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IPv6 Deployment Status
draft-ietf-v6ops-ipv6-deployment-05

Document Type Active Internet-Draft (v6ops WG)
Authors Giuseppe Fioccola , Paolo Volpato , Nalini Elkins , Jordi Palet Martinez , Gyan Mishra , Chongfeng Xie
Last updated 2022-05-02 (Latest revision 2022-03-07)
Replaces draft-vf-v6ops-ipv6-deployment
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draft-ietf-v6ops-ipv6-deployment-05
V6OPS                                                        G. Fioccola
Internet-Draft                                                P. Volpato
Intended status: Informational                       Huawei Technologies
Expires: September 8, 2022                                     N. Elkins
                                                         Inside Products
                                                       J. Palet Martinez
                                                        The IPv6 Company
                                                               G. Mishra
                                                            Verizon Inc.
                                                                  C. Xie
                                                           China Telecom
                                                           March 7, 2022

                         IPv6 Deployment Status
                  draft-ietf-v6ops-ipv6-deployment-05

Abstract

   This document provides an overview of IPv6 deployment status and a
   view on how the transition to IPv6 is progressing among network
   operators and enterprises.  It also aims to analyze the related
   challenges and therefore encourage actions and more investigations in
   those areas where the industry has not taken a clear and unified
   approach.

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
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 September 8, 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  IPv4 vs IPv6: The Global Picture  . . . . . . . . . . . . . .   5
     2.1.  IPv4 Address Exhaustion . . . . . . . . . . . . . . . . .   5
     2.2.  IPv6 Users  . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  IPv6 Web Content  . . . . . . . . . . . . . . . . . . . .   7
     2.4.  IPv4 addresses per capita and IPv6 status . . . . . . . .   7
   3.  A Survey on IPv6 Deployments  . . . . . . . . . . . . . . . .  10
     3.1.  IPv6 Allocations and Networks . . . . . . . . . . . . . .  10
     3.2.  IPv6 among Network Operators  . . . . . . . . . . . . . .  12
     3.3.  IPv6 among Enterprises  . . . . . . . . . . . . . . . . .  14
       3.3.1.  Government and Universities . . . . . . . . . . . . .  15
     3.4.  Observations on Industrial Internet . . . . . . . . . . .  17
     3.5.  Observations on Content and Cloud Service Providers . . .  17
     3.6.  Application Transition  . . . . . . . . . . . . . . . . .  18
   4.  Towards an IPv6 Overlay Service Design  . . . . . . . . . . .  18
     4.1.  IPv6 introduction . . . . . . . . . . . . . . . . . . . .  19
     4.2.  IPv6-only Service Delivery  . . . . . . . . . . . . . . .  20
   5.  IPv6-only Underlay Network Deployment . . . . . . . . . . . .  21
   6.  IPv6 Benefits . . . . . . . . . . . . . . . . . . . . . . . .  23
   7.  Common IPv6 Challenges  . . . . . . . . . . . . . . . . . . .  25
     7.1.  Transition Choices  . . . . . . . . . . . . . . . . . . .  25
       7.1.1.  Service Providers . . . . . . . . . . . . . . . . . .  25
       7.1.2.  Enterprises and Industrial Internet . . . . . . . . .  26
       7.1.3.  Cloud and Data Centers  . . . . . . . . . . . . . . .  27
       7.1.4.  CEs and user devices  . . . . . . . . . . . . . . . .  28
     7.2.  Government and Regulators . . . . . . . . . . . . . . . .  28
     7.3.  Network Management and Operations . . . . . . . . . . . .  29
     7.4.  Performance . . . . . . . . . . . . . . . . . . . . . . .  29
       7.4.1.  IPv6 packet loss and latency  . . . . . . . . . . . .  30
       7.4.2.  Customer Experience . . . . . . . . . . . . . . . . .  30
     7.5.  IPv6 security . . . . . . . . . . . . . . . . . . . . . .  31
       7.5.1.  Protocols security issues . . . . . . . . . . . . . .  32
       7.5.2.  IPv6 Extension Headers and Fragmentation  . . . . . .  33
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  33
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  34
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  34

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   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     12.2.  Informative References . . . . . . . . . . . . . . . . .  36
   Appendix A.  Summary of Questionnaire and Replies for network
                operators  . . . . . . . . . . . . . . . . . . . . .  42
   Appendix B.  Summary of Questionnaire and Replies for enterprises  44
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   [RFC6036] described IPv6 deployment scenarios adopted or foreseen by
   a number of Internet Service Providers (ISPs) who responded to a
   technical questionnaire in early 2010.  In doing that, [RFC6036]
   provided practices and plans expected to take place in the following
   years.  Since the publication of [RFC6036], several other documents
   contributed to discuss the transition to IPv6 in operational
   environments.  To name a few:

      - [RFC6180] discussed IPv6 deployment models and transition
      mechanisms, recommending those that showed to be effective in
      operational networks.

      - [RFC6883] provided guidance and suggestions for Internet content
      providers and Application Service Providers (ASPs).

      - [RFC7381] introduced the guidelines of IPv6 deployment for
      enterprises.

   It is worth mentioning here also [RFC6540] that not only recommended
   the support of IPv6 to all IP-capable nodes, but it was referenced in
   the IAB Statement on IPv6 [IAB], which represented a major step in
   driving the IETF as well as other Standard Developing Organizations
   (SDOs) to assume the use of IPv6 in their works.

   In more recent times, organizations such as ETSI provided more
   contributions to the use of IPv6 in operational environments,
   targeting IPv6 in different industry segments.  As a result,
   [ETSI-IP6-WhitePaper], was published to provide an updated view on
   the IPv6 best practices adopted so far, in particular in the ISPs
   domain.

   Considering all of the above, and after more than ten years since the
   publication of [RFC6036] it may be interesting to verify where the
   transition of the Internet to IPv6 currently stands, what major steps
   have been accomplished and what is still missing.  Some reasons
   justify such questions:

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      - In some areas, the lack of publicly available IPv4 addresses
      forced both carriers and content providers to shift to IPv6 to
      support the introduction of new applications, in particular in
      wireless networks.

      - Some governmental actions took place to encourage or even
      enforce, at different degrees, the adoption of IPv6 in certain
      countries.

      - Looking at the global adoption of IPv6, this seems to have
      reached a threshold that justifies speaking of native, end-to-end
      IPv6 connectivity (between a user's device and a content on a
      site) at the IPv6 service layer.

   This document intends to explode such statements, providing a survey
   of the status of IPv6 deployment and highlighting both the
   achievements and remaining obstacles in the transition to IPv6-only
   networks.  The target is to give an updated view of the practices and
   plans already described in [RFC6036], to encourage further actions
   and more investigations in those areas that are still under
   discussion, and to present the main incentives for the adoption of
   IPv6.  The expectation is that this process may help to understand
   what is missing and how to improve the current IPv6 deployment
   strategies of network operators, enterprises, content and cloud
   service providers.

   The initial section of this document reports some data about the
   status of IPv6.  The exhaustion of IPv4 as well as the measured
   adoption of IPv6 at the users' and the content's side will be
   discussed.  Comparing both IPv4 and IPv6, this latter has a higher
   growth rate.  While this fact alone does not permit to conclude that
   the definitive transition to IPv6 is undergoing, at least testifies
   that a portion of the ICT industry has decided to invest and deploy
   IPv6 at large.

   The next section provides a survey of IPv6 deployments in different
   environments, including ISPs, enterprises, cloud providers and
   universities.  Data from some well-known analytics will be discussed.
   In addition, two independent polls among network operators and
   enterprises will also be presented.

   Then, a section on IPv6 overlay service design will describe the IPv6
   transition approaches for Mobile BroadBand (MBB), Fixed BroadBand
   (FBB) and Enterprise services.  At present, Dual-Stack (DS) is the
   most deployed solution for IPv6 introduction, while 464XLAT and Dual-
   Stack Lite (DS-Lite) seem the preferred ones for those players that
   have already enabled IPv6-only service delivery.  A section on IPv6

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   underlay network deployment will also focus on the common approaches
   for the transport network.

   The last parts of the document will analyze the incentives brought by
   IPv6 as well as the general challenges to be faced to move forward in
   the transition.  Specific attention will be given to operational,
   performance and security issues.  All these considerations will be
   input for the final section of the document that aims to highlight
   the areas still requiring improvement and some actions that the
   industry might consider to favor the adoption of IPv6.

2.  IPv4 vs IPv6: The Global Picture

   This section deals with some key questions related to IPv6, namely
   the status of IPv4 exhaustion, often considered as one of the
   triggers to switch to IPv6, the number of IPv6 end users, a primary
   measure to sense IPv6 adoption, and the percentage of websites
   reachable over IPv6.  The former is constantly measured by the
   Regional Internet Registries (RIRs) and the next subsection provides
   an indication of where we currently stand.  The utilization of IPv6
   at both the end user's side and the content's side has also been
   monitored by several institutions worldwide as these two parameters
   provide a first-order indication on the real adoption of IPv6.

2.1.  IPv4 Address 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 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 5.2 million IPv4 addresses, while the
   reserved pool includes another 12 million, for a total of "usable"
   addresses equal to 17.3 million (-5.5% year over year, comparing 2021
   against 2020).  The same reference, in table 1, shows that the total
   IPv4 allocated pool equals to 3.685 billion addresses (+0.027% year
   over year).  The ratio between the "usable" addresses and the total
   allocated brings to 0.469% of remaining space (from 0.474% at the end
   of 2020).

   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

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   the general shift to cloud.  Anyway, it should be noted that, in some
   cases, private address space cannot provide adequate address and the
   reuse of addresses may make the network even more complex.  The
   transfer of IPv4 addresses also contributes to mitigate the need of
   addresses.  As an example, [IGP-GT] and [NRO] show the amount of
   transfers to recipient organizations in the different regions.  Cloud
   Service Providers (CSPs) appear to be the most active in buying
   available addresses to satisfy their need of providing IPv4
   connectivity to their tenants.  But, since each address blocks of
   Internet is licensed by a specific resource-holder and stored for the
   verification of the authenticity, frequent address transfer may
   affect the global assignment process.

2.2.  IPv6 Users

   The count of the IPv6 users is the key parameter to get an immediate
   understanding of the adoption of IPv6.  Some organizations constantly
   track the usage of IPv6 by aggregating data from several sources.  As
   an example, the Internet Society constantly monitors the volume of
   IPv6 traffic for the networks that joined the WorldIPv6Launch
   initiative [WIPv6L].  The measurement aggregates statistics from
   organizations such as [Akm-stats] that provides data down to the
   single network level measuring the number of hits to their content
   delivery platform.  For the scope of this document, we follow the
   approach used by APNIC to quantify the adoption of IPv6 by means of a
   script that runs on a user's device [CAIDA].  To give a rough
   estimation of the relative growth of IPv6, the next table aggregates
   the total number of estimated IPv6-capable users at January 2022, and
   compares it against the total Internet users, as measured by
   [POTAROO2].

   +--------+--------+--------+--------+--------+--------+--------+
   |        |  Jan   |  Jan   |  Jan   |  Jan   |  Jan   |  CAGR  |
   |        |  2018  |  2019  |  2020  |  2021  |  2022  |        |
   +--------+--------+--------+--------+--------+--------+--------+
   |  IPv6  |  513.07|  574.02|  989.25|1,136.28|1,207.61|  23.9% |
   +--------+--------+--------+--------+--------+--------+--------+
   | World  |3,410.27|3,470.36|4,065.00|4,091.62|4,093.69|   4.7% |
   +--------+--------+--------+--------+--------+--------+--------+
   | Ratio  |   15.0%|   16.5%|   24.3%|   27.8%|   29.5%|  18.4% |
   +--------+--------+--------+--------+--------+--------+--------+

         Figure 1: IPv6-capable users against total (in millions)

   Two figures appear: first, the IPv6 Internet population is growing
   with a two-digits Compound Annual Growth Rate (CAGR), and second, the
   ratio IPv6 over total is also growing steadily.

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2.3.  IPv6 Web Content

   [W3Tech] keeps track of the use of several technical components of
   websites.  The utilization of IPv6 for websites is shown in the next
   table.

   +------------+-------+-------+-------+-------+-------+------+
   |  Wolrdwide |  Jan  |  Jan  |  Jan  |  Jan  |  Jan  | CAGR |
   |  Websites  |  2018 |  2019 |  2020 |  2021 |  2022 |      |
   +------------+-------+-------+-------+-------+-------+------+
   |% of IPv6   | 11.4% | 13.3% | 15.0% | 17.5% | 20.6% | 15.9%|
   +------------+-------+-------+-------+-------+-------+------+

                    Figure 2: Usage of IPv6 in websites

   Looking at the growth rate, it may appear not particularly high.  It
   has to be noted, though, that not all websites are equal.  The
   largest content providers, which already support IPv6, generate a lot
   more IPv6-based content than small websites.  [Csc6lab] measured at
   the beginning of January 2022 that out of the world top 500 sites
   ranked by [Alx], 203 are IPv6-enabled (+3.6% from January 2021 to
   January 2022).  If we consider that the big content providers (such
   as Google, Facebook, Netflix) generate more than 50% of the total
   mobile traffic [SNDVN], and in some cases even more up to 65%
   ([ISOC1] [HxBld]), the percentage of content accessible over IPv6 is
   clearly more relevant than the number of enabled IPv6 websites.

   Related to that, a question that sometimes arises is whether the
   content stored by content providers would be all accessible on IPv6
   in the hypothetical case of a sudden IPv4 switch-off.  Even if this
   is pure speculation, the numbers above may bring to state that this
   is likely the case.  This would reinforce the common thought that, in
   quantitative terms, most of content is accessible via IPv6.

2.4.  IPv4 addresses per capita and IPv6 status

   The IPv4 addresses per capita ratio measures the quantity of IPv4
   addresses allocated to a given country divided by the population of
   that country.  It is a theoretical ratio, anyhow it provides an
   indication of the imbalanced distribution of the IPv4 addresses
   worldwide.  It clearly derives from the allocation of addresses made
   in the early days of the Internet by the most advanced countries.

   The sources for measuring the IPv4 addresses per capita ratio are the
   allocations done by the RIRs and the statistics about the world
   population.  In our case, we take the distribution files of
   [POTAROO2], which summarize the most useful information.  We then

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   compare the obtained ratio against the measured adoption of IPv6.  As
   explained in section 2.2, this is expressed as the number of IPv6
   capable users over the total Internet population of the considered
   country.  The result is shown in the following table, where some of
   countries with the highest number of IPv4 allocations are reported.
   The table is ordered based on the IPv4 addresses per capita ratio.

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   +------------------------+-----------------+-----------------+
   |Country                 |  IPv4 per capita|  IPv6 deployment|
   +------------------------+-----------------+-----------------+
   |United States of America|             4.89|            47.1%|
   +------------------------+-----------------+-----------------+
   |Sweden                  |             2.97|            11.8%|
   +------------------------+-----------------+-----------------+
   |Netherlands             |             2.93|            35.5%|
   +------------------------+-----------------+-----------------+
   |Switzerland             |             2.75|            34.9%|
   +------------------------+-----------------+-----------------+
   |Republic of Korea       |             2.19|            17.1%|
   +------------------------+-----------------+-----------------+
   |Australia               |             1.91|            28.8%|
   +------------------------+-----------------+-----------------+
   |Canada                  |             1.85|            32.4%|
   +------------------------+-----------------+-----------------+
   |United Kingdom          |             1.65|            33.2%|
   +------------------------+-----------------+-----------------+
   |Belgium                 |             1.62|            62.0%|
   +------------------------+-----------------+-----------------+
   |Japan                   |             1.50|            36.7%|
   +------------------------+-----------------+-----------------+
   |Germany                 |             1.48|            53.0%|
   +------------------------+-----------------+-----------------+
   |France                  |             1.27|            42.1%|
   +------------------------+-----------------+-----------------+
   |Austria                 |             1.24|            29.2%|
   +------------------------+-----------------+-----------------+
   |Italy                   |             0.91|             4.7%|
   +------------------------+-----------------+-----------------+
   |Spain                   |             0.69|             3.0%|
   +------------------------+-----------------+-----------------+
   |Poland                  |             0.55|            14.7%|
   +------------------------+-----------------+-----------------+
   |Brazil                  |             0.41|            38.7%|
   +------------------------+-----------------+-----------------+
   |Russian Federation      |             0.31|             9.7%|
   +------------------------+-----------------+-----------------+
   |China (*)               |             0.24|            60.1%|
   +------------------------+-----------------+-----------------+
   |India                   |             0.03|            76.9%|
   +------------------------+-----------------+-----------------+

               Figure 3: IPv4 per capita and IPv6 deployment

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   (*) The IPv6 deployment information in China is derived from
   [CN-IPv6].

   It is clear that a direct correlation between the two measures is not
   always straightforward.  One may expect that a low IPv4 addresses per
   capita ratio should correspond to high IPv6 deployment.  This is true
   for India and, relatively, for Brazil, but other countries such as
   the Russian Federation, Poland, Spain and Italy are still quite
   dependent on IPv4.

   The opposite effect should apply for countries with a high value for
   same ratio.  While this is true for Sweden and the Republic of Korea,
   which have a relatively low IPv6 deployment, for other countries at
   the top of the list this does not apply.  The USA, Germany, France,
   Belgium all have a good level of IPv6 deployment, while other
   countries such the Netherlands, Switzerland, the UK, Canada,
   Australia, Japan are just following with around one third of their
   Internet population using IPv6.

   The reasons for having high or medium-to-high IPv6 deployment may be
   quite different from country to country.  For example, in West
   European countries such as Belgium, France, Germany the outcome
   depends on a mix of government and regulation activities which
   incentivized the adoption of IPv6 in the recent years.  In some cases
   it has been industry self-regulation which created the traction for a
   bigger IPv6 adoption.

   The IPv6 adoption in USA, China and India comes from different needs.
   Mobile operators have anticipated the usage of IPv6 to cope with the
   lack of available addresses (India) and to support new services and
   applications.  In addition to that, all National governments have
   issues specific policies to bring IPv6 deployment forward.

3.  A Survey on IPv6 Deployments

   Right after the count of the IPv6 users, it is fundamental to
   understand the status of IPv6 in terms of concrete adoption in
   operational networks.  This section deals with the status of IPv6
   among carriers, service and content providers, enterprises and
   research institutions.

3.1.  IPv6 Allocations and Networks

   RIRs are responsible for allocating IPv6 address blocks to ISPs, LIRs
   (Local Internet Registries) as well as enterprises or other
   organizations.  An ISP/LIR will use the allocated block to assign
   addresses to their end users.  For example, a mobile carrier will
   assign one or several /64 prefixes to the User Equipment (UE).

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   Several analytics are available from the RIRs.  Here we are
   interested to those relevant to IPv6.  The next table shows the
   amount of individual allocations, per RIR, in the time period
   2017-2021 [APNIC2].

   +---------+-------+-------+-------+-------+-------+---------+------+
   | Registry|  Dec  |  Dec  |  Dec  |  Dec  |  Dec  |Cumulated| CAGR |
   |         |  2017 |  2018 |  2019 |  2020 |  2021 |         |      |
   +---------+-------+-------+-------+-------+-------+---------+------+
   | AFRINIC |   112 |   110 |   115 |   109 |   136 |    582  | 51%  |
   |  APNIC  | 1,369 | 1,474 | 1,484 | 1,498 | 1,392 |  7,217  | 52%  |
   |   ARIN  |   684 |   659 |   605 |   644 |   671 |  3,263  | 48%  |
   |  LACNIC | 1,549 | 1,448 | 1,614 | 1,801 |   730 |  7,142  | 47%  |
   | RIPE NCC| 2,051 | 2,620 | 3,104 | 1,403 | 2,542 | 11,720  | 55%  |
   |         |       |       |       |       |       |         |      |
   |  Total  | 5,765 | 6,311 | 6,922 | 5,455 | 5,471 | 29,924  | 51%  |
   +---------+-------+-------+-------+-------+-------+---------+------+

                   Figure 4: IPv6 allocations worldwide

   Overall, the trend is positive, witnessing the vivacity around IPv6.
   The decline of IPv6 allocations in 2020 (remarkable for RIPE NCC) and
   2021 (in LACNIC), could be explained with the COVID-19 measures that
   may have affected the whole industry.

   [APNIC2] also compares the number of allocations for both address
   families.  Differently from what happened in 2020, when CAGR was
   higher for the IPv6 allocations, in 2021 IPv4 stayed a little ahead
   (53.6% versus 50.9%).

   +--------+-------+-------+-------+-------+-------+----------+------+
   | Address|  Dec  |  Dec  |  Dec  |  Dec  |  Dec  | Cumulated| CAGR |
   | family |  2017 |  2018 |  2019 |  2020 |  2021 |          |      |
   +--------+-------+-------+-------+-------+-------+----------+------+
   |  IPv6  | 5,765 | 6,311 | 6,922 | 5,455 | 5,471 |   29,924 | 50.9%|
   |        |       |       |       |       |       |          |      |
   |  IPv4  | 8,091 | 9,707 |13,112 | 6,263 | 7,829 |   45,002 | 53.6%|
   |        |       |       |       |       |       |          |      |
   +--------+-------+-------+-------+-------+-------+----------+------+

                 Figure 5: Allocations per address family

   As noted, the pandemic may have influenced the ICT industry including
   the dynamic of the address allocations.  The number of IPv4
   allocations in 2021 includes many allocations of small address ranges
   (e.g. /24) [APNIC2].  On the contrary, a single IPv6 allocation is

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   large enough to cope with the need of an operators for many years.
   After an operator receives an IPv6 /30 or /32 allocation it is
   unlikely that a new request of addresses is repeated in the short
   term.  Hence the two CAGR values in the table should not be compared
   directly as the weight of the allocations is different.

   The next table is based on [APNIC3], [APNIC4] and shows the
   percentage of Autonomous System (AS) numbers supporting IPv6 compared
   to the total ASes worldwide.  The number of IPv6-capable ASes
   increased from 24.3% in January 2018 to 38.7% in January 2022.  This
   equals to 18% CAGR for IPv6-enabled networks, highlighting how IPv6
   is growing faster than IPv4, since the CAGR value for the total of
   IPv6 and IPv4 networks grew of just 5%.

   +------------+-------+-------+-------+-------+-------+------+
   | Advertised |  Jan  |  Jan  |  Jan  |  Jan  |  Jan  | CAGR |
   |    ASN     |  2018 |  2019 |  2020 |  2021 |  2022 |      |
   +------------+-------+-------+-------+-------+-------+------+
   |IPv6-capable| 14,500| 16,470| 18,650| 21,400| 28,140|  18% |
   |            |       |       |       |       |       |      |
   | Total ASN  | 59,700| 63,100| 66,800| 70,400| 72,800|   5% |
   |            |       |       |       |       |       |      |
   |   Ratio    | 24.3% | 26.1% | 27.9% | 30.4% | 38.7% |      |
   +------------+-------+-------+-------+-------+-------+------+

                 Figure 6: Percentage of IPv6-capable ASes

   The tables above provide an aggregated view of the allocations
   dynamic.  Apart from the recent times influenced by the pandemic, the
   general trend related to IPv6 adoption is positive.  What the
   aggregated view does not tell us is the split between the different
   types of organizations.  The next sections of this chapter will zoom
   into each specific area to highlight the relative status.

3.2.  IPv6 among Network Operators

   Only a few public references describing the status of IPv6 in
   specific networks are available.  An example is the case of Reliance
   Jio [RlncJ].  To understand the degree of adoption of IPv6 in the
   operators' domain, it is necessary to consult the data provided by
   those organizations that constantly track the usage of IPv6.  Among
   the others, we have the Internet Society that constantly monitors the
   volume of IPv6 traffic for the networks that joined the
   WorldIPv6Launch initiative [WIPv6L] and Akamai [Akm-stats] that
   collects statistics both at a country level and at the single
   operator's network measuring the number of hits to their content
   delivery platform.  In addition to them, the RIRs also provide

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   detailed information about the prefixes allocated and the ASes
   associated to each operator.  Overall, the vast majority of the
   operators worldwide have enabled IPv6 and provide IPv6-based services
   even if the degree of adoption varies quite greatly based on local
   market demand, regulatory actions, and political decisions (e.g.
   [RIPE3] to look at the relative differences across the European
   market).

   As it was proposed at the time of [RFC6036], also in the case of this
   document a survey was submitted to a group of service providers in
   Europe (see Appendix A for the complete poll), to understand the
   details about their plans about IPv6 and their technical preferences
   towards its adoption.  Such poll does not pretend to give an
   exhaustive view on the IPv6 status, but to integrate the available
   data with some insights that may be relevant to the discussion.

   The poll reveals that the majority of the operators interviewed has
   plans concerning IPv6 (79%).  Of them, 60% has already ongoing
   activities, while 33% is expected to start activities in a 12-months
   time-frame.  The transition to IPv6 involves all business segments:
   mobile (63%), fixed (63%), and enterprises (50%).

   The reasons to move to IPv6 vary.  The majority of the operators that
   do have a plan for IPv6 perceives issues related to IPv4 depletion
   and prefer to avoid the use of private addressing schemes (48%) to
   save the NAT costs.  Global IPv4 address depletion and the run out of
   private address space recommended in [RFC1918] are reported as the
   important drivers for IPv6 deployment.  In some cases, the adoption
   of IPv6 is driven by innovation strategy (as the enabler of new
   services, 13%) or is introduced because of 5G/IoT, which play the
   role of business incentive to IPv6 (20%).  In a few cases,
   respondents highlight the availability of National Regulatory
   policies requiring to enable IPv6 together with the launch of 5G
   (13%).  Enterprise customers demand is also a reason to introduce
   IPv6 (13%).

   From a technical preference standpoint, Dual-Stack is the most
   adopted solution, both in wireline (59%) and in cellular networks
   (39%).  In wireline, the second most adopted mechanism is DS-Lite
   (19%), while in cellular networks the second preference goes to
   464XLAT (21%).

   In the majority of the cases, the interviewed operators do not see
   any need to transition their network as a whole.  They consider to
   touch or to replace only what it is needed.  CE (47%), BNG (20%), CGN
   devices (33%), mobile core (27%) are the components that may be
   affected by transition or replacement.  It is interesting to see that
   most of the network operators have no major plans to transition the

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   transport network (metro and backbone) soon, since they do not see
   business reasons.  It seems that there is no pressure to move to
   native IPv6-only forwarding in the short term, anyway the future
   benefit of IPv6 may justify the shift in the long term.

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

3.3.  IPv6 among Enterprises

   As described in [RFC7381], enterprises face different challenges than
   operators.  Some publicly available statistics also show that the
   deployment of IPv6 lags behind other sectors.

   [NST_1] provides estimations on deployment status of IPv6 for more
   than 1000 second level domains such as example.com, example.net or
   example.org belonging to organizations in the United States.  The
   measurement encompasses many industries, including
   telecommunications, so that the term "enterprises" is a bit loose to
   this extent.  In any case, it provides a first indication of IPv6
   adoption in several US industry sectors.  The analysis tries to infer
   whether IPv6 is supported by looking from "outside" a company's
   network.  It takes into consideration the support of IPv6 to external
   services such as Domain Name System (DNS), mail and website.
   Overall, for around the 66.85% of the considered domains there is an
   active DNS Name Server (NS) v6 record but only 6.3% have IPv6 support
   for their websites and 21.2% have IPv6-based mail services as of
   January 2022.

   [BGR_1] have similar data for China.  The measurement considers 478
   second or third level domains such as example.cn or example.com.cn.
   74% have IPv6 support for DNS, 0% have IPv6-based mail services, 20%
   have IPv6-based websites.

   [CNLABS_1] provides the status in India.  Of the 104 measured
   domains, 51.9% are IPv6-enablesd, 15.4% have IPv6 support in DNS,
   16.3% have IPv6 support for the mail service.

   A poll submitted to a group of large enterprises in North America
   (see Appendix B) show that the operational issues are likely to be
   more critical than for operators.

   Looking at current implementations, almost one third has dual-stacked
   networks, while 20% declares that portions of their networks are
   IPv6-only. 35% of the enterprises are stuck at the training phase.
   In no cases the network is fully IPv6-based.

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   Speaking of training, the most critical needs are in the field of
   IPv6 security and IPv6 troubleshooting (both highlighted by the two
   thirds of respondents), followed by IPv6 fundamentals (57.41%).

   Coming to implementation, the three areas of concern are IPv6
   security (31.48%), training (27.78%), application conversion
   (25.93%).  Interestingly, 33.33% of respondents think that all three
   areas are all simultaneously of concern.

   The full poll is reported in Appendix B.

3.3.1.  Government and Universities

   This section focuses specifically on governments and academia, due to
   the relevance of both domains in the process of IPv6 adoption.  The
   already mentioned organizations that estimates the IPv6 status
   provide a deep focus on IPv6 in the network domains associated with
   governmental and education-related agencies.

   As far as governmental institutions or agencies are concerned,
   [NST_2] provides analytics on the degree of support that IPv6 gives
   to DSN, mail and websites across 1283 second level domains associated
   with US Federal agencies.  These domains are in the form of
   example.gov or example.fed.  The script used by [NST_2] have also
   been employed to measure the same analytics in other countries.  For
   China [BGR_2] looks at 52 third level domains such as example.gov.cn.
   [CNLABS_2] provides statistics for 618 Indian government-related
   domains (ranging from the second to the fifth level).  [IPv6Forum]
   analyzes 19 governmental domains connected to either the European
   Union or its member States.

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   +--------------+----------+---------+---------+---------+
   |Country       | Domains  |   DNS   |  Mail   | Website |
   |              | analyzed |         |         |         |
   +--------------+----------+---------+---------+---------+
   |China         |     52   |   0.0%  |   0.0%  |   98.1% |
   |              |          |         |         |         |
   +--------------+----------+---------+---------+---------+
   |European      |     19   |  47.4%  |   0.0%  |   21.1% |
   |Union (*)     |          |         |         |         |
   +--------------+----------+---------+---------+---------+
   |India         |    618   |   7.6%  |   6.5%  |    7.1% |
   |              |          |         |         |         |
   +--------------+----------+---------+---------+---------+
   |United States |   1283   |  87.1%  |  14.0%  |   51.7% |
   |of America    |          |         |         |         |
   +--------------+----------+---------+---------+---------+

        Figure 7: IPv6 support for external-facing services across
                         governmental institutions

   (*) Both EU and European governments domains are considered.

   Looking at the USA, the support given by IPv6 to the services is
   higher than that in the enterprise sector discussed in the previous
   section.  This is likely to depend on the directions set by [US-CIO]
   through the mandate to transition to IPv6.  In the case of India, the
   degree of support seems still quite low.  This is also true for
   China, with the notable exception of the percentage of IPv6-enabled
   government-related organizations websites.

   Similar statistics are also available for higher education.  [NST_3]
   measures the data coming from 346 second level domains of
   universities in the US, such as example.edu.  [BGR_3] looks at 111
   Chinese education-related domains such as example.edu.cn.  [CNLABS_3]
   analyzes 100 domains in India (mostly third level), while [IPv6Forum]
   lists 118 universities in the European Union (second level).

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   +--------------+----------+---------+---------+---------+
   |Country       | Domains  |   DNS   |  Mail   | Website |
   |              | analyzed |         |         |         |
   +--------------+----------+---------+---------+---------+
   |China         |    111   |  36.9%  |   0.0%  |   77.5% |
   |              |          |         |         |         |
   +--------------+----------+---------+---------+---------+
   |European      |    118   |  83.9%  |  43.2%  |   35.6% |
   |Union         |          |         |         |         |
   +--------------+----------+---------+---------+---------+
   |India         |    100   |  31.0%  |  54.0%  |    5.0% |
   |              |          |         |         |         |
   +--------------+----------+---------+---------+---------+
   |United States |    346   |  49.1%  |  19.4%  |   21.7% |
   |of America    |          |         |         |         |
   +--------------+----------+---------+---------+---------+

        Figure 8: IPv6 support for external-facing services across
                               universities

   Overall, the universities have wider support of IPv6-based services
   if compared with the other sectors.  Apart from a couple of
   exceptions (e.g. the support of IPv6 mail in China and IPv6 web sites
   in India), the numbers shown in the table above indicate a good
   support of IPv6.

3.4.  Observations on Industrial Internet

   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
   discovery.

   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
   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.

3.5.  Observations on Content and Cloud Service Providers

   Both 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] have been the drivers to adopt IPv6
   in several CSP networks.

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   Several public references, as reported in Section 7.1.3, discuss how
   most of the major players find themselves at different stages in the
   transition to IPv6-only in their Data Center (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.

3.6.  Application Transition

   The preliminary step to take full benefit of the IPv6 capabilities is
   to write or adapt the application software for use in IPv6 networks
   (see, as an example, [ARIN-SW]).

   It is worth mentioning Happy Eyeballs [RFC6555] and Happy Eyeballs 2
   [RFC8305] as a major aspect of application transition and porting to
   IPv6.  All host and network router OS's by default prefer IPv6 over
   IPv4.

   Happy Eyeballs plays an important role and is extremely helpful when
   applications are migrated from IPv4 to IPv6 having a single DNS name
   with both A and AAAA record.  In this way all applications can
   migrate to IPv6 as IPv6 is preferred over IPv4 and so all IPv6 dual-
   stacked hosts can communicate using same URL to the server via IPv6
   and all IPv4 hosts can as well use the same URL to communicate via
   IPv4.  Eventually when all host endpoints are dual-stacked, the
   application servers can migrate from dual stack to IPv6-only.  For
   external connectivity to the internet, web proxy can be used
   providing 6to6 or 4to6 proxy to the internet.  This allows
   application servers on the internal network to change to IPv6-only
   once all host endpoints are all dual-stacked.

   At the current stage, the full support of IPv6 is not yet complete
   [Wikipedia], as issues remains in particular for applications known
   not to work properly behind NAT64.

4.  Towards an IPv6 Overlay Service Design

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

   Two approaches are usually considered [ETSI-IP6-WhitePaper], namely:
   (1) IPv6 introduction, and (2) IPv6-only.  Depending on their
   specific plans and requirements, operators may consider either of the
   two or both.  The usual approach sees them as two sequential stages,
   i.e. deal with IPv6 introduction first and then move to IPv6-only.
   In some cases, operators may instead jump directly to IPv6-only to

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   avoid the operational burden of a transient phase.  IPv6 introduction
   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 IPv6-only may occur.  In this latter
   case, the service is delivered solely on IPv6, including the traffic
   originated from IPv4-based nodes.  For this reason, the IPv6-only
   stage is also called IPv4aaS (IPv4 as a Service).

   The consolidated approach foresees to enable IPv6 in the network
   (sometimes referred to as the underlay) and move progressively to the
   service layer.  Recently, the attention has shifted to enabling IPv6
   at the service layer (the overlay) leaving the transition of the
   network to IPv6 at a later stage.  This relates to the increased
   adoption of the transition mechanisms described in this section.

4.1.  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 [RFC4213] at the Customer Edge router (CE)

   o  IPv6-in-IPv4 tunneling, e.g. with IPv6 Rapid Deployment (6rd) or
      Generic Routing Encapsulation (GRE).

   Based on information provided by operators with the answers to the
   poll (Appendix A), Dual-Stack appears to be 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, which appears more
   robust, and easier to troubleshoot and support.

   With Dual-Stack, IPv6 can be introduced together with other network
   upgrades 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 the IPv6
   transition.  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 CE has both IPv4 and IPv6 addresses 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.

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   For example, NAT64 can enable IPv6-only hosts to access IPv4 servers.
   The backbone network underlay can also be IPv4 or IPv6.

   Although the Dual-Stack IPv6 transition provides advantages in the
   IPv6 introductory 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.  It also means
   requiring more IPv4 addresses, so an increase in both Capital
   Expenses (CAPEX) and Operating Expenses (OPEX).  Even if private
   addresses are being used via Carrier-Grade NAT (CGN), there is extra
   investment in the CGN devices, logs storage and helpdesk to track
   CGN-related issues.

   For this reason, when IPv4 traffic is vanishingly small or when IPv6
   usage increases to more than a given percentage, which highly depends
   on each network, it could be advantageous to switch to the IPv6-only
   stage with IPv4aaS.  It is difficult to establish the criterion for
   switching (e.g. to properly identify the upper bound of the IPv4
   decrease or the lower bound of the IPv6 increase).  In addition to
   the technical factors, the switch to IPv6-only may also include a
   loss of customers.  Based on operational experience and some
   measurements of network operators participating in World IPv6 Launch
   [WIPv6L] where, at June 2021, out of 346 entries 108 exceed 50% of
   IPv6 traffic volume (31.2%), 72 overcome 60% (20.8%), while 37 go
   beyond 75% (10.7%), the consensus to move to IPv6-only is when IPv6
   traffic volume is between 50% and 60%, which easily happens from
   since the moment IPv6 is deployed in networks where residential
   customers traffic is higher than business traffic (because major
   content providers, as already explained, already use IPv6).

4.2.  IPv6-only Service Delivery

   The second stage, named IPv6-only and including IPv4 support via
   IPv4aaS, can be a complex decision that depends on several factors,
   such as economic aspects, policy and government regulation.

   [I-D.ietf-v6ops-transition-comparison] discusses and compares the
   technical merits of the most common transition solutions for
   IPv6-only service delivery, 464XLAT [RFC6877], DS-lite [RFC6333],
   Lightweight 4over6 (lw4o6) [RFC7596], MAP-E [RFC7597], and MAP-T
   [RFC7599], but without providing an explicit recommendation.  As the
   poll highlights Appendix A, the most widely deployed IPv6 transition
   solution in the MBB domain is 464XLAT while in the FBB space is DS-
   Lite.

   Both of them are IPv6-only solutions providing IPv4aaS.  IPv4aaS
   offers Dual-Stack service to users and allows an operator to run
   IPv6-only in the network (typically, the access network).  It needs

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   to be observed that an increasing number of operators, also in the
   FBB area, tend to prefer 464XLAT over the other transition
   mechanisms, especially in the case of MBB/FBB convergence.

   While it cannot be always the case, IPv6-only transition technologies
   such as 464XLAT require much less IPv4 public addresses
   [I-D.ietf-v6ops-transition-comparison], because they make a more
   efficient usage without restricting the number of ports per
   subscriber.  This contributes to reduce troubleshooting costs and to
   remove some operational issues related to permanent black-listing of
   IPv4 address blocks when used via CGN in some services.  For example,
   Sony Play Station Network or OpenDNS imply a higher rotation of IPv4
   prefixes in CGN, until they get totally blocked, which means extra
   CAPEX in new IPv4 transfers.

   IPv6-only may be facilitated by the natural upgrade or replacement of
   CEs because of newer technologies (tripe-play, higher bandwidth WAN
   links, better WiFi technologies, etc.).  The CAPEX and OPEX of other
   parts of the network may be lowered (for example CGN and associated
   logs) due to the operational simplification of the network.

   In terms of addressing needs, for specific applications such as in
   the case of large mobile operators or large DCs, even the full
   private address space [RFC1918] is not large enough.  Also, Dual-
   Stack likely leads to duplication of network resources and operations
   to support both IPv6 and IPv4, which increases the amount of state
   information in the network.  For this reason, in some scenarios (e.g.
   MBB or DCs) IPv6-only stage could be more efficient from the start
   since the IPv6 introduction phase.

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

5.  IPv6-only Underlay Network Deployment

   IPv6-only alone can be misinterpreted as not supporting IPv4.  It can
   be referred to different portions of the network, to the underlay
   network, to the overlay network (services), as also mentioned in
   [I-D.palet-v6ops-ipv6-only].

   As opposed to the IPv6-only service delivery (with IPv4aaS) discussed
   in the previous sections, the IPv6-only network means that the whole
   network (both operator underlay transport and customer traffic
   overlay) uses IPv6 as the network protocol for all traffic delivery,
   but some operators may do IPv6-only at the access network only.  This
   can be accomplished on a case-by-case basis.

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   As a matter of fact, IPv4 reachability must be provided for a long
   time to come over IPv6 for IPv6-only endpoints.  Most operators are
   leveraging CGN to extend the life of IPv4 instead of going with
   IPv4aaS.

   When operators (both enterprises and service providers) start to
   migrate from an IPv4 core, MPLS LDPv4 core, SR-MPLSv4 core to
   introduce IPv6 in the underlay, they do not necessarily need to dual
   stack the underlay to maintain both IPv4 and IPv6 address families in
   the transport layer.  Forwarding plane complexity on the Provider (P)
   core should be kept simple as a single protocol only core.  An
   example could be Softwire Mesh Framework [RFC5565] which is based on
   a standard single protocol IPv4-Only or IPv6-Only for core where
   where IPv4 packets can be tunneled over 4to6 MPLS software over an
   IPv6-Only core.

   Hence, when operators decide to migrate to an IPv6 underlay, the
   Provider (P) core should be IPv4-only or IPv6-only while Dual-Stack
   is not the best choice.  The underlay could be IPv6-only and allows
   IPv4 packets to be tunneled using VPN over an IPv6-only core and
   leveraging Advertising IPv4 Network Layer Routing Information (NLRI)
   with an IPv6 Next Hop [RFC8950].  Indeed, [RFC8950] specifies the
   extensions necessary to allow advertising IPv4 NLRI, Virtual Private
   Network Unicast (VPN-IPv4) NLRI, Multicast Virtual Private Network
   (MVPN-IPv4) NLRI with a Next Hop address that belongs to the IPv6
   protocol.  And also, [I-D.ietf-bess-ipv6-only-pe-design] allows dual-
   stacked functionality without having to dual-stack the interface and
   without any tunneling mechanisms, resulting in OPEX savings for the
   elimination of IPv4 addressing and BGP peering.  This also enables
   the quick deployment of IPv6 in a core or Data Center network without
   provisioning IPv6 links with global unicast address, that can be a
   long process in very large networks.

   Regarding the IPv6 underlay network deployment for Access Network
   (AN) Metro Edge BNG to NG edge, the current trend is to keep MPLS
   Data Plane IPv4-only and run IPv4/IPv6 Dual Stack to the Access
   Network (AN) to Customer RG edge node.

   As operators do the transition in the future to IPv6 metro and
   backbone network, e.g.  Segment Routing over IPv6 data plane (SRv6),
   they are able to start the elimination of IPv4 from the underlay
   transport network while continuing to provide overlay IPv4 services.
   Basically, as also showed by the poll among network operators, from a
   network architecture perspective, it is not recommended to apply
   Dual-Stack to the transport network per reasons mentioned above about
   the forwarding plane complexities.

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   If we consider IPv6-only to mean both operator underlay network and
   customer VPN traffic, that 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.

6.  IPv6 Benefits

   A comparison of the technical and operational characteristics of IPv4
   and IPv6 should quite easily highlight the merits of the latter.  On
   the other hand, the long path IPv6 is still taking to become the
   dominant network protocol shows that those merits are either not
   clear enough or not sufficient against other market, managerial or
   financial reasons.  The scope of this section is to list what are
   generally considered the benefits of IPv6, following discussions at
   the IETF and other communities.  The list below does not mean to be
   exhaustive; it tries to collect some facts about the use of IPv6.

   1.  Address space advantage: this is probably the most well-known
       characteristic of IPv6.  The address space is orders of magnitude
       wider than IPv4's.  With the emergence of new digital
       technologies, such as 5G, IoT and Cloud, new use cases have come
       into being, posing new requirements to IP networks.  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 to Internet
       technology and services.  Other sections of this paper have
       already mentioned the efforts of both network and content
       providers to evolve their internal infrastructures to be
       IPv6-only to solve the issue of a constrained address space.
       From an operational perspective, the wide IPv6 address space
       avoids the typical renumbering activities that take place either
       when two networks merge or when an infrastructure needs to span
       across multiple geographic regions.

   2.  Government and regulation incentives: the shift to IPv6 is
       beneficial to create the market conditions to foster innovation
       and competition.  This is, as an example, one of conclusions
       highlighted in [ARCEP]: "This dearth of IPv4 addresses means that
       the internet will not stop working but it will stop growing.
       This shortage is also resulting in a significant increase in the
       price being charged for these addresses in the secondary market,
       which creates a real barrier to entry for new entrants to the
       internet.  It has therefore become imperative, for the sake of
       competition and innovation, that all internet players switch over
       to IPv6".  Governments have a huge responsibility in promoting

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       IPv6 deployment.  Some of them are 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 bid.  This will encourage the network
       operators and vendors who do not want to miss out on government
       related bids to evolve their infrastructures 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].  In China, the government launched IPv6 action plan in
       2017, which requires that networks, applications and terminal
       devices will fully support the adoption of IPv6 by the end of
       2025 [CN].

   3.  New functionality and standard: it has been already mentioned the
       IAB statement [IAB], which asks the IETF, as well as other
       Standards Developing Organizations (SDOs), 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.  [RFC6540] recommends that all networking standards assume
       the use of IPv6 and be written so they do not require IPv4.  In
       addition, every RIR worldwide strongly recommends immediate IPv6
       adoption.  This is an incentive to network equipment vendors to
       endorse IPv6 and view it as the standards-based solution to the
       IPv4 address shortage.  The introduction of new functionality is
       one of the technical benefit of IPv6 due to the flexible
       structure of the packet header.  The IETF is currently active in
       defining operational recommendations for the usage of Extension
       Headers and Options left open by the base standards.

   4.  Future Proof: IPv6 was designed from scratch to be future-proof,
       despite some incompatibilities with IPv4.  For example,
       mechanisms to translate back and forth from IPv4 to IPv6 are
       already in place in mobile networks worldwide.  This allows to
       introduce newer generations of mobile services, as in the case of
       5G applications.  While exceptions may exist, IPv6 foresees the
       absence of NAT along the network path.  This allows an operator
       to remove the technical constraints of handling NAT and the
       relevant cost.  A side effect to that, this approach brings the
       connectivity model back to the end-to-end client/server paradigm.
       Worth noting, the vast majority of terminals is IPv6-capable.
       Content is also greatly available on IPv6.  The service

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       connectivity, from terminal to content, in particular in mobile
       networks, is reality.

7.  Common IPv6 Challenges

   There are some areas of improvement, that are often mentioned in the
   literature and during the discussions on IPv6 deployment.  This
   section highlights these common IPv6 challenges in order to encourage
   more investigations on these aspects.

7.1.  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 approaches that service providers
   and enterprises may take and the related challenges.

7.1.1.  Service Providers

   For fixed operators, the massive software upgrade of CEs to support
   Dual-Stack already started in most of service provider networks.  On
   average, looking at the global statistics, the IPv6 traffic
   percentage is currently between 30% and 40% of IPv6.  As highlighted
   earlier, 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, CE costs, CGN
   costs and so on.

      Fixed Operators with a Dual-Stack architecture, can start defining
      and apply a new strategy when reaching the limit in terms of
      number of IPv4 addresses available.  This can be done through CGN
      or with an IPv6-only approach (IPv4aaS).

      On the one hand, most of the fixed operators remain attached to a
      Dual-Stack architecture and have already employed CGN.  In this
      case it is likely that CGN boosts their ability to supply IPv4
      connectivity to CEs for more years to come.  On the other hand,
      only few fixed operators have chosen to move to IPv6-only.

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   For mobile operators, the situation is quite different since, in some
   cases, mobile operators are already stretching their IPv4 address
   space since CGN translation levels have been reached and no more IPv4
   public pool addresses are available.

      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 address scarcity issue.

   For both fixed and mobile operators the approach for the transition
   is not unique and this bring different challenges in relation to the
   network architecture and related costs.  So each operator needs to do
   own evaluations for the transition based on the specific situation.

7.1.2.  Enterprises and Industrial Internet

   At present, the key driver for enterprises relies on upstream service
   providers.  If they run out of IPv4 addresses, it is likely that they
   start providing native IPv6 and non-native IPv4.  So for other
   networks trying to reach enterprise networks, the IPv6 experience
   could be better than the transitional IPv4 if the enterprise deploys
   IPv6 in its public-facing services.  IPv6 also shows its advantages
   in the case of acquisition, indeed when an enterprise merges two
   networks which use IPv4 private addresses, the address space of the
   two networks may overlap and this makes the merge difficult.  Since
   several governments are introducing IPv6 policy, all the enterprises
   providing consulting service to governments are also required to
   support IPv6 and to show their technical expertise in the IPv6 arena.

   Enterprises are shielded from IPv4 address depletion issues due to
   Enterprises predominantly using Proxy and Non internet routable
   private [RFC1918], thus do not have the business requirement or
   technical justification to migrate to IPv6.  Enterprises need to find
   a business case and a strong motivation for IPv6 transition to
   justify additional CAPEX and OPEX.  Also, since ICT is not the core
   business for most of the enterprises, ICT budget is often constrained
   and cannot expand considerably.  However, there are examples of big
   enterprises that are considering IPv6 to achieve business targets
   through a more efficient IPv6 network and to introduce newer services
   which require future-proof IPv6 network architectures.

   Enterprises worldwide, in particular small and medium-sized, are
   quite late to adopt IPv6, especially on internal networks.  In most
   cases, the enterprise engineers and technicians don't know well how
   IPv6 works and the problem of application porting to IPv6 looks quite

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   difficult, even if technically is not a big issue.  As highlighted in
   the relevant poll, the technicians may want to get trained but the
   management 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 IPv6.  In 2019 and 2020, there has been a concerted
   effort by some grass roots non-profits working with ARIN and APNIC to
   provide training [ARIN-CG] [ISIF-ASIA-G].

   For enterprises, the challenge is that of "First Mover Disadvantage".
   Compared to network operators that may feel the need of a network
   evolution towards IPv6, enterprises typically upgrade to new
   technologies and architectures, such as IPv6, only if it gains them
   revenue, and this is evident, at least in the short term.

   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,
   as for enterprises, it is important to provide an easy way to
   familiarize system architects and software developers with the IPv6
   protocol.

   For Industrial Internet and related IIoT applications, it would be
   desirable to be able to implement a truly distributed system without
   dependencies to central components.  In this regard the distributed
   IIoT applications can leverage the configuration-less characteristic
   of IPv6.  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.

7.1.3.  Cloud and Data Centers

   Most 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.  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.

   It is interesting to look at how much traffic in a network is going
   to Caches and Content Delivery Networks (CDNs).  The response is
   expected to be an high percentage, at least higher than 50% in most
   of the cases.  Since all the key Caches and CDNs are IPv6-ready
   [Cldflr], [Akm], [Ggl], [Ntflx], [Amzn], [Mcrsft], [Vrzn].  So the

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   percentage of traffic going to the key Caches/CDNs is a good
   approximation of the potential IPv6 traffic in a network.

   The challenge for CSPs is related to the support of non-native IPv4
   since most CSPs provide native IPv6.  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 could be charged to their
   customers.

7.1.4.  CEs and user devices

   It can be noted that most of the user devices (e.g. smartphones) are
   already IPv6-enabled since so many years.  But there are exceptions,
   for example, smartTVs and Set-Top Box (STBs) typically had IPv6
   support since few years ago, however not all the economies replace
   them at the same pace.

   As already mentioned, ISPs who historically provided public IPv4
   addresses to their customers generally still have those IPv4
   addresses (unless they chose to transfer them).  Some have chosen to
   put new customers on CGN but without touching existing customers.
   Because of the extremely small number of customers who notice that
   IPv4 is done via NAT444, it could be less likely to run out of IPv4
   addresses and private IPv4 space.  But as IPv4-only devices and
   traffic reduce, then the need to support private and public IPv4
   become less.  So the complete support of CEs to IPv6 is also an
   important challenge and incentive to overcome Dual-Stack towards
   IPv6-only with IPv4aaS [ANSI].

7.2.  Government and Regulators

   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

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   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].  China is another example of govern
   supporting a country-wide adoption.

7.3.  Network Management and Operations

   There are important IPv6 complementary solutions related to
   Operations, Administration and Maintenance (OAM) that look not so
   complete compared to IPv4.  Network Management System (NMS) has a
   central role in the modern networks for both network operators and
   enterprises and its transition is a fundamental challenge.  This is
   because some IPv6 products are not field-proven as for IPv4 even if
   traditional protocols (e.g.  SNMP, RADIUS) already supports IPv6.  In
   addition, incompatible vendor roadmap for the development of new NMS
   features affects the confidence of network operators or enterprises.
   For example, YANG is the configuration language for networking but in
   the real world the data modeling is still vendor dependent.

   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 transition.  Staff has to be aware of the best
   practices for managing IPv4 and IPv6 assets.  In addition to network
   nodes, network management applications and equipment need to be
   properly configured and in some cases also replaced.  This may
   introduce more complexity and costs for the transition.

7.4.  Performance

   People tend to compare the performance of IPv6 versus IPv4 to argue
   or motivate the IPv6 transition.  In some cases, IPv6 behaving
   "worse" than IPv4 may be used as an argument for avoiding the full
   adoption of IPv6.  However, there are some aspects where IPv6 is
   filling the gap to IPv4.  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.  While performance is
   undoubtedly an important issue to consider and worth further
   investigation, reality is that a definitive answer cannot be found on
   what IP version performs better.  Depending on the specific use case
   and application, IPv6 is better; in others the same applies to IPv4.

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7.4.1.  IPv6 packet loss and latency

   [APNIC5] provides a measurement of both the failure rate and RTT of
   IPv6 compared against IPv4.  Both measures are based on scripts that
   employs the three-way handshake of TCP.  As such, the measurement of
   the failure rate does not provide a direct measurement of packet loss
   (that would need an Internet-wide measurement campaign).  Said that,
   despite IPv4 is still performing better, the difference seems to have
   decreased in recent years.  Two reports, namely [RIPE1] and
   [APRICOT], discussed the associated trend, showing how the average
   worldwide failure rate of IPv6 is still a bit worse than IPv4.
   Reasons for this effect may be found in endpoints with an unreachable
   IPv6 address, routing instability or firewall behavior.  Yet, this
   worsening effect may appear as disturbing for a plain transition to
   IPv6.

   [APNIC5] also 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.  Regions (e.g.  Western Europe, Northern
   America, Southern Asia) and Countries (e.g.  US, India, Germany) with
   an advanced deployment of IPv6 (e.g. >45%) are showing that IPv6 has
   better performance 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 CDNs are also available [MAPRG],
   [INFOCOM].  The TCP connect time is still higher for IPv6 in both
   cases, even if the gap has reduced over the analysis time window.

7.4.2.  Customer Experience

   It is not totally clear if the Customer Experience is in some way
   perceived as better when IPv6 is used instead of IPv4.  In some cases
   it has been publicly reported by IPv6 content providers, that users
   have a better experience when using IPv6-only compared to IPv4
   [ISOC2].  This could be explained because in the case of an IPv6 user
   connecting to an application hosted in an IPv6-only Data Centers, the
   connection is end-to-end, without translations.  Instead, when using
   IPv4 there is a NAT translation either in the CE or in the service
   provider's network, in addition to IPv4 to IPv6 (and back to IPv4)
   translation in the IPv6-only content provider Data Center.  [ISOC2],

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   [FB] provide reasons in favor of IPv6.  In other cases, the result
   seems to be still slightly in favor of IPv4 [INFOCOM], [MAPRG], even
   if the difference between IPv4 and IPv6 tends to vanish over time.

7.5.  IPv6 security

   Another point that is sometimes considered as a challenge when
   discussing the transition to IPv6 is related to the Security.
   [RFC9099] analyzes the operational security issues in several places
   of a network (enterprises, service providers and residential users).
   It is also worth considering the additional security issues brought
   into existence by the applied IPv6 transition technologies used to
   implement IPv4aaS, e.g. 464XLAT, DS-Lite.  Some hints are in the
   paper [ComputSecur].

   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.  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 [ISOC3], 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.

   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.
   However, this is turning also in the other way around, as with more

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   IPv6 deployment there may be older IPv4 flaws not discovered or even
   not resolved anymore by vendors.

   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
   networks.

   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.

7.5.1.  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
      Mechanisms)

   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 add new security threats and
   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.

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

7.5.2.  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.  Some documents, e.g.
   [I-D.hinden-6man-hbh-processing], [I-D.bonica-6man-ext-hdr-update],
   [I-D.peng-v6ops-hbh] analyze and provide guidance regarding the
   processing procedures of IPv6 Extension Headers.

   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
   isolated).

   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 important 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 node.
   [I-D.vasilenko-v6ops-ipv6-oversized-analysis] analyzes available
   standards for the resolution of oversized packet drops.

8.  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.

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9.  Contributors

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

10.  Acknowledgements

   The authors of this document would like to thank Brian Carpenter,
   Fred Baker, Alexandre Petrescu, Barbara Stark, Haisheng Yu(Johnson),
   Dhruv Dhody, Gabor Lencse, Shuping Peng, Daniel Voyer, Daniel
   Bernier, Hariharan Ananthakrishnan, Donavan Fritz, Igor Lubashev,
   Erik Nygren, Eduard Vasilenko and Xipeng Xiao for their comments and
   review of this document.

11.  IANA Considerations

   This document has no actions for IANA.

12.  References

12.1.  Normative References

   [I-D.ietf-v6ops-transition-comparison]
              Lencse, G., Martinez, J. P., Howard, L., Patterson, R.,
              and I. Farrer, "Pros and Cons of IPv6 Transition
              Technologies for IPv4aaS", draft-ietf-v6ops-transition-
              comparison-02 (work in progress), March 2022.

   [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,
              <https://www.rfc-editor.org/info/rfc1918>.

   [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,
              <https://www.rfc-editor.org/info/rfc3756>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <https://www.rfc-editor.org/info/rfc3971>.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213,
              DOI 10.17487/RFC4213, October 2005,
              <https://www.rfc-editor.org/info/rfc4213>.

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   [RFC6036]  Carpenter, B. and S. Jiang, "Emerging Service Provider
              Scenarios for IPv6 Deployment", RFC 6036,
              DOI 10.17487/RFC6036, October 2010,
              <https://www.rfc-editor.org/info/rfc6036>.

   [RFC6180]  Arkko, J. and F. Baker, "Guidelines for Using IPv6
              Transition Mechanisms during IPv6 Deployment", RFC 6180,
              DOI 10.17487/RFC6180, May 2011,
              <https://www.rfc-editor.org/info/rfc6180>.

   [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,
              <https://www.rfc-editor.org/info/rfc6333>.

   [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,
              <https://www.rfc-editor.org/info/rfc6540>.

   [RFC6583]  Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
              Neighbor Discovery Problems", RFC 6583,
              DOI 10.17487/RFC6583, March 2012,
              <https://www.rfc-editor.org/info/rfc6583>.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <https://www.rfc-editor.org/info/rfc6877>.

   [RFC6883]  Carpenter, B. and S. Jiang, "IPv6 Guidance for Internet
              Content Providers and Application Service Providers",
              RFC 6883, DOI 10.17487/RFC6883, March 2013,
              <https://www.rfc-editor.org/info/rfc6883>.

   [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,
              <https://www.rfc-editor.org/info/rfc7381>.

   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
              Farrer, "Lightweight 4over6: An Extension to the Dual-
              Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
              July 2015, <https://www.rfc-editor.org/info/rfc7596>.

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   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <https://www.rfc-editor.org/info/rfc7597>.

   [RFC7599]  Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
              and T. Murakami, "Mapping of Address and Port using
              Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July
              2015, <https://www.rfc-editor.org/info/rfc7599>.

   [RFC8950]  Litkowski, S., Agrawal, S., Ananthamurthy, K., and K.
              Patel, "Advertising IPv4 Network Layer Reachability
              Information (NLRI) with an IPv6 Next Hop", RFC 8950,
              DOI 10.17487/RFC8950, November 2020,
              <https://www.rfc-editor.org/info/rfc8950>.

   [RFC9099]  Vyncke, E., Chittimaneni, K., Kaeo, M., and E. Rey,
              "Operational Security Considerations for IPv6 Networks",
              RFC 9099, DOI 10.17487/RFC9099, August 2021,
              <https://www.rfc-editor.org/info/rfc9099>.

12.2.  Informative References

   [Akm]      Akamai, "IPv6 Adaptation",
              <https://www.akamai.com/us/en/multimedia/documents/
              product-brief/ipv6-adaptation-product-brief.pdf>.

   [Akm-stats]
              Akamai, "IPv6 Adoption Visualization", 2021,
              <https://www.akamai.com/uk/en/resources/our-thinking/
              state-of-the-internet-report/state-of-the-internet-ipv6-
              adoption-visualization.jsp>.

   [Alx]      Alexa, "The top 500 sites on the web", 2021,
              <https://www.alexa.com/topsites>.

   [Amzn]     Amazon, "Announcing Internet Protocol Version 6 (IPv6)
              support for Amazon CloudFront, AWS WAF, and Amazon S3
              Transfer Acceleration", <https://aws.amazon.com/es/about-
              aws/whats-new/2016/10/ipv6-support-for-cloudfront-waf-and-
              s3-transfer-acceleration/>.

   [ANSI]     ANSI/CTA, "ANSI/CTA Standard Host and Router Profiles for
              IPv6", 2020, <https://shop.cta.tech/products/host-and-
              router-profiles-for-ipv6>.

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   [APNIC1]   APNIC, "IPv6 Capable Rate by country (%)", 2022,
              <https://stats.labs.apnic.net/ipv6>.

   [APNIC2]   APNIC2, "Addressing 2021", 2022,
              <https://blog.apnic.net/2022/01/19/ip-addressing-in-
              2021/>.

   [APNIC3]   APNIC, "BGP in 2020 - The BGP Table", 2021,
              <https://blog.apnic.net/2021/01/05/bgp-in-2020-the-bgp-
              table/>>.

   [APNIC4]   APNIC, "BGP in 2021 - The BGP Table", 2022,
              <https://blog.apnic.net/2022/01/06/bgp-in-2021-the-bgp-
              table/>>.

   [APNIC5]   APNIC, "Average RTT Difference (ms) (V6 - V4) for World
              (XA)", 2022, <https://stats.labs.apnic.net/v6perf/XA>.

   [APRICOT]  Huston, G., "Average RTT Difference (ms) (V6 - V4) for
              World (XA)", 2020,
              <https://2020.apricot.net/assets/files/APAE432/ipv6-
              performance-measurement.pdf>.

   [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,
              <https://www.arcep.fr/uploads/tx_gsavis/19-1386.pdf>.

   [ARIN-CG]  ARIN, "Community Grant Program: IPv6 Security,
              Applications, and Training for Enterprises", 2020,
              <https://www.arin.net/about/community_grants/recipients/>.

   [ARIN-SW]  ARIN, "Preparing Applications for IPv6",
              <https://www.arin.net/resources/guide/ipv6/
              preparing_apps_for_v6.pdf>.

   [BGR_1]    BIIGROUP, "China Commercial IPv6 and DNSSEC Deployment
              Monitor", 2022,
              <http://218.2.231.237:5001/cgi-bin/generate>.

   [BGR_2]    BIIGROUP, "China Government IPv6 and DNSSEC Deployment
              Monitor", 2022,
              <http://218.2.231.237:5001/cgi-bin/generate_gov>.

   [BGR_3]    BIIGROUP, "China Education IPv6 and DNSSEC Deployment
              Monitor", 2022,
              <http://218.2.231.237:5001/cgi-bin/generate_edu>.

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   [CAIDA]    APNIC, "Client-Side IPv6 Measurement", 2020,
              <https://www.cmand.org/workshops/202006-v6/
              slides/2020-06-16-client-side.pdf>.

   [CAIR]     Cisco, "Cisco Annual Internet Report (2018-2023) White
              Paper", 2020,
              <https://www.cisco.com/c/en/us/solutions/collateral/
              executive-perspectives/annual-internet-report/white-paper-
              c11-741490.html>.

   [Cldflr]   Cloudflare, "Understanding and configuring Cloudflare's
              IPv6 support", <https://support.cloudflare.com/hc/en-us/
              articles/229666767-Understanding-and-configuring-
              Cloudflare-s-IPv6-support>.

   [CN]       China.org.cn, "China to speed up IPv6-based Internet
              development", 2017, <http://www.china.org.cn/
              business/2017-11/27/content_41948814.htm>.

   [CN-IPv6]  National IPv6 Deployment and Monitoring Platform, "Active
              IPv6 Internet users", 2022,
              <https://www.china-ipv6.cn/#/activeconnect/simpleInfo>.

   [CNLABS_1]
              CNLABS, "Industry IPv6 and DNSSEC Statistics", 2022,
              <https://cnlabs.in/IPv6_Mon/generate_industry.html>.

   [CNLABS_2]
              CNLABS, "Industry IPv6 and DNSSEC Statistics", 2022,
              <https://cnlabs.in/IPv6_Mon/generate_gov.html>.

   [CNLABS_3]
              CNLABS, "Industry IPv6 and DNSSEC Statistics", 2022,
              <https://cnlabs.in/IPv6_Mon/generate_industry.html>.

   [ComputSecur]
              Computers & Security (Elsevier), "Methodology for the
              identification of potential security issues of different
              IPv6 transition technologies: Threat analysis of DNS64 and
              stateful NAT64", DOI 10.1016/j.cose.2018.04.012, 2018.

   [Csc6lab]  Cisco, "World - Display Content Data", 2022,
              <https://6lab.cisco.com/stats/>.

   [ETSI-IP6-WhitePaper]
              ETSI, "ETSI White Paper No. 35: IPv6 Best Practices,
              Benefits, Transition Challenges and the Way Forward",
              ISBN 979-10-92620-31-1, 2020.

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   [FB]       Saab, P., "Facebook IPv6 Experience", 2015,
              <https://youtu.be/An7s25FSK0U>.

   [G_stats]  Google, "Google IPv6 Per-Country IPv6 adoption", 2021,
              <https://www.google.com/intl/en/ipv6/
              statistics.html#tab=per-country-ipv6-adoption>.

   [Ggl]      Google, "Introduction to GGC",
              <https://support.google.com/interconnect/
              answer/9058809?hl=en>.

   [HxBld]    HexaBuild, "IPv6 Adoption Report 2020", 2020,
              <https://hexabuild.io/assets/files/HexaBuild-IPv6-
              Adoption-Report-2020.pdf>.

   [I-D.bonica-6man-ext-hdr-update]
              Bonica, R. and T. Jinmei, "Inserting, Processing And
              Deleting IPv6 Extension Headers", draft-bonica-6man-ext-
              hdr-update-07 (work in progress), February 2022.

   [I-D.hinden-6man-hbh-processing]
              Hinden, R. M. and G. Fairhurst, "IPv6 Hop-by-Hop Options
              Processing Procedures", draft-hinden-6man-hbh-
              processing-01 (work in progress), June 2021.

   [I-D.ietf-bess-ipv6-only-pe-design]
              Mishra, G., Mishra, M., Tantsura, J., Madhavi, S., Yang,
              Q., Simpson, A., and S. Chen, "IPv6-Only PE Design for
              IPv4-NLRI with IPv6-NH", draft-ietf-bess-ipv6-only-pe-
              design-00 (work in progress), September 2021.

   [I-D.palet-v6ops-ipv6-only]
              Martinez, J. P., "IPv6-only Terminology Definition",
              draft-palet-v6ops-ipv6-only-05 (work in progress), March
              2020.

   [I-D.peng-v6ops-hbh]
              Peng, S., Li, Z., Xie, C., Qin, Z., and G. Mishra,
              "Processing of the Hop-by-Hop Options Header", draft-peng-
              v6ops-hbh-06 (work in progress), August 2021.

   [I-D.vasilenko-v6ops-ipv6-oversized-analysis]
              Vasilenko, E., Xipeng, X., and D. Khaustov, "IPv6
              Oversized Packets Analysis", draft-vasilenko-v6ops-ipv6-
              oversized-analysis-01 (work in progress), September 2021.

   [IAB]      IAB, "IAB Statement on IPv6", 2016,
              <https://www.iab.org/2016/11/07/iab-statement-on-ipv6/>.

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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/
              https://www.internetgovernance.org/wp-content/uploads/
              IPv6-Migration-Study-final-report.pdf>.

   [INFOCOM]  Doan, T., "A Longitudinal View of Netflix: Content
              Delivery over IPv6 and Content Cache Deployments", 2020,
              <https://dl.acm.org/doi/abs/10.1109/
              INFOCOM41043.2020.9155367>.

   [IPv6Forum]
              IPv6Forum, "Estimating IPv6 & DNSSEC External Service
              Deployment Status", 2022,
              <https://www.ipv6forum.com/IPv6-Monitoring/index.html>.

   [ISIF-ASIA-G]
              ISIF Asia, "Internet Operations Research Grant: IPv6
              Deployment at Enterprises. IIESoc. India", 2020,
              <https://isif.asia/2020-grantees/>.

   [ISOC1]    Internet Society, "State of IPv6 Deployment 2018", 2018,
              <https://www.internetsociety.org/resources/2018/state-of-
              ipv6-deployment-2018/>.

   [ISOC2]    Internet Society, "Facebook News Feeds Load 20-40% Faster
              Over IPv6", 2015,
              <https://www.internetsociety.org/blog/2015/04/facebook-
              news-feeds-load-20-40-faster-over-ipv6/>.

   [ISOC3]    Internet Society, "IPv6 Security FAQ", 2019,
              <https://www.internetsociety.org/wp-
              content/uploads/2019/02/Deploy360-IPv6-Security-FAQ.pdf>.

   [MAPRG]    Bajpai, V., "Measuring YouTube Content Delivery over
              IPv6", 2017, <https://www.ietf.org/proceedings/99/slides/
              slides-99-maprg-measuring-youtube-content-delivery-over-
              ipv6-00.pdf>.

   [Mcrsft]   Microsoft, "IPv6 for Azure VMs available in most regions",
              <https://azure.microsoft.com/en-us/updates/ipv6-for-azure-
              vms/>.

   [NRO]      NRO, "Internet Number Resource Status Report", 2021,
              <https://www.nro.net/wp-content/uploads/NRO-Statistics-
              2021-Q3-FINAL.pdf>.

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   [NST_1]    NIST, "Estimating Industry IPv6 and DNSSEC External
              Service Deployment Status", 2022, <https://fedv6-
              deployment.antd.nist.gov/cgi-bin/generate-com>.

   [NST_2]    NIST, "Estimating USG IPv6 and DNSSEC External Service
              Deployment Status", 2022, <https://fedv6-
              deployment.antd.nist.gov/cgi-bin/generate-gov>.

   [NST_3]    NIST, "Estimating University IPv6 and DNSSEC External
              Service Deployment Status", 2022, <https://fedv6-
              deployment.antd.nist.gov/cgi-bin/generate-edu>.

   [Ntflx]    Netflix, "Enabling Support for IPv6",
              <https://netflixtechblog.com/enabling-support-for-
              ipv6-48a495d5196f>.

   [POTAROO1]
              POTAROO, "IP Addressing through 2021", 2022,
              <https://www.potaroo.net/ispcol/2022-01/addr2021.html>.

   [POTAROO2]
              POTAROO, "IPv6 Resource Allocations", 2022,
              <https://www.potaroo.net/bgp/iso3166/v6cc.html>.

   [RFC5565]  Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
              Framework", RFC 5565, DOI 10.17487/RFC5565, June 2009,
              <https://www.rfc-editor.org/info/rfc5565>.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
              2012, <https://www.rfc-editor.org/info/rfc6555>.

   [RFC8305]  Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
              Better Connectivity Using Concurrency", RFC 8305,
              DOI 10.17487/RFC8305, December 2017,
              <https://www.rfc-editor.org/info/rfc8305>.

   [RIPE1]    Huston, G., "Measuring IPv6 Performance", 2016,
              <https://ripe73.ripe.net/wp-content/uploads/
              presentations/35-2016-10-24-v6-performance.pdf>.

   [RIPE2]    RIPE, "IPv6 Security", 2019,
              <https://www.ripe.net/support/training/material/ipv6-
              security/ipv6security-slides.pdf>.

   [RIPE3]    RIPE, "IPv6", 2021,
              <https://www.ripe.net/participate/meetings/roundtable/26-
              january-2021/ipv6_roundtable_-jan-2021.pdf>.

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   [RlncJ]    Reliance Jio, "IPv6-only adoption challenges and
              standardization requirements", 2020,
              <https://datatracker.ietf.org/meeting/109/materials/
              slides-109-v6ops-ipv6-only-adoption-challenges-and-
              standardization-requirements-03>.

   [SNDVN]    SANDVINE, "Sandvine releases 2020 Mobile Internet
              Phenomena Report: YouTube is over 25% of all mobile
              traffic", 2020, <https://www.sandvine.com/press-releases/
              sandvine-releases-2020-mobile-internet-phenomena-report-
              youtube-is-over-25-of-all-mobile-traffic>.

   [US-CIO]   The CIO Council, "Memorandum for Heads of Executive
              Departments and Agencies. Completing the Transition to
              Internet Protocol Version 6 (IPv6)", 2020,
              <https://www.cio.gov/assets/resources/internet-protocol-
              version6-draft.pdf>.

   [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/
              documents/2020/03/02/2020-04202/request-for-comments-on-
              updated-guidance-for-completing-the-transition-to-the-
              next-generation>.

   [Vrzn]     Verizon, "Verizon Digital Media Services announces IPv6
              Compliance", <https://www.verizondigitalmedia.com/blog/
              verizon-digital-media-services-announces-
              ipv6-compliance/>.

   [W3Tech]   W3Tech, "Historical yearly trends in the usage statistics
              of site elements for websites", 2021, <https://w3techs.com
              /technologies/history_overview/site_element/all/y>.

   [Wikipedia]
              Wikipedia, "Comparison of IPv6 support in common
              applications", <https://en.wikipedia.org/wiki/
              Comparison_of_IPv6_support_in_common_applications>.

   [WIPv6L]   World IPv6 Launch, "World IPv6 Launch - Measurements",
              2021, <https://www.worldipv6launch.org/measurements/>.

Appendix A.  Summary of Questionnaire and Replies for network operators

   A survey was proposed to more than 50 service providers in the
   European region during the third quarter of 2020 to ask for their
   plans on IPv6 and the status of IPv6 deployment.

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   40 people, representing 38 organizations, provided a response.  This
   appendix summarizes the results obtained.

   Respondents' business
                               Convergent  Mobile  Fixed
       Type of operators       82%         8%      11%

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

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

   b.  What are 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?

   Answer 1.A (38 respondents)

                           Yes     No
       Plans availability  79%     21%

                           Mobile  Fixed   Enterprise  Don't answer
       Business segment    63%     63%     50%         3%

   Answer 1.B (29 respondents)

   Even this was an open question, some common answers can be found.

   14 respondents (48%) highlighted issues related to IPv4 depletion.
   The reason to move to IPv6 is to avoid private and/or overlapping
   addresses.

   For 6 respondents (20%) 5G/IoT is a business incentive to introduce
   IPv6.

   4 respondents (13%) also highlight that there is a National
   regulation request to enable IPv6 associated with the launch of 5G.

   4 respondents (13%) consider IPv6 as a part of their innovation
   strategy or an enabler for new services.

   4 respondents (13%) introduce IPv6 because of Enterprise customers
   demand.

   Answer 1.C (30 respondents)

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                   On-going  In 12 months  After 12 months  Don't answer
      Timeframe    60%       33%           0%               7%

   Answer 1.D (28 respondents for cellular, 27 for wireline)

      Transition in use   Dual-Stack  464XLAT  MAP-T  Don't answer
      Cellular            39%         21%      4%     36%

      Transition in use   Dual-Stack  DS-Lite  6RD/6VPE   Don't answer
      Wireline            59%         19%      4%         19%

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

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

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

   Answer 2.A (30 respondents)

                          Yes  No   Don't answer
      Need of changing    43%  33%  23%

                          CEs     Routers  BNG  CGN   Mobile core
      What to change      47%     27%      20%  33%   27%

   Answer 2.B (22 respondents)

                            Yes  Future  No
      Plans for transition   9%   9%      82%

Appendix B.  Summary of Questionnaire and Replies for enterprises

   The Industry Network Technology Council (INTC) developed the
   following poll to verify the need or willingness of medium-to-large
   US-based enterprises for training and consultancy on IPv6
   (https://industrynetcouncil.org/).

   54 organizations provided an answer.

   Question 1.  How much IPv6 implementation have you done at your
   organization? (54 respondents)

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      None                                            16.67%
      Some people have gotten some training           16.67%
      Many people have gotten some training            1.85%
      Web site is IPv6 enabled                         7.41%
      Most equipment is dual-stacked                  31.48%
      Have an IPv6 transition plan for entire network  5.56%
      Running native IPv6 in many places              20.37%
      Entire network is IPv6-only                      0.00%

   Question 2.  What kind of help or classes would you like to see INTC
   do? ( 54 respondents)

      Classes/labs on IPv6 security                   66.67%
      Classes/labs on IPv6 fundamentals               55.56%
      Classes/labs on address planning/network conf.  57.41%
      Classes/labs on IPv6 troubleshooting            66.67%
      Classes/labs on application conversion          35.19%
      Other                                           14.81%

   Question 3.  As you begin to think about the implementation of IPv6
   at your organization, what areas do you feel are of concern? (54
   respondents)

      Security                    31.48%
      Application conversion      25.93%
      Training                    27.78%
      All the above               33.33%
      Don't know enough to answer 14.81%
      Other                        9.26%

Authors' Addresses

   Giuseppe Fioccola
   Huawei Technologies
   Riesstrasse, 25
   Munich  80992
   Germany

   Email: giuseppe.fioccola@huawei.com

   Paolo Volpato
   Huawei Technologies
   Via Lorenteggio, 240
   Milan  20147
   Italy

   Email: paolo.volpato@huawei.com

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

   Email: nalini.elkins@insidethestack.com

   Jordi Palet Martinez
   The IPv6 Company
   Molino de la Navata, 75
   La Navata - Galapagar, Madrid  28420
   Spain

   Email: jordi.palet@theipv6company.com

   Gyan S. Mishra
   Verizon Inc.

   Email: gyan.s.mishra@verizon.com

   Chongfeng Xie
   China Telecom

   Email: xiechf@chinatelecom.cn

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