Internet Engineering Task Force A. Vives
Internet-Draft J. Palet
Expires: August 24, 2005 Consulintel
P. Savola
CSC/FUNET
February 20, 2005
IPv6 Security Problem Statement
draft-vives-v6ops-ipv6-security-ps-03.txt
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
Today, each network is often secured by a unique device (i.e.
security gateway or firewall) that becomes a bottleneck for the
end-to-end security model with IPv6. The deployment of IPv6 enabled
devices and networks bring some issues, which must be addressed by
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security administrators in order to guarantee at least the same level
of security that is obtained nowadays with IPv4 and network-based
(including perimeter-based) security schemes, allowing at the same
time all the IPv6 advantages.
The most important issues are the rediscovery of end-to-end
communications, the availability of IPsec in all IPv6 stacks, the
increase in the number and type of IP devices and also the increase
in the number of nomadic devices, connecting to different networks
that could have different security policies.
The security policies and architectures currently applied in Internet
with IPv4 do no longer apply for end-to-end security models which
IPv6 will need. This document outlines the advantages and drawbacks
of both security schemes: network/perimeter-based and distributed.
This document aims to identify IPv6 issues that justify the need of a
distributed security model for IPv6, that is, simply to show that a
security problem will arise with the deployment of IPv6 networks if
nothing is done.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Network-based versus Host-based Security . . . . . . . . . . . 5
2.1 Network-based Security . . . . . . . . . . . . . . . . . . 5
2.2 Host-based Security . . . . . . . . . . . . . . . . . . . 7
3. IPv6 Issues . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 End-to-End . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 IPsec-encrypted ESP-traffic in transport mode . . . . . . 11
3.3 Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4 Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4.1 Link-local addresses . . . . . . . . . . . . . . . . . 13
3.4.2 New Multicast addresses . . . . . . . . . . . . . . . 13
3.5 Multihoming . . . . . . . . . . . . . . . . . . . . . . . 14
3.6 Randomly Generated Addresses . . . . . . . . . . . . . . . 14
3.7 Neighbor Discovery Weakness . . . . . . . . . . . . . . . 15
3.8 Routing Header . . . . . . . . . . . . . . . . . . . . . . 15
3.9 Home Address Option . . . . . . . . . . . . . . . . . . . 16
3.10 Embedded Devices . . . . . . . . . . . . . . . . . . . . . 16
4. Other Issues . . . . . . . . . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1 Normative References . . . . . . . . . . . . . . . . . . . 17
7.2 Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . 19
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1. Introduction
This document will cope only with IPv6 issues related to security,
i.e., it will try to answer the following question: How would the
deployment of IPv6 affect the security of a network? This network
could be a dual-stack network with IPv6 traffic from IPv6 capable
nodes, or an IPv6 only network.
The deployment of IPv6 enabled devices and networks forces the
security administrator to consider several issues:
o The rediscovery of end-to-end communications.
o The availability of IPsec in all IPv6 stacks.
o The increase in the number and type of IP devices.
o The increase in the number of nomadic devices, connecting and
moving between different networks.
The security policies and architectures currently applied in Internet
with IPv4 no longer apply for end-to-end security models which IPv6
will enable. This document outlines the advantages and drawbacks of
both the security schemes: network/perimeter-based and distributed.
Also IPv6 issues will be identified that justify the need of
distributed security for IPv6, that is, simply to show that a
security problem will arise with the deployment of IPv6 networks if
traditional schemes are used.
The following issues are out of scope of this document and will be
addressed elsewhere:
o State the security requirements for the described IPv6 scenarios.
o Propose a solution or architecture to address the problem stated
in this document.
o To address security problems derived from the use of transition
mechanisms.
Last but not least, this document contains a brief definition of what
we understand by "security". We use security in the "big scope" of
the word, trying to include as much as possible. In other words, a
host, a network or some information, will be secure when no attacks
could succeed against them. A success will mean compromise of
availability, integrity, confidentiality or authenticity. The
realistic objective is to be as much secure as possible in a precise
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moment. It will be part of the requirements to establish which kind
of security is given using a number of mechanisms.
For clarity, in the rest of this document, network-based security
includes also the perimeter-based model.
2. Network-based versus Host-based Security
In this section two different approaches are analyzed to be used
later in the rationale about the security problems that IPv6 could
introduce
2.1 Network-based Security
This is the most used scheme, where the security of a host depends on
the point of the network it is connected to.
The perimeter scheme is the simplest one (see Fig. 1) and is based
in the topology of the network. The security policy is enforced in a
central host or firewall (FW), which provides secure network
connectivity to one or more network segments. The FW will be what an
"outside" host sees when tries to attack the network. Attacks coming
from the same LAN segment are not protected by the FW. Different
nodes (even different addresses in the same node) may have different
policies.
In a more advanced form of perimeter security, the different networks
could be protected from each other, or a number of internal firewalls
could be used as well. This way some networks could be protected
from hosts in other internal network
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/-------\
/ \
| Internet |
\ /
\---+---/
|
| Policy Enforcement Point
+---+---+
LAN-1 | | DMZ-1
----+---------+ FW +-------+----
| | | |
+-+--+ +---+---+ +--+-+
| H1 | | | S1 |
+----+ |LAN-2 +----+
|
+----+ |
| H2 +--+
+----+ |
Figure 1: Perimeter Security
This model is based on the following assumptions:
o The threats come from "outside" the FW, basically the Internet.
o Everybody from the same LAN segment is trusted.
o The protected nodes won't go "outside" where FW won't be able to
protect them.
o There are no backdoors on the network (modem, WLAN, other
connections).
o The hosts will not need to be accessed directly from outside (at
least in a general manner, i.e., potentially all ports on all
hosts).
The main advantage of this scheme is its simplicity and easiness as
the elements and points of configuration are reduced to the minimum,
requiring few/no protocols and mechanisms to implement the security.
In case of a more complex configuration, where multiple FW are
deployed within an organization network, the complexity will
increase.
The drawbacks of this model are:
o This is a centralized model: Single point of failure for both
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performance and availability. If the FW fails, then all the
networks connected to it loose network connectivity unless
specific fail-over techniques are applied.
o A big percentage of the threats come from inside the FW, and are
not addressed by this security model, especially when internal
firewalls are not deployed.
o The most dangerous threats, in the sense that one may not be able
to protect from them, come from inside the FW.
o The FW usually acts as NAT and/or proxy box, interfering or even
disallowing end-to-end communications. In complex configurations,
even more than one level of NAT/proxy could appear.
o Transport mode secured communications (using IPsec ESP for
example) need special solutions ([1]).
o The same security policy may be enforced for all the nodes of each
network connected to the FW, but it is also possible to have
separate policies for all hosts. In any case, an error in the FW
will equally expose all hosts in a network.
o Virtual organizations, for example those using GRID models, don't
work with traditional centralized security models.
o The lack of secure end-to-end prevents innovation.
2.2 Host-based Security
Host based security model, already introduced by [2], is based on the
idea of enforcing the security policy in each network host from a
central control point.
The three main elements identified in the distributed security model
are:
o Policy Specification Language.
o Policy Exchange Protocol.
o Authentication of Entities.
The basic idea is simple: the Security Policy is centrally defined
using the Policy Specification Language and distributed to each host
by means of the Policy Exchange Protocol. The Network Entities need
to be authenticated in order to be trusted, for example to allow an
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incoming connection or to trust the received Security Policy.
The biggest challenge, however, is trusting that the hosts comply to
the rules they've received, for example that the user can't just
disable the firewall if (s)he dislike the policy; of course, this
only can happen in the case (s)he has administrative rights for that
(often not the case in non-personal systems, those not owned by the
end user). It seems that one ore more network entities would have to
keep watch over the hosts in order to detect if they are not
following the received policy. At first look the more appropriated
entity seems to be one that knows the security policy, for example
the one that distributes it.
From a security point of view this model somehow eases the work to
the "enemies", putting the Policy Enforcement Point in their hands.
So not only mechanisms to prevent direct attacks to the security
solution must be developed but mechanisms to minimize the
consequences.
/-------\
/ \
| Internet |
+------+ \ /
|Sec. | \---+---/
|Policy| |
+--+---+ |
| /-+-\
| | \ / | LAN-3
-+---+------+ x +-------+--
LAN-1 | (*) | / \ | | (*)Policy Enforcement Point
+--+-+ \-+-/ +-+--+
| H1 | | LAN-2 | H3 |
+----+ | +----+
| (*)
+--+-+
| H2 |
+----+
Figure 2: Host-based Security
This model is based on the following assumptions:
o Each host can be uniquely and securely identified.
o The security policy could be applied in one or more of the
following levels: network, transport and application.
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o The threat comes from anywhere in the network.
o The intruder has no physical access to the protected network hosts
(what about malicious users? See other topics section).
o "Outside" hosts may be able to access all hosts "Inside",
depending on the policies.
The advantages of this model are:
o The security policy can be host-specific.
o A host can take better decisions as it knows what it is doing or
trying to do, that means it can better detect strange packets.
For example, it could allow mail traffic to only one application
on the system.
o Enables the usage of end-to-end applications level security (e.g.,
web services security standards).
o Enables better protection from attacks by the "internal" users,
and possibly even to a degree from those in the local segment.
For example address spoofing can be detected and avoided coming
from the same LAN segment, without router participation.
o Can protect a host independent of the topology, i.e., wherever the
host is connected.
o Does not need specific devices to secure a host (consider the case
of a single host with a CPE (Customer Premises Equipment), if the
CPE has no (user-controllable) firewall functions).
o Can control the outgoing attempts from each host, avoiding local
network misbehavior or malicious practices.
o The collection of audit information could be more complete in a
distributed model, despite the processing of that information is
done in a distributed or centralized fashion.
o It maintains the centralized control of the security policies,
from where they are distributed to each host (central decisions,
local enforcement).
The drawbacks of this model are:
o It is more complex than the perimeter one.
o The uniqueness and secured identification of hosts is not trivial,
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for example using certificates [2].
o The hosts must be trusted (or designed appropriately) so that they
will operate according to the policy. For example, it must be
impossible to disable the firewall functions or if the policy is
not followed network communication is not allowed.
o A host that becomes compromised or infected with a worm or virus
in any case can't be trusted to operate according to the policies,
as the worms/viruses probably first create holes or disable the
protections if they can.
o It may be challenging to design the system so that policy updates
are made available to the nodes which may not be network-reachable
all the time.
o It may be difficult to distinguish a misbehaving application from
a legitimate application (for example, many email worms may be
channeled through the MUA which must be authorized to send the
mails to operate correctly).
o Because of having a centralized Policy Decision Point (PDP) from
where the Security Policies are distributed a weakness is
introduced in form of a central point of failure unless more
complexity is added, for example with a distributed/replicated
system.
o The host security is in some sense 'server-dependant'. It must be
able to detect the lost of connectivity with the PDP and act in
consequence. It also seems that being disconnected from the PDP
for a long period could be dangerous.
3. IPv6 Issues
When IPv6 is deployed, either in an existing IPv4 network or in a new
IPv6-only network, the security administrator must take into account
that IPv6 traffic will be different from the IPv4.
IPv6 enabled nodes will likely have global addresses, which means
they may be reachable from any other IPv6 node in the Internet. A
security administrator can prevent this by using local addressing
and/or firewalls, but the benefits of IPv6 may not be fully realized
if so.
The differences between IPv4 and IPv6 change the type of attacks
which IPv6 networks are likely to see.
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Also mention that there are studies that conclude that the rollout of
dedicated IPv4 firewalls in the internal network to regulate internal
network communication causes the same work that dedicated firewalling
on hosts.
3.1 End-to-End
The global availability of end-to-end communication is one of the
benefits of IPv6, and provides the required framework for further
innovation, where technologies like P2P and GRID, among others, can
be widely spread with no problems in a seamless way. However,
end-to-end communication also means that every host should be
reachable from any other host, including the ones from "outside". It
can lead to an increase in the possibility of being attacked, such as
cracking, DoS, etc.
In the network-based security model, these threats are normally
solved by disabling every end-to-end communications between inside
and outside, but this is not a solution for those who want to use
end-to-end communications.
Some possible solutions to cracking are outlined in [3], one of them
being a host firewall.
Several researches are ongoing regarding DoS prevention, and some of
these solutions need to be adopted to provide security for such
end-to-end communications.
3.2 IPsec-encrypted ESP-traffic in transport mode
As stated in [3], section 5, there is a problem with the IPv6
encrypted traffic (IPsec ESP mechanism in transport mode, for
example) and the network-based security model.
The idea is that a host inside the network can establish an encrypted
communication channel with other host outside of the network. A
middlebox (for example the perimeter firewall) won't be able to
inspect the contents of such a communication.
In [3] some possible solutions are outlined, one of them being a host
firewall.
3.3 Mobility
In parallel to the increase in the number of devices, IPv6
facilitates that those devices are "mobile", that is, can easily move
from one network to another using Mobile IPv6 or just disconnecting
from one and connecting to another.
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Because of the amount of addresses available and the facilities given
by Autoconfiguration mechanisms together with the mentioned rise of
the number of IP devices, this kind of behavior should be taken into
account by the security administrator, as these devices will be
connected to networks where they have no control and consequently, no
responsibility.
A possible solution for these devices is the use of host based
security, enabled in every network it is connected. The policies and
mechanisms should be described elsewhere.
3.4 Addresses
Regarding the addresses in IPv6 must be taken into account that:
o The amount of addresses is much bigger for a given network.
o Each host will have more than one address which are probably
globally routable.
o An IPv6 node can use randomly generated addresses [4].
o The IPv6 addresses are more human error prone that the IPv4 ones.
That means:
o To scan a given network whole range of addresses and ports will
take a really big effort [5]. It would be easier to do that by
sniffing a LAN segment looking for existent addresses.
o The common way of identifying a host by means of its IP address
will be more difficult to use.
o If a host uses randomly generated addresses [4], it could be
problematic to identify a host using its IP address for security
policy matching purposes.
o The Security Administrator should be careful when establishing,
for example, an ACL (Access Control List) as the common practice
is to use raw IP addresses (instead of DNS names). Some mechanism
would be desirable to prevent these mistakes.
Regarding the scan of addresses, [5] demonstrates that the "brute
force" scanning would make no sense for an IPv6 address range,
typically a minimum of /64.
A host based security scheme would protect the other hosts from the
compromised one.
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The idea behind all this is that the new IPv6 address scheme and
mechanisms will somehow protect from existent attack techniques but
we can be sure that they will adapt themselves to the new scheme and
we have to act consequently being prepared.
The IPv6 addressing scheme eases the work of identifying a user host,
becoming a privacy threat. There are two IPv6 features to be
considered, the host identifier created from the MAC address by the
address autoconfiguration and the user network prefix.
The first one could be used to identify a user independently of the
network to which it is attached. As a solution the randomly
generated addresses were defined.
The second one refers to the fact that every user will receive at
least a /64 prefix and so all the hosts coming from one user network
could be identified by the network prefix. In IPv4 it is common to
use a temporary address assignment scheme for the home user,
resulting in changes of its assigned address.
3.4.1 Link-local addresses
In IPv6 we have got the link-local addresses that allows a host that
connects to a network to have IP connectivity without any external
help.
Even if this is quite useful, also represents a security problem
because allows a host to attack the network it is connected to. This
must be taken into account by the security administrator.
As a guideline, we should not simply rely on trusting by default
those sessions which are from link local addresses. It is better to
restrict to use link local address to some fundamental services,
until the host is trusted.
3.4.2 New Multicast addresses
In IPv6 new multicast addresses are defined than identifies resources
in a well known manner. This can enable an enemy to locate and
attack those key resources with no need of a time consuming address
search.
This kind of addresses have an scope field. This means that many of
such services would have either link-local scope. Note that these
addresses are used for the protocol itself, for example in the
autoconfiguration process. This kind of addresses must be taken into
account by a security solution that addresses inside attacks.
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There are also global-scope addresses that must be published to the
outside. This kind of services must be protected and monitored by a
security solution that addresses outside attacks.
For an updated IPv6 multicast addresses list see [6].
3.5 Multihoming
As said above the IPv6 capable interface could have more than one
IPv6 global address. This will be the case in multihomed networks,
where more than one network prefix could be used to have access to
the IPv6 world.
If the security policy is based on rules which use IP addresses as an
identifier, it must be taken into account that a single host could be
behind different addresses with different prefixes.
Also the case of a host with more than one interface, each one with
one or more different addresses should be taken into account. If
more than one interface is using the network infrastructure with
different addresses, the Security Administrator should be able to
identify that the same host is behind all these addresses.
3.6 Randomly Generated Addresses
Whatever security model is being used, in case of using randomly
generated addresses, the host identifier part is randomly generated
by the host to be used temporarily [4].
The consequence is that it will be harder for a security
administrator to define a policy rule (access rule) in the security
enforcement point to identify end nodes in all cases. For example a
node could generate a DoS attack generating a lot of traffic using a
random source address. The security administrator could not just
block the host's network prefix because there could be other valid
hosts within that network. Even in the case of a detection
mechanism, the attacking node could change its random source address.
So the Security Administrator should take into account the randomly
generated addresses when receiving incoming packets from outside of
its security domain. Its decision could be for example to allow
access to public services, like web servers, but not to allow or put
special attention to connections to end nodes inside its network. To
put special attention could be for example, to inspect packets up to
application level or to dedicate more IDS resources.
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3.7 Neighbor Discovery Weakness
As said above, one of the assumptions of the host-based security
model is that all hosts in the network are non trusted, the possible
threats coming from the same LAN segment must be taken into account,
in this case the ones coming from Neighbor Discovery (ND) [7][8].
Note that this is not possible within the network-based security
model, although some detection mechanism could be implemented,
nothing can be done to protect the hosts.
There are some ways to interfere in the normal behavior of the
autoconfiguration process, causing redirection of traffic and/or DoS
(Denial of Service).
Special attention must be put on Router Advertisement (RA), Router
Solicitation (RS), Neighbor Solicitation (NS), Neighbor Advertisement
(NA) and Redirect messages. See [9] for a detailed explanation of
possible threats.
Using host firewalls and/or IDS (Intrusion Detection Systems) for
protecting hosts against these threats is very likely a wrong
approach, as that would basically imply reinventing SEND [10][11]; it
is better to use SEND instead.
There is no easy protection against these threats as the ND features
(e.g., using link-local or the unspecified addresses) are needed
before a host can authorize itself to the other network components.
3.8 Routing Header
IPv6 protocol defines some extension headers, among them is the
Routing Header [12]. All IPv6 endpoints are required to process this
header resulting in the forwarding of the IPv6 packet.
Using the routing header a list of one or more nodes through which
the packet must pass, in its path from source to destination, is
created. Basically what happens is that the destination address is
changed in each host where the routing header is processed. This
mechanism, for example, could be used to reach hosts beyond
network-based security mechanisms.
The security administrator should establish, in the Security Policy,
which hosts, if any, are allowed to forward IPv6 packets with routing
header. The security solution must be able to assure that this
policy is accomplished by all the hosts under its control. This can
be achieved, for example, by disabling IP stack processing of routing
headers or by filtering packets with routing headers in each host.
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The routing header is used in Mobile IPv6. If this functionality is
allowed in the network the Security Administrator must take it into
account. For example, if administrators filter packets with
routing-header, but don't filter ICMPv6 packets regarding
Return-Routability, Mobile IPv6 will succeed in route-optimization
but can't make the communication because packets with routing-header
are rejected. Hence, Mobile IPv6 does not work at all in such
configuration.
3.9 Home Address Option
IPv6 protocol defines some extension headers, among them is the Home
Address [13]. All IPv6 endpoints should accept this header.
Basically what happens is that the source address of the packet is
changed by the Home Address option's address. It is used in a packet
sent by a mobile node while away from home, to inform the recipient
of the mobile node's home address. This could be used for spoofing.
Because this option was defined for Mobile IPv6 use, the security
administrator should reject the packet with home address option
unless Mobile IPv6 is allowed.
3.10 Embedded Devices
With the deployment of IPv6 we can expect the avenue of a big amount
of new IPv6-enabled devices with few resources, low computing
capacity, even low battery capacity. In some cases, this kind of
devices will not be able even to perform the minimum set of functions
required by the Host-based Security Model.
It also should be taken into account that the convergence of both the
IPsec capability of every IPv6 stack and the avenue of small devices
with few CPU resources could be used for DoS attacks.
This should be taken into account when the security requirements are
outlined and by the proposed solutions.
4. Other Issues
Further elaboration is required (TBD) on:
o Malicious users: We can't protect the network from malicious users
that have physical access to network hosts in the protected
network. The objective is to minimize the danger they can cause.
o In the host-based security, the host that stores and distributes
the security policies seems to be the best option to be the one
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that acts as IDS information collector.
5. Security Considerations
This document is concerned entirely with security.
6. Acknowledgements
The authors would like to acknowledge the inputs of Brian Carpenter,
Satoshi Kondo, Shinsuke Suzuki, Peter Bieringer and the European
Commission support in the co-funding of the Euro6IX project, where
this work is being developed.
7. References
7.1 Normative References
7.2 Informative References
[1] "IETF midcom WG",
<http://www.ietf.org/html.charters/midcom-charter.html>.
[2] Bellovin, S., "Distributed Firewalls", November 1999,
<http://www.research.att.com/~smb/papers/distfw.pdf>.
[3] Savola, P., "Firewalling Considerations for IPv6",
Internet-Draft draft-savola-v6ops-firewalling-02, October 2003.
[4] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[5] Chown, T., "IPv6 Implications for TCP/UDP Port Scanning",
Internet-Draft draft-chown-v6ops-port-scanning-implications-01,
July 2004.
[6] "IANA's IPv6 Multicast Addresses List",
<http://www.iana.org/assignments/ipv6-multicast-addresses>.
[7] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[8] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[9] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba,
"Dynamic Authorization Extensions to Remote Authentication Dial
In User Service (RADIUS)", RFC 3576, July 2003.
Vives, et al. Expires August 24, 2005 [Page 17]
Internet-Draft IPv6 Security Problem Statement February 2005
[10] Arkko, J., Kempf, J., Sommerfeld, B., Zill, B. and P. Nikander,
"SEcure Neighbor Discovery (SEND)",
Internet-Draft draft-ietf-send-ndopt-06, July 2004.
[11] Aura, T., "Cryptographically Generated Addresses (CGA)",
Internet-Draft draft-ietf-send-cga-06, April 2004.
[12] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[13] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
Authors' Addresses
Alvaro Vives Martinez
Consulintel
San Jose Artesano, 1
Alcobendas - Madrid
E-28108 - Spain
Phone: +34 91 151 81 99
Fax: +34 91 151 81 98
Email: alvaro.vives@consulintel.es
Jordi Palet Martinez
Consulintel
San Jose Artesano, 1
Alcobendas - Madrid
E-28108 - Spain
Phone: +34 91 151 81 99
Fax: +34 91 151 81 98
Email: jordi.palet@consulintel.es
Pekka Savola
CSC/FUNET
Espoo
Finland
Email: psavola@funet.fi
Vives, et al. Expires August 24, 2005 [Page 18]
Internet-Draft IPv6 Security Problem Statement February 2005
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