Network Working Group C. Vogt
Internet-Draft Universitaet Karlsruhe (TH)
Expires: April 11, 2006 J. Arkko
Ericsson Research NomadicLab
October 8, 2005
A Taxonomy and Analysis of Enhancements to Mobile IPv6 Route
Optimization
draft-irtf-mobopts-ro-enhancements-03.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 11, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes and evaluates strategies to enhance Mobile
IPv6 route optimization, on the basis of existing proposals, in order
to motivate and guide further research in this context.
Vogt & Arkko Expires April 11, 2006 [Page 1]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 A Note on Public Key Infrastructures . . . . . . . . . . . 4
1.2 A Note on Source Address Filtering . . . . . . . . . . . . 5
2. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
3. Mobility-Related Security Threats . . . . . . . . . . . . . 7
4. Mobile IPv6 Route Optimization . . . . . . . . . . . . . . . 8
4.1 Protocol Overview . . . . . . . . . . . . . . . . . . . . 8
4.2 Analysis of Correspondent Registrations . . . . . . . . . 10
5. Objectives for Enhancement . . . . . . . . . . . . . . . . . 11
5.1 Latency Optimizations . . . . . . . . . . . . . . . . . . 11
5.2 Security Enhancements . . . . . . . . . . . . . . . . . . 12
5.3 Signaling Optimizations . . . . . . . . . . . . . . . . . 13
5.4 Robustness Enhancements . . . . . . . . . . . . . . . . . 13
5.5 Functionality Enhancements . . . . . . . . . . . . . . . . 14
6. Enhancements Toolbox . . . . . . . . . . . . . . . . . . . . 14
6.1 IP-Address Tests . . . . . . . . . . . . . . . . . . . . . 14
6.2 Protected Tunnels . . . . . . . . . . . . . . . . . . . . 15
6.3 Optimistic Behavior . . . . . . . . . . . . . . . . . . . 16
6.4 Proactive IP-Address Tests . . . . . . . . . . . . . . . . 16
6.5 Concurrent IP-Address Tests . . . . . . . . . . . . . . . 17
6.6 Diverted Routing . . . . . . . . . . . . . . . . . . . . . 19
6.7 Credit-Based Authorization . . . . . . . . . . . . . . . . 20
6.8 Heuristic Monitoring . . . . . . . . . . . . . . . . . . . 23
6.9 Crypto-Based Idendifiers . . . . . . . . . . . . . . . . . 23
6.10 Pre-Configuration . . . . . . . . . . . . . . . . . . . 25
6.11 Opportunistic Security Associations . . . . . . . . . . 27
6.12 Prefix-Based Certificates . . . . . . . . . . . . . . . 27
6.13 Mobile and Correspondent Routers . . . . . . . . . . . . 28
7. Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1 Categorization of Techniques . . . . . . . . . . . . . . . 29
7.2 Static Configuration . . . . . . . . . . . . . . . . . . . 30
7.3 CGA-Based Optimizations . . . . . . . . . . . . . . . . . 30
7.4 Credit-Based Improvements . . . . . . . . . . . . . . . . 30
7.5 New Approaches To Certificates . . . . . . . . . . . . . . 31
8. Future Research . . . . . . . . . . . . . . . . . . . . . . 31
8.1 Research at Other Protocol Layers . . . . . . . . . . . . 32
8.2 Further Route Optimization Research . . . . . . . . . . . 32
8.3 Experimentation and Simulation . . . . . . . . . . . . . . 33
9. Security Considerations . . . . . . . . . . . . . . . . . . 34
10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . 34
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . 43
Vogt & Arkko Expires April 11, 2006 [Page 2]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
1. Introduction
RFC 3775 [39] specifies mobility support for IPv6, or Mobile IPv6,
which allows mobile nodes to migrate active transport connections and
application sessions from one IPv6 address to another. For backward
compatibility with correspondent nodes that do not implement the
recommended mobility extensions, RFC 3775 introduces a "home agent",
which proxies a mobile node at a permanent "home address". A roaming
mobile node connects to the home agent through a bidirectional tunnel
and can so communicate, from its local "care-of address", as if it
was present at the home address. The mobile node keeps the home
agent updated on its current care-of address. Signaling messages are
protected through IPsec.
In order to reduce the increased packet-propagation delays of
bidirectional tunneling, RFC 3775 defines route optimization. This
enables nodes to communicate on the direct path provided that the
correspondent node can cache a binding between the mobile node's home
address and current care-of address. The challenge with route
optimization is that an administrative relationship between the
mobile node and the correspondent node can generally not be
presupposed. So how can the two authenticate and authorize the
signaling messages that they exchange?
Mobile IPv6 solves this problem by verifying a routing property of
the mobile node. Specifically, the mobile node is checked to be
reachable at its home address and current care-of address. This is
called the "return-routability procedure". It takes place right
before a mobile node registers a new care-of address with a
correspondent node and is periodically repeated in case the mobile
node does not move for a while.
The advantage of the return-routability procedure is that it is
lightweight and does not require pre-shared authentication material.
It also requires no state at the correspondent node. On the other
hand, the two reachability tests can lead to a handoff delay
unacceptable for many real-time or interactive applications like
voice over IP (VoIP) and video conferencing. Also, the security that
the return-routability procedure guarantees might not be sufficient
for security-sensitive applications. And finally, periodically
refreshing a registration at a correspondent node implies a hidden
signaling overhead that may prevent mobile nodes from hibernation
during times of inactivity.
Accordingly, a willingness to enhance Mobile IPv6 route optimization
can be observed. This document describes and evaluates different
route-optimization enhancement strategies on the basis of existing
proposals. It is meant to provide a conceptual framework for further
Vogt & Arkko Expires April 11, 2006 [Page 3]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
work, which was found to be inevitable in the context of route
optimization. Many scientists volunteered to review this document.
Their names are duely recorded in Section 2. Section 3 describes the
security threats that route-optimization protocols need to take into
account. Section 4 explains and analyzes how route optimization is
realized in RFC 3775, and Section 5 identifies potential objectives
for enhancement. Different enhancement strategies are discussed,
based on existing proposals, in Section 6. Section 7 analyzes the
different approaches, and Section 8 identifies opportunities for
further research. Section 9 and Section 10 conclude the document.
1.1 A Note on Public Key Infrastructures
Mobile IPv6 route optimization verifies a mobile node's authenticity
through a routing property. An alternative is cryptographic
authentication, which requires a binding between a node's identity
and some sort of secret information. While some proposals suggest to
install shared secrets into end nodes when possible (cf.
Section 6.10), pre-configuration is not an option for general
Internet use for scalability reasons. Authentication based on a
public-key infrastructure (PKI) does not require pair-wise pre-
configuration. Here, the secret information is the private component
of a public/private key pair, and the binding between a node's
identity and private key exists indirectly through the cryptographic
properties of public/private key pairs and a binding between the
identity and the public key. An authority trusted by both end nodes
issues a certificate which effects this latter binding.
Large-scale use of a PKI, however, was considered insuitable for
mobility management due to the following reasons.
o There are differing opinions on whether a PKI could scale up to
hundreds of millions of mobile nodes. Some people argue they do,
as there are already examples of certification authorities
responsible for millions of certificates. But more important than
the expected increase in the number of certificates would be a
shift in application patterns. Nowadays, public-key cryptography
is used only for those applications that require strong,
cryptographic authentication. If it was used for mobility
management as well, certificate checks would become mandatory for
any type of application, leading to more checks per user. Busy
servers with mobility support might not be reluctant to spent the
processing resources required for this depending on the service
they provide.
o Revoked certificates are identified on Certificate Revocation
Lists (CRLs), which correspondent nodes with mobility support
would have to acquire from certification authorities. CRLs must
Vogt & Arkko Expires April 11, 2006 [Page 4]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
be kept up to date, requiring periodic downloads. This and the
act of checking a certificate against a CRL create overhead which
some correspondent nodes might be unwilling to spend.
o Certificate verification may take some time and hence interrupt
ongoing applications. This can be disturbing from the user's
perspective, especially when route optimization starts in the
middle of a session, or the session is very short-term anyway.
o The bigger a PKI grows, the more attractive it becomes as an
attack target, endangering the Internet as a whole.
o There is little experience with using home addresses as
identifiers in the certificates. Although the home address could
theoretically be placed into a certificate's Alternate Name field,
the entities responsible for IP-address assignment and
certification are usually not the same, and it may not be easy to
coordinate the two.
For these reasons, this document does not consider direct
authentication of mobile nodes based on a PKI. Nevertheless, it does
evaluate certificate-based techniques which make the problems
identified above more tractable (cf. Section 6.12).
1.2 A Note on Source Address Filtering
RFC 3775 uses care-of-address tests to probe a mobile node's presence
at its claimed location. Alternatively, verification of care-of
addresses may be based on infrastructure in the mobile node's local
access network. For instance, the infrastructure can verify that the
IP source addresses of all packets leaving the network are correct.
"Ingress filtering" [49][47] provides this feature to the extent that
it inspects the prefix of IP source addresses and ensures topological
correctness. Network-access providers who use ingress filtering
normally deploy the technique in their first-hop and site-exit
routers. Similarly, ISPs may filter packets originating from a
downstream network.
Ingress filtering may eventually provide a way to replace care-of-
address tests. But there are still a number of uncertainties today:
o By definition, ingress filtering can prevent source-address
spoofing only from those networks that do deploy the technique.
As a consequence, ingress filtering needs to be widely, preferably
universally, deployed in order to constitute Internet-wide
protection. As long as an attacker can get network access without
filters, all Internet nodes remain vulnerable.
Vogt & Arkko Expires April 11, 2006 [Page 5]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
o There is little incentive for ISPs to deploy ingress filtering
other than conscientiousness. Legal or regulatory prescription as
well as financial motivation does not exist. A corrupt ISP might
even have a financial incentive to not deploy the technique, if
redirection-based DoS attacks using route optimization ever become
possible and are exploited for financial gain. A similar issue
was, e.g., observed with email spam.
o Ingress filtering is most effective, and easiest to configure, at
the first-hop router. However, since only prefixes are checked,
the filters inevitably get less precise the further upstream they
are enforced. This issue is inherent in the technique, so the
best solution is checking packets as close to the originating
nodes as possible, preferably in the first-hop routers themselves.
o A popular implementation of ingress filtering is "Reverse Path
Forwarding" (RPF). This technique relies on routes to be
symmetric, which is oftentimes the case between edge networks and
ISPs, but far less often between peering ISPs. Alternatives to
RPF are either manual configured access lists, or dynamic
approaches which are more relaxed, and thereby less secure, than
RPF [47].
o Another problem with ingress filtering is multi-homing. When a
router attempts to forward to one ISP a packet with a source-
address prefix from another ISP, filters at the second ISP would
block the packet. The IETF seeks to find a way around this [38].
For instance, one could tunnel the packet to the topologically
correct ISP, or one could allow source-address changes by means of
a locator-identifier split [23].
o Finally, RFC 3775 defines an Alternative Care-of Address option
that mobile nodes can use to carry a care-of address within a BU
outside of the IPv6 header. Such an address is not subject to
inspection by ingress filtering and would have to be verified
through other means [6].
Although these problems are expected to get solved eventually, there
is currently little knowledge on how applicable and deployable, as a
candidate for care-of-address verification, ingress filtering will
be. High investments or administrative hurdles could prevent a
large, preferably universal deployment of ingress filtering, which
would hinder Internet-wide protection, as mentioned in the first
bullet. For these reasons, this document does not consider ingress
filtering as a viable alternative to care-of-address tests, although
things may be different in the future.
Vogt & Arkko Expires April 11, 2006 [Page 6]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
2. Acknowledgements
This document was thoroughly reviewed, in alphabetical order, by
Samita Chakrabarti, Francis Dupont, Thierry Ernst, Gerardo Giaretta,
James Kempf, Rajeev Koodli, Gabriel Montenegro, Vidya Narayanan, and
Fan Zhao. The authors wish to thank these folks for their valuable
comments and suggestions.
3. Mobility-Related Security Threats
Route optimization allows a node to redirect those packets, that a
correspondent node would otherwise send to one IP address (the home
address), to a second IP address (the current care-of address). A
route optimization protocol must incorporate appropriate measures to
prevent misuse of this ability. There is a number of threats that
emanate from unprotected route optimization, all of which are
explained and analyzed in detail in [20]. Below is a high-level
categorization of mobility-related attacks, confined to the
information necessary to understand the remainder of this document.
Impersonation attacks
An attack in which the perpetrator claims to own a victim's home
address and binds this to a care-of address of its own choice.
This allows the attacker to impersonate the victim to the victim's
correspondent node without being on the path between those peers.
This is called "space-shifting". The attacker can also install
the illegitimate binding well before it eventually launches the
attack. This is accordingly known as "time-shifting". There are
different flavors of impersonation attack in the context of
mobility. The attacker can communicate on behalf of the victim
without involving the victim. The attacker can eavesdrop on
packets exchanged between the victim and its correspondent node
without interacting, or it can modify those packets and act as a
man in the middle. Finally, the attacker can simply divert the
victim's packets to an arbitrary, possibly non-existent IP address
so that attempts of the victim and its peer to reach each other
are without effect.
Resource-exhaustion attacks
An attack in which the perpetrator exploits memory or processing
resources at a victim which the mobility protocol requires the
victim to allocate. The victim could be a mobile node, a home
agent, or a stationary correspondent node implementing mobility
support. One example of a resource-exhaustion attack is a flood
of bogus Binding Update messages that the attacker sends to a
mobility-enabled, albeit stationary media server.
Vogt & Arkko Expires April 11, 2006 [Page 7]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Flooding attacks
An attack in which the perpetrator redirects its own packets to a
victim in order to clog the victim's network access. In contrast
to resource-exhaustion attacks, flooding attacks primarily target
network attachment rather than memory or processing resources.
Yet, the adverse effects on the ability to communicate can be very
similar in both attack types.
4. Mobile IPv6 Route Optimization
Mobile IPv6 route optimization requires the mobile node to bind its
current care-of address to its home address at both the home agent
and the correspondent node. This is called a "home registration" and
a "correspondent registration", respectively. The following is a
brief summary and analysis of the registration processes as a minimum
basis for deriving objectives for enhancement. Details on the Mobile
IPv6 protocol can be found in [39]; [20] provides a more elaborate
security analysis.
4.1 Protocol Overview
Figure 1 illustrates the home and correspondent registration. The
former is a two-way handshake between the mobile node, which sends a
Binding Update message with its home and current care-of address, and
the home agent, which responds with a Binding Acknowledgement
message. Home registrations are protected through IPsec, typically
using ESP authentication and encryption. Establishment of a IPsec
security associations requires external knowledge for mutual
authentication. This may be pre-configured into mobile nodes and
home agents as it is assumed that the nodes have an administrative
relationship.
Vogt & Arkko Expires April 11, 2006 [Page 8]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Mobile Correspondent
Node Home Agent Node
| | |
| | |
~~+~~ Handover | |
| | |
|--Binding Update---------->| |
| | |
| | |
|<-------------Binding Ack--| |
| | |
| | |
|--Home Test Init---------->|-------------------------->|
|--Care-of Test Init----------------------------------->|
| | |
| | |
|<--------------------------|<---------------Home Test--|
|<----------------------------------------Care-of Test--|
| |
| |
|--Binding Update-------------------------------------->|
| |
| |
|<-----------------------------------------Binding Ack--|
| |
Figure 1: Mobile IPv6 Registration Procedure
Pre-configuration is impossible for general Internet use, however, so
correspondent registrations must be protected differently. The key
observation is that, for the purpose of Mobile IPv6 route
optimization, authentication boils down to verifying that a mobile
node is reachable at its home address, by which transport protocols
and applications evenually identify the mobile node. Successful
authentication together with a proven reachability at the current
care-of address authorizes the mobile node to bind its home address
to that care-of address. This implies two address tests, the
"return-routability procedure", which the mobile node initiates with
the Home Test Init and Care-of Test Init messages. The correspondent
node responds by returning two tokens, one with the Home Test
message, another with the Care-of Test message. The Home Test Init
and Home Test messages are sent via the home address. An IPsec
tunnel between the mobile node and the home agent, based on the
existing security association, protects these messages part-way. The
Care-of Test Init and Care-of Test messages take the direct path and
are consequently unprotected. Finally, the mobile node derives a key
from both received tokens and and sends to the correspondent node a
Vogt & Arkko Expires April 11, 2006 [Page 9]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Binding Update message authenticated with that key. The
correspondent node returns a Binding Acknowledgement message.
According to Figure 1, the mobile node awaits a successful home
registration before it initiates the correspondent registration. In
contrast to such "conservative" behavior, a more "optimistic"
approach is to execute the home registration and the return-
routability procedure in parallel [56].
The correspondent node does not need to explicitly store the tokens
which it sends to the mobile node during the return-routability
procedure. Accillary information is communicated in the protocol so
that it can re-calculate the tokens. Correspondent registrations are
valid for up to seven minutes after which they must be refreshed.
There is no upper lifetime for home registrations.
4.2 Analysis of Correspondent Registrations
The two address tests increase the latency of correspondent
registrations. Even though the return-routability procedure may be
initiated in parallel with the home registration, it still takes
longer than the home registration, typically due to the home-address
test, and so has an undesired effect on applications. Conservative
behavior avoids a useless return-routability procedure in case the
home registration fails. This comes at the cost of an additional
round trip when the home registration is successful. Optimistic
behavior requires one round-trip time of signaling time less, but the
return-routability procedure will be in vain should the corresponding
home registration fail.
The return-routability procedure prevents impersonation attacks
unless the attacker is on the path between its victim and the
victim's correspondent node (in the case of a stationary victim) or
from the correspondent node to the victim's home agent (if the victim
is mobile). In case the attacker has access to the critical path, it
can spoof a Home Test Init message on behalf of the victim and
eavesdrop on the returning Home Test message. Then, the impersonator
can send the victim's peer a Care-of Test Init message with a care-of
address through which it is itself reachable. The attacker thus
learns the tokens necessary to generate an authenticated Binding
Update message on behalf of the victim. However, this vulnerability
to perpetrators on the routing path conforms with an objective to
prevent new attack types introduced by mobility support, but to
disregard threats that already exist in an Internet without mobility
support.
Similarly, the return-routability procedure does not protect against
redirection-based flooding attacks if the attacker is already on the
Vogt & Arkko Expires April 11, 2006 [Page 10]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
path between the victim and the correspondent node. Such an attacker
can launch a flooding attack already without the help of Mobile IPv6,
simply by establishing an upper-layer connection on behalf of the
victim. For instance, an on-path attacker can effect a large file
download from an FTP server, using its victim's IP address during the
initial TCP handshake.
Periodic correspondent registrations ensure that a mobile node
remains reachable at both its home and care-of addresses. This
prevents space- and time-shift attacks.
A correspondent node does not need to explicitly store any
information during the return-routability procedure. This saves the
correspondent node from attacks against memory resources, but may
lead to malicious exhaustion of its processing capacities. The
computational overhead necessary to re-calculate a token is rather
moderate, however. This allows the correspondent node to implement
its own resource-management policies for situations of increased
workload.
5. Objectives for Enhancement
This section identifies three goals for enhancement of RFC-3775 route
optimization: reduced signaling latency, higher security, lower
signaling overhead, increased protocol robustness, additional
functionality. The objectives are herein discussed from a
requirements perspective; the technical means to reach the objectives
is not considered, nor is the feasibility of achieving them.
5.1 Latency Optimizations
A disadvantage of route optimization is that a mobile node must run a
return-routability procedure before it can inform the correspondent
node about its new care-of address. Therefore, a correspondent
registration takes more time than a home registration. It consumes,
at a minimum, one and a half round-trip times until the correspondent
node receives the BU, assuming that the mobile node performs the
home-address and care-of-address tests in parallel. An additional
one-way time is needed until the first packet from the correspondent
node, and possibly an optional BA, arrives at the new care-of
address. Note that the CoTI, CoT, BU are transmitted on the direct
path between the mobile node and the correspondent node, whereas the
HoTI and HoT go through the home agent. The actual latency of the
return-routability procedure is governed by the path with a longer
round-trip time.
Note that the delay for the return-routability procedure is sometimes
estimated as 1.5 round-trip times. This includes an additional one-
Vogt & Arkko Expires April 11, 2006 [Page 11]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
way time to compensate for the longer delay of the HoTI/HoT exchange,
which goes through the home agent. However, this simple estimation
does not reflect situations in which the home agent is far away or
on-path. The analysis in this document therefore uses a single
round-trip time for the return-routability procedure and
differentiates between the two address tests where necessary.
Direct communications to the correspondent node can optimistically
start right after the BU has been sent (i.e., once the return-
routability procedure is complete). But if the mobile node requests
a BA, communications are usually delayed until the BA is received.
Similarly, optimistic mobile nodes are allowed by RFC 3775 to start
their return-routability procedure right after sending a Binding
Update message to their home agent. They can so reduce the latency
for the correspondent registration. But more generally, mobile nodes
wait for the home registration to be completed and acknowledged
before initiating the correspondent registration.
Depending on the type of application, the above delays can be an
issue. Interactive, real-time applications, like voice over IP, are
an example where the delays may cause perceptible quality
degradations. Even fast bulk-data transfer can be affected if the
lack of packets during the movement period is interpreted as
congestion and leads to a new TCP slow start. There appears to be
general consensus that faster mechanisms for route optimization are
needed.
Note that the handover delay from an application's perspective is not
just the latency of the IP mobility mechanism, but also includes
delays at the IP layer and the link layer. The delays introduced by
the rest of the stack can be significant (cf. Section 8.1).
5.2 Security Enhancements
The return-routability procedure is lightweight and prevents
mobility-related attacks reasonably well. The level of security it
provides is sometimes insufficient, however. One may in particular
attempt to limit what on-path attackers can do. Attackers that
operate in the same networks as one of the communication end points
are also a threat that one may want to avoid. There are existing
proposals that offer higher security in Mobile IPv6 [30] and in other
mobility-management protocols such as HIP [28].
However, even with better security for mobility management, the
Internet as a whole cannot become any safer than the non-mobile
Internet. For instance, on-path attackers can cause denial of
service, or inspect and modify cleartext packets, already without
Vogt & Arkko Expires April 11, 2006 [Page 12]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
misusing a mobility-management protocol. Applications that require
strong security are therefore generally advised to end-to-end
mechanisms such as IPsec or TLS. But even communications that are
protected on an end-to-end basis are vulnerable to denial of service.
Better route-optimization security may become necessary in the
future, if technological improvements remove some of the existing
mobility-unrelated vulnerabilities of the Internet. For instance,
the use of Secure Neighbor Discovery [24] in a network where one of
the communication end points resides can remove some of the existing
threats.
5.3 Signaling Optimizations
As mentioned in Section 4, correspondent registrations have a maximum
lifetime of seven minutes and must be refreshed in case they are not
updated to a different care-of address in the meantime. The reason
for this is to reasonably reduce the window of vulnerability to time-
and space-shift attacks, where an attacker eavesdrops on unencrypted
authentication material exchanged during the return-routability
procedure and launches an impersonation attack at a later time and
from a different, probably more amenable location. Periodic re-
registrations limit the likelihood and feasibility of such off-path
attacks, since the attacker would have to get back on path whenever
the authentication material is due to be refreshed.
A calculation in [2] shows that the seven-minute refreshment interval
implies a signaling overhead of 7.16 bits per second when a mobile
node communicates with a stationary node. The overhead doubles if
both peers are mobile. On one hand, this signaling overhead is
certainly negligible when the nodes actually communicate. On the
other hand, it may cause problems for mobile nodes that are inactive
and stay at the same location for a while, but still want to have
route optimization ready with some correspondent node. These nodes
typically prefer to go to standby mode to conserve battery power.
Finally, the periodic refreshments consume a fraction of the wireless
bandwidth that one could use more efficiently. This shows that an
optimization for reduced signaling would be benefical and could have
an impact on the deployment of Mobile IPv6.
5.4 Robustness Enhancements
Route optimization has the potential to allow the mobile node and
correspondent node to continue communication during a period of home-
agent unavailability. This could be due to failure of the home
agent, e.g. The protocol defined in RFC 3775 does not achieve this
independence from the home agent because correspondent registrations
involve the home agent and are limited in their lifetime (cf.
Vogt & Arkko Expires April 11, 2006 [Page 13]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Section 4).
5.5 Functionality Enhancements
As per RFC 3775, a mobile node's home address and current care-of
address are carried in all route-optimized packets. The course of
the mobile node is therefore trackable, both by the correspondent
node as well as by a third party. This can be an issue in situations
where the mobile node prefers not to reveal its location. Location
privacy, however, is inherently not supported by Mobile IPv6 route
optimization. A workaround is to fall back to bidirectional
tunneling when location privacy becomes an issue. Packets that carry
the mobile node's care-of address are then only transferred between
the mobile node and the home agent, and they can be encrypted through
IPsec ESP [36][14] on that path. However, the mobile node may have
to periodically re-establish its IPsec security associations so that
it cannot be tracked through its SPIs.
Scenarios where location privacy is desired are one example where
Mobile IPv6 proves insufficient. Early improvement efforts have
already started in this area [11][5][26][27]. There may also be
other deployment scenarios where the applicability of Mobile IPv6 is
limited and could be extended.
6. Enhancements Toolbox
This section introduces a number of techniques, a "toolbox", that can
be used in the construction of an efficient and secure route-
optimization protocol. The section starts with the standard
mechanisms used in RFC 3775 and continues with additional techniques
that have been proposed as enhancements or alternatives.
It is important to mention that many enhancement techniques are
insufficient or insecure when applied on their own, because the scope
of each of them is usually limited to a certain sub-issue. It is the
combination of a set of techniques that makes an efficient and secure
route-optimization mechanism possible. Different techniques also
have different trade-offs with respect to, say, universal
applicability versus efficiency.
6.1 IP-Address Tests
RFC 3775 uses IP-address tests to ensure that a mobile node is live
and on the path to a specific destination address: The home-address
test provides evidence that the mobile node owns the home address it
wants to use; the care-of-address test serves to preventing flooding
attacks related to spoofed care-of addresses. The use of two IP-
address tests requires four messages. Both tests can be performed in
Vogt & Arkko Expires April 11, 2006 [Page 14]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
parallel, so they can be completed in one round-trip time. As
specified in RFC 3775, IP-address tests can be stateless for the
correspondent node, making their use in denial-of-service attacks
harder.
A home-address test can most efficiently be initiated by the mobile
node itself, as the correspondent node can thus delay state creation
until the mobile node has authenticated. Yet, conceptually, either
the mobile node or the correspondent node could start a care-of-
address test. RFC 3775 uses mobile-node-initiated IP-address tests,
whereas [8] proposes a way to have the correspondent node send the
first message. [13] follows this latter approach as well. The
correspondent-node-driven approach has advantages when authentication
is done through other means than a home-address test. Since RFC 3775
does use the home-address test for authentication, letting the mobile
node initiate both IP-address test allows for more efficient
parallelization.
IP-address tests are a zero-configuration approach that is
independent of ancillary infrastructure. The subsequent disadvantage
is that IP-address tests can only guarantee that a peer is on the
path to the probed IP address, not that the peer truly owns this IP
address. On the other hand, the types of attacks that an on-path
attacker can do with route optimization are the same that an on-path
attacker can do without route optimization anyway, so there is
actually no significant new threat.
6.2 Protected Tunnels
RFC 3775 protects part of the signaling communications between a
mobile node and its home agent through an authorized and, optionally,
encrypted tunnel. This prevents other nodes on the path between the
mobile node and the home agent---potentially eavesdroppers in the
mobile node's wireless access network---from seeing a home-address
test.
Given the starting point that we cannot assume a pre-existing end-to-
end security relationship between the mobile node and the
correspondent node, this protection exists only for the mobile node's
side. In case the correspondent node is stationary, the path between
the home agent and the correspondent node remains unprotected. An
attacker on that path can still perform attacks, but these attacks
are similar to those that an on-path attacker can anyway do without
route optimization. So, as with IP-address tests, the intent here is
not to introduce any significant new threat to the Internet. The
same is true in case the correspondent node is mobile. It then has
its own home agent, and it is the path between the two home agents
that stays unprotected.
Vogt & Arkko Expires April 11, 2006 [Page 15]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
6.3 Optimistic Behavior
RFC 3775 leaves quite a bit of freedom for a mobile node with respect
to scheduling signaling and data packets. An optimistic mobile node
can initiate the return-routability procedure right after sending the
BU to its home agent, even before it has gotten a BA back.
The mobile node must wait for the home agent's BA before it can send
a BU to the correspondent node. However, the mobile node may start
sending data packets to the correspondent node right after it has
sent this BU without having to wait for a BA from the correspondent
node.
The drawback of the described optimistic behavior is that a dropped,
re-ordered, or rejected BU can cause data packets to be dropped.
Such packet loss would also have an effect on pessimistic signaling,
however. As a result, further experimentation and simulation may be
needed to quantify to the effects of optimistic techniques under
different conditions.
6.4 Proactive IP-Address Tests
Let the post-movement time period during which a mobile node and
correspondent node cannot fully communicate be the "critical phase".
The critical phase spans a home registration and a correspondent
registration including a return-routability procedure. One technique
to shorten the critical phase is to move some of these tasks to an
earlier stage. In particular, the home-address test can be done
proactively before a handover, instead of doing it afterwards,
without violating the base specification. This is discussed in [31].
A Home Keygen Token is generally valid for 3.5 minutes.
Consequently, the mobile node must initiate a proactive home-address
test at least every 3.5 minutes if it seeks to have available a fresh
Home Keygen Token at all times. This is especially helpful if the
mobile node cannot foresee the next handover. Alternatively, the
mobile node may be able to receive a trigger from its local link
layer indicating that a handover is imminent. In this case, the
mobile node may initiate the home-address test right in time instead
of doing it periodically every 3.5 minutes. Note, however, that the
mobile node must re-initiate the correspondent registration anyway--
and, thus, the home-address test--after the maximum binding lifetime
of seven minutes. Link-layer triggers can therefore save the mobile
node at most every second home-address test. The frequency of
proactive home-address tests could be reduced by additional
techniques such as [2].
Another optimization possibility is performing a care-of address test
Vogt & Arkko Expires April 11, 2006 [Page 16]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
before the movement. This is possible only if the mobile node is
capable of attaching to two networks simultaneously.
6.5 Concurrent IP-Address Tests
If one assumes that a mobile node can attach to only a single network
at a time, executing the care-of-address test proactively before a
handover is not an option. However, one may authorize a mobile node
to start using a new care-of address right after the handover,
without doing the care-of-address test first, with the restriction
that a care-of-address test be initiated rightaway. The peers could
then already exchange packets through the new care-of address while
the test is being executed. In recent literature, one refers to the
care-of address as "unverified" when the correspondent node does not
yet know the result of the concurrent care-of-address test, and one
calls it "verified" thereafter. The lifetime of the associated
binding can be limited to a few seconds as long as the care-of
address is unverified, and it can be extended once it becomes
verified.
It is important to understand that concurrency is legitimate only for
care-of-address tests. In contrast, home-address tests are done for
mobile-node authentication, which must be done before any signaling
messages are accepted. Authentication guarantees that only the
legitimate mobile node can create or update a binding pertaining to
its home address. However, both IP-address tests are in general
simultaneously performed during the critical handover period, and one
can expect the home-address test to have a longer latency than the
care-of-address test. The full benefit of eliminating the care-of-
address tests from the critical handover period by means of
concurrency can therefore only unfold if some other mechanism is used
to move the home-address tests out of the critical handover period as
well. For instance, one can do the home-address tests proactively
before a handover as suggested in Section 6.4, or one may use
cryptographically generated home addresses as proposed further down
in Section 6.9. Figure 2 illustrates concurrent care-of-address
tests as used in [31].
Vogt & Arkko Expires April 11, 2006 [Page 17]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Mobile Correspondent
Node Home Agent Node
| | |
| | |
|--Home Test Init (HoTI)--->|-------------------------->|
| | |
| | |
|<--------------------------|<---------Home Test (HoT)--|
| | |
| |
~~+~~ Handover |
| |
|--Early Binding Update (EBU)-------------------------->|
|<==========Resume Upper-Layer Communications==========>|
|--Care-of Test Init (CoTI)---------------------------->|
| |
| |
|<----------------------------Early Binding Ack (EBA)---|
|<---------------------------------Care-of Test (CoT)---|
| |
| |
|--Binding Update (BU)--------------------------------->|
| |
| |
|<------------------------------------Binding Ack (BA)--|
| |
Figure 2: Concurrent Care-of Address Tests
Concurrent care-of-address tests were first proposed in [31] where
they were combined with proactive home-address tests. In [31], as
soon as the mobile node has configured a new care-of address after a
handover, it sends to the correspondent node an Early Binding Update
(EBU) message. The mobile node signs the EBU with a message-
authentication code keyed only with the Home Keygen Token that the
mobile node has previously retrieved through a proactive home-address
test. Upon reception of the EBU, the correspondent node creates a
tentative binding for the new care-of address, which can then be used
while the care-of-address test is being executed. When the care-of-
address is done, the mobile node sends a standard BU to the
correspondent node, concluding the registration procedure.
From the reception of an EBU to the reception of the corresponding
standard BU, the correspondent node cannot be sure whether the mobile
node is actually present at the claimed new care-of address. A
malicious node may misuse this property to redirect packets to a
third party's IP address during this phase of uncertainty. Under
Vogt & Arkko Expires April 11, 2006 [Page 18]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
many circumstances, this will not be acceptable even if the lifetime
for an unverified care-of address is tentative only, and there needs
to be external protection. Techniques like those described in
Section 6.7 or Section 6.8 can help.
6.6 Diverted Routing
Given that the per-movement signaling takes some time, a mobile node
can optionally request its traffic to be routed through its home
address while this signaling is being completed. The performance
impact of this technique depends on the length of the critical phase
as well as on the capacity and latency of the direct path and the
path through the home agent. With respect to the packets that the
correspondent node sends, the following analysis can be made.
The correspondent node does not know that the mobile node has moved
until it has been told. It continues to send packets to the mobile
node's old care-of address until that time. These packets are
usually lost and must be retransmitted by upper-layer mechanisms. In
addition, even the request to delete or deactivate a binding requires
some security-related signaling to prevent misuse by unauthorized
nodes. Zero packet loss can generally only be achieved through local
repair techniques in the mobile node's access network, or if the
mobile node can simultaneously attach to two IP networks.
Once the correspondent node knows that the old care-of address is
stale, it can send further packets to the home address. If one
assumes that the correspondent registration for the new care-of
address involves messages through the home agent, it is obvious that
at least some of these packets reach the mobile node before the new
binding is set up. After all, signaling and data packets travel the
same path.
It depends on the capacity and latency of the path through the home
agent relative to the latency of the direct path for how long the
correspondent node should continue to send packets to the home
address. If the former path has a high latency, it might be better
to queue some of the packets until the correspondent registration is
complete and packets can be directly sent to the mobile node. One
potential research direction is to look at whether the properties of
the paths could be learned during the signaling and then used to
decide the optimal time when the correspondent node should start
queueing packets.
The situation for the packets that the mobile node sends is similar:
Although the mobile node knows immediately that it has moved, RFC
3775 does not allow the mobile node to route-optimize packets from
new care-of address until it has formally updated the correspondent
Vogt & Arkko Expires April 11, 2006 [Page 19]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
node about the new care-of address. Of course, the mobile node may
buffer packets until the correspondent registration is done so that
no packets get lost.
Diverted routing appeared originally in [31] and has since been used
also in [9].
6.7 Credit-Based Authorization
As described in Section 6.5, handover latency may be reduced by
already using a new care-of address while the care-of-address test is
in progress. The prerequesite is that sufficient protection is
provided against redirection-based third-party flooding. One way of
doing this is through Credit-Based Authorization. Credit-Based
Authorization for concurrent care-of-address tests prevents
illegitimate packet redirection until the validity of the address has
been established. This is accomplished based on the following three
hypotheses:
1. A flooding attacker typically seeks to somehow multiply the
packets it generates itself for the purpose of its attack because
bandwidth is an ample resource for many attractive victims.
2. An attacker can always cause unamplified flooding by sending
packets to its victim directly.
3. Consequently, the additional effort required to set up a
redirection-based flooding attack would pay off for the attacker
only if amplification could be obtained this way.
On this basis, rather than eliminating malicious packet redirection
in the first place, Credit-Based Authorization prevents any
amplification that can be reached through it. This is accomplished
by limiting the data a correspondent node can send to an unverified
care-of address of a mobile node by the data recently received from
that mobile node. (See Section 6.5 for a definition on when a
care-of address is verified and when it is unverified.) Redirection-
based flooding attacks thus become less attractive than, e.g., pure
direct flooding, where the attacker itself sends bogus packets to the
victim.
Figure 3 illustrates Credit-Based Authorization: The correspondent
node measures the bytes received from the mobile node. When the
mobile node changes to a new care-of address, the correspondent node
labels this address UNVERIFIED and sends packets there as long as the
sum of the packet sizes does not exceed the measured, received data
volume. The mobile node's reachability at the new care-of address
meanwhile gets verified. When the care-of-address test completes
with success, the correspondent node relabels the care-of address
from UNVERIFIED to VERIFIED. As of then, packets can be sent to the
Vogt & Arkko Expires April 11, 2006 [Page 20]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
new care-of address without restrictions. When insufficient credit
is left while the care-of address is still UNVERIFIED, the
correspondent node stops sending further packets until address
verification completes.
+-------------+ +--------------------+
| Mobile Node | | Correspondent Node |
+-------------+ +--------------------+
| |
address |----------------------->| credit += size(packet)
verified | |
|----------------------->| credit += size(packet)
|<-----------------------| don't change credit
| |
+ address change |
address |<-----------------------| credit -= size(packet)
unverified |----------------------->| credit += size(packet)
|<-----------------------| credit -= size(packet)
| |
|<-----------------------| credit -= size(packet)
| X credit < size(packet) ==> drop!
| |
+ address change |
address | |
verified |<-----------------------| don't change credit
| |
Figure 3: Credit-Based Authorization
The correspondent node ensures that the mobile node's acquired credit
gradually decrease over time. Such "credit aging" prevents a
malicious node from building up credit at a very slow speed and using
this, all at once, for a severe burst of redirected packets.
Allocating a mobile node's credit based on the packets that the
mobile node sends and reducing the credit based on packets that the
mobile node receives is defined as "CBA Inbound Mode". (The
correspondent node is in control of credit allocation, and it
computes the credit based on inbound packets received from the mobile
node.) A nice property of CBA Inbound Mode is that it does not
require support from the mobile node. The mobile node neither needs
to understand that CBA is effective at the correspondent node, nor
does it have to have an idea of how much credit it currently has.
With applications that send comparable data volumes into both
directions, CBA Inbound Mode works fine. On the other hand, in
Inbound Mode, CBA may prevent the mobile node from collecting the
Vogt & Arkko Expires April 11, 2006 [Page 21]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
amount of credit it needs for a handover when applications with
asymmetric traffic patterns are in use. For instance, file transfers
and media streaming are characterized by high throughput towards the
client, typically the mobile node, and comparably little throughput
towards the serving correspondent node. To better accommodate such
applications, "CBA Outbound Mode" was designed.
With CBA Outbound Mode, credit allocation is based on packets that
the mobile node receives from the correspondent node rather than on
packets that the mobile node sends. New credit is allocated while
the mobile node's current care-of address is verified; existing
credit is used up while the care-of address is unverified. Thus, it
is the data flow from the correspondent node to the mobile node that
is responsible for both credit allocation and reduction, resolving
the issue with applications producing asymmetric traffic patterns.
It is less obvious for CBA Outbound Mode why it outrules flooding-
attack amplification than it is for CBA Inbound Mode. The key
observation is that a mobile node invests comparable effort for
packet reception as for packet transmission in terms of bandwidth,
memory, and processing capacity. It is therefore legitimate to give
a mobile node credit for packets that it has received and processed.
The question is, though, how the correspondent node can determine how
many of the packets sent to a mobile node are actually received and
processed by that mobile node. Relying on transport-layer
acknowledgements is not an option as such messages can easily be
faked. CBA Outbound Mode hence defines its own feedback mechanism,
Care-of Address Spot Checks, which is robust to spoofing. With
Care-of Address Spot Checks, the correspondent node periodically tags
packets that it sends to the mobile node with a random, unguessable
number, a so-called Spot Check Token. When the mobile node receives
a packet with an attached Spot Check Token, it buffers the token
until it sends the next packet to the correspondent node. The Spot
Check Token is then included in this packet. Upon reception, the
correspondent node verifies whether the returned Spot Check Token
matches a token recently sent to the mobile node. New credit is
allocated in proportion to the ratio between the number of
successfully returned Spot Check Tokens and the total number of
tokens sent. This implies that new credit is approximately
proportional to the fraction of packets have made their way at least
up to the mobile node's IPv6 stack. The preciseness of Care-of
Address Spot Checks can be traded with overhead through the frequency
with which packets are tagged with Spot Check Tokens.
An interesting question is whether CBA Outbound Mode could be misused
by an attacker that has an asymmetric connection to the Internet.
Wide-spread digital subscriber lines (DSL), for instance, typically
have a much higher download rate than upload rate. The limited
Vogt & Arkko Expires April 11, 2006 [Page 22]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
upload rate would render most denial-of-service attempts through
direct flooding meaningless. But the strong download rate could be
misused to illegitimately build up credit at one or many
correspondent nodes. The credit could then be used for a more
potent, redirection-based flooding attack. The reason why this has
so far not been considered an issue is that, in order to build up
enough credit at the remote end, the attacker would first have to
expose itself to the same packet flood that it could then redirect
towards the victim.
6.8 Heuristic Monitoring
Heuristic approaches to protect concurrent care-of-address tests are
conceivable as well. For instance, one may consider a lifetime limit
for unverified care-of addresses which, supplemented by a heuristic
for misuse detection, can prevent, or at least effectually
discourage, misuse of such addresses. The challenge here seems to be
a feasible heuristic: On one hand, the heuristic must be sufficiently
rigid to catch any malicious intents at the other side. On the other
hand, it should not have a negative impact on a fair-minded mobile
node's communications.
Another problem with heuristics is that they are usually reactive.
The correspondent node can only respond to misbehavior after it
appeared. If the response comes quickly, attacks may simply not be
worthwhile. But premature actions should be avoided, of course. One
must also bear in mind that an attacker may be able to use different
home addresses, and it is in general impossible for the correspondent
node to see that the set of home addresses belongs to the same node.
The attacker may also use multiple correspondent nodes for its attack
in an attempt to amplify the result.
6.9 Crypto-Based Idendifiers
A crypto-based identifier (CBID) is an identifier with a strong
cryptographic binding to the public component of its owner's public/
private key pair [51]. CBIDs offer three main advantages: First,
spoofing attacks against a CBID are much harder than attacks against
a non-cryptographic identifier like a domain name or a Mobile IPv6
home address. Though an attacker may always create its own CBID, it
is unlikely to find a public/private key pair that produces someone
else's. Second, CBIDs fulfill exactly the purpose that certificates
do, so they do not depend on a certification infrastructure. Third,
CBID can be used to bind a public key to an IP address, in which case
they are called Cryptographically Generated Addresses (CGA) [52][53].
A CGA is syntactically just an ordinary IPv6 address. It has a
standard routing prefix and an interface identifier generated from a
Vogt & Arkko Expires April 11, 2006 [Page 23]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
hash on the CGA owner's public key and some additional parameters. A
CGA allows the owner to assert a claim on its address: It can sign a
to-be-authenticated message with its private key and attach its
public key along with the parameters necessary to recompute the CGA.
The recipient of this message can then verify whether the address is
correct.
Many applications are conceivable where CGAs can be advantageous. In
Mobile IPv6, CGAs can bind a mobile node's home or care-of address to
its public key. CGAs were originally described in [52] and in [53],
and they have later been used in [30], [42], [9], and others. It
should be mentioned that, although CGAs are a replacement for the
home-address test in most cases, at least one initial home-address
test must be made. This ensures that the network prefix of the home
address is correct, and that the mobile node is really reachable at
this address. Being able to omit the home-address test in subsequent
correspondent registrations allows the peers to communicate
independently of home-agent availability.
Since only the interface identifier of a CGA is cryptographically
generated, flooding a network or a link is still an issue. As a
result, CGAs should be employed together with a care-of-address test
in scenarios where redirection-based flooding attacks are a concern.
An initial home-address test is typically required, too, in order to
avoid that the deletion of a binding causes a flood upon a faked home
address.
One limitation of CGAs compared to other types of CBIDs is that the
hash on the CGA owner's public key can only be 62 bits long. The
rest of the address is occupied by a 64-bit routing prefix as well as
the universal/local and individual/group bits. A brute-force
attacker might thus be able to find a public/private key pair that
produces a certain CGA. It could then claim ownership over this CGA.
The threat can usually be contained by including the address prefix
in the hash computation, so that an attacker, in case it did find the
right public/private key pair, could not form CGAs for multiple
networks from it.
To resolve collisions in case CGAs are used as care-of addresses, a
collision count is part of the input to the CGA hash function.
Increasing the collision count by one changes the result of the hash
function, so new CGAs can be successively tried until an unused one
is found. On the other hand, the collision count also helps an
attacker in faking a CGA: It may use the same private/public-key pair
to efficiently generate multiple CGAs. For this reason, the
collision count is usually limited to a few bytes only.
Higher security can be achieved through longer CBIDs. For instance,
Vogt & Arkko Expires April 11, 2006 [Page 24]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
a node's primary identifier in the "Host Identity Protocol" (HIP)
[28] is a 128-bit hash on the node's public key. It is used as an
IP-address replacement at stack layers above IP. This CBID is not
routable, so there needs to be some external location mechanism if a
node wants to contact a peer of which it only knows the identifier.
6.10 Pre-Configuration
The return-routability procedure was designed for communication peers
that do not share an a-priori security association. In order to
thwart off-path attacks nonetheless, the procedure can establish only
very short-living security associations. However, in certain,
restricted scenarios, it may be possible to pre-configure mobile and
correspondent nodes with security associations. Such security
associations can have much longer lifetimes because pre-configuration
is inherently more secure than the plaintext token exchange from the
return-routability procedure.
Pre-configuration has two major benefits. The first one is strong,
cryptographic authentication and encryption, which can be applied to
both signaling and data packets. The second advantage is lower
signaling delay, because the additional round-trip time otherwise
needed for the return-routability procedure can be spared. The
obvious disadvantage of pre-configuration is its limited
applicability.
It is important to recognize the necessity to unambiguously bind a
security association to the home address that it is to protect. With
regards to the return-routability procedure, this binding is realized
by routing the HoTI and HoT through the home address. In the case of
a pre-configured security association, the association must be
related to the home address as part of the configuration. Note that
this affects both secret-key and public-key cryptography.
Two proposals for pre-configuration are currently under discussion in
the IETF as optional enhancements to RFC 3775. [19] re-uses most from
the standard authentication and authorization procedure defined in
RFC 3775. The only difference is that mobile nodes are endowed with
the information they need to compute Home and Care-of Keygen Tokens
themselves rather than having to obtain them through the return-
routability procedure. [7] replaces the standard RFC-3775 concepts
with IPsec and the Internet Key Exchange (IKE) protocol.
From a technical standpoint, a pre-configured security association
can only replace a home-address test, not a care-of-address test.
After all, a correspondent node cannot verify, based on the
association alone, whether a mobile node is actually present at the
announced care-of address. The problem is circumvented in [19] by
Vogt & Arkko Expires April 11, 2006 [Page 25]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
postulating that the correspondent node has sufficient trust in the
mobile node to believe that the care-of address is correct. However,
this assumption discourages the use of pre-configuration in scenarios
where such trust is unavailable. For instance, a mobile-phone
operator may be able to configure subscribers with secret keys for
authorization to a particular service, but it may not be able to
vouch that all subscribers use this service in a trustworthy manner.
And even if peers initially trust each other, subsequently one or the
other can be infected with malware and become untrustworthy.
Another way to avoid the problem of care-of-address verification is
to rely on access networks to filter out packets with incorrect IP
source addresses (cf. Section 1.2). This approach is taken in [7].
However, the problem with local filtering is that it must be deployed
everywhere an attacker may possibly access the Internet in order to
be fully protective. Otherwise, an attacker can always find a place
from where a spoofing attack is possible, endangering IP nodes
anywhere. As things stand, the assumption that deployment of
filtering techniques be universal is speculative.
Both of the above two assumptions can be eliminated through care-of-
address tests, facilitating the use of pre-configuration in spite of
lacking trust relationships or the existence of access networks
without local filtering techniques. Of course, using a care-of-
address test partly vitiates the handover-latency improvement that
can be reached otherwise. But there may still be a positive impact
on handover latency, because pre-configuration eliminates the
triangular home-address test through the home agent, whereas the
care-of-address test uses the direct, and typically faster, path
between the communicating nodes. For increased performance, a
concurrent care-of-address test can be used in combination with
credit-based authorization or heuristic monitoring. It should also
be noted that pre-configuration facilitates stronger authentication
mechanisms than the return-routability procedure, and thus the use of
route optimization may become more suitable for applications with
high security requirements.
That said, it seems like a good idea to make the pre-configuration
protocol customizable to different environments. Is there a small
group of people who trust each other? Then group members are
unlikely to spoof care-of addresses, and the care-of-address test
might be omitted. Or is the group of users large and users are
primarily unknown to each other like the customer base of a big ISP?
Then, proper authentication does usually not imply trust, and it is
infeasible to use pre-configured keys without checking a mobile
node's reachability. Traceability techniques are not necessarily a
compensation for the missing care-of-address test, because they are a
reactive measure, whereas a care-of-address test is a proactive one.
Vogt & Arkko Expires April 11, 2006 [Page 26]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
6.11 Opportunistic Security Associations
An intermediate approach between short-term security associations
from the return-routability procedure on one hand, and static
security associations available via pre-configuration on the other,
is to set up an "opportunistic", medium-term security association
upon first contact. Subsequent signaling can then be unambiguously
bound to the initial contact. Such security associations can be used
over a longer period of time than those afforded by the return-
routability procedure.
On-demand security associations for IPsec are traditionally
established by executing IKE between two peers. This works well when
the negotiated keys are securely bound to the entity that they are to
protect. However, the to-be-protected entity in Mobile IPv6 is a
plain IPv6 home address, which is syntactically indistinguishable
from other IPv6 addresses. Given that no direct authentication
between the peers is generally feasible, there is no way for a mobile
node to prove possession of its home address either. This would
allow an attacker to do the IKE exchange pretending to own an
arbitrary victim's IP address, and to at will redirect the victim's
traffic from that time on. Although the attacker would have to be on
the path between the victim and the correspondent node while running
IKE, it could move off the path once the keys have been exchanged.
As the victim lacks the keys, it cannot even re-claim its IP address.
As a result, opportunistic security associations must be bound to the
right home addresses through some additional technique when used in
the context of Mobile IPv6. For instance, they can be combined with
an initial, one-time home-address test, or IKE can be run through the
home address. Another way is using CGAs as proposed in [9].
No matter how they are secured, opportunistic security associations
cannot be leveraged to prove the correctness of a care-of address.
They hence fail to solve the problem with redirection-based flooding
attacks, and should only be applied in conjunction with care-of-
address tests. Semi-permanent security associations were first
developed in [4] where they were called "Purpose Built Keys" (PBK).
6.12 Prefix-Based Certificates
The Mobile IPv6 base specification avoids strong authentication
cryptography for signaling between mobile nodes and correspondent
nodes. One reason for this is that PKI for general Internet use has
generally been considered impossible to set up. This is primarily
due to the current separation of IP-address assignment and security
infrastructures. Another reason is that limited power resources and
processing capacity at the mobile nodes generally rule out any
Vogt & Arkko Expires April 11, 2006 [Page 27]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
complex cryptographic operations. Robustness to resource-exhaustion
attacks requires a similar restrictiveness on the correspondent-node
side.
However, Certificate-based Binding Updates (CBU) [29] are a useful
simplification: A home agent is assigned a certificate that binds
the home-network prefix to the home agent's public key.
Correspondent nodes can trust the home agent based on the
certificate, and the home agent vouches for the trustworthiness of
the mobile nodes it serves. The advantage is that, rather than
having to issue a certificate per mobile node, only a certificate per
home-network prefix is required. This makes the infrastructure
problem more tractable.
The reduction in the number of potentially required certificates
makes certificate-based approaches to mobile-node authentication more
feasible than it is today. The approach also avoids heavy
computations at mobile nodes since public-key cryptography is handled
by the home agent. On the other hand, the processing overhead at
correspondent nodes actually increases compared to standard
correspondent registrations. This may not be an issue since
resources at stationary correspondent nodes are usually higher than
those of many mobile devices. But it may be an issue if the
correspondent node is a popular web server or other central resource
that cannot afford doing complex cryptographic operations. One
should, however, bear in mind that the increased overhand implies a
higher risk to resource-exhaustion attacks.
CBU does not solve the issue with care-of-address spoofing: A
vouching home agent does not prevent a malicious mobile node from
faking its care-of address. The culprit could cheat its home agent,
or it could cooperate with it. This said, CBU should be combined
with a care-of-address test that rules out redirection-based flooding
attacks. A combination of concurrent care-of-address tests and CBA
(cf. Section 6.7) can be used to keep the signaling delay during
handover as low as it currently is in [29].
6.13 Mobile and Correspondent Routers
A special scenario where mobility optimizations are useful is one
where an entire network moves. Mobile nodes within a moving network
stick together and connect to the Internet through a single "mobile
router". It is relatively straightforward to support network
mobility [41] by using a single home agent and a single tunnel
between the mobile router and that home agent. Mobile nodes then
don't have to be mobility-aware. On the other hand, supporting route
optimization for moving networks [34][35][3][33] is more complicated.
One way of doing this is to have the mobile router handle route
Vogt & Arkko Expires April 11, 2006 [Page 28]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
optimization on behalf of the mobile nodes. This requires the mobile
router to modify incoming and outgoing packets such that they can be
routed on the direct path between the end nodes. The mobile router
would also have to perform Mobile IPv6 signaling on behalf of the
mobile nodes.
A similar optimization applies to a network of correspondent nodes.
Those could communicate with mobile nodes, through a "correspondent
router", in a route-optimized way without themselves being mobility-
aware. While RFC 3775 route optimization requires all correspondent
nodes to be modified, this can be avoided if mobility is managed by a
router in the correspondent nodes' network. Note that neither a
mobile router nor a correspondent router needs to be the first-hop
router. It may also be located further down the path between the
communicating end nodes.
7. Analysis
This section analyzes the techniques presented in Section 6 in
relation to each other and in the context of the enhancement
objectives described in Section 5. The techniques are categorized
first. Some recent proposals for route-optimization enhancement,
which rely on one or combine multiple of these techniques, are
subsequently evaluated. The section concludes with a number of
opportunities for further research in the area of route optimization.
7.1 Categorization of Techniques
The techniques presented in Section 6 can be charactized in three
respects: (a) their benefit, in terms of reduced latency, increased
security, or lower signaling overhead; (b) their costs, in terms of
hardware upgrades, software modifications, and manual configuration;
and (c) their applicability to different scenarios and ease of
deployability. Certainly, the objective for route-optimization
improvement is to gain significant improvement in many scenarios at
low costs.
But it seems that trade-offs are oftentimes necessary. For instance,
IP-address tests don't require any upgrades to the network
infrastructure and work well for peers who do not know each other.
At the other end, pre-configuration has high benefits in terms of
reduced signaling latency and overhead as well as increased security.
But these advantages apply to acquainted nodes only. The following
sections elaborate on this categorization considering a subset of the
techniques described in Section 6.
Vogt & Arkko Expires April 11, 2006 [Page 29]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
7.2 Static Configuration
The Home Keygen Token exchange from the return-routability procedure
is the default authentication technique used in Mobile IPv6. It
facilitates reasonable security even between nodes that have no pre-
existing relationship. On the other hand, nodes that do share a
common secret should be allowed to omit the home-address test if the
secret is tied to the home address in use. This can be beneficial in
certain scenarios where the home-address test causes a long handover
latency due to packet redirection through the home agent.
Note that a pre-configured shared secret alone cannot replace the
care-of-address test. Eliminating the care-of-address test requires
additional mechanisms for address authorization and/or a means for
identification of the responsible node in case of misbehavior. It is
evident that pre-configuration is most effective when both the home-
and the care-of-address test can be eliminated.
Alternatively, one could retain the care-of-address test, but avoid
its latency by doing it in a concurrent way (cf. Section 6.5). This
is a good example of how multiple improvement proposals can be
combined into a single, more applicable optimization.
7.3 CGA-Based Optimizations
CGAs can guarantee that a mobile node is the legitimate owner of its
home address. They provide higher assurance than the pure use of
routing paths. This facilitates a significant reduction in the
number of signaling messages per correspondent registration as well
as the periodicity of these registrations. In addition, the public
keys used in the CGA technique allow packets to be transferred
privately, a feature that can be used for both data encryption and
for other route-optimization enhancements.
CGAs use complexer algorithms compared to pre-configuration
techniques, but don't require peers to be acquainted. This greatly
increased applicability and deployability. As with pre-
configuration, CGA-based optimizations still depend on a care-of-
address test, but may do it in a concurrent way to reduce latency.
7.4 Credit-Based Improvements
CBA allows peers to use a new care-of address early after a handover
and to verify the address in parallel with already using it. This
eliminates the handover latency that the reachability check entails
when performed during the critical handover period.
Too rapid movements may lessen the improvement CBA can yield, as the
Vogt & Arkko Expires April 11, 2006 [Page 30]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
average time a mobile node's care-of address is verified should be at
least as long as it is unverified. CBA Inbound Mode may also be
problematic when the mobile node sends too little data to acquire
sufficient credit. But a simple analysis shows that a TCP download
where a mobile node sends acknowledgements only (one every two
segments) works fine with CBA given handover frequencies do not
exceed one every 15 seconds. This gives the peers 500 milliseconds
for accomplishing the concurrent care-of-address test.
CBA can be integrated into any mobility protocol that verifies IP
addresses through probing. Protocols that may benefit are, for
instance, other Mobile IPv6 optimization techniques described in this
paper such those based on CGAs or pre-configuration. Moreover, in
scenarios where a home agent cannot trust in the correctness of the
registered mobile nodes' care-of addresses, CBA-based concurrent
care-of-address tests could be proscribed for home registrations.
The same is true for Hierarchical Mobile IPv6, which, as it stands,
assumes that a MAP can be confident that mobile nodes use correct on-
link care-of addresses, and so gets around the care-of-address test.
Finally, CBA can be used to relax requirements for periodic re-
authorization as proposed in [2].
7.5 New Approaches To Certificates
CBU effect a compromise between the strong authentication facilitated
through certificates on one side and applicability and ease of
deployability on the other side. This is achieved through "trust
indirection": The CN may trust a certain operator's home agent, who
in turn is supposed to enforce correct behavior of its mobile nodes.
There is ongoing work on the integration of AAA with Mobile IPv6
[17]. The current focus is on authentication between mobile nodes
and home agents with the intention to replace the IPsec-based
authentication protocol for home registrations. But the concept of
security proxies proposed in [29] may as well be re-used for
enhancements to the AAA infrastructure.
8. Future Research
Mobility-related optimizations are currently actively studied by many
researchers at different protocol layers. The preceding sections
identify ideas and existing proposals for enhancing route
optimization. While some of the basic methods are fairly well
understood and are being deployed, there are a number of interesting,
newer approaches that deserve to be studied in more detail. This
section discusses research directions that appear fruitful, or
necessary in the future, and that go beyond the existing proposals
Vogt & Arkko Expires April 11, 2006 [Page 31]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
described so far.
8.1 Research at Other Protocol Layers
The efficiency and security related to movements does not depend on
Mobile IPv6 route optimization alone, even if researchers often pose
their analysis in that light. A movement that is visible at the IP
layer involves all lower layers as well. This includes layer 2
attachment procedures; layer 2 security mechanisms such as
negotiation, authentication, and key agreement; IPv6 Router and
Neighbor Discovery; as well as IPv6 Address Autoconfiguration and
Duplicate Address Detection. A complete network attachment typically
requires over twenty link- and IP-layer messages, assuming that
features necessary for a commercial deployment (such as security) are
turned on.
A significant research question is the performance of the network-
access stack as a whole. Current protocol stacks have a number of
limitations in addition to the long attachment delays [44], such as
denial-of-service vulnerabilities, difficulties in trusting a set of
access nodes distributed to physically insecure locations, or the
inability to retrieve sufficient information for making a handoff
decision.
A number attempts are ongoing to improve various parts of the stack,
mostly focusing on handover performance. These include link-layer
enhancements, parameter tuning [55], network-access authentication
mechanisms [1], fast-handover mechanisms [50], AAA architectures
[25], and IP-layer attachment improvements [16]. It is uncertain how
far this optimization can be taken by only looking at the different
parts individually. An integrated approach may be necessary to gain
more significant improvements [45].
It is also unclear at this time which components are the most
critical ones. [44] suggests that mobility-related signaling
contributes only under 10% of the overall delay in an IEEE 802.11
environment. The most significant delays are caused at the link
layer and for IPv6 attachment. However, the results are not
conclusive due to the high deviation between the measurements. The
results can also be affected by a number of conditions, such as the
availability of specific link-layer optimizations, or the type of
security mechanism used for Mobile IPv6 home registrations.
8.2 Further Route Optimization Research
The primary driver to improve route optimization appears to be better
efficiency for a few usage scenarios, such as fast movements or the
ability to reduce signaling frequencies for hosts in standby mode.
Vogt & Arkko Expires April 11, 2006 [Page 32]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Ongoing work addresses these aspects already quite well, and many of
the suggested methods are reasonably stable in this regard. It is
expected that further, perhaps smaller improvements will continue to
be achieved through research and parameter tuning far into the
future.
Research on infrastructure-based route optimization like [43] is
clearly a longer-term project. Mobile and correspondent routers can
be advantageous in large networks of mobile or correspondent nodes,
respectively, especially if the end nodes don't support route
optimization themselves. It would also be interesting to investigate
into how mobile and correspondent routers can be integrated with
infrastructure-based security solutions, such as [48]. Also, the
ideas of the Certificate-Based Binding Update Protocol could be
useful in this light.
The following is a list of interesting ideas for new route-
optimization research.
o Local mobility or local repair optimizations that require no
configuration.
o Care-of-address verification mechanisms that employ lower-layer
assistance or Secure Neighbor Discovery.
o The introduction of optimizations developed in the context of
Mobile IPv6 to HIP or other mobility protocols, or to link-layer
mobility solutions.
o The extension of the developed techniques to full multi-
addressing, including also multi-homing.
o Further development of techniques that are based on "asymmetric
cost wars" [46], such as CBA.
o Integrated techniques taking into account both link and IP layer
mobility tasks.
8.3 Experimentation and Simulation
As discussed earlier, the contribution of different stack parts to
the overall movement latency is still unclear. The following is a
list of areas where measurements and experimentation can yield
further, valuable insight.
Vogt & Arkko Expires April 11, 2006 [Page 33]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
o Measurements of a realistic network scenario, enabling all
features that would likely be needed in a commercial deployment.
These features include link-layer access control, for instance.
Similarly, it is necessary to consider support for existing
enhancement proposals.
o Measurements and simulations of the performance impacts that
existing enhancement proposals have on the different parts of the
stack.
o Measurements and comparisons of different implementations that are
based on the same specification. For instance, it would be
valuable to know how much implementations differ with regards to
the use of parallelism that RFC 3775 allows in home and
correspondent registrations, or with respect to early packet
transmission before reception of a BA.
o Measurements of the impact that network conditions such as packet
loss can have on existing and new route-optimization mechanisms.
o Statistical data collection on the behavior of mobile nodes in
different networks. Route-optimization techniques behave
differently depending on what the frequency of movements is, or
what traffic streams appear during a mobile node's lifetime.
o Measurements or simulations of the performance that existing
route-optimization schemes show under different application
scenarios, such as the use of applications with symmetric vs.
asymmetric traffic patterns.
9. Security Considerations
Security issues related to route optimization are an integral part of
this paper and are as such discussed throughout the paper.
10. Conclusions
Mobility-related optimizations are currently actively studied by many
researchers. Some of the basic techniques--such as the return-
routability procedure, pre-configured keys, or CGAs--are either
already being deployed or can expected to be in the near future. A
growing number of new proposals are being studied that attempt to
optimize these basic techniques further, or to make them better
applicable to a particular scenario.
Many of the current proposals are mature enough to withstand close
scrutiny. Their relative advantages are rather subjective, however.
For instance, some proposals are very efficient, but have a high cost
Vogt & Arkko Expires April 11, 2006 [Page 34]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
in terms of configuration, whereas others do not require
configuration, but are slower. It hence appears likely that more
than one new method will have to be standardized. Deployment
experience is also important, so publication of a few alternative
methods as RFCs would be desirable.
It is interesting to see that most if not all current proposals had
predecessors that were shown to be insecure. For instance, the
initial return-routability procedure as well as the first versions of
CGAs were published before the threat of flooding attacks was fully
understood. Concurrent care-of-address tests were also first
suggested with insufficient protection against flooding attacks. And
several proposals employing semi-permanent security associations have
initially suffered from impersonation attacks. This shows the need
to reserve a sufficient amount of time for community analysis and
review of new methods.
Another interesting observation is that most mature proposals combine
a number of techniques and do not rely on any single approach. This
is due to the intricate nature of the problem: to build a mechanism
that is efficient and at the same time avoids a quite significant
number of potential security vulnerabilities.
On the other hand, it is also necessary to avoid overly expensive or
complex solutions. For instance, in evaluating the security needs
for route optimization, it is important to compare these needs to
other vulnerabilities, e.g., denial-of-service attacks, that already
exist for on-path attackers in an Internet without mobility support.
Of course, a mobility-management protocol should not make these
vulnerabilities worse. But since the issues already exist, it is not
necessarily a requirement that they be solved by a mobility-
management protocol.
There is a natural performance limit of route optimization due to
end-to-end signaling. Future applications may have latency
requirements that route optimization cannot satisfy. This is where
local optimizations such as FMIPv6 and HMIPv6 become necessary.
While HMIPv6 still benefits from enhancements to route optimization,
FMIPv6 allows peers to postpone global signaling and parallelize it
with upper-layer communications. This is an exemplar for the trade-
off between good performance and high investment costs.
A significant research question is the overall performance of the
network stack in a mobile setting. This includes mobility management
at the IP layer, but is not limited to it. Current network-access
protocol stacks have a number of limitations, such as long attachment
and movement latencies or significant denial-of-service
vulnerabilities. It is uncertain whether further, significant
Vogt & Arkko Expires April 11, 2006 [Page 35]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
benefits can be achieved if one continues to look at the different
parts of the network stack individually. Most likely, a more
comprehensive approach is needed. It is also unclear at this time
which components of the network stack are the most critical ones to
optimize.
Other significant research questions include what effect network
conditions such as packet loss can have on current proposals, and to
what degree proposals depend on specific application patterns. Our
current understanding about the different traffic patterns and their
effects on mobility is limited, and experiments, modelling, and
simulations will be needed. Finally, an interesting piece of
research would be to measure the performance of route optimization
relative to bidirectional tunneling from a user's perspective.
Vogt & Arkko Expires April 11, 2006 [Page 36]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
11. References
[1] Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access Control",
IEEE Standard 802.1X, September 2001.
[2] Arkko, J. and C. Vogt, "Credit-Based Authorization for Binding
Lifetime Extension",
draft-arkko-mipv6-binding-lifetime-extension-00 (work in
progress), May 2004.
[3] Bernardos, C., "Mobile IPv6 Route Optimisation for Network
Mobility (MIRON)", draft-bernardos-nemo-miron-00 (work in
progress), July 2005.
[4] Bradner, S., Mankin, A., and J. Schiller, "A Framework for
Purpose-Built Keys (PBK)", draft-bradner-pbk-frame-06 (work in
progress), June 2003.
[5] Daley, G., "Location Privacy and Mobile IPv6",
draft-daley-mip6-locpriv-00 (work in progress), January 2004.
[6] Dupont, F., "A note about 3rd party bombing in Mobile IPv6",
draft-dupont-mipv6-3bombing-01 (work in progress),
January 2005.
[7] Dupont, F. and J. Combes, "Using IPsec between Mobile and
Correspondent IPv6 Nodes", draft-dupont-mipv6-cn-ipsec-01 (work
in progress), June 2004.
[8] Dupont, F. and J. Combes, "Care-of Address Test for MIPv6 using
a State Cookie", draft-dupont-mipv6-rrcookie-00 (work in
progress), January 2005.
[9] Haddad, W., Madour, L., Arkko, J., and F. Dupont, "Applying
Cryptographically Generated Addresses to Optimize MIPv6 (CGA-
OMIPv6)", draft-haddad-mip6-cga-omipv6-02 (work in progress),
June 2004.
[10] Haddad, W. and S. Krishnan, "Optimizing Mobile IPv6 (OMIPv6)",
draft-haddad-mipv6-omipv6-01 (work in progress), February 2004.
[11] Haddad, W., "Privacy for Mobile and Multi-homed Nodes: MoMiPriv
Problem Statement", draft-haddad-momipriv-problem-statement-00
(work in progress), October 2004.
[12] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-00
(work in progress), June 2004.
Vogt & Arkko Expires April 11, 2006 [Page 37]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
[13] Nikander, P., "End-Host Mobility and Multi-Homing with Host
Identity Protocol", draft-ietf-hip-mm-01 (work in progress),
February 2005.
[14] Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-08 (work in progress), March 2004.
[15] Loughney, J., "IPv6 Node Requirements",
draft-ietf-ipv6-node-requirements-11 (work in progress),
August 2004.
[16] Moore, N., "Optimistic Duplicate Address Detection for IPv6",
draft-ietf-ipv6-optimistic-dad-01 (work in progress),
June 2004.
[17] Patel, A., Leung, K., Khalil, M., Akhtar, H., and K. Chowdhury,
"Authentication Protocol for Mobile IPv6",
draft-ietf-mip6-auth-protocol-00 (work in progress), July 2004.
[18] Patel, A., "Problem Statement for bootstrapping Mobile IPv6",
draft-ietf-mip6-bootstrap-ps-00 (work in progress), July 2004.
[19] Perkins, C., "Preconfigured Binding Management Keys for Mobile
IPv6", draft-ietf-mip6-precfgKbm-00 (work in progress),
April 2004.
[20] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E.
Nordmark, "Mobile IP version 6 Route Optimization Security
Design Background", draft-ietf-mip6-ro-sec-01 (work in
progress), July 2004.
[21] Koodli, R., "Fast Handovers for Mobile IPv6",
draft-ietf-mipshop-fast-mipv6-02 (work in progress), July 2004.
[22] Soliman, H., Castelluccia, C., Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 mobility management (HMIPv6)",
draft-ietf-mipshop-hmipv6-02 (work in progress), June 2004.
[23] Huston, G., "Architectural Approaches to Multi-Homing for
IPv6", draft-ietf-multi6-architecture-04 (work in progress),
February 2005.
[24] Arkko, J., Kempf, J., Sommerfeld, B., Zill, B., and P.
Nikander, "SEcure Neighbor Discovery (SEND)",
draft-ietf-send-ndopt-06 (work in progress), July 2004.
[25] Arbaugh, W. and B. Aboba, "Experimental Handoff Extension to
RADIUS", draft-irtf-aaaarch-handoff-04 (work in progress),
Vogt & Arkko Expires April 11, 2006 [Page 38]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
November 2003.
[26] Koodli, R., "IP Address Location Privacy and IP Mobility",
draft-koodli-mip6-location-privacy-00 (work in progress),
February 2005.
[27] Koodli, R., "Solutions for IP Address Location Privacy in the
presence of IP Mobility",
draft-koodli-mip6-location-privacy-solutions-00 (work in
progress), February 2005.
[28] Moskowitz, R., Nikander, P., and P. Jokela, "Host Identity
Protocol", draft-moskowitz-hip-09 (work in progress),
February 2004.
[29] Bao, F., "Certificate-based Binding Update Protocol (CBU)",
draft-qiu-mip6-certificated-binding-update-02 (work in
progress), August 2004.
[30] Roe, M., Aura, T., O'Shea, G., and J. Arkko, "Authentication of
Mobile IPv6 Binding Updates and Acknowledgments",
draft-roe-mobileip-updateauth-02 (work in progress),
March 2002.
[31] Vogt, C., Bless, R., Doll, M., and T. Kuefner, "Early Binding
Updates for Mobile IPv6",
draft-vogt-mip6-early-binding-updates-00 (work in progress),
February 2004.
[32] Vogt, C., Arkko, J., Bless, R., Doll, M., and T. Kuefner,
"Credit-Based Authorization for Mobile IPv6 Early Binding
Updates", draft-vogt-mipv6-credit-based-authorization-00 (work
in progress), May 2004.
[33] Wakikawa, R., "Optimized Route Cache Protocol (ORC)",
draft-wakikawa-nemo-orc-01 (work in progress), November 2004.
[34] Zhao, F., Wu, F., and S. Jung, "NEMO Route Optimization Problem
Statement and Analysis", draft-zhao-nemo-ro-ps-01 (work in
progress), February 2005.
[35] "NEMO Route Optimisation Problem Statement",
draft-clausen-nemo-ro-problem-statement-00 (work in progress),
October 2004.
[36] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
Vogt & Arkko Expires April 11, 2006 [Page 39]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
[37] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[38] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
Multihoming Architectures", RFC 3582, August 2003.
[39] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[40] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
Protect Mobile IPv6 Signaling Between Mobile Nodes and Home
Agents", RFC 3776, June 2004.
[41] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
January 2005.
[42] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[43] Vadali, R., Li, J., Wu, Y., and G. Cao, "Agent-Based Route
Optimization for Mobile IP", Proceedings of the IEEE Vehicular
Technology Conference, October 2001.
[44] Alimian, A. and B. Aboba, "Analysis of Roaming Techniques",
IEEE Contribution 11-04-0377r1 2004.
[45] Arkko, J., Eronen, P., Nikander, P., and V. Torvinen, "Secure
and Efficient Network Access", Extended abstract to be
presented in the DIMACS workshop, November 2004.
[46] Arkko, J. and P. Nikander, "Weak Authentication: How to
Authenticate Unknown Principals without Trusted Parties",
Proceedings of Security Protocols Workshop 2002, Cambridge, UK,
April 16-19, 2002.
[47] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[48] Castelluccia, Claude., Montenegro, Gabriel., Laganier, Julien.,
and Christoph. Neumann, "Hindering Eavesdropping via IPv6
Opportunistic Encryption", Proceedings of the European
Symposium on Research in Computer Security , September 2004.
[49] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
Vogt & Arkko Expires April 11, 2006 [Page 40]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
[50] Mishra, A., Shin, M., Arbaugh, W., Lee, I., and K. Jang,
"Proactive Key Distribution to Support Fast and Secure
Roaming", IEEE Contribution 11-03-084r1-I, January 2003.
[51] Montenegro, G. and Claude. Castelluccia, "Crypto-Based
Identifiers (CBIDs): Concepts and Applications", ACM
Transactions on Information and System Security Vol. 7, No.
1, February 2004.
[52] Nikander, P., "Denial-of-Service, Address Ownership, and Early
Authentication in the IPv6 World", Proceedings of the Cambridge
Security Protocols Workshop, April 2001.
[53] O'Shea, G. and M. Roe, "Child-proof Authentication for MIPv6",
Computer Communications Review, April 2001.
[54] Paxson, V., "An Analysis of Using Reflectors for Distributed
Denial-of-Service Attacks", Computer Communication Review
31(3)., July 2001.
[55] Velayos, H. and G. Karlsson, "Techniques to Reduce IEEE 802.11b
MAC Layer Handover Time", Laboratory for Communication
Networks, KTH, Royal Institute of Technology, Stockholm,
Sweden, TRITA-IMIT-LCN R 03:02, April 2003.
[56] Vogt, C., "Samitas Review of
draft-irtf-mobopts-ro-enhancements-00", IETF MIP6 and Mobopts
mailing lists, http://www.atm.tut.fi/list-archive/MIPv6-2005/
msg00677.html, June 2005.
Authors' Addresses
Christian Vogt
Institute of Telematics
Universitaet Karlsruhe (TH)
P.O. Box 6980
76128 Karlsruhe
Germany
Email: chvogt@tm.uka.de
URI: http://www.tm.uka.de/~chvogt/
Vogt & Arkko Expires April 11, 2006 [Page 41]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Jari Arkko
Ericsson Research NomadicLab
FI-02420 Jorvas
Finland
Email: jari.arkko@ericsson.com
Vogt & Arkko Expires April 11, 2006 [Page 42]
Internet-Draft MIP6 Route Optimization Enhancements October 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Vogt & Arkko Expires April 11, 2006 [Page 43]
