien Bournelle
GET/INT
9 rue Charles Fourier
Evry 91011
France
Email: julien.bournelle@int-evry.fr
Rafa Marin Lopez
University of Murcia
30071 Murcia
Spain
EMail: rafa@dif.um.es
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