draft-ietf-mip6-ro-sec-03.txt   rfc4225.txt 
Network Working Group P. Nikander Network Working Group P. Nikander
Internet-Draft J. Arkko Request for Comments: 4225 J. Arkko
Expires: December 3, 2005 Ericsson Research Nomadic Lab Category: Informational Ericsson Research NomadicLab
T. Aura T. Aura
Microsoft Research Microsoft Research
G. Montenegro G. Montenegro
Microsoft Corporation Microsoft Corporation
E. Nordmark E. Nordmark
Sun Microsystems Sun Microsystems
June 2005 December 2005
Mobile IP version 6 Route Optimization Security Design Background
draft-ietf-mip6-ro-sec-03
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document is an account of the rationale behind the Mobile IPv6 This document is an account of the rationale behind the Mobile IPv6
(MIPv6) Route Optimization Security Design. The purpose of this (MIPv6) Route Optimization security design. The purpose of this
document is to present the thinking and to preserve the reasoning document is to present the thinking and to preserve the reasoning
behind the Mobile IPv6 Security Design in 2001-2002. behind the Mobile IPv6 security design in 2001 - 2002.
The document has two target audiences: (1) MIPv6 implementors so that The document has two target audiences: (1) helping MIPv6 implementors
they can better understand the design choices in MIPv6 security to better understand the design choices in MIPv6 security procedures,
procedures; and (2) people dealing with mobility or multi-homing so and (2) allowing people dealing with mobility or multi-homing to
that they can avoid a number of potential security pitfalls in their avoid a number of potential security pitfalls in their designs.
design.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction ....................................................3
1.1 Assumptions about the Existing IP Infrastructure . . . . . 5 1.1. Assumptions about the Existing IP Infrastructure ...........4
1.1.1 A note on source addresses and ingress filtering . . . 6 1.2. The Mobility Problem and the Mobile IPv6 Solution ..........6
1.2 The Mobility Problem and the Mobile IPv6 Solution . . . . 7 1.3. Design Principles and Goals ................................8
1.3 Design Principles and Goals . . . . . . . . . . . . . . . 9 1.3.1. End-to-End Principle ..................................8
1.3.1 End-to-end principle . . . . . . . . . . . . . . . . . 9 1.3.2. Trust Assumptions .....................................8
1.3.2 Trust assumptions . . . . . . . . . . . . . . . . . . 9 1.3.3. Protection Level ......................................8
1.3.3 Protection level . . . . . . . . . . . . . . . . . . . 10 1.4. About Mobile IPv6 Mobility and its Variations ..............9
1.4 About Mobile IPv6 Mobility and its Variations . . . . . . 10 2. Avenues of Attack ...............................................9
2. Avenues of Attack . . . . . . . . . . . . . . . . . . . . . . 11 2.1. Target ....................................................10
2.1 Target . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2. Timing ....................................................10
2.2 Timing . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3. Location ..................................................11
2.3 Location . . . . . . . . . . . . . . . . . . . . . . . . . 12 3. Threats and Limitations ........................................11
3. Threats and limitations . . . . . . . . . . . . . . . . . . . 13 3.1. Attacks Against Address 'Owners' ("Address Stealing").. ...12
3.1 Attacks against address 'owners' (also known as 3.1.1. Basic Address Stealing ...............................12
address 'stealing') . . . . . . . . . . . . . . . . . . . 14 3.1.2. Stealing Addresses of Stationary Nodes ...............13
3.1.1 Basic address stealing . . . . . . . . . . . . . . . . 14 3.1.3. Future Address Sealing ...............................14
3.1.2 Stealing addresses of stationary nodes . . . . . . . . 15 3.1.4. Attacks against Secrecy and Integrity ................15
3.1.3 Future address stealing . . . . . . . . . . . . . . . 15 3.1.5. Basic Denial-of-Service Attacks ......................16
3.1.4 Attacks against Secrecy and Integrity . . . . . . . . 16 3.1.6. Replaying and Blocking Binding Updates ...............16
3.1.5 Basic Denial of Service Attacks . . . . . . . . . . . 17 3.2. Attacks Against Other Nodes and Networks (Flooding) .......16
3.1.6 Replaying and Blocking Binding Updates . . . . . . . . 18 3.2.1. Basic Flooding .......................................17
3.2 Attacks against other nodes and networks (flooding) . . . 18 3.2.2. Return-to-Home Flooding ..............................18
3.2.1 Basic flooding . . . . . . . . . . . . . . . . . . . . 18 3.3. Attacks against Binding Update Protocols ..................18
3.2.2 Return-to-home flooding . . . . . . . . . . . . . . . 20 3.3.1. Inducing Unnecessary Binding Updates .................19
3.3 Attacks against binding update protocols . . . . . . . . . 20 3.3.2. Forcing Non-Optimized Routing ........................20
3.3.1 Inducing Unnecessary Binding Updates . . . . . . . . . 20 3.3.3. Reflection and Amplification .........................21
3.3.2 Forcing Non-Optimized Routing . . . . . . . . . . . . 22 3.4. Classification of Attacks .................................22
3.3.3 Reflection and Amplification . . . . . . . . . . . . . 22 3.5. Problems with Infrastructure-Based Authorization ..........23
3.4 Classification of attacks . . . . . . . . . . . . . . . . 24 4. Solution Selected for Mobile IPv6 ..............................24
3.5 Problems with infrastructure based authorization . . . . . 24 4.1. Return Routability ........................................24
4. The solution selected for Mobile IPv6 . . . . . . . . . . . . 27 4.1.1. Home Address Check ...................................26
4.1 Return Routability . . . . . . . . . . . . . . . . . . . . 27 4.1.2. Care-of-Address Check ................................27
4.1.1 Home Address check . . . . . . . . . . . . . . . . . . 29 4.1.3. Forming the First Binding Update .....................27
4.1.2 Care-of-Address check . . . . . . . . . . . . . . . . 30 4.2. Creating State Safely .....................................28
4.1.3 Forming the first Binding Update . . . . . . . . . . . 30 4.2.1. Retransmissions and State Machine ....................29
4.2 Creating state safely . . . . . . . . . . . . . . . . . . 30 4.3. Quick expiration of the Binding Cache Entries .............29
4.2.1 Retransmissions and state machine . . . . . . . . . . 32 5. Security Considerations ........................................30
4.3 Quick expiration of the Binding Cache Entries . . . . . . 32 5.1. Residual Threats as Compared to IPv4 ......................31
5. Security considerations . . . . . . . . . . . . . . . . . . . 34 5.2. Interaction with IPsec ....................................31
5.1 Residual Threats as Compared to IPv4 . . . . . . . . . . . 34 5.3. Pretending to Be One's Neighbor ...........................32
5.2 Interaction with IPsec . . . . . . . . . . . . . . . . . . 35 5.4. Two Mobile Nodes Talking to Each Other ....................33
5.3 Pretending to be one's neighbor . . . . . . . . . . . . . 36 6. Conclusions ....................................................33
5.4 Two mobile nodes talking to each other . . . . . . . . . . 36 7. Acknowledgements ...............................................34
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 38 8. Informative References .........................................34
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 39
8. Informative References . . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 40
Intellectual Property and Copyright Statements . . . . . . . . 41
1. Introduction 1. Introduction
Mobile IPv4 is based on the idea of supporting mobility on top of Mobile IPv4 is based on the idea of supporting mobility on top of
existing IP infrastructure, without requiring any modifications to existing IP infrastructure, without requiring any modifications to
the routers, the applications, or the stationary end hosts. However, the routers, the applications, or the stationary end hosts. However,
in Mobile IPv6 [7] (as opposed to Mobile IPv4) the stationary end in Mobile IPv6 [6] (as opposed to Mobile IPv4), the stationary end
hosts may provide support for mobility, i.e., route optimization. In hosts may provide support for mobility, i.e., route optimization. In
route optimization a correspondent node (CN), i.e., a peer for a route optimization, a correspondent node (CN) (i.e., a peer for a
mobile node, learns a binding between the mobile node's stationary mobile node) learns a binding between the mobile node's stationary
home address and its current temporary care-of-address. This binding home address and its current temporary care-of address. This binding
is then used to modify the handling of outgoing (as well as the is then used to modify the handling of outgoing (as well as the
processing of incoming) packets, leading to security risks. The processing of incoming) packets, leading to security risks. The
purpose of this document is to provide a relatively compact source purpose of this document is to provide a relatively compact source
for the background assumptions, design choices, and other information for the background assumptions, design choices, and other information
needed to understand the route optimization security design. This needed to understand the route optimization security design. This
document does not seek to compare the relative security of Mobile document does not seek to compare the relative security of Mobile
IPv6 and other mobility protocols, or to list all the alternative IPv6 and other mobility protocols, or to list all the alternative
security mechanisms that were discussed during the Mobile IPv6 design security mechanisms that were discussed during the Mobile IPv6 design
process. For a summary of the latter, we refer the reader to [1]. process. For a summary of the latter, we refer the reader to [1].
Even though incidental implementation suggestions are included for Even though incidental implementation suggestions are included for
illustrative purposes, the goal of this document is not to provide a illustrative purposes, the goal of this document is not to provide a
guide to implementors. The goal of this document is to explain the guide to implementors. Instead, it is to explain the design choices
design choices and rationale behind the current route optimization and rationale behind the current route optimization design. The
design. The authors participated in the design team which produced authors participated in the design team that produced the design and
the design, and hope, via this note, to capture some of the lessons hope, via this note, to capture some of the lessons and reasoning
and reasoning behind that effort. behind that effort.
The intent is to document the thinking behind that design effort, as The authors' intent is to document the thinking behind that design
it was. Even though this note may incorporate more recent effort as it was. Even though this note may incorporate more recent
developments in order to illustrate the issues, it is not our intent developments in order to illustrate the issues, it is not our intent
to present a new design. Rather, along with the lessons learned, to present a new design. Rather, along with the lessons learned,
there is some effort to clarify differing opinions, questionable there is some effort to clarify differing opinions, questionable
assumptions, or newly discovered vulnerabilities, should such new assumptions, or newly discovered vulnerabilities, should such new
information be available today. This is also very important, because information be available today. This is also very important, because
it may benefit the working group's hindsight as it revises or it may benefit the working group's hindsight as it revises or
improves the Mobile IPv6 specification. improves the Mobile IPv6 specification.
To fully understand the security implications of the relevant design To fully understand the security implications of the relevant design
constraints it is necessary to briefly explore the nature of the constraints, it is necessary to explore briefly the nature of the
existing IP infrastructure, the problems Mobile IP aims to solve, and existing IP infrastructure, the problems Mobile IP aims to solve, and
the design principles applied. In the light of this background, we the design principles applied. In the light of this background, we
can then explore IP based mobility in more detail, and have a brief can then explore IP-based mobility in more detail and have a brief
look at the security problems. The background is given in the rest look at the security problems. The background is given in the rest
of this section, starting from Section 1.1. of this section, starting from Section 1.1.
While the introduction in Section 1.1 may appear redundant to those Although the introduction in Section 1.1 may appear redundant to
readers who are already familiar with Mobile IPv6, it may be valuable readers who are already familiar with Mobile IPv6, it may be valuable
to read it anyway. The approach taken in this document is very to read it anyway. The approach taken in this document is very
different from the one in the Mobile IPv6 specification. That is, we different from that in the Mobile IPv6 specification. That is, we
have explicitly aimed to expose the implicit assumptions and design have explicitly aimed to expose the implicit assumptions and design
choices made in the base Mobile IPv6 design, while the Mobile IPv6 choices made in the base Mobile IPv6 design, while the Mobile IPv6
specification aims to state the result of the design. By specification aims to state the result of the design. By
understanding the background it is much easier to understand the understanding the background, it is much easier to understand the
source of some of the related security problems, and to understand source of some of the related security problems, and to understand
the limitations intrinsic to the provided solutions. the limitations intrinsic to the provided solutions.
In particular, this document explains how the adopted design for In particular, this document explains how the adopted design for
"Return Routability" (RR) protects against the identified threats "Return Routability" (RR) protects against the identified threats
(Section 3). This is true except for attacks on the RR protocol (Section 3). This is true except for attacks on the RR protocol
itself, which require other countermeasures based on heuristics and itself, which require other countermeasures based on heuristics and
judicious implementation (Section 3.3). judicious implementation (Section 3.3).
The rest of this document is organized as follows: after this The rest of this document is organized as follows: after this
introductory section, we start by considering the avenues of attack introductory section, we start by considering the avenues of attack
in Section 2. The security problems and countermeasures are studied in Section 2. The security problems and countermeasures are studied
in detail in Section 3. Section 4 explains the overall operation and in detail in Section 3. Section 4 explains the overall operation and
design choices behind the current security design. In Section 5 we design choices behind the current security design. Section 5
analyze the design and discuss the remaining threats. Finally analyzes the design and discuss the remaining threats. Finally,
Section 6 concludes this document. Section 6 concludes this document.
1.1 Assumptions about the Existing IP Infrastructure 1.1. Assumptions about the Existing IP Infrastructure
One of the design goals in the Mobile IP design was to make mobility One of the design goals in the Mobile IP design was to make mobility
possible without changing too much. This was especially important possible without changing too much. This was especially important
for IPv4, with its large installed base, but the same design goals for IPv4, with its large installed base, but the same design goals
were inherited by Mobile IPv6. Some alternative proposals take a were inherited by Mobile IPv6. Some alternative proposals take a
different approach and propose larger modifications to the Internet different approach and propose larger modifications to the Internet
architecture (see Section 1.4). architecture (see Section 1.4).
To understand Mobile IPv6, it is important to understand the MIPv6 To understand Mobile IPv6, it is important to understand the MIPv6
design view of the base IPv6 protocol and infrastructure. The most design view of the base IPv6 protocol and infrastructure. The most
important base assumptions can be expressed as follows: important base assumptions can be expressed as follows:
1. The routing prefixes available to a node are determined by its 1. The routing prefixes available to a node are determined by its
current location, and therefore the node must change its IP current location, and therefore the node must change its IP
address as its moves. address as it moves.
2. The routing infrastructure is assumed to be secure and well 2. The routing infrastructure is assumed to be secure and well
functioning, delivering packets to their intended destinations as functioning, delivering packets to their intended destinations as
identified by the destination address. identified by destination address.
While these may appear to be trivial, let us explore them a little Although these assumptions may appear to be trivial, let us explore
further. Firstly, in current IPv6 operational practice the IP them a little further. First, in current IPv6 operational practice
address prefixes are distributed in a hierarchical manner. This the IP address prefixes are distributed in a hierarchical manner.
limits the number of routing table entries each individual router This limits the number of routing table entries each individual
needs to handle. An important implication is that the topology router needs to handle. An important implication is that the
determines what globally routable IP addresses are available at a topology determines what globally routable IP addresses are available
given location. That is, the nodes cannot freely decide what at a given location. That is, the nodes cannot freely decide what
globally routable IP address to use, but must rely on the routing globally routable IP address to use; they must rely on the routing
prefixes served by the local routers via Router Advertisements or by prefixes served by the local routers via Router Advertisements or by
a DHCP server. In other words, IP addresses are just what the name a DHCP server. In other words, IP addresses are just what the name
says, addresses, i.e., locators. says, addresses (i.e., locators).
Secondly, in the current Internet structure, the routers collectively Second, in the current Internet structure, the routers collectively
maintain a distributed database of the network topology, and forward maintain a distributed database of the network topology and forward
each packet towards the location determined by the destination each packet towards the location determined by the destination
address carried in the packet. To maintain the topology information, address carried in the packet. To maintain the topology information,
the routers must trust each other, at least to a certain extent. The the routers must trust each other, at least to a certain extent. The
routers learn the topology information from the other routers, and routers learn the topology information from the other routers, and
they have no option but to trust their neighbor routers about distant they have no option but to trust their neighbor routers about distant
topology. At the borders of administrative domains, policy rules are topology. At the borders of administrative domains, policy rules are
used to limit the amount of perhaps faulty routing table information used to limit the amount of perhaps faulty routing table information
received from the peer domains. While this is mostly used to weed received from the peer domains. While this is mostly used to weed
out administrative mistakes, it also helps with security. The aim is out administrative mistakes, it also helps with security. The aim is
to maintain a reasonably accurate idea of the network topology even to maintain a reasonably accurate idea of the network topology even
if someone is feeding faulty information to the routing system. if someone is feeding faulty information to the routing system.
In the current Mobile IPv6 design it is explicitly assumed that the In the current Mobile IPv6 design, it is explicitly assumed that the
routers and the policy rules are configured in a reasonable way, and routers and the policy rules are configured in a reasonable way, and
that the resulting routing infrastructure is trustworthy enough. that the resulting routing infrastructure is trustworthy enough.
That is, it is assumed that the routing system maintains accurate That is, it is assumed that the routing system maintains accurate
information of the network topology, and that it is therefore able to information of the network topology, and that it is therefore able to
route packets to their destination locations. If this assumption is route packets to their destination locations. If this assumption is
broken, the Internet itself is broken in the sense that packets go to broken, the Internet itself is broken in the sense that packets go to
wrong locations. Such a fundamental malfunction of the Internet wrong locations. Such a fundamental malfunction of the Internet
would render hopeless any other effort to assure correct packet would render hopeless any other effort to assure correct packet
delivery (e.g., any efforts due to Mobile IP security delivery (e.g., any efforts due to Mobile IP security
considerations). considerations).
1.1.1 A note on source addresses and ingress filtering 1.1.1. A Note on Source Addresses and Ingress Filtering
Some of the threats and attacks discussed in this document take Some of the threats and attacks discussed in this document take
advantage of the ease of source address spoofing. That is, in the advantage of the ease of source address spoofing. That is, in the
current Internet it is possible to send packets with a false source current Internet it is possible to send packets with a false source
IP address. The eventual introduction of ingress filtering is IP address. The eventual introduction of ingress filtering is
assumed to prevent this. When ingress filtering is used, traffic assumed to prevent this. When ingress filtering is used, traffic
with spoofed addresses is not forwarded. This filtering can be with spoofed addresses is not forwarded. This filtering can be
applied at different network borders such as those between an applied at different network borders, such as those between an
Internet service provider (ISP) and its customers, between downstream Internet service provider (ISP) and its customers, between downstream
and upstream ISPs, between peer ISPs, etc [6]. Obviously, the and upstream ISPs, or between peer ISPs [5]. Obviously, the
granularity of ingress filters specifies how much you can "spoof granularity of ingress filters specifies how much you can "spoof
inside a prefix". For example, if an ISP ingress filters a inside a prefix". For example, if an ISP ingress filters a
customer's link, but the customer does nothing, anything inside the customer's link but the customer does nothing, anything inside the
customer's /48 prefix could be spoofed, or if the customer does customer's /48 prefix could be spoofed. If the customer does
filtering at LAN subnets, anything inside the /64 prefixes could be filtering at LAN subnets, anything inside the /64 prefixes could be
spoofed. Despite the limitations imposed by such "in-prefix spoofed. Despite the limitations imposed by such "in-prefix
spoofing", in general, ingress filtering enables traffic to be spoofing", in general, ingress filtering enables traffic to be
traceable to its real source network [6]. traceable to its real source network [5].
However, ingress filtering helps if and only if a large part of the However, ingress filtering helps if and only if a large part of the
Internet uses it. Unfortunately, there are still some issues (e.g. Internet uses it. Unfortunately, there are still some issues (e.g.,
in the presence of site multi-homing) which, although not in the presence of site multi-homing) that, although not
insurmountable, do require careful handling, and are likely to limit insurmountable, do require careful handling, and that are likely to
or delay its usefulness [6]. limit or delay its usefulness [5].
1.2 The Mobility Problem and the Mobile IPv6 Solution 1.2. The Mobility Problem and the Mobile IPv6 Solution
The Mobile IP design aims to solve two problems at the same time. The Mobile IP design aims to solve two problems at the same time.
Firstly, it allows transport layer sessions (TCP connections, UDP- First, it allows transport layer sessions (TCP connections, UDP-
based transactions) to continue even if the underlying host(s) move based transactions) to continue even if the underlying host(s) move
and change their IP addresses. Secondly, it allows a node to be and change their IP addresses. Second, it allows a node to be
reached through a static IP address, a home address (HoA). reached through a static IP address, a home address (HoA).
The latter design choice can also be stated in other words: Mobile The latter design choice can also be stated in other words: Mobile
IPv6 aims to preserve the identifier nature of IP addresses. That IPv6 aims to preserve the identifier nature of IP addresses. That
is, Mobile IPv6 takes the view that IP addresses can be used as is, Mobile IPv6 takes the view that IP addresses can be used as
natural identifiers of nodes, as they have been used since the natural identifiers of nodes, as they have been used since the
beginning of the Internet. This must be contrasted to proposed and beginning of the Internet. This must be contrasted to proposed and
existing alternative designs where the identifier and locator natures existing alternative designs where the identifier and locator natures
of the IP addresses have been separated (see Section 1.4) of the IP addresses have been separated (see Section 1.4).
The basic idea in Mobile IP is to allow a home agent (HA) to work as The basic idea in Mobile IP is to allow a home agent (HA) to work as
a stationary proxy for a mobile node (MN). Whenever the mobile node a stationary proxy for a mobile node (MN). Whenever the mobile node
is away from its home network, the home agent intercepts packets is away from its home network, the home agent intercepts packets
destined to the node, and forwards the packets by tunneling them to destined to the node and forwards the packets by tunneling them to
the node's current address, the care-of-address (CoA). The transport the node's current address, the care-of address (CoA). The transport
layer (e.g., TCP, UDP) uses the home address as a stationary layer (e.g., TCP, UDP) uses the home address as a stationary
identifier for the mobile node. Figure 1 illustrates this basic identifier for the mobile node. Figure 1 illustrates this basic
arrangement. arrangement.
The basic solution requires tunneling through the home agent, thereby
leading to longer paths and degraded performance. This tunneling is
sometimes called triangular routing since it was originally planned
that the packets from the mobile node to its peer could still
traverse directly, bypassing the home agent.
+----+ +----+ +----+ +----+
| MN |=#=#=#=#=#=#=#=#=tunnel=#=#=#=#=#=#=#=#|#HA | | MN |=#=#=#=#=#=#=#=#=tunnel=#=#=#=#=#=#=#=#|#HA |
+----+ ____________ +-#--+ +----+ ____________ +-#--+
| CoA ___/ \_____ # Home Link | CoA ___/ \_____ # Home Link
-+-------/ Internet * * *-*-*-*-#-#-#-#----- -+-------/ Internet * * *-*-*-*-#-#-#-#-----
| * * | * Home Address | * * | * Home Address
\___ * * _____/ + * -+ \___ * * _____/ + * -+
\_____*______/ | MN | \_____*______/ | MN |
* + - -+ * + - -+
+----+ +----+
| CN | Data path as * * * * | CN | Data path as * * * *
+----+ it appears to correspondent node +----+ it appears to correspondent node
Real data path # # # # Real data path # # # #
Figure 1: Basic Mode of Operation in Mobile IPv6 Figure 1. Basic Mode of Operation in Mobile IPv6
The basic solution requires tunneling through the home agent, thereby
leading to longer paths and degraded performance. This tunneling is
sometimes called triangular routing since it was originally planned
that the packets from the mobile node to its peer could still
traverse directly, bypassing the home agent.
To alleviate the performance penalty, Mobile IPv6 includes a mode of To alleviate the performance penalty, Mobile IPv6 includes a mode of
operation that allows the mobile node and its peer, a correspondent operation that allows the mobile node and its peer, a correspondent
node (CN), to exchange packets directly, bypassing the home agent node (CN), to exchange packets directly, bypassing the home agent
completely after the initial setup phase. This mode of operation is completely after the initial setup phase. This mode of operation is
called route optimization (RO). When route optimization is used, called route optimization (RO). When route optimization is used, the
the mobile node sends its current care-of-address to the mobile node sends its current care-of address to the correspondent
correspondent node using binding update (BU) messages. The node, using binding update (BU) messages. The correspondent node
correspondent node stores the binding between the home address and stores the binding between the home address and care-of address into
care-of address into its Binding Cache. its Binding Cache.
Whenever MIPv6 route optimization is used, the correspondent node Whenever MIPv6 route optimization is used, the correspondent node
effectively functions in two roles. Firstly, it is the source of the effectively functions in two roles. Firstly, it is the source of the
packets it sends, as usual. Secondly, it acts as the first router packets it sends, as usual. Secondly, it acts as the first router
for the packets, effectively performing source routing. That is, for the packets, effectively performing source routing. That is,
when the correspondent node is sending out packets, it consults its when the correspondent node is sending out packets, it consults its
MIPv6 route optimization data structures, and reroutes the packets if MIPv6 route optimization data structures and reroutes the packets, if
necessary. A Binding Cache Entry (BCE) contains the home address and necessary. A Binding Cache Entry (BCE) contains the home address and
the care-of-address of the mobile node, and records the fact that the care-of address of the mobile node, and records the fact that
packets destined to the home address should now be sent to the packets destined to the home address should now be sent to the
destination address. Thus, it represents a local routing exception. destination address. Thus, it represents a local routing exception.
The packets leaving the correspondent node are source routed to the The packets leaving the correspondent node are source routed to the
care-of-address. Each packet includes a routing header that contains care-of address. Each packet includes a routing header that contains
the home address of the mobile node. Thus, logically, the packet is the home address of the mobile node. Thus, logically, the packet is
first routed to the care-of-address, and then virtually from the first routed to the care-of address and then, virtually, from the
care-of-address to the home address. In practice, of course, the care-of address to the home address. In practice, of course, the
packet is consumed by the mobile node at the care-of-address, and the packet is consumed by the mobile node at the care-of address; the
header just allows the mobile node to select a socket associated with header just allows the mobile node to select a socket associated with
the home address instead of one with the care-of-address. However, the home address instead of one with the care-of address. However,
the mechanism resembles source routing since there is routing state the mechanism resembles source routing, as there is routing state
involved at the correspondent node, and a routing header is used. involved at the correspondent node, and a routing header is used.
Nevertheless, this routing header is special (type 2) to avoid the Nevertheless, this routing header is special (type 2) to avoid the
risks associated with using the more general (type 0) variant. risks associated with using the more general (type 0) variant.
1.3 Design Principles and Goals 1.3. Design Principles and Goals
The MIPv6 design and security design aimed to follow the end-to-end The MIPv6 design and security design aimed to follow the end-to-end
principle, to duly notice the differences in trust relationships principle, to notice the differences in trust relationships between
between the nodes, and to be explicit about delivering a practical the nodes, and to be explicit about delivering a practical (instead
(instead of an over-ambitious) level of protection. of an over-ambitious) level of protection.
1.3.1 End-to-end principle 1.3.1. End-to-End Principle
Perhaps the leading design principle for Internet protocols is the so Perhaps the leading design principle for Internet protocols is the
called end-to-end principle [4][9]. According to this principle, it so-called end-to-end principle [4][11]. According to this principle,
is beneficial to avoid polluting the network with state, and to limit it is beneficial to avoid polluting the network with state, and to
new state creation to the involved end nodes. limit new state creation to the involved end nodes.
In the case of Mobile IPv6, the end-to-end principle is applied by In the case of Mobile IPv6, the end-to-end principle is applied by
restricting mobility related state primarily to the home agent. restricting mobility-related state primarily to the home agent.
Additionally, if route optimization is used, the correspondent nodes Additionally, if route optimization is used, the correspondent nodes
also maintain a soft state relating to the mobile nodes' current also maintain a soft state relating to the mobile nodes' current
care-of-addresses, the Binding Cache. This can be contrasted to an care-of addresses, the Binding Cache. This can be contrasted to an
approach that would use individual host routes within the basic approach that would use individual host routes within the basic
routing system. Such an approach would create state on a huge number routing system. Such an approach would create state on a huge number
of routers around the network. In Mobile IPv6, only the home agent of routers around the network. In Mobile IPv6, only the home agent
and the communicating nodes need to create state. and the communicating nodes need to create state.
1.3.2 Trust assumptions 1.3.2. Trust Assumptions
In the Mobile IPv6 security design, different approaches were chosen In the Mobile IPv6 security design, different approaches were chosen
for securing the communication between the mobile node and its home for securing the communication between the mobile node and its home
agent and between the mobile node and its correspondent nodes. In agent and between the mobile node and its correspondent nodes. In
the home agent case it was assumed that the mobile node and the home the home agent case, it was assumed that the mobile node and the home
agent know each other through a prior arrangement, e.g., due to a agent know each other through a prior arrangement, e.g., due to a
business relationship. In contrast, it was strictly assumed that the business relationship. In contrast, it was strictly assumed that the
mobile node and the correspondent node do not need to have any prior mobile node and the correspondent node do not need to have any prior
arrangement, thereby allowing Mobile IPv6 to function in a scalable arrangement, thereby allowing Mobile IPv6 to function in a scalable
manner, without requiring any configuration at the correspondent manner, without requiring any configuration at the correspondent
nodes. nodes.
1.3.3 Protection level 1.3.3. Protection Level
As a security goal, Mobile IPv6 design aimed to be "as secure as the As a security goal, Mobile IPv6 design aimed to be "as secure as the
(non-mobile) IPv4 Internet" was at the time of the design, in the (non-mobile) IPv4 Internet" was at the time of the design, in the
period 2001-2002. In particular, that means that there is little period 2001-2002. In particular, that means that there is little
protection against attackers that are able to attach themselves protection against attackers that are able to attach themselves
between a correspondent node and a home agent. The rationale is between a correspondent node and a home agent. The rationale is
simple: in the 2001 Internet, if a node was able to attach itself to simple: in the 2001 Internet, if a node was able to attach itself to
the communication path between two arbitrary nodes, it was able to the communication path between two arbitrary nodes, it was able to
disrupt, modify, and eavesdrop all the traffic between the two nodes, disrupt, modify, and eavesdrop all the traffic between the two nodes,
unless IPsec protection was used. Even when IPsec was used, the unless IPsec protection was used. Even when IPsec was used, the
attacker was still able to selectively block communication by simply attacker was still able to block communication selectively by simply
dropping the packets. The attacker in control of a router between dropping the packets. The attacker in control of a router between
the two nodes could also mount a flooding attack by redirecting the the two nodes could also mount a flooding attack by redirecting the
data flows between the two nodes (or, more practically, an equivalent data flows between the two nodes (or, more practically, an equivalent
flow of bogus data) to a third party. flow of bogus data) to a third party.
1.4 About Mobile IPv6 Mobility and its Variations 1.4. About Mobile IPv6 Mobility and its Variations
Taking a more abstract angle, IPv6 mobility can be defined as a Taking a more abstract angle, IPv6 mobility can be defined as a
mechanism for managing local exceptions to routing information in mechanism for managing local exceptions to routing information in
order to direct packets that are sent to one address (the home order to direct packets that are sent to one address (the home
address) to another address (the care-of-address). It is managing in address) to another address (the care-of address). It is managing in
the sense that the local routing exceptions (source routes) are the sense that the local routing exceptions (source routes) are
created and deleted dynamically, based on the instructions sent by created and deleted dynamically, according to instructions sent by
the mobile node. It is local in the sense that the routing the mobile node. It is local in the sense that the routing
exceptions are valid only at the home agent, and in the correspondent exceptions are valid only at the home agent, and in the correspondent
nodes if route optimization is used. The created pieces of state are nodes if route optimization is used. The created pieces of state are
exceptions in the sense that they override the normal topological exceptions in the sense that they override the normal topological
routing information carried collectively by the routers. routing information carried collectively by the routers.
Using the terminology introduced by J. Noel Chiappa [12], we can say Using the terminology introduced by J. Noel Chiappa [14], we can say
that the home address functions in the dual role of being an end- that the home address functions in the dual role of being an end-
point identifier (EID) and a permanent locator. The care-of-address point identifier (EID) and a permanent locator. The care-of address
is a pure, temporary locator, which identifies the current location is a pure, temporary locator, which identifies the current location
of the mobile node. The correspondent nodes effectively perform of the mobile node. The correspondent nodes effectively perform
source routing, redirecting traffic destined to the home address to source routing, redirecting traffic destined to the home address to
the care-of-address. This is even reflected in the packet structure: the care-of address. This is even reflected in the packet structure:
the packets carry an explicit routing header. the packets carry an explicit routing header.
The relationship between EIDs and permanent locators has been The relationship between EIDs and permanent locators has been
exploited by other proposals. Their technical merits and security exploited by other proposals. Their technical merits and security
problems, however, are beyond the scope of this document. problems, however, are beyond the scope of this document.
2. Avenues of Attack 2. Avenues of Attack
Based on the discussion above it should now be clear that the dangers From the discussion above, it should now be clear that the dangers
in Mobile IPv6 lie in creation (or deletion) of the local routing that Mobile IPv6 must protect from lie in creation (or deletion) of
exceptions. In Mobile IPv6 terms, the danger is in the possibility the local routing exceptions. In Mobile IPv6 terms, the danger is in
of unauthorized creation of Binding Cache Entries (BCE). The effects the possibility of unauthorized creation of Binding Cache Entries
of an attack differ depending on the target of the attack, the timing (BCE). The effects of an attack differ depending on the target of
of the attack, and the location of the attacker. the attack, the timing of the attack, and the location of the
attacker.
2.1 Target 2.1. Target
Basically, the target of an attack can be any node or network in the Basically, the target of an attack can be any node or network in the
Internet (stationary or mobile). The basic differences lie in the Internet (stationary or mobile). The basic differences lie in the
goals of the attack: does the attacker aim to divert (steal) the goals of the attack: does the attacker aim to divert (steal) the
traffic destined to and/or sourced at the target node, or does it aim traffic destined to and/or sourced at the target node, or does it aim
to cause denial-of-service to the target node or network. The target to cause denial-of-service to the target node or network? The target
does not typically play much of an active role attack. As an does not typically play much of an active role attack. As an
example, an attacker may launch a denial-of-service attack on a given example, an attacker may launch a denial-of-service attack on a given
node A by contacting a large number of nodes, claiming to be A, and node, A, by contacting a large number of nodes, claiming to be A, and
subsequently diverting the traffic at these other nodes so that A is subsequently diverting the traffic at these other nodes so that A is
harmed by no longer being able to receive packets from those nodes. no longer able to receive packets from those nodes. A itself need
A itself need not be involved at all before its communications start not be involved at all before its communications start to break.
to break. Furthermore, A is not necessarily a mobile node; it may Furthermore, A is not necessarily a mobile node; it may well be
very well be stationary. stationary.
Mobile IPv6 uses the same class of IP addresses for both mobile nodes Mobile IPv6 uses the same class of IP addresses for both mobile nodes
(i.e., home and care-of addresses) and stationary nodes. That is, (i.e., home and care-of addresses) and stationary nodes. That is,
mobile and stationary addresses are indistinguishable from each mobile and stationary addresses are indistinguishable from each
other. Attackers can take advantage of this by taking any IP address other. Attackers can take advantage of this by taking any IP address
and using it in a context where normally only mobile (home or care-of and using it in a context where, normally, only mobile (home or
addresses) appear. This means that attacks that otherwise would only care-of) addresses appear. This means that attacks that otherwise
concern mobiles are, in fact, a threat to all IPv6 nodes. would only concern mobile nodes are, in fact, a threat to all IPv6
nodes.
In fact, the role of being a mobile node appears to be most In fact, a mobile node appears to be best protected, since a mobile
protected, since in that role a node does not need to maintain state node does not need to maintain state about the whereabouts of some
about the whereabouts of some remote nodes. Conversely, the role of remote nodes. Conversely, the role of being a correspondent node
being a correspondent node appears to be the weakest point since appears to be the weakest, since there are very few assumptions upon
there are very few assumptions upon which it can base its state which it can base its state formation. That is, an attacker has a
formation. That is, an attacker has much easier task to fool a much easier task in fooling a correspondent node to believe that a
correspondent node to believe that a presumably mobile node is presumably mobile node is somewhere it is not, than in fooling a
somewhere it is not, than to fool a mobile node itself into believing mobile node itself into believing something similar. On the other
something similar. On the other hand, since it is possible to attack hand, since it is possible to attack a node indirectly by first
a node indirectly by first targetting its peers, all nodes are targeting its peers, all nodes are equally vulnerable in some sense.
equally vulnerable in some sense. Furthermore, a (usually) mobile Furthermore, a (usually) mobile node often also plays the role of
node often also plays the role of being a correspondent node, since being a correspondent node, since it can exchange packets with other
it can exchange packets with other mobile nodes (see also mobile nodes (see also Section 5.4).
Section 5.4).
2.2 Timing 2.2. Timing
An important aspect in understanding Mobile IPv6 related dangers is An important aspect in understanding Mobile IPv6-related dangers is
timing. In a stationary IPv4 network, an attacker must be between timing. In a stationary IPv4 network, an attacker must be between
the communication nodes at the same time as the nodes communicate. the communication nodes at the same time as the nodes communicate.
With the Mobile IPv6 ability of creating binding cache entries, the With the Mobile IPv6 ability of creating binding cache entries, the
situation changes. A new danger is created. Without proper situation changes. A new danger is created. Without proper
protection, an attacker could attach itself between the home agent protection, an attacker could attach itself between the home agent
and a correspondent node for a while, create a BCE at the and a correspondent node for a while, create a BCE at the
correspondent node, leave the position, and continuously update the correspondent node, leave the position, and continuously update the
correspondent node about the mobile node's whereabouts. This would correspondent node about the mobile node's whereabouts. This would
make the correspondent node send packets destined to the mobile node make the correspondent node send packets destined to the mobile node
to an incorrect address as long as the BCE remained valid, i.e., to an incorrect address as long as the BCE remained valid, i.e.,
typically until the correspondent node is rebooted. The converse typically until the correspondent node is rebooted. The converse
would also be possible: an attacker could also launch an attack by would also be possible: an attacker could also launch an attack by
first creating a BCE and then letting it expire at a carefully first creating a BCE and then letting it expire at a carefully
selected time. If a large number of active BCEs carrying large selected time. If a large number of active BCEs carrying large
amounts of traffic expired at the same time, the result might be an amounts of traffic expired at the same time, the result might be an
overload towards the home agent or the home network. (See overload towards the home agent or the home network. (See Section
Section 3.2.2 for a more detailed explanation.) 3.2.2 for a more detailed explanation.)
2.3 Location 2.3. Location
In a static IPv4 Internet, an attacker can only receive packets In a static IPv4 Internet, an attacker can only receive packets
destined to a given address if it is able to attach itself to or destined to a given address if it is able to attach itself to, or to
control a node on the topological path between the sender and the control, a node on the topological path between the sender and the
recipient. On the other hand, an attacker can easily send spoofed recipient. On the other hand, an attacker can easily send spoofed
packets from almost anywhere. If Mobile IPv6 allowed sending packets from almost anywhere. If Mobile IPv6 allowed sending
unprotected Binding Updates, an attacker could create a BCE on any unprotected Binding Updates, an attacker could create a BCE on any
correspondent node from anywhere in the Internet, simply by sending a correspondent node from anywhere in the Internet, simply by sending a
fraudulent Binding Update to the correspondent node. Instead of fraudulent Binding Update to the correspondent node. Instead of
being required to be between the two target nodes, the attacker could being required to be between the two target nodes, the attacker could
act from anywhere in the Internet. act from anywhere in the Internet.
In summary, by introducing the new routing exception (binding cache) In summary, by introducing the new routing exception (binding cache)
at the correspondent nodes, Mobile IPv6 introduces the dangers of at the correspondent nodes, Mobile IPv6 introduces the dangers of
time and space shifting. Without proper protection, Mobile IPv6 time and space shifting. Without proper protection, Mobile IPv6
would allow an attacker to act from anywhere in the Internet and well would allow an attacker to act from anywhere in the Internet and well
before the time of the actual attack. In contrast, in the static before the time of the actual attack. In contrast, in the static
IPv4 Internet the attacking nodes must be present at the time of the IPv4 Internet, the attacking nodes must be present at the time of the
attack and they must be positioned in a suitable way, or the attack attack and they must be positioned in a suitable way, or the attack
would not be possible in the first place. would not be possible in the first place.
3. Threats and limitations 3. Threats and Limitations
This section describes attacks against Mobile IPv6 Route Optimization This section describes attacks against Mobile IPv6 Route Optimization
and related protection mechanisms. The goal of the attacker can be and what protection mechanisms Mobile IPv6 applies against them. The
to corrupt the correspondent node's binding cache and to cause goal of the attacker can be to corrupt the correspondent node's
packets to be delivered to a wrong address. This can compromise binding cache and to cause packets to be delivered to a wrong
secrecy and integrity of communication and cause denial-of-service address. This can compromise secrecy and integrity of communication
(DoS) both at the communicating parties and at the address that and cause denial-of-service (DoS) both at the communicating parties
receives the unwanted packets. The attacker may also exploit and at the address that receives the unwanted packets. The attacker
features of the Binding Update (BU) mechanism to exhaust the may also exploit features of the Binding Update (BU) mechanism to
resources of the mobile node, the home agent, or the correspondent exhaust the resources of the mobile node, the home agent, or the
nodes. The aim of this section is to provide an overview of the correspondent nodes. The aim of this section is to provide an
various protocol mechanisms and their limitations. The details of overview of the various protocol mechanisms and their limitations.
the mechanisms are covered in Section 4. The details of the mechanisms are covered in Section 4.
It is essential to understand that some of the threats are more It is essential to understand that some of the threats are more
serious than others, some can be mitigated but not removed, some serious than others, that some can be mitigated but not removed, that
threats may represent acceptable risk, and some threats may be some threats may represent acceptable risk, and that some threats may
considered too expensive to the attacker to be worth preventing. be considered too expensive to the attacker to be worth preventing.
We consider only active attackers. The rationale behind this is that We consider only active attackers. The rationale behind this is that
in order to corrupt the binding cache, the attacker must sooner or in order to corrupt the binding cache, the attacker must sooner or
later send one or more messages. Thus, it makes little sense to later send one or more messages. Thus, it makes little sense to
consider attackers that only observe messages but do not send any. consider attackers that only observe messages but do not send any.
In fact, some active attacks are easier, for the average attacker, to In fact, some active attacks are easier, for the average attacker, to
launch than a passive one would be. That is, in many active attacks launch than a passive one would be. That is, in many active attacks
the attacker can initiate binding update processing at any time, the attacker can initiate binding update processing at any time,
while most passive attacks require the attacker to wait for suitable while most passive attacks require the attacker to wait for suitable
messages to be sent by the target nodes. messages to be sent by the target nodes.
Nevertheless, an important class of passive attacks remains, namely, Nevertheless, an important class of passive attacks remains: attacks
attacks on privacy. It is well known that by simply examining on privacy. It is well known that simply by examining packets,
packets, eavesdroppers can track the movements of individual nodes eavesdroppers can track the movements of individual nodes (and
(and potentially, users) [3] Mobile IPv6 exacerbates the problem by potentially, users) [3]. Mobile IPv6 exacerbates the problem by
adding more potentially sensitive information into the packets (e.g., adding more potentially sensitive information into the packets (e.g.,
Binding Updates, routing headers or home address options). This Binding Updates, routing headers or home address options). This
document does not address these attacks. document does not address these attacks.
We first consider attacks against nodes that are supposed to have a We first consider attacks against nodes that are supposed to have a
specified address (Section 3.1), continuing with flooding attacks specified address (Section 3.1), continuing with flooding attacks
(Section 3.2) and attacks against the basic Binding Update protocol (Section 3.2) and attacks against the basic Binding Update protocol
(Section 3.3). After that we present a classification of the attacks (Section 3.3). After that, we present a classification of the
(Section 3.4). Finally, we consider the applicability of solutions attacks (Section 3.4). Finally, we consider the applicability of
relying on some kind of a global security infrastructure solutions relying on some kind of a global security infrastructure
(Section 3.5). (Section 3.5).
3.1 Attacks against address 'owners' (also known as address 'stealing') 3.1. Attacks Against Address 'Owners' ("Address Stealing")
The most obvious danger in Mobile IPv6 is address "stealing", i.e., The most obvious danger in Mobile IPv6 is address "stealing", when an
an attacker illegitimately claims to be a given node at a given attacker illegitimately claims to be a given node at a given address
address, and then tries to "steal" traffic destined to that address. and tries to "steal" traffic destined to that address. We first
We first describe the basic variant of this attack, follow with a describe the basic variant of this attack, follow with a description
description of how the situation is affected if the target is a of how the situation is affected if the target is a stationary node,
stationary node, and continue with more complicated issues related to and continue with more complicated issues related to timing (so
timing (so called "future" attacks), confidentiality and integrity, called "future" attacks), confidentiality and integrity, and DoS
and DoS aspects. aspects.
3.1.1 Basic address stealing 3.1.1. Basic Address Stealing
If Binding Updates were not authenticated at all, an attacker could If Binding Updates were not authenticated at all, an attacker could
fabricate and send spoofed binding updates from anywhere in the fabricate and send spoofed binding updates from anywhere in the
Internet. All nodes that support the correspondent node Internet. All nodes that support the correspondent node
functionality would become unwitting accomplices to this attack. As functionality would become unwitting accomplices to this attack. As
explained in Section 2.1, there is no way of telling which addresses explained in Section 2.1, there is no way of telling which addresses
belong to mobile nodes that really could send binding updates and belong to mobile nodes that really could send binding updates and
which addresses belong to stationary nodes (see below), so which addresses belong to stationary nodes (see below), so
potentially any node (including "static" nodes) are vulnerable. potentially any node (including "static" nodes) is vulnerable.
+---+ original +---+ new packet +---+ +---+ original +---+ new packet +---+
| B |<----------------| A |- - - - - - ->| C | | B |<----------------| A |- - - - - - ->| C |
+---+ packet flow +---+ flow +---+ +---+ packet flow +---+ flow +---+
^ ^
| |
| False BU: B -> C | False BU: B -> C
| |
+----------+ +----------+
| Attacker | | Attacker |
+----------+ +----------+
Figure 2: Basic Address Stealing Figure 2. Basic Address Stealing
Consider an IP node A sending IP packets to another IP node B. The Consider an IP node, A, sending IP packets to another IP node, B.
attacker could redirect the packets to an arbitrary address C by The attacker could redirect the packets to an arbitrary address, C,
sending a Binding Update to A. The home address (HoA) in the binding by sending a Binding Update to A. The home address (HoA) in the
update would be B and the care-of address (CoA) would be C. After binding update would be B and the care-of address (CoA) would be C.
receiving this binding update, A would send all packets intended for After receiving this binding update, A would send all packets
the node B to the address C. See Figure 2. intended for the node B to the address C. See Figure 2.
The attacker might select the care-of address to be either its own The attacker might select the care-of address to be either its own
current address, another address in its local network, or any other current address, another address in its local network, or any other
IP address. If the attacker selected a local care-of address IP address. If the attacker selected a local care-of address
allowing it to receive the packets, it would be able to send replies allowing it to receive the packets, it would be able to send replies
to the correspondent node. Ingress filtering at the attacker's local to the correspondent node. Ingress filtering at the attacker's
network does not prevent the spoofing of Binding Updates but forces local+ network does not prevent the spoofing of Binding Updates but
the attacker either to choose a care-of address from inside its own forces the attacker either to choose a care-of address from inside
network or to use the Alternate care-of address sub-option. its own network or to use the Alternate care-of address sub-option.
The binding update authorization mechanism used in the MIPv6 security The binding update authorization mechanism used in the MIPv6 security
design is primarily intended to mitigate this threat, and to limit design is primarily intended to mitigate this threat, and to limit
the location of attackers to the path between a correspondent node the location of attackers to the path between a correspondent node
and the home agent. and the home agent.
3.1.2 Stealing addresses of stationary nodes 3.1.2. Stealing Addresses of Stationary Nodes
The attacker needs to know or guess the IP addresses of both the The attacker needs to know or guess the IP addresses of both the
source of the packets to be diverted (A in the example above) and the source of the packets to be diverted (A in the example above) and the
destination of the packets (B). This means that it is difficult to destination of the packets (B, above). This means that it is
redirect all packets to or from a specific node because the attacker difficult to redirect all packets to or from a specific node because
would need to know the IP addresses of all the nodes with which it is the attacker would need to know the IP addresses of all the nodes
communicating. with which it is communicating.
Nodes with well-known addresses, such as servers and those using Nodes with well-known addresses, such as servers and those using
stateful configuration, are most vulnerable. Nodes that are a part stateful configuration, are most vulnerable. Nodes that are a part
of the network infrastructure, such as DNS servers, are particularly of the network infrastructure, such as DNS servers, are particularly
interesting targets for attackers, and particularly easy to identify. interesting targets for attackers and particularly easy to identify.
Nodes that frequently change their address and use random addresses Nodes that frequently change their address and use random addresses
are relatively safe. However, if they register their address into are relatively safe. However, if they register their address into
Dynamic DNS, they become more exposed. Similarly, nodes that visit Dynamic DNS, they become more exposed. Similarly, nodes that visit
publicly accessible networks such as airport wireless LANs risk publicly accessible networks such as airport wireless LANs risk
revealing their addresses. IPv6 addressing privacy features [3] revealing their addresses. IPv6 addressing privacy features [3]
mitigate these risks to an extent but it should be noted that mitigate these risks to an extent, but note that addresses cannot be
addresses cannot be completely recycled while there are still open completely recycled while there are still open sessions that use
sessions that use those addresses. those addresses.
Thus, it is not the mobile nodes that are most vulnerable to address Thus, it is not the mobile nodes that are most vulnerable to address
stealing attacks, it is the well known static servers. Furthermore, stealing attacks; it is the well-known static servers. Furthermore,
the servers often run old or heavily optimized operating systems, and the servers often run old or heavily optimized operating systems and
may not have any mobility related code at all. Thus, the security may not have any mobility related code at all. Thus, the security
design cannot be based on the idea that mobile nodes might somehow be design cannot be based on the idea that mobile nodes might somehow be
able to detect if someone has stolen their address, and reset the able to detect whether someone has stolen their address, and reset
state at the correspondent node. Instead, the security design must the state at the correspondent node. Instead, the security design
make reasonable measures to prevent the creation of fraudulent must make reasonable measures to prevent the creation of fraudulent
binding cache entries in the first place. binding cache entries in the first place.
3.1.3 Future address stealing 3.1.3. Future Address Sealing
If an attacker knows an address that a node is likely to select in If an attacker knows an address that a node is likely to select in
the future, it can launch a "future" address stealing attack. The the future, it can launch a "future" address stealing attack. The
attacker creates a Binding Cache Entry using the home address that it attacker creates a Binding Cache Entry with the home address that it
anticipates the target node will use. If the Home Agent allows anticipates the target node will use. If the Home Agent allows
dynamic home addresses, the attacker may be able to do this dynamic home addresses, the attacker may be able to do this
legitimately. That is, if the attacker is a client of the Home legitimately. That is, if the attacker is a client of the Home Agent
Agent, and able to acquire the home address temporarily, it may be and is able to acquire the home address temporarily, it may be able
able to do so, and then return the home address back to the Home to do so and then to return the home address to the Home Agent once
Agent once the BCE is in place. the BCE is in place.
Now, if the BCE state had a long expiration time, the target node Now, if the BCE state had a long expiration time, the target node
would acquire the same home address while the BCE is still effective, would acquire the same home address while the BCE is still effective,
and the attacker would be able to launch a successful man-in-the- and the attacker would be able to launch a successful man-in-the-
middle or denial-of-service attack. The mechanism applied in the middle or denial-of-service attack. The mechanism applied in the
MIPv6 security design is to limit the lifetime of Binding Cache MIPv6 security design is to limit the lifetime of Binding Cache
Entries to a few minutes. Entries to a few minutes.
Note that this attack applies only to fairly specific conditions. Note that this attack applies only to fairly specific conditions.
There are also some variations of this attack that are theoretically There are also some variations of this attack that are theoretically
possible under some other conditions. However, all of these attacks possible under some other conditions. However, all of these attacks
are limited by the Binding Cache Entry lifetime, and therefore not a are limited by the Binding Cache Entry lifetime, and therefore they
real concern with the current design. are not a real concern with the current design.
3.1.4 Attacks against Secrecy and Integrity 3.1.4. Attacks against Secrecy and Integrity
By spoofing Binding Updates, an attacker could redirect all packets By spoofing Binding Updates, an attacker could redirect all packets
between two IP nodes to itself. By sending a spoofed binding update between two IP nodes to itself. By sending a spoofed binding update
to A, it could capture the data intended to B. That is, it could to A, it could capture the data intended to B. That is, it could
pretend to be B and highjack A's connections with B, or establish new pretend to be B and highjack A's connections with B, or it could
spoofed connections. The attacker could also send spoofed binding establish new spoofed connections. The attacker could also send
updates to both A and B and insert itself in the middle of all spoofed binding updates to both A and B and insert itself in the
connections between them (man-in-the-middle attack). Consequently, middle of all connections between them (man-in-the-middle attack).
the attacker would be able to see and modify the packets sent between Consequently, the attacker would be able to see and modify the
A and B. See Figure 3. packets sent between A and B. See Figure 3.
Original data path, before man-in-the-middle attack Original data path, before man-in-the-middle attack
+---+ +---+ +---+ +---+
| A | | B | | A | | B |
+---+ +---+ +---+ +---+
\___________________________________/ \___________________________________/
Modified data path, after the falsified binding updates Modified data path, after the falsified binding updates
+---+ +---+ +---+ +---+
| A | | B | | A | | B |
+---+ +---+ +---+ +---+
\ / \ /
\ / \ /
\ +----------+ / \ +----------+ /
\---------| Attacker |-------/ \---------| Attacker |-------/
+----------+ +----------+
Figure 3: Man-in-the-Middle Attack Figure 3. Man-in-the-Middle Attack
Strong end-to-end encryption and integrity protection, such as Strong end-to-end encryption and integrity protection, such as
authenticated IPSec, can prevent all the attacks against data secrecy authenticated IPsec, can prevent all the attacks against data secrecy
and integrity. When the data is cryptographically protected, spoofed and integrity. When the data is cryptographically protected, spoofed
binding updates could result in denial of service (see below) but not binding updates could result in denial of service (see below) but not
in disclosure or corruption of sensitive data beyond revealing the in disclosure or corruption of sensitive data beyond revealing the
existence of the traffic flows. Two fixed nodes could also protect existence of the traffic flows. Two fixed nodes could also protect
communication between themselves by refusing to accept binding communication between themselves by refusing to accept binding
updates from each other. Ingress filtering, on the other hand, does updates from each other. Ingress filtering, on the other hand, does
not help because the attacker is using its own address as the care-of not help, as the attacker is using its own address as the care-of
address and is not spoofing source IP addresses. address and is not spoofing source IP addresses.
The protection adopted in MIPv6 Security Design is to authenticate The protection adopted in MIPv6 Security Design is to authenticate
(albeit weakly) the addresses by return routability (RR), which (albeit weakly) the addresses by return routability (RR), which
limits the topological locations from which the attack is possible limits the topological locations from which the attack is possible
(see Section 4.1). (see Section 4.1).
3.1.5 Basic Denial of Service Attacks 3.1.5. Basic Denial-of-Service Attacks
By sending spoofed binding updates, the attacker could redirect all By sending spoofed binding updates, the attacker could redirect all
packets sent between two IP nodes to a random or nonexistent address packets sent between two IP nodes to a random or nonexistent address
(or addresses). As a result, it might be able to stop or disrupt (or addresses). As a result, it might be able to stop or disrupt
communication between the nodes. This attack is serious because any communication between the nodes. This attack is serious because any
Internet node could be targeted, including fixed nodes belonging to Internet node could be targeted, including fixed nodes belonging to
the infrastructure (e.g., DNS servers) which are also vulnerable. the infrastructure (e.g., DNS servers) that are also vulnerable.
Again, the selected protection mechanism is return routability (RR). Again, the selected protection mechanism is return routability (RR).
3.1.6 Replaying and Blocking Binding Updates 3.1.6. Replaying and Blocking Binding Updates
Any protocol for authenticating binding updates has to consider Any protocol for authenticating binding updates has to consider
replay attacks. That is, an attacker may be able to replay recently replay attacks. That is, an attacker may be able to replay recently
authenticated binding updates to the correspondent and, consequently, authenticated binding updates to the correspondent and, consequently,
direct packets to the mobile node's previous location. As with to direct packets to the mobile node's previous location. As with
spoofed binding updates, this could be used both for capturing spoofed binding updates, this could be used both for capturing
packets and for DoS. The attacker could capture the packets and packets and for DoS. The attacker could capture the packets and
impersonate the mobile node if it reserved the mobile's previous impersonate the mobile node if it reserved the mobile's previous
address after the mobile node has moved away and then replayed the address after the mobile node has moved away and then replayed the
previous binding update to redirect packets back to the previous previous binding update to redirect packets back to the previous
location. location.
In a related attack, the attacker blocks binding updates from the In a related attack, the attacker blocks binding updates from the
mobile at its new location, e.g., by jamming the radio link or by mobile at its new location, e.g., by jamming the radio link or by
mounting a flooding attack, and takes over its connections at the old mounting a flooding attack. The attacker then takes over the
location. The attacker will be able to capture the packets sent to mobile's connections at the old location. The attacker will be able
the mobile and to impersonate the mobile until the correspondent's to capture the packets sent to the mobile and to impersonate the
Binding Cache entry expires. mobile until the correspondent's Binding Cache entry expires.
Both of the above attacks require the attacker to be on the same Both of the above attacks require that the attacker be on the same
local network with the mobile, where it can relatively easily observe local network with the mobile, where it can relatively easily observe
packets and block them even if the mobile does not move to a new packets and block them even if the mobile does not move to a new
location. Therefore, we believe that these attacks are not as location. Therefore, we believe that these attacks are not as
serious as ones that can be mounted from remote locations. The serious as ones that can be mounted from remote locations. The
limited lifetime of the Binding Cache entry and the associated nonces limited lifetime of the Binding Cache entry and the associated nonces
limit the time frame within which the replay attacks are possible. limit the time frame within which the replay attacks are possible.
Replay protection is provided by the sequence number and MAC in the Replay protection is provided by the sequence number and MAC in the
Binding Update. To not undermine this protection, correspondent Binding Update. To not undermine this protection, correspondent
nodes must exercise care upon deleting a binding cache entry, as per nodes must exercise care upon deleting a binding cache entry, as per
section 5.2.8 ("Preventing Replay Attacks") in [7]. section 5.2.8 ("Preventing Replay Attacks") in [6].
3.2 Attacks against other nodes and networks (flooding) 3.2. Attacks Against Other Nodes and Networks (Flooding)
By sending spoofed binding updates, an attacker could redirect By sending spoofed binding updates, an attacker could redirect
traffic to an arbitrary IP address. This could be used to overload traffic to an arbitrary IP address. This could be used to overload
an arbitrary Internet address with an excessive volume of packets an arbitrary Internet address with an excessive volume of packets
(known as a 'bombing attack'). The attacker could also target a (known as a 'bombing attack'). The attacker could also target a
network by redirecting data to one or more IP addresses within the network by redirecting data to one or more IP addresses within the
network. There are two main variations of flooding: basic flooding network. There are two main variations of flooding: basic flooding
and return-to-home flooding. We consider them separately. and return-to-home flooding. We consider them separately.
3.2.1 Basic flooding 3.2.1. Basic Flooding
In the simplest attack, the attacker knows that there is a heavy data In the simplest attack, the attacker knows that there is a heavy data
stream from node A to B and redirects this to the target address C. stream from node A to B and redirects this to the target address C.
However, A would soon stop sending the data because it is not However, A would soon stop sending the data because it is not
receiving acknowledgments from B. receiving acknowledgements from B.
(B is attacker) (B is attacker)
+---+ original +---+ flooding packet +---+ +---+ original +---+ flooding packet +---+
| B |<================| A |==================>| C | | B |<================| A |==================>| C |
+---+ packet flow +---+ flow +---+ +---+ packet flow +---+ flow +---+
| ^ | ^
\ / \ /
\__________________/ \__________________/
False binding update + false acknowledgements False binding update + false acknowledgements
Figure 4: Basic Flooding Attack Figure 4. Basic Flooding Attack
A more sophisticated attacker would act itself as B; see Figure 4. A more sophisticated attacker would act itself as B; see Figure 4.
It would first subscribe to a data stream (e.g. a video stream) and It would first subscribe to a data stream (e.g., a video stream) and
then redirects this stream to the target address C. The attacker redirect this stream to the target address C. The attacker would
would even be able to spoof the acknowledgements. For example, even be able to spoof the acknowledgements. For example, consider a
consider a TCP stream. The attacker would perform the TCP handshake TCP stream. The attacker would perform the TCP handshake itself and
itself and thus know the initial sequence numbers. After redirecting thus know the initial sequence numbers. After redirecting the data
the data to C, the attacker would continue to send spoofed to C, the attacker would continue to send spoofed acknowledgements.
acknowledgments. It would even be able to accelerate the data rate It would even be able to accelerate the data rate by simulating a
by simulating a fatter pipe [10]. fatter pipe [12].
This attack might be even easier with UDP/RTP. The attacker could This attack might be even easier with UDP/RTP. The attacker could
create spoofed RTCP acknowledgements. Either way, the attacker would create spoofed RTCP acknowledgements. Either way, the attacker would
be able to redirect an increasing stream of unwanted data to the be able to redirect an increasing stream of unwanted data to the
target address without doing much work itself. It could carry on target address without doing much work itself. It could carry on
opening more streams and refreshing the Binding Cache entries by opening more streams and refreshing the Binding Cache entries by
sending a new binding update every few minutes. Thus, the limitation sending a new binding update every few minutes. Thus, the limitation
of BCE lifetime to a few minutes does not help here without of BCE lifetime to a few minutes does not help here without
additional measures. additional measures.
During the Mobile IPv6 design process, the effectiveness of this During the Mobile IPv6 design process, the effectiveness of this
attack was debated. It was mistakenly assumed that the target node attack was debated. It was mistakenly assumed that the target node
would send a TCP Reset to the source of the unwanted data stream, would send a TCP Reset to the source of the unwanted data stream,
which would then stop sending. In reality, all practical TCP/IP which would then stop sending. In reality, all practical TCP/IP
implementations fail to send the Reset. The target node drops the implementations fail to send the Reset. The target node drops the
unwanted packets at the IP layer because it does not have a Binding unwanted packets at the IP layer because it does not have a Binding
Update List entry corresponding to the Routing Header on the incoming Update List entry corresponding to the Routing Header on the incoming
packet. Thus, the flooding data is never processed at the TCP layer packet. Thus, the flooding data is never processed at the TCP layer
of the target node and no Reset is sent. This means that the attack of the target node, and no Reset is sent. This means that the attack
using TCP streams is more effective than was originally believed. using TCP streams is more effective than was originally believed.
This attack is serious because the target can be any node or network, This attack is serious because the target can be any node or network,
not only a mobile one. What makes it particularly serious compared not only a mobile one. What makes it particularly serious compared
to the other attacks is that the target itself cannot do anything to to the other attacks is that the target itself cannot do anything to
prevent the attack. For example, it does not help if the target prevent the attack. For example, it does not help if the target
network stops using Route Optimization. The damage is compounded if network stops using Route Optimization. The damage is compounded if
these techniques are used to amplify the effect of other distributed these techniques are used to amplify the effect of other distributed
denial of service (DDoS) attacks. Ingress filtering in the denial-of-service (DDoS) attacks. Ingress filtering in the
attacker's local network prevents the spoofing of source addresses attacker's local network prevents the spoofing of source addresses
but the attack would still be possible by setting the Alternate but the attack would still be possible by setting the Alternate
care-of address sub-option to the target address. care-of address sub-option to the target address.
Again, the protection mechanism adopted for MIPv6 is return Again, the protection mechanism adopted for MIPv6 is return
routability. This time it is necessary to check that there is indeed routability. This time it is necessary to check that there is indeed
a node at the new care-of-address, and that the node is the one that a node at the new care-of address, and that the node is the one that
requested redirecting packets to that very address (see requested redirecting packets to that very address (see Section
Section 4.1.2). 4.1.2).
3.2.2 Return-to-home flooding 3.2.2. Return-to-Home Flooding
A variation of the bombing attack targets the home address or the A variation of the bombing attack would target the home address or
home network instead of the care-of-address or a visited network. the home network instead of the care-of address or a visited network.
The attacker would claim to be a mobile with the home address equal The attacker would claim to be a mobile with the home address equal
to the target address. While claiming to be away from home, the to the target address. While claiming to be away from home, the
attacker would start downloading a data stream. The attacker would attacker would start downloading a data stream. The attacker would
then send a binding update cancellation (i.e. a request to delete the then send a binding update cancellation (i.e., a request to delete
binding from the Binding Cache), or just allow the cache entry to the binding from the Binding Cache) or just allow the cache entry to
expire. Either would redirect the data stream to the home network. expire. Either would redirect the data stream to the home network.
As when bombing a care-of-address, the attacker can keep the stream As when bombing a care-of address, the attacker can keep the stream
alive and even increase the data rate by spoofing acknowledgments. alive and even increase the data rate by spoofing acknowledgements.
When successful, the bombing attack against the home network is just When successful, the bombing attack against the home network is just
as serious as the one against a care-of-address. as serious as that against a care-of address.
The basic protection mechanism adopted is return routability. The basic protection mechanism adopted is return routability.
However, it is hard to fully protect against this attack; see However, it is hard to fully protect against this attack; see Section
Section 4.1.1. 4.1.1.
3.3 Attacks against binding update protocols 3.3. Attacks against Binding Update Protocols
Security protocols that successfully protect the secrecy and Security protocols that successfully protect the secrecy and
integrity of data can sometimes make the participants more vulnerable integrity of data can sometimes make the participants more vulnerable
to denial-of-service attacks. In fact, the stronger the to denial-of-service attacks. In fact, the stronger the
authentication, the easier it may be for an attacker to use the authentication, the easier it may be for an attacker to use the
protocol features to exhaust the mobile's or the correspondent's protocol features to exhaust the mobile's or the correspondent's
resources. resources.
3.3.1 Inducing Unnecessary Binding Updates 3.3.1. Inducing Unnecessary Binding Updates
When a mobile node receives an IP packet from a new correspondent via When a mobile node receives an IP packet from a new correspondent via
the home agent, it may initiate the binding update protocol. An the home agent, it may initiate the binding update protocol. An
attacker can exploit this by sending the mobile node a spoofed IP attacker can exploit this by sending the mobile node a spoofed IP
packet (e.g. ping or TCP SYN packet) that appears to come from a new packet (e.g., ping or TCP SYN packet) that appears to come from a new
correspondent node. Since the packet arrives via the home agent, the correspondent node. Since the packet arrives via the home agent, the
mobile node may start the binding update protocol with the mobile node may start the binding update protocol with the
correspondent node. The decision as to whether or not to initiate correspondent node. The decision as to whether to initiate the
the binding update procedure may depend on several factors (including binding update procedure may depend on several factors (including
heuristics, cross layer information, configuration options, etc) and heuristics, cross layer information, and configuration options) and
is not specified by Mobile IPv6. Not initiating the binding update is not specified by Mobile IPv6. Not initiating the binding update
procedure automatically may alleviate these attacks, but will not, in procedure automatically may alleviate these attacks, but it will not,
general, avoid them completely. in general, prevent them completely.
In a real attack the attacker would induce the mobile node to In a real attack the attacker would induce the mobile node to
initiate binding update protocols with a large number of initiate binding update protocols with a large number of
correspondent nodes at the same time. If the correspondent addresses correspondent nodes at the same time. If the correspondent addresses
are real addresses of existing IP nodes, then most instances of the are real addresses of existing IP nodes, then most instances of the
binding update protocol might even complete successfully. The binding update protocol might even complete successfully. The
entries created in the Binding Cache are correct but useless. In entries created in the Binding Cache are correct but useless. In
this way, the attacker can induce the mobile to execute the binding this way, the attacker can induce the mobile to execute the binding
update protocol unnecessarily, which can drain the mobile's update protocol unnecessarily, which can drain the mobile's
resources. resources.
A correspondent node (i.e., any IP node) can also be attacked in a A correspondent node (i.e., any IP node) can also be attacked in a
similar way. The attacker sends spoofed IP packets to a large number similar way. The attacker sends spoofed IP packets to a large number
of mobiles with the target node's address as the source address. of mobiles, with the target node's address as the source address.
These mobiles will initiate the binding update protocol with the These mobiles will initiate the binding update protocol with the
target node. Again, most of the binding update protocol executions target node. Again, most of the binding update protocol executions
will complete successfully. By inducing a large number of will complete successfully. By inducing a large number of
unnecessary binding updates, the attacker is able to consume the unnecessary binding updates, the attacker is able to consume the
target node's resources. target node's resources.
This attack is possible against any binding update authentication This attack is possible against any binding update authentication
protocol. The more resources the binding update protocol consumes, protocol. The more resources the binding update protocol consumes,
the more serious the attack. Hence, strong cryptographic the more serious the attack. Therefore, strong cryptographic
authentication protocol is more vulnerable to the attack than a weak authentication protocol is more vulnerable to the attack than a weak
one or unauthenticated binding updates. Ingress filtering helps a one or unauthenticated binding updates. Ingress filtering helps a
little, since it makes it harder to forge the source address of the little, since it makes it harder to forge the source address of the
spoofed packets, but it does not completely eliminate this threat. spoofed packets, but it does not completely eliminate this threat.
A node should protect itself from the attack by setting a limit on A node should protect itself from the attack by setting a limit on
the amount of resources, i.e., processing time, memory, and the amount of resources (i.e., processing time, memory, and
communications bandwidth, which it uses for processing binding communications bandwidth) that it uses for processing binding
updates. When the limit is exceeded, the node can simply stop updates. When the limit is exceeded, the node can simply stop
attempting route optimization. Sometimes it is possible to process attempting route optimization. Sometimes it is possible to process
some binding updates even when a node is under the attack. A mobile some binding updates even when a node is under the attack. A mobile
node may have a local security policy listing a limited number of node may have a local security policy listing a limited number of
addresses to which binding updates will be sent even when the mobile addresses to which binding updates will be sent even when the mobile
node is under DoS attack. A correspondent node (i.e., any IP node) node is under DoS attack. A correspondent node (i.e., any IP node)
may similarly have a local security policy listing a limited set of may similarly have a local security policy listing a limited set of
addresses from which binding updates will be accepted even when the addresses from which binding updates will be accepted even when the
correspondent is under a binding update DoS attack. correspondent is under a binding update DoS attack.
The node may also recognize addresses with which they have had The node may also recognize addresses with it had meaningful
meaningful communication in the past and only send binding updates to communication in the past and only send binding updates to, or accept
or accept them from those addresses. Since it may be impossible for them from, those addresses. Since it may be impossible for the IP
the IP layer to know about the protocol state in higher protocol layer to know about the protocol state in higher protocol layers, a
layers, a good measure of the meaningfulness of the past good measure of the meaningfulness of the past communication is
communication is probably per-address packet counts. Alternatively, probably per-address packet counts. Alternatively, Neighbor
Neighbor Discovery [2] (section 5.1, Conceptual Data Structures) Discovery [2] (Section 5.1, Conceptual Data Structures) defines the
defines the Destination Cache as a set of entries about destinations Destination Cache as a set of entries about destinations to which
to which traffic has been sent recently. Thus, implementors may wish traffic has been sent recently. Thus, implementors may wish to use
to use the information in the Destination Cache. the information in the Destination Cache.
Section 11.7.2 ("Correspondent Registration") in [7] does not specify Section 11.7.2 ("Correspondent Registration") in [6] does not specify
when such a route optimization procedure should be initiated. It when such a route optimization procedure should be initiated. It
does indicate when it may justifiable to do so, but these hints are does indicate when it may justifiable to do so, but these hints are
not enough. This remains an area where more work is needed. not enough. This remains an area where more work is needed.
Obviously, given that route optimization is optional, any node that Obviously, given that route optimization is optional, any node that
finds the processing load excessive or unjustified may simply turn it finds the processing load excessive or unjustified may simply turn it
off (either selectively or completely). off (either selectively or completely).
3.3.2 Forcing Non-Optimized Routing 3.3.2. Forcing Non-Optimized Routing
As a variant of the previous attack, the attacker can prevent a As a variant of the previous attack, the attacker can prevent a
correspondent node from using route optimization by filling its correspondent node from using route optimization by filling its
Binding Cache with unnecessary entries so that most entries for real Binding Cache with unnecessary entries so that most entries for real
mobiles are dropped. mobiles are dropped.
Any successful DoS attack against a mobile or a correspondent node Any successful DoS attack against a mobile or correspondent node can
can also prevent the processing of binding updates. We have also prevent the processing of binding updates. We have previously
previously suggested that the target of a DoS attack may respond by suggested that the target of a DoS attack may respond by stopping
stopping route optimization for all or some communication. route optimization for all or some communication. Obviously, an
Obviously, an attacker can exploit this fallback mechanism and force attacker can exploit this fallback mechanism and force the target to
the target to use the less efficient home agent based routing. The use the less efficient home agent-based routing. The attacker only
attacker only needs to mount a noticeable DoS attack against the needs to mount a noticeable DoS attack against the mobile or
mobile or correspondent, and the target will default to non-optimized correspondent, and the target will default to non-optimized routing.
routing.
The target node can mitigate the effects of the attack by reserving The target node can mitigate the effects of the attack by reserving
more space for the Binding Cache, by reverting to non-optimized more space for the Binding Cache, by reverting to non-optimized
routing only when it cannot otherwise cope with the DoS attack, by routing only when it cannot otherwise cope with the DoS attack, by
trying aggressively to return to optimized routing, or by favoring trying aggressively to return to optimized routing, or by favoring
mobiles with which it has an established relationship. This attack mobiles with which it has an established relationship. This attack
is not as serious as the ones described earlier, but applications is not as serious as the ones described earlier, but applications
that rely on Route Optimization could still be affected. For that rely on Route Optimization could still be affected. For
instance, conversational multimedia sessions can suffer drastically instance, conversational multimedia sessions can suffer drastically
from the additional delays caused by triangle routing. from the additional delays caused by triangle routing.
3.3.3 Reflection and Amplification 3.3.3. Reflection and Amplification
Attackers sometimes try to hide the source of a packet flooding Attackers sometimes try to hide the source of a packet-flooding
attack by reflecting the traffic from other nodes [1]. That is, attack by reflecting the traffic from other nodes [1]. That is,
instead of sending the flood of packets directly to the target, the instead of sending the flood of packets directly to the target, the
attacker sends data to other nodes, tricking them to send the same attacker sends data to other nodes, tricking them to send the same
number, or more, packets to the target. Such reflection can hide the number, or more, packets to the target. Such reflection can hide the
attacker's address even when ingress filtering prevents source attacker's address even when ingress filtering prevents source
address spoofing. Reflection is particularly dangerous if the address spoofing. Reflection is particularly dangerous if the
packets can be reflected multiple times, if they can be sent into a packets can be reflected multiple times, if they can be sent into a
looping path, or if the nodes can be tricked into sending many more looping path, or if the nodes can be tricked into sending many more
packets than they receive from the attacker, because such features packets than they receive from the attacker, because such features
can be used to amplify the traffic by a significant factor. When can be used to amplify the traffic by a significant factor. When
designing protocols, one should avoid creating services that can be designing protocols, one should avoid creating services that can be
used for reflection and amplification. used for reflection and amplification.
Triangle routing would easily create opportunities for reflection: a Triangle routing would easily create opportunities for reflection: a
correspondent node receives packets (e.g. TCP SYN) from the mobile correspondent node receives packets (e.g., TCP SYN) from the mobile
node and replies to the home address given by the mobile node in the node and replies to the home address given by the mobile node in the
Home Address Option (HAO). The mobile might not really be a mobile Home Address Option (HAO). The mobile might not really be a mobile
and the home address could actually be the target address. The and the home address could actually be the target address. The
target would only see the packets sent by the correspondent and could target would only see the packets sent by the correspondent and could
not see the attacker's address (even if ingress filtering prevents not see the attacker's address (even if ingress filtering prevents
the attacker from spoofing its source address). the attacker from spoofing its source address).
+----------+ TCP SYN with HAO +-----------+ +----------+ TCP SYN with HAO +-----------+
| Attacker |-------------------->| Reflector | | Attacker |-------------------->| Reflector |
+----------+ +-----------+ +----------+ +-----------+
| |
| TCP SYN-ACK to HoA | TCP SYN-ACK to HoA
V V
+-----------+ +-----------+
| Flooding | | Flooding |
| target | | target |
+-----------+ +-----------+
Figure 5: Reflection Attack Figure 5. Reflection Attack
A badly designed binding update protocol could also be used for A badly designed binding update protocol could also be used for
reflection: the correspondent would respond to a data packet by reflection: the correspondent would respond to a data packet by
initiating the binding update authentication protocol, which usually initiating the binding update authentication protocol, which usually
involves sending a packet to the home address. In that case, the involves sending a packet to the home address. In that case, the
reflection attack can be discouraged by copying the mobile's address reflection attack can be discouraged by copying the mobile's address
into the messages sent by the mobile to the correspondent. (The into the messages sent by the mobile to the correspondent. (The
mobile's source address is usually the same as the care-of address mobile's source address is usually the same as the care-of address,
but an Alternative care-of address suboption can specify a different but an Alternative Care-of Address sub-option can specify a different
care-of address.) Some of the early proposals for MIPv6 security care-of address.) Some of the early proposals for MIPv6 security
used this approach, and were prone to reflection attacks. used this approach and were prone to reflection attacks.
In some of the proposals for binding update authentication protocols, In some of the proposals for binding update authentication protocols,
the correspondent node responded to an initial message from the the correspondent node responded to an initial message from the
mobile with two packets (one to the home address, one to the care-of mobile with two packets (one to the home address, one to the care-of
address). It would have been possible to use this to amplify a address). It would have been possible to use this to amplify a
flooding attack by a factor of two. Furthermore, with public-key flooding attack by a factor of two. Furthermore, with public-key
authentication, the packets sent by the correspondent might have been authentication, the packets sent by the correspondent might have been
significantly larger than the one that triggers them. significantly larger than the one that triggers them.
These types of reflection and amplification can be avoided by These types of reflection and amplification can be avoided by
ensuring that the correspondent only responds to the same address ensuring that the correspondent only responds to the same address
from which it received a packet, and only with a single packet of the from which it received a packet, and only with a single packet of the
same size. These principles have been applied to MIPv6 security same size. These principles have been applied to MIPv6 security
design. design.
3.4 Classification of attacks 3.4. Classification of Attacks
Sect. Attack name Target Sev. Mitigation Sect. Attack name Target Sev. Mitigation
--------------------------------------------------------------------- ---------------------------------------------------------------------
3.1.1 Basic address stealing MN Med. RR 3.1.1 Basic address stealing MN Med. RR
3.1.2 Stealing addresses of stationary nodes Any High RR 3.1.2 Stealing addresses of stationary nodes Any High RR
3.1.3 Future address stealing MN Low RR, lifetime 3.1.3 Future address stealing MN Low RR, lifetime
3.1.4 Attacks against Secrecy and Integrity MN Low RR, IPsec 3.1.4 Attacks against secrecy and integrity MN Low RR, IPsec
3.1.5 Basic Denial of Service Attacks Any Med. RR 3.1.5 Basic denial-of-service attacks Any Med. RR
3.1.6 Replaying and Blocking Binding Updates MN Low lifetime, 3.1.6 Replaying and blocking binding updates MN Low lifetime,
sequence number, seq number,
MAC MAC
3.2.1 Basic flooding Any High RR 3.2.1 Basic flooding Any High RR
3.2.2 Return-to-home flooding Any High RR 3.2.2 Return-to-home flooding Any High RR
3.3.1 Inducing Unnecessary Binding Updates MN, CN Med. heuristics 3.3.1 Inducing unnecessary binding updates MN, CN Med. heuristics
3.3.2 Forcing Non-Optimized Routing MN Low heuristics 3.3.2 Forcing non-optimized routing MN Low heuristics
3.3.3 Reflection and Amplification N/A Med. BU design 3.3.3 Reflection and amplification N/A Med. BU design
Figure 6: Summary of Discussed Attacks Figure 6. Summary of Discussed Attacks
Figure 6 gives a summary of the attacks discussed. As it stands at Figure 6 gives a summary of the attacks discussed. As it stands at
the time of writing, the return-to-the-home flooding and the the time of writing, the return-to-the-home flooding and the
induction of unnecessary binding updates look like the threats induction of unnecessary binding updates look like the threats
against which we have the smallest amount of protection, compared to against which we have the least amount of protection, compared to
their severity. their severity.
3.5 Problems with infrastructure based authorization 3.5. Problems with Infrastructure-Based Authorization
Early in the MIPv6 design process it was assumed that plain IPsec Early in the MIPv6 design process, it was assumed that plain IPsec
could be the default way to secure Binding Updates with arbitrary could be the default way to secure Binding Updates with arbitrary
correspondent nodes. However, this turned out to be impossible. correspondent nodes. However, this turned out to be impossible.
Plain IPsec relies on an infrastructure for key management, which, to Plain IPsec relies on an infrastructure for key management, which, to
be usable with any arbitrary pair of nodes, would need to be global be usable with any arbitrary pair of nodes, would need to be global
in scope. Such a "global PKI" does not exist, nor is it expected to in scope. Such a "global PKI" does not exist, nor is it expected to
come into existence any time soon. come into existence any time soon.
Other more minor issues that also surfaced at the time were: (1) More minor issues that also surfaced at the time were: (1)
insufficient filtering granularity for the state of IPsec at the insufficient filtering granularity for the state of IPsec at the
time, (2) cost to establish a security association (in terms of CPU time, (2) cost to establish a security association (in terms of CPU
and round trip times) and (3) expressing the proper authorization (as and round trip times), and (3) expressing the proper authorization
opposed to just authentication) for binding updates [11]. These (as opposed to just authentication) for binding updates [13]. These
issues are solvable, and, in particular, (1) and (3) have been issues are solvable, and, in particular, (1) and (3) have been
addressed for IPsec usage with binding updates between the mobile addressed for IPsec usage with binding updates between the mobile
node and the home agent [8]. node and the home agent [7].
But the lack of a global PKI remains unsolved. However, the lack of a global PKI remains unsolved.
One way of providing a global key infrastructure for mobile IP could One way to provide a global key infrastructure for mobile IP could be
be DNSSEC. Such a scheme is not completely supported by the existing DNSSEC. Such a scheme is not completely supported by the existing
specifications, as it constitutes a new application of the KEY RR, specifications, as it constitutes a new application of the KEY RR,
something explicitly limited to DNSSEC [5]. Nevertheless, if one something explicitly limited to DNSSEC [8] [9] [10]. Nevertheless,
were to define it, one could proceed along the following lines: A if one were to define it, one could proceed along the following
secure reverse DNS that provided a public key for each IP address lines: A secure reverse DNS that provided a public key for each IP
could be used to verify that a binding update is indeed signed by an address could be used to verify that a binding update is indeed
authorized party. However, in order to be secure, each link in such signed by an authorized party. However, in order to be secure, each
a system must be secure. That is, there must be a chain of keys and link in such a system must be secure. That is, there must be a chain
signatures all the way down from the root (or at least starting from of keys and signatures all the way down from the root (or at least
a trust anchor common to the mobile node and the correspondent node) starting from a trust anchor common to the mobile node and the
to the given IP address. Furthermore, it is not enough that each key correspondent node) to the given IP address. Furthermore, it is not
be signed by the key above it in the chain. It is also necessary enough that each key be signed by the key above it in the chain. It
that each signature explicitly authorize the lower key to manage the is also necessary that each signature explicitly authorize the lower
corresponding address block below. key to manage the corresponding address block below.
Even though it would be theoretically possible to build a secure Even though it would be theoretically possible to build a secure
reverse DNS infrastructure along the lines shown above, the practical reverse DNS infrastructure along the lines shown above, the practical
problems would be daunting. Whereas the delegation and key signing problems would be daunting. Whereas the delegation and key signing
might work close to the root of the tree, it would probably break might work close to the root of the tree, it would probably break
down somewhere along the path to the individual nodes. Notice that a down somewhere along the path to the individual nodes. Note that a
similar delegation tree is currently being proposed for Secure similar delegation tree is currently being proposed for Secure
Neighbor Discovery [13], although in this case only routers (not Neighbor Discovery [15], although in this case only routers (not
necessarily every single potential mobile node) need to secure such a necessarily every single potential mobile node) need to secure such a
certificate. Furthermore, checking all the signatures on the tree certificate. Furthermore, checking all the signatures on the tree
would place a considerable burden on the correspondent nodes, making would place a considerable burden on the correspondent nodes, making
route optimization prohibitive, or at least justifiable only in very route optimization prohibitive, or at least justifiable only in very
particular circumstances. Finally, it is not enough to simply check particular circumstances. Finally, it is not enough simply to check
if the mobile node is authorized to send binding updates containing a whether the mobile node is authorized to send binding updates
given Home Address, because to protect against flooding attacks the containing a given home address, because to protect against flooding
care-of address must also be verified. attacks, the care-of address must also be verified.
Relying on this same secure DNS infrastructure to verify care-of- Relying on this same secure DNS infrastructure to verify care-of
addresses would be even harder than verifying home addresses. addresses would be even harder than verifying home addresses.
Instead, a different method would be required, e.g., a return Instead, a different method would be required, e.g., a return
routability procedure. If so, the obvious question is whether the routability procedure. If so, the obvious question is whether the
gargantuan cost of deploying the global secure DNS infrastructure is gargantuan cost of deploying the global secure DNS infrastructure is
worth the additional protection it affords, as compared to simply worth the additional protection it affords, as compared to simply
using return routability for both home address and care-of address using return routability for both home address and care-of address
verification. verification.
4. The solution selected for Mobile IPv6 4. Solution Selected for Mobile IPv6
The current Mobile IPv6 route optimization security has been The current Mobile IPv6 route optimization security has been
carefully designed to prevent or mitigate the threats that were carefully designed to prevent or mitigate the threats that were
discussed in Section 3. The goal has been to produce a design with a discussed in Section 3. The goal has been to produce a design with a
level of security which is close to that of a static IPv4 based level of security close to that of a static IPv4-based Internet, and
Internet, and with a cost in terms of packets, delay and processing with an acceptable cost in terms of packets, delay, and processing.
that is not excessive. The result is not what one would expect: the The result is not what one would expect: it is definitely not a
result is definitely not a traditional cryptographic protocol. traditional cryptographic protocol. Instead, the result relies
Instead, the result relies heavily on the assumption of an heavily on the assumption of an uncorrupted routing infrastructure
uncorrupted routing infrastructure, and builds upon the idea of and builds upon the idea of checking that an alleged mobile node is
checking that an alleged mobile node is indeed reachable both through indeed reachable through both its home address and its care-of
its home address and its care-of-address. Furthermore, the lifetime address. Furthermore, the lifetime of the state created at the
of the state created at the corresponded nodes is deliberately corresponded nodes is deliberately restricted to a few minutes, in
restricted to a few minutes, in order to limit the potential threat order to limit the potential threat from time shifting.
from time shifting.
In this section we describe the solution in reasonable detail (for This section describes the solution in reasonable detail (for further
further details see the specification), starting from Return details see the specification), starting from Return Routability
Routability (Section 4.1), continuing with a discussion about state (Section 4.1), continuing with a discussion about state creation at
creation at the correspondent node (Section 4.2), and completing the the correspondent node (Section 4.2), and completing the description
description with a discussion about the lifetime of Binding Cache with a discussion about the lifetime of Binding Cache Entries
Entries (Section 4.3). (Section 4.3).
4.1 Return Routability 4.1. Return Routability
Return Routability (RR) is the name of the basic mechanism deployed Return Routability (RR) is the name of the basic mechanism deployed
by Mobile IPv6 route optimization security design. RR is based on by Mobile IPv6 route optimization security design. RR is based on
the idea that a node should be able to verify that there is a node the idea that a node should be able to verify that there is a node
that is able to respond to packets sent to a given address. The that is able to respond to packets sent to a given address. The
check yields false positives if the routing infrastructure is check yields false positives if the routing infrastructure is
compromised or if there is an attacker between the verifier and the compromised or if there is an attacker between the verifier and the
address to be verified. With these exceptions, it is assumed that a address to be verified. With these exceptions, it is assumed that a
successful reply indicates that there is indeed a node at the given successful reply indicates that there is indeed a node at the given
address, and that the node is willing to reply to the probes sent to address, and that the node is willing to reply to the probes sent to
it. it.
The basic return routability mechanism consist of two checks, a Home The basic return routability mechanism consists of two checks, a Home
Address check (see Section 4.1.1) and a care-of-address check (see Address check (see Section 4.1.1) and a care-of-address check (see
Section 4.1.2). The packet flow is depicted in Figure 7. First the Section 4.1.2). The packet flow is depicted in Figure 7. First, the
mobile node sends two packets to the correspondent node: a Home Test mobile node sends two packets to the correspondent node: a Home Test
Init (HoTI) packet is sent through the home agent, and a Care-of Test Init (HoTI) packet is sent through the home agent, and a Care-of Test
Init (CoTI) directly. The correspondent node replies to both of Init (CoTI) directly. The correspondent node replies to both of
these independently by sending a Home Test (HoT) in response to the these independently by sending a Home Test (HoT) in response to the
Home Test Init and a Care-of Test (CoT) in response to the Care-of Home Test Init and a Care-of Test (CoT) in response to the Care-of
Test Init. Finally, once the mobile node has received both the Home Test Init. Finally, once the mobile node has received both the Home
Test and Care-of Test packets, it sends a Binding Update to the Test and Care-of Test packets, it sends a Binding Update to the
correspondent node. correspondent node.
+------+ 1a) HoTI +------+ +------+ 1a) HoTI +------+
skipping to change at page 28, line 21 skipping to change at page 25, line 35
| |2b| CoT / / | |2b| CoT / /
| | | / / | | | / /
| | | 3) BU / / | | | 3) BU / /
V | V / / V | V / /
+------+ 1a) HoTI / / +------+ 1a) HoTI / /
| |<----------------/ / | |<----------------/ /
| CN | 2a) HoT / | CN | 2a) HoT /
| |------------------/ | |------------------/
+------+ +------+
Figure 7: Return Routability Packet Flow Figure 7. Return Routability Packet Flow
It might appear that the actual design was somewhat convoluted. That It might appear that the actual design was somewhat convoluted. That
is, the real return routability checks are the message pairs < Home is, the real return routability checks are the message pairs < Home
Test, Binding Update > and < Care-of Test, Binding Update >. The Test, Binding Update > and < Care-of Test, Binding Update >. The
Home Test Init and Care-of Test Init packets are only needed to Home Test Init and Care-of Test Init packets are only needed to
trigger the test packets, and the Binding Update acts as a combined trigger the test packets, and the Binding Update acts as a combined
routability response to both of the tests. routability response to both of the tests.
There are two main reasons behind this design: There are two main reasons behind this design:
o avoidance of reflection and amplification (see Section 3.3.3), and o avoidance of reflection and amplification (see Section 3.3.3), and
o avoidance of state exhaustion DoS attacks (see Section 4.2). o avoidance of state exhaustion DoS attacks (see Section 4.2).
The reason for sending two Init packets instead of one is the The reason for sending two Init packets instead of one is to avoid
avoidance of amplication. The correspondent node does not know amplification. The correspondent node does not know anything about
anything about the mobile node, and therefore it just receives an the mobile node, and therefore it just receives an unsolicited IP
unsolicited IP packet from some arbitrary IP address. In a way, this packet from some arbitrary IP address. In a way, this is similar to
is similar to a server receiving a TCP SYN from a previously unknown a server receiving a TCP SYN from a previously unknown client. If
client. If the correspondent node were to send two packets in the correspondent node were to send two packets in response to an
response to an initial trigger, that would provide the potential for initial trigger, that would provide the potential for a DoS
a DoS amplification effect, as discussed in Section 3.3.3. amplification effect, as discussed in Section 3.3.3.
This scheme also avoids providing for a potential reflection attack. This scheme also avoids providing for a potential reflection attack.
If the correspondent node were to reply to an address other than the If the correspondent node were to reply to an address other than the
source address of the packet, that would create a reflection effect. source address of the packet, that would create a reflection effect.
Thus, the only safe mechanism possible for a naive correspondent is Thus, the only safe mechanism possible for a naive correspondent is
to reply to each received packet with just one packet, and to send to reply to each received packet with just one packet, and to send
the reply to the source address of the received packet. Hence, two the reply to the source address of the received packet. Hence, two
initial triggers are needed instead of just one. initial triggers are needed instead of just one.
Let us now consider the two return routability tests separately. In Let us now consider the two return routability tests separately. In
the following sections, the derivation of cryptographic material from the following sections, the derivation of cryptographic material from
each of these is shown in a simplified manner. For the real formulas each of these is shown in a simplified manner. For the real formulas
and more detail, please refer to [7]. and more detail, please refer to [6].
4.1.1 Home Address check 4.1.1. Home Address Check
The Home Address check consists of a Home Test (HoT) packet and a The Home Address check consists of a Home Test (HoT) packet and a
subsequent Binding Update (BU). It is triggered by the arrival of a subsequent Binding Update (BU). It is triggered by the arrival of a
Home Test Init (HoTI). A correspondent node replies to a Home Test Home Test Init (HoTI). A correspondent node replies to a Home Test
Init by sending a Home Test to the source address of the Home Test Init by sending a Home Test to the source address of the Home Test
Init. The source address is assumed to be the home address of a Init. The source address is assumed to be the home address of a
mobile node, and therefore the Home Test is assumed to be tunneled by mobile node, and therefore the Home Test is assumed to be tunneled by
the Home Agent to the mobile node. The Home Test contains a the Home Agent to the mobile node. The Home Test contains a
cryptographically generated token, home keygen token, which is formed cryptographically generated token, home keygen token, which is formed
by calculating a hash function over the concatenation of a secret key by calculating a hash function over the concatenation of a secret
Kcn known only by the correspondent node, the source address of the key, Kcn, known only by the correspondent node, the source address of
Home Test Init packet, and a nonce. the Home Test Init packet, and a nonce.
home keygen token = hash(Kcn | home address | nonce | 0) home keygen token = hash(Kcn | home address | nonce | 0)
An index to the nonce is also included in the Home Test packet, An index to the nonce is also included in the Home Test packet,
allowing the correspondent node to find the appropriate nonce more allowing the correspondent node to find the appropriate nonce more
easily. easily.
The token allows the correspondent node to make sure that any binding The token allows the correspondent node to make sure that any binding
update received subsequently has been created by a node that has seen update received subsequently has been created by a node that has seen
the Home Test packet; see Section 4.2. see Section 4.2. the Home Test packet; see Section 4.2.
In most cases the Home Test packet is forwarded over two different In most cases, the Home Test packet is forwarded over two different
segments of the Internet. It first traverses from the correspondent segments of the Internet. It first traverses from the correspondent
node to the Home Agent. On this trip, it is not protected and any node to the Home Agent. On this trip, it is not protected and any
eavesdropper on the path can learn its contents. The Home Agent then eavesdropper on the path can learn its contents. The Home Agent then
forwards the packet to the mobile node. This path is taken inside an forwards the packet to the mobile node. This path is taken inside an
IPsec ESP protected tunnel, making it impossible for the outsiders to IPsec ESP protected tunnel, making it impossible for the outsiders to
learn the contents of the packet. learn the contents of the packet.
At first it may sound unnecessary to protect the packet between the At first, it may sound unnecessary to protect the packet between the
home agent and the mobile node since it travelled unprotected between home agent and the mobile node, since it travelled unprotected
the correspondent node and the mobile node. If all links in the between the correspondent node and the mobile node. If all links in
Internet were equally insecure, the situation would indeed be so, the the Internet were equally insecure, the additional protection would
additional protection would be unnecessary. However, in most be unnecessary. However, in most practical settings the network is
practical settings the network is likely to be more secure near the likely to be more secure near the home agent than near the mobile
Home Agent than near the Mobile Node. For example, if the home agent node. For example, if the home agent hosts a virtual home link and
hosts a virtual home link and the mobile nodes are never actually at the mobile nodes are never actually at home, an eavesdropper should
home, an eavesdropper should be close to the correspondent node or on be close to the correspondent node or on the path between the
the path between the correspondent node and the home agent, since it correspondent node and the home agent, since it could not eavesdrop
could not eavesdrop at the home agent. If the correspondent node is at the home agent. If the correspondent node is a major server, all
a major server, all the links on the path between it and the Home the links on the path between it and the home agent are likely to be
Agent are likely to be fairly secure. On the other hand, the Mobile fairly secure. On the other hand, the Mobile Node is probably using
Node is probably using wireless access technology, making it wireless access technology, making it sometimes trivial to eavesdrop
sometimes trivial to eavesdrop on its access link. Thus, it is on its access link. Thus, it is fairly easy to eavesdrop on packets
fairly easy to eavesdrop on packets that arrive at the mobile node. that arrive at the mobile node. Consequently, protecting the HA-MN
Consequently, protecting the HA-MN path is likely to provide real path is likely to provide real security benefits even when the CN-HA
security benefits even when the CN-HA path remains unprotected. path remains unprotected.
4.1.2 Care-of-Address check 4.1.2. Care-of-Address Check
From the correspondent node's point of view, the Care-of-Address From the correspondent node's point of view, the Care-of-Address
check is very similar to the Home check. The only difference is that check is very similar to the home check. The only difference is that
now the source address of the received Care-of Test Init packet is now the source address of the received Care-of Test Init packet is
assumed to be the care-of-address of the mobile node. Furthermore, assumed to be the care-of address of the mobile node. Furthermore,
the token is created in a slightly different manner in order to make the token is created in a slightly different manner in order to make
it impossible to use home tokens for care-of tokens or vice versa. it impossible to use home tokens for care-of tokens or vice versa.
care-of keygen token = hash(Kcn | care-of address | nonce | 1) care-of keygen token = hash(Kcn | care-of address | nonce | 1)
The Care-of Test traverses only one leg, directly from the The Care-of Test traverses only one leg, directly from the
correspondent node to the mobile node. It remains unprotected all correspondent node to the mobile node. It remains unprotected all
along the way, making it vulnerable to eavesdroppers near the along the way, making it vulnerable to eavesdroppers near the
correspondent node, on the path from the correspondent node to the correspondent node, on the path from the correspondent node to the
mobile node, or near the mobile node. mobile node, or near the mobile node.
4.1.3 Forming the first Binding Update 4.1.3. Forming the First Binding Update
When the mobile node has received both the Home Test and Care-of Test When the mobile node has received both the Home Test and Care-of Test
messages, it creates a binding key Kbm by taking a hash function over messages, it creates a binding key, Kbm, by computing a hash function
the concatenation of the tokens received. over the concatenation of the tokens received.
This key is used to protect the first and the subsequent binding This key is used to protect the first and the subsequent binding
updates, as long as the key remains valid. updates, as long as the key remains valid.
Note that the key Kbm is available to anyone that is able to receive Note that the key Kbm is available to anyone who is able to receive
both the Care-of Test and Home Test messages. However, they are both the Care-of Test and Home Test messages. However, they are
normally routed by different routes through the network, and the Home normally routed by different routes through the network, and the Home
Test is transmitted over an encrypted tunnel from the home agent to Test is transmitted over an encrypted tunnel from the home agent to
the mobile node (see also Section 5.4). the mobile node (see also Section 5.4).
4.2 Creating state safely 4.2. Creating State Safely
The correspondent node may remain stateless until it receives the The correspondent node may remain stateless until it receives the
first Binding Update. That is, it does not need to record receiving first Binding Update. That is, it does not need to record receiving
and replying to the Home Test Init and Care-of Test Init messages. and replying to the Home Test Init and Care-of Test Init messages.
The Home Test Init/Home Test and Care-of Test Init/Care-of Test The Home Test Init/Home Test and Care-of Test Init/Care-of Test
exchanges take place in parallel but independently from each other. exchanges take place in parallel but independently of each other.
Thus, the correspondent can respond to each message immediately and Thus, the correspondent can respond to each message immediately, and
it does not need to remember doing that. This helps in potential it does not need to remember doing that. This helps in potential
Denial-of-Service situations: no memory needs to be reserved when denial-of-service situations: no memory needs to be reserved for
processing Home Test Init and Care-of Test Init messages. processing Home Test Init and Care-of Test Init messages.
Furthermore, Home Test Init and Care-of Test Init processing is Furthermore, Home Test Init and Care-of Test Init processing is
designed to be lightweight, and it can be rate limited if necessary. designed to be lightweight, and it can be rate limited if necessary.
When receiving a first binding update, the correspondent node goes When receiving a first binding update, the correspondent node goes
through a rather complicated procedure. The purpose of this through a rather complicated procedure. The purpose of this
procedure is to ensure that there is indeed a mobile node that has procedure is to ensure that there is indeed a mobile node that has
recently received a Home Test and a Care-of Test that were sent to recently received a Home Test and a Care-of Test that were sent to
the claimed home and care-of-addresses, respectively, and to make the claimed home and care-of addresses, respectively, and to make
sure that the correspondent node does not unnecessarily spend CPU or sure that the correspondent node does not unnecessarily spend CPU or
other resources while performing this check. other resources while performing this check.
Since the correspondent node does not have any state when the binding Since the correspondent node does not have any state when the binding
update arrives, the binding update itself must contain enough update arrives, the binding update itself must contain enough
information so that relevant state can be created. The binding information so that relevant state can be created. To that end, the
update contains the following pieces of information for that: binding update contains the following pieces of information:
Source address: The care-of address specified in the Binding Update Source address: The care-of address specified in the Binding Update
must be equal to the source address used in the Care-of Test Init must be equal to the source address used in the Care-of Test Init
message. Notice that this applies to the effective Care-of message. Notice that this applies to the effective Care-of
Address of the Binding Update. In particular, if the Binding Address of the Binding Update. In particular, if the Binding
Update includes an Alternate Care-of Address (AltCoA) [7], the Update includes an Alternate Care-of Address (AltCoA) [6], the
effective CoA is, of course, this AltCoA. Thus, the Care-of Test effective CoA is, of course, this AltCoA. Thus, the Care-of Test
Init must have originated from the AltCoA. Init must have originated from the AltCoA.
Home address: The home address specified in the Binding Update must Home address: The home address specified in the Binding Update must
be equal to the source address used in the Home Test Init message. be equal to the source address used in the Home Test Init message.
Two nonce indices: These are copied over from the Home Test and Two nonce indices: These are copied over from the Home Test and
Care-of Test messages, and together with the other information Care-of Test messages, and together with the other information
they allow the correspondent node to re-create the tokens sent in they allow the correspondent node to re-create the tokens sent in
the Home Test and Care-of Test messages and used for creating Kbm. the Home Test and Care-of Test messages and used for creating Kbm.
Without them the correspondent node might need to try the 2-3
Without them, the correspondent node might need to try the 2-3
latest nonces, leading to unnecessary resource consumption. latest nonces, leading to unnecessary resource consumption.
Message Authentication Code (MAC): The binding update is Message Authentication Code (MAC): The binding update is
authenticated by computing a MAC function over the care-of- authenticated by computing a MAC function over the care-of
address, the correspondent node's address and the binding update address, the correspondent node's address and the binding update
message itself. The MAC is keyed with the key Kbm. message itself. The MAC is keyed with the key Kbm.
Given the addresses, the nonce indices and thereby the nonces, and Given the addresses, the nonce indices (and thereby the nonces) and
the key Kcn, the correspondent node can re-create the home and the key Kcn, the correspondent node can re-create the home and care-
care-of tokens at the cost of a few memory lookups and computation of of tokens at the cost of a few memory lookups and computation of one
one MAC and one hash function. MAC and one hash function.
Once the correspondent node has re-created the tokens, it hashes the Once the correspondent node has re-created the tokens, it hashes the
tokens together, giving the key Kbm. If the Binding Update is tokens together, giving the key Kbm. If the Binding Update is
authentic, Kbm is cached together with the binding. This key is then authentic, Kbm is cached together with the binding. This key is then
used to verify the MAC that protects integrity and origin of the used to verify the MAC that protects integrity and origin of the
actual Binding Update. Note that the same Kbm may be used for a actual Binding Update. Note that the same Kbm may be used for a
while, until either the mobile node moves (and needs to get a new while, until the mobile node moves (and needs to get a new care-of-
care-of-address token), the care-of token expires, or the home token address token), the care-of token expires, or the home token expires.
expires.
4.2.1 Retransmissions and state machine 4.2.1. Retransmissions and State Machine
Note that since the correspondent node may remain stateless until it Note that since the correspondent node may remain stateless until it
receives a valid binding update, the mobile node is solely receives a valid binding update, the mobile node is solely
responsible for retransmissions. That is, the mobile node should responsible for retransmissions. That is, the mobile node should
keep sending the Home Test Init / Care-of Test Init messages until it keep sending the Home Test Init / Care-of Test Init messages until it
receives a Home Test / Care-of Test, respectively. Similarly, it may receives a Home Test / Care-of Test, respectively. Similarly, it may
need to send the binding update a few times in the case it is lost need to send the binding update a few times in the case it is lost
while in transit. while in transit.
4.3 Quick expiration of the Binding Cache Entries 4.3. Quick expiration of the Binding Cache Entries
A Binding Cache Entry, along with the key Kbm, represents the return A Binding Cache Entry, along with the key Kbm, represents the return
routability state of the network at the time when the Home Test and routability state of the network at the time when the Home Test and
Care-of Test messages were sent out. Now, it is possible that a Care-of Test messages were sent out. It is possible that a specific
specific attacker is able to eavesdrop a Home Test message at some attacker is able to eavesdrop a Home Test message at some point of
point of time but not later. If the Home Test had an infinite or a time, but not later. If the Home Test had an infinite or a long
long lifetime, that would allow the attacker to perform a time lifetime, that would allow the attacker to perform a time shifting
shifting attack (see Section 2.2). That is, in the current IPv4 attack (see Section 2.2). That is, in the current IPv4 architecture
architecture an attacker on the path between the correspondent node an attacker on the path between the correspondent node and the home
and the home agent is able to perform attacks only as long as the agent is able to perform attacks only as long as the attacker is able
attacker is able to eavesdrop (and possibly disrupt) communications to eavesdrop (and possibly disrupt) communications on that particular
on that particular path. A long living Home Test, and consequently path. A long living Home Test, and consequently the ability to send
the ability to send valid binding updates for a long time, would valid binding updates for a long time, would allow the attacker to
allow the attacker to continue its attack even after the attacker is continue its attack even after the attacker is no longer able to
no longer able to eavesdrop on the path. eavesdrop on the path.
To limit the seriousness of this and other similar time shifting To limit the seriousness of this and other similar time shifting
threats, the validity of the tokens is limited to a few minutes. threats, the validity of the tokens is limited to a few minutes.
This effectively limits the validity of the key Kbm and the lifetime This effectively limits the validity of the key Kbm and the lifetime
of the resulting binding updates and binding cache entries. of the resulting binding updates and binding cache entries.
While short life times are necessary given the other aspects of the Although short lifetimes are required by other aspects of the
security design and the goals, they are clearly detrimental for security design and the goals, they are clearly detrimental for
efficiency and robustness. That is, a Home Test Init / Home Test efficiency and robustness. That is, a Home Test Init / Home Test
message pair must be exchanged through the home agent every few message pair must be exchanged through the home agent every few
minutes. These messages are unnecessary from a purely functional minutes. These messages are unnecessary from a purely functional
point of view, thereby representing overhead. What is worse, though, point of view, thereby representing overhead. What is worse, though,
is that they make the home agent a single point of failure. That is, is that they make the home agent a single point of failure. That is,
if the Home Test Init / Home Test messages were not needed, the if the Home Test Init / Home Test messages were not needed, the
existing connections from a mobile node to other nodes could continue existing connections from a mobile node to other nodes could continue
even when the home agent fails, but the current design forces the even when the home agent fails, but the current design forces the
bindings to expire after a few minutes. bindings to expire after a few minutes.
This concludes our walkthrough of the selected security design. The This concludes our walk-through of the selected security design. The
cornerstones of the design were the employment of the return cornerstones of the design were the employment of the return
routability idea in the Home Test, Care-of Test and binding update routability idea in the Home Test, Care-of Test, and binding update
messages, the ability to remain stateless until a valid binding messages, the ability to remain stateless until a valid binding
update is received, and the limiting of the binding life times to a update is received, and the limiting of the binding life times to a
few minutes. Next we briefly discuss some of the remaining threats few minutes. Next we briefly discuss some of the remaining threats
and other problems inherent to the design. and other problems inherent to the design.
5. Security considerations 5. Security Considerations
In this section we give a brief analysis of the security design, This section gives a brief analysis of the security design, mostly in
mostly in the light of what was known at the time the design was the light of what was known when the design was completed in Fall
completed in fall 2002. It should be noted that this section does 2002. It should be noted that this section does not present a proper
not present a proper security analysis of the protocol, but merely security analysis of the protocol; it merely discusses a few issues
discusses a few issues that were known at the time the design was that were known at the time the design was completed.
completed.
It should be kept in mind that the MIPv6 RO security design was never It should be kept in mind that the MIPv6 RO security design was never
intended to be fully secure. Instead, as we stated earlier, the goal intended to be fully secure. Instead, as we stated earlier, the goal
was to be roughly as secure as non-mobile IPv4 was known to be at the was to be roughly as secure as non-mobile IPv4 was known to be at the
time of the design. As it turns out, the result is slightly less time of the design. As it turns out, the result is slightly less
secure than IPv4, but the difference is small and most likely to be secure than IPv4, but the difference is small and most likely
insignificant in real life. insignificant in real life.
The known residual threats as compared with IPv4 are discussed in The known residual threats as compared with IPv4 are discussed in
Section 5.1. Considerations related to the application of IPsec to Section 5.1. Considerations related to the application of IPsec to
authorize route optimization are discussed in Section 5.2. authorize route optimization are discussed in Section 5.2. Section
Section 5.3 discusses an attack against neighboring nodes. Finally, 5.3 discusses an attack against neighboring nodes. Finally, Section
Section 5.4 deals with the special case of two mobile nodes 5.4 deals with the special case of two mobile nodes conversing and
conversing and performing the route optimization procedure with each performing the route optimization procedure with each other.
other.
5.1 Residual Threats as Compared to IPv4 5.1. Residual Threats as Compared to IPv4
As we mentioned in Section 4.2, the lifetime of a binding represents As we mentioned in Section 4.2, the lifetime of a binding represents
a potential time shift in an attack. That is, an attacker that is a potential time shift in an attack. That is, an attacker that is
able to create a false binding is able to reap the benefits of the able to create a false binding is able to reap the benefits of the
binding for as long as the binding lasts, or, alternatively, is able binding as long as the binding lasts. Alternatively, the attacker is
to delay a return-to-home flooding attack (Section 3.2.2) until the able to delay a return-to-home flooding attack (Section 3.2.2) until
binding expires. This is a difference from IPv4 where an attacker the binding expires. This is different from IPv4, where an attacker
may continue an attack only as long as it is on the path between the may continue an attack only as long as it is on the path between the
two hosts. two hosts.
Since the binding lifetimes are severely restricted in the current Since the binding lifetimes are severely restricted in the current
design, the ability to do a time shifting attack is equivalently design, the ability to do a time shifting attack is equivalently
restricted. restricted.
Threats possible because of the introduction of route optimization Threats possible because of the introduction of route optimization
are, of course, not present in a baseline IPv4 internet are, of course, not present in a baseline IPv4 internet (Section
(Section 3.3). In particular, inducing unnecessary binding updates 3.3). In particular, inducing unnecessary binding updates could
could potentially be a severe attack, but this would be most likely potentially be a severe attack, but this would be most likely due to
due to faulty implementations. As an extreme measure, a faulty implementations. As an extreme measure, a correspondent node
correspondent node can protect against these attacks by turning off can protect against these attacks by turning off route optimization.
route optimization. If so, it becomes obvious that the only residual If so, it becomes obvious that the only residual attack against which
attack against which there is no clear-cut prevention (other than its there is no clear-cut prevention (other than its severe limitation as
severe limitation as currently specified) is the time shifting attack currently specified) is the time shifting attack mentioned above.
mentioned above.
5.2 Interaction with IPsec 5.2. Interaction with IPsec
A major motivation behind the current binding update design was A major motivation behind the current binding update design was
scalability, which implied the ability to run the protocol without scalability, which implied the ability to run the protocol without
any existing security infrastructure. An alternative would have been any existing security infrastructure. An alternative would have been
to rely on existing trust relationships, perhaps in the form of a to rely on existing trust relationships, perhaps in the form of a
special purpose Public Key Infrastructure in conjunction with IPsec. special-purpose Public Key Infrastructure in conjunction with IPsec.
That would have limited scalability, making route optimization That would have limited scalability, making route optimization
available only in environments where it is possible to create available only in environments where it is possible to create
appropriate IPsec security associations between the mobile nodes and appropriate IPsec security associations between the mobile nodes and
the corresponding nodes. the corresponding nodes.
There clearly are situations where there exists an appropriate There clearly are situations where there exists an appropriate
relationship between a mobile node and the correspondent node. For relationship between a mobile node and the correspondent node. For
example, if the correspondent node is a server that has pre- example, if the correspondent node is a server that has pre-
established keys with the mobile node, that would be the case. established keys with the mobile node, that would be the case.
However, entity authentication or an authenticated session key is not However, entity authentication or an authenticated session key is not
necessarily sufficient for accepting Binding Updates. necessarily sufficient for accepting Binding Updates.
Home Address Check: If one wants to replace the home address check Home Address Check: If one wants to replace the home address check
with cryptographic credentials, these must carry proper with cryptographic credentials, these must carry proper
authorization for the specific home address, and care must be authorization for the specific home address, and care must be
taken to make sure that the issuer of the certificate is entitled taken to make sure that the issuer of the certificate is entitled
to express such authorization. At the time of the design work, to express such authorization. At the time of the design work,
the route optimization security design team was not aware of the route optimization security design team was not aware of
standardized certificate formats to do this, although more recent standardized certificate formats to do this, although more recent
efforts within the IETF are addressing this issue. Notice that efforts within the IETF are addressing this issue. Note that
there is plenty of motivation to do so, as any pre-existing there is plenty of motivation to do so, as any pre-existing
relationship with a correspondent node would involve the mobile relationship with a correspondent node would involve the mobile
node's home address (instead of any of its possible care-of node's home address (instead of any of its possible care-of
addresses). Accordingly, the IKE exchange would most naturally addresses). Accordingly, the IKE exchange would most naturally
run between the correspondent node and the mobile node's home run between the correspondent node and the mobile node's home
address. This still leaves open the issue of checking the mobile address. This still leaves open the issue of checking the mobile
node's care-of address. node's care-of address.
Care-of Address Check: As for the care-of address check, in Care-of Address Check: As for the care-of-address check, in
practice, it seems highly unlikely that nodes could completely practice, it seems highly unlikely that nodes could completely
replace the care-of address check with credentials. Since the replace the care-of-address check with credentials. Since the
care-of addresses are ephemeral, in general it is very difficult care-of addresses are ephemeral, in general it is very difficult
for a mobile node to present credentials that taken at face value for a mobile node to present credentials that taken at face value
(by an arbitrary correspondent node) guarantee no misuse for, say, (by an arbitrary correspondent node) guarantee no misuse for, say,
flooding attacks (Section 3.2). As discussed before, a flooding attacks (Section 3.2). As discussed before, a
reachability check goes a long way to alleviate such attacks. reachability check goes a long way to alleviate such attacks.
Notice that, as part of the normal protocol exchange, establishing Notice that, as part of the normal protocol exchange, establishing
IPsec security associations via IKE includes one such reachability IPsec security associations via IKE includes one such reachability
test. However, as per the previous section, the natural IKE test. However, as per the previous section, the natural IKE
protocol exchange runs between the correspondent node and the protocol exchange runs between the correspondent node and the
mobile node's home address. Hence, another reachability check is mobile node's home address. Hence, another reachability check is
needed to check the care-of address at which the node is currently needed to check the care-of address at which the node is currently
reachable. If this address changes, such a reachability test is reachable. If this address changes, such a reachability test is
likewise necessary, and is included in ongoing work aimed at likewise necessary, and it is included in ongoing work aimed at
securely updating the node's current address. securely updating the node's current address.
Nevertheless, the Mobile IPv6 base specification [7] does not specify Nevertheless, the Mobile IPv6 base specification [6] does not specify
how to use IPsec together with the mobility procedures between the how to use IPsec together with the mobility procedures between the
mobile node and correspondent node. On the other hand, the mobile node and correspondent node. On the other hand, the
specification is carefully written to allow the creation of the specification is carefully written to allow the creation of the
binding management key Kbm through some different means. binding management key Kbm through some different means.
Accordingly, where an appropriate relationship exists between a Accordingly, where an appropriate relationship exists between a
mobile node and a correspondent node, the use of IPsec is possible, mobile node and a correspondent node, the use of IPsec is possible,
and is, in fact, being pursued in more recent work. and is, in fact, being pursued in more recent work.
5.3 Pretending to be one's neighbor 5.3. Pretending to Be One's Neighbor
One possible attack against the security design is to pretend to be a One possible attack against the security design is to pretend to be a
neighboring node. To launch this attack, the mobile node establishes neighboring node. To launch this attack, the mobile node establishes
route optimization with some arbitrary correspondent node. While route optimization with some arbitrary correspondent node. While
performing the return routability tests and creating the binding performing the return routability tests and creating the binding
management key Kbm, the attacker uses its real home address but a management key Kbm, the attacker uses its real home address but a
faked care-of address. Indeed, the care-of address would be the faked care-of address. Indeed, the care-of address would be the
address of the neighboring node on the local link. The attacker is address of the neighboring node on the local link. The attacker is
able to create the binding since it receives a valid Home Test able to create the binding since it receives a valid Home Test
normally, and it is able to eavesdrop on the Care-of Test as it normally, and it is able to eavesdrop on the Care-of Test, as it
appears on the local link. appears on the local link.
This attack would allow the mobile node to divert unwanted traffic This attack would allow the mobile node to divert unwanted traffic
towards the neighboring node, resulting in an flooding attack. towards the neighboring node, resulting in an flooding attack.
However, this attack is not very serious in practice. Firstly, it is However, this attack is not very serious in practice. First, it is
limited in the terms of location, since it is only possible against limited in the terms of location, since it is only possible against
neighbors. Secondly, the attack works also against the attacker, neighbors. Second, the attack works also against the attacker, since
since it shares the local link with the target. Thirdly, a similar it shares the local link with the target. Third, a similar attack is
attack is possible with Neighbor Discovery spoofing. possible with Neighbor Discovery spoofing.
5.4 Two mobile nodes talking to each other 5.4. Two Mobile Nodes Talking to Each Other
When two mobile nodes want to establish route optimization with each When two mobile nodes want to establish route optimization with each
other, some care must be exercised in order not to reveal the reverse other, some care must be exercised in order not to reveal the reverse
tokens to an attacker. In this situation, both mobile nodes act tokens to an attacker. In this situation, both mobile nodes act
simultaneously in the mobile node and the correspondent node roles. simultaneously in the mobile node and the correspondent node roles.
In the correspondent node role, the nodes are vulnerable to attackers In the correspondent node role, the nodes are vulnerable to attackers
that are co-located at the same link. Such an attacker is able to that are co-located at the same link. Such an attacker is able to
learn both the Home Test and Care-of Test sent by the mobile node, learn both the Home Test and Care-of Test sent by the mobile node,
and therefore it is able to spoof the location of the other mobile and therefore it is able to spoof the location of the other mobile
host to the neighboring one. What is worse is that the attacker can host to the neighboring one. What is worse is that the attacker can
obtain a valid Care-of Test itself, combine it with the Home Test, obtain a valid Care-of Test itself, combine it with the Home Test,
and then claim to the neighboring node that the other node has just and then claim to the neighboring node that the other node has just
arrived at the same link. arrived at the same link.
There is an easy way to avoid this attack. In the correspondent node There is an easy way to avoid this attack. In the correspondent node
role, the mobile node should tunnel the Home Test messages which it role, the mobile node should tunnel the Home Test messages that it
sends through its home agent. This prevents the co-located attacker sends through its home agent. This prevents the co-located attacker
from learning any valid Home Test messages. from learning any valid Home Test messages.
6. Conclusions 6. Conclusions
In this document we have discussed the security design rationale for This document discussed the security design rationale for the Mobile
the Mobile IPv6 Route Optimization. We have tried to describe the IPv6 Route Optimization. We have tried to describe the dangers
dangers created by Mobile IP Route Optimization, the security goals created by Mobile IP Route Optimization, the security goals and
and background of the design, and the actual mechanisms employed. background of the design, and the actual mechanisms employed.
We started the discussion with a background tour to the IP routing We started the discussion with a background tour to the IP routing
architecture the definition of the mobility problem. After that we architecture the definition of the mobility problem. After that, we
covered the avenues of attack: the targets, the time shifting covered the avenues of attack: the targets, the time shifting
abilities, and the possible locations of an attacker. We outlined a abilities, and the possible locations of an attacker. We outlined a
number of identified threat scenarios, and discussed how they are number of identified threat scenarios, and discussed how they are
mitigated in the current design. Finally, in Section 4 we gave an mitigated in the current design. Finally, in Section 4 we gave an
overview of the actual mechanisms employed, and the rational behind overview of the actual mechanisms employed, and the rational behind
them. them.
As far as we know today, the only significant difference between the As far as we know today, the only significant difference between the
security of an IPv4 internet and that of an internet with Mobile IPv6 security of an IPv4 Internet and that of an Internet with Mobile IPv6
(and route optimization): time shifting attacks. Nevertheless, these (and route optimization) concerns time shifting attacks.
are severely restricted in the current design. Nevertheless, these are severely restricted in the current design.
We have also briefly covered some of the known subtleties and We have also briefly covered some of the known subtleties and
shortcomings, but that discussion cannot be exhaustive. It is quite shortcomings, but that discussion cannot be exhaustive. It is quite
probable that new subtle problems will be discovered with the design. probable that new subtle problems will be discovered with the design.
As a consequence, it is most likely that the design needs to be As a consequence, it is most likely that the design needs to be
revised in the light of experience and insights. revised in the light of experience and insight.
7. Acknowledgements 7. Acknowledgements
Hesham Soliman for reminding us about the threat explained in We are grateful for: Hesham Soliman for reminding us about the threat
Section 5.3. Francis Dupont for first discussing the case of two explained in Section 5.3, Francis Dupont for first discussing the
mobile nodes talking to each other (Section 5.4) and sundry other case of two mobile nodes talking to each other (Section 5.4) and for
comments. Pekka Savola for his help in Section 1.1.1. Elwyn Davies sundry other comments, Pekka Savola for his help in Section 1.1.1,
for his thorough editorial review. and Elwyn Davies for his thorough editorial review.
8. Informative References 8. Informative References
[1] Aura, T., Roe, M., and J. Arkko, "Security of Internet Location [1] Aura, T., Roe, M., and J. Arkko, "Security of Internet Location
Management", Proc. 18th Annual Computer Security Applications Management", Proc. 18th Annual Computer Security Applications
Conference, pages 78-87, Las Vegas, NV USA, IEEE Press., Conference, pages 78-87, Las Vegas, NV, USA, IEEE Press,
December 2002. December 2002.
[2] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery [2] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998. for IP Version 6 (IPv6)", RFC 2461, December 1998.
[3] Narten, T. and R. Draves, "Privacy Extensions for Stateless [3] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001. Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[4] Bush, R. and D. Meyer, "Some Internet Architectural Guidelines [4] Bush, R. and D. Meyer, "Some Internet Architectural Guidelines
and Philosophy", RFC 3439, December 2002. and Philosophy", RFC 3439, December 2002.
[5] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource [5] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Record (RR)", RFC 3445, December 2002.
[6] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004. Networks", BCP 84, RFC 3704, March 2004.
[7] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in [6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004. IPv6", RFC 3775, June 2004.
[8] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to [7] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
Protect Mobile IPv6 Signaling Between Mobile Nodes and Home Protect Mobile IPv6 Signaling Between Mobile Nodes and Home
Agents", RFC 3776, June 2004. Agents", RFC 3776, June 2004.
[9] Chiappa, J., "Will The Real "End-End Principle" Please Stand [8] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
Up?", date unknown. "DNS Security Introduction and Requirements", RFC 4033, March
2005.
[10] Savage, S., Cardwell, N., Wetherall, D., and T. Anderson, "TCP [9] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
Congestion Control with a Misbehaving Receiver", Computer "Resource Records for the DNS Security Extensions", RFC 4034,
Communication Review 29:5, 1999. March 2005.
[11] Nikander, P., "Denial-of-Service, Address Ownership, and [10] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
Early Authentication in the IPv6 World", Security Protocols 9th "Protocol Modifications for the DNS Security Extensions", RFC
International Workshop, Cambridge, UK, April 25-27 2001, 4035, March 2005.
LNCS 2467, pages 12-26, Springer, 2002.
[12] Chiappa, J., "Endpoints and Endpoint Names: A Proposed [11] Chiappa, J., "Will The Real 'End-End Principle' Please Stand
Enhancement to the Internet Architecture", date unknown. Up?", Private Communication, April 2002.
[13] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [12] Savage, S., Cardwell, N., Wetherall, D., and T. Anderson, "TCP
Congestion Control with a Misbehaving Receiver", ACM Computer
Communication Review, 29:5, October 1999.
[13] Nikander, P., "Denial-of-Service, Address Ownership, and Early
Authentication in the IPv6 World", Security Protocols 9th
International Workshop, Cambridge, UK, April 25-27 2001, LNCS
2467, pages 12-26, Springer, 2002.
[14] Chiappa, J., "Endpoints and Endpoint Names: A Proposed
Enhancement to the Internet Architecture", Private
Communication, 1999.
[15] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005. Neighbor Discovery (SEND)", RFC 3971, March 2005.
Authors' Addresses Authors' Addresses
Pekka Nikander Pekka Nikander
Ericsson Research Nomadic Lab Ericsson Research Nomadic Lab
JORVAS FIN-02420 JORVAS FIN-02420
FINLAND FINLAND
Phone: +358 9 299 1 Phone: +358 9 299 1
Email: pekka.nikander@nomadiclab.com EMail: pekka.nikander@nomadiclab.com
Jari Arkko Jari Arkko
Ericsson Research Nomadic Lab Ericsson Research Nomadic Lab
JORVAS FIN-02420
FINLAND
EMail: jari.arkko@ericsson.com
Tuomas Aura Tuomas Aura
Microsoft Research Microsoft Research Ltd.
Roger Needham Building
7 JJ Thomson Avenue
Cambridge CB3 0FB
United Kingdom
EMail: Tuomaura@microsoft.com
Gabriel Montenegro Gabriel Montenegro
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
USA USA
Email: gabriel_montenegro_2000@yahoo.com EMail: gabriel_montenegro_2000@yahoo.com
Erik Nordmark Erik Nordmark
Sun Microsystems Sun Microsystems
17 Network Circle
Menlo Park, CA 94025
USA
Intellectual Property Statement EMail: erik.nordmark@sun.com
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Internet Society. Internet Society.
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