MIP6 Working Group V. Devarapalli
Internet-Draft Nokia
Expires: April 26, 2006 F. Dupont
Point6
October 23, 2005
Mobile IPv6 Operation with IKEv2 and the revised IPsec
draft-ietf-mip6-ikev2-ipsec-04.txt
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Copyright (C) The Internet Society (2005).
Abstract
This document describes Mobile IPv6 operation with the revised IPsec
architecture and IKEv2.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. General Requirements . . . . . . . . . . . . . . . . . . . 4
4.2. Policy Requirements . . . . . . . . . . . . . . . . . . . 5
4.3. IPsec Protocol Processing Requirements . . . . . . . . . . 6
4.4. Dynamic Keying Requirements . . . . . . . . . . . . . . . 8
5. Selector Granularity Considerations . . . . . . . . . . . . . 8
6. Manual Configuration . . . . . . . . . . . . . . . . . . . . . 9
6.1. Binding Updates and Acknowledgements . . . . . . . . . . . 9
6.2. Return Routabililty Messages . . . . . . . . . . . . . . . 10
6.3. Mobile Prefix Discovery Messages . . . . . . . . . . . . . 11
6.4. Payload Packets . . . . . . . . . . . . . . . . . . . . . 12
7. Dynamic Configuration . . . . . . . . . . . . . . . . . . . . 12
7.1. Security Policy Database Entries . . . . . . . . . . . . . 12
7.1.1. Binding Updates and Acknowledgements . . . . . . . . . 13
7.1.2. Return Routability Messages . . . . . . . . . . . . . 14
7.1.3. Mobile Prefix Discovery Messages . . . . . . . . . . . 14
7.1.4. Payload Packets . . . . . . . . . . . . . . . . . . . 15
7.2. Security Association negotiation using IKEv2 . . . . . . . 16
7.3. Movements and Dynamic Keying . . . . . . . . . . . . . . . 18
8. The use of EAP authentication . . . . . . . . . . . . . . . . 19
9. Dynamic Home Address Configuration . . . . . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
13.1. Normative References . . . . . . . . . . . . . . . . . . . 22
13.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . . . . 25
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1. Introduction
RFC 3776 describes how IPsec [12] is used with Mobile IPv6 [2] to
protect the signaling messages. It also illustrates examples of
Security Policy Database and Security Association Database entries
that can be used to protect Mobile IPv6 signaling messages.
The IPsec architecture has been revised [5]. Among the many changes,
the list of selectors has been expanded to included the Mobility
Header message type. This has an impact on how security policies and
security associations are configured for protecting mobility header
messages. It becomes easier to differentiate between the various
Mobility Header messages based on the type value instead of checking
if a particular mobility header message is being sent on a tunnel
interface between the mobile node and the home agent, as it was in
RFC 3776. The revised IPsec architecture specification also includes
ICMP message type and code as selectors. This makes it possible to
protect Mobile Prefix Discovery messages without applying the same
security associations to all ICMPv6 messages.
This document discusses new requirements for the home agent and the
mobile node to use the revised IPsec architecture and IKEv2.
Section 4 lists the requirements. Section 6 and Section 7 describe
the required Security Policy Database (SPD) and Security Association
Database (SAD) entries.
The Internet Key Exchange (IKE) has also been substantially revised
and simplified [4]. Section 7.2 of this document describes how IKEv2
can be used to setup security associations for Mobile IPv6.
The use of EAP within IKEv2 is allowed to authenticate the mobile
node to the home agent. This is described in Section 8. A method
for dynamically configuring a home address from the home agent using
the Configuration Payload in IKEv2 is described in Section 9.
2. Terminology
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 [1].
3. Packet Formats
The mobile node and the home agent MUST support the packet formats as
defined in Section 3 of RFC 3776. This document does not update the
packet formats described in RFC 3776.
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4. Requirements
This section describes mandatory rules and requirements for all
Mobile IPv6 mobile nodes and home agents so that IPsec, with IKEv2 as
the key negotiation protocol, can be used to protect traffic between
the mobile node and the home agent. Many of the requirements are
repeated from RFC 3776 to make this document self-contained and
complete.
4.1. General Requirements
o RFC 3775 states that manual configuration of IPsec security
associations MUST be supported and automated key management MAY be
supported. This document does not make any recommendations
regarding the support of manual IPsec configuration and dynamic
IPsec configuration. This document just describes the use of
manually created IPsec security associations and the use of IKEv2
as the automated IPsec key management protocol for protecting
Mobile IPv6 signaling messages.
o ESP encapsulation for Binding Updates and Binding Acknowledgements
MUST be supported and used.
o ESP encapsulation in tunnel mode for the Home Test Init and Home
Test messages tunneled between the mobile node and the home agent
MUST be supported and SHOULD be used.
o ESP encapsulation of the ICMPv6 messages related to mobile prefix
discovery MUST be supported and SHOULD be used.
o ESP encapsulation of the payload packets tunneled between the
mobile node and the home agent MAY be supported and used.
o If multicast group membership control protocols or stateful
address autoconfiguration protocols are supported, payload data
protection MUST be supported for those protocols.
o The home agent and the mobile node MAY support authentication
using EAP in IKEv2 as described in Section 8.
o The home agent and the mobile node MAY support remote
configuration of home address as described in Section 9. When the
home agent receives a configuration payload with a CFG_REQUEST for
INTERNAL_IP6_ADDR, it must reply with a valid home address for the
mobile node. The home agent can pick a home address from a local
database or from a DHCPv6 server on the home link.
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4.2. Policy Requirements
The following requirements are related to the configuration of
security policy database on the home agent and the mobile node.
o RFC 3776 required configuration of the security policies per
interface in order to be able to differentiate between mobility
header messages sent to the home agent and tunneled through the
home agent to the correspondent node. Since the Mobility Header
message type is a selector, it is now easy to differentiate
between HoTi and HoT messages from other mobility header messages.
Therefore per-interface configuration of security policies is not
required.
o The home agent MUST be able to prevent a mobile node from using
its security association to send a Binding Update on behalf of
another mobile node. With manual IPsec configuration, the home
agent MUST be able to verify that a security association was
created for a particular home address. With dynamic keying, it
should be possible for the home agent to verify that the identity
presented in the IKE_AUTH exchange is allowed to create security
associations for a particular home address.
o The home agent MAY use the Peer Authorization Database (PAD) [5]
to store per-mobile node state. The PAD entry for a mobile node
can contain a shared key, public key or a trust anchor to verify
the mobile node's certificate for authenticating the mobile node.
o As required in the base specification [7], when a packet destined
to the receiving node is matched against IPsec security policy or
selectors of a security association, an address appearing in a
Home Address destination option is considered as the source
address of the packet.
Note that the home address option appears before IPsec headers.
Section 11.3.2 of the base specification describes one possible
implementation approach for this: The IPsec policy operations can
be performed at the time when the packet has not yet been modified
per Mobile IPv6 rules, or has been brought back to its normal form
after Mobile IPv6 processing. That is, the processing of the Home
Address option is seen as a fixed transformation of the packets
that does not affect IPsec processing.
o Similarly, a home address within a Type 2 Routing header destined
to the receiving node is considered as the destination address of
the packet, when a packet is matched against IPsec security policy
or selectors of a security association.
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Similar implementation considerations apply to the Routing header
processing as was described above for the Home Address destination
option.
o When the mobile node returns home and de-registers with the Home
Agent, the tunnel between the home agent and the mobile node's
care-of address is torn down. The security policy entries, which
were used for protecting tunneled traffic between the mobile node
and the home agent MUST be made inactive (for instance, by
removing them and installing them back later through an API). The
corresponding security associations could be kept as they are or
deleted depending on how they were created. If the security
associations were created dynamically using IKE, they are
automatically deleted when they expire. If the security
associations were created through manual configuration, they MUST
be retained and used later when the mobile node moves away from
home again. The security associations protecting Binding Updates
and Acknowledgements, and prefix discovery SHOULD NOT be deleted
as they do not depend on care-of addresses and can be used again.
o The mobile node MUST use the Home Address destination option in
Binding Updates and Mobile Prefix Solicitations, sent to the home
agent from a care-of address, so that the home address is visible
when the IPsec policy checks are made.
o The home agent MUST use the Type 2 Routing header in Binding
Acknowledgements and Mobile Prefix Advertisements sent to the
mobile node, again due to the need to have the home address
visible when the policy checks are made.
4.3. IPsec Protocol Processing Requirements
The following lists requirements for IPsec processing at the Home
Agent and the mobile node.
o The home agent and mobile node SHOULD support Mobility Header
message type as an IPsec selector.
o The home agent and mobile node SHOULD support ICMPv6 message type
as an IPsec selector.
o The home agent MUST be able to distinguish between HoTi messages
sent to itself, when it is acting as a Correspondent Node, from
those sent to Correspondent Nodes when it is acting as a home
agent, based on the destination address of the packet.
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o When securing Binding Updates, Binding Acknowledgements, and
prefix discovery, both the mobile nodes and the home agents MUST
support and SHOULD use the Encapsulating Security Payload (ESP)
[6] header in transport mode and MUST use a non-null payload
authentication algorithm to provide data origin authentication,
connectionless integrity and optional anti-replay protection.
o Tunnel mode IPsec ESP MUST be supported and SHOULD be used for the
protection of packets belonging to the return routability
procedure. A non-null encryption transform and a non-null
authentication algorithm MUST be applied.
o When ESP is used to protect Binding Updates, there is no
protection for the care-of address that appears in the IPv6 header
outside the area protected by ESP. It is important for the home
agent to verify that the care-of address has not been tampered
with. As a result, the attacker would have redirected the mobile
node's traffic to another address. In order to prevent this,
Mobile IPv6 implementations MUST use the Alternate Care-of Address
mobility option in Binding Updates sent by mobile nodes while away
from home. The exception to this is when the mobile node returns
home and sends a Binding Update to the home agent in order to de-
register.
When IPsec is used to protect return routability signaling or
payload packets, the mobile node MUST set the source address it
uses for the outgoing tunnel packets to the current primary care-
of address.
o When IPsec is used to protect return routability signaling or
payload packets, IPsec security associations are needed to provide
this protection. When the care-of address for the mobile node
changes as a result of an accepted Binding Update, special
treatment is needed for the next packets sent using these security
associations. The home agent MUST set the new care-of address as
the destination address of these packets, as if the outer header
destination address in the security association had changed.
Similarly, the home agent starts to expect the new source address
in the tunnel packets received from the mobile node.
Such address changes can be implemented, for instance, through an
API from the Mobile IPv6 implementation to the IPsec
implementation. One such API is described in [14]. It should be
noted that the use of such an API and the address changes MUST
only be done based on the Binding Updates received by the home
agent and protected by the use of IPsec. Address modifications
based on other sources, such as Binding Updates to the
correspondent nodes protected by return routability, or open
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access to an API from any application may result in security
vulnerabilities.
4.4. Dynamic Keying Requirements
The following requirements are related to the use of a dynamic key
management protocol by the mobile node and the home agent.
Section 7.2 describes the use of IKEv2 as the dynamic key management
protocol.
o The mobile node MUST use its care-of address as source address in
protocol exchanges, when using dynamic keying.
o The mobile node and the home agent MUST create security
associations based on the home address, so that the security
associations survive change in care-of address. When using IKEv2
as the key exchange protocol, the home address should be carried
as the initiator IP address in the TSi payload during the
CREATE_CHILD_SA exchange [4].
o If the mobile node has used IKEv2 to establish security
associations with its home agent, it should follow the procedures
discussed in Section 11.7.1 and 11.7.3 of the base specification
[2] to determine whether the IKE endpoints can be moved or if the
IKE SA has to be re-established.
o If the home agent has used IKEv2 to establish security
associations with the mobile node, it should follow the procedures
discussed in Section 10.3.1 and 10.3.2 of the base specification
[2] to determine whether the IKE endpoints can be moved or if the
IKE SA has to be re-established.
5. Selector Granularity Considerations
IPsec implementations are compatible with this document even if they
do not support fine grain selectors such as the Mobility Header
message type and ICMPv6 message type. For various reasons, some
implementations may choose to support only coarse grain selectors
(i.e., addresses and in some case protocol field) for forwarded
traffic. As finer grain selectors give a better control, i.e., the
protection is only applied when required, the examples in the
document always use the finest granularity.
The following describes different ways of setting up IPsec policies
for protecting Mobile IPv6 messages:
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o The IPsec implementations on the mobile node and the home agent
support fine grain selectors, including the Mobility Header
message type This is the case assumed in the IPsec SPD and SAD
examples in this document.
o The IPsec implementations only support selectors at a protocol
level. The protection of Return Routability Messages uses a setup
similar to the regular payload packets to the correspondent node
with the protocol selector set to Mobility Header messages. All
tunneled Mobility Header messages will be protected.
o The last case is where the protocol selector is not available or
for privacy considerations all traffic tunneled between the mobile
node and the home agent is protected. This uses IPsec tunnel SA
with the protocol selector set to 'any'.
The last case where all tunneled traffic is protected introduces some
additional considerations:
o If there is just one IPsec SA providing protection for all
traffic, then the SA MUST fulfill the requirements for protecting
the Return Routability messages which require confidentiality
protection. There can also be separate tunnel mode SPD entries
for protecting the Return Routability messages with a higher
priority.
6. Manual Configuration
This section describes the SPD and SAD entries that can be used to
protect Mobile IPv6 signaling messages. The SPD and SAD entries are
only example configurations. A particular mobile node implementation
and a home agent implementation could configure different SPD and SAD
entries as long as they provide the required security of the Mobile
IPv6 signaling messages.
For the examples described in this document, a mobile node with home
address, "home_address_1", primary care-of address,
"care_of_address_1", a home agent with address, "home_agent_1" and a
user of the mobile node with identity "user_1" are assumed. If the
home address of the mobile node changes, the SPD and SAD entries need
to re-created or updated for the new home address.
6.1. Binding Updates and Acknowledgements
The following are the SPD and SAD entries on the mobile node and the
home agent to protect Binding Updates and Acknowledgements.
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mobile node SPD-S:
- IF source = home_address_1 & destination = home_agent_1 &
proto = MH & local_mh_type =BU & remote_mh_type =
BAck
Then use SA SA1 (OUT) and SA2 (IN)
mobile node SAD:
- SA1(OUT, spi_a, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = MH & mh_type = BU
- SA2(IN, spi_b, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = MH & mh_type = BAck
home agent SPD-S:
- IF source = home_agent_1 & destination = home_address_1 &
proto = MH & local_mh_type = BAck & remote_mh_type
= BU
Then use SA SA2 (OUT) and SA1 (IN)
home agent SAD:
- SA2(OUT, spi_b, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = MH & mh_type = BAck
- SA1(IN, spi_a, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = MH & mh_type = BU
6.2. Return Routabililty Messages
The following are the SPD and SAD entries on the mobile node and the
home agent to protect Return Routability messages.
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mobile node SPD-S:
- IF source = home_address_1 & destination = any &
proto = MH & local_mh_type = HoTi & remote_mh_type = HoT
Then use SA SA3 (OUT) and SA4 (IN)
mobile node SAD:
- SA3(OUT, spi_c, home_agent_1, ESP, TUNNEL):
source = home_address_1 & destination = any & proto = MH &
mh_type = HoTi
- SA4(IN, spi_d, care_of_address_1, ESP, TUNNEL):
source = any & destination = home_address_1 & proto = MH &
mh_type = HoT
home agent SPD-S:
- IF destination = home_address_1 & source = any &
proto = MH & local_mh_type = HoT & remote_mh_type =
HoTi
Then use SA SA4 (OUT) and SA3 (IN)
home agent SAD:
- SA4(OUT, spi_d, care_of_address_1, ESP, TUNNEL):
source = any & destination = home_address_1 & proto = MH &
mh_type = HoT
- SA3(IN, spi_c, home_agent_1, ESP, TUNNEL):
source = home_address_1 & destination = any & proto = MH &
mh_type = HoTi
6.3. Mobile Prefix Discovery Messages
The following are the SPD and SAD entries used to protect Mobile
Prefix Discovery messages.
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mobile node SPD-S:
- IF source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6 & local_icmp6_type = MPS &
remote_icmp6_type = MPA
Then use SA SA5 (OUT) and SA6 (IN)
mobile node SAD:
- SA5(OUT, spi_e, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6 & icmp6_type = MPS
- SA6(IN, spi_f, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6 & icmp6_type = MPA
home agent SPD-S:
- IF source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6 & local_icmp6_type = MPA &
remote_icmp6_type = MPS
Then use SA SA6 (OUT) and SA5 (IN)
home agent SAD:
- SA6(OUT, spi_f, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6 & icmp6_type = MPA
- SA5(IN, spi_e, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6 & icmp6_type = MPS
6.4. Payload Packets
Regular payload traffic between the mobile node and the correspondent
node tunneled through the home agent can be protected by IPsec, if
required. The mobile node and the home agent use ESP in tunnel mode
to protect the tunneled traffic. The SPD and SAD entries shown in
Section 5.2.4 of [3] are applicable here.
7. Dynamic Configuration
This section describes the use of IKEv2 to setup the required
security associations.
7.1. Security Policy Database Entries
The following sections describe the security policy entries on the
mobile node and the home agent. The SPD entries are only example
configurations. A particular mobile node implementation and a Home
Agent implementation could configure different SPD entries as long as
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they provide the required security of the Mobile IPv6 signaling
messages.
In the examples shown below, the identity of the user of the mobile
node is assumed to be user_1, the home address of the mobile node is
assumed to be home_address_1, he primary care-of address of the
mobile node is assumed to be care_of_address_1 and the IPv6 address
of the Home Agent is assumed to be home_agent_1.
7.1.1. Binding Updates and Acknowledgements
The following are the SPD entries on the mobile node and the home
agent for protecting Binding Updates and Acknowledgements.
mobile node SPD-S:
- IF source = home_address_1 & destination = home_agent_1 &
proto = MH & local_mh_type = BU & remote_mh_type = BAck
Then use SA ESP transport mode
IDi = user_1, IDr = home_agent_1,
TSi = home_address_1, MH, BU
TSr = home_agent_1, MH, BAck
home agent SPD-S:
- IF source = home_agent_1 & destination = home_address_1 &
proto = MH & local_mh_type = BAck & remote_mh_type = BU
Then use SA ESP transport mode
IDi = home_agent_1, IDr = user_1
TSi = home_agent_1, MH, BAck
TSr = home_address_1, MH, BU
In the examples shown above, the home address of the mobile node
might not be available all the time. For instance, the mobile node
might have not configured a home address yet. When the mobile node
acquires a new home address, it must either add the address to the
corresponding SPD entries or create the SPD entries for the home
address.
The home agent should have named SPD entries per mobile node, based
on the identity of the mobile node. The identity of the mobile node
is stored in the "Name" selector in the SPD [5]. The home address
presented by the mobile node during the IKE negotiation is stored as
the remote IP address in the resultant IPsec security associations.
The home agent MAY also have generic SPD entries to prevent mobility
header traffic that requires IPsec protection from bypassing the
IPsec filters.
The Mobility Header message type is negotiated by placing it in the
most significant eight bits of the 16 bit local "port" selector
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during IKEv2 exchange. For more details, refer to [5]. The TSi and
TSr payloads in the above examples will contain many other selectors
apart from home_address_1. For the sake of brevity, we show only
those values that relevant for Mobile IPv6.
7.1.2. Return Routability Messages
The following are the SPD entries on the mobile node and the home
agent for protecting the Return Routability messages.
mobile node SPD-S:
- IF source = home_address_1 & destination = any &
proto = MH & local_mh_type = HoTi &
remote_mh_type = HoT
Then use SA ESP tunnel mode
IDi = user_1, IDr = home_agent_1,
TSi = home_address_1, MH, HoTi
TSr = any, MH, HoT
outer src addr = care_of_address_1,
outer dst addr = home_agent_1,
inner src addr = home_address_1
home agent SPD-S:
- IF source = any & destination = home_address_1 &
proto = MH & local_mh_type = HoT &
remote_mh_type = HoTi
Then use SA ESP tunnel mode
IDi = home_agent_1, IDr = user_1
TSi = any, MH, HoT
TSr = home_address_1, MH, HoTi
outer src addr = home_agent_1,
outer dst addr = care_of_address_1,
inner dst addr = home_address_1
When the mobile node's care-of address changes the SPD entries on
both the mobile node and the home agent must be updated. The home
agent knows about the change in care-of address of the mobile node
when it receives a Binding Update from the mobile node.
7.1.3. Mobile Prefix Discovery Messages
The following are the SPD entries on the mobile node and the home
agent for protecting Mobile Prefix Discovery messages.
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mobile node SPD-S:
- IF source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6 & local_mh_type = MPS &
remote_mh_type = MPA
Then use SA ESP transport mode
IDi = user_1, IDr = home_agent_1,
TSi = home_address_1, ICMPv6, MPS
TSr = home_agent_1, ICMPv6, MPA
home agent SPD-S:
- IF source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6 & local_mh_type = MPA &
remote_mh_type = MPS
Then use SA ESP transport mode
IDi = home_agent_1, IDr = user_1
TSi = home_agent_1, ICMPv6, MPA
TSr = home_address_1, ICMPv6, MPS
In the examples shown above, the home address of the mobile node
might not be available all the time. When the mobile node acquires a
new home address, it must add the address to the corresponding SPD
entries.
The TSi and TSr payloads in the above examples will contain many
other selectors apart from home_address_1. For brevity, they are not
show here.
7.1.4. Payload Packets
The following are the SPD entries on the mobile node and the home
agent if payload traffic exchanged between the mobile node and its
Correspondent Node needs to be protected. The SPD entries are
similar to the entries for protecting Return Routability messages and
have lower priority than the above SPD entries.
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mobile node SPD-S:
- IF interface = IPv6 tunnel to home_agent_1 & proto = X
Then use SA ESP tunnel mode
IDi = user_1, IDr = home_agent_1,
TSi = home_address_1, X, port
TSr = any, X, port
outer src addr = care_of_address_1
outer dst addr = home_agent_1,
inner src addr = home_address_1
home agent SPD-S:
- IF interface = IPv6 tunnel to home_address_1 & proto = X
Then use SA ESP tunnel mode
IDi = home_agent_1, IDr = user_1,
TSi = any, X, port
TSr = home_address_1, X, port
outer src addr = home_agent_1,
outer dst addr = care_of_address_1,
inner dst addr = home_address_1
7.2. Security Association negotiation using IKEv2
Mobile IPv6 signaling messages are typically initiated by the mobile
node. The mobile node sends a Binding Update to the home agent
whenever it moves and acquires a new care-of address.
The mobile node initiates an IKEv2 protocol exchange if the required
security associations are not present. A possible mechanism used for
mutual authentication is a shared secret between the mobile node and
the home agent. The home agent uses the identity of the mobile node
to identify the corresponding shared secret. When a public key based
mechanism is available, it should be the preferred mechanism for
mutual authentication: private keys are used to generate the AUTH
payload and identities are verified with certificate information
transmitted by CERT payloads. If the mobile node is configured with
the home agent information including the public key that corresponds
to the home agent, then the mobile node MAY exclude the CERTREQ
payload in its IKE_AUTH third message. Similarly, the home agent MAY
exclude the CERTREQ payload in its IKE_SA_INIT second message if it
is configured with the mobile node information.
If a shared secret is being used, the mobile node uses the shared
secret to generate the AUTH payload in the IKE_AUTH exchange. If the
mobile node is using a public key based mechanism, then it uses its
private key to generate the AUTH payload in the IKE_AUTH exchange.
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Mobile Node Home Agent
----------- ----------
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ]
HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, SAi2, TSi, TSr}
-->
<-- HDR, SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}
The mobile node should always includes its identity in the IDi
payload in the IKE_AUTH exchange. The mobile node could use the
following different types of identities to identity itself to the
home agent.
o Home Address - The mobile node could use its statically configured
home address as its identity. In this case the ID Type field is
set to ID_IPV6_ADDR.
o FQDN - The mobile node can use a Fully Qualified Domain Name as
the identifier and set the ID Type field to ID_FQDN.
o RFC 822 identifier - If the mobile node uses a RFC 822 identifier
[10], it sets the ID Type field to ID_RFC822_ADDR.
In the IKE_AUTH exchange, the mobile node includes the home address
and the appropriate selectors in the TSi (Traffic Selector-initiator)
payload to negotiate IPsec security associations for protecting the
Binding Update and Binding Acknowledgement messages. The mobile node
MAY use a range of selectors that includes the mobility message types
for Binding Update and Binding Acknowledgement to use the same pair
of IPsec security association for both messages.
After the IKE_AUTH exchange completes, the mobile node initiates
CREATE_CHILD_SA exchanges to negotiate additional security
associations for protecting Return Routability signaling, Mobile
Prefix Discovery messages and optionally payload traffic. The
CREATE_CHILD_SA exchanges are protected by the security association
created during the IKE_AUTH exchange. If a correspondent node, that
is also a mobile node, initiates the return routability exchange,
then the home agent initiates the CREATE_CHILD_SA exchange to
negotiate security associations for protecting Return Routabilty
messages.
It is important that the security associations are created based on
the home address of the mobile node, so that the security
associations survive care-of address change. The mobile node MUST
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use its home address as the initiator IP address in the TSi payload
in the CREATE_CHILD_SA exchange in order to create the security
associations for the home address.
Mobile Node Home Agent
----------- ----------
HDR, SK {[N], SA, Ni, [KEi],
[TSi, TSr]} -->
<-- HDR, SK {SA, Nr, [KEr],
[TSi, TSr]}
When PKI based authentication is used between the mobile node and the
Home Agent, the identity presented by the mobile node in the IDi
payload must correspond to the identity in the certificate obtained
by the Home Agent. The home agent uses the identity presented in the
IDi payload to lookup the policy and the certificate that corresponds
to the mobile node. If the mobile node presents its home address in
the IDi payload, then the home agent MUST verify that the home
address matches the address in the iPAddress field in the
SubjectAltName extension [9].
When the mobile node uses its home address in the IDi field,
implementations are required to match the source address in the outer
most IP header with the IP address in the IDi field [9]. This
verification step, however, should be configurable [9]. With Mobile
IPv6, this verification step will always fail because the source
address in the IP header is the care-of address and the IP address in
the IDi field is the home address. Therefore, this verification step
MUST be disabled.
7.3. Movements and Dynamic Keying
If the mobile node moves and its care-of address changes, the IKEv2
SA might not be valid, unless the mobility extensions defined in [13]
are implemented by both the mobile node and the home agent. RFC 3775
defines a mechanism based on the successful exchange of Binding
Update and Binding Acknowledgement messages. The mobile node
establishes the IKE SA with the home agent using its primary care-of
address. The IKE SA endpoints are updated on the home agent when it
receives the Binding Update from the mobile node's new care-of
address and on the mobile node when it sends the Binding Update to
the home agent or when it receives the Binding acknowledgement sent
by the home agent. This capability to change IKE endpoints is
indicated through setting the Key Management Capability (K) flag [2]
in the Binding Update and Binding Acknowledgement messages. If the
mobile node or the home agent does not support this capability, then
an IKEv2 exchange MUST be initiated to re-establish a new IKE SA.
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8. The use of EAP authentication
In addition to using public key signatures and shared secrets, EAP
[11] can be used with IKEv2 for authenticating the mobile node to the
home agent.
The mobile node indicates that it wants to use EAP by including the
IDi payload but leaving out the AUTH payload in the first message
during the IKE_AUTH exchange. The home agent then includes an EAP
payload if it is willing to use an extensible authentication method.
Security associations are not created until the subsequent IKE_AUTH
exchange after successful EAP authentication. The use of EAP adds at
least two round trips to the IKE negotiation.
Mobile Node Home Agent
------------ ----------
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ]
HDR, SK {IDi, [CERTREQ,] [IDr,]
SAi2, TSi, TSr}-->
<-- HDR, SK {IDr, [CERT,] AUTH,
EAP }
HDR, SK {EAP} -->
<-- HDR, SK {EAP (success)}
HDR, SK {AUTH} -->
<-- HDR, SK {AUTH, SAr2, TSi,
TSr}
Some EAP methods generate a shared key on the mobile node and the
Home Agent once the EAP authentication succeeds. In this case, the
shared key is used to generate the AUTH payloads in the subsequent
messages. The shared key, if used to generate the AUTH payloads,
MUST NOT be used for any other purpose. For more details, refer to
[4].
The use of EAP between the mobile node and the home agent might
require the home agent to contact an authorization server like the
AAA Home server, on the home link, to authenticate the mobile node.
Please refer to [7] for more details.
The IKEv2 specification [4] requires that public key based mechanism
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be used to authenticate the home agent to the mobile node, when EAP
is used. This should be used by default by the mobile node and the
home agent. If the EAP method that is used, supports mutual
authentication and key generation, then the mobile node MAY use EAP
itself to authenticate the home agent. The mobile node can request
this by including the EAP_ONLY_AUTHENTICATION notification payload
[8] in message 3. If the home agent supports the
EAP_ONLY_AUTHENTICATION notification payload and agrees to use EAP,
it omits the public key based AUTH and CERT payloads in message 4.
If the home agent does not support this mechanism, it rejects it by
including an AUTH payload in message 4. More details can be found in
[8].
9. Dynamic Home Address Configuration
The mobile node can dynamically configure a home address by including
a Configuration Payload in the IKE_AUTH exchange, with a request for
an address from the home link. The mobile node should include an
INTERNAL_IP6_ADDRESS attribute in the CFG_REQUEST Payload. The
mobile node MAY also include the INTERNAL_IP6_SUBNET attribute if it
wants to obtain information about the IPv6 prefixes on the home link.
If the mobile node wants to configure a DNS server from the home link
it can request for the DNS server information by including an
INTERNAL_IP6_DNS attribute in the CFG_REQUEST payload.
When the home agent receives a configuration payload with a
CFG_REQUEST for INTERNAL_IP6_ADDRESS, it replies with a valid home
address for the mobile node. The INTERNAL_IP6_ADDRESS attribute in
the CFG_REPLY contains the prefix length of the home prefix in
addition to a 128 bit home address. The home agent could use a local
database or contact a DHCPv6 server on the home link to allocate a
home address. The Home Agent should also include an
INTERNAL_ADDRESS_EXPIRY attribute to indicate to the mobile node, the
duration for which the dynamically allocated home address is valid.
Mobile Node Home Agent
----------- ----------
HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, CP(CFG_REQUEST),
SAi2, TSi, TSr}
-->
<-- HDR, SK {IDr, [CERT,] AUTH,
CP(CFG_REPLY), SAr2,
TSi, TSr}
The mobile node could suggest a home address that it wants to use in
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the CFG_REQUEST. For example, this could be a home address that it
was allocated before or could be an address the mobile node auto-
configured from the IPv6 prefix on the home link. The Home Agent
could let the mobile node use the same home address by setting the
INTERNAL_IP6_ADDRESS attribute in the CFG_REPLY payload to the same
home address. If the home agent wants the mobile node to use a
different home address, it sends a new home address in the
INTERNAL_IP_ADDRESS attribute in the CFG_REPLY payload. The Mobile
Node MUST stop using its old home address and start using the newly
allocated home address.
In case the home agent is unable to allocate a home address for the
mobile node during the IKE_AUTH exchange, it MUST send a Notify
Payload with an INTERNAL_ADDRESS_FAILURE message.
10. Security Considerations
This document describes how IPsec can be used to secure Mobile IPv6
signaling messages. Please refer to RFC 3775 for security
considerations related to the use of IPsec with Mobile IPv6.
A misbehaving mobile node could create IPsec security associations
for a home address that belongs to another mobile node. Therefore,
the home agent should check if a particular mobile node is authorized
to use a home address before creating IPsec security associations for
the home address. If the home address is assigned as described in
Section 9, the home agent MUST associate the home address with the
identity used in IKE negotiation. The home agent MAY store the
assigned home address in the SPD entries created for the mobile node.
The use of EAP for authenticating the mobile node to the home agent
is described in Section 8. This document recommends that if the EAP
method used, supports mutual authentication, then EAP itself be used
for authenticating the home agent to the mobile node also. This runs
contrary to the recommendation in [4]. The home agent can ignore the
recommendation in this document and implement EAP authentication as
described in the IKEv2 specification. Security considerations
related to the use of EAP with IKEv2 are described in [4] and [8].
11. IANA Considerations
This document requires no action from IANA.
12. Acknowledgements
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The author would like to thank Mika Joutsenvirta, Pasi Eronen,
Francis Dupont, Jari Arkko, Gerardo Giaretta and Shinta Sugimoto for
reviewing the draft.
Many of the requirements listed in Section 4 are copied from RFC
3776. Therefore, the authors of RFC 3776 are acknowledged.
13. References
13.1. 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.
[3] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
Protect Mobile IPv6 Signaling Between Mobile Nodes and Home
Agents", RFC 3776, June 2004.
[4] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-17 (work in progress), October 2004.
[5] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", draft-ietf-ipsec-rfc2401bis-06 (work in progress),
April 2005.
[6] Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-10 (work in progress), March 2005.
13.2. Informative References
[7] Giaretta, G., "Goals for AAA-HA interface",
draft-giaretta-mip6-aaa-ha-goals-00 (work in progress),
September 2004.
[8] Eronen, P., "Extension for EAP Authentication in IKEv2",
draft-eronen-ipsec-ikev2-eap-auth-03 (work in progress),
April 2005.
[9] Korver, B., "The Internet IP Security PKI Profile of IKEv1/
ISAKMP, IKEv2, and PKIX",
draft-ietf-pki4ipsec-ikecert-profile-05 (work in progress),
August 2005.
[10] Crocker, D., "Standard for the format of ARPA Internet text
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messages", STD 11, RFC 822, August 1982.
[11] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[12] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[13] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
draft-ietf-mobike-protocol-01 (work in progress), July 2005.
[14] Sugimoto, S., "PF_KEY Extension as an Interface between Mobile
IPv6 and IPsec/IKE", draft-sugimoto-mip6-pfkey-migrate-01 (work
in progress), September 2005.
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Authors' Addresses
Vijay Devarapalli
Nokia Research Center
313 Fairchild Drive
Mountain View, CA 94043
USA
Email: vijay.devarapalli@nokia.com
Francis Dupont
Point6
c/o GET/ENST Bretagne
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: Francis.Dupont@enst-bretagne.fr
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