Internet Engineering Task Force J. Palet
Internet-Draft M. Diaz
Expires: October 20, 2004 Consulintel
April 21, 2004
Evaluation of IPv6 Auto-Transition Mechanism
draft-palet-v6ops-auto-trans-00.txt
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Abstract
This draft evaluates a method called "auto-transition" to ensure that
any device can obtain IPv6 connectivity at any time and whatever
network is attached to.
The method looks for the best transition mechanism according to
performance criteria as well as the scenario where the device is
located.
By implementing such auto-transition method in either or both end
nodes or middle boxes (CPEs), users can always obtain IPv6
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connectivity with no human intervention.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Auto-Transition Overview . . . . . . . . . . . . . . . . . . . 3
3. Auto-Transition Requirements . . . . . . . . . . . . . . . . . 4
3.1 Selection of the proper transition mechanism . . . . . . . 5
3.2 Change of transition mechanism . . . . . . . . . . . . . . 7
3.3 New transition mechanisms . . . . . . . . . . . . . . . . 8
3.3.1 Layer 2 tunnels . . . . . . . . . . . . . . . . . . . 8
3.3.2 Layer 3 tunnels . . . . . . . . . . . . . . . . . . . 9
3.3.3 Layer 4 tunnels . . . . . . . . . . . . . . . . . . . 10
3.4 Discovery of the IPv6 End Point . . . . . . . . . . . . . 10
4. Nomadicity Considerations . . . . . . . . . . . . . . . . . . 11
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1 Normative References . . . . . . . . . . . . . . . . . . . . 14
8.2 Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . 17
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1. Introduction
The main goal is to facilitate the IPv6 deployment in a seamless way
for devices, users and applications. Lots of devices and applications
around us will benefit obtaining IPv6 connectivity everywhere: home
automation, wearable devices, cars, PDAs, mobile phones, peer-to-peer
applications, remote control applications, etc. IPv6 is suitable to
solve the network requirements that those devices/applications will
need: addressing space, end-to-end secure peer-to-peer communication,
autoconfiguration features and so on.
IPv6 provides autoconfiguration features, enabling devices to work
according to the plug-and-play philosophy, that is with no manual
intervention. However they only can be applied once the device has
obtained IPv6 connectivity. On the other hand, while native IPv6
connectivity is not available everywhere, there is not a good
"auto-transition" to ensure this connectivity.
While devices are located in a native IPv6 environment, no manual
intervention is required, so non technical users can take advantage
of IPv6. However until all or most of the networks are IPv6 native,
we need to ensure that the same devices and users can use a
transition mechanism that ensures the best possible IPv6
connectivity, without any technical knowledge. Is not acceptable
require to the users to make manual configurations in order to get
the IPv6 connectivity.
The mechanism will deal with all the tasks required to configure
automatically the best IPv6 connectivity at anytime, in any network
scenario, which include native IPv6 connectivity detection and
transition mechanism selection if required. It can be implemented
either in stand-alone devices (hosts, PDA, etc.) or middle boxes like
CPE routers.
2. Auto-Transition Overview
When the device is attached to the network, the mechanism first must
check if native IPv6 connectivity is possible. If so, either or both
stateless [1] or stateful autoconfiguration [2] mechanism are
performed. Otherwise, the auto-transition mechanism should try to
obtain IPv6 connectivity by using the best transition mechanism
according to the network where the devices is attached.
Later, the conditions of the network can change, even the user/device
can change the location while moving. Consequently the attachment
point to the network can be different, and the previous transition
mechanism no longer be so convenient. The auto-transition mechanism
has to monitor periodically the network parameters (i.e. IPv4
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address, loss, delays, etc.) in order to detect those changes and
decide if another transition mechanism different to the one currently
being used is convenient and provides better performance to activate
it.
All this process should be ideally automatic in order to avoid the
user to make any manual configuration. At the most, users only should
introduce some parameters by means of a wizard during the
installation process of the application that implements the
auto-transition mechanism, but once it is up and running, all the
tasks should be made by the system and no manual intervention
required.
This approach should be available at least in two kind of platforms.
o End devices: Devices that do not intend to provide IPv6
connectivity to others. They are typically devices that would get
IPv6 connectivity by means of Router Advertisement if they were
attached to a native IPv6 scenario. Examples are hosts, PDAs,
mobile phones, cameras, home automation devices, white goods,
consumer electronics, etc.
o CPE devices: Devices that are located between two different
networks or networks segments. Typically routers, IPv4 NAT boxes,
etc. They should provide native IPv6 connectivity to the whole
network(s) located behind them by announcing an IPv6 prefix. With
this approach this kind of devices will be plug-and-play, so users
only have to attach them to the network and they will deal with
all the tasks to get IPv6 connectivity. A few applications include
home networks, hotels, hot-spots and so on.
3. Auto-Transition Requirements
The best IPv6 connectivity, in principle, is obviously the native one
if available, since it should not add extra delays in the
communication neither introduce more complexity to the networks.
Consequently the auto-transition mechanism first must check if IPv6
native connectivity is available. However it strongly depends on the
ISP support and can be expected that in the first IPv6 deployment
stage, only a few ISPs will provide it.
If native connectivity is not available the auto-transition mechanism
must choose the right transition mechanism to be used to ensure the
connectivity.
A number of transition mechanism have been defined already: Teredo,
TB/TS, TSP, STEP, ISATAP, 6to4, tunnels, etc. All of them work when
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the host willing to get IPv6 connectivity has a public IPv4 address.
Even some of them also work when the host is located behind a NAT box
that allows proto-41 forwarding [3]. However there are other kind of
NAT boxes that prevent the current transition mechanisms to work, so
there is a gap that could be filled with new kind of solutions,
possibly layer 2 or layer 4 tunnels.
The adequate selection of the proper transition mechanism is one of
the keys of the auto-transition concept.
3.1 Selection of the proper transition mechanism
A few scenarios with particular network requirements had been defined
already ([4], [5], [6], [7]). Not all the transition scenarios fit in
such network scenarios, as being evaluated at [8], trying to make the
best fit to each scenario.
The auto-transition mechanism may take into account the results shown
in [8], although it is also possible a wider focus to select the best
transition mechanism to be used. What the end user always demands is
the best performance on the IPv6 connectivity, so it should be the
main criteria to choose the right transition mechanism.
Distance, delays, loss, bandwidth, etc., are some of the related
parameters that could be used as metrics to be measured for knowing
the link performance. A device can present different values of such
metrics according to the transition mechanism that is being used even
when attached to the same network.
A combination of all the metrics could provide a fine evaluation of
the connection performance. However in order to make the mechanism as
simple as possible only delay and loss should be considered.
According to this philosophy the auto-transition mechanism could
operate by means of the following simple algorithm:
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loop
detect_scenario
if (native_IPv6_available and native_priority)
use_native_IPv6_connectivity
else
if (first_check or performance_check_allowed)
check_performance
use_best_mechanism
endif
endif
configure_connectivity
wait (link_check_timeout)
endloop
Figure 1: Simple Auto-transition algorithm
It is important to note what each task or parameter means:
o detect_scenario: This task deals with detecting the scenario where
the device willing to have IPv6 connectivity is located. It could
check if native IPv6 is available, if a public IPv4 address is
available, if a NAT is being used and what type, if there is a
proxy or firewall, or if other protocols can be operated.
o native_IPv6_available: Detects if native IPv6 is available.
o native_priority: Detects if native IPv6 has priority, for
instance, even in the case the performance is lower than
alternative transition mechanism that may be used. This condition
could be set by the OS, or even under user or applications
control.
o use_native_IPv6_connectivity: Configure the interface to use
native IPv6 connectivity, using stateless or stateful
autoconfiguration, upon their availability.
o first_check: Defines if this is the first time this check is being
done after an interface reset.
o performance_check_allowed: Defines if the performance of the
selected mechanism can be measured after selected, for instance,
to avoid traffic being generated in non-flat rate links (3GPP,
ISDN, ...).
o check_performance: According to the detected scenario, a number of
mechanisms could be used. This task checks the performance that
each of such transition mechanism provides, including native IPv6
if available, by measuring delays and losses. The mechanism subset
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will be defined by taking into account [8], but others could be
considered.
o use_best_mechanism: According to the measurement results, the best
mechanism is selected.
o configure_connectivity: Either native IPv6 connectivity or the
best available transition mechanism is configured.
o link_check_timeout: Once the IPv6 connectivity is obtained, the
auto-transition mechanism periodically monitors the link status.
The delay between consecutive checks is defined by this variable.
A possible list of mechanism to be checked, ordered by preference
could be:
1. Native IPv6 Connectivity
2. TS with proto-41 ([3])
3. TS with UDP
4. ISATAP
5. STEP
6. 6to4
7. Teredo
3.2 Change of transition mechanism
Change of transition mechanism refers to the task to abandon the
transition mechanism that is actually being used and start to use
another one that presents better performance. This is not an easy
task at all, since it involves at least two important issues:
1. To maintain the current IPv6 address. This is a must since
otherwise applications with communications opened will not work.
Specially important is the case which the auto-transition
mechanism is implemented in border devices that provide native
IPv6 connectivity to the whole network. Either the prefix network
(i.e. RA), or the IPv6 addresses (i.e. DHCPv6) that they provide,
must be able to keep the IPv6 addressing parameters. If the
auto-transition mechanism has to include the possibility of
changing the transition mechanism used without discarding the
current connection state, it is necessary to define a method that
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solves this issue. MIPv6 concepts could be applied.
2. User authentication without human intervention. The philosophy of
the auto-transition mechanism is that all the processes are done
automatically, with no human intervention. So, for instance, if
the device running the auto-transition mechanism needs to contact
with a TB different to the actual one, and it requires user
authentication, the process should be transparent to the user. It
could be based on parameters (login and password) configured
through the wizard during the installation process. AAA
mechanisms should be used.
3.3 New transition mechanisms
A number of devices do not allow tunnel-based transition mechanism to
work properly. They are both NAT boxes, proxies or firewalls. Even
building IPv6 tunnels over UDP is not always possible since some
middle boxes do not forward those packets.
When this happens it is required that the auto-transition mechanism
uses a method that cannot be rejected by the middle box. The
following solutions could be considered:
3.3.1 Layer 2 tunnels
By using layer 2 encapsulating methods (L2TP [9], PPTP [10], PPPoE
[11]), the middle boxes barriers can be easily overcome since this
kind of protocols are very used when building layer 2 VPN.
Consequently, one of the following protocol stacks might be used.
+--------+ +--------+
| IPv6 | | IPv6 |
+--------+ +--------+
| PPP | | PPP |
+--------+ +--------+ +--------+
| L2TP | | PPTP | | IPv6 |
+--------+ +--------+ +--------+
| UDP | | TCP | | PPP |
+--------+ +--------+ +--------+
| IPv4 | | IPv4 | | IPv4 |
+--------+ +--------+ +--------+
L2TP tunnel PPTP tunnel PPPoE tunnel
Figure 2: Layer 2 tunnels
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This kind of solution does not seem to be efficient due to the
following drawbacks:
o It requires that the TS is configured as VPN L2 server.
o Overloaded stack. IPv6 connection will have low performance.
o Complicated deployment and management due to the control plane for
L2TP and PPTP.
o Authentication is a must with PPP. It means added complexity.
3.3.2 Layer 3 tunnels
VPN's built by mean of layer 3 tunnels can be a solution to allow
IPv6 connections cross NAT boxes with no proto-41 forwarding
capabilities as well as proxies and firewalls.
+--------+ +--------+
| IPv6 | | IPv6 |
+--------+ +--------+ +--------+
| IPv4 | | IPv4 | | IPv6 |
+--------+ +--------+ +--------+
| PPP | | IPsec | | IPv4 |
+--------+ +--------+ +--------+
| IPv4 | | IPv4 | | IPv4 |
+--------+ +--------+ +--------+
PPP-IPv4 IPsec IPv4-IPv4
Figure 3: Layer 3 tunnels
Compared to the Layer 2 tunnels, the layer 3 tunnels have the
following advantages:
o Less overloaded stacks.
o Tunnel management simpler.
o There are some implementations (VTun, cIPE, TINC).
However it also have important drawbacks:
o It requires that the TS is configured as VPN L2 server.
o Some NAT's could not support those.
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3.3.3 Layer 4 tunnels
The last resort is to try to overcome the middle barriers by means of
the use of frequently used application protocols. There are two well
known possibilities that frequently will not create difficulties with
neither proxies nor firewalls: HTTP and SSH. Furthermore, they
neither have problems with NAT boxes. The protocol stack for this
solution is as follows:
+--------+ +--------+
| IPv6 | | IPv6 |
+--------+ +--------+
| HTTP | | SSH |
+--------+ +--------+
| TCP | | TCP |
+--------+ +--------+
| IPv4 | | IPv4 |
+--------+ +--------+
HTTP tunnel SSH tunnel
Figure 4: Layer 4 tunnels
The main advantage of this approach is the simplicity for the
configuration of the tunnel. Furthermore the tunnels can be secured
by means of either SSL (using HTTPS instead of HTTP) or SSH.
According to the different alternatives, it sounds reasonable that
the better solution could be Layer 4-based tunnels since it is
simpler than the others, and always will work, but the performance
will not be optimal. Instead Layer 3 and Layer 2-based tunnels should
be taken into account in implementations of the auto-transition
mechanism in order to guarantee the IPv6 connectivity by covering all
the possible alternatives.
The usage of those new mechanism is discouraged, unless there is no
other choice. In any case, the standardization of those different
tunnel options is out of the scope of this document.
3.4 Discovery of the IPv6 End Point
Devices running the auto-transition mechanism need to know where to
find the IPv6 (tunnel) end point or tunnel server (TS) that provides
them the IPv6 connectivity. If native IPv6 connectivity is provided
by the ISP and used, this TS will be obviously the link end point and
no further work is required. This is slightly more complex when a
transition mechanism is required to obtain the IPv6 connectivity.
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Having in mind that users want plug-and-play devices/services, and
that most of them do not have any knowledge about how the transition
mechanism works or where the nearest Tunnel Broker/Tunnel Sever, 6to4
relay, etc. are located, it is required considering the
auto-discovery of the IPv6 TS, so the device can find it
automatically.
Different transition mechanisms have different IPv6 type of end
points. For example, the Tunnel Broker/Tunnel Server uses mainly 6in4
tunnels; TSP can used either 6in4 or IPv6 over UDP tunnels; Teredo
uses IPv6 over UDP tunnel, etc. Furthermore, each transition
mechanism has its own tunnel setup handshake, so it is not only
important to know where the nearest IPv6 TS is located but also what
type of transition mechanism/s is able to manage.
On the other hand, there are situations where people are crowded,
i.e. either conferences, airports, urban areas with high population
density, etc. In this scenario is very likely that most of the users
choose a particular IPv6 TS, usually because it is nearer or more
well known. It is possible that while there exist a few IPv6 TS
attending many connections, there can exist a lot of them that are
not being used. In this way, most of the users have poor performance
in their connections while users using TS without congestion will
have good performance. It would be desirable that there were some
kind of load balancing in order to uniformly distribute the IPv6
tunnel requests among all available IPv6 TS.
The different approaches to cope with this issue are analysed in
[12].
4. Nomadicity Considerations
When users move across networks, several situations are possible.
From the network point of view, users can or cannot maintain the IPv6
address assigned from their home TS. From the transition mechanisms
point of view, the new one can or cannot require an authentication
process. So clearly some considerations are required regarding the
auto-transition mechanism behavior while user is moving.
1. Nodes that do not need to maintain the IPv6 address assigned from
their home TS. They are typically nomadic users who get
connectivity to "passive" Internet users (browsing, emailing,
etc.), but do not need to be "identified" from Internet
(nevertheless this situation is changing with next generation p2p
applications, VoIP, etc.). Looking for the best IPv6 connectivity
can lead the auto-transition mechanism to define as the best TS
one of the following:
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* TSs that do not require authentication process. They are TSs
that provide IPv6 connectivity and they do not make any
authentication process (TEREDO, 6to4, etc.). This approach
does not represent any innovation, so the auto-transition
mechanism just contact to the TS and the IPv6 connectivity is
obtained.
* TSs that require authentication process. They are TSs that
only provide IPv6 connectivity to authenticated users (users
that previously were somehow registered in the entity
providing the IPv6 TS service or some related entity).
Automatic AAA mechanism must be defined, in order to ensure
the no-human intervention requirement. The TS can or cannot
belong to the entity which the user was registered. If so,
authentication process is simpler. However, a global
authentication only will be possible if there are roaming
agreements between the entity that is selected to obtain IPv6
connectivity and the "home" entity which the user is
registered. These roaming agreements could be used for billing
purposes among others. If there are not such agreements,
automatic connectivity is not possible and the auto-transition
mechanism has to options:
+ To choose an alternative transition mechanism, even
although it does not offer the best performance.
+ To inform to the user that the best IPv6 connection is only
possible if a new manual registration/authentication
process is done.
* The behavior should be defined during the wizard installation
process of the auto-transition implementation.
2. Nodes that need to maintain the IPv6 address assigned from their
home TS. Users belonging to this group are typically users with
either server or peer-to-peer applications, devices that need to
be tracked (cars, suitcases, etc.), etc. MIPv6 should be applied
to this kind of nodes, but the following considerations must to
taken into account by the auto-transition mechanism:
* Mobility capability should be an option that should be
configured by means of the installation wizard. If chosen, the
first time that the auto-transition mechanism is run, it must
check if a Home Agent (HA) exists either in the current IPv6
network or in the TS. In fact, this option should condition
the order of searching for the best transition mechanism to
get IPv6 connectivity. In this way, only mechanisms compatible
with the presence of HA should be taken into account
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(mechanisms providing static IPv6 network prefix like TB, TSP,
ISATAP, etc.). The auto-transition mechanism should record the
mechanism used to get IPv6 connectivity. Some transition
mechanisms like ISATAP, allow the HA deployment into the home
network which the nomadic device is initially attached.
Others, like TB, could be deployed in different networks from
the one where the device is physically attached, but the HA
could be implemented into the TS that provides the IPv6
connectivity. On the other hand, the auto-transition mechanism
should discard transition mechanisms that build the IPv6
network prefix from the IPv4 address (6to4, TEREDO, etc.).
This is required because it is no possible the deployment of
the HA into the same IPv6 network, so no mobility features
would be possible. If no HA is discovered the first time that
the auto-transition mechanism is run, then no MIPv6 support is
possible, so the user should be informed and the usual
auto-transition algorithm must be applied to get IPv6
connectivity.
* Once the node is away from home network, it needs to get IPv6
connectivity. The auto-transition mechanism should first check
if it possible to maintain the same IPv6 home address,
according to the mechanism used, before moving for getting the
home address. There are some kinds of transition mechanism
that allow this operation like a TB with several TS
associated. In this scenario, the node first gets the IPv6
home address from a TS. After the node move to other location,
it could get IPv6 connectivity from a different TS that is
associated to the same TB. It is possible that either the new
TS has the same /64 network prefix that the old TS or it can
be configured by the TB to forward/send tunneled packets
coming/going from/to the nomadic node. In this way the nomadic
device could maintain the IPv6 home address. Even if the new
TS does not belong to the same TB but there are roaming
agreements between the involved entities, the maintenance of
the IPv6 address/prefix could be possible. How to do this
configuration is out of scope of this document.
* If the IPv6 home address can not be maintained, then once the
nomadic device has a new IPv6 address by means of any
transition mechanism, it must contact to the HA to communicate
the care of address following MIPv6.
Other considerations pointed out in [12] should be taken into
account.
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5. Conclusions
TBD.
6. Security Considerations
The auto-transition mechanism should secure at least the following
points:
1. Communication with TS for administrative purposes.
2. Communication with TS for authentication purposes.
3. Tunnel building is according to the chosen TS.
4. General tunnel security consideration pointed at [13].
7. Acknowledgements
This memo was written as a consequence of real experience using IPv6
when traveling, number of talks during IETF meetings and specially
the work with the unmanaged, ISP and enterprise v6ops design teams.
The authors would also like to acknowledge the European Commission
support in the co-funding of the Euro6IX project, where this work is
being developed.
8. References
8.1 Normative References
8.2 Informative References
[1] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[2] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[3] Palet, J., "Forwarding Protocol 41 in NAT Boxes",
draft-palet-v6ops-proto41-nat-03 (work in progress), October
2003.
[4] Huitema, C., "Evaluation of Transition Mechanisms for Unmanaged
Networks", draft-ietf-v6ops-unmaneval-01 (work in progress),
February 2004.
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[5] Lind, M., "Scenarios and Analysis for Introducing IPv6 into ISP
Networks", draft-ietf-v6ops-isp-scenarios-analysis-01 (work in
progress), February 2004.
[6] Wiljakka, J., "Analysis on IPv6 Transition in 3GPP Networks",
draft-ietf-v6ops-3gpp-analysis-09 (work in progress), March
2004.
[7] Bound, J., "IPv6 Enterprise Network Scenarios",
draft-ietf-v6ops-ent-scenarios-01 (work in progress), February
2004.
[8] Savola, P. and J. Soininen, "Evaluation of v6ops Tunneling
Scenarios and Mechanisms", draft-savola-v6ops-tunneling-01
(work in progress), April 2004.
[9] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G. and
B. Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661,
August 1999.
[10] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little, W. and
G. Zorn, "Point-to-Point Tunneling Protocol", RFC 2637, July
1999.
[11] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D. and
R. Wheeler, "A Method for Transmitting PPP Over Ethernet
(PPPoE)", RFC 2516, February 1999.
[12] Palet, J. and M. Diaz, "Evaluation of v6ops Auto-discovery for
Tunneling Mechanisms", draft-palet-v6ops-tun-auto-disc-00 (work
in progress), April 2004.
[13] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for
IPv6 Hosts and Routers", draft-ietf-v6ops-mech-v2-02 (work in
progress), February 2004.
Authors' Addresses
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
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Miguel Angel Diaz Fernandez
Consulintel
San Jose Artesano, 1
Alcobendas - Madrid
E-28108 - Spain
Phone: +34 91 151 81 99
Fax: +34 91 151 81 98
EMail: miguelangel.diaz@consulintel.es
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Palet & Diaz Expires October 20, 2004 [Page 17]