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Versions: (draft-vandevelde-v6ops-nap) 00 01 02 03 04 05 06 RFC 4864

Network Working Group                                    G. Van de Velde
Internet-Draft                                                   T. Hain
Expires: April 25, 2006                                         R. Droms
                                                           Cisco Systems
                                                            B. Carpenter
                                                         IBM Corporation
                                                                E. Klein
                                                     Tel Aviv University
                                                        October 22, 2005


                  IPv6 Network Architecture Protection
                     <draft-ietf-v6ops-nap-02.txt>

Status of this Memo

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   This Internet-Draft will expire on April 25, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   Although there are many perceived benefits to Network Address
   Translation (NAT), its primary benefit of "amplifying" available
   address space is not needed in IPv6.  In addition to NAT's many



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   serious disadvantages, there is a perception that other benefits
   exist, such as a variety of management and security attributes that
   could be useful for an Internet Protocol site.  IPv6 does not support
   NAT by design and this document shows how Network Architecture
   Protection (NAP) using IPv6 can provide the same or more benefits
   without the need for NAT.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Perceived Benefits of NAT and its Impact on IPv4 . . . . . . .  6
     2.1.  Simple Gateway between Internet and Private Network  . . .  6
     2.2.  Simple Security due to Stateful Filter Implementation  . .  6
     2.3.  User/Application tracking  . . . . . . . . . . . . . . . .  7
     2.4.  Privacy and Topology Hiding  . . . . . . . . . . . . . . .  8
     2.5.  Independent Control of Addressing in a Private Network . .  9
     2.6.  Global Address Pool Conservation . . . . . . . . . . . . .  9
     2.7.  Multihoming and Renumbering with NAT . . . . . . . . . . . 10
   3.  Description of the IPv6 Tools  . . . . . . . . . . . . . . . . 10
     3.1.  Privacy Addresses (RFC 3041) . . . . . . . . . . . . . . . 10
     3.2.  Unique Local Addresses . . . . . . . . . . . . . . . . . . 11
     3.3.  DHCPv6 Prefix Delegation . . . . . . . . . . . . . . . . . 12
     3.4.  Untraceable IPv6 Addresses . . . . . . . . . . . . . . . . 12
   4.  Using IPv6 Technology to Provide the Market Perceived
       Benefits of NAT  . . . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Simple Gateway between Internet and Internal Network . . . 13
     4.2.  IPv6 and Simple Security . . . . . . . . . . . . . . . . . 13
     4.3.  User/Application Tracking  . . . . . . . . . . . . . . . . 15
     4.4.  Privacy and Topology Hiding using IPv6 . . . . . . . . . . 15
     4.5.  Independent Control of Addressing in a Private Network . . 16
     4.6.  Global Address Pool Conservation . . . . . . . . . . . . . 17
     4.7.  Multihoming and Renumbering  . . . . . . . . . . . . . . . 17
   5.  Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . 18
     5.1.  Medium/large private networks  . . . . . . . . . . . . . . 18
     5.2.  Small Private Networks . . . . . . . . . . . . . . . . . . 20
     5.3.  Single User Connection . . . . . . . . . . . . . . . . . . 21
     5.4.  ISP/Carrier Customer Networks  . . . . . . . . . . . . . . 22
   6.  IPv6 Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . 23
     6.1.  Subnet Topology Masking  . . . . . . . . . . . . . . . . . 23
     6.2.  Minimal Traceability of Privacy Addresses  . . . . . . . . 23
     6.3.  Renumbering Procedure  . . . . . . . . . . . . . . . . . . 23
     6.4.  Site Multihoming . . . . . . . . . . . . . . . . . . . . . 24
     6.5.  Untraceable Addresses  . . . . . . . . . . . . . . . . . . 24
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   9.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 24
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25



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   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 25
     11.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  Additional Benefits due to Native IPv6 and
                Universal Unique Addressing . . . . . . . . . . . . . 27
     A.1.  Universal Any-to-Any Aonnectivity  . . . . . . . . . . . . 27
     A.2.  Auto-configuration . . . . . . . . . . . . . . . . . . . . 27
     A.3.  Native Multicast Services  . . . . . . . . . . . . . . . . 28
     A.4.  Increased Security Protection  . . . . . . . . . . . . . . 28
     A.5.  Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 29
     A.6.  Merging Networks . . . . . . . . . . . . . . . . . . . . . 29
     A.7.  Community of interest  . . . . . . . . . . . . . . . . . . 29
   Appendix B.  Revision history  . . . . . . . . . . . . . . . . . . 30
     B.1.  Changes from *-vandevelde-v6ops-nap-00 to
           *-vandevelde-v6ops-nap-01  . . . . . . . . . . . . . . . . 30
     B.2.  Changes from *-vandevelde-v6ops-nap-01 to
           *-ietf-v6ops-nap-00  . . . . . . . . . . . . . . . . . . . 30
     B.3.  Changes from *-ietf-v6ops-nap-00 to *-ietf-v6ops-nap-01  . 30
     B.4.  Changes from *-ietf-v6ops-nap-01 to *-ietf-v6ops-nap-02  . 30
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
   Intellectual Property and Copyright Statements . . . . . . . . . . 36






























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1.  Introduction

   Although there are many perceived benefits to Network Address
   Translation (NAT), its primary benefit of "amplifying" available
   address space is not needed in IPv6.  The serious disadvantages of
   ambiguous "private" address space and of Network Address Translation
   (NAT) [1][5] have been well documented [4][6].  However, given its
   wide market acceptance NAT undoubtedly has some perceived benefits.
   Indeed, in an Internet model based on universal any-to-any
   connectivity, product marketing departments have driven a perception
   hat some connectivity and security concerns can only be solved by
   using a NAT device or by using logically separated Local Area Network
   (LAN) address spaces.  This document describes the reasons for
   utilizing a NAT device in an IPv4 environment that are regularly
   cited in marketing pronouncements.  It then shows how these needs can
   be met without using NAT in an IPv6 network.  Some of the IPv6
   solutions offer advantages beyond the equivalent IPv4 NAT solution.
   The use of the facilities from IPv6 described in this document avoids
   the negative impacts of address translation.

   As far as security and privacy is concerned, this document considers
   how to mitigate a number of threats.  Some are obviously external,
   such as having a hacker trying to penetrate your network, or having a
   worm infected machine outside your network trying to attack it.  Some
   are local such as a disgruntled employee disrupting business
   operations, or the unintentional negligence of a user downloading
   some malware which then proceeds to attack any device on the LAN.
   Some may be inherent in the device hardware ("embedded") such as
   having some firmware in a domestic appliance "call home" to its
   manufacturer without the user's consent.

   This document describes several techniques that may be combined on an
   IPv6 site to protect the integrity of its network architecture.
   These techniques, known collectively as Network Architecture
   Protection (NAP), retain the concept of a well defined boundary
   between "inside" and "outside" the private network, and allow
   firewalling, topology hiding, and privacy.  NAP will achieve these
   security goals without address translation whilst maintaining any-to-
   any connectivity.

   IPv6 Network Architecture Protection can be summarized in the
   following table.  It presents the marketed "benefits" of NAT with a
   cross-reference of how those are delivered in both the IPv4 and IPv6
   environments.







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        benefit                IPv4                     IPv6
   +------------------+-----------------------+-----------------------+
   | Simple Gateway   |  DHCP - single        |  DHCP-PD - arbitrary  |
   | as default router|  address upstream     |  length customer      |
   | and address pool |  DHCP - limited       |  prefix upstream      |
   | manager          |  number of individual |  SLAAC via RA         |
   |                  |  devices downstream   |  downstream           |
   |                  |  see section 2.1      |  see section 4.1      |
   +------------------|-----------------------|-----------------------+
   |  Simple Security |  Filtering side       |  Explicit Context     |
   |                  |  effect due to lack   |  Based Access Control |
   |                  |  of translation state |  (Reflexive ACL)      |
   |                  |  see section 2.2      |  see section 4.2      |
   +------------------|-----------------------|-----------------------+
   |  Local usage     |  NAT state table      |  Address uniqueness   |
   |  tracking        |                       |                       |
   |                  |  see section 2.3      |  see section 4.3      |
   +------------------|-----------------------|-----------------------+
   |  End-system      |  NAT transforms       |  Temporary use        |
   |  privacy         |  device ID bits in    |  privacy addresses    |
   |                  |  the address          |                       |
   |                  |  see section 2.4      |  see section 4.4      |
   +------------------|-----------------------|-----------------------+
   |  Topology hiding |  NAT transforms       |  Untraceable addresses|
   |                  |  subnet bits in the   |  using IGP host routes|
   |                  |  address              |  /or MIPv6 tunnels for|
   |                  |                       |  stationary systems   |
   |                  |  see section 2.4      |  see section 4.4      |
   +------------------|-----------------------|-----------------------+
   |  Addressing      |  RFC 1918             |  RFC 3177 & ULA       |
   |  Autonomy        |                       |                       |
   |                  |  see section 2.5      |  see section 4.5      |
   +------------------|-----------------------|-----------------------+
   |  Global Address  |  RFC 1918             |  340,282,366,920,938, |
   |  Pool            |                       |  463,463,374,607,431, |
   |  Conservation    |                       |  768,211,456          |
   |                  |                       |  (3.4*10^38) addresses|
   |                  |  see section 2.6      |  see section 4.6      |
   +------------------|-----------------------|-----------------------+
   |  Renumbering and |  Address translation  |  Preferred lifetime   |
   |  Multi-homing    |  at border            |  per prefix & Multiple|
   |                  |                       |  addresses per        |
   |                  |                       |  interface            |
   |                  |  see section 2.7      |  see section 4.7      |
   +------------------+-----------------------+-----------------------+

   This document first identifies the perceived benefits of NAT in more
   detail, and then shows how IPv6 NAP can provide each of them.  It



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   concludes with a IPv6 NAP case study and a gap analysis of work that
   remains to be done for a complete NAP solution.


2.  Perceived Benefits of NAT and its Impact on IPv4

   This section provides insight into the generally perceived benefits
   of the use of IPv4 NAT as extolled by product marketing.  The goal of
   this description is not to analyze these benefits or discuss the
   accuracy of the perception (detailed discussions in [4]), but to
   describe the deployment requirements and set a context for the later
   descriptions of the IPv6 approaches for dealing with those
   requirements.

2.1.  Simple Gateway between Internet and Private Network

   A NAT device can connect a private network with any kind of address
   (ambiguous [RFC 1918] or global registered address) towards the
   Internet.  The address space of the private network can be built from
   globally unique addresses, from ambiguous address space or from both
   simultaneously.  Without needing specific configuration, the NAT
   device enables access between the client side of a distributed
   client-server application in the private network and the server side
   in the public Internet.

   Wide-scale deployments have shown that using NAT to attach a private
   IPv4 network to the Internet is simple and practical for the non-
   technical end user.  Frequently a simple user interface, or even a
   default configuration is sufficient for configuring both device and
   application access rights.

   Additionally, thanks to successful marketing campaigns it is
   perceived by end users that their equipment is protected from the
   malicious entities and attackers on the public IPv4 Internet.

2.2.  Simple Security due to Stateful Filter Implementation

   A firewall doesn't fully secure a network, because many attacks come
   from inside or are at a layer higher than the firewall can protect
   against.  In the final analysis, every system has to be responsible
   for its own security, and every process running on a system has to be
   robust in the face of challenges like stack overflows etc.  What a
   firewall does is prevent a network administration from having to pay
   for bandwidth to carry unauthorized traffic, and in so doing reduce
   the probability of certain kinds of attacks across the protected
   boundary.

   A distributed security mechanism to protect the end-systems may help



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   in the above situation; however, to deploy such a system is quite
   complex and may depend upon behaviour per operating system and
   release version.  Also it will only be reliable if a mechanism such
   as 'trusted computing' is implemented in the end-system; without this
   enhancement administrators will be unwilling to trust the behavior of
   end-systems.  As a result it will probably not be available in the
   next couple of years for end-user organizations.  End-system-only
   security mechanisms do not protect the network infrastructure from
   being misused for transit, or against Distributed Denial of Service
   (DDOS) attacks against individual systems inside: and this is the
   area where a NAT device is perceived to provide some protection.

   It is frequently believed that through its session-oriented
   operation, NAT puts in an extra barrier to keep the private network
   protected from outside influences.  Since a NAT device typically
   keeps state only for individual sessions, attackers, worms, etc.
   cannot exploit this state to attack a host in general and on any
   port.  This benefit may be partially real, however, experienced
   hackers are well aware of NAT devices and are very familiar with
   private address space, and have devised methods of attack (such as
   trojan horses) that readily penetrate NAT boundaries.  For these
   reasons the sense of security provided by NAT is actually an
   illusion.

   Address translation does not provide security in itself; for example,
   consider a configuration with static NAT translation and all inbound
   ports translating to a single machine.  In such a scenario the
   security risk for that machine is identical to the case with no NAT
   device in the communication path.  As result there is no specific
   security value in the address translation function.  The perceived
   security comes from the lack of pre-established or permanent mapping
   state.  Dynamically establishing state in response to internal
   requests reduces the threat of unexpected external connections to
   internal devices.

   In some cases, NAT operators (including domestic users) may be
   obliged to configure quite complex port mapping rules to allow
   external access to local applications such as a multi-player game or
   web servers.  In this case the NAT actually adds management
   complexity compared to a simple router.  In situations where two or
   more devices need to host the same application this complexity shifts
   from difficult to impossible.

2.3.  User/Application tracking

   Although NATs create temporary state for active sessions, in general
   they provide limited capabilities for the administrator of the NAT to
   gather information about who in the private network is requesting



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   access to which Internet location.  This could in theory be done by
   logging the network address translation details of the private and
   the public addresses from the NAT device's state database.

   The checking of this database is not always a simple task, especially
   if Port Address Translation is used.  It also has an unstated
   assumption that the administrative instance has a mapping between an
   IPv4-address and a network element or user at all times, or the
   administrator has a time-correlated list of the address/port
   mappings.

2.4.  Privacy and Topology Hiding

   The goal of 'topology hiding' is to provide devices on the private
   network with an identifier (IPv4 address) which an entity outside the
   network can use to communicate with or to reference the private
   network devices in protocols but prevents the external entity making
   a correlation between the topological location of the private device
   and the address on the local network.

   The ability of NAT to provide Internet access to a large community of
   users by the use of a single (or a few) global IPv4 routable
   addresses offers a simple mechanism to hide the internal topology of
   a network.  In this scenario the large community will be represented
   in the Internet by a single (or a few) IPv4 address(es).

   The use of NAT then results in a user behind a NAT gateway actually
   appearing on the Internet as a user inside the NAT box itself; i.e.,
   the IPv4 address that appears on the Internet is only sufficient to
   identify the NAT.  When concealed behind a NAT it is impossible to
   tell from the outside which member of a family, which customer of an
   Internet cafe, or which employee of a company generated or received a
   particular packet.  Thus, although NATs do nothing to provide
   application level privacy, they do prevent the external tracking and
   profiling of individual host computers by means of their IP
   addresses, usually known as 'device profiling'.  At the same time a
   NAT creates a smaller pool of addresses for a much more focused point
   of attack.

   There is a similarity with privacy based on application level
   proxies.  When using an application level gateway for browsing the
   web for example, the 'privacy' of a web user can be provided by
   masking the true identity of the original web user towards the
   outside world (although the details of what is - or is not - logged
   at the NAT/proxy will be different).

   Some enterprises prefer to hide as much as possible of their internal
   network topology from outsiders.  Mostly this is achieved by blocking



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   "traceroute" etc., but NAT of course entirely hides the internal
   subnet topology, which some network managers believe is a useful
   precaution to mitigate scanning attacks.  Scanning for IPv6 can be
   much harder in comparison with IPv4 as described in [18].

   Once a list of available devices and IP addresses has been mapped, a
   port-scan on these IP addresses can be performed.  Scanning works by
   tracking which ports do not receive unreachable errors from either
   the firewall or host.  With the list of open ports an attacker can
   optimize the time needed for a successful attack by correlating it
   with known vulnerabilities to reduce the number of attempts.  For
   example, FTP usually runs on port 21, and HTTP usually runs on port
   80.  Any vulnerable open ports could be used for initiating attacks
   on an end system.

2.5.  Independent Control of Addressing in a Private Network

   Many private IPv4 networks take benefit from using the address space
   defined in RFC 1918 to enlarge the available addressing space for
   their private network, and at the same time reduce their need for
   globally routable addresses.  This type of local control of address
   resources allows a clean and hierarchical addressing structure in the
   network.

   Another benefit is due to the usage of independent addresses on
   majority of the network infrastructure there is an increased ability
   to change provider with less operational difficulties.

   Section 2.7 describes some disadvantages that appear if independent
   networks using [RFC1918] addresses have to be merged.

2.6.  Global Address Pool Conservation

   Due to the ongoing depletion of the IPv4 address range, the remaining
   pool of unallocated IPv4 addresses is below 30%.  While mathematical
   models based on historical IPv4 prefix consumption periodically
   attempt to predict the future exhaustion date of the IPv4 address
   pool, a direct result of this continuous resource consumption is that
   the administrative overhead for acquiring globally unique IPv4
   addresses will continue increasing in direct response to tightening
   allocation policies.  In response to the increasing administrative
   overhead many Internet Service Providers (ISPs) have already resorted
   to the ambiguous addresses defined in RFC 1918 behind a NAT for the
   various services they provide as well as connections for their end
   customers.  This happens even though that private address-space is
   strictly limited in size.  In turn this has restricted the number of
   and types of applications that can be deployed by these ISPs and
   their customers.  Forced into this limiting situation such customers



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   can rightly claim that despite the optimistic predictions of
   mathematical models the global pool of IPv4 addresses is effectively
   already exhausted, especially for larger enterprises.

2.7.  Multihoming and Renumbering with NAT

   Allowing a network to be multihomed and renumbering a network are
   quite different functions.  However, making a network multihomed is
   often a transitional state required as part of network renumbering,
   and NAT interacts with both in the same way.

   For enterprise networks, it is highly desirable to provide resiliency
   and load-balancing to be connected to more than one Internet Service
   Provider (ISP) and to be able to change ISPs at will.  This means
   that a site must be able to operate under more than one CIDR prefix
   [14] and/or readily change its CIDR prefix.  Unfortunately, IPv4 was
   not designed to facilitate either of these maneuvers.  However, if a
   site is connected to its ISPs via NAT boxes, only those boxes need to
   deal with multihoming and renumbering issues.

   Similarly, if two enterprise IPv4 networks need to be merged and
   RFC1918 addresses are used, there is a high probability of address
   overlaps.  In those situations it may well be that installing a NAT
   box between them will avoid the need to renumber one or both.  For
   any enterprise, this can be a short term financial saving, and allow
   more time to renumber the network components.  The long term solution
   is a single network without usage of NAT to avoid the ongoing
   operational complexity of overlapping addresses.

   The addition of an extra NAT as a solution may be sufficient for some
   networks; however when the merging networks were already using
   address translation it will create huge problems due to
   administrative difficulties of overlapping address speaces in the
   merged networks.


3.  Description of the IPv6 Tools

   This section describes several features that can be used as part of
   the NAP solution to emulate the protection features associated with
   IPv4 NAT.

3.1.  Privacy Addresses (RFC 3041)

   There are situations where it is desirable to prevent device
   profiling, for example by web sites that are accessed from the
   device; IPv6 privacy addresses were defined to provide that
   capability.  IPv6 addresses consist of a routing prefix, subnet-id



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   part (SID) and an interface identifier part (IID).  For interfaces
   that contain embedded IEEE Link Identifiers the interface identifier
   is typically derived from it, though this practice facilitates
   tracking and profiling of a device as it moves around the Internet.
   RFC 3041 describes an extension to IPv6 stateless address
   autoconfiguration (SLAAC) for interfaces [7].  Use of the privacy
   address extension causes nodes to generate global-scope addresses
   from interface identifiers that change over time, even in cases where
   the interface contains an embedded IEEE link identifier.  Changing
   the interface identifier (thus the global-scope addresses generated
   from it) over time makes it more difficult for eavesdroppers and
   other information collectors to identify when addresses used in
   different transactions actually correspond to the same node.  A
   relatively short valid lifetime for the privacy address also has the
   side effect of reducing the attack profile of a device, as it is not
   directly attackable once it stops answering at the temporary use
   address.

   While the primary implementation and source of randomized RFC 3041
   addresses is expected to be from end-systems running stateless
   autoconfiguration, there is nothing that prevents a DHCP server from
   running the RFC 3041 algorithm for any new IEEE identifier it hears,
   then remembering that for future queries.  This would allow using
   them in DNS for registered services since the assumption of a server
   based deployment would be a persistent value that minimizes DNS
   churn.  A DHCP based deployment would also allow for local policy to
   periodically change the entire collection of end device addresses
   while maintaining some degree of central knowledge and control over
   which addresses should be in use at any point in time.

   Randomizing the IID, as defined in RFC 3041, only precludes tracking
   of the lower 64 bits of the IPv6 address.  Masking of the subnet ID
   will require additional approaches as discussed below in 3.4.
   Additional considerations are discussed in [17].

3.2.  Unique Local Addresses

   Local network and application services stability during periods of
   intermittent connectivity between one or more providers requires
   address management autonomy.  Such autonomy in a single routing
   prefix environment would lead to massive expansion of the global
   routing tables, so IPv6 provides for simultaneous use of multiple
   prefixes.  The Unique Local Address prefix (ULA) [13] has been set
   aside for use in local communications.  The ULA address prefix for
   any network is routable over a locally defined collection of routers.
   These prefixes are not intended to be routed on the public global
   Internet; large scale inter-domain distribution of routes to ULA
   prefixes would have a negative impact on global route aggregation.



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   ULAs have the following characteristics:
   o  Globally unique prefix
      *  Allows networks to be combined or privately interconnected
         without creating any address conflicts or requiring renumbering
         of interfaces using these prefixes
      *  If accidentally leaked outside of a network via routing or DNS,
         it is highly unlikely that there will be a conflict with any
         other addresses
   o  ISP independent and can be used for communications inside of a
      network without having any permanent or intermittent Internet
      connectivity
   o  Well-known prefix to allow for easy filtering at network
      boundaries preventing leakage of local routes and packets.
   o  In practice, applications may treat these addresses like global
      scoped addresses but address selection algorithms need to
      distinguish between ULAs and ordinary global scope unicast
      addresses.  Mixing the two kinds of addresses is likely to lead to
      undeliverable packets.

3.3.  DHCPv6 Prefix Delegation

   The Prefix Delegation (DHCP-PD) options [11] provide a mechanism for
   automated delegation of IPv6 prefixes using the Dynamic Host
   Configuration Protocol (DHCP) [9].  This mechanism (DHCP-PD) is
   intended for delegating a long-lived prefix from a delegating router
   (incorporating a DHCPv6 server) to a requesting router, possibly
   across an administrative boundary, where the delegating router does
   not require knowledge about the topology of the links in the network
   to which the prefixes will be assigned.

3.4.  Untraceable IPv6 Addresses

   These should be globally routable IPv6 addresses which can be
   randomly and independently assigned to IPv6 devices.

   The random assignment is intended to mislead the outside world about
   the structure of the local network.  However the local network needs
   to maintain a correlation between the location of the device and the
   untraceable IPv6 address.  This correlation could be done by
   generating IPv6 host route entries or by utilizing an indirection
   device such as a Mobile IPv6 Home Agent.

   The main goal of untraceable IPv6 addresses is to create an
   apparently amorphous network infrastructure as seen from external
   networks to protect the local infrastructure from malicious outside
   influences and from mapping of any correlation between the network
   activities of multiple devices from external networks.  When using
   untraceable IPv6 addresses, it could be that two apparently



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   sequential addresses are allocated to devices on very different parts
   of the local network instead of belonging to devices adjacent to each
   other on the same subnet.


4.  Using IPv6 Technology to Provide the Market Perceived Benefits of
    NAT

   The facilities in IPv6 described in Section 3 can be used to provide
   the protection perceived to be associated with IPv4 NAT.  This
   section gives some examples of how IPv6 can be used securely.

4.1.  Simple Gateway between Internet and Internal Network

   As a simple gateway, the device manages both packet routing and local
   address management.  A basic IPv6 router could have a default
   configuration to advertise inside the site a locally generated random
   ULA prefix, independently from the state of any external
   connectivity.  This would allow local nodes to communicate amongst
   themselves prior to establishing a global connection.  If the network
   happened to concatenate with another local network, this is highly
   unlikely to result in address collisions.  A more secure network
   environment can be established by having the referenced ULA addresses
   statically configured on the network devices as this decreases the
   dynamic aspects of the network, however the operational overhead is
   increased.

   With external connectivity the simple gateway could also use DHCP-PD
   to acquire a routing prefix from the service provider for use when
   connecting to the global Internet.  End-system connections involving
   other nodes on the global Internet will always use the global IPv6
   addresses [9] derived from this prefix delegation.  It should be
   noted that the address selection policy table in end-systems needs to
   be correctly set up so that true global prefixes are distinguished
   from ULAs and will be used for the source address in preference when
   the destination is not a ULA.

   In the very simple case there is no explicit routing protocol and a
   single default route is used out to the global Internet.  A slightly
   more complex case might involve local routing protocols, but with the
   entire local network sharing a common global prefix there would still
   not be a need for an external routing protocol as a default route
   would continue to be consistent with the connectivity.

4.2.  IPv6 and Simple Security

   The vulnerability of an IPv6 host is similar to that of an IPv4 host
   directly connected towards the Internet.  The use of firewall and



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   Intrusion Detection Systems (IDS) is recommended.  A proxy may be
   used for certain applications, but with the caveat that the end to
   end transparancy is broken.  However, with IPv6, the following
   protections are available without the use of NAT while maintaining
   end-to-end reachability:
   1.  Short lifetimes on privacy extension suffixes reduce the attack
       profile since the node will not respond to the address once the
       address is no longer valid.
   2.  IPsec is a mandatory service for IPv6 implementations.  IPsec
       functions to prevent session hijacking, prevent content
       tampering, and optionally masks the packet contents.  While IPsec
       might be available in IPv4 implementations, deployment in NAT
       environments either breaks the protocol or requires complex
       helper services with limited functionality or efficiency.
   3.  The size of the address space of a typical subnet (64 bits of
       IID) will make an effective network ping sweep and resulting
       port-scan virtually impossible due to the number of possible
       combinations available, provided that IIDs are essentially
       randomly distributed across the available space.  This protection
       is nullified if the attacker has no access to a local connection.
       If an attacker has local access then he could use ND [3] and
       ping6 to ff02::1 to detect local neighbors.  (Of course, a
       locally connected attacker has many scanning options with IPv4 as
       well.)  It is recommended for site administrators to take [18]
       into consideration to achieve the expected goal.  This protection
       will also be nullified if IIDs are configured in a group near the
       start of the IID space.

   IPv4 NAT was not developed as a security mechanism.  Despite
   marketing messages to the contrary it is not a security mechanism,
   and hence it will offer some security holes while many people assume
   their network is secure due to the usage of NAT.  IPv6 security best
   practices will avoid this kind of illusory security but can only do
   this if correctly configured firewalls and IDS systems are used at
   the perimeter where some IPv4 networks have relied on NATs.

   To implement simple security for IPv6 in, for example, a DSL
   connected home network, the DSL broadband gateway/router should be
   equipped with stateful firewall capabilities.  These should provide a
   default configuration which provides a minimum set of connectivity
   for users in the home network (e.g., just to external HTTP servers)
   with incoming traffic limited to return traffic resulting from
   outgoing packets (sometimes known as reflective session state) with
   an easy interface which allows users to create additional 'pinholes'
   for specific purposes.

   Administrators and the designers of configuration interfaces for
   simple IPv6 Firewalls need to provide a means of documenting the



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   security caveats that arise from a given set configuration rules so
   that users (who are normally oblivious to such things) can be made
   aware of the risks.  As rules are improved iteratively, the goal will
   be to make use of the IPv6 Internet more secure for oblivious users.

   Assuming the network administrator is aware of [18] the increased
   size of the IPv6 address will make topology probing much harder, and
   almost impossible for IPv6 devices.  The intention of topology
   probing is to identify a selection of the available hosts inside an
   enterprise.  This mostly starts with a ping-sweep.  Since the IPv6
   subnets are 64 bits worth of address space, this means that an
   attacker has to send out a simply unrealistic number of pings to map
   the network, and virus/worm propagation will be thwarted in the
   process.  At full rate 40Gbps (400 times the typical 100Mbps LAN, and
   13,000 times the typical DSL/Cable access link) it takes over 5000
   years to scan a single 64 bit space.

4.3.  User/Application Tracking

   IPv6 enables the collection of information about data flows.  Due to
   the fact that all addresses used for Internet and intra-/inter-site
   communication are unique, it is possible for an enterprise or ISP to
   get very detailed information on any communication exchange between
   two or more devices.  This enhances the capability of data-flow
   tracking for security audits compared with IPv4 NAT, because in IPv6
   a flow between a sender and receiver will always be uniquely
   identified due to the unique IPv6 source and destination addresses.

4.4.  Privacy and Topology Hiding using IPv6

   Partial host privacy is achieved in IPv6 using pseudo-random privacy
   addresses [RFC 3041] which are generated as required, so that a
   session can use an address that is valid only for a limited time.
   Exactly as with IPv4 NAT, this only allows such a session to be
   traced back to the subnet that originates it, but not immediately to
   the actual host.

   Due to the large IPv6 address space available there is plenty of
   freedom to randomize subnet allocations.  By doing this, it is
   possible to reduce the correlation between a subnet and its location.
   When doing both subnet and IID randomization [RFC 3041] a casual
   snooper won't be able to deduce much about the networks topology.
   The obtaining of a single address will tell the snooper very little
   about other addresses.  This is different from IPv4 where address
   space limitations cause this to be not true.  In most usage cases
   this concept should be sufficient for address privacy and topology
   hiding.




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   In the case where a network administrator wishes to fully conceal the
   internal IPv6 topology, and the majority of its host computer
   addresses, a possible option is to run all internal traffic using
   Unique Local Addresses (ULA) since such packets can by definition
   never exit the site.  For hosts that do in fact need to generate
   external traffic, by using multiple IPv6 addresses (ULAs and one or
   more global addresses), it will be possible to hide and mask some or
   all of the internal network.  As discussed in Section 3.1, there are
   multiple parts to the IPv6 address, and different techniques to
   manage privacy for each.

   There are two possible scenarios for the extreme situation when a
   network manager also wishes to fully conceal the internal IPv6
   topology.

   o  One could use explicit host routes and remove the correlation
      between location and IPv6 address.  This solution does however
      show severe scalability issues.
   o  The other technology to fully hide the internal topology would be
      to use a tunneling mechanism.  Mobile IPv6 without route
      optimization is one example.  In this example the public facing
      addresses are indirected via an edge Home Agent (HA).  This
      indirection method truly masks the internal topology as all nodes
      with global access appear to share a common prefix.  The downside
      of using this method is that it makes usage of middleware like a
      Home Agent (HA).


4.5.  Independent Control of Addressing in a Private Network

   IPv6 provides for autonomy in local use addresses through ULAs.  At
   the same time IPv6 simplifies simultaneous use of multiple addresses
   per interface so that an IPv6 NAT is not required between the ULA and
   the public Internet.  Nodes that need access to the public Internet
   may have a ULA for local use, and will have a global use address
   because the global use IPv6 address space is not a scarce resource
   like the global use IPv4 space.  While global IPv6 allocation policy
   is managed through the Regional Internet Registries, it is expected
   that they will continue with derivatives of [RFC 3177] for the
   foreseeable future.

   When using IPv6, the need to ask for more address space will become
   far less likely due to the increased size of the subnets.  These
   subnets typically allow 2^64 addresses per subnet and an enterprise
   will typically receive a /48 which allows segmentation into at least
   2^16 different subnets.

   The ongoing subnet size maintenance may become simpler when IPv6



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   technology is utilised.  If IPv4 address space is optimised one has
   to look periodically into the number of hosts on a segment and the
   subnet size allocated to the segment; an enterprise today may have a
   mix of /28 - /23 size subnets for example, and may shrink/grow these
   as their network user base changes.  For IPv6 all subnets have /64
   prefixes.

4.6.   Global Address Pool Conservation

   IPv6 provides sufficient space to completely avoid the need for
   overlapping address space,
   340,282,366,920,938,463,463,374,607,431,768,211,456 (3.4*10^38) total
   possible addresses.  As previously discussed, the serious
   disadvantages of ambiguous address space have been well documented,
   and with sufficient space there is no need to continue the
   increasingly aggressive conservation practices that are necessary
   with IPv4.  While IPv6 allocation policies and ISP business practice
   will continue to evolve, the recommendations in RFC 3177 are based on
   the technical potential of the vast IPv6 address space.  That
   document demonstrates that there is no resource limitation which will
   require the adoption of the IPv4 workaround of ambiguous space behind
   a NAT.  As an example of the direct contrast, many expansion oriented
   IPv6 deployment scenarios result in multiple IPv6 addresses per
   device, as opposed to the constriction of IPv4 scenarios where
   multiple devices are forced to share a scarce global address.

4.7.  Multihoming and Renumbering

   Multihoming and renumbering remain technically challenging with IPv6
   (see the Gap Analysis below).  However, IPv6 was designed to allow
   sites and hosts to run with several simultaneous CIDR-like prefixes
   and thus with several simultaneous ISPs.  An address selection
   mechanism [10] is specified so that hosts will behave consistently
   when several addresses are simultaneously valid.  The fundamental
   difficulty that IPv4 has in this regard therefore does not apply to
   IPv6.  IPv6 sites can and do run today with multiple ISPs active, and
   the processes for adding and removing active prefixes at a site have
   been documented [12] and [19].

   The IPv6 address space allocated by the ISP will be dependent upon
   the connecting Service provider.  This may result in a renumbering
   effort if the network changes from Service Provider.  When changing
   ISPs or ISPs readjusting their addressing pool, DHCP-PD [11] can be
   used as an almost zero-touch external mechanism for prefix change in
   conjunction with a ULA prefix for internal connection stability.
   With appropriate management of the lifetime values and overlap of the
   external prefixes, a smooth make-before-break transition is possible
   as existing communications will continue on the old prefix as long as



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   it remains valid, while any new communications will use the new
   prefix.


5.  Case Studies

   In presenting these case studies we have chosen to consider
   categories of network divided first according to their function
   either as carrier/ISP networks or end user (such as enterprise)
   networks with the latter category broken down according to the number
   of connected end hosts.  For each of these category of networks we
   can use IPv6 Network Architecture Protection to achieve a secure and
   flexible infrastructure, which provides an enhanced network
   functionality in comparison with the usage of address translation.

   o  Medium/Large Private Networks (typically >10 connections)
   o  Small Private Networks (typically 1 to 10 connections)
   o  Single User Connection (typically 1 connection)
   o  ISP/Carrier Customer Networks


5.1.  Medium/large private networks

   The majority of private enterprise networks fall into this category.
   Many of these networks have one or more exit points to the Internet.
   Though these organizations have sufficient resources to acquire
   addressing independence when using IPv4 there are several reasons why
   they might choose to use NAT in such a network.  For the ISP there is
   no need to import the IPv4 address range from the remote end-
   customer, which facilitates IPv4 route summarization.  The customer
   can use a larger IPv4 address range (probably with less-
   administrative overhead) by the use of RFC 1918 and NAT.  The
   customer also reduces the overhead in changing to a new ISP, because
   the addresses assigned to devices behind the NAT do not need to be
   changed when the customer is assigned a different address by a new
   ISP.  By using address translation one avoids the need for network
   renumbering.  Finally, the customer can provide privacy for its hosts
   and the topology of its internal network if the internal addresses
   are mapped through NAT.

   It is expected that there will be enough IPv6 addresses available for
   all networks and appliances for the foreseeable future.  The basic
   IPv6 address range an ISP allocates for a private network is large
   enough (currently /48) for most of the medium and large enterprises,
   while for the very large private enterprise networks address-ranges
   can be concatenated.  A single /48 allocation provides an enterprise
   network with 65536 different /64 prefixes.




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   The summarization benefit for the ISP results from the IPv6
   allocation rules.  This means that the ISP will provide the
   enterprise with an IPv6 address-range (typically one or multiple
   range(s) of '/48') from its RIR assigned IPv6 address-space.  The
   goal of this assignment mechanism is to decrease the total amount of
   entries in the internet routing table.  If the ISP adopts appropriate
   policies there is high probability that an enterprise requiring
   additional space could acquire an adjacent address block.

   To mask the identity of a user on a network of this type, the usage
   of IPv6 privacy extensions may be advised.  This technique is useful
   when an external element wants to track and collect all information
   sent and received by a certain host with known IPv6 address.  Privacy
   extensions add a random factor to the host part of an IPv6 address
   and will make it very hard for an external element to keep
   correlating the IPv6 address to a host on the inside network.  The
   usage of IPv6 privacy extensions does not mask the internal network
   structure of an enterprise network.

   If there is need to mask the internal structure towards the external
   IPv6 internet, then some form of 'untraceable' addresses may be used.
   These addresses will be derived from a local pool, and may be
   assigned to those hosts for which topology masking is required or
   which want to reach the IPv6 Internet or other external networks.
   The technology to assign these addresses to the hosts could be based
   on DHCPv6.  To complement the 'Untraceable' addresses it is needed to
   have at least awareness of the IPv6 address location when routing an
   IPv6 packet through the internal network.  This could be achieved by
   'route-injection' in the network infrastructure.  This route-
   injection could be done based on /128 host-routes to each device that
   wants to connect to the Internet using an untraceable address.  This
   will provide the most dynamic masking, but will have a scalability
   limitation, as an IGP is typically not designed to carry many
   thousands of IPv6 prefixes.  A large enterprise may have thousands of
   hosts willing to connect to the Internet.  Less flexible masking
   could be to have time-based IPv6 prefixes per link or subnet.  This
   may reduce the amount of route entries in the IGP by a significant
   factor, but has as trade-off that masking is time and subnet based.

   The dynamic allocation of 'Untraceable' addresses can also limit the
   IPv6 access between local and external hosts to those local hosts
   being authorized for this capability.  Dynamically allocated
   'Untraceable' addresses may also facilitate and simplify the
   connectivity to the outside networks during renumbering, because the
   existing IPv6 central address pool could be swapped for the newly
   allocated IPv6 address pool.

   The use of permanent ULA addresses on a site provides the benefit



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   that even if an enterprise would change its ISP, the renumbering will
   only affect those devices that have a wish to connect beyond the
   site.  Internal servers and services would not change their allocated
   IPv6 ULA address, and the service would remain available even during
   global address renumbering.

5.2.  Small Private Networks

   Also known as SOHO (Small Office/Home Office) networks, this category
   describes those networks which have few routers in the topology, and
   usually have a single network egress point.  Typically these networks
   are:

   o  connected via either a dial-up connection or broadband access
   o  don't have dedicated Network Operation Center (NOC)
   o  and through economic pressure are typically forced today to use
      NAT

   In most cases the received global IPv4 prefix is not fixed over time
   and is too long (very often just a /32 just giving a single address)
   to provide every node in the private network with a unique globally
   usable address.  Fixing either of those issues typically adds an
   administrative overhead for address management to the user.  This
   category may even be limited to receiving ambiguous IPv4 addresses
   from the service provider based on RFC 1918.  An ISP will typically
   pass along the higher administration cost attached to larger address
   blocks, or IPv4 prefixes that are static over time, due to the larger
   public address pool each of those requires.

   As a direct response to explicit charges per public address most of
   this category has deployed NAPT (port demultiplexing NAT) to minimize
   the number of addresses in use.  Unfortunately this also limits the
   Internet capability of the equipment to being mainly a receiver of
   Internet data (client), and makes it quite hard for the equipment to
   become a world wide Internet server (i.e.  HTTP, FTP, etc.) due to
   the stateful operation of the NAT equipment.  Even when there is
   sufficient technical knowledge to manage the NAT to enable a server,
   only one server of any given protocol type is possible per address,
   and then only when the address from the ISP is public.

   When deploying IPv6 NAP in this environment, there are two approaches
   possible with respect to IPv6 addressing.
   o  DHCPv6 Prefix-Delegation
   o  ISP provides a static IPv6 address-range

   For the DHCPv6-PD solution, a dynamic address allocation approach is
   chosen.  By means of the enhanced DHCPv6 protocol it is possible to
   have the ISP push down an IPv6 prefix range automatically towards the



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   small private network and populate all interfaces in that small
   private network dynamically.  This reduces the burden for
   administrative overhead because everything happens automatically.

   For the static configuration the mechanisms used could be the same as
   for the medium/large enterprises.  Typically the need for masking the
   topology will not be of high priority for these users, and the usage
   of IPv6 privacy extensions could be sufficient.

   For both alternatives the ISP has the unrestricted capability for
   summarization of its RIR allocated IPv6 prefix, while the small
   private network administrator has all flexibility in using the
   received IPv6 prefix to its advantage because it will be of
   sufficient size to allow all the local nodes to have a public address
   and full range of ports available whenever necessary.

   While a full prefix is expected to be the primary deployment model
   there may be cases where the ISP provides a single IPv6 address for
   use on a single piece of equipment (PC, PDA, etc.).  This is expected
   to be rare though, because in the IPv6 world the assumption is that
   there is an unrestricted availability of a large amount of globally
   routable and unique address space.  If scarcity was the motivation
   with IPv4 to provide RFC 1918 addresses, in this environment the ISP
   will not be motivated to allocate private addresses towards the
   single user connection because there are enough global addresses
   available at essentially the same cost.  Also if the single device
   wants to mask its identity to the called party or its attack profile
   over a short time window it will need to enable IPv6 privacy
   extensions, which in turn leads to the need for a minimum allocation
   of a /64 prefix rather than a single address.

5.3.  Single User Connection

   This group identifies the users which are connected via a single IPv4
   address and use a single piece of equipment (PC, PDA, etc.).  This
   user may get an ambiguous IPv4 address (frequently imposed by the
   ISP) from the service provider which is based on RFC 1918.  If
   ambiguous addressing is utilized, the service provider will execute
   NAT on the allocated IPv4 address for global Internet connectivity.
   This also limits the internet capability of the equipment to being
   mainly a receiver of Internet data, and makes it quite hard for the
   equipment to become a world wide internet server (i.e.  HTTP, FTP,
   etc.) due to the stateful operation of the NAT equipment.

   When using IPv6 NAP, this group will identify the users which are
   connected via a single IPv6 address and use a single piece of
   equipment (PC, PDA, etc.).




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   In IPv6 world the assumption is that there is unrestricted
   availability of a large amount of globally routable and unique IPv6
   addresses.  The ISP will not be motivated to allocate private
   addresses towards the single user connection because he has enough
   global addresses available, if scarcity was the motivation with IPv4
   to provide RFC 1918 addresses.  If the single user wants to mask his
   identity, he may choose to enable IPv6 privacy extensions.

5.4.  ISP/Carrier Customer Networks

   This group refers to the actual service providers that are providing
   the IPv4 access and transport services.  They tend to have three
   separate IPv4 domains that they support:
   o  For the first they fall into the Medium/large private networks
      category (above) for their own internal networks, LANs etc.
   o  The second is the Operations network which addresses their
      backbone and access switches, and other hardware, this is separate
      for both engineering reasons as well as simplicity in managing the
      security of the backbone.
   o  The third is the IP addresses (single or blocks) that they assign
      to customers.  These can be registered addresses (usually given to
      category 5.1 and 5.2 and sometimes 5.3) or can be from a pool of
      RFC 1918 addresses used with NAT for single user connections.
      Therefore they can actually have two different NAT domains that
      are not connected (internal LAN and single user customers).

   When IPv6 NAP is utilized in these three domains then for the first
   category it will be possible to use the same solutions as described
   in Section 5.1.  The second domain of the ISP/carrier is the
   Operations network.  This environment tends to be a closed
   environment, and consequently communication can be done based on ULA
   addresses, however, in this environment, stable IPv6 Provider
   Independent addresses can be used in preference to ULA addresses.
   This would give a solid and scalable configuration with respect to a
   local IPv6 address plan.  By the usage of proper network edge
   filters, outside access to the closed environment can be avoided.
   The third is the IPv6 addresses that ISP/carrier network assign to
   customers.  These will typically be assigned with prefix lengths
   terminating on nibble boundaries to be consistent with the DNS PTR
   records.  As scarcity of IPv6 addresses is not a concern, it will be
   possible for the ISP to provide global routable IPv6 prefixes without
   a requirement for address translation.  An ISP may for commercial
   reasons still decide to restrict the capabilities of the end users by
   other means like traffic and/or route filtering etc.

   If the carrier network is a mobile provider, then IPv6 is encouraged
   in comparison with the combination of IPv4+NAT for 3GPP attached
   devices.  When looking in chapter 2.3 of RFC3314 'Recommendations for



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   IPv6 in 3GPP Standards' [15] it is found that the IPv6 WG recommends
   that one or more /64 prefixes should be assigned to each primary PDP
   context.  This will allow sufficient address space for a 3GPP-
   attached node to allocate privacy addresses and/or route to a multi-
   link subnet, and will discourage the use of NAT within 3GPP-attached
   devices.


6.  IPv6 Gap Analysis

   Like IPv4 and any major standards effort, IPv6 standardization work
   continues as deployments are ongoing.  This section discusses several
   topics for which additional standardization, or documentation of best
   practice, is required to fully realize the benefits of NAP.  None of
   these items are show-stoppers for immediate usage of NAP in roles
   where there are no current gaps.

6.1.  Subnet Topology Masking

   There really is no functional gap here as a centrally assigned pool
   of addresses in combination with host routes in the IGP is an
   effective way to mask topology.  If necessary a best practice
   document could be developed describing the interaction between DHCP
   and various IGPs which would in effect define Untraceable Addresses.

   As an alternative, some work in Mobile IP to define a policy message
   where a mobile node would learn from the Home Agent.  It should not
   try to inform its correspondent about route optimization and thereby
   expose its real location.  A border Home Agent using internal
   tunneling to the logical mobile node (potentially static) can
   completely mask all internal topology, while avoiding the strain from
   a large number of host routes in the IGP.  This work should be
   pursued in the IETF.

6.2.  Minimal Traceability of Privacy Addresses

   Privacy addresses (RFC 3041) may certainly be used to limit the
   traceability of external traffic flows back to specific hosts, but
   lacking a topology masking component above they would still reveal
   the subnet address bits.  For complete privacy a best practice
   document describing the combination of privacy addresses with
   topology masking may be required.  This work remains to be done, and
   should be pursued by the IETF.

6.3.  Renumbering Procedure

   Documentation of site renumbering procedures [12] is completed and is
   in the RFC-editor's queue.  It should also be noticed that ULAs may



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   help here too, since a change of ISP prefix will only affect hosts
   that need an externally routeable address as well as an ULA.

6.4.  Site Multihoming

   This complex problem has never been completely solved for IPv4, which
   is exactly why NAT has been used as a partial solution.  For IPv6,
   after several years' work, the IETF has converged on an architectural
   approach intended with service restoration as initial aim [20].
   Again, ULAs may help since they will provide stable addressing for
   internal communications that are not affected by multihoming.

6.5.  Untraceable Addresses

   The details of the untraceable addresses, along with any associated
   mechanisms such as route injection, must be worked out and specified.


7.  IANA Considerations

   This document requests no action by IANA


8.  Security Considerations

   While issues which are potentially security related are discussed
   throughout the document, the approaches herein do not introduce any
   new security concerns.  Product marketing departments have widely
   sold IPv4 NAT as a security tool and suppliers have been implementing
   address translation functionality in their firewalls, though the
   misleading nature of those claims has been previously documented in
   RFC 2663 [2] and RFC 2993 [4].

   This document defines IPv6 approaches which collectively achieve the
   goals of the network manager without the negative impact on
   applications or security that are inherent in a NAT approach.  To the
   degree that these techniques improve a network manager's ability to
   explicitly know about or control access, and thereby manage the
   overall attack exposure of local resources, they act to improve local
   network security.  In particular the explicit nature of a content
   aware firewall in NAP will be a vast security improvement over the
   NAT artifact where lack of translation state has been widely sold as
   a form of protection.


9.  Conclusion

   This document has described a number of techniques that may be



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   combined on an IPv6 site to protect the integrity of its network
   architecture.  These techniques, known collectively as Network
   Architecture Protection, retain the concept of a well defined
   boundary between "inside" and "outside" the private network, and
   allow firewalling, topology hiding, and privacy.  However, because
   they preserve address transparency where it is needed, they achieve
   these goals without the disadvantage of address translation.  Thus,
   Network Architecture Protection in IPv6 can provide the benefits of
   IPv4 Network Address Translation without the corresponding
   disadvantages.

   The document has also identified a few ongoing IETF work items that
   are needed to realize 100% of the benefits of NAP.


10.  Acknowledgements

   Christian Huitema has contributed during the initial round table to
   discuss the scope and goal of the document, while the European Union
   IST 6NET project acted as a catalyst for the work documented in this
   note.  Editorial comments and contributions have been received from:
   Fred Templin, Chao Luo, Pekka Savola, Tim Chown, Jeroen Massar,
   Salman Asadullah, Patrick Grossetete, Fred Baker, Jim Bound, Mark
   Smith, Alain Durand, John Spence, Christian Huitema, Mark Smith,
   Elwyn Davies, Daniel Senie, Soininen Jonne, Lindqvist Erik Kurt and
   other members of the v6ops WG.


11.  References

11.1.  Normative References

   [1]   Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E.
         Lear, "Address Allocation for Private Internets", BCP 5,
         RFC 1918, February 1996.

   [2]   Srisuresh, P. and M. Holdrege, "IP Network Address Translator
         (NAT) Terminology and Considerations", RFC 2663, August 1999.

   [3]   Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
         for IP Version 6 (IPv6)", RFC 2461, December 1998.

   [4]   Hain, T., "Architectural Implications of NAT", RFC 2993,
         November 2000.

   [5]   Srisuresh, P. and K. Egevang, "Traditional IP Network Address
         Translator (Traditional NAT)", RFC 3022, January 2001.




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   [6]   Holdrege, M. and P. Srisuresh, "Protocol Complications with the
         IP Network Address Translator", RFC 3027, January 2001.

   [7]   Narten, T. and R. Draves, "Privacy Extensions for Stateless
         Address Autoconfiguration in IPv6", RFC 3041, January 2001.

   [8]   IAB and IESG, "IAB/IESG Recommendations on IPv6 Address
         Allocations to Sites", RFC 3177, September 2001.

   [9]   Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
         Carney, "Dynamic Host Configuration Protocol for IPv6
         (DHCPv6)", RFC 3315, July 2003.

   [10]  Draves, R., "Default Address Selection for Internet Protocol
         version 6 (IPv6)", RFC 3484, February 2003.

   [11]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
         Configuration Protocol (DHCP) version 6", RFC 3633,
         December 2003.

   [12]  Baker, F., "Procedures for Renumbering an IPv6 Network without
         a Flag Day", draft-ietf-v6ops-renumbering-procedure-05 (work in
         progress), March 2005.

   [13]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
         Addresses", draft-ietf-ipv6-unique-local-addr-09 (work in
         progress), January 2005.

11.2.  Informative References

   [14]  Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter-
         Domain Routing (CIDR): an Address Assignment and Aggregation
         Strategy", RFC 1519, September 1993.

   [15]  Wasserman, M., "Recommendations for IPv6 in Third Generation
         Partnership Project (3GPP) Standards", RFC 3314,
         September 2002.

   [16]  Savola, P. and B. Haberman, "Embedding the Rendezvous Point
         (RP) Address in an IPv6 Multicast Address", RFC 3956,
         November 2004.

   [17]  Dupont, F. and P. Savola, "RFC 3041 Considered Harmful
         (draft-dupont-ipv6-    rfc3041harmful-05.txt)", June 2004.

   [18]  Chown, T., "IPv6 Implications for TCP/UDP Port Scanning (chown-
         v6ops- port-scanning-implications-01.txt)", July 2004.




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   [19]  Chown, T., Tompson, M., Ford, A., and S. Venaas, "Things to
         think about when Renumbering an IPv6 network
         (draft-chown-v6ops-renumber-thinkabout-03)", October 2004.

   [20]  Huston, G., "Architectural Commentary on Site Multi-homing
         using a Level 3 Shim  (draft-ietf-shim6-arch-00.txt)",
         July 2004.


Appendix A.  Additional Benefits due to Native IPv6 and Universal Unique
             Addressing

   The users of native IPv6 technology and global unique IPv6 addresses
   have the potential to make use of the enhanced IPv6 capabilities, in
   addition to the benefits offered by the IPv4 technology.

A.1.  Universal Any-to-Any Aonnectivity

   One of the original design points of the Internet was any-to-any
   connectivity.  The dramatic growth of Internet connected systems
   coupled with the limited address space of the IPv4 protocol spawned
   address conservation techniques.  NAT was introduced as a tool to
   reduce demand on the limited IPv4 address pool, but the side effect
   of the NAT technology was to remove the any-to-any connectivity
   capability.  By removing the need for address conservation (and
   therefore NAT), IPv6 returns the any-to-any connectivity model and
   removes the limitations on application developers.  With the freedom
   to innovate unconstrained by NAT traversal efforts, developers will
   be able to focus on new advanced network services (i.e. peer-to-peer
   applications, IPv6 embedded IPsec communication between two
   communicating devices, instant messaging, Internet telephony, etc..)
   rather than focusing on discovering and traversing the increasingly
   complex NAT environment.

   It will also allow application and service developers to rethink the
   security model involved with any-to-any connectivity, as the current
   edge firewall solution in IPv4 may not be sufficient for Any-to-any
   service models.

A.2.  Auto-configuration

   IPv6 offers a scalable approach to minimizing human interaction and
   device configuration.  Whereas IPv4 implementations require touching
   each end system to indicate the use of DHCP vs. a static address and
   management of a server with the pool size large enough for the
   potential number of connected devices, IPv6 uses an indication from
   the router to instruct the end systems to use DHCP or the stateless
   auto configuration approach supporting a virtually limitless number



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   of devices on the subnet.  This minimizes the number of systems that
   require human interaction as well as improves consistency between all
   the systems on a subnet.  In the case that there is no router to
   provide this indication, an address for use on the local link only
   will be derived from the interface media layer address.

A.3.  Native Multicast Services

   Multicast services in IPv4 were severely restricted by the limited
   address space available to use for group assignments and an implicit
   locally defined range for group membership.  IPv6 multicast corrects
   this situation by embedding explicit scope indications as well as
   expanding to 4 billion groups per scope.  In the source specific
   multicast case, this is further expanded to 4 billion groups per
   scope per subnet by embedding the 64 bits of subnet identifier into
   the multicast address.

   IPv6 allows also for innovative usage of the IPv6 address length, and
   makes it possible to embed the multicast 'Rendez-Vous Point' (or RP)
   [16] directly in the IPv6 multicast address when using ASM multicast.
   this is not possible with limited size of the IPv4 address.  This
   approach also simplifies the multicast model considerably, making it
   easier to understand and deploy.

A.4.  Increased Security Protection

   The security protection offered by native IPv6 technology is more
   advanced than IPv4 technology.  There are various transport
   mechanisms enhanced to allow a network to operate more securely with
   less performance impact:
   o  IPv6 has the IPsec technology directly embedded into the IPv6
      protocol.  This allows for simpler peer-to-peer encryption and
      authentication, once a simple key/trust management model is
      developed, while the usage of some other less secure mechanisms is
      avoided (i.e. md5 password hash for neighbor authentication).
   o  On a local network, any user will have more security awareness.
      This awareness will motivate the usage of simple firewall
      applications/devices to be inserted on the border between the
      external network and the local (or home network) as there is no
      Address Translater and hance no false safety perception.
   o  All flows on the Internet will be better traceable due to a unique
      and globally routable source and destination IPv6 address.  This
      may facilitate an easier methodology for back-tracing DoS attacks
      and avoid illegal access to network resources by simpler traffic
      filtering.
   o  The usage of private address-space in IPv6 is now provided by
      Unique Local Addresses, which will avoid conflict situations when
      merging networks and securing the internal communication on a



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      local network infrastructure due to simpler traffic filtering
      policy.
   o  The technology to enable source-routing on a network
      infrastructure has been enhanced to allow this feature to
      function, without impacting the processing power of intermediate
      network devices.  The only devices impacted with the source-
      routing will be the source and destination node and the
      intermediate source-routed nodes.  This impact behavior is
      different if IPv4 is used, because then all intermediate devices
      would have had to look into the source-route header.

A.5.  Mobility

   Anytime, anywhere, universal access requires MIPv6 services in
   support of mobile nodes.  While a Home Agent is required for initial
   connection establishment in either protocol version, IPv6 mobile
   nodes are able to optimize the path between them using the MIPv6
   option header while IPv4 mobile nodes are required to triangle route
   all packets.  In general terms this will minimize the network
   resources used and maximize the quality of the communication.

A.6.   Merging Networks

   When two IPv4 networks want to merge it is not guaranteed that both
   networks would be using different address-ranges on some parts of the
   network infrastructure due to the legitimate usage of RFC 1918
   private addressing.  This potential overlap in address space may
   complicate a merge of two and more networks dramatically due to the
   additional IPv4 renumbering effort. i.e. when the first network has a
   service running (NTP, DNS, DHCP, HTTP, etc..) which need to be
   accessed by the 2nd merging network.  Similar address conflicts can
   happen when two network devices from these merging networks want to
   communicate.

   With the usage of IPv6 the addressing overlap will not exist because
   of the existence of the Unique Local Address usage for private and
   local addressing.

A.7.  Community of interest

   Although some Internet-enabled devices will function as fully-fledged
   Internet hosts, it is believed that many will be operated in a highly
   restricted manner functioning largely or entirely within a Community
   of Interest.  By Community of Interest we mean a collection of hosts
   that are logically part of a group reflecting their ownership or
   function.  Typically, members of a Community of Interest need to
   communicate within the community but should not be generally
   accessible on the Internet.  They want the benefits of the



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   connectivity provided by the Internet, but do not want to be exposed
   to the rest of the world.  This functionality will be available
   through the usage of NAP and native IPv6 dataflows, without any
   stateful device in the middle.  It will also allow to build virtual
   organization networks on the fly, which is very difficult to do in
   IPv4+NAT scenarios.


Appendix B.  Revision history

B.1.  Changes from *-vandevelde-v6ops-nap-00 to
      *-vandevelde-v6ops-nap-01
   o  Document introduction has been revised and overview table added
   o  Comments and suggestions from nap-00 draft have been included.
   o  Initial section of -00 draft 2.6 and 4.6 have been aggregated into
      a new case study section 5.
   o  The list of additional IPv6 benefits has been been placed into
      appendix.
   o  new security considerations section added.
   o  GAP analysis revised.
   o  Section 2.6 and 4.6 have been included.

B.2.  Changes from *-vandevelde-v6ops-nap-01 to *-ietf-v6ops-nap-00
   o  Change of Draft name from *-vandevelde-v6ops-nap-01.txt to *-ietf-
      v6ops-nap-00.txt.
   o  Editorial changes.

B.3.  Changes from *-ietf-v6ops-nap-00 to *-ietf-v6ops-nap-01
   o  Added text in Chapter 2.2 and 4.2 to address more details on
      firewall and proxy
   o  Revised Eric Klein contact details
   o  Added note in 4.2 that control over the proposed statefull-filter
      should be by a simple user-interface

B.4.  Changes from *-ietf-v6ops-nap-01 to *-ietf-v6ops-nap-02
   o  General Note: Header more consistent capitelized.
   o  Section 1: para 3: s/...and privacy and will... translation./
      ...and privacy.  NAP will achieve these security goals without
      address transaltion whilst maintaining any-to-any connectivity./
   o  Section 1: Various editorial changes happened
   o  Section 2.1: Changed: 'Frequently a simple user interface is
      sufficient for configuring'. into 'Frequently a simple user
      interface, or no user interface is sufficient'
   o  Section 2.2: (Simple Security ) Better not to use the word -evil-
      in the text
   o  Section 2.2: changed 'provided by NAT are actually ' into
      'provided by NAT is actually'




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   o  Section 2.2: para 3: s/actually false/actually an illusion/
   o  Section 2.2: para 2: added 'Also it will only be reliable if a
      mechanism such as 'trusted computing' is implemented in the end-
      system; without this enhancement administrators will be unwilling
      to trust the behavior of end-systems.
   o  Section 2.3: para 1: s/of the NAT devices state/from the NAT
      device's state/
   o  Section 2.4: para1: clarified the definition of topology hiding
   o  Section 2.4: last sentence of next-to-last paragraph, added
      punctuation at end of sentence.
   o  Section 2.4: added first line: When mentioning 'topology hiding'
      the goal is to make a reference that an entity outside the network
      can not make a correlation between the location of a device and
      the address of a device on the local network.
   o  Section 2.4: para 1: s/reflected/represented/
   o  Section 2.5: last par: added reference: 'Section 2.7 describes
      some disadvantages that appear if independednt networks using
      [RFC1918] addresses have to be merged.'
   o  Section 2.6: Added text that private address-space is not
      limitless
   o  Section 2.6: Various editorial changes
   o  Section 2.7: Para 1 editorial revised
   o  Section 2.7: last para: s/This solution/The addition of an extra
      NAT as a solution/
   o  Section 2.7: s/highly desirable to be/highly desirable due to
      resiliency and load-balancing to be/
   o  Section 2.7: added text on the reason why there are overlapping
      addresses
   o  Section 2.7: last para: s/merged address space/overlapping address
      speaces in the merged networks/
   o  Section 3.1: Para 1 editorial changes
   o  Section 3.1: s/by contacted web sites, so IPv6/by web sites that
      are accessed from the device: IPv6 /
   o  Section 3.1: s/as that would have a serious negative impact on
      global routing/as that would have a negative effect on global
      route aggregation
   o  Section 3.2: s3.2: Par 1 editorial revised and noted that ULA in
      global routing table is not scalable
   o  Section 3.2: s3.2: Noted that it is not always interresting to mix
      ULA with global as that may lead to SAS issues
   o  Section 3.3: last para: s/delegating router/delegating router
      (incorporating a DHCPv6 server)/, s/across an administrative/
      possibly across an administrative/
   o  Section 3.4: Changed: 'random assignment has as purpose' to
      'random assignment has a purpose'
   o  Section 3.4: para 2: Replace first sentence with: 'The random
      assignment is intended to mislead the outside world about the
      structure of the local network.'



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   o  Section 3.4: para 2: s/there is a correlation/needs to maintain a
      correlation/
   o  Section 3.4: para 2: s/like a/such as a/
   o  Section 3.4: para 3: s/unpredictable/amorphous/, s/or from
      mapping/and from mapping of/
   o  Section 3.4: para 3: s/are reachable on/are allocated to devices
      on/
   o  Section 3.4: para 3: s/belonging to the same subnet next to each
      other/belonging to devices adjacent to each other on the same
      subnet/
   o  Section 3.4: s/aggregation device/indirection device/
   o  Section 4.1: splitted the 1 section up into 2 separate sections
   o  Section 4.1: s/ End node connections involving other nodes on the
      global Internet will always use the global IPv6 addresses [9]
      derived from this prefix delegation./ End node connections
      involving other nodes on the global Internet will always use the
      global IPv6 addresses [9] derived from this prefix delegation.  It
      should be noted that the policy table needs to be correctly set up
      so that true global prefixes are distinguished from ULAs and will
      be used for the source address in preference when the destination
      is not a ULA/
   o  Section 4.1: A more secure network environment can be established
      by having the referenced ULA addresses statically configured on
      the network devices as this decreases the dynamic aspects of the
      network, however the operational overhead is increased.
   o  Section 4.2:Added note that IID should be randomized for port-scan
      protection
   o  Section 4.2: Removed text: This is an automated procedure of
      sending Internet Control Message Protocol (ICMP) echo requests
      (also known as PINGs) to a range of IP addresses and recording
      replies.  This can enable an attacker to map the network.
   o  Section 4.2: paragraph beginning: "This simple rule...".  The
      first sentence in this paragraph was overly-long.  The sentence
      has been fragmented
   o  Section 4.2: para 1: s/similar as for an/similar to that of an/
   o  Section 4.2: para 1: s/Internet, and firewall and IDS systems are/
      Internet.  The use of firewall and Intrusion Detection Systems
      (IDS) is/
   o  Section 4.2: para 1: s/but has/but with/
   o  Section 4.2: para 1: s/end to end/end-to-end/
   o  Section 4.2: Item 3: s/amount/number/
   o  Section 4.2: Item 3: s/This goes from the assumption that the
      attacker has no/This protection is nullified if the attacker has/
   o  Section 4.2: para after Item 3: s/pose/offer/ (or provide).
   o  Section 4.2: para after Item 3: s/best- practices/best practices/
   o  Section 4.2: para after example firewall rules: s/create similar
      protection and security holes the typical IPv4 NAT device will
      offer/provide (non-)protection and create security holes similar



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      to those offered to a network using a typical IPv4 NAT device/
   o  Section 4.2: para next but one after firewall rules: s/What one
      does when topology probing is to get an idea of the available
      hosts/The intention of topology probing is to identify a selection
      of the available hosts/
   o  Section 4.2: s/This is directly the opposite of what IPv6 security
      best practices are trying to achieve./IPv6 security best practices
      will avoid this kind of illusory security but can only do this if
      correctly configured firewalls and IDS systems are used at the
      perimeter where some IPv4 networks have relied on NATs.
   o  Section 4.2: s/ It is recommended for site administrators to take
      [17] into consideration to achieve the expected goal./ It is
      recommended for site administrators to take [17] into
      consideration to achieve the expected goal.  This protection will
      also be nullified if IIDs are configured in a group near the start
      of the IID space./
   o  Section 4.2: Removed the example study and added complementiory
      text to describe a potential behavior
   o  Section 4.4: rewrite of the section to reduce the importance of
      the MIpv^ and tunneled solution
   o  Section 4.4: (Privacy and Topology Hiding) Mobile IP is suggested
      in the text, however text is added that any kind of tunneling
      should do the trick.
   o  Section 4.4: para 2: after 'As discussed above' inserted '(see
      Section 3.1)'
   o  Section 4.4: para 3: s/consolidated on/indirected via/
   o  Section 4.4: para 3: s/topololgy masked/each topology masked/
   o  Section 4.4: para 3: Expanded acronym COA
   o  Section 4.4: para 3: s/rack mounted/static/
   o  Section 4.4: Rephrasing of text happened in this section
   o  Section 4.5: change: "so that a NAT is not required" to: "so that
      IPv6 address translation is not required".
   o  Section 4.5: changed 'periodically to look' into 'to look
      periodically'
   o  Section 4.5: change: "2^64 hosts" to: "2^64 addresses".
   o  Section 4.5: Removed the statement '(or even defined)
   o  Section 4.6: last para: s/which will lead to the IPv4 practice/
      which will require the adoption of the IPv4 workaround/
   o  Section 4.6: s/the IPv4 constricting scenarios of multiple devices
      sharing a/the constriction of IPv4 scenarios where multiple devies
      are forced to share a/
   o  Section 4.7: s/as the zero-touch external/as an almost zero-touch
      external/
   o  Section 5: Replaced first three sentences with: In presenting
      these case studies we have chosen to consider categories of
      network divided first according to their function either as
      carrier/ISP networks or end user (such as enterprise) networks
      with the latter category broken down according to the number of



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      connected end hosts.
   o  Section 5: bullet points: s/connection/connected end hosts/
   o  Section 5.1: s/addressing independence/addressing independence
      when using IPv4/
   o  Section 5.1: last para: s/is only affecting/will only affect/
   o  Section 5.1: changed 'alloaction' into 'allocation'
   o  Section 5.1: changed: '(typically a one or' into '(typically one
      or'
   o  section 5.1: changed: s/allocation/assignment/ in one of the
      paragraphs
   o  section 5.2: para 1: s?is too long?is too long (very often just a
      /32 just giving a single address)?
   o  Section 5.4: (Case study: ISP networks) ULA usage for ISP/
      Carrier-grade networks is mentioned in the draft, while it was
      suggested that for these NW the PI addresses are already very
      stable and they should be qualified for setting up proper
      filtering -> removed ULA from this section.
   o  Section 5.4: changed 'intra- communication' into 'communication'
   o  Section 5.4: s/chapter 5.1/Section 5.1/
   o  Section 6.1: (Completion of work on ULAs) Text revision to reflect
      current state of ULA or remove the chapter?  Chapter removed ...
      ULA specification is in the RFC-editor queue.
   o  Section 6.3: (Minimal Traceability) Better to say "topology
      masking _may be_ required" instead of "is required", because
      whether this is needed or not is a value judgment.
   o  Section 6.4: (Renumbering Procedure) Renumbering procedure is in
      RFC queue.  The section corrected in the current state?
   o  Section 6.4: s/well solved/completely solved/
   o  In general the whole chapter 6 has been revised to reflect current
      status





















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Authors' Addresses

   Gunter Van de Velde
   Cisco Systems
   De Kleetlaan 6a
   Diegem  1831
   Belgium

   Phone: +32 2704 5473
   Email: gunter@cisco.com


   Tony Hain
   Cisco Systems
   500 108th Ave. NE
   Bellevue, Wa.
   USA

   Email: alh-ietf@tndh.net


   Ralph Droms
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Email: rdroms@cisco.com


   Brian Carpenter
   IBM Corporation
   Sauemerstrasse 4
   Rueschlikon,   8803
   Switzerland

   Email: brc@zurich.ibm.com


   Eric Klein
   Tel Aviv University
   Tel Aviv,
   Israel

   Phone:
   Email: ericlklein@softhome.net





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Acknowledgment

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