MIP6 A. Patel, Editor
Internet-Draft Cisco
Expires: September 16, 2005 March 18, 2005
Problem Statement for bootstrapping Mobile IPv6
draft-ietf-mip6-bootstrap-ps-02.txt
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Copyright Notice
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Abstract
A mobile node needs at least the following information: a home
address, home agent address and a security association with home
agent to register with the home agent. The process of obtaining this
information is called bootstrapping. This document discuss the
issues involved with how the mobile node can be bootstrapped for
Mobile IPv6 and various potential deployment scenarios for
bootstrapping the mobile node.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Overview of the Problem . . . . . . . . . . . . . . . . . 3
1.2 What is Bootstrapping? . . . . . . . . . . . . . . . . . . 4
1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Motivation for bootstrapping . . . . . . . . . . . . . . . . . 10
5.1 Addressing . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1.1 Dynamic Home Address Assignment . . . . . . . . . . . 10
5.1.2 Dynamic Home Agent Assignment . . . . . . . . . . . . 11
5.1.3 Management requirements . . . . . . . . . . . . . . . 12
5.2 Security Infrastructure . . . . . . . . . . . . . . . . . 12
5.2.1 Integration with AAA Infrastructure . . . . . . . . . 12
5.2.2 "Opportunistic" or "Local" Discovery . . . . . . . . . 13
5.3 Topology Change . . . . . . . . . . . . . . . . . . . . . 13
5.3.1 Dormant Mode Mobile Nodes . . . . . . . . . . . . . . 13
6. Network Access and Mobility services . . . . . . . . . . . . . 14
7. Deployment scenarios . . . . . . . . . . . . . . . . . . . . . 16
7.1 Mobility Service Subscription Scenario . . . . . . . . . . 16
7.2 Integrated ASP network scenario . . . . . . . . . . . . . 16
7.3 Third party MSP scenario . . . . . . . . . . . . . . . . . 17
7.4 Infrastructure-less scenario . . . . . . . . . . . . . . . 18
8. Parameters for authentication . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9.1 Security Requirements of Mobile IPv6 . . . . . . . . . . . 21
9.2 Threats to the Bootstrapping Process . . . . . . . . . . . 22
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1 Normative References . . . . . . . . . . . . . . . . . . . . 25
12.2 Informative References . . . . . . . . . . . . . . . . . . . 25
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 26
Intellectual Property and Copyright Statements . . . . . . . . 27
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1. Introduction
Mobile IPv6 [RFC3775] specifies mobility support based on the
assumption that a mobile node has a trust relationship with an entity
called the home agent. Once the home agent address has been learned
for example via manual configuration, via anycast discovery
mechanisms, via DNS lookup; Mobile IPv6 signaling messages between
the mobile node and the home agent are secured with IPsec or
authentication protocol [I-D.ietf-mip6-mn-auth-protocol-02]. The
requirements for this security architecture are created with
[RFC3775] and the details of this procedure are described in
[RFC3776].
In [RFC3775] there is an implicit requirement that the MN be
provisioned with enough information that will permit it to register
successfully with its home agent. However, having this information
statically provisioned creates practical deployment issues.
This document serves to define the problem of bootstrapping.
Bootstrapping is defined as the process of the mobile node obtaining
enough information, so that it can successfully register with an
appropriate home agent.
The requirements for bootstrapping could consider various scenarios/
network deployment issues. It is the basic assumption of this
document that certain minimal parameters (seed information) is
available to the mobile node to aid in bootstrapping. The exact seed
information available differs depending on the deployment scenario.
This document defines/describes various deployment scenarios and
provides for a set of minimal parameters that are available in each
deployment scenario.
This document stops short of suggesting the various solutions to
obtaining information on the mobile node. Such details will be
available from separate documents.
1.1 Overview of the Problem
Mobile IPv6 [RFC3775] expects the mobile node to have a static home
address, home agent address (or anycast address and do dynamic home
agent discovery of Home Agent using ICMP messages) and a security
association with a home agent (multiple home agents on the home
network if dynamic home agent discovery is in use and multiple home
agents are deployed.)
This static provisioning of information has various problems as
discussed in Section 5.
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The aim of this draft is to:
o Define bootstrapping.
o Identify sample deployment scenarios where MIPv6 will be deployed,
taking into account the relationship between the subscriber and
the service provider.
o Identify the minimal set of information required on the Mobile
Node (and/or) in the network in order for the mobile node to
obtain address and security credentials, to register with the home
agent.
1.2 What is Bootstrapping?
Bootstrapping is defined as obtaining enough information at the
mobile node, so that the mobile node can successfully register with
an appropriate home agent. Specifically, this means obtaining the
home agent address, home address and security credentials for the
mobile node and home agent to authenticate and mutually construct
security credentials for Mobile IPv6 without requiring
preconfiguration.
Typically, bootstrapping happens when a mobile node does not have all
the information it needs to setup the Mobile IPv6 service. This
includes, but is not limited to MN not having any information when it
boots up for the first time (out of the box), it does not retain any
information during reboots, is instructed by the Home Agent (via some
form of signalling) to do so etc.
Also, in certain scenarios, after the MN bootstraps for the first
time (out of the box), subsequent bootstrapping is implementation
dependent. For instance, the MN may bootstrap everytime it boots,
bootstrap everytime on prefix change, bootstrap periodically to
anchor to an optimal (distance, load etc) HA, etc.
1.3 Terminology
General mobility terminology can be found in
[I-D.ietf-seamoby-mobility]. The following additional terms are used
here:
Trust relationship
In the context of this draft, trust relationship means that two
parties in question, typically the user of the mobile host and the
mobility or access service provider, have some sort of prior
contact in which the mobile host was provisioned with credentials.
These credentials allow the mobile host to authenticate itself to
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the mobility or access service authorizer and to prove its
authorization to obtain service.
Infrastructureless relationship
In the context of this draft, an infrastructureless relationship
is one in which the user of the mobile host and the mobility or
access service provider have no previous contact and the mobile
host is not required to supply credentials to authenticate and
prove authorization for service. Mobility and/or network access
service is provided without any authentication or authorization.
Infrastructureless in this context does not mean that there is no
network infrastructure, such as would be the case for an ad hoc
network.
Credentials
Data or mechanism used by a mobile host to authenticate itself to
a mobility or access network service provider and prove
authorization to receive service. User name/passwords, one time
password cards, public/private key pairs with certificates,
biometric information, etc. are some examples.
ASA
Access Service Authorizer. A network operator that authenticates
a mobile host and establishes the mobile host's authorization to
receive Internet service.
ASP
Access Service Provider. A network operator that provides direct
IP packet forwarding to and from the end host.
Serving Network Access Provider
A network operator that is the mobile host's ASP but not its ASA.
The serving network accesss provider may or may not additionally
provide mobility service.
Home Network Access Provider
A network operator that is both the mobile host's ASP and ASA.
The home network access provider may or may not additionally
provide mobility service (note that this is a slighlty different
definition from RFC 3775).
IASP
Integrated Access Service Provider. A service provider that
provides both authorization for network access and also provides
mobility service.
MSA
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Mobility Service Authorizer. A service provider that authorizes
Mobile IPv6 service.
MSP
Mobility Service Provider. A service provider that provides
Mobile IPv6 service. In order to obtain such service, the mobile
host must be authenticated and prove authorization to obtain the
service.
Home Mobility Service Provider
A MSP that both provides mobility service and authorizes it.
Serving Mobility Service Provider
A MSP that provides mobility service but depends on another
service provider to authorize it.
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2. Assumptions
o A basic assumption in the Mobile IPv6 RFC [RFC3775] is that there
is a trust relationship between the mobile node and MSP. This
trust relationship can be direct, or indirect through, for
instance, an ASP that has a contract with the MSP. This trust
relationship can be used to bootstrap the MN.
One typical way of verifying the trust relationship is using
authentication, authorization, and accounting (AAA).
infrastructure. In this document, two distinct uses of AAA are
considered:
AAA for Network Access
This functionality provides authentication and authorization to
access the network (obtain address and send/receive packets).
AAA for Mobility Service
This functionality provides authentication and authorization
for mobility services.
These functionalities may be implemented in a single entity or in
different entities, depending on the service models described in
Section 6 or deployment scenarios as described in Section 7.
o Yet another assumption is that some identifier, such as NAI, as
defined in [I-D.ietf-mip6-mn-ident-option-02] or [RFC2794] is
provisioned on the MN which permits the MN to identify itself to
the ASP and ASP.
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3. Design Goals
A solution to the bootstrapping problem has the following design
goals:
o The following information must be available at the end of
bootstrapping, to enable the MN to register with the HA.
* MN's home agent address
* MN's home address
* IPsec SA between MN and HA, IKE pre-shared secret between MN
and HA or shared secret/security association for authentication
protocol [I-D.ietf-mip6-mn-auth-protocol-02]
o The bootstrapping procedure can be triggered at any time, either
by the MN or by the network. Bootstrapping can occur, for
instance due to administrative action, information going stale, HA
indicating the MN etc. Bootstrapping may be initiated even when
the MN is registered with the HA and has all the required
credentials. This may typically happen to refresh/renew the
credentials.
o Subsequent protocol interaction (for example updating the IPsec
SA) can be executed between the MN and the HA itself without
involving the infrastructure that was used during bootstrapping.
o Solutions to the bootstrapping problem should enable storage of
user-specific information on entities other than the home agent.
o Solutions to the bootstrapping problem should not exclude storage
of user-specific information on entities other than the home
agent.
o Configuration information which is exchanged between the mobile
node and the home agent needs to be secured using integrity and
replay protection. Confidentiality protection should be provided
if necessary.
o All feasible deployment scenarios, along with the relevant
authentication/authorization models should be considered.
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4. Non-Goals
This following issues are clearly outside the scope of bootstrapping:
o Home prefix renumbering is not explicity supported as part of
bootstrapping. If the MN executes the bootstrap procedures
everytime it powers-on (as opposed to caching state information
from previous bootstrap process), then home network renumbering is
taken care of automatically.
o Bootstrapping in the absence of a trust relationship between MN
and any provider is not considered.
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5. Motivation for bootstrapping
5.1 Addressing
The default bootstrapping described in the Mobile IPv6 base
specification [RFC3775] has a tight binding to the home addresses and
home agent addresses.
In this section, we discuss the problems caused by the currently
tight binding to home addresses and home agent addresses.
5.1.1 Dynamic Home Address Assignment
Currently, the home agent uses the mobile node's home address for
authorization. When manual keying is used, this happens through the
security policy database, which specifies that a certain security
association may only use a specific home address. When dynamic
keying is used, the home agent ensures that the IKE Phase 1 identity
is authorized to request security associations for the given home
address. Mobile IPv6 uses IKEv1, which is unable to update the
security policy database based on a dynamically assigned home
address. As a result, static home address assignment is really the
only home address configuration technique compatible with the current
specification.
However, support for dynamic home address assignment would be
desirable for the following reasons:
DHCP-based address assignment
Some ASPs may want to use DHCPv6 from the home network to
configure home addresses.
Recovery from a duplicate address collision
It may be necessary to recover from a collision of addresses on
the home network.
Addressing privacy
It may be desirable to establish randomly generated addresses as
in RFC 3041 and use them for a short period of time.
Unfortunately, current protocols make it possible to use such
addresses only from the visited network. As a result, these
addresses can not be used for communications lasting longer than
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the attachment to a particular visited network.
Ease of deployment
In order to simplify the deployment of Mobile IPv6, it is
desirable to free users and administrators from the task of
allocating home addresses and specifying them in the security
policy database.
This is consistent with the general IPv6 design goal of using
autoconfiguration wherever possible.
Prefix changes in the home network
The Mobile IPv6 specification contains support for a mobile node
to autoconfigure a home address based on its discovery of prefix
information on the home subnet [RFC3775]. Autoconfiguration in
case of network renumbering is done by replacing the existing
network prefix with the new network prefix.
Subsequently, the MN needs to update the mobility binding in the
HA to register the newly configured Home Address. However, the MN
may not be able to register the newly configured address with the
HA if a security association related to that reconfigured Home
Address does not exist in the MN and the HA. This situation is
not handled in the current MIPv6 specification [RFC3775].
5.1.2 Dynamic Home Agent Assignment
Currently, the address of the home agent is specified in the security
policy database. Support for multiple home agents requires the
configuration of multiple security policy database entries.
However, support for dynamic home agent assignment would be desirable
for the following reasons:
Home agent discovery
The Mobile IPv6 specification contains support for a mobile node
to autoconfigure a home agent address based on a discovery
protocol [RFC3775].
Independent network management
An ASP may want to dynamically assign home agents in different
subnets, that is, not require that a roaming mobile node have a
fixed home subnet.
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Local home agents
The mobile node's home ASP may want to allow a local roaming
partner ASP to assign a local home agent for the mobile node.
This is useful both from the point of view of communications
efficiency, and has also been mentioned as one approach to support
location privacy.
Ease of deployment
MSP may want to allow "opportunistic" discovery and utilization of
its mobility services without any prearranged contact. These
scenarios will require dynamic home address assignment.
5.1.3 Management requirements
As described earlier, new addresses invalidate configured security
policy databases and authorization tables. Regardless of the
specific protocols used, there is a need for either an automatic
system for updating the security policy entries, or manual
configuration. These requirements apply to both home agents and
mobile nodes, but it can not be expected that mobile node users are
capable of performing the required tasks.
5.2 Security Infrastructure
5.2.1 Integration with AAA Infrastructure
The current IKEv1-based dynamic key exchange protocol described in
[RFC3776] has no integration with backend authentication,
authorization and accounting techniques unless the authentication
credentials and trust relationships use certificates or pre-shared
secrets.
Using certificates may require the ASP to deploy a PKI, which may not
be possible or desirable in certain circumstances. Where a
traditional AAA infrastructure is used, the home agent is not able to
leverage authentication and authorization information established
between the mobile node, the foreign AAA server, and the home AAA
server when the mobile node gains access to the foreign network, in
order to authenticate the mobile node's identity and determine if the
mobile node is authorized for mobility service.
The lack of connection to the AAA infrastructure also means the home
agent does not know where to issue accounting records at appropriate
times during the mobile node's session, as determined by the business
relationship between the home ASP and the mobile node's owner.
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Presumably, some backend AAA protocol between the home agent and home
AAA could be utilized, but IKEv1 does not contain support for
exchanging full AAA credentials with the mobile node. It is
worthwhile to note that IKEv2 provides this feature.
5.2.2 "Opportunistic" or "Local" Discovery
The home agent discovery protocol does not support an "opportunistic"
or local discovery mechanisms in an ASP's local access network. It
is expected that the mobile node must know the prefix of the home
subnet in order to be able to discover a home agent. It must either
obtain that information through prefix update or have it statically
configured. A more typical pattern for interdomain service discovery
in the Internet is that the client (mobile node in this case) knows
the domain name of the service, and uses DNS in some manner to find
the server in the other domain. For local service discovery, DHCP is
typically used.
5.3 Topology Change
5.3.1 Dormant Mode Mobile Nodes
The description of the protocol to push prefix information to mobile
nodes in Section 10.6 in [RFC3775] has an implicit assumption that
the mobile node is active and taking IP traffic. In fact, many, if
not most, mobile devices will be in a low power "dormant mode" to
save battery power, or even switched off, so they will miss any
propagation of prefix information. As a practical matter, if this
protocol is used, an ASP will need to keep the old prefix around and
handle any queries to the old home agent anycast address on the old
subnet, whereby the mobile node asks for a new home agent as
described in Section 11.4, until all mobile nodes are accounted for.
Even then, since some mobile nodes are likely to be turned off for
long periods, some owners would need to be contacted by other means,
reducing the utility of the protocol.
Bootstrapping does not explicitly try to solve this problem of home
network renumbering when MN is in dormant mode. If the MN can
configure itself after it 'comes back on' by reinitiating the
bootstrapping process, then network renumbering problem is fixed as a
side-effect.
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6. Network Access and Mobility services
This section defines some terms as it pertains to authentication and
practical network deployment/roaming scenarios. This description
lays the ground work for Section 7. The focus is on the 'service'
model since, ultimately, it is the provider providing the service
that wants to authenticate the mobile (and vice-versa for mutual
authentication between provider and the user of the service).
Network access service enables a host to send and receive IP packets
on the Internet or an intranet. IP address configuration and IP
packet forwarding capabilities are required to deliver this service.
A network operator providing this service is called an access service
provider (ASP). An ASP can, for example, be a commercial ASP, the IT
department of an enterprise network, or the maintainer of a home
(residential) network.
If the mobile host is within the geographical area in which network
access service is not provided by its home network access service
provider, the mobile host is roaming. The home network access
service provider in this case acts as the access service authorizer,
but the actual network access is provided by the serving network
access provider. During the authentication and authorization prior
to the mobile host having Internet access, the serving network access
provider may simply act as a routing agent for authentication and
authorization back to the access service authorizer, or it may
require an additional authentication and authorization step itself.
An example of a roaming situation is when a business person is using
a hotspot service in an airport, and the hotspot service provider has
a roaming agreement with the business person's cellular provider. In
that case, the hotspot network is acting as the serving network
access provider, while the cellular network is acting as the access
service authorizer. When the business person moves from the hotspot
network to the cellular network, the cellular network is both the
home access service provider and the access service authorizer.
Mobility service using Mobile IPv6 is conceptually and possibly also
in practice separate from network access service, though of course
network access is required prior to providing mobility. Mobile IPv6
service enables an IPv6 host to maintain its reachability despite
changing its network attachment point (subnets). A network operator
providing Mobile IPv6 service is called a mobility service provider
(MSP). Granting Mobile IPv6 service requires a host to authenticate
and prove authorization for the service. A network operator that
authenticates a mobile host and authorizes mobility service is called
a mobility service authorizer. If both types of operation are
performed by the same operator, that operator is called a home
mobility service provider. If authentication and authorization is
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provided by one operator and the actual service is provider by
another, the operator providing the service is called the serving
mobility service provider. The serving MSP must contact the mobile
host's mobility service authorizer to check the mobile host's
authorization prior to granting mobility service.
The service model defined here clearly separates the entity providing
the service from the entity that authentications and authorizes the
service. In the case of basic network access, this supports the
traditional and well-known roaming model, in which inter-operator
roaming agreements allow a host to obtain network access in areas
where their home network access provider does not have coverage. In
the case of mobility service, this allows a roaming mobile host to
obtain mobility service in the local operator's network while having
that service authorized by the home operator. The service model also
allows mobility service and network access service to be provided by
different entities. This allows a network operator with no wireless
access, like, for example, an enterprise network operator, to deploy
a Mobile IPv6 home agent for mobility service while the actual
wireless network access is provided by the serving network access
providers with which the enterprise operator has a contract. Here
are some other possible combinations of ASPs and MSPs:
o The serving ASP might be the home ASP. Similarly, the serving MSP
might be the home MSP.
o The home ASP and the home MSP may be the same operator, or not.
When they are the same, the same set of credentials may be used
for both services.
o The serving ASP and the serving MSP may be the same operator, or
not.
o It is possible that serving ASP and home MSP are the same
operator.
Similarly the home ASP and serving MSP may be the same. Also, the
ASA and MSA may be the same.
These entities and possible combinations must be taken into
consideration when solving the Mobile IPv6 bootstraping problem.
They impact home agent discovery, home address configuration, and
mobile node to home agent authentication aspects.
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7. Deployment scenarios
This section describes the various network deployment scenarios. The
various combinations of service providers as described in Section 6
are considered.
For each scenario, the underlying assumptions are described. The
basic assumption is that there is a trust relationship between mobile
user and the MSP. Typically, this trust relationship is between the
mobile user and AAA in the MSA's network. Seed information needed to
bootstrap the mobile node is considered in two cases:
o AAA authentication is mandatory for network access
o AAA authentication is not part of network access. The seed
information is described further in Section 8.
7.1 Mobility Service Subscription Scenario
Many commercial deployments are based on the assumption that mobile
nodes have a subscription with a service provider. In particular, in
this scenario the MN has a subscription with an MSP, called the home
MSP, for Mobile IPv6 service. As stated in Section 6, the MSP is
responsible of setting up a home agent on a subnet that acts as a
Mobile IPv6 home link. As a consequence, the home MSP should
explicitly authorize and control the whole bootstrapping procedure.
Since the MN is assumed to have a pre-established trust relationship
with its home provider, it must be configured with an identity and
credentials, for instance an NAI and a shared secret by some
out-of-band means before bootstrapping, for example by manual
configuration.
In order to guarantee ubiquitous service, the MN should be able to
bootstrap MIPv6 operations with its home MSP from any possible access
location, such as an open network or a network managed by an ASP,
that may be different from the MSP and may not have any
pre-established trust relationship with it.
7.2 Integrated ASP network scenario
In this scenario, the ASP and MSP are the same ASP. MN shares
security credentials for access to the network and these credentials
can be used to bootstrap MIPv6. This bootstrapping can be done
during the same phase as access authentication/authorization or at a
later time (probably based on some state created during access
authentication/authorization).
Figure 1 describes an example AAA design for integrated ASP scenario.
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+----------------------------+
| IASP(ASP+MSP) |
+----+ +-----+ +----+ |
| MN |--- | NAS | | HA | |
+----+ +-----+ +----+ |
| \ \ |
| \ +------+ \ +-------+ |
| -|AAA-NA| -|AAA-MIP| |
| +------+ +-------+ |
+----------------------------+
NAS: Network Access Server
AAA-NA: AAA for network access
AAA-MIP: AAA for Mobile IP service
Figure 1: Integrated ASP network
7.3 Third party MSP scenario
Mobility service has traditionally been provided by the same entity
that authenticates and authorizes the subscriber for network access.
This is certainly the only model support by the base Mobile IPv6
specification.
In the 3rd party mobility service provider scenario, the subscription
for mobility service is made with one entity (home MSA for instance a
corporate network), but the actual mobility service is provided by
yet another entity (such as an operator specializing on this service,
the serving MSP). These two entities have a trust relationship.
Transitive trust among the mobile node and these two entities may be
used to assure the participants that they are dealing with, are
trustworthy peers.
This arrangement is similar to the visited - home operator roaming
arrangement for network access.
Figure 2 describes an example network for third party MSP scenario.
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+--------------+ +--------+
| | |Serving |
| ASP | | MSP |
+----+ +-----+ | | +----+ |
| MN |--- | NAS | | | | HA | | +-------------------+
+----+ +-----+ |===| +----+ | | Home MSP |
| \ | | \ | | (e.g.corporate NW)|
| \ +------+ | | \ | +-------+ |
| -|AAA-NA| | | -------|AAA-MIP| |
| +------+ | | | | +-------+ |
+------------ + +--------+ +-------------------+
Figure 2: Third Party MSP network
7.4 Infrastructure-less scenario
Infrastructure refers to network entities like AAA, PKI, HLR etc.
Infrastructure-less implies that there is no dependency on any
elements in the network with which the user has any form of trust
relationship.
In such a scenario, there is absolutely no relationship between host
and infrastructure.
A good example of infrastructure-less environment for MIP6
bootstrapping is the IETF network at IETF meetings. It is possible
that there could be MIP6 service available on this network (i.e a
MIPv6 HA). However there is not really any AAA infrastructure or for
that matter any trust relationship that a user attending the meeting
has with any entity in the network.
This specific scenario is not supported in this document. The reason
for this is described in Section 9.
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8. Parameters for authentication
The following is a list of parameters that are used as the seed for
the bootstrapping procedure. The parameters vary depending on
whether authentication for network access is independent of
authentication for mobility services or not. Authentication for
network access is always independent of authentication for mobility
services if different client identities are used for network access
and mobility services.
o Parameter Set 1
In this case, authentication for network access is independent of
authentication for mobility services.
If the home agent address is not known to the mobile node the
following parameter is needed for discovering the home agent
address:
* The domain name or FQDN of the home agent
This parameter may be derived in various ways such as (but not
limited to) static configuration, use of the domain name from the
network access NAI (even if AAA for network access is not
otherwise used) or use of the domain name of the serving ASP where
the domain name may be obtained via DHCP in the serving ASP.
If the home agent address is not known but the home subnet prefix
is known, Dynamic Home Agent Address Discovery of Mobile IPv6 may
be used for discovering the home agent address and the above
parameter may not be used.
When the home agent address is known to the mobile node, the
following parameter is needed for performing mutual authentication
between the mobile node and the home agent by using IKE:
* IKE credentials(*)
In the case where the home agent does not have the entire set of
IKE credentials, the home agent may communicate with other entity
(for example a AAA server) to perform mutual authentication in
IKE. In such a case, the IKE credentials include the credentials
used between the mobile node and the other entity. In the case
where a AAA protocol is used for the communication between the
home agent and the other entity during the IKE procedure, AAA for
Mobile IPv6 service may be involved in IKE.
If authentication protocol [I-D.ietf-mip6-mn-auth-protocol-02] is
used, the shared key based security association with home agent is
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needed.
o Parameter Set 2
In this case, some dependency exists between authentication for
network access and authentication for mobility services in that a
security association that is established as a result of
authentication for network access is re-used for authentication
for mobility services.
All required information including IKE credentials are
bootstrapped from the following parameter:
* Network access credentials(*)
(*) A pair of a NAI and a pre-shared secret is an example set of
credentials. A pair of an NAI and a public key, which may be
provided as a digital certificate, is another example set of
credentials.
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9. Security Considerations
There are two aspects of security for the Mobile IPv6 bootstrapping
problem:
1. The security requirements imposed on the outcome of the
bootstrapping process by RFC 3775 and other RFCs used by Mobile
IPv6 for security.
2. The security of the bootstrapping process itself, in the sense of
threats to the bootstrapping process imposed by active or passive
attackers.
Note that the two are related, in that if the bootstrapping process
is compromised, the level of security required by RFC 3775 may not be
obtained.
The following two sections discuss these issues.
9.1 Security Requirements of Mobile IPv6
The Mobile IPv6 specification in RFC 3775 requires the establishment
of a collection of IPsec SAs between the home agent and mobile host
to secure the signaling traffic for Mobile IP, and, optionally, also
to secure data traffic. The security of an IPsec SA required by the
relevent IPsec RFCs must be quite strong. Provisioning of keys and
other cryptographic material during the establishment of the SA
through bootstrapping must be done in a manner such that authenticity
is proved and confidentiality is ensured. In addition, the
generation of any keying material or other cryptographic material for
the SA must be done in a way such that the probability of compromise
after the SA is in place is minimized. The best way to minimize the
probability of such a compromise is to have the cryptographic
material only known or calculable by the two end nodes that share the
SA, in this case, the home agent and mobile host. If other parties
are involved in the establishing the SA, through key distribution for
example, the process should follow the constraints [eap_keying]
designed to provide equivalent security.
RFC 3775 also requires a trust relationship as defined in Section 1.3
between the mobile host and mobility service provider. This is
necessary, for instance, to ensure that fradulent mobile hosts which
attempt to flood other mobile hosts with traffic can not only be shut
off but tracked down [I-D.rosec]. An infrastructureless relationship
as defined in Section 1.3 does not satisfy this requirement. Any
bootstrapping solution must include a trust relationship between
mobile host and mobility service provider. Solutions that depend on
an infrastructureless relationship are out of scope for
bootstrapping.
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Another requirement is that a home address is authorized to one
specific host at a time. RFC 3775 requires this in order to that
misbehaving mobile hosts can be shut down. This implies that, in
addition to the IPsec SA, the home agent must somehow authorize the
mobile host for a home address. The authorization can be either
implicit (for example, as a side effect of the authentication for
mobility service) or explicit. The authorization can either be done
at the time the SA is created or dynamically managed through a first
come, first served allocation policy.
9.2 Threats to the Bootstrapping Process
Various attacks are possible on the bootstrapping process itself.
These attacks can compromise the process such that the RFC 3775
requirements for Mobile IP security are not met, or they can serve to
simply disrupt the process such that bootstrapping cannot complete.
Here are some possible attacks:
o An attacking network entity purporting to offer the mobile host a
legitimate home agent address or boostrapping for the IPsec SAs
may, instead, offer a bogus home agent address or configure bogus
SAs that allow the home agent to steal the mobile host's traffic
or otherwise disrupts the mobile host's mobility service.
o An attacking mobile host may attempt to steal mobility service by
offering up fake credentials to a bootstrapping network entity or
otherwise disrupt the home agent's ability to offer mobility
service.
o A man in the middle on the link between the mobile host and the
bootstrapping network entity could steal credentials or other
sensitive information and use that to steal mobility service or
deny it to the legitimate owner of the credentials. Refer to
Section 7.15 in [2284bis] and [I-D.mariblanca-aaa-eap-lla-00] for
further information.
o An attacker could arrange for a distributed denial of service
attack on the bootstrapping entity, to disrupt legitimate users
from bootstrapping.
In addition to these attacks, there are other considerations that are
important in achieving a good security design. As mobility and
network access authentication are separate services, keys generated
for these services need to be cryptographically separate, separately
named, and have separate lifetimes, including if the keys are
generated from the same authentication credentials This is necessary
because a mobile host must be able to move from one serving (or
roaming) network access provider to another without needing to change
its mobility access provider. Finally, basic cryptographic processes
must provide for multiple algorithms in order to accommodate the
widely varying deployment needs.
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10. Contributors
This contribution is a joint effort of the problem statement design
team of the Mobile IPv6 WG. The contributors include Basavaraj
Patil, Gerardo Giaretta, Jari Arkko, James Kempf, Yoshihiro Ohba,
Ryuji Wakikawa, Hiroyuki Ohnishi, Mayumi Yanagiya Samita Chakrabarti,
Gopal Dommety, Kent Leung, Alper Yegin, Hannes Tschofenig, Vijay
Devarapalli, Kuntal Chowdury.
The design team members can be reached at:
Basavaraj Patil basavaraj.patil@nokia.com
Gerardo Giaretta gerardo.giaretta@tilab.com
Jari Arkko jari.arkko@kolumbus.fi
James Kempf kempf@docomolabs-usa.com
Yoshihiro Ohba yohba@tari.toshiba.com
Ryuji Wakikawa ryuji@sfc.wide.ad.jp
Hiroyuki Ohnishi ohnishi.hiroyuki@lab.ntt.co.jp
Mayumi Yanagiya yanagiya.mayumi@lab.ntt.co.jp
Samita Chakrabarti Samita.Chakrabarti@eng.sun.com
Gopal Dommety gdommety@cisco.com
Kent Leung kleung@cisco.com
Alper Yegin alper.yegin@samsung.com
Hannes Tschofenig hannes.tschofenig@siemens.com
Vijay Devarapalli vijayd@iprg.nokia.com
Kuntal Chowdury kchowdury@starentnetworks.com
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11. Acknowledgments
Special thanks to James Kempf and Jari Arkko for writing the initial
version of the bootstrapping statement. Thanks to John Loughney for
a detailed editorial review.
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12. References
12.1 Normative References
[I-D.ietf-mip6-mn-auth-protocol-02]
Patel et. al., A., "Authentication Protocol for Mobile
IPv6", draft-ietf-mip6-auth-protocol-02.txt (work in
progress), November 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-mip6-auth-protocol-02.txt>
.
[I-D.ietf-seamoby-mobility]
Manner, J. and M. Kojo, "Mobility Related Terminology",
draft-ietf-seamoby-mobility-terminology-06 (work in
progress), February 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-seamoby-mobility-terminology
-06.txt>
.
[RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access
Identifier Extension for IPv4", RFC 2794, March 2000.
[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.
12.2 Informative References
[2284bis] Levkowetz, Ed., H., "Extensible Authentication Protocol
(EAP)", February 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-eap-rfc2284bis-09.txt>
.
[I-D.giaretta-mip6-authorization-eap]
Giaretta, G., "MIPv6 Authorization and Configuration based
on EAP", draft-giaretta-mip6-authorization-eap-00 (work in
progress), February 2004,
<http://www.ietf.org/internet-drafts/draft-giaretta-mip6-authorization-eap-0
0.txt>
.
[I-D.ietf-mip6-mn-ident-option-02]
Patel, A., Leung, K., Akthar, H., Khalil, M. and K.
Chowdhury, "Mobile Node Identifier Option for Mobile
IPv6", draft-ietf-mip6-mn-ident-option-02.txt (work in
progress), February 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-mip6-mn-ident-option-02.txt>
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.
[I-D.kempf-mip6-bootstrap]
Kempf, J. and J. Arkko, "The Mobile IPv6 Bootstrapping
Problem", draft-kempf-mip6-bootstrap-00 (work in
progress), March 2004,
<http://www.ietf.org/internet-drafts/draft-kempf-mip6-bootstrap-00.txt>
.
[I-D.mariblanca-aaa-eap-lla-00]
Mariblanca, D., "EAP lower layer attributes for AAA
protocols", May 2004,
<http://www.ietf.org/internet-drafts/draft-mariblanca-aaa-eap-lla-00.txt>
.
[I-D.rosec]
Nikander, P., Arkko, J., Aura, T., Montenegro, G. and E.
Nordmark, "Mobile IP version 6 Route Optimization Security
Design Background", draft-ietf-mip6-ro-sec-02 (work in
progress), October 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-mip6-ro-sec-02.txt>
.
[eap_keying]
Aboba et. al., B., "Extensible Authentication Protocol
(EAP) Key Management Framework",
draft-ietf-eap-keying-05.txt (work in progress), February
2005,
<http://www.ietf.org/internet-drafts/draft-ietf-eap-keying-05.txt>
.
Author's Address
Alpesh Patel
Cisco
170 W. Tasman Drive
San Jose, CA 95134
USA
Phone: +1 408 853 9580
EMail: alpesh@cisco.com
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Patel, Editor Expires September 16, 2005 [Page 27]
