Network Working Group                                    G. Van de Velde
Internet-Draft                                                   T. Hain
Expires: January 1, 2007                                        R. Droms
                                                           Cisco Systems
                                                            B. Carpenter
                                                         IBM Corporation
                                                                E. Klein
                                                     Tel Aviv University
                                                           June 30, 2006

                  IPv6 Network Architecture Protection

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   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 address translation.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Perceived Benefits of NAT and its Impact on IPv4 . . . . . . .  7
     2.1.  Simple Gateway between Internet and Private Network  . . .  7
     2.2.  Simple Security due to Stateful Filter  Implementation . .  7
     2.3.  User/Application tracking  . . . . . . . . . . . . . . . .  8
     2.4.  Privacy and Topology Hiding  . . . . . . . . . . . . . . .  9
     2.5.  Independent Control of Addressing in a Private  Network  . 10
     2.6.  Global Address Pool Conservation . . . . . . . . . . . . . 10
     2.7.  Multihoming and Renumbering with NAT . . . . . . . . . . . 11
   3.  Description of the IPv6 Tools  . . . . . . . . . . . . . . . . 12
     3.1.  Privacy Addresses (RFC 3041) . . . . . . . . . . . . . . . 12
     3.2.  Unique Local Addresses . . . . . . . . . . . . . . . . . . 13
     3.3.  DHCPv6 Prefix Delegation . . . . . . . . . . . . . . . . . 14
     3.4.  Untraceable IPv6 Addresses . . . . . . . . . . . . . . . . 14
   4.  Using IPv6 Technology to Provide the Market Perceived
       Benefits of NAT  . . . . . . . . . . . . . . . . . . . . . . . 14
     4.1.  Simple Gateway between Internet and Internal Network . . . 14
     4.2.  IPv6 and Simple Security . . . . . . . . . . . . . . . . . 15
     4.3.  User/Application Tracking  . . . . . . . . . . . . . . . . 17
     4.4.  Privacy and Topology Hiding using IPv6 . . . . . . . . . . 17
     4.5.  Independent Control of Addressing in a Private  Network  . 20
     4.6.  Global Address Pool Conservation . . . . . . . . . . . . . 20
     4.7.  Multihoming and Renumbering  . . . . . . . . . . . . . . . 21
   5.  Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . 21
     5.1.  Medium/large private networks  . . . . . . . . . . . . . . 22
     5.2.  Small Private Networks . . . . . . . . . . . . . . . . . . 23
     5.3.  Single User Connection . . . . . . . . . . . . . . . . . . 25
     5.4.  ISP/Carrier Customer Networks  . . . . . . . . . . . . . . 25
   6.  IPv6 Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . 26
     6.1.  Simple Security  . . . . . . . . . . . . . . . . . . . . . 27
     6.2.  Subnet Topology Masking  . . . . . . . . . . . . . . . . . 27
     6.3.  Minimal Traceability of Privacy Addresses  . . . . . . . . 27
     6.4.  Site Multihoming . . . . . . . . . . . . . . . . . . . . . 28
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 28
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28
   9.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 28
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29

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     11.1. Normative References . . . . . . . . . . . . . . . . . . . 29
     11.2. Informative References . . . . . . . . . . . . . . . . . . 30
   Appendix A.  Additional Benefits due to Native IPv6 and
                Universal   Unique Addressing . . . . . . . . . . . . 31
     A.1.  Universal Any-to-Any Connectivity  . . . . . . . . . . . . 31
     A.2.  Auto-configuration . . . . . . . . . . . . . . . . . . . . 31
     A.3.  Native Multicast Services  . . . . . . . . . . . . . . . . 32
     A.4.  Increased Security Protection  . . . . . . . . . . . . . . 32
     A.5.  Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 33
     A.6.  Merging Networks . . . . . . . . . . . . . . . . . . . . . 33
     A.7.  Community of interest  . . . . . . . . . . . . . . . . . . 33
   Appendix B.  Revision history  . . . . . . . . . . . . . . . . . . 34
     B.1.  Changes from *-vandevelde-v6ops-nap-00 to
           *-vandevelde-v6ops-nap-01  . . . . . . . . . . . . . . . . 34
     B.2.  Changes from *-vandevelde-v6ops-nap-01 to
           *-ietf-v6ops-nap-00  . . . . . . . . . . . . . . . . . . . 34
     B.3.  Changes from *-ietf-v6ops-nap-00 to *-ietf-v6ops-nap-01  . 34
     B.4.  Changes from *-ietf-v6ops-nap-01 to *-ietf-v6ops-nap-02  . 34
     B.5.  Changes from *-ietf-v6ops-nap-02 to *-ietf-v6ops-nap-03  . 38
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
   Intellectual Property and Copyright Statements . . . . . . . . . . 42

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1.  Introduction

   There have been periodic claims that IPv6 will require a Network
   Address Translation (NAT), because in IPv4 people use NAT to
   accomplish that person's preferred task.  This document will explain
   why those pronouncements are false by showing how to accomplish the
   task goal without address translation.  Although there are many
   perceived benefits to NAT, its primary benefit of "amplifying"
   available address space is not needed in IPv6.  The serious
   disadvantages and impact on applications by ambiguous address space
   and Network Address Translation [1] [5] have been well documented [4]
   [6] so there will not be much additional discussion here.  However,
   given its wide deployment NAT undoubtedly has some perceived
   benefits, though the bulk of those using it have not evaluated the
   technical trade-offs.  Indeed, product marketing departments have
   effectively driven a perception that some connectivity and security
   concerns can only be solved by using a NAT device, without any
   mention of the negative impacts on applications.  This is amplified
   through the widespread sharing of vendor best practice documents and
   sample configurations that do not differentiate the translation
   function of address expansion from the state function of limiting

   This document describes the goals for utilizing a NAT device in an
   IPv4 environment that are regularly cited as solutions for perceived
   problems.  It then shows how these needs can be met without using the
   header modification feature of NAT in an IPv6 network.  It should be
   noted that this document is 'informational', as it discusses
   approaches that will work to accomplish the goals.  It is
   specifically not a BCP that is recommending any one approach.

   As far as security and privacy are concerned, this document considers
   how to mitigate a number of threats.  Some are obviously external,
   such as having a hacker or a worm infected machine outside trying to
   penetrate and attack the local network.  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 from within.  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

   Another consideration discussed is the view that NAT can be used to
   fulfill the goals of a security policy.  At a technical level the
   translation process fundamentally can not produce security because
   mangling the address in the header does not fulfill any useful
   security functions; in fact it breaks the ability to produce an audit
   trail which is a fundamental security tool.  That said, the artifacts

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   of NAT devices do provide some value.
   1.  The need to establish state before anything gets through from
       outside to inside solves one set of problems.
   2.  The need to stop receiving any packets when finished with a flow
       solves a set of problems
   3.  the need to appear to be attached at the edge of the network
       solves a set of problems
   4.  and the ability to have addresses that are not publicly routed
       solves yet another set (mostly changes where the state is and
       scale requirements for the first one).

   This document describes several techniques that may be combined in an
   IPv6 deployment to protect the integrity of its network architecture.
   It will focus on the 'how to accomplish a goal' perspective, leaving
   most of the 'why that goal' perspective for other documents.  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 regaining the ability for arbitrary any-
   to-any connectivity.

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

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          Goal                 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    |
   |                  |  see section 2.4      |  see section 4.4      |
   |  Addressing      |  RFC 1918             |  RFC 3177 & 4193      |
   |  Autonomy        |  see section 2.5      |  see section 4.5      |
   |  Global Address  |  RFC 1918             |  17*10^18 subnets     |
   |  Pool            |  << 2^48 application  |  3.4*10^38 addresses  |
   |  Conservation    |  end points           | full port list / addr |
   |                  |  topology restricted  | unrestricted topology |
   |                  |  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
   concludes with a IPv6 NAP case study and a gap analysis of work that

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   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.  The goal of this description is not to
   analyze these benefits or 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 addresses allocated
   from any part of the space (ambiguous [RFC 1918] or global registered
   & unregistered address) towards the Internet, though extra effort is
   needed when the same range exists on both sides of the NAT.  The
   address space of the private network can be built from globally
   unique addresses, from ambiguous address space or from both
   simultaneously.  In the simple case of private use addresses, 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 located in the public Internet.

   Wide-scale deployments have shown that using NAT to act as a simple
   gateway attaching 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.

   This simplicity comes at a price as the resulting topology puts
   restrictions on applications.  The NAT simplicity works well when the
   applications are limited to a client/server model with the server
   deployed on the public side of the NAT.  For peer-to-peer, multi-
   party, or servers deployed on the private side of the NAT, helper
   technologies must be available.  These helper technologies are
   frequently complex to develop and manage, creating a hidden cost to
   this 'simple gateway'.

2.2.  Simple Security due to Stateful Filter  Implementation

   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 specific host on any other
   port, though in the port overload case of NAPT attacking all active

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   ports will impact a potentially wide number of hosts.  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.

   The act of 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 of NAT 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.  This role, often marketed as a
   firewall, is really an arbitrary artifact while a real firewall has
   explicit management controls.

   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 or otherwise use the
   same public port this complexity shifts from difficult to impossible.

2.3.  User/Application tracking

   One usage of NAT is for the local network administrator to track user
   and application traffic.  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 access to which Internet location.
   This is done by periodically logging the network address translation
   details of the private and the public addresses from the NAT device's
   state database.

   The subsequent 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 a private IPv4-address and a network element or user at all
   times, or the administrator has a time-correlated list of the
   address/port mappings.

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2.4.  Privacy and Topology Hiding

   One goal of 'topology hiding' is to prevent external entities from
   making a correlation between the topological location of devices 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

   The use of NAT then results in a user behind a NAT gateway actually
   appearing from 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 so all internal nodes appear to exist
   at the demarcation edge.  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 systems 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, where the adversary does not need to
   scan the entire local network but can instead concentrate on the
   active ports associated with the NAT adress.  By periodically
   scanning the limited 16 bit port range on the public side of the NAT,
   the attack will routinely find all ports that are open to active

   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 network managers prefer to hide as much as possible of their
   internal network topology from outsiders as a useful precaution to
   mitigate scanning attacks.  Mostly this is achieved by blocking
   "traceroute" etc., though NAT entirely hides the internal subnet
   topology.  Scanning is a particular concern in IPv4 networks because
   the subnet size is small enough that once the topology is known it is
   easy to find all the hosts, then start scanning them for vulnerable
   ports.  Once a list of available devices 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

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   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 access to an end
   system to command it to start initiating attacks on others.

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 sufficiently large pool for a clean and
   hierarchical addressing structure in the local 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

   While the widespread use of IPv4+NAT has reduced the potential
   consumption rate, the ongoing depletion of the IPv4 address range has
   already taken the remaining pool of unallocated IPv4 addresses below
   25%.  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 the private use address-space is strictly limited
   in size.  Some deployments have already outgrown that space and have
   begun cascading NAT to continue expanding, though this practice
   eventually breaks down over routing ambiguity.  Additionally, while
   we are unlikely to know the full extent of the practice (because it
   is hidden behind a nat), service providers have been known to
   announce previously unallocated public space to their customers (to
   avoid the problems associated with the same address space appearing
   on both sides), only to find that once that space was formally

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   allocated and being publicly announced their customers couldn't reach
   the registered networks.

   The number of and types of applications that can be deployed by these
   ISPs and their customers is restricted by the ability to overload the
   port range on the public side of the most public NAT in the path.
   The limit of this approach is something substantially less than 2^48
   possible active **application** endpoints (approximately [2^32 minus
   2^29] * [2* 2^16 minus well known port space]), as distinct from
   addressable devices each with their own application endpoint range.
   Those who advocate layering of NAT frequently forget to mention that
   there are topology restrictions placed on the applications.  Forced
   into this limiting situation such customers can rightly claim that
   despite the optimistic predictions of mathematical models, the global
   pool of IPv4 addresses is effectively already exhausted.

2.7.  Multihoming and Renumbering with NAT

   Allowing a network to be multihomed and renumbering a network are
   quite different functions.  However these are argued together as
   reasons for using NAT, because 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
   [15] 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 spaces in the
   merged networks.

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3.  Description of the IPv6 Tools

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

   The reader must clearly distinguish between features of IPv6 that
   were fully defined when this document was drafted and those that were
   potential features that still required more work to define them.  The
   latter are summarized later in the 'Gap Analysis' section of this
   document.  However, we do not distinguish in this document between
   fully defined features of IPv6 and those that were already widely
   implemented at the time of writing.

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
   as it moves around the Internet.  IPv6 privacy addresses were defined
   to provide that capability.  IPv6 addresses consist of a routing
   prefix, subnet-id part (SID) and an interface identifier part (IID).
   As originally defined, IPv6 stateless address auto-configuration
   (SLAAC) will typically embed the IEEE Link Identifier of the
   interface as the IID part, though this practice facilitates tracking
   and profiling of a device through the consistent IID.  RFC 3041 [7]
   describes an extension to SLAAC to enhance device privacy.  Use of
   the privacy address extension causes nodes to generate global-scope
   addresses from interface identifiers that change over time,
   consistent with system administrator policy.  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 auto-
   configuration, there is nothing that prevents a DHCP server from
   running the RFC 3041 algorithm for any new IEEE identifier it hears
   in a request, then remembering that for future queries.  This would
   allow using them in DNS for registered services since the assumption
   of a DHCP 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

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   Randomizing the IID, as defined in RFC 3041, is effectively a sparse
   allocation technique which 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 [18].

3.2.  Unique Local Addresses

   Achieving the goal of autonomy, that many perceive as a value of NAT,
   is required for local network and application services stability
   during periods of intermittent connectivity or moving between one or
   more providers.  Such autonomy in a single routing prefix environment
   would lead to massive expansion of the global routing tables (as seen
   in IPv4), so IPv6 provides for simultaneous use of multiple prefixes.
   The Unique Local Address prefix (ULA) [14] 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
   as large scale inter-domain distribution of routes for ULA prefixes
   would have a negative impact on global route aggregation.

   ULAs have the following characteristics:
   o  For all practical purposes a globally unique prefix
      *  Allows networks to be combined or privately interconnected
         without creating 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 only intermittent Internet
   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 may need to
      distinguish between ULAs and ordinary global scope unicast
      addresses to assure stability.  The policy table defined in [10]
      is one way to bias this selection, by giving higher preference to
      FC00::/7 over 2001::/3.  Mixing the two kinds of addresses may
      lead to undeliverable packets during times of instability, but
      that mixing is not likely to happen when the rules of RFC 3484 are

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3.3.  DHCPv6 Prefix Delegation

   One of the functions of a simple gateway is managing the local use
   address range.  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 (possibly 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

   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
   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.

   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.  For smaller deployments this correlation
   could be done by generating IPv6 host route entries, or for larger
   ones by utilizing an indirection device such as a Mobile IPv6 Home
   Agent.  Additional details are in section 4.7.

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

   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 should have a default
   configuration to advertise inside the site a locally generated random
   ULA prefix, independently from the state of any external

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   connectivity.  This would allow local nodes to communicate amongst
   themselves independent of the state of a global connection.  If the
   network happened to concatenate with another local network, the
   randomness in ULA creation is highly unlikely to result in address

   With external connectivity the simple gateway should 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 derived from this prefix delegation.  It should be noted
   that the address selection policy table in end-systems defined in RFC
   3484 should be configured to prefer the ULA prefix range over the
   DHCP-PD prefix range when the goal is to keep local communications
   stable during periods of transient external connectivity.

   In the very simple case there is no explicit routing protocol on
   either side of the gateway, and a single default route is used
   internally pointing out to the global Internet.  A slightly more
   complex case might involve local internal 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 the service
   provider could install a route for the prefix delegated via DHCP-PD
   pointing toward the connecting link.

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
   Intrusion Detection Systems (IDS) is recommended for those that want
   boundary protection in addition to host defenses.  A proxy may be
   used for certain applications, but with the caveat that the end to
   end transparency 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 its
       lifetime becomes invalid.
   2.  IPsec is a mandatory service for IPv6 implementations.  IPsec
       functions to authenticate the correspondent, prevent session
       hijacking, prevent content tampering, and optionally masks the
       packet contents.  While IPsec might be available in IPv4
       implementations and works the same way, 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 a complete subnet ping sweep virtually impossible
       due to the potential number of combinations available.  Reducing

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       the security threat of port scans on identified nodes requires
       sparse distribution within the subnet to minimize the probability
       of scans finding adjacent nodes.  Provided that IIDs are
       essentially randomly distributed across the available space,
       address scanning based attacks will effectively fail.  This
       protection exists if the attacker has no direct access to the
       specific subnet and therefore is trying to scan it remotely.  If
       an attacker has local access then he could use ND [3] and ping6
       to the link-scope multicast ff02::1 to detect the IEEE based
       address of local neighbors, then apply the global prefix to those
       to simplify its search (of course, a locally connected attacker
       has many scanning options with IPv4 as well).  This scanning
       protection will be nullified if IIDs are configured in any
       structured groupings within the IID space.

   Assuming the network administrator is aware of [19] 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 full-duplex 40Gbps (400 times the typical
   100Mbps LAN, and 13,000 times the typical DSL/Cable access link) it
   takes over 5000 years to scan the entirety of a single 64 bit subnet.

   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
   address the same threats if correctly configured firewalls and IDS
   systems are used at the perimeter.

            It must be noted that even a firewall doesn't fully secure
            a network. 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.

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   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 where incoming traffic is limited to return
   traffic resulting from outgoing packets (sometimes known as
   reflective session state).  There should also be an easy interface
   which allows users to create inbound 'pinholes' for specific purposes
   such as online-gaming.  Another consideration would be the capability
   for service provider mediated pinhole management where things like
   voice call signaling could dynamically establish pinholes based on
   predefined authentication rules.

   Administrators and the designers of configuration interfaces for
   simple IPv6 firewalls need to provide a means of documenting the
   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 without increasing
   the perceived complexity for users who just want to accomplish a

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.

   At the same time, this tracking is per address.  In environments
   where the goal is tracking back to the user, additional external
   information will be necessary correlating a user with an address.  In
   the case of short lifetime privacy address usage, this external
   information will need to be based on more stable information such as
   the layer 2 media address.

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.
   This only allows such a session to be traced back to the subnet that
   originates it, but not immediately to the actual host, where IPv4 NAT
   is only traceable to the most public NAT interface.

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   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, with the cost being a more complex internal routing

   As discussed in Section 3.1, there are multiple parts to the IPv6
   address, and different techniques to manage privacy for each which
   may be combined to protect the entire address.  In the case where a
   network administrator wishes to fully isolate the internal IPv6
   topology, and the majority of its internal use addresses, one option
   is to run all internal traffic using Unique Local Addresses (ULA).
   By definition this prefix block is not to be advertised into the
   public routing system, so without a routing path external traffic
   will never reach the site.  For the set of hosts that do in fact need
   to interact externally, by using multiple IPv6 prefixes (ULAs and one
   or more global addresses) all of the internal nodes that do not need
   external connectivity, and the internally used addresses of those
   that do will be masked from the outside.  The policy table defined in
   [10] provides a mechanism to bias the selection process when multiple
   prefixes are in use such that the ULA would be preferred when the
   correspondent is also local.

   There are other scenarios for the extreme situation when a network
   manager also wishes to fully conceal the internal IPv6 topology.  In
   these cases the goal in replacing the IPv4 NAT approach is to make
   all of the topology hidden nodes appear from the outside to logically
   exist at the edge of the network, just as they would when behind a

   o  One approach uses explicit host routes in the IGP to remove the
      external correlation between physical topology attachment point
      and end-to-end IPv6 address.  In the figure below the hosts would
      be allocated prefixes from one or more logical subnets, and would
      inject host routes to internally identify their real attachment
      point.  This solution does however show severe scalability issues
      and requires hosts to participate in the IGP, as well as having
      the firewall block all external to internal traceroute for the
      logical subnet.  The specific limitations are dependent on the IGP
      protocol, the physical topology, and the stability of the system.
      In any case the approach should be limited to uses with
      substantially fewer than the maximum number of routes that the IGP

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      can support (generally between 5,000 and 50,000 total entries
      including subnet routes).
   o  Another technical approach to fully hide the internal topology is
      use of a tunneling mechanism.  Mobile IPv6 without route
      optimization is one approach for using an automated tunnel, as it
      always starts in tunnel mode via the Home Agent (HA).  In this
      deployment model the application perceived addresses of the nodes
      are routed via the edge HA.  This indirection method truly masks
      the internal topology, as from outside the local network all nodes
      with global access appear to share the prefix of one or more
      logical subnets attached to the HA rather than their real
      attachment point.  While turning off all binding updates would
      appear to be necessary to prevent leakage of topology information,
      that approach would also force all internal traffic using the home
      address to route via the HA tunnel, which may be undesirable.  A
      more efficient method would be to allow internal route
      optimizations while dropping outbound binding updates at the
      firewall.  Another approach for the internal routes would be to
      use the policy table of RFC 3484 to bias a ULA prefix as preferred
      internally, leaving the Home Address external for use.  The
      downsides of using the MIPv6 tunneling method is that it makes
      usage of middleware like a Home Agent (HA) and consumes slightly
      more bandwidth for the tunnel overhead.
   o  Another method (where the layer 2 topology allows) uses a virtual
      lan approach to logically attach the devices to one or more
      subnets on the edge router.  The downsides of this approach is
      that all internal traffic would be directed over sub-optimal paths
      via the edge router, as well as the complexity of managing a
      distributed logical lan.

                       | Simple Gateway   |-+-+-+-+-+-+-+-+--
                       |  or Home Agent   |  Logical subnets
                       |                  |-+-+-+-+-+-+-+-+--
                       +------------------+  for topology
                                 |           hidden nodes
               Real internal  -------------+-
               topology       |            |
                              |           -+----------

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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 because nodes that need access to the public
   Internet will have a global use address as well.  When using IPv6,
   the need to ask for more address space will become far less likely
   due to the increased size of the subnets, along with an allocation
   policy that recognizes table fragmentation is also an important
   consideration.  While global IPv6 allocation policy is managed
   through the Regional Internet Registries, it is expected that they
   will continue with derivatives of [8] for the foreseeable future so
   the number of subnet prefixes available to an organization should not
   be a limitation which would create an artificial demand for NAT.

   Ongoing subnet address maintenance may become simpler when IPv6
   technology is utilized.  Under IPv4 address space policy restrictions
   each subnet must be optimized, so one has to look periodically into
   the number of hosts on a segment and the subnet size allocated to the
   segment and rebalance.  For example an enterprise today may have a
   mix of IPv4 /28 - /23 size subnets, and may shrink/grow these as
   their network user base changes.  For IPv6 all subnets have /64
   prefixes which will reduce the operational and configuration

4.6.  Global Address Pool Conservation

   IPv6 provides sufficient space to completely avoid the need for
   overlapping address space.  Since allocations in IPv6 are based on
   subnets rather than hosts a reasonable way to look at the pool is
   that there are about 17*10^18 unique subnet values where sparse
   allocation practice within those provides for new opportunities such
   as SEND 3971 [12].  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

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   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 through
   a NAT.

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 allocated
   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 regard to multiple addresses
   therefore does not apply to IPv6.  IPv6 sites can and do run today
   with multiple ISPs active, and the processes for adding, removing,
   and renumbering active prefixes at a site have been documented in
   [13] and [20].

   The IPv6 address space allocated by the ISP will be dependent upon
   the connecting Service provider.  This will likely result in a
   renumbering effort when the network changes between service
   providers.  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 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 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)

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   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, academic, research, or government
   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 in IPv4 one
   avoids the expensive process of 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.  The goal of this assignment mechanism is to
   decrease the total amount of entries in the public Internet routing
   table.  A single /48 allocation provides an enterprise network with
   65536 different /64 subnet prefixes.

   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 time-limited 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 specific host on the inside
   network.  The usage of IPv6 privacy extensions does not mask the
   internal network structure of an enterprise network.

   When 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 appear to exist at the external edge
   of the network, and may be assigned to those hosts for which topology

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   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 or static configuration.  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 'host based
   route- injection' in the local 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.

   An alternative for larger deployments is to leverage the tunneling
   aspect of MIPv6 even for non-mobile devices.  With the logical subnet
   being allocated as attached to the edge Home Agent, the real
   attachment and internal topology are masked from the outside.
   Dropping outbound binding updates at the firewall is also necessary
   to avoid leaking the attachment information.

   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 which will complicate auditing systems.  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.

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

   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

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   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 external
   access to a server, only one server can be mapped per protocol/
   port-number per address, and then only when the address from the ISP
   is publicly routed.  When there is an upstream NAT providing private
   address space to the ISP side of the private NAT, additional
   negotiation with the ISP will be necessary to provide an inbound
   mapping, if that is even possible.

   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
   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

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   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 it will be likely that
   the single device wants to mask its identity to the called party or
   its attack profile over a shorter time window than the life of the
   ISP attachment, so 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.).

   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 IP access and transport services.  They tend to have three
   separate IP domains that they support:

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   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 IPv4 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.  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
   IPv6 in 3GPP Standards' [16] 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

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

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   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.  Simple Security

   Dynamic pinhole management is an area for further study.  Several
   partial solutions exist including ICE, UPNP, as well as alternative
   proposals for Service Provider based control.  The 'simple' aspect of
   the security provided by a stateful firewall will require some degree
   of automation to mask the technical complexity from the consumer that
   only wants a secure environment with working applications.

6.2.  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 for smaller deployments.  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 for larger deployments, there is no gap in the HA
   tunneling approach when firewalls are configured to block outbound
   binding update messages.  A border Home Agent using internal
   tunneling to the logical mobile node (potentially rack mounted) can
   completely mask all internal topology, while avoiding the strain from
   a large number of host routes in the IGP.  Some optimization work
   could be done in Mobile IP to define a policy message where a mobile
   node would learn from the Home Agent that it should not try to inform
   its correspondent about route optimization and thereby expose its
   real location.  This optimization which reduces the load on the
   firewall would result in less optimal internal traffic routing as
   that would also transit the HA.  Trade-off's for this optimization
   work should be investigated in the IETF.

6.3.  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.

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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 of work, the IETF has converged on an
   architectural approach intended with service restoration as initial
   aim [21].  When this document was drafted, the IETF was actively
   defining the details of this approach to the multihoming problem.
   The approach appears to be most suitable for small and medium sites,
   though it will conflict with firewall state procedures.  At this time
   there are also active discussions in the address registries
   investigating the possibility of assigning provider-independent
   address space.  Their challenge is finding a reasonable metric for
   limiting the number of organizations that would qualify for a global
   routing entry.  Additional work appears to be necessary to satisfy
   the entire range of requirements.

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
   [2] and [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 audit 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

   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]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
         Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [13]  Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering
         an IPv6 Network without a Flag Day", RFC 4192, September 2005.

   [14]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
         Addresses", RFC 4193, October 2005.

11.2.  Informative References

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

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

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

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

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

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   [20]  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.

   [21]  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 Connectivity

   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 only on the local link
   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 'Rendezvous Point' (or RP)
   [17] 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 authentication and
      encryption, 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 Translator and hence 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
   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
   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 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 from the public Internet.  They want the benefits of the
   connectivity provided by the Internet, but do not want to be exposed

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   to the rest of the world.  The ability in NAP to virtualize the
   topology and mask portions of it is applied to the community,
   creating arbitrary groupings.  It will also allow building 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
   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 placed into
   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 *-
   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 capitalized.
   o  Section 1: para 3: s/...and privacy and will... translation./
      ...and privacy.  NAP will achieve these security goals without
      address translation 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 independent networks using
      [RFC1918] addresses have to be merged.'
   o  Section 2.6: Added text that private address-space is not
   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
   o  Section 2.7: last para: s/merged address space/overlapping address
      spaces 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 interesting 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
   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
   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
   o  Section 3.4: s/aggregation device/indirection device/
   o  Section 4.1: split 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 complementary
      text to describe a potential behavior
   o  Section 4.4: rewrite of the section to reduce the importance of
      the MIPv6 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
   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
      devices are forced to share a/
   o  Section 4.7: s/as the zero-touch external/as an almost zero-touch
   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 'allocation' into 'allocation'
   o  Section 5.1: changed: '(typically a one or' into '(typically one
   o  section 5.1: changed: s/allocation/assignment/ in one of the
   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

B.5.  Changes from *-ietf-v6ops-nap-02 to *-ietf-v6ops-nap-03
   o  Editorial changes in response to IESG review comments and
   o  Introduction: clarified impact & goal for limited additional NAT
      discussion here / modified tone wrt marketing / grammar cleanup
   o  Introduction: s/market acceptance/deployment
   o  Introduction: noted that users do not evaluate technical trade-
      offs and that marketing does not mention the downside of address
   o  Introduction: added paragraph about why nat != security
   o  Table1: s/benefit/Goal/ s/ULA/4193/ removed long numeric string /
      added app end points & number of subnets
   o  Section 2: tone reduction about marketing
   o  Section 2.1: grammar cleanup / clarified point about use of public
      space / added paragraph about topology restrictions / removed last
      paragraph about security

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   o  Section 2.2: moved paragraph about firewalls to 4.2 / deleted
      discussion about distributed security / clarified point about port
   o  Section 2.3: Added opening sentence to explain the goal of the
      section / changed comment about theory to an absolute / qualified
      logging and checking times
   o  Section 2.4: deleted confusing/redundant comments about identifier
      / clarified point about nodes appearing to be at the edge / added
      clarification that focused scanning on the port range reaches
      active nodes
   o  Section 2.5: clarified that the reason for autonomy is large space
      & impact was on the local network
   o  Section 2.6: clarified point about reduction of IPv4 consumption
      rate / s/30%/25% / added point about limitations of cascaded nat /
      added para about limited app endpoints as well as topology
   o  Section 2.7: clarification about why multihoming & renumbering are
      discussed together / point about sparse allocation / s/speaces/
   o  Section 3: s/emulate/replace / added para about 'gaps' being
      discussed later
   o  Section 3.1: Cleaned up description of SLAAC & 3041 / specified
      server as DHCP / added comment about sparse allocation
   o  Section 3.2: grammar cleanup / updated reference from ID to RFC
      4193 / added point about policy table in 3484 to bias ULA over ISP
   o  Section 3.3: Clarification about goal for section
   o  Section 3.4: reorder paragraphs to put goal up front
   o  Section 4.1: s/could/should/ s/prior to establishing/independent
      of the state of / clarified why concatenation would not collide /
      another comment about the 3484 table for ULA biasing / clarified
      point about lack of routing protocol
   o  Section 4.2: clarified point about firewall at boundary /
      clarified point about valid lifetime / clarified point that IPsec
      works the same w/o NAT / added point about authenticating
      correspondent / clarified that the scanning threat is addresses as
      ports are the same once an address is known / rearranged paragraph
      to keep scanning thread together / inserted firewall discussion
      moved from 2.2 / clarified role of simple firewall / added comment
      about service provider mediated pinhole management
   o  Section 4.3: added paragraph about tracking privacy address use
   o  Section 4.4: clarified point about tracking wrt NAT / added
      comment about IGP complexity / s/conceal/isolate/ s/possible/
      potential/ reworded ULA description which was technically
      backwards / additional description of the goal / added picture and
      referenced it from descriptions converted options to descriptive
      list / added discussion about blocking binding updates / added
      vlan option / s/would be to use/uses to make it clear this already

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      works / para 2 s/prefixes/addresses and replaced last part of the
      sentence to clarify what was being hidden.
   o  Section 4.5: Grammar cleanup / clarification about policy
   o  Section 4.6: replaced long number string with power qnty of
      subnets / added reference to new capabilities like SEND
   o  Section 4.7: s/CIDR-like/CIDR allocated/ s/this/to multiple
      addresses/ s/may/will likely/ s/if/when/ s/from SP/between sp/
      Updated reference for renumbering proceedure to RFC 4192
   o  Section 5: d/of these/
   o  Section 5.1: s/private enterprise/private enterprise, academic,
      research, or government / deleted redundant discussion about /48
      allocation / added discussion about larger deployments using
      tunneling /
   o  Section 5.2: clarification of overload on port vs. protocol /
      added comment about upstream NAT / clarified 3041 use as short
   o  Section 5.3: capitalize Internet
   o  Section 5.4: s/IPv4/IP as role is not version specific / deleted
      comment about preference to ULA.
   o  Section 6.1: (security) inserted section discussing need for
      dynamic pinhole management
   o  Section 6.2: (topology mask) added comment about deployment scale
      / added comment about firewall blocking BU / clarified point about
      future work being an optimization to reduce firewall load
   o  Section 6.3: (tracability) grammar cleanup
   o  Section 6.4: (renumbering) Cut section since it is no longer a gap
   o  Section A.2: word order - moved 'only'
   o  Section A.6: deleted 'legitimate'
   o  Section A.7: clarified how NAP delivers community of interest
   o  Spell check

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Authors' Addresses

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

   Phone: +32 2704 5473

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


   Ralph Droms
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719


   Brian Carpenter
   IBM Corporation
   Sauemerstrasse 4
   Rueschlikon,   8803


   Eric Klein
   Tel Aviv University
   Tel Aviv,


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