IKEv2 Mobility and Multihoming T. Kivinen
(mobike) Safenet, Inc.
Internet-Draft H. Tschofenig
Expires: January 19, 2006 Siemens
July 18, 2005
Design of the MOBIKE Protocol
draft-ietf-mobike-design-03.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The MOBIKE (IKEv2 Mobility and Multihoming) working group is
developing extensions for the Internet Key Exchange Protocol version
2 (IKEv2). These extensions should enable an efficient management of
IKE and IPsec Security Associations when a host possesses multiple IP
addresses and/or where IP addresses of an IPsec host change over time
(for example, due to mobility).
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This document discusses the involved network entities, and the
relationship between IKEv2 signaling and information provided by
other protocols. Design decisions for the MOBIKE protocol,
background information and discussions within the working group are
recorded.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Mobility Scenario . . . . . . . . . . . . . . . . . . . . 7
3.2 Multihoming Scenario . . . . . . . . . . . . . . . . . . . 8
3.3 Multihomed Laptop Scenario . . . . . . . . . . . . . . . . 9
4. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Design Considerations . . . . . . . . . . . . . . . . . . . . 13
5.1 Indicating Support for MOBIKE . . . . . . . . . . . . . . 13
5.2 Changing a Preferred Address and Multi-homing Support . . 13
5.2.1 Storing a single or multiple addresses . . . . . . . . 14
5.2.2 Indirect or Direct Indication . . . . . . . . . . . . 15
5.2.3 Connectivity Tests using IKEv2 Dead-Peer Detection . . 16
5.3 Simultaneous Movements . . . . . . . . . . . . . . . . . . 17
5.4 NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 18
5.5 Changing addresses or changing the paths . . . . . . . . . 20
5.6 Return Routability Tests . . . . . . . . . . . . . . . . . 20
5.7 Employing MOBIKE results in other protocols . . . . . . . 23
5.8 Scope of SA changes . . . . . . . . . . . . . . . . . . . 24
5.9 Zero Address Set . . . . . . . . . . . . . . . . . . . . . 25
5.10 IPsec Tunnel or Transport Mode . . . . . . . . . . . . . . 25
5.11 Message Representation . . . . . . . . . . . . . . . . . . 26
6. Security Considerations . . . . . . . . . . . . . . . . . . . 28
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
9. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 31
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.1 Normative references . . . . . . . . . . . . . . . . . . . 32
10.2 Informative References . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 34
Intellectual Property and Copyright Statements . . . . . . . . 35
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1. Introduction
The purpose of IKEv2 is to mutually authenticate two hosts, establish
one or more IPsec Security Associations (SAs) between them, and
subsequently manage these SAs (for example, by rekeying or deleting).
IKEv2 enables the hosts to share information that is relevant to both
the usage of the cryptographic algorithms that should be employed
(e.g., parameters required by cryptographic algorithms and session
keys) and to the usage of local security policies, such as
information about the traffic that should experience protection.
IKEv2 assumes that an IKE SA is created implicitly between the IP
address pair that is used during the protocol execution when
establishing the IKEv2 SA. This means that, in each host, only one
IP address pair is stored for the IKEv2 SA as part of a single IKEv2
protocol session, and, for tunnel mode SAs, the hosts places this
single pair in the outer IP headers. Existing documents make no
provision to change this pair after an IKE SA is created.
There are scenarios where one or both of the IP addresses of this
pair may change during an IPsec session. In principle, the IKE SA
and all corresponding IPsec SAs could be re-established after the IP
address has changed. However, this can be problematic, as the device
might be too slow for this task. Moreover, manual user interaction
(for example when using SecurID cards) might be required as part of
the IKEv2 authentication procedure. Therefore, an automatic
mechanism is neeed that updates the IP addresses associated with the
IKE SA and the IPsec SAs. MOBIKE provides such a mechanism.
The work of the MOBIKE working group and therefore this document is
based on the assumption that the mobility and multi-homing extensions
are developed for IKEv2 [I-D.ietf-ipsec-ikev2]. As IKEv2 is built on
the architecture described in RFC2401bis [I-D.ietf-ipsec-rfc2401bis],
all protocols developed within the MOBIKE working group must be
compatible with both IKEv2 and the architecture described in
RFC2401bis. The document does not aim to neither provide support
IKEv1 [RFC2409] nor the architecture described in RFC2401 [RFC2401].
This document is structured as follows. After introducing some
important terms in Section 2 a number of relevant usage scenarios are
discussed in Section 3. Section 4 discusses the interoperation of
MOBIKE with other protocols and processes that may run in the local
machine. Finally, Section 5 discusses design considerations
affecting the MOBIKE protocol. The document concludes in Section 6
with security considerations.
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2. Terminology
This section introduces the terminology that is used in this
document.
Peer:
A peer is an IKEv2 endpoint. In addition, a peer implements the
MOBIKE extensions, as defined in this and related documents.
Available address:
An address is said to be available if the following conditions are
met:
* The address has been assigned to an interface.
* If the address is an IPv6 address, we additionally require (a)
that the address is valid as defined in RFC 2461 [RFC2461], and
(b) that the address is not tentative as defined in RFC 2462
[RFC2462]. In other words, we require the address assignment
to be complete.
Note that this explicitly allows an address to be optimistic as
defined in [I-D.ietf-ipv6-optimistic-dad].
* If the address is an IPv6 address, it is a global unicast or
unique site-local address, as defined in [I-D.ietf-ipv6-unique-
local-addr]. That is, it is not an IPv6 link-local. Where
IPv4 is considered, it is not an RFC 1918 [RFC1918] address.
* The address and interface is acceptable for sending and
receiving traffic according to a local policy.
This definition is taken from [I-D.arkko-multi6dt-failure-
detection]
.
Locally Operational Address:
An address is said to be locally operational if it is available
and its use is locally known to be possible and permitted. This
definition is taken from [I-D.arkko-multi6dt-failure-detection].
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Operational address pair:
A pair of operational addresses are said to be an operational
address pair, if and only if bidirectional connectivity can be
shown between the two addresses. Note that sometimes it is
necessary to consider connectivity on a per-flow level between two
endpoints needs to be tested. This differentiation might be
necessary to address certain Network Address Translation types or
specific firewalls. This definition is taken from [I-D.arkko-
multi6dt-failure-detection] and adapted for the MOBIKE context.
Although it is possible to further differentiate unidirectional
and bidirectional operational address pairs, only bidirectional
connectivity is relevant to this document and unidirectional
connectivity is out of scope.
Path:
The sequence of routers traversed by the MOBIKE and IPsec packets
exchanged between the two peers. Note that this path may be
affected not only by the involved source and destination IP
addresses, but also by the transport protocol. Since MOBIKE and
IPsec packets have a different appearance on the wire they might
be routed along a different path, for example by load balancers.
This definition is taken from [RFC2960] and adapted to the MOBIKE
context.
Primary Path:
The sequence of routers traversed by an IP packet that carries the
default source and destination addresses is said to be the Primary
Path. This definition is taken from [RFC2960] and adapted to the
MOBIKE context.
Preferred Address:
The IP address of a peer to which MOBIKE and IPsec traffic should
be sent by default. A given peer has only one active preferred
address at a given point in time, except for the small time period
where it switches from an old to a new preferred address. This
definition is taken from [I-D.ietf-hip-mm] and adapted to the
MOBIKE context.
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Peer Address Set:
We denote the two peers of a MOBIKE session by peer A and peer B.
A peer address set is the subset of locally operational addresses
of peer A that is sent to peer B. A policy available at peer A
indicates which addresses are included in the peer address set.
Such a policy might be created either manually or automatically
through interaction with other mechanisms that indicate new
available addresses.
Terminology regarding NAT types (e.g. Full Cone, Restricted Cone,
Port Restricted Cone and Symmetric), can be found in Section 5 of
[RFC3489]. For mobility related terminology (e.g. Make-before-break
or Break-before-make) see [RFC3753].
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3. Scenarios
In this section we discuss three typical usage scenarios for the
MOBIKE protocol.
3.1 Mobility Scenario
Figure 1 shows a break-before-make mobility scenario where a mobile
node changes its point of network attachment. Prior to the change,
the mobile node had established an IPsec connection with a security
gateway which offered, for example, access to a corporate network.
The IKEv2 exchange that facilitated the set up of the IPsec SA(s)
took place over the path labeled as 'old path'. The involved packets
carried the MN's "old" IP address and were forwarded by the "old"
access router (OAR) to the security gateway (GW).
When the MN changes its point of network attachment, it obtains a new
IP address using statefu address configuration techniques or via the
stateless address autoconfiguration mechanism. The goal of MOBIKE,
in this scenario, is to enable the MN and the GW to continue using
the existing SAs and to avoid setting up a new IKE SA. A protocol
exchange, denoted by 'MOBIKE Address Update', enables the peers to
update their state as necessary.
Note that in a break-before-make scenario the MN obtains the new IP
address after it can no longer be reached at the old IP address. In
a make-before-break scenario, the MN is, for a given period of time,
reachable at both the old and the new IP address. MOBIKE should work
in both the above scenarios.
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(Initial IKEv2 Exchange)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>v
Old IP +--+ +---+ v
address |MN|------> |OAR| -------------V v
+--+ +---+ Old path V v
. +----+ v>>>>> +--+
.move | R | -------> |GW|
. | | >>>>> | |
v +----+ ^ +--+
+--+ +---+ New path ^ ^
New IP |MN|------> |NAR|--------------^ ^
address +--+ +---+ ^
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>^
(MOBIKE Address Update)
---> = Path taken by data packets
>>>> = Signaling traffic (IKEv2 and MOBIKE)
...> = End host movement
Figure 1: Mobility Scenario
3.2 Multihoming Scenario
Another MOBIKE usage scenario is depicted in Figure 2. In this
scenario, the MOBIKE peers are equipped with multiple interfaces (and
multiple IP addresses). Peer A has two interface cards with two IP
addresses, IP_A1 and IP_A2, and peer B has two IP addresses, IP_B1
and IP_B2. Each peer selects one of its IP addresses as the
preferred address which is used for subsequent communication.
Various reasons, (e.g hardware or network link failures), may require
a peer to switch from one interface to another.
+------------+ +------------+
| Peer A | *~~~~~~~~~* | Peer B |
| |>>>>>>>>>> * Network *>>>>>>>>>>| |
| IP_A1 +-------->+ +--------->+ IP_B1 |
| | | | | |
| IP_A2 +********>+ +*********>+ IP_B2 |
| | * * | |
+------------+ *~~~~~~~~~* +------------+
---> = Path taken by data packets
>>>> = Signaling traffic (IKEv2 and MOBIKE)
***> = Potential future path through the network
(if Peer A and Peer B change their preferred
address)
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Figure 2: Multihoming Scenario
Note that MOBIKE does not aim to support load balancing between
multiple IP addresses. That is, each peer uses only one of the
available IP addresses at a given point in time.
3.3 Multihomed Laptop Scenario
The third scenario we consider is about a laptop, which has multiple
interface cards and therefore several ways to connect to the network.
It may for example have a fixed Ethernet card, a WLAN interface, a
GPRS adaptor, a Bluetooth interface or USB hardware. Not all
interfaces are connected to the network at all times for a number of
reasons (e.g., cost, availability of certain link layer technologies,
user convenience). The mechanism that determines which interfaces
are connected to the network at any given point in time is outside
the scope of the MOBIKE protocol and, as such, this document.
However, as the laptop changes its point of attachment to the
network, the set of IP addresses under which the laptop is reachable,
changes too.
Even if IP addresses change due to interface switching or mobility,
the IP address obtained via the configuration payloads within IKEv2
remain unaffected. The IP address obtained via the IKEv2
configuration payloads allow the configuration of the inner IP
address of the IPsec tunnel. As such, applications might not detect
any change at all.
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4. Framework
The working group will develop a MOBIKE protocol which needs to
perform the following operations:
o inform the other peer about the peer address set
o inform the other peer about the preferred address
o test connectivity along a path and thereby to detect an outage
situation
o change the preferred address
o change the peer address set
o Ability to deal with Network Address Translation devices
The technical details of these functions are discussed below.
Although MOBIKE will have to interact with other mechanisms, the
working group is chartered to leave this aspect outside the scope.
When a MOBIKE peer initiates a protocol exchange it needs to define a
peer address set based on the IP addresses available to it. The peer
may want to make this set available to the other peer. The IKEv2
Initiator does not need to indicate which of the addresses in the
peer address set is its preferred address. This is because the
Initiator has to place its preferred address into the source IP
address field of the IP header with the initial message exchange.
Additionally, the Initiator expects incoming signaling messages to
arrive at this address. The peer address set and the preferred
address are defined based on interaction with other components within
a host. In some cases, the peer address set may be available before
the initial protocol exchange and does not change during the lifetime
of the IKE-SA. The preferred address might change due to policy
reasons. Section 3 describes three scenarios in which the peer
address set is modified (by adding or deleting addresses). In these
scenarios the preferred address may change as well.
A modification of the peer address set or a change of the preferred
address typically is the result of the MOBIKE peer's local policy and
by the interaction with other protocols (such as DHCP or IPv6
Neighbor Discovery).
Figure 3 shows an example protocol interaction between a pair of
MOBIKE peers. MOBIKE interacts with the IPsec engine using the
PF_KEY API [RFC2367]. Using this API, the MOBIKE daemon can create
entries in the Security Association (SAD) and Security Policy
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Databases (SPD). The IPsec engine may also interact with IKEv2 and
MOBIKE daemon using this API. The content of the Security Policy and
Security Association Databases determines what traffic is protected
with IPsec in which fashion. MOBIKE, on the other hand, receives
information from a number of sources that may run both in kernel-mode
and in user-mode. Information relevant for MOBIKE might be stored in
a database. The contents of such a database, along with the
occurrence of events of which the MOBIKE process is notified, form
the basis on which MOBIKE decides regarding the set of available
addresses, the peer address set, and the preferred address. Policies
may also affect the selection process.
The a peer address set and the preferred address needs to be
available to the other peer. In order to address certain failure
cases, MOBIKE should perform connectivity tests between the peers
(potentially over a number of different paths). Although a number of
address pairs may be available for such tests, the most important is
the pair (source address, destination address) of the primary path.
This is because this pair is selected for sending and receiving
MOBIKE signaling and IPsec traffic. If a problem along this primary
path is detected (e.g., due to a router failure) it is necessary to
switch to a new primary path. In order to be able to do so quickly,
it may be helpful to perform connectivity tests of other paths
periodically. Such a technique would also help in identifying
previously disconnected paths that become operational.
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+-------------+ +---------+
|User-space | | MOBIKE |
|Protocols | +-->>| Daemon |
|relevant for | | | |
|MOBIKE | | +---------+
+-------------+ | ^
User Space ^ | ^
++++++++++++++++++++++++++++ API ++++++ API ++++ PF_KEY ++++++++
Kernel Space v | v
_______ | v
+-------------+ / \ | +--------------+
|Routing | / Trigger \ | | IPsec |
|Protocols |<<-->>| Database |<<-+ +>+ Engine |
| | \ / | | (+Databases) |
+-----+---+---+ \_______/ | +------+-------+
^ ^ ^ | ^
| +---------------+-------------+--------+-----+
| v | | |
| +-------------+ | | |
I | |Kernel-space | | | | I
n | +-------->+Protocols +<----+-----+ | | n
t v v |relevant for | | v v v t
e +----+---+-+ |MOBIKE | | +-+--+-----+-+ e
r | Input | +-------------+ | | Outgoing | r
f | Packet +<--------------------------+ | Interface | f
==a>|Processing|===============================| Processing |=a>
c | | | | c
e +----------+ +------------+ e
s s
===> = IP packets arriving/leaving a MOBIKE node
<-> = control and configuration operations
Figure 3: Framework
Please note that Figure 3 illustrates an example of how a MOBIKE
implementation could work. Hence, it serves illustrative purposes
only.
Extensions of the PF_KEY interface required by MOBIKE are also within
the scope of the working group. Finally, certain optimizations for
wireless environments are also covered.
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5. Design Considerations
This section discusses aspects affecting the design of the MOBIKE
protocol.
5.1 Indicating Support for MOBIKE
In order for MOBIKE to function, both peers must implement the MOBIKE
extension of IKEv2. If one or none of the peers supports MOBIKE,
then, whenever an IP address changes, IKEv2 will have to be re-run in
order to create a new IKE SA and the respective IPsec SAs. In
MOBIKE, a peer needs to be confident that its address change messages
are understood by the other peer. If these messages are not
understood, it is possible that connectivity between the peers is
lost.
One way to ensure that a peer receives feedback on whether or not its
messages are understood by the other peer, is by using IKEv2
messaging for MOBIKE and to mark some messages as "critical".
According to the IKEv2 specification, such messages either have to be
understood by the receiver, or an error message has to be returned to
the sender.
A second way to ensure receipt of the above-mentioned feedback is by
using Vendor ID payloads that are exchanged during the initial IKEv2
exchange. These payloads would then indicate whether or not a given
peer supports the MOBIKE protocol.
A third approach would use the Notify payload which is also used for
NAT detection (via NAT_DETECTION_SOURCE_IP and
NAT_DETECTION_DESTINATION_IP payloads).
Both a Vendor ID and a Notify payload may be used to indicate the
support of certain extensions.
Note that a MOBIKE peer could also attempt to execute MOBIKE
opportunistically with the critical bit set when an address change
has occurred. The drawback of this approach is, however, that an
unnecessary MOBIKE message exchange is introduced.
Although Vendor ID payloads and Notifications are technically
equivalent, Notifications are already used in IKEv2 as a capability
negotiation mechanism. Hence, Notifications and Vendor ID payloads
are the preferred mechanisms.
5.2 Changing a Preferred Address and Multi-homing Support
From MOBIKE's point of view, support for multi-homing is inherently
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provided by the fact that it manages a set of peer addresses, rather
than a single address. Further, MOBIKE provides mechanisms to change
a peer's preferred IP address. Each peer needs to learn the
preferred address and the peer address set.
5.2.1 Storing a single or multiple addresses
One design decision is whether an IKE-SA should be associated with a
single IP address or multiple IP addresses. One option is that a
peer can provide a list of addresses to its counterpart which can
then be used as destination addresses.
Note that MOBIKE does not support load balancing, i.e., only one IP
address is set to a preferred address at a time and changing the
preferred address typically requires some MOBIKE signaling.
Another option is to only communicate one address to the other peer
and both peers only use that address when communicating. If this
address cannot be used anymore then an address update is sent to the
other peer that changes the preferred address.
Alternatively, if peer A, for example,provides a peer address set
with multiple IP addresses then peer B can recover from a failure of
the preferred address without further communication with peer A. That
is, if it detects that the primary path does not work anymore it can
either switch to a new preferred address locally (i.e., changing the
source IP address of outgoing MOBIKE messages) or to try an IP
address from A's peer address set (i.e., changing the destination
address). If peer B only received a single IP address from peer A
for A then peer B can only change its own preferred address. Peer B
would have to wait for an address update from peer A with a new IP
address in order to fix the problem.
The main advantage of storing only a single IP address for the remote
peer is that it makes retransmission handling easier. Moreover, it
simplifies the recovery procedure. The peer whose IP address changed
must start the recovery process and send the new IP address to the
other peer. However, connectivity failures along the path are not
well addressed with advertising a single IP address.
The single IP address approach does not work if both peers change
their IP addresses at the same time, for example if both hosts move
simultaneously, even though multiple addresses are available to the
two peers. The IKEv2 implementation might also require window size
to be larger than 1 because the MOBIKE peer needs to be able to send
the IP address change notifications before it switches to another
address. Depending on the occurrence of return routability checks,
retransmissions policies and similar message exchanges a window size
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larger than 1 might be required to deal with more than one pending
response at the same time. Furthermore, the single IP address
approach does not really benefit much from indirect indications as
the peer receiving these indications might not be able to fix the
situation by itself (e.g., even if a peer receives an ICMP host
unreachable message for the old IP address, it cannot try another IP
address, since it does not know any).
The problems with IP address lists lie mostly in their complexity.
Notification and recovery processes are more complicated. Both ends
can recover from the IP address changes. However, both peers should
not attempt to recover at the same time or nearly the same time as
this could cause them to lose connectivity. The MOBIKE protocol is
required to prevent this.
The previous discussion is independent of the question of how many
addresses to send in a single MOBIKE message. A MOBIKE message might
be able to carry more than one IP address (with the IP address list
approach) or a single address only. A NAT does not change addresses
carried inside the MOBIKE message but it can change IP address (and
transport layer addresses) in the IP header and Transport Protocol
header (if NAT traversal is enabled as part of configuration or
dynamically through the NAT discovery mechanism. Furthermore, a
MOBIKE message carrying the peer address set could be idempotent
(i.e., always resending the full address list) or the protocol may
allow add/delete operations to be specified. [I-D.dupont-ikev2-
addrmgmt], for example, offers an approach which defines add/delete
operations. The same is true for the dynamic address reconfiguration
extension for SCTP [I-D.ietf-tsvwg-addip-sctp].
5.2.2 Indirect or Direct Indication
An indication to change the preferred IP address might be either
direct or indirect.
Direct indication:
A direct indication means that the other peer will send an message
with the address change. This can, for example, be accomplished
by having MOBIKE sending an authenticated address update
notification with a different preferred address.
Indirect indication:
An indirect indication to change the preferred address can be
obtained by observing the environment. An indirect indication
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might, for example, be the receipt of an ICMP message or
information about a link failure. This information should be seen
as a hint and should not cause a change of the remote peer's
preferred address. Depending on the local policy, MOBIKE may
decide to perform a dead-peer detection exchange for the preferred
address pair (or another address pair from the peer address set).
When a peer detects that the other end started to use a different
source IP address than before, it might want to authorize the new
preferred address (if not already authorized). Authorization aims
to ensure that a particular peer is allowed to use the indicated
address. Claiming to be at an arbitrary address without
performing a return-routability test or without verifying that the
IP address is listed within a certificate opens the door for
various denial of service attacks. Hence a peer may also start a
connectivity test of this particular address.
If more information is available to the MOBIKE daemon then a more
intelligent decision regarding the selection of a new primary path
can be made.
5.2.3 Connectivity Tests using IKEv2 Dead-Peer Detection
This section discusses the suitability of the IKEv2 dead-peer
detection (DPD) mechanism for connectivity tests between address
pairs. The basic IKEv2 DPD mechanism is not modified by MOBIKE but
it needs to be investigated whether it can be used for MOBIKE
purposes as well.
The IKEv2 DPD mechanism involves sending an empty informational
exchange packet to a given address of the remote peer. On receipt,
the remote peer responds with an acknowledgement. If no
acknowledgement is received after a certain timeout period (and after
couple of retransmissions), the remote peer is considered to be not
reachable at the address in question. On the other hand, receipt of
IPsec protected acknowledgement is a guarantee that the other peer is
reachable at the address in question.
When reusing dead-peer detection in MOBIKE for connectivity tests it
seems to be reasonable to try other IP addresses (if they are
available) in case of an unsuccessful connectivity test for a given
address pair. Dead-peer detection messages using a different address
pair should use the same message-id as the original dead-peer
detection message (i.e. they are simply retransmissions of the dead-
peer detection packet using different destination IP address). If
different message-id is used then it violates constraints placed by
the IKEv2 specification on the DPD message with regard to the
mandatory ACK for each message-id, causing the IKEv2 SA to be
deleted.
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If MOBIKE strictly follows the guidelines of the dead-peer detection
mechanism in IKEv2 then an IKE-SA should be marked as dead and
deleted if the connectivity test for all available address pairs
fails. Note that this is not in-line with the approach used, for
example, in SCTP where a failed connectivity test for an address does
not lead to (a) the IP address or IP address pair to be marked as
dead and (b) delete state. Connectivity tests will be continued for
the address pairs in hope that the problem will recover soon. This
comparison with SCTP aims to point at another IETF protocol that aims
to address the multi-homing problem (although with a different scope
and a different layer).
Note that IKEv2 implementations may have a window size of 1, and
therefore be unable to initiate a dead-peer detection exchange while
another exchange is pending. As a result, all other exchanges are
subject to an identical retransmission policy as used for the dead-
peer detection. To use a different policy for different message
types seems to be reasonable.
The dead-peer detection mechanism for the other IP address pairs can
also be executed simultaneously if the window size larger than 1,
meaning that after the initial timeout period of the preferred
address expires, DPD packets are sent simultaneously to all other
address pairs. It is necessary to differentiate acknowledgement
messages in order to determine which address pair is operational.
The source IP address of the acknowledgement can be used for this
purpose.
The protocol should also be nice to the network, meaning, that when
some core link goes down, and a large number of MOBIKE clients notice
this, they should not start sending a large number of messages while
trying to recover from the problem. This may be particularly
unfortunate because packets may be dropped because of congestion in
the first place. If MOBIKE clients simultaneously try to test all
possible address pairs by executing connectivity tests then the
congestion problem only gets worse.
Also note that the IKEv2 dead-peer detection is not sufficient for
the return routability check. See Section 5.6 for more information.
5.3 Simultaneous Movements
MOBIKE does not aim to provide a mobility solution that allows
simultaneous movements. Instead, the MOBIKE working group focuses on
selected scenarios as described in Section 3. Some of the scenarios
assume that one peer has a fixed set of addresses (from which some
subset might be in use). Thus it cannot move to an address that is
unknown to the other peer. Situations in which both peers move
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simultaneously are outside the scope of the MOBIKE WG. MOBIKE has
not been chartered to deal with the rendezvous problem, or with the
introduction of new entities in the network.
Note that if only a single address is stored in the peer address set
(instead of an address list) we might end up in the case where it
seems that both peers changed their addresses at the same time (e.g.,
if both nodes change their addresses at the same time). This is
something that the MOBIKE protocol must deal with.
Three cases can be differentiated:
o Two mobile nodes obtain a new address at the same time, and then
being unable to tell each other where they are (in a break-before-
make scenario). This problem is called the rendezvous problem,
and is traditionally solved by introducing another third entity,
for example, the home agents (in Mobile IPv4/IPv6) or forwarding
agents (in the Host Identity Protocol). Essentially, solving this
problem requires the existence of additional infrastructure nodes.
o Simultaneous changes to addresses such that at least one of the
new addresses is known to the other peer before the change
occurred.
o No simultaneous changes at all.
5.4 NAT Traversal
IKEv2 supports legacy NAT traversal. This feature is known as NAT-T
which allows IKEv2 to work even if a NAT along the path between the
Initiator and the Responder modifies the source and possibly the
destination IP address. With NAPT even the transport protocol
identifiers are modified (which then requires UDP encapsulation for
exchanged IPsec protected data traffic). Therefore, the MOBIKE
daemon needs to obtain to required IP address informationfrom the IP
header (if a NAT was detected that modified the IP header) rather
than from the protected payload. This problem is not new and is an
issues of every mobility protocol where the most important
information exchanged is the IP address .
One of the goals in the MOBIKE protocol is to securely exchange one
or more addresses of the peer address set and to securely set the
primary address. If no other protocol is used to securely retrieve
the IP address and port information allocated by the NAT then it is
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not possible to tackle all attacks against MOBIKE. Section 6
discusses this aspect in more detail. Various approaches to solve
the problem have been presented:
o Securely retrieving IP address and port information allocated by
the NAT using a protocol different from MOBIKE. This approach is
outside the scope of the MOBIKE working group since other working
groups, such as MIDCOM and NSIS, already deal with this problem.
The MOBIKE protocol can benefit from the interaction with these
protocols but the interaction with these protocols it outside the
scope of this document.
o Design a protocol in such a way that NAT boxes are able to inspect
(or even participate) in the protocol exchange. This approach was
taken with the Host Identity Protocol but is not an option for
IKEv2 and MOBIKE since most IKEv2 messages are encrypted with the
established IKE SA. This prevents the NAT from learning required
information from the protocol exchange in a similar fashion as in
HIP.
o Disable NAT-T by indicating the desire never to use information
from the (unauthenticated) header. While this approach prevents
some security problems it effectively disallows the protocol to
work in environments with NATs.
There is no way to distinguish the whether there is a NAT device
along the path that modifies the header information in packets or an
adversary mounting an attack. If a NAT is detected during the
creation of an IKE SA, that should automatically disable the MOBIKE
extensions and use NAT-T.
A design question is whether NAT detection capabilities should be
enabled only during the initial IKEv2 exchange or also during
subsequent message exchanges. If MOBIKE is executed with no NAT
along the path when the IKE SA was created, then a NAT which appears
after moving to a new network cannot be dealt with if NAT detection
is enabled only during the initial exchange. Hence, it is desirable
to also support a scenario where a MOBIKE peer moves from a subnet
that is not behind a NAT to a network that is.
A NAT prevention mechanism can be used to make sure that no adversary
can interact with the protocol if no NAT is expected between the
Initiator and the Responder. (reference? Explanation?)
Whether or not MOBIKE should support NAT traversal is one of the most
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important design decisions.
5.5 Changing addresses or changing the paths
A design decision is whether it is enough for the MOBIKE protocol to
detect dead addresses, or it also needs to detect dead paths. Dead
address detection refers to the ability to establish whether or not a
given IP address pair is operational. Dead path detection refers to
the ability to establish whether or not all possible (local/remote)
address pairs are operational (or at least find one such pair).
While performing just one address change is simpler, the existence of
locally operational addresses is not, however, a guarantee that
communications can be established with the peer. A failure in the
routing infrastructure can prevent the sent packets from reaching
their destination.
5.6 Return Routability Tests
Changing the preferred address and subsequently using it for
communication is associated with an authorization decision: Is a peer
allowed to use this address? Does this peer own this address? Two
mechanisms have been proposed in the past to allow a peer to
determine the answer to this question:
o The addresses a peer is using are part of a certificate.
[RFC3554] which is introduced by this approach. If the other peer
is, for example, a security gateway with a limited set of fixed IP
addresses, then the security gateway may have a certificate with
all the IP addresses appear in the certificate.
o A return routability check is performed by the remote peer before
the address is updated in that peer's Security Association
Database. This is done in order provide a certain degree of
confidence to the remote peer that local peer is reachable at the
indicated address.
Without taking an authorization decision a malicious peer can
redirect traffic towards a third party or a blackhole.
A MOBIKE peer should not use an IP addressed provided by another
MOBIKE peer as a primary address without computing the authorization
decision. If the addresses are part of the certificate then it is
not necessary to execute the weaker return-routability test. The
return-routability test is a form of authorization check, although it
provides weaker guarantees then the inclusion of the IP address as
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part of a certificate. If multiple addresses are communicated to the
remote peer then some of these addresses may be already verified even
if the primary address is still operational.
Another option is to use the [I-D.dupont-mipv6-3bombing] approach
which suggests to perform a return routability test only when an
address update needs to be sent from some address other than the
indicated preferred address.
Finally it would be possible not to execute return routability checks
at all. In case of indirect change notifications we only move to the
new preferred address after successful dead-peer detection (i.e., a
response to a DPD test) on the new address, which is already a return
routability check. With a direct notification the authenticated peer
may have provided an authenticated IP address. Thus it is would be
possible to simply trust the MOBIKE peer to provide a proper IP
address. There is no way an adversary can successfully launch an
attack by injecting faked addresses since it does not know the IKE SA
and the corresponding keying material.A protection against an
internal attacker, i.e. the authenticated peer forwarding its traffic
to the new address, is not provided. This might be an issue when
extensions are added to IKEv2 that do not require authentication of
end points (e.g., opportunistic security using anonymous Diffie-
Hellman). On the other hand we know the identity of the peer in that
case. The identity of the IKEv2 Initiator and the IKEv2 Responder
can take various forms: IP address, FQDN, DN, email address alike
identifiers, etc.
It seems that there it is also a policy issue when to schedule a
return routability test.
The basic format of the return routability check could be similar to
dead-peer detection, but the problem is that if that fails then the
IKEv2 specification requires the IKE SA to be deleted. Because of
this a different type of exchange is required and thereby avoiding
modifications to the IKEv2 specification.
There are potential attacks if a return routability check does not
include some kind of nonce. The valid end point could send an
address update notification for a third party, trying to get all the
traffic to be sent there, causing a denial of service attack. If the
return routability checks does not contain any cookies or other
random information not known to the other end, then that valid node
could reply to the return routability checks even when it cannot see
the request. This might cause a peer to move the traffic to a
location where the original recipient cannot be reached.
The IKEv2 NAT-T mechanism does not perform return routability checks.
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It simply uses the last seen source IP address used by the other peer
as the destination address to send response packets. An adversary
can change those IP addresses, and can cause the response packets to
be sent to wrong IP address. The situation is self-fixing when the
adversary is no longer able to modify packets and the first packet
with an unmodified IP address reaches the other peer. Mobility
environments make this attack more difficult for an adversary since
it requires the adversary to be located somewhere on the individual
paths ({CoA1, ..., CoAn} towards the destination IP address) have a
shared path or if the adversary is located near the MOBIKE client
then it needs to follow the user mobility patterns. With IKEv2
NAT-T, the genuine client can cause third party bombing by
redirecting all the traffic pointed to him to third party. As the
MOBIKE protocol tries to provide equal or better security than IKEv2
NAT-T mechanism it should protect against these attacks.
There may be return routability information available from the other
parts of the system too (as shown in Figure 3), but the checks done
may have a different quality. There are multiple levels for return
routability checks:
o None, no tests
o A party willing to answer the return routability check is located
along the path to the claimed address (). This is the basic form
of return routability test.
o There is an answer from the tested address, and that answer was
authenticated, integrity and replay protected.
o There was an authenticated, integrity and replay protected answer
from the peer, but it is not guaranteed to originate at the tested
address or path to it (because the peer can construct a response
without seeing the request).
The return routability checks do not protect against 3rd party
bombing if the attacker is along the path, as the attacker can
forward the return routability checks to the real peer (even if those
packets are cryptographically authenticated).
If the address to be tested is carried inside the MOBIKE payload,
then the adversary cannot forward packets. Thus 3rd party bombings
are prevented.
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If the reply packet can be constructed without seeing the request
packet (for example, if there is no nonce, challenge or similar
mechanism to show liveness), then the genuine peer can cause 3rd
party bombing, by replying to those requests without seeing them at
all.
Other levels might only provide a guarantee that there is a node at
the IP address which replied to the request. There is no indication
as to whether or not the reply is fresh, and whether or not the
request may have been transmitted from a different source address.
5.7 Employing MOBIKE results in other protocols
If MOBIKE has learned about new locations or verified the validity of
a remote address through a return routability check, can this
information be useful for other protocols?
When considering the basic MOBIKE VPN scenario, the answer is no.
Transport and application layer protocols running inside the VPN
tunnel are unaware of the outer addresses or their status.
Similarly, IP layer tunnel termination at a gateway rather than a
host endpoint limits the benefits for "other protocols" that could be
informed -- all application protocols at the other side are unaware
of IPsec, IKE, or MOBIKE.
However, it is conceivable that future uses or extensions of the
MOBIKE protocol make such information distribution useful. For
instance, if transport mode MOBIKE and SCTP were made to work
together, it would potentially be useful for SCTP to learn about the
new addresses at the same time as MOBIKE. Similarly, various IP
layer mechanisms may make use of the fact that a return routability
test of a specific type has been performed. However, care should be
exercised in all these situations .
[I-D.crocker-celp] discusses the use of common locator information
pools in a IPv6 multi-homing context; it assumed that both transport
and IP layer solutions are be used in order to support multi-homing,
and that it would be beneficial for different protocols to coordinate
their results in some way, for instance by sharing throughput
information of address pairs. This may apply to MOBIKE as well,
assuming it co-exists with non-IPsec protocols that are faced with
the same or similar multi-homing choices.
Nevertheless, all of this is outside the scope of current MOBIKE base
protocol design and may be addressed in future work. (so why do you
elaborate so much on this stuff?)
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5.8 Scope of SA changes
Most sections of this document discuss design considerations for
updating and maintaining addresses in the database entries that
relate to an IKE-SA. However, changing the preferred address also
affects the entries of the IPsec SA database. The outer tunnel
header addresses (source and destination IP addresses) need to be
modified according to the primary path to allow the IPsec protected
data traffic to travel along the same path as the MOBIKE packets (if
we only consider the IP header information). If the MOBIKE messages
and the IPsec protected data traffic travel along a different path
then NAT handling is severely complicated.
The basic question is then how the IPsec SAs are changed to use the
new address pair (the same address pair as the MOBIKE signaling
traffic -- the primary path). One option is that when the IKE SA
address is changed then automatically all IPsec SAs associated with
it are moved along with it to new address pair. Another option is to
have a separate exchange to move the IPsec SAs separately.
If IPsec SAs should be updated separately then a more efficient
format than the notification payload is needed to preserve bandwidth.
A notification payload can only store one SPI per payload. A
separate payload which would have list of IPsec SA SPIs and new
preferred address. If there is a large number of IPsec SAs, those
payloads can be quite large unless ranges of SPI values are
supported. If we automatically move all IPsec SAs when the IKE SA
moves, then we only need to keep track which IKE SA was used to
create the IPsec SA, and fetch the IP addresses. Note that IKEv2
[I-D.ietf-ipsec-ikev2] already requires implementations to keep track
which IPsec SAs are created using which IKE SA.
If we do allow each IPsec SA address set to be updated separately,
then we can support scenarios, where the machine has fast and/or
cheap connections and slow and/or expensive connections, and it wants
to allow moving some of the SAs to the slower and/or more expensive
connection, and prevent the move, for example, of the news video
stream from the WLAN to the GPRS link.
On the other hand, even if we tie the IKE SA update to the IPsec SA
update, then we can create separate IKE SAs for this scenario, e.g.,
we create one IKE SA which have both links as endpoints, and it is
used for important traffic, and then we create another IKE SA which
have only the fast and/or cheap connection, which is then used for
that kind of bulk traffic.
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5.9 Zero Address Set
One of the features which is potentially useful is for the peer to
announce that it will now disconnect for some time, i.e. it will not
be reachable at all. For instance, a laptop might go to suspend
mode. In this case the it could send address notification with zero
new addresses, which means that it will not have any valid addresses
anymore. The responder of that kind of notification would then
acknowledge that, and could then temporarily disable all SAs and
therefore stop sending traffic. If any of the SAs gets any packets
they are simply dropped. This could also include some kind of ACK
spoofing to keep the TCP/IP sessions alive (or simply set the TCP/IP
keepalives and timeouts large enough not to cause problems), or it
could simply be left to the applications, e.g. allow TCP/IP sessions
to notice the link is broken.
The local policy could then indicate how long the peer should allow
remote peers to remain disconnected.
From a technical point of view this feature addresses two aspects:
o There is no need to transmit IPsec data traffic. IPsec protected
data needs to be dropped which saves bandwidth. This does not
provide a functional benefit, i.e., nothing breaks if this feature
is not provided.
o MOBIKE signaling messages are also ignored. The IKE-SA must not
be deleted and the suspend functionality (realized with the zero
address set) may require the IKE-SA to be tagged with a lifetime
value since the IKE-SA should not be kept in alive for an
undefined period of time. Note that IKEv2 does not require that
the IKE-SA has a lifetime associated with it. In order to prevent
the IKE-SA from being deleted the dead-peer detection mechanism
needs to be suspended as well.
Due to the fact that this extension would be complicated, a first
version of the MOBIKE protocol will not provide this feature.
5.10 IPsec Tunnel or Transport Mode
Current MOBIKE design is focused only on the VPN type usage and
tunnel mode. Transport mode behaviour would also be useful, but will
be discussed in future documents.
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5.11 Message Representation
The IP address change notifications can be sent either via an
informational exchange already specified in the IKEv2, or via a
MOBIKE specific message exchange. Using informational exchange has
the main advantage that it is already specified in the IKEv2 and
implementations incorporate the functionality already.
Another question is the format of the address update notifications.
The address update notifications can include multiple addresses, of
which some may be IPv4 and some IPv6 addresses. The number of
addresses is most likely going to be limited in typical environments
(with less than 10 addresses). The format may need to indicate a
preference value for each address. The format could either contain a
preference number that determines the relative order of the
addresses, or it could simply be ordered, according to preference,
list of IP addresses. While two addresses can have the same
preference value an ordered list avoids this situation.
Even if load balancing is currently outside the scope of MOBIKE,
future work might include. The selected format needs to be flexible
enough to include additional information (e.g. to enable load
balancing). This may be realized with an reserved field, which can
later be used to store additional information. As there may arise
other information which may have to be tied to an address in the
future, a reserved field seems like a prudent design in any case.
There are two formats that place IP address lists into a message.
One includes each IP address as separate payload (where the payload
order indicates the preference value, or the payload itself might
include the preference value), or we can put the IP address list as
one payload to the exchange, and that one payload will then have
internal format which includes the list of IP addresses.
Having multiple payloads with each one having carrying one IP address
makes the protocol probably easier to parse, as we can already use
the normal IKEv2 payload parsing procedures.. It also offers an easy
way for the extensions, as the payload probably contains only the
type of the IP address (or the type is encoded to the payload type),
and the IP address itself, and as each payload already has length
associated to it, we can detect if there is any extra data after the
IP address. Some implementations might have problems parsing IKEv2
payloads that are longer than a certain threshold, but if the sender
sends them in the most preferred first, the receiver can only use the
first addresses.
Having all IP addresses in one big MOBIKE specified internal format
provides more compact encoding, and keeps the MOBIKE implementation
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more concentrated to one module. It also avoids problems of packets
arriving in an order different from what they were sent.
Another choice is which type of payloads to use. IKEv2 already
specifies a notify payload. It includes some extra fields (SPI size,
SPI, protocol etc), which gives 4 bytes of the extra overhead, and
there is the notify data field, which could include the MOBIKE
specific data.
Another option would be to have a custom payload type, which then
includes the information needed for the MOBIKE protocol.
MOBIKE might send the full peer address list once one of the IP
addresses changes (either addresses are added, removed, the order
changes or the preferred address is updated) or an incremental
update. Sending incremental updates provides more compact packets
(meaning we can support more IP addresses), but on the other hand
have more problems in the synchronization and packet reordering
cases, i.e., the incremental updates must be processed in order, but
for full updates we can simply use the most recent one, and ignore
old ones, even if they arrive after the most recent one (IKEv2
packets have message id which is incremented for each packet, thus we
know the sending order easily).
Note that each peer needs to communicate its peer address set to the
other peer.
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6. Security Considerations
As all the messages are already authenticated by the IKEv2 there is
no problem that any attackers would modify the contents of the
packets. The IP addresses in the IP header of the packets are not
authenticated, thus the protocol defined must take care that they are
only used as an indication that something might be different, and
that do not cause any direct actions.
An attacker can also spoof ICMP error messages in an effort to
confuse the peers about which addresses are not working. At worst
this causes denial of service and/or the use of non-preferred
addresses.
One type of attack that needs to be taken care of in the MOBIKE
protocol is the "flooding attack" type. See [I-D.ietf-mip6-ro-sec]
and [Aur02] for more information about flooding attacks.
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7. IANA Considerations
This document does not introduce any IANA considerations.
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8. Acknowledgments
This document is the result of discussions in the MOBIKE working
group. The authors would like to thank Jari Arkko, Pasi Eronen,
Francis Dupont, Mohan Parthasarathy, Paul Hoffman, Bill Sommerfeld,
James Kempf, Vijay Devarapalli, Atul Sharma, Bora Akyol, Joe Touch,
Udo Schilcher, Tom Henderson, Andreas Pashalidis and Maureen Stillman
for their input.
We would like to particularly thank Pasi Eronen for tracking open
issues on the MOBIKE mailing list. He helped us to make good
progress on the document.
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9. Open Issues
This document is not yet complete, the following open issues need to
be addressed in a future version:
o Section 4 needs an example to better illustrate the functionality
of MOBIKE
o Section 6 requires a more detailed discussion about the potential
security vulnerabilities and corresponding countermeasures.
o Some text is needed to address the implications of unidirectional
connectivity aspect for MOBIKE (see also issue #19).
o A discussion about the scalability aspects of connectivity tests
would be benefical.
o More details are necessary to describe the implications of NAT
traversal for MOBIKE.
A complete list of issues is available at
http://www.vpnc.org/ietf-mobike/issues.html.
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10. References
10.1 Normative references
[I-D.ietf-ipsec-ikev2]
Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-17 (work in progress),
October 2004.
[I-D.ietf-ipsec-rfc2401bis]
Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", draft-ietf-ipsec-rfc2401bis-06 (work
in progress), April 2005.
10.2 Informative References
[I-D.arkko-multi6dt-failure-detection]
Arkko, J., "Failure Detection and Locator Selection in
Multi6", draft-arkko-multi6dt-failure-detection-00 (work
in progress), October 2004.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[I-D.dupont-mipv6-3bombing]
Dupont, F., "A note about 3rd party bombing in Mobile
IPv6", draft-dupont-mipv6-3bombing-02 (work in progress),
June 2005.
[I-D.ietf-mip6-ro-sec]
Nikander, P., "Mobile IP version 6 Route Optimization
Security Design Background", draft-ietf-mip6-ro-sec-03
(work in progress), May 2005.
[I-D.ietf-hip-mm]
Nikander, P., "End-Host Mobility and Multi-Homing with
Host Identity Protocol", draft-ietf-hip-mm-01 (work in
progress), February 2005.
[I-D.crocker-celp]
Crocker, D., "Framework for Common Endpoint Locator
Pools", draft-crocker-celp-00 (work in progress),
February 2004.
[RFC3489] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy,
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"STUN - Simple Traversal of User Datagram Protocol (UDP)
Through Network Address Translators (NATs)", RFC 3489,
March 2003.
[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L., and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 2000.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[I-D.ietf-tsvwg-addip-sctp]
Stewart, R., "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration",
draft-ietf-tsvwg-addip-sctp-12 (work in progress),
June 2005.
[I-D.dupont-ikev2-addrmgmt]
Dupont, F., "Address Management for IKE version 2",
draft-dupont-ikev2-addrmgmt-07 (work in progress),
May 2005.
[RFC3554] Bellovin, S., Ioannidis, J., Keromytis, A., and R.
Stewart, "On the Use of Stream Control Transmission
Protocol (SCTP) with IPsec", RFC 3554, July 2003.
[I-D.ietf-ipv6-optimistic-dad]
Moore, N., "Optimistic Duplicate Address Detection for
IPv6", draft-ietf-ipv6-optimistic-dad-05 (work in
progress), February 2005.
[I-D.ietf-ipv6-unique-local-addr]
Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-unique-local-addr-09 (work in
progress), January 2005.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2367] McDonald, D., Metz, C., and B. Phan, "PF_KEY Key
Management API, Version 2", RFC 2367, July 1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Kivinen & Tschofenig Expires January 19, 2006 [Page 33]
Internet-Draft Design of the MOBIKE Protocol July 2005
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[Aur02] Aura, T., Roe, M., and J. Arkko, "Security of Internet
Location Management", In Proc. 18th Annual Computer
Security Applications Conference, pages 78-87, Las Vegas,
NV USA, December 2002.
Authors' Addresses
Tero Kivinen
Safenet, Inc.
Fredrikinkatu 47
HELSINKI FIN-00100
FI
Email: kivinen@safenet-inc.com
Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: Hannes.Tschofenig@siemens.com
URI: http://www.tschofenig.com
Kivinen & Tschofenig Expires January 19, 2006 [Page 34]
Internet-Draft Design of the MOBIKE Protocol July 2005
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