One document matched: draft-ietf-mip6-whyauthdataoption-07.txt
Differences from draft-ietf-mip6-whyauthdataoption-06.txt
Network Working Group B. Patil
Internet-Draft Nokia
Intended status: Informational G. Dommety
Expires: May 6, 2009 Cisco
November 2, 2008
Why Authentication Data suboption is needed for MIP6
draft-ietf-mip6-whyauthdataoption-07.txt
Status of this Memo
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Abstract
Mobile IPv6 defines a set of signaling messages that enable the
mobile node (MN) to authenticate and perform registration with its
home agent (HA). These authentication signaling messages between the
mobile node and home agent are secured by an IPsec SA that is
established between the MN and HA. The MIP6 working group has
specified a mechanism to secure the binding update and binding
acknowledgement messages using an authentication option, similar to
the authentication option in Mobile IPv4, carried within the
signaling messages that are exchanged between the MN and HA to
establish a binding. This document provides the justifications as to
why the authentication option mechanism was needed for Mobile IPv6
deployment in certain environments.
Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Applicability Statement . . . . . . . . . . . . . . . . . . . 6
5. Justification for the use of the authentication option . . . . 7
5.1. Motivation for use of authentication option in
cdma2000 wireless networks . . . . . . . . . . . . . . . . 7
5.2. Additional arguments for the use of Authentication
option . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Application of Mobile IPv6 in CDMA Networks . . . . . . . . . 11
6.1. IPv4 based mobility architecture in cdma2000 networks . . 11
6.2. IPv6 based mobility architecture in cdma2000 networks . . 12
6.2.1. Overview of the mobility operation in IPv6 based
cdma2000 networks . . . . . . . . . . . . . . . . . . 13
6.2.2. Authentication and Security details . . . . . . . . . 14
7. Limitations of the Authentication Protocol option . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 21
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . . 23
12.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . . . 26
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1. 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 [RFC2119].
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2. Introduction
Mobile IPv6 relies on the IPsec Security Association between the
Mobile Node (MN) and the Home Agent (HA) for authentication of the MN
to its HA before a binding cache can be created at the HA. An
alternate mechanism that does not rely on the existence of the IPsec
SA between the MN and HA for authenticating the MN is needed in
certain deployment environments. This document captures the reasons
that were outlined, and explains why such a mechanism was considered
essential to ensure the applicability of MIP6 as a protocol for wider
deployment. It was noted that the alternate solution does not imply
that the IPsec based solution would be deprecated. It simply meant
that in certain deployment scenarios there was a need for supporting
MIP6 without an IPsec SA between the MN and HA. So the alternate
solution would be in addition to the IPsec based mechanism specified
in the base RFCs, RFC 3775 [RFC3775], RFC 3776 [RFC3776] and RFC 4877
[RFC4877]. It was noted that some of the challenges of deploying
MIP6 in certain types of networks arose from the dependence on IKE
which did not integrate will with a AAA backend infrastructure.
IKEv2 solves this problem. However at the time of discussion on the
need for the authentication protocol, the specification for using
Mobile IPv6 Operation with IKEv2 and the revised IPsec Architecture
[RFC4877] was still work in progress and as a result an alternative
solution needed. This document is intended to capture for archival
purposes the reasoning behind the need for the authentication
protocol which is specified in [RFC4285]. It should be noted that
some of the arguments for justifying the specification of the
authentication protocol have been made redundant as a result of the
specification of Mobile IPv6 operation with IKEv2 [RFC4877]. However
some of the arguments discussed in this document are still applicable
and justify usage of the authentication protocol in certain
deployment environments.
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3. Background
Mobile IPv6 signaling involves several messages. These include:
o The Binding update/Binding ACK between the mobile node and the
home agent.
o The route optimization signaling messages which include HoTI/Hot,
CoTI/CoT and BU/BAck between the MN and CN. HoTI and HoT
signaling messages are routed through the MNs HA.
o Mobile prefix solicitation and advertisements between the MN and
HA.
o Home agent discovery by MNs.
The signaling messages between the MN and HA are secured using the
IPsec SA that is established between these entities. The exception
to this are the messages involved in the home agent discovery
process. [RFC4877] specifies the establishment of the IPsec SA using
IKEv2.
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4. Applicability Statement
The authentication option specified in the Authentication Protocol
for MIP6 [RFC4285] provides a solution for MIP6 deployment in
environments which an operator may not require IPsec based security
for the signaling. The reasons for an operator choosing to deploy
MIP6 without mandating IPsec based security for signaling messages
between the MN and HA could be many. Some of these are for example:
1. Operators deploying MIP6 in cellular networks may consider IPsec
and IKEv2 as adding overhead to the limited bandwidth over the
air interface. The overhead here is in terms of the bytes that
IPsec and IKEv2 introduce to the signaling.
2. Operators may consider the number of messages between the MN and
HA that are required to establish the IPsec SA as too many. The
number of transactions chew into the capacity of limited
bandwidth air interfaces when MIP6 is used in such environments.
It also adds additional latency to the establishment of the
binding.
3. In many deployments the authentication credentials already exist
in a AAA server. These credentials are used for authenticating a
user and authorizing network access. The same credentials and
security parameters can be reused for MIP6 security as well.
4. Dynamic assignment of home agents is needed in certain
deployments to minmize the latency of the backhaul. This is done
by allocating an HA in a visited network for example. Requiring
IPsec SAs with home agents that are dynamically assigned is an
overhead especially when the HA is in a visited network.
5. Signaling messages between the MN and HA may be in certain
deployments over secure link-layers. The lower layers provide
ciphering and security for the messages and hence the need for
IPsec to do the same for MIP6 messages does not exist.
One such example of networks that have such characteristics are cdma
networks as defined in the 3GPP2 X.S0011-002-D [3GPP2 X.S0011-002-D]
specification. Mobile WiMAX (Worldwide interoperability for
Microwave Access) which is based on IEEE 802.16e also specifies in
the network architecture the use of MIP6, with the default security
for signaling being the authentication protocol (RFC4285). The WiMAX
network architecture specifications are available at: [WiMAX-NWG].
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5. Justification for the use of the authentication option
The following two sections provide the reasoning for standardizing
the authentication option based registration process for Mobile IPv6.
Section 5.1 provides the key arguments for the use of authentication
option. Section 5.2 provides further explanation and additional
motivations for the authentication option.
5.1. Motivation for use of authentication option in cdma2000 wireless
networks
cdma2000 networks deployed and operational today use Mobile IPv4 for
IP mobility. Operators have gained a significant amount of
operational experience in the process of deploying and operating
these networks. 3GPP2 has specified Mobile IPv6 in Revision D of the
3GPP2 X.S0011-002-D [3GPP2 X.S0011-002-D] specification (which
specifies the packet data architecture). The following are the
deployment constraints that existing CDMA networks have to deal with
when deploying Mobility service based on IPv6:
o Operators intend to leverage the Mobile IPv4 deployment and
operational experience by ensuring that Mobile IPv6 has a similar
deployment and operating model.
o Operators will have two parallel networks, one that offers IPv4
mobility with MIP4 and another providing IPv6 mobility using MIP6.
o The same backend subscriber profile database, security keys etc.
are intended to be used for both Mobile IPv4 and, Mobile IPv6
service. However from a security standpoint, the reuse of the
same keys with multiple algorithms/protocols is a bad idea.
o The same user configuration information, i.e the identity and keys
associated with a user will be used for IP mobility service in
IPv4 and/or IPv6 networks. The only security association that is
preconfigured is a shared secret between the mobile node and the
home-AAA server. This was in contrast with an earlier version of
the Mobile IPv6 model which required an IPsec SA between the MN
and HA. At the time of this writing the IKEV2 based solution for
establishing an IPsec SA [RFC4877] was not available. IKEv2 does
enable integration with a a AAA backend.
o At the time of specifying the authentication protocol, the Mobile
IPv6 specification did not support the dynamic assignment of home
agent and home address. However work done in the MIP6 working
group on bootstrapping of Mobile IPv6 as specified in [RFC5026]
and MIP6-bootstrapping for the Integrated Scenario
[I-D.ietf-mip6-bootstrapping-integrated-dhc] addresses this
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deficiency. The mechanism defined in Authentication protocol for
Mobile IPv6 [RFC4285] is capable of handling authentication even
in the case of dynamic assignments (and is similar to what is used
in current MIPv4 deployments).
Consequently, MIP6 as specified at the time the authentication
protocol was being specifid did not satisfy many of the deployment
requirements. The Authentication protocol for MIP6 [RFC4285] along
with the MN Identifier option for MIP6 [RFC4283] are enabling the
deployment of Mobile IPv6 in a manner that is similar to what is
deployed in cdma2000 networks today. This authentication model is
very similar to the one adopted by the MIPv4 WG. This is explained
in detail in the 3GPP2 X.S0011-002-D [3GPP2 X.S0011-002-D]
specification.
The earlier MIP6 deployment model which requires an IPsec SA which is
either configured manually or established using IKE does not have
synergy with the deployment models of 3GPP2 or WiMAX networks. This
issue has however been alleviated with the publication of RFC4877
which enables the establishment of an IPsec SA using IKEv2 and is
also able to integrate with the backend AAA infrastrucuture that is
responsible for the authentication of the MN in 3GPP2 and WiMAX
networks.
5.2. Additional arguments for the use of Authentication option
The use of IPsec for performing Registration with a home agent is not
always an optimal solution. While it is true that IPsec is an
integral part of the IPv6 stack, it is still a considerable overhead
from a deployment perspective of using IPsec as the security
mechanism for the signaling messages between the MN and HA. This
statement is a result of experience gained from deployment of Mobile
IPv4. MIP4 does not rely on IPsec for securing the Registration
signaling messages.
Deployment of Mobile IPv6 on a large scale is possible only when the
protocol is flexible for being adapted to various scenarios. The
scenario being considered is the deployment in cdma2000 net- works or
WiMAX networks. cdma2000 networks are currently deployed in many
countries today and WiMAX deployments are beginning. The packet data
network architecture of cdma2000 [3GPP2 X.S0011-002-D] includes a
MIP4 foreign agent/Home agent and a Radius based AAA infrastrucutre
for authentication, authorization and accounting purposes. The AAA
infrastructure provides the authentication capability in the case of
Mobile IPv4.
Typically, the Mobile Node shares a security association with the
AAA-Home entity. This is the preferred mode of operation over having
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a shared secret between the MN and HA because the AAA-Home entity
provides a central location for provisioning and administering the
shared secrets for a large number of mobiles (millions). This mode
of operation also makes dynamic home address and dynamic home agent
assignment easier. A similar approach is needed for the deployment
of Mobile IPv6 in these networks. There is no practical mechanism to
use IPsec directly with the AAA infrastructure with out the use of
IKE or some other mechanism that enables the establishment of the
IPsec SA between the MN and HA.
Mobile IPv6 as specified in RFC3775 and RFC3776 is based on a very
specific model for deployment. It anticipates the Mobile nodes
having a static home IPv6 address and a designated home agent. This
is not practical in most deployment scenarios being considered. An
IPsec SA is expected to be created, either via manual keying or
established dynamically by using IKE or IKEv2. These assumptions do
not necessarily fit in very well for the deployment model envisioned
in cdma2000 or WiMAX networks. These limitations have however been
overcome as a result of the bootstrapping specifications as per
[RFC5026] and MIP6-bootstrapping for the Integrated Scenario
[I-D.ietf-mip6-bootstrapping-integrated-dhc]
cdma2000 and WiMAX networks would prefer to allocate home addresses
to MNs on a dynamic basis. The advantage of doing so is the fact
that the HA can be assigned on a link that is close to the MNs point
of attachment. While route-optimization negates the benefit of
having a home-agent on a link close to the MN, it cannot be always
guaranteed that the MN and CN will use or support route optimization.
There may also be instances where the operator prefers to not allow
route optimization for various reasons such as accounting aggregation
or enforcing service contracts. In such cases an HA that is close to
the MNs point of attachment reduces the issues of latency etc. of
forward and reverse tunnelling of packets between the MN and HA.
cdma2000 networks that are operational today have large numbers of
subscribers who are authenticated via the AAA infrastrucure.
Deployment of Mobile IPv6 should leverage the existing AAA
infrastructure. The security model needed in these networks is an SA
between the MN and AAA-Home entity. This is the primary security
association that should be used for authenticating and authorizing
users to utilize MIPv6 service. This SA is then used for
establishing session keys between the MN and the dynamically assigned
HA for authenticating subsequent binding updates and binding
acknowledgements between them. Establishing an IPsec SA between the
MN and HA using AAA infrastrucure was not specified for Mobile IPv6
at the time the Authentication protocol was being specified. RFC3776
explains how IKE is used for establishing the SA between the MN and
HA. [RFC4877] has been published subsequently and hence the issue of
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establishing an IPsec SA dynamically between the MN and HA no longer
exists. cdma2000 network operators would prefer to assign home
addresses to the MN on a dynamic basis and do this preferably using
the AAA infrastrucutre which contains subscriber profile and
capability information. This was not possible prior to the
specification of the bootstrapping mechanism in [RFC5026].
A large subset of MNs in cdma2000 networks do not have IKE
capability. As a result the use of RFC3776 for setting up the MN-HA
IPsec SA is not an option. It should also be noted that IKE requires
several transactions before it is able to establish the IPsec SA.
[RFC4877] specifies the establishment of an IPsec SA between the MN
and HA using IKEv2. It is possible that not all MNs in a deployment
will support IKEv2 and hence an alternative mechanism provides the
needed flexibility.
cdma2000 network operators are extremely conscious in terms of the
number of messages sent and received over the air-interface for
signaling. The overhead associated with sending/receiving a large
number of signaling messages over the air interface has a direct
impact on the overall capacity and cost for the operator.
Optimization of the number of messages needed for using a service
like Mobile IPv6 is of great concern. As a result the use of IKE for
Mobile IPv6 deployment is considered as being suboptimal in certain
network architectures and deployment scenarios from the perspective
of message overhead.
Another downside of IKE for setting up the IPsec SA between the MN
and HA is that IKE does not integrate very well with the Radius based
AAA back-end. Since operators rely on the AAA infrastrucure to
provision subscribers as well as define profiles, keys etc. in the
AAA-Home, there is no getting away from the use of AAA in cdma2000
networks. IKEv2 does address this problem. However from a timeline
perspective the availability of IKEv2 specifications for Mobile IPv6
Operation with IKEv2 and the revised IPsec Architecture [RFC4877] and
implementations did not meet the need of operators that were relying
on 3GPP2 specifications. With the specification of IKEv2 and
publication of RFC4877 the integration with AAA backends is no longer
an issue.
In summary the model of Mobile IPv6 deployment which mandated the
existence of an IPsec SA between the MN and HA, as specified in RFCs
3775 and 3776, was too rigid and did not meet the requirements of
operators building networks based on the cdma2000 [3GPP2
X.S0011-002-D] specifications. To address this shortcoming, the
authentication protocol [RFC4285] was specified.
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6. Application of Mobile IPv6 in CDMA Networks
Sections 6.1 and 6.2 describe the IPv4 based mobility architecture in
cdma networks and IPv6 based mobility architecture in cdma Networks
respectively. For further details associated with the description
below, please refer to Section 5, "MIP6 Operation", in 3GPP2
specification [3GPP2 X.S0011-002-D].
6.1. IPv4 based mobility architecture in cdma2000 networks
The figure below shows a high level view of the key network elements
that play a role in providing IP mobility using Mobile IPv4.
+--------------+ +----------------------+
| +------+ | | +------+ |
| | | | | | | |
| |F-AAA | | | |H-AAAH| |
| | +-------------------+ | |
| +---+--+ | | +--+---+ |
| | | | | |
| | | | | |
+------+ | +---+--+ | | +--+---+ |
| | | | | | | | | |
| MN +- -|- -+ PDSN + -- -- -- -- - + HA | |
| | | | /FA | | | | | |
+------+ | +------+ | | +------+ |
| | | |
+--------------+ +----------------------+
Figure 1: cdma2000 packet data network architecture with Mobile IPv4
The cdma mobility architecture based on MIPv4 is explained below. In
this architecture, mobility is tightly integrated with the AAA
infrastructure. The Mobile is configured with a NAI (Network Access
Identifier) and a MN-AAA Key. The MN-AAA key is a shared Key that is
shared between the MN and the Home AAA server.
Below is the access link setup procedure:
(1) Bring up PPP on MN/PDSN (access router link). PPP
authentication is skipped. Mobile IP Authentication is
performed via the FA.
(2) PDSN sends a Mobile IP challenge to the MN on PPP link (RFC
3012).
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(3) MN sends a MIP registration request (RRQ), which includes the
users NAI, challenge and a MN-AAA extension which has challenge
response and a MN-HA extension which is generated based on the
MN-HA key.
(4) PDSN extracts the MIP NAI/Challenge and response from MIP MN-AAA
extension sends an Access Request to F-AAA (challenge/response
using MD5).
(5) F-AAA may forward it to H-AAA if needed (based on realm).
(6) AAA authenticates the chap-challenge/response and returns
"success" if authentication succeeds.
(7) PDSN forwards Registration Request (RRQ) to HA.
(8) HA authenticates the RRQ (MHAE extension). HA may optionally
authenticate with AAA infrastructure (just like PDSN as in #4).
(9) If authentication is successful, HA creates a binding and sends
a success Registration Reply (RRP) to PDSN.
(10) PDSN creates a visitor entry and forwards the RRP to MN.
6.2. IPv6 based mobility architecture in cdma2000 networks
Due to the need for co-existence with MIPv4, and having the same
operational model, the 3GPP2 standards body is adopting the following
mobility architecture for MIPv6.
Access Domain Home Domain
+--------------+ +----------------------+
| +------+ | | +------+ |
| | | | | | | |
| |F-AAA | | | |H-AAA | |
| | +-------------------+ | |
| +---+--+ | | +--+---+ |
| | | | | |
| | | | | |
+------+ | +---+--+ | | +--+---+ |
| | | | | | | | | |
| MN +- -|- -+ PDSN + -- -- -- -- - + HA | |
| | | | /AR | | | | | |
+------+ | +------+ | | +------+ |
| | | |
+--------------+ +----------------------+
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Figure 2: cdma2000 packet data network architecture with Mobile IPv6
The Mobile is configured with an NAI (Network Access Identifier) and
a MN-AAA Key. The MN-AAA key is a shared Key between the MN and the
Home AAA server.
6.2.1. Overview of the mobility operation in IPv6 based cdma2000
networks
The following steps explain at a very generic level the operation of
IP mobility in cdma2000 networks:
(1) The MN performs Link Layer establishment. This includes setting
up the PPP link. PPP-Chap authentication is performed. This is
authenticated by the PDSN/AR by sending an Access Request to the
F-AAA (and to the H-AAA when/if needed). Optionally, the MN
acquires bootstrap information from the Home Network (via the
PDSN; PDSN receives this information in Access Accept). The
bootstrap information includes Home address and Home agent
assignment. The MN uses stateless DHCPv6 [RFC3736] to obtain
the bootstrap information from the PDSN.
(2) The MN begins to use the HoA that was assigned in step 1. If no
HoA was assigned at step 1, the MN generates (auto-configures)
an IPv6 global unicast address based on the prefix information
received at step 1.
(3) At this step the MN sends a Binding Update to the selected Home
Agent. In the BU, the MN includes the NAI option, timestamp
option and MN-AAA auth option.
(4) The HA extracts the NAI, authenticator etc. from the BU and
sends an access request to the Home RADIUS server.
(5) The Home RADIUS server authenticates and authorizes the user and
sends back a RADIUS Access-Accept to the HA indicating
successful authentication and authorization.
(6) At this step the HA performs a replay check with the ID field in
the received BU. The HA also performs proxy Duplicate Address
Detection (DAD) on the MN's home address (global) using proxy
Neighbor Solicitation as specified in RFC 2461.
(7) Assuming that proxy DAD is successful, the HA sends back a
Binding Acknowledgment to the MN. In this BA message the HA
includes the MN-HA mobility option, NAI mobility option and the
ID mobility option.
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6.2.2. Authentication and Security details
Access Link Setup, Access Authentication and Bootstrapping:
(1) MN brings up PPP session. PDSN triggers the MN to perform CHAP
authentication, as part of access authentication, while bringing
up PPP link.
(2) The MN is authenticated using PPP-CHAP by the H-AAA (Home AAA),
via the F-AAA (Foreign AAA).
(3) H-AAA may optionally send HoA and HA IP address to the PDSN for
bootstrapping the MN (skipping details).
Mobile IPv6 Authentication:
The Call Flow for the initial authentication (the number in the
parenthesis corresponds to the explanation below)
MN HA H-AAA
| BU to HA (4) | RADIUS Access-ReQ(5)
|------------------------------------>|------------------->|(6)
| (includes NAI option, MN-ID option, | |
| Mesg ID option, MN-AAA Auth Option) |RADIUS Access-Accept|(7)
|
|<-------------------|
| | |
| HA/AAAH authenticates MN
|
| |(8)
|
| |
|
| BA to MN (9) |
|
|<------------------------------------|--------------------|
| (including MN-ID option, | (10)
| Message ID option, |
| MN-HA auth options) | |
Figure 3: Flow diagram for initial authentication
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(4) MN sends Binding Update (BU) to the HA. Binding Update is
authenticated using MN-AAA option. The authenticator in MN-AAA
option is calculated using hash of BU and MN-AAA shared key. It
uses HMAC_SHA1 algorithm. The SPI field in MN-AAA is set to 3
(defined in the draft) BU also includes NAI and timestamp among
other details. The hash of BU includes the 'timestamp' option
and thus provides proof of liveness to prevent replay.
(5) HA on receiving the BU, extracts the NAI, timestamp,
authenticator from MN-AAA option and generates hash of BU. HA
sends an Access Request to the AAA and puts this information in
3gpp2 defined VSAs (Vendor Specific Attributes). The NAI is put
in username in Access Request. The other attributes sent are:
timestamp option, hash of the BU (till SPI field of MN-AAA auth
option) and the authentication data from MN-AAA auth option.
(6) AAA (Radius server which interprets these attributes),
authenticates the MN based on the hash of BU and authenticator.
Proceed to step 7
(7) AAA calculates a session key based on MN-AAA shared secret and
timestamp and sends this to HA in Access-Accept (in a 3gpp2
defined VSA).
(8) (skipping details for timestamp processing at HA) HA creates a
binding and a security association per Authentication Protocol
for MIP6 [RFC4285]. The key for this association is retrieved
from Access Accept and is referred to as session key. HA
associates a fixed SPI of 5 with this SA and is associated with
the binding for the MN
(9) HA sends a Binding Acknowledgement (BA) to the MN. BA has the
MN-HA authentication option, authenticated using the session
key. This option has the SPI set to 5.
(10) On receiving a BA, MN calculates the session-key (using same
method as AAA) and associates it with SPI value of 5.
MN derives the session key and SA using the timestamp in the BU that
the MN sent and the MN-AAA shared key. The MN uses this key to
authenticate the MN-HA option in Binding Ack. If authentication is
successful, MN creates a security association with SPI=5. This key
is used to authenticate further BU to the HA using the MN-HA auth
option. Once the binding lifetime expires and binding is deleted,
the binding as well as the security association based on the
Integrity Key is removed at the MN and HA.
Migration from MobileIPv4 to MobileIPv6 utilizes the same network
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architecture and specially the same AAA infrastructure. Thus, it is
natural to have similar signaling in MIP6 as in MIP4, specifically
the authentication with AAA infrastructure.
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7. Limitations of the Authentication Protocol option
While the authentication protocol as specified in [RFC4285] provides
Mobile IPv6 [RFC3775] deployments a certain degree of flexibility it
does have a few disadvantages as well. These are:
(1) The route optimization feature specified in RFC3775 requires a
secure transport (IPsec/ESP mode) between the MN and HA. In
cases where the authentication protocol (RFC4285) is used as the
means for securing the MIP6 signaling between the MN and HA,
route optimization should be switched off unless the security of
the signaling between the MN and HA can be guaranteed via other
means (such as link layer security in the case of 3GPP2
networks).
(2) The MIP6 protocol is responsible for the security of the
signaling messages as opposed to relying on IPsec for providing
the security.
(3) In 3GPP2 networks, link-layer security mechanisms, ingress
filtering at the PDSN, and various network domain security
mechanisms largely ensure that reverse tunnelled packets
received by the HA do not have spoofed source addresses, and
their contents have not been modified. This implies the HA can
determine the specific MN which sent the packet simply by
verifying the outer source IP address matches the currently
registered care-of address. Authentication of payload packets
can be necessary for e.g.:
- Authenticating signalling messages other than BU/BAck
between the MN and HA, such as ICMPv6, MLD, and DHCPv6.
- Enforcing access control to the network behind the HA.
- Accounting or other flow-specific processing performed by
the HA.
This means the authentication option is of limited
applicability in environments where the HA can received
reverse tunneled packets with spoofed source IP addresses
and/or modified contents.
(4) As described in [RFC4285], the authentication option assumes
that the MN-AAA shared key and security association are created
by out-of-band mechanisms. These mechanisms are specific to
specific deployment environments. IKEv2, on the other hand,
supports a wide range of authentication mechanisms, such as
certificates and EAP methods, and is independent of the access
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network technology being used. However, it would be possible to
specify a similar authentication and key management protocol for
the authentication option in the future.
(5) Sending the long-term user identity (NAI) in clear raises
privacy concerns. These concerns are addressed by access
network and network domain security mechanisms in 3GPP2
networks, but do limit the applicability in networks where
sniffing other users' traffic is possible.
(6) RFC 4285 does not specify a mechanism for creating the MN-HA
shared key and SA from the MN-AAA SA (unlike similar Mobile IPv4
mechanisms defined in [RFC3957], and thus rely on deployment
specific mechanisms not standardized in IETF.
(7) The authentication option does not support negotiation of
cryptographic algorithms.
(8) The replay protection mechanisms in [RFC4285] rely on
timestamps, and thus requires reasonably synchronized clocks (by
default, +/- 7 seconds). This assumes the MN implements, and is
configured to use, some mechanism for synchronizing its clock.
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8. Security Considerations
When MIP6 signaling messages use IPsec with ESP encapsulation, they
are accorded privacy on the links over which the messages traverse.
When MIP6 signaling messages are secured using the authentication
protocol, such ciphering capability will have to be enabled by the
underlying link layers. It should be noted that the MIP6 signaling
messages are susceptible to snooping/sniffing when the authentication
protocol [RFC4285] is used. Route optimization messages need to be
secured between the MN and HA and this is not possible with the
authentication protocol. Howver route optimization is not supported
in the current specification of the authentication protocol in
[RFC4285].
Security issues with RFC4285 are specifically:
1. Key length. This is being addressed in the 4285bis I-D
[I-D.ietf-mip6-rfc4285bis] at the present time.
2. The keys used for securing the signaling between the MN and HA
are derived from a security association that exists between the
MN and AAA. The MIP6 keys which are bootstrapped from the MN-AAA
SA are transient. Limiting the lifetime of the keys to shorter
periods should be recommended.
3. Location privacy is an issue in the absence of lower layer
security in the case of shared links.
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9. IANA Considerations
This document has no actions for IANA.
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10. Conclusion
Mobile IPv6 has been published as a standards track RFC [RFC3775] in
2004. Deployment of this protocol on a large scale is in the
interest of the IETF and the working group as well as that of many
people who have worked on this. A rigid model for deployment will
cause the protocol to be limited to an academic exercise only. It is
extremely critical that the working group consider the needs of the
industry and the deployment scenarios and address them accordingly.
This document captures the reasoning behind the need for the
authentication protocol which has been published as RFC 4285.
RFC4877 has alleviated some of the issues that have been of primary
concern and motivators for the authentication protocol. However the
IETF should consider the architectures of networks such as 3GPP2 and
WiMAX and their security models and enable deployment of Mobile IPv6
without requiring IPsec.
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11. Acknowledgements
The authors would like to thank Alpesh Patel, AC Mahendra, Kuntal
Chowdhury and Vijay Devarapalli for their input and discussions.
Jari Arkko has reviewed the ID and provided valuable feedback.
Thomas Narten has provided valuable reviews and made significant
improvements to the text in this document. In his role as the IETF
liaison to 3GPP2, Thomas Narten has ensured that the IETF understands
the 3GPP2 requirements. Pasi Eronen in his role as the Security AD
has reviewed and helped improve the document. Vidya Narayanan has
reviewed the document from a security directorate perspective and
provided input that has been incorporated.
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12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997,
<ftp://ftp.isi.edu/in-notes/rfc2119>.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3776] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
Protect Mobile IPv6 Signaling Between Mobile Nodes and
Home Agents", RFC 3776, June 2004.
[RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, April 2004.
[RFC4283] Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
Chowdhury, "Mobile Node Identifier Option for Mobile IPv6
(MIPv6)", RFC 4283, November 2005.
[I-D.ietf-mip6-rfc4285bis]
Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
Chowdhury, "Authentication Protocol for Mobile IPv6",
draft-ietf-mip6-rfc4285bis-03 (work in progress),
July 2008.
12.2. Informative References
[RFC4285] Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
Chowdhury, "Authentication Protocol for Mobile IPv6",
RFC 4285, January 2006.
[RFC4877] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
IKEv2 and the Revised IPsec Architecture", RFC 4877,
April 2007.
[RFC5026] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
Bootstrapping in Split Scenario", RFC 5026, October 2007.
[RFC3957] Perkins, C. and P. Calhoun, "Authentication,
Authorization, and Accounting (AAA) Registration Keys for
Mobile IPv4", RFC 3957, March 2005.
[I-D.ietf-mip6-bootstrapping-integrated-dhc]
Chowdhury, K. and A. Yegin, "MIP6-bootstrapping for the
Integrated Scenario",
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draft-ietf-mip6-bootstrapping-integrated-dhc-06 (work in
progress), April 2008.
[3GPP2 X.S0011-002-D]
"3GPP2 X.S0011-002-D "cdma2000 Wireless IP Network
Standard: Simple IP and Mobile IP Access Services; http://
www.3gpp2.org/Public_html/specs/
X.S0011-002-D_v1.0_060301.pdf "", February 2006.
[WiMAX-NWG]
"WiMAX End-to-End Network Systems Architecture http://
www.wimaxforum.org/technology/documents/
WiMAX_Forum_Network_Architecture_Stage_2-3_Rel_1v1.2.zip",
May 2008.
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Authors' Addresses
Basavaraj Patil
Nokia
6021 Connection Drive
Irving, TX 75039
USA
Email: basavaraj.patil@nokia.com
Gopal Dommety
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Email: gdommety@cisco.com
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