IPv6 Deployment Status

Document Type Active Internet-Draft (v6ops WG)
Authors Giuseppe Fioccola  , Paolo Volpato  , Nalini Elkins  , Gyan Mishra  , Chongfeng Xie 
Last updated 2021-04-08 (latest revision 2021-04-07)
Replaces draft-vf-v6ops-ipv6-deployment
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V6OPS                                                        G. Fioccola
Internet-Draft                                                P. Volpato
Intended status: Informational                       Huawei Technologies
Expires: October 9, 2021                                       N. Elkins
                                                         Inside Products
                                                               G. Mishra
                                                            Verizon Inc.
                                                                  C. Xie
                                                           China Telecom
                                                           April 7, 2021

                         IPv6 Deployment Status


   Looking globally, IPv6 is growing faster than IPv4 and this means
   that the collective wisdom of the networking industry has selected
   IPv6 for the future.  This document provides an overview of IPv6
   transition deployment status and a view on how the transition to IPv6
   is progressing among network operators and enterprises that are
   introducing IPv6 or have already adopted an IPv6-only solution.  It
   also aims to analyze the transition challenges and therefore
   encourage actions and more investigations on some areas that are
   still under discussion.  The overall IPv6 incentives are also

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 9, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  IPv4 Adress Exhaustion  . . . . . . . . . . . . . . . . . . .   4
   3.  The global picture of IPv6  . . . . . . . . . . . . . . . . .   5
     3.1.  IPv6 users  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  IPv6 allocations and networks . . . . . . . . . . . . . .   5
   4.  Survey among Network Operators  . . . . . . . . . . . . . . .   7
   5.  Considerations for Enterprises  . . . . . . . . . . . . . . .   8
   6.  Observations on Content and Cloud Service Providers . . . . .   8
   7.  Industrial Internet application . . . . . . . . . . . . . . .   8
   8.  IPv6 deployments worldwide  . . . . . . . . . . . . . . . . .   9
     8.1.  IPv6 service design for Mobile, Fixed broadband and
           enterprises . . . . . . . . . . . . . . . . . . . . . . .   9
       8.1.1.  IPv6 introduction . . . . . . . . . . . . . . . . . .   9
       8.1.2.  IPv6-only service delivery  . . . . . . . . . . . . .  10
   9.  Findings of the IPv6 Survey . . . . . . . . . . . . . . . . .  11
   10. IPv6 incentives . . . . . . . . . . . . . . . . . . . . . . .  12
   11. Call for action . . . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  Transition choices . . . . . . . . . . . . . . . . . . .  13
       11.1.1.  Service providers  . . . . . . . . . . . . . . . . .  13
       11.1.2.  Enterprises  . . . . . . . . . . . . . . . . . . . .  14
       11.1.3.  Cloud and Data Centers . . . . . . . . . . . . . . .  16
       11.1.4.  Industrial Internet  . . . . . . . . . . . . . . . .  16
       11.1.5.  Government and Regulators  . . . . . . . . . . . . .  17
     11.2.  Network Operations . . . . . . . . . . . . . . . . . . .  17
     11.3.  Performance  . . . . . . . . . . . . . . . . . . . . . .  18
       11.3.1.  IPv6 latency . . . . . . . . . . . . . . . . . . . .  18

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       11.3.2.  IPv6 packet loss . . . . . . . . . . . . . . . . . .  18
       11.3.3.  Router's performance . . . . . . . . . . . . . . . .  19
     11.4.  IPv6 security  . . . . . . . . . . . . . . . . . . . . .  19
       11.4.1.  Protocols security issues  . . . . . . . . . . . . .  20
       11.4.2.  IPv6 Extension Headers and Fragmentation . . . . . .  21
       11.4.3.  Oversized IPv6 packets . . . . . . . . . . . . . . .  21
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  22
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  22
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     16.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Appendix A.  Summary of Questionnaire and Replies . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   The focus of this document is to provide a survey of the deployed
   IPv6 transition technologies and to highlight the difficulties in the
   transition.  This process helps to understand what is missing and how
   to improve the current IPv6 deployment strategies of network
   operators, enterprises, content and cloud service providers.  The
   objective is to give an updated view of the practices and plans
   already described in [RFC6036].  The scope is to report the current
   IPv6 status and encourage actions and more investigations on some
   areas that are still under discussion as well as the main incentives
   for the IPv6 adoption.

   [RFC6180] discussed the IPv6 deployment models and migration tools.
   [RFC6036] described the Service Provider Scenarios for IPv6
   Deployment, [RFC7381] introduced the guidelines of the IPv6
   deployment for Enterprise and [RFC6883] provided guidance and
   suggestions for Internet Content Providers and Application Service
   Providers.  On the other hand, this document focuses on the end-to-
   end services and in particular on the device - network - content
   communication chain.

   [ETSI-IP6-WhitePaper] reported the IPv6 Best Practices, Benefits,
   Transition Challenges and the Way Forward.  IPv6 is becoming a
   priority again and a new wave of IPv6 deployment is expected, due the
   exhaustion of the IPv4 address space since 2010, in addition
   technologies like 5G, cloud, IoT require its use, governments and
   standard bodies (including IETF) demand it, and the device - network
   - content communication chain is calling for its adoption.  In this
   regard it is possible to mention the IAB Statement on IPv6 stating
   that "IETF will stop requiring IPv4 compatibility in new or extended

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   The following sections go through the issue of IPv4 address
   exhaustion and give the global picture of IPv6 to show how IPv6 is
   growing faster than IPv4 worldwide in all measures including number
   of users, percentage of content, and amount of traffic.  This
   testifies that the key Internet industry players have decided
   strategically to invest and deploy IPv6 in large-scale to sustain the
   Internet growth.

   Then it is presented the survey among network operators as well as
   considerations and observations for enterprises and content and cloud
   service providers about the IPv6 deployment and the considerations
   that have come out.  IPv6 transition solutions for Mobile BroadBand
   (MBB), Fixed BroadBand (FBB) and enterprise services are ready.
   Dual-Stack is the most deployed solution for IPv6 introduction, while
   464XLAT and Dual Stack Lite (DS-Lite) seem the most suitable for
   IPv6-only service delivery.

   Finally, The IPv6 incentives are presented but the general IPv6
   challenges are also reported in particular in relation to
   Architecture, Operations, Performance and Security issues.  These
   considerations aim to start a call for action on the areas of
   improvement, that are often mentioned as reason for not deploying

2.  IPv4 Adress Exhaustion

   According to [CAIR] there will be 29.3 billion networked devices by
   2023, up from 18.4 billion in 2018.  This poses the question on
   whether the IPv4 address space can sustain such a number of
   allocations and, consequently, if this is affecting the process of
   its exhaustion.  The answer is not straightforward as many aspects
   have to be considered.

   On the one hand, the RIRs are reporting scarcity of available and
   still reserved addresses.  Table 3 of [POTAROO1] shows that the
   available pool of the five RIRs counts a little more than 6 million
   IPv4 address, while the reserved pool includes another 12 million,
   for a total of "usable" addresses equal to 18.3 million.  The same
   reference, in table 1, shows that the total IPv4 allocated pool
   equals 3.684 billion addresses.  The ratio between the "usable"
   addresses and the total allocated brings to 0.005% of remaining

   On the other, [POTAROO1] again highlights the role of both NAT and
   the address transfer to counter the IPv4 exhaustion.  NAT systems
   well fit in the current client/server model used by most of the
   available Internet applications, with this phenomenon amplified by
   the general shift to cloud.  The transfer of IPv4 addresses also

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   contributes to mitigate the the need of addresses.  As an example,
   [IGP-GT] shows the amount of transfers to recipient organizations in
   the ARIN region in 2018.  Cloud Service Providers (CSPs) appear to be
   the most active is buying available addresses to satisfy their need
   of providing IPv4 connectivity to their tenants.

3.  The global picture of IPv6

   The utilization of IPv6 has been monitored by many agencies and
   institutions worldwide.  Different analytics have been made
   available, ranging from the number of IPv6 users, its relative
   utilization over the Internet, to the number of carriers able to
   route IPv6 network prefixes.  [ETSI-IP6-WhitePaper] provided several
   of those analytics.  The scope of this section then is to summarize
   the status of the IPv6 adoption, so to get an indication of the
   relevance of IPv6 today.  For the analytics listed here, the trend
   over the past five years is given, expressed as the Compound Annual
   Growth Rate (CAGR).  In general, this shows how IPv6 has grown in the
   past few years, and that is growing faster than IPv4.

3.1.  IPv6 users

   [ETSI-IP6-WhitePaper] provided the main statistics about the
   utilization of IPv6 worldwide and references the organizations that
   make their measurement publicly available through their web sites.
   To give a rough estimation of the relative growth of IPv6, the next
   table shows the total number of estimated IPv6 users at December 2020
   as measured by [POTAROO2], [APNIC1].

   |        |  Dec  |  Dec  |  Dec   |  Dec   |  Dec   |  CAGR  |
   |        |  2016 |  2017 |  2018  |  2019  |  2020  |        |
   | World  | 300.85| 473.14| 543.04 | 990.19 |1,201.09|   41%  |

               Figure 1: IPv6 users worldwide (in millions)

3.2.  IPv6 allocations and networks

   Regional Internet Registries (RIRs) are responsible for assigning an
   IPv6 address block to ISPs or enterprises.  An ISP will use the
   assigned block to provide addresses to their end users.  For example,
   a mobile carrier will assign one or several /64 prefixes to the end
   users.  Several analytics are available for the RIRs.  The next table
   shows the amount of individual allocations, per RIR, in the time
   period 2016-2020 [APNIC2].

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   | Registry|  Dec  |  Dec  |  Dec  |  Dec  |  Dec  |Cumulated| CAGR |
   |         |  2016 |  2017 |  2018 |  2019 |  2020 |         |      |
   | AFRINIC |   116 |   112 |   110 |   115 |   109 |    562  | 48%  |
   |  APNIC  | 1,681 | 1,369 | 1,474 | 1,484 | 1,498 |  7,506  | 45%  |
   |   ARIN  |   646 |   684 |   659 |   605 |   644 |  3,238  | 50%  |
   |  LACNIC | 1,009 | 1,549 | 1,448 | 1,614 | 1,801 |  7,421  | 65%  |
   | RIPE NCC| 2,141 | 2,051 | 2,620 | 3,104 | 1,403 | 11,319  | 52%  |
   |         |       |       |       |       |       |         |      |
   |  Total  | 5,593 | 5,765 | 6,311 | 6,922 | 5,455 | 30,046  | 52%  |

                   Figure 2: IPv6 allocations worldwide

   Note that the decline in 2020 of IPv6 allocations from the RIPE NCC
   could be explained with the COVID-19 measures that affect many
   European countries.  Anyway countries all over the world have been
   similarly affected, but the decline in IPv6 allocation activity in
   2020 is only seen in the data from the RIPE NCC.

   [APNIC2] also compares the number of allocations for both address
   families, and the result is in favor of IPv6.  The average yearly
   growth is 52% for IPv6 in the period 2016-2020 versus 49% for IPv4, a
   sign that IPv6 is growing bigger than IPv4.  This is described in the
   next table.

   | Address| Dec  | Dec  |  Dec   |  Dec   |  Dec  | Cumulated | CAGR |
   | family | 2016 | 2017 |  2018  |  2019  |  2020 |           |      |
   |  IPv6  | 5,593| 5,765|  6,311 |  6,922 | 5,455 |   30,046  | 52%  |
   |        |      |      |        |        |       |           |      |
   |  IPv4  |10,515| 9,437| 10,192 | 14,019 | 7,437 |   51,600  | 49%  |
   |        |      |      |        |        |       |           |      |

                 Figure 3: Allocations per address family

   The next table is based on [APNIC3], [APNIC4] and shows the
   percentage of ASes supporting IPv6 compared to the total ASes
   worldwide.  The number of IPv6-capable ASes increases from 22.6% in
   January 2017 to 30.4% in January 2021.  This equals to 14% CAGR for
   IPv6 enabled networks.  This also shows that the number of networks
   supporting IPv6 is growing faster than the ones supporting IPv4,
   since the total (IPv6 and IPv4) networks grow at 6% CAGR.

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   | Advertised |  Jan  |  Jan  |  Jan  |  Jan  |  Jan  | CAGR |
   |    ASN     |  2017 |  2018 |  2019 |  2020 |  2021 |      |
   |IPv6-capable| 12,700| 14,500| 16,470| 18,600| 21,400|  14% |
   |            |       |       |       |       |       |      |
   | Total ASN  | 56,100| 59,700| 63,100| 66,800| 70,400|   6% |
   |            |       |       |       |       |       |      |
   |   Ratio    | 22.6% | 24.3% | 26.1% | 27.8% | 30.4% |      |

                 Figure 4: Percentage of IPv6-capable ASes

4.  Survey among Network Operators

   It was started an IPv6 poll to more than 50 network operators about
   the status of IPv6 deployment.  This poll reveals that more than 30
   operators will migrate fixed and mobile users to IPv6 in next 2
   years.  The IPv6 Poll has been submitted in particular to network
   operators considering that, as showed by the previous section, both
   user devices and contents seem more ready for IPv6.  The answers to
   the questionnaire can be found in Appendix.

   The main Questions asked are:

      * Do you plan to move more fixed or mobile or enterprise users to
      IPv6  (e.g.  Dual-Stack) or IPv6-only in the next 2 years?  What
      are the reasons to do so?  Which transition solution will you use,
      Dual-Stack, DS-Lite, 464XLAT, MAP-T/E?

      * Do you need to change network devices for the above goal?  Will
      you migrate your metro or backbone or backhaul network to support

   The result of this questionnaire highlights that major IPv6 migration
   will happen in next 2 years.  Dual Stack is always the most adopted
   solution and the transition to IPv6-only is motivated in particular
   by business reasons like the 5G and IoT requirements.  In addition it
   is worth mentioning that the migration of transport network (metro
   and backbone) is not considered a priority today for many network
   operators and the focus is in particular on the end to end IPv6

   More details about the answers received can be found in the Appendix.

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5.  Considerations for Enterprises

   As described in [RFC7381], enterprises face different challenges than
   operators.  The overall problem for many enterprises is to handle
   IPv6-based connectivity to the upstream providers, while supporting a
   mixed IPv4/IPv6 domain in the internal network.

   The business reasons for IPv6 is unique to each enterprise especially
   for the internal network.  But the most common drivers are on the
   external network due to the fact that when Internet service
   providers, run out of IPv4 addresses, they will provide native IPv6
   and non-native IPv4.  So for client networks trying to reach
   enterprise networks, the IPv6 experience will be better than the
   transitional IPv4 if the enterprise deploys IPv6 in its public-facing
   services.  Enterprise that is or will be expanding into emerging
   markets or that partners with other companies who use IPv6 (larger
   enterprise, governments, service providers) has to deploy IPv6 or
   plan to do in the near term to support the long term goals.  As an
   example it is possible to mention the emerging energy market and in
   partiuclar SmartGrid where high density of IP-enabled endpoints are
   needed and IPv6 is a key technology.

6.  Observations on Content and Cloud Service Providers

   The number of addresses required to connect all of the virtual and
   physical elements in a Data Center and the necessity to overcome the
   limitation posed by [RFC1918] has been the driver to adopt IPv6 in
   several Content and Cloud Service Provider (CSP) networks.

   Several public references discuss how most of the major players find
   themselves at different stages in the transition to IPv6-only in
   their DC infrastructure.  In some cases, the transition already
   happened and the DC infrastructure of these hyperscalers is
   completely based on IPv6.  This can be considered a good sign because
   the end-to-end connectivity between a client (e.g. an application on
   a smartphone) and a server (a Virtual Machine in a DC) may be based
   on IPv6.

7.  Industrial Internet application

   There are potential advantages for implementing IPv6 for IIoT
   (Industrial Internet of Things) applications, in particular the large
   IPv6 address space, the automatic IPv6 configuration and resource

   However, there are still many obstacles that prevent its pervasive
   use.  The key problems identified are the incomplete or immature tool
   support, the dependency on manual configuration and the poor

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   knowledge of the IPv6 protocols among insiders.  To advance and ease
   the use of IPv6 for smart manufacturing systems and IIoT applications
   in general, a generic approach to remove these pain points is
   therefore highly desirable.

8.  IPv6 deployments worldwide

   This section reports the most deployed approaches for the IPv6
   migration in MBB, FBB and enterprise.

8.1.  IPv6 service design for Mobile, Fixed broadband and enterprises

   The consolidated strategy, as also described in
   [ETSI-IP6-WhitePaper], is based on two stages, namely: (1) IPv6
   introduction, and (2) IPv6-only.  The first stage aims at delivering
   the service in a controlled manner, where the traffic volume of
   IPv6-based services is minimal.  When the service conditions change,
   e.g.  when the traffic grows beyond a certain threshold, then the
   move to the second stage may occur.  In this latter case, the service
   is delivered solely on IPv6.

8.1.1.  IPv6 introduction

   In order to enable the deployment of an IPv6 service over an underlay
   IPv4 architecture, there are two possible approaches:

   o  Enabling Dual-Stack at the CPE

   o  Tunneling IPv6 traffic over IPv4, e.g. with 6rd.

   So, from a technical perspective, the first stage is based on Dual-
   Stack [RFC4213] or tunnel-based mechanisms such as Generic Routing
   Encapsulation (GRE), IPv6 Rapid Deployment (6rd), Connection of IPv6
   Domains via IPv4 Clouds (6to4), and others.

   Dual-Stack [RFC4213] is more robust, and easier to troubleshoot and
   support.  Based on information provided by operators with the answers
   to the poll (see Appendix A), it can be stated that Dual-Stack is
   currently the most widely deployed IPv6 solution, for MBB, FBB and
   enterprises, accounting for about 50% of all IPv6 deployments, see
   both Appendix A and the statistics reported in [ETSI-IP6-WhitePaper].
   Therefore, for operators that are willing to introduce IPv6 the most
   common approach is to apply the Dual-Stack transition solution.

   With Dual-Stack, IPv6 can be introduced together with other network
   upgrade and many parts of network management and IT systems can still
   work in IPv4.  This avoids major upgrade of such systems to support
   IPv6, which is possibly the most difficult task in IPv6 transition.

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   In other words, the cost and effort on the network management and IT
   system upgrade are moderate.  The benefits are to start to
   accommodate future services and save the NAT costs.

   The CPE has only an IPv6 address at the WAN side and uses an IPv6
   connection to the operator gateway, e.g.  Broadband Network Gateway
   (BNG) or Packet Gateway (PGW) / User Plane Function (UPF).  However,
   the hosts and content servers can still be IPv4 and/or IPv6.  For
   example, NAT64 can enable IPv6 hosts to access IPv4 servers.  The
   backbone network underlay can also be IPv4 or IPv6.

   Although the Dual-Stack IPv6 transition is a good solution to be
   followed in the IPv6 introduction stage, it does have few
   disadvantages in the long run, like the duplication of the network
   resources and states, as well as other limitations for network
   operation.  For this reason, when IPv6 increases to a certain limit,
   it would be better to switch to the IPv6-only stage.

8.1.2.  IPv6-only service delivery

   The second stage, named here IPv6-only, can be a complex decision
   that depends on several factors, such as economic factors, policy and
   government regulation.

   [I-D.lmhp-v6ops-transition-comparison] discusses and compares the
   technical merits of the most common transition solutions for
   IPv6-only service delivery, 464XLAT, DS-lite, Lightweight 4over6
   (lw4o6), MAP-E, and MAP-T, but without providing an explicit
   recommendation.  As the poll highlights, the most widely deployed
   IPv6 transition solution for MBB is 464XLAT and for FBB is DS-Lite.

   Based on the survey among network operators in Appendix A it is
   possible to analyze the IPv6 transition technologies that are already
   deployed or that will be deployed.  The different answers to the
   questionnaire and in particular [ETSI-IP6-WhitePaper] reported
   detailed statistics on that and it can be stated that, besides Dual-
   Stack, the most widely deployed IPv6 transition solution for MBB is
   464XLAT [RFC6877], and for FBB is DS-Lite [RFC6333], both of which
   are IPv6-only solutions.

   Looking at the different feedback from network operators, in some
   cases, even when using private addresses, such as space
   [RFC1918], the address pool is not large enough, e.g. for large
   mobile operators or large Data Centers (DCs), Dual-Stack is not
   enough, because it still requires IPv4 addresses to be assigned.
   Also, Dual-Stack will likely lead to duplication of several network
   operations both in IPv6 and IPv4 and this increases the amount of
   state information in the network with a waste of resources.  For this

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   reason, in some scenarios (e.g.  MBB or DCs) IPv6-only stage could be
   more efficient from the start since the IPv6 introduction phase with
   Dual-Stack may consume more resources (for example CGNAT costs).

   So, in general, it is possible to state that, when the Dual-Stack
   disadvantages outweigh the IPv6-only complexity, it makes sense to
   migrate to IPv6-only.  Some network operators already started this
   process, while others are still waiting.

9.  Findings of the IPv6 Survey

   Global IPv4 address depletion is reported by most network operators
   as the important driver for IPv6 deployment.  Indeed, the main reason
   for IPv6 deployment given is related to the run out of private space [RFC1918].  5G and IoT service deployment is another
   incentive not only for business reasons but also for the need of more

   The answers in Appendix shows that the IPv6 deployment strategy is
   based mainly on Dual Stack architecture and most of the network
   operators are migrating or plan to migrate in the next few years.
   The main motivation is related to the depletion of IPv4 addresses and
   to save the NAT costs.

   It is interesting to see that most of the network operators have no
   big plans to migrate transport network (metro and backbone) soon,
   since they do not see business reasons.  It seems that there is no
   pressure to migrate to native IPv6 forwarding in the short term,
   anyway the future benefit of IPv6 may justify in the long term a
   migration to native IPv6.  Some network operators also said that a
   software upgrade can be enough to support IPv6 where it is needed for

   This survey demonstrates that full replacement of IPv4 will take long
   time.  Indeed the transition to IPv6 has different impacts and
   requirements depending on the network segment:

   o  It is possible to say that almost all mobile devices are already
      IPv6 capable while for fixed access most of the CPEs are Dual
      Stack.  Data Centers are also evolving and deploying IPv6 to cope
      with the increasing demand of cloud services.

   o  While the access network seems not strongly impacted because it is
      mainly based on layer 2 traffic, regarding Edge and BNG, most
      network operators that provide IPv6 connectivity runs BNG devices
      in Dual Stack in order to distribute both IPv4 and IPv6.

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   o  For Metro and Backbone, the trend is to keep MPLS Data Plane and
      run IPv6/IPv4 over PE devices at the border.  All MPLS services
      can be guaranteed in IPv6 as well through 6PE/6VPE protocols.

   In this scenario it is clear that the complete deployment of a full
   IPv6 data plane will take more time.  If we look at the long term
   evolution, IPv6 can bring other advantages like introducing advanced
   protocols developed only on IPv6 (e.g.  SRv6) to implement all the
   controlled SLA services aimed by the 5G technology and beyond.

10.  IPv6 incentives

   It is possible to state that IPv6 adoption is no longer optional,
   indeed there are several incentives for the IPv6 deployment:

      Technical incentives: all Internet technical standard bodies and
      network equipment vendors have endorsed IPv6 and view it as the
      standards-based solution to the IPv4 address shortage.  The IETF,
      as well as other SDOs, need to ensure that their standards do not
      assume IPv4.  The IAB expects that the IETF will stop requiring
      IPv4 compatibility in new or extended protocols.  Future IETF
      protocol work will then optimize for and depend on IPv6.  It is
      recommended that all networking standards assume the use of IPv6
      and be written so they do not require IPv4 ([RFC6540]).  In
      addition, every Internet registry worldwide strongly recommends
      immediate IPv6 adoption.

      Business incentives: with the emergence of new digital
      technologies, such as 5G, IOT and Cloud, new use cases have come
      into being and posed more new requirements for IPv6 deployment.
      Over time, numerous technical and economic stop-gap measures have
      been developed in an attempt to extend the lifetime of IPv4, but
      all of these measures add cost and complexity to network
      infrastructure and raise significant barriers to innovation.  It
      is widely recognized that full transition to IPv6 is the only
      viable option to ensure future growth and innovation in Internet
      technology and services.  Several large networks and Data Centers
      have already evolved their internal infrastructures to be
      IPv6-only.  Forward looking large corporations are also working
      toward migrating their enterprise networks to IPv6-only

      Governments incentives: governments have a huge responsibility in
      promoting IPv6 deployment within their countries.  There are
      example of governments already adopting policies to encourage IPv6
      utilization or enforce increased security on IPv4.  So, even
      without funding the IPv6 transition, governments can recommend to
      add IPv6 compatibility for every connectivity, service or products

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      bid.  This will encourage the network operators and vendors who
      don't want to miss out on government related bids to evolve their
      infrastructure to be IPv6 capable.  Any public incentives for
      technical evolution will be bonded to IPv6 capabilities of the
      technology itself.  In this regard, in the United States, the
      Office of Management and Budget is calling for an implementation
      plan to have 80% of the IP-enabled resources on Federal networks
      be IPv6-only by 2025.  If resources cannot be converted, then the
      Federal agency is required to have a plan to retire them.  The
      Call for Comment is at [US-FR] and [US-CIO].

11.  Call for action

   There are some areas of improvement, that are often mentioned in the
   literature and during the discussions on IPv6 deployment.  This
   section lists these topics and wants to start a call for action to
   encourage more investigations on these aspects.

11.1.  Transition choices

   From an architectural perspective, a service provider or an
   enterprise may perceive quite a complex task the transition to IPv6,
   due to the many technical alternatives available and the changes
   required in management and operations.  Moreover, the choice of the
   method to support the transition may depend on factors specific to
   the operator's or the enterprise's context, such as the IPv6 network
   design that fits the service requirements, the deployment strategy,
   and the service and network operations.

   This section briefly highlights the basic approaches that service
   providers and enterprises may take.  The scope is to raise the
   discussion whether actions may be taken that allow to overcome the
   issues highlighted and further push the adoption of IPv6.

11.1.1.  Service providers

   For a service provider, the IPv6 transition often refers to the
   service architecture (also referred to as overlay) and not to the
   network architecture (underlay).  IPv6 is introduced at the service
   layer when a service requiring IPv6-based connectivity is deployed in
   an IPv4-based network.  In this case, as already mentioned in the
   previous sections, a strategy is based on two stages: IPv6
   introduction and IPv6-only.

   For fixed operators, the massive CPE software upgrade to support Dual
   Stack started in most of service providers network and the traffic
   percentage is currently between 30% and 40% of IPv6, looking at the
   global statistics.  This is valid for a network operator that

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   provides Dual Stack and gives the same opportunity for end terminal
   applications to choose freely the path that they want and assuming a
   normal internet usage.  Anyway, it is interesting to see that in the
   latest years all major content providers have already implemented
   dual stack access to their services and most of them have implemented
   IPv6-only in their Data Centers.  This aspect could affect the
   decision on the IPv6 adoption for an operator, but there are also
   other aspects like the current IPv4 addressing status, CPE costs,
   CGNAT costs and so on.  Most operators already understood the need to
   adopt IPv6 in their networks and services, and also to promote the
   diffusion into their clients, while others are still at the edge of a
   massive implementation decision.  Indeed, two situations are

      Operators that have already employed CGNAT and have introduced
      IPv6 in their networks, so they remain attached to a Dual Stack
      architecture.  Although IPv6 brought them to a more technological
      advanced state, CGNAT, on the other end, boosts for some time
      their ability to supply CPE IPv4 connectivity.

      Operators with a Dual Stack architecture that have introduced IPv6
      both in the backbone and for the CPEs, but when reaching the limit
      in terms of number of IPv4 addresses available, they need to start
      defining and start to apply a new strategy that can be through
      CGNAT or with an IPv6-only approach.

   For mobile operators, the situation is different since they are
   stretching their IPv4 address space since CGNAT translation levels
   have been reached and no more IPv4 public pool addresses are
   available.  The new requirements from IoT services, 5G 3GPP release
   implementations, Voice over Long-Term Evolution (VoLTE) together with
   the constraints of national regulator lawful interception are seen as
   major drivers for IPv6.  For these reasons, two situations are

      Some mobile operators choose to implement Dual-Stack as first and
      immediate mitigation solution.

      Other mobile operators prefer to move to IPv6-only solution(e.g.
      464XLAT) since Dual-Stack only mitigates and does not solve
      completely the IPv4 number scarcity issue.

11.1.2.  Enterprises

   The dual stage approach described in the previous sections can be
   still applicable for enterprises, even if the priorities to apply
   either stage are different since they have to consider both the
   internal and external network:

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      It is possible to start with Dual-Stack on hosts/OS and then in
      client network distribution layer.  This allows the IPv6
      introduction independently since both hosts/OS and client networks
      belong to the domain of the enterprise.

      Dual-Stack can be further extended to WAN/campus core/edge
      routers.  Also, as temporary solution, the use of NAT64 is
      recommended for servers/apps only capable of IPv4.  Enterprise
      Data Center is also to be considered for the IPv6 transition.  In
      this regard the application support needs to be taken into
      account, even if virtualization should make DCs simpler and more

      There are additional challenges also related to the campus network
      and the cloud interconnection, indeed the networking may be not
      homogeneous.  IPv6 could help to build a flat network by
      leveraging SD-WAN integration.  The perspective of IPv6-only could
      also ensure better end-to-end performance.

   Enterprises (private, managed networks) in US and Europe have failed
   to adopt IPv6, especially on internal networks.  Other countries, in
   particular in Asia, who faced a shortage of IPv4 addresses, have
   moved somewhat more quickly.  But, even there, the large "brick-and-
   mortar" enterprises find no business reason to adopt IPv6.

   The enterprise engineers and technicians also don't know how IPv6
   works.  The technicians want to get trained yet the management does
   not feel that they do not want to pay for such training because they
   do not see a business need for adoption.  This creates an unfortunate
   cycle where misinformation about the complexity of the IPv6 protocol
   and unreasonable fears about security and manageability combine with
   the perceived lack of urgent business needs to prevent adoption of

   In 2019 and 2020, there has been a concerted effort by some grass
   roots non-profits working with ARIN and APNIC to provide training

   Having said that, some problems such as the problem of application
   conversion from IPv6 are quite difficult.  The reliance of the
   economic, governmental, and military enterprise organizations on
   computer applications is great; the number of legacy systems, and
   ossification at such organizations, is also great.  A number of
   mission-critical computer applications were written in the 1970's.
   While they have the source code, no one at the enterprise may be
   familiar with the application nor do they have the funds for external
   resources.  So, transitioning to IPv6 is quite difficult.

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   The problem may be that of "First Mover Disadvantage".
   Understandably, corporations, having responsibility to their
   stockholders, have upgraded to new technologies and architectures,
   such as IPv6, only if it gains them revenue.  Thus, legacy programs
   and technical debt accumulate.

11.1.3.  Cloud and Data Centers

   It was already highlighted how CSPs have adopted IPv6 in their
   internal infrastructure but are also active in gathering IPv4
   addresses on the transfer market to serve the current business needs
   of IPv4 connectivity.  This is primarily directed to serve the
   transition to cloud of enterprise's applications.

   As noted in the previous section, most enterprises do not consider
   the transition to IPv6 as a priority.  To this extent, the use of
   IPv4-based network services by the CSPs will last.  Yet, CSPs are
   struggling to buy IPv4 addresses.  If, in the next years, the
   scarcity of IPv4 addresses becomes more evident, it is likely that
   the cost of buying an IPv4 address by a CSP will be charged to an
   enterprise as a fee.  From a financial standpoint this effect might
   be taken into consideration when evaluating the decision of moving to

11.1.4.  Industrial Internet

   As the most promising protocol for network applications, IPv6 is
   frequently mentioned in relation to Internet of Things and Industry
   4.0.  However, its industrial adoption, in particular in smart
   manufacturing systems, has been much slower than expected.  Indeed,
   it is important to provide an easy way to familiarize system
   architects and software developers with the IPv6 protocol and its
   role in the application development life cycle in order to limit the
   dependency on manual configuration and improve the tool support.

   It is possible to differentiate types of data and access to
   understand how and where the IPv6 transition can happen.  In the
   control network, determinism is required with full operational
   visibility and control, as well as reliability and availability.  In
   monitoring IoT, best effort can be acceptable and low OPEX, zero-
   touch functions autoconfiguration, zero-configuration.  For
   diagnostics and alerts, trust and transmissions that do not impact
   the control network are needed.  For safety, guarantees in terms of
   redundancy, latency similar to the control network but with total
   assurance, is necessary.

   For IIoT applications, it would be desirable to be able to implement
   a truly distributed system without dependencies to central components

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   like a DHCP server.  In this regard the distributed IIoT applications
   can leverage the configuration-less characteristic of IPv6 and in
   this regard all the possible problems and compatibility issues with
   IPv6 link local addresses, SLAAC (StateLess Address Auto
   Configuration) needs to be investigated.

   In addition, it could be interesting to have the ability to use IP
   based communication and standard application protocols at every point
   in the production process and further reduce the use of specialized
   communication systems like PLCs (Programmable Logic Controllers) and
   fieldbuses for real-time control to subsystems where this is
   absolutely necessary.

11.1.5.  Government and Regulators

   The slogan should be "stimulate if you can, regulate if you must".
   The global picture shows that the deployment of IPv6 worldwide is not
   uniform at all [G_stats], [APNIC1].  Countries where either market
   conditions or local regulators have stimulated the adoption of IPv6
   show clear sign of growth.

   As an example, zooming into the European Union area, countries such
   as Belgium, France and Germany are well ahead in terms of IPv6
   adoption.  The French National Regulator, Arcep, can be considered a
   good reference of National support to IPv6.  [ARCEP] introduced an
   obligation for the operators awarded with a license to use 5G
   frequencies (3.4-3.8GHz) in Metropolitan France to be IPv6
   compatible.  As stated, "the goal is to ensure that services are
   interoperable and to remove obstacles to using services that are only
   available in IPv6, as the number of devices in use continues to soar,
   and because the RIPE NCC has run out of IPv4 addresses".  A slow
   adoption of IPv6 could prevent new Internet services to widespread or
   create a barrier to entry for newcomers to the market. "IPv6 can help
   to increase competition in the telecom industry, and help to
   industrialize a country for specific vertical sectors".

   A renewed industrial policy might be advocated in other countries and
   regions to stimulate IPv6 adoption.  As an example, in the United
   States, the Office of Management and Budget is also calling for IPv6
   adoption [US-FR], [US-CIO].

11.2.  Network Operations

   An important factor is represented by the need for training the
   network operations workforce.  Deploying IPv6 requires it as policies
   and procedures have to be adjusted in order to successfully plan and
   complete an IPv6 migration.  Staff has to be aware of the best
   practices for managing IPv4 and IPv6 assets.  In addition to network

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   nodes, network management applications and equipment need to be
   properly configured and in same cases also replaced.  This may
   introduce more complexity and costs for the migration.

11.3.  Performance

   Despite their relative differences, people tend to compare the
   performance of IPv6 versus IPv4, even if these differences are not so
   important for applications.  In some cases, IPv6 behaving "worse"
   than IPv4 tends to re-enforce the justification of not moving towards
   the full adoption of IPv6.  This position is supported when looking
   at available analytics on two critical parameters: packet loss and
   latency.  These parameters have been constantly monitored over time,
   but only a few extensive researches and measurement campaigns are
   currently providing up-to-date information.  This paragraph will look
   briefly at both of them, considering the available measurements.
   Operators are invited to bring in their experience and enrich the
   information reported below.

11.3.1.  IPv6 latency

   [APNIC5] constantly compares the latency of both address families.
   Currently, the worldwide average is still in favor of IPv4.  Zooming
   at the country or even at the operator level, it is possible to get
   more detailed information and appreciate that cases exist where IPv6
   is faster than IPv4.  [APRICOT] highlights how when a difference in
   performance exists it is often related to asymmetric routing issues.
   Other possible explanations for a relative latency difference lays on
   the specificity of the IPv6 header which allows packet fragmentation.
   In turn, this means that hardware needs to spend cycles to analyze
   all of the header sections and when it is not capable of handling one
   of them it drops the packet.  Even considering this, a difference in
   latency stands and sometimes it is perceived as a limiting factor for
   IPv6.  A few measurement campaigns on the behavior of IPv6 in Content
   Delivery Networks (CDN) are also available [MAPRG-IETF99], [INFOCOM].
   The TCP connect time is still higher for IPv6 in both cases, even if
   the gap has reduced over the analysis time window.

11.3.2.  IPv6 packet loss

   [APNIC5] also provides the failure rate of IPv6.  Two reports, namely
   [RIPE1] and [APRICOT], discussed the associated trend, showing how
   the average worldwide failure rate of IPv6 worsened from around 1.5%
   in 2016 to a value exceeding 2% in 2020.  Reasons for this effect may
   be found in endpoints with an unreachable IPv6 address, routing
   instability or firewall behaviours.  Yet, this worsening effect may
   appeae as disturbing for a plain transition to IPv6.  Operators are

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   once again invited to share their experience and discuss the
   performance of IPv6 in their network scenarios.

11.3.3.  Router's performance

   It is worth mentioning the aspect of Router's performance too.  IPv6
   is 4 times longer than IPv4 and it is possible to do a simple
   calculation: the same memory on routers could permit to have 1/4 of
   different tables (routing, filtering, next hop).  Anyway most of the
   routers showed a remarkably similar throughput and latency for IPv4
   and IPv6.  For smaller software switching platforms, some tests
   reported a lower throughput for IPv6 compared to IPv4 only in case of
   smaller packet sizes, while for larger hardware switching platforms
   there was no throughput variance between IPv6 and IPv4 both at larger
   frame sizes and at the smaller packet size.

11.4.  IPv6 security

   IPv6 presents a number of exciting possibilities for the expanding
   global Internet, however, there are also noted security challenges
   associated with the transition to IPv6.  [I-D.ietf-opsec-v6] analyzes
   the operational security issues in several places of a network
   (enterprises, service providers and residential users).

   The security aspects have to be considered to keep the same level of
   security as it exists nowadays in an IPv4-only network environment.
   The autoconfiguration features of IPv6 will require some more
   attention for the things going on at the network level.  Router
   discovery and address autoconfiguration may produce unexpected
   results and security holes.  The IPsec protocol implementation has
   initially been set as mandatory in every node of the network, but
   then relaxed to recommendation due to extremely constrained hardware
   deployed in some devices e.g., sensors, Internet of Things (IoT).

   There are some concerns in terms of the security but, on the other
   hand, IPv6 offers increased efficiency.  There are measurable
   benefits to IPv6 to notice, like more transparency, improved
   mobility, and also end to end security (if implemented).

   As reported in [ISOC], comparing IPv6 and IPv4 at the protocol level,
   one may probably conclude that the increased complexity of IPv6
   results in an increased number of attack vectors, that imply more
   possible ways to perform different types attacks.  However, a more
   interesting and practical question is how IPv6 deployments compare to
   IPv4 deployments in terms of security.  In that sense, there are a
   number of aspects to consider.

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   Most security vulnerabilities related to network protocols are based
   on implementation flaws.  Typically, security researchers find
   vulnerabilities in protocol implementations, which eventually are
   "patched" to mitigate such vulnerabilities.  Over time, this process
   of finding and patching vulnerabilities results in more robust
   implementations.  For obvious reasons, the IPv4 protocols have
   benefited from the work of security researchers for much longer, and
   thus IPv4 implementations are generally more robust than IPv6.

   Besides the intrinsic properties of the protocols, the security level
   of the resulting deployments is closely related to the level of
   expertise of network and security engineers.  In that sense, there is
   obviously much more experience and confidence with deploying and
   operating IPv4 networks than with deploying and operating IPv6

   Finally, implementation of IPv6 security controls obviously depends
   on the availability of features in security devices and tools.
   Whilst there have been improvements in this area, there is a lack of
   parity in terms of features and/or performance when considering IPv4
   and IPv6 support in security devices and tools.

11.4.1.  Protocols security issues

   It is important to say that IPv6 is not more or less secure than IPv4
   and the knowledge of the protocol is the best security measure.

   In general there are security concerns related to IPv6 that can be
   classified as follows:

   o  Basic IPv6 protocol (Basic header, Extension Headers, Addressing)

   o  IPv6 associated protocols (ICMPv6, NDP, MLD, DNS, DHCPv6)

   o  Internet-wide IPv6 security (Filtering, DDoS, Transition

   ICMPv6 is an integral part of IPv6 and performs error reporting and
   diagnostic functions.  Since it is used in many IPv6 related
   protocols, ICMPv6 packet with multicast address should be filtered
   carefully to avoid attacks.  Neighbor Discovery Protocol (NDP) is a
   node discovery protocol in IPv6 which replaces and enhances functions
   of ARP.  Multicast Listener Discovery (MLD) is used by IPv6 routers
   for discovering multicast listeners on a directly attached link, much
   like Internet Group Management Protocol (IGMP) is used in IPv4.

   These IPv6 associated protocols like ICMPv6, NDP and MLD are
   something new compared to IPv4, so they adds new security threats and

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   the related solutions are still under discussion today.  NDP has
   vulnerabilities [RFC3756] [RFC6583].  The specification says to use
   IPsec but it is impractical and not used, on the other hand, SEND
   (SEcure Neighbour Discovery) [RFC3971] is not widely available.

   [RIPE2] describes the most important threats and solutions regarding
   IPv6 security.

11.4.2.  IPv6 Extension Headers and Fragmentation

   IPv6 Extension Headers imply some issues, in particular their
   flexibility also means an increased complexity, indeed security
   devices and software must process the full chain of headers while
   firewalls must be able to filter based on Extension Headers.
   Additionally, packets with IPv6 Extension Headers may be dropped in
   the public Internet.

   There are some possible attacks through EHs, for example RH0 can be
   used for traffic amplification over a remote path and it is
   deprecated.  Other attacks based on Extension Headers are based on
   IPv6 Header Chains and Fragmentation that could be used to bypass
   filtering, but, to mitigate this effect, Header chain should go only
   in the first fragment and the use of the IPv6 Fragmentation Header is
   forbidden in all Neighbor Discovery messages.

   Fragment Header is used by IPv6 source node to send a packet bigger
   than path MTU and the Destination host processes fragment headers.
   There are several threats related to fragmentation to pay attention
   to e.g. overlapping fragments (not allowed) resource consumption
   while waiting for last fragment (to discard), atomic fragments (to be

11.4.3.  Oversized IPv6 packets

   A lot of additional functionality has been added to IPv6 primarily by
   adding Extension Headers and/or using overlay encapsulation.  All of
   the these expand the packet size and this could lead to oversized
   packets that would be dropped on some links.

   It is better to investigate the potential problems with oversized
   packets in the first place.  Fragmentation must not be done in
   transit and a better solution needs to be found, e.g. upgrade all
   links to bigger MTU or follow specific recommendations at the source

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12.  Security Considerations

   This document has no impact on the security properties of specific
   IPv6 protocols or transition tools.  The security considerations
   relating to the protocols and transition tools are described in the
   relevant documents.

13.  Contributors

   Sebastien Lourdez
   Post Luxembourg
   Email: sebastien.lourdez@post.lu

14.  Acknowledgements

   The authors of this document would like to thank Brian Carpenter,
   Fred Baker, Jordi Palet Martinez, Alexandre Petrescu, Barbara Stark,
   Haisheng Yu(Johnson), Dhruv Dhody, Gabor Lencse, Shuping Peng for
   their comments and review of this document.

15.  IANA Considerations

   This document has no actions for IANA.

16.  References

16.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

16.2.  Informative References

   [APNIC1]   APNIC, "IPv6 Capable Rate by country (%)", 2020,

   [APNIC2]   APNIC2, "Addressing 2020", 2021,

   [APNIC3]   APNIC, "BGP in 2019 - The BGP Table", 2020,

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   [APNIC4]   APNIC, "IPv6 in 2020", 2021,

   [APNIC5]   APNIC, "Average RTT Difference (ms) (V6 - V4) for World
              (XA)", 2020, <https://stats.labs.apnic.net/v6perf/XA>.

   [APRICOT]  Huston, G., "Average RTT Difference (ms) (V6 - V4) for
              World (XA)", 2020,

   [ARCEP]    ARCEP, "Arcep Decision no 2019-1386, Decision on the terms
              and conditions for awarding licences to use frequencies in
              the 3.4-3.8GHz band", 2019,

   [ARIN-CG]  ARIN, "Community Grant Program: IPv6 Security,
              Applications, and Training for Enterprises", 2020,

   [CAIR]     Cisco, "Cisco Annual Internet Report (2018-2023) White
              Paper", 2020,

              ETSI, "ETSI White Paper No. 35: IPv6 Best Practices,
              Benefits, Transition Challenges and the Way Forward",
              ISBN 979-10-92620-31-1, 2020.

   [G_stats]  Google, "Google IPv6 Per-Country IPv6 adoption", 2021,

              Vyncke, E., Kk, C., Kaeo, M., and E. Rey, "Operational
              Security Considerations for IPv6 Networks", draft-ietf-
              opsec-v6-21 (work in progress), November 2019.

              Lencse, G., Martinez, J., Howard, L., Patterson, R., and
              I. Farrer, "Pros and Cons of IPv6 Transition Technologies
              for IPv4aaS", draft-lmhp-v6ops-transition-comparison-06
              (work in progress), January 2021.

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   [IGP-GT]   Internet Governance Project, Georgia Tech, "The hidden
              standards war: economic factors affecting IPv6
              deployment", 2019, <https://via.hypothes.is/

   [INFOCOM]  Doan, T., "A Longitudinal View of Netflix: Content
              Delivery over IPv6 and Content Cache Deployments", 2020,

              ISIF Asia, "Internet Operations Research Grant: IPv6
              Deployment at Enterprises. IIESoc. India", 2020,

   [ISOC]     Internet Society, "IPv6 Security FAQ", 2019,

              Bajpai, V., "Measuring YouTube Content Delivery over
              IPv6", 2017, <https://www.ietf.org/proceedings/99/slides/

              POTAROO, "Addressing 2020", 2020,

              POTAROO, "IPv6 Resource Distribution Reports", 2021,

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, DOI 10.17487/RFC3756, May 2004,

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,

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   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213,
              DOI 10.17487/RFC4213, October 2005,

   [RFC6036]  Carpenter, B. and S. Jiang, "Emerging Service Provider
              Scenarios for IPv6 Deployment", RFC 6036,
              DOI 10.17487/RFC6036, October 2010,

   [RFC6180]  Arkko, J. and F. Baker, "Guidelines for Using IPv6
              Transition Mechanisms during IPv6 Deployment", RFC 6180,
              DOI 10.17487/RFC6180, May 2011,

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,

   [RFC6540]  George, W., Donley, C., Liljenstolpe, C., and L. Howard,
              "IPv6 Support Required for All IP-Capable Nodes", BCP 177,
              RFC 6540, DOI 10.17487/RFC6540, April 2012,

   [RFC6583]  Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
              Neighbor Discovery Problems", RFC 6583,
              DOI 10.17487/RFC6583, March 2012,

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,

   [RFC6883]  Carpenter, B. and S. Jiang, "IPv6 Guidance for Internet
              Content Providers and Application Service Providers",
              RFC 6883, DOI 10.17487/RFC6883, March 2013,

   [RFC7381]  Chittimaneni, K., Chown, T., Howard, L., Kuarsingh, V.,
              Pouffary, Y., and E. Vyncke, "Enterprise IPv6 Deployment
              Guidelines", RFC 7381, DOI 10.17487/RFC7381, October 2014,

   [RIPE1]    Huston, G., "Measuring IPv6 Performance", 2016,

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   [RIPE2]    RIPE, "IPv6 Security", 2019,

   [US-CIO]   The CIO Council, "Memorandum for Heads of Executive
              Departments and Agencies. Completing the Transition to
              Internet Protocol Version 6 (IPv6)", 2020,

   [US-FR]    Federal Register, "Request for Comments on Updated
              Guidance for Completing the Transition to the Next
              Generation Internet Protocol, Internet Protocol Version 6
              (IPv6)", 2020, <https://www.federalregister.gov/

Appendix A.  Summary of Questionnaire and Replies

   This Appendix summarizes the questionnaire and the replies received.

   1.  Do you have plan to move more fixed or mobile or enterprise users
   to IPv6 in the next 2 years?

   a.  If yes, fixed, or mobile, or enterprise?

   b.  What're the reasons to do so?

   c.  When to start: already on going, in 12 months, after 12 months?

   d.  Which transition solution will you use, Dual-Stack, DS-Lite,
   464XLAT, MAP-T/E?

   2.  Do you need to change network devices for the above goal?

   a.  If yes, what kind of devices: CPE, or BNG/mobile core, or NAT?

   b.  Will you migrate your metro or backbone or backhaul network to
   support IPv6?

   Some answers below:

   Answer 1: (1) Yes, IPv6 migration strategy relies upon the deployment
   of Dual Stack architecture.  IPv4 service continuity designs is based
   on DS-Lite for fixed environments and 464XLAT for mobile
   environments.  No plans to move towards MAP-E or MAP-T solutions for
   the time being.  (2) Yes, it's a matter of upgrading CPE, routers

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   (including BNGs), etc.  Tunneling options (ISATAP, TEREDO, 6rd) will
   also be used for migration.

   Answer 2: (1) Yes, at this moment we widely use IPv6 for mobile
   services while we are using DS-Lite for fixed services (FTTH and
   DSL).  (2) We have no pressure to migrate to native IPv6 forwarding
   in the short term and it would represent a significant work without
   clear immediate benefit or business rationale.  However we may see a
   future benefit with SRv6 which may justify in the long term a
   migration to native IPv6.

   Answer 3: (1) Yes, fixed.  The IP depletion topic is crucial, so we
   need to speed up the DS-Lite deployment and also Carrier Grade NAT
   introduction.  (2) Yes, CGNAT introduction.

   Answer 4: (1) No, we are rolling IPv6 users back to IPv4.  DS-Lite.
   (2) No, it was already done.  IPv6 works worse than IPv4. it is

   Answer 5: (1) Yes, all 3.  Target is Dual-stack for fixed, mobile and
   enterprise. (2) Yes, we are adding specific services cards inside our
   FTTH equipment for dealing with CGNAT.  Metro and backbone are
   already Dual Stack.

   Answer 6: (1) Yes, Enterprises customer demand is high and the
   transition is on going through Dual-Stack. (2) No big plan for
   transport network.

   Answer 7: No such requirements

   Answer 8: (1) Yes, mobile.  The Internet APN is not yet enabled for
   IPv6, this will be done soon. 464XLAT will be used to save on RFC1918
   address space.  (2) Yes, PGW; Metro is already IPv6 and Backbone is
   currently IPv4/MPLS.  No native IPv6 planned as for now.

   Answer 9: (1) Yes, Dual-Stack for all 3.  Not all services are
   available on IPv6.  IPv6 adoption has been stated from many years but
   still not finished.  Dual-Stack is used. (2) No, at the moment it is
   6PE solution.  No plan to migrate on native IPv6.

   Answer 10: (1) Yes, all 3.  Ongoing transition with Dual-stack and
   464XLAT. (2) No plan for Metro and Backbone.

   Answer 11: No such requirements.

   Answer 12: (1) Yes, mobile and fixed.  To mitigate IPv4 exhaustion in
   12 months, Dual-Stack is used. (2) No (hopefully).  Managed by
   software upgrade.

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   Answer 13: (1) Yes, on Mobile and Fixed.  Mobile: IPv4 exhaustion for
   the RAN transport and IPv6 roll out ongoing.  Fixed: Enterprises are
   requesting IPv6 and also competitors are offering it.  Mobile: dual
   stack and 6VPE; Enterprise: Dual Stack and 6VPE. (2) No, maybe only a
   software upgrade.

   Answer 14: (1) Yes, fixed.  IPv4 address depletion, on going, Dual-
   Stack with NAT444. (2) No.

   Answer 15: (1) Yes, Mobile.  Running out of private IPv4 address
   space and do not want to overlap addresses.  Transition on going
   through 464XLAT. (2) Not yet, this is not the most pressing concern
   at the moment but it is planned.

   Answer 16: No, already on Dual-Stack for many years.  Discussing

   Answer 17: (1) Yes, all 3, strategy on going, Dual-Stack, MAP-T. (2)
   Yes, CPE, BR Dual-Stack.

   Answer 18: (1) Yes, Mobile, due to address deficit.  It would be very
   likely 464XLAT. (2) It is not clear at the moment.  Still under
   investigation.  CPE, Mobile Core, NAT.  For IPv6 native support no
   plans for today.

   Answer 19: No.  Difficult to do it for enterprises, and don't really
   care for residential customers.

   Answer 20: (1) Yes, fixed, mobile.  IP space depletion.  Mobile and
   Backbone are already done, Fixed is becoming Dual-Stack. (2) Yes,
   ordinary CPE and small routers.  Some of them needs just software
   upgrade.  Backbone done, no plan for metro and backhaul.

   Answer 21: No such requirements

   Answer 22: (1) Yes, mobile, we have few enterprise requests for IPv6;
   fixed already Dual-Stack.  We are in the exhaustion point in public
   IPv4 usage in mobile so we need to move to IPv6 in the terminals.
   Dual-Stack deployment is ongoing. (2) No, all devices already support
   dual-stack mode.  No migration needed.  We already support IPv6
   forwarding in our backbone.

   Answer 23: No, already Dual-Stack

   Answer 24: (1) Yes, fixed.  DS-Lite. (2) Yes, BNG supporting CGNAT.

   Answer 25: (1) Yes, fixed.  DS-Lite will be deployed. (2) Yes.

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   Answer 26: (1) Yes, Mobile (Fixed already Dual-Stack).  IPv4
   depletion and Business customers are asking for it.  Dual-Stack will
   be deployed. (2) No.

   Answer 27: (1) Yes, Mobile.  Dual-Stack is on going. (2) Yes, MBH,
   mobile core.

   Answer 28: No such requirements.

   Answer 29: (1) Yes, fixed and mobile, enterprise is not certain.
   IPv4 addressing is not enough, fixed and mobile should be started in
   12 months. (2) Telco Cloud, BNG and PEs already support IPv6.

   Answer 30: (1) Yes, all 3.  Government has pushed.  Dual-Stack for
   FBB in 12 months. (2) Yes, RGs have not good readiness, but not much
   could be done about it.  PPPoE access does not create problem in
   access and aggregation.  BNG should only change configuration.

   Answer 31: (1) Yes, mobile for 5G sites.  Plan to use IPv6 soon. 6VPE
   in the beginning, then migrate to Dual-stack. (2) IP BH devices
   already support IPv6.

   Answer 32: No.

   Answer 33: Yes, Enterprises.  We are running short of IPV4 addresses.
   In our Internet Core IPV4/IPV6 Dual Stack was already introduced.
   The rollout of IPV6 services is slow and we started with business
   services.  From customer perspective Dual Stack is still a "must
   have" and this will be true for many years to come.  Another thought
   is related to regulatory obligations.  Anyway a total switch from
   IPv4 to IPv6 will not be possible for many more years.

   Answer 34: No, we have no plans to introduce new wave of IPv6 in our

   Answer 35: (1) Yes. Fixed, Enterprise.  IPv4 addressing is not
   enough.  Dual Stack deployment is ongoing. (2) Yes, CPE for metro and

   Answer 36: (1) Yes, Fixed, Enterprise.  Dual-Stack. (2) Yes, CPE for
   IPv6 service delivery support.

   Answer 37: Yes, mobile and enterprise. 6PE is deployed on the PEs,
   and dual-stack.  The PE supports IPv6 by modifying the live network
   configuration or upgrading the software.

   Answer 38: Yes, both home broadband and enterprise services support
   IPv6.  IPv6 services are basic capabilities of communication

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   networks.  Currently 6RD, dual stack (native IPv6) in the future.
   The dual-stack feature does not require device changes.  The home
   gateway is connected to the switch and the BNG.  The Dual Stack can
   be supported through configuration changes.  Both the metro and
   backbone networks use MPLS to provide bearer services and do not
   require IPv6 capabilities.  IPv6 is not enabled on both the metro and
   backbone networks.  IPv6 services are implemented through 6VPE.

   Answer 39: (1) Yes, Enterprises B2B needs more IP addresses.  Dual-
   Stack is already on going. (2) No, BNG/mobile core and NAT.  Metro
   and Backbone already support today.

   Answer 40: Not for now.

Authors' Addresses

   Giuseppe Fioccola
   Huawei Technologies
   Riesstrasse, 25
   Munich  80992

   Email: giuseppe.fioccola@huawei.com

   Paolo Volpato
   Huawei Technologies
   Via Lorenteggio, 240
   Milan  20147

   Email: paolo.volpato@huawei.com

   Nalini Elkins
   Inside Products
   36A Upper Circle
   Carmel Valley  CA 93924
   United States of America

   Email: nalini.elkins@insidethestack.com

   Gyan S. Mishra
   Verizon Inc.

   Email: gyan.s.mishra@verizon.com

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   Chongfeng Xie
   China Telecom

   Email: xiechf.bri@chinatelecom.cn

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