Pros and Cons of IPv6 Transition Technologies for IPv4aaS

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IPv6 Operations Working Group                                 G. Lencse
Internet Draft                                                     BUTE
Intended status: Informational                        J. Palet Martinez
Expires: April 2018                                    The IPv6 Company
                                                              L. Howard
                                                           R. Patterson
                                                                 Sky UK
                                                       October 22, 2018

         Pros and Cons of IPv6 Transition Technologies for IPv4aaS


   Several IPv6 transition technologies can be used to provide IPv4-as-
   a-service (IPv4aaS) to the customers, while the ISPs have only IPv6
   in their access and or core network. All these technologies have
   their advantages and disadvantages. Depending on several various
   conditions and preferences, different technologies may prove to be
   the most appropriate solution. This document examines the five most
   prominent IPv4aaS technologies considering several different aspects
   in order to provide network operators with an easy to use guideline
   for selecting the technology that suit their needs the best.

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   This Internet-Draft will expire on April 22, 2019.

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Table of Contents

   1. Introduction ................................................. 3
   2. High-level Architectures and their Consequences .............. 3
      2.1. Service Provider Network Traversal ...................... 3
      2.2. IPv4 Address Sharing .................................... 4
   3. Detailed Analysis ............................................ 4
      3.1. Architectural Differences ............................... 4
         3.1.1. 464XLAT ............................................ 4
         3.1.2. DS-Lite ............................................ 5
         3.1.3. Lw4o6 .............................................. 5
         3.1.4. MAP-E .............................................. 6
         3.1.5. MAP-T .............................................. 6
         3.1.6. Basic Comparison ................................... 6
      3.2. Tradeoff between Port Number Efficiency and Stateless
             Operation ............................................. 7
      3.3. Support for Server Operation ............................ 9
      3.4. Support and Implementations ............................. 9
         3.4.1. OS Support ......................................... 9
         3.4.2. Support in Cellular and Broadband Networks ......... 9
         3.4.3. Implementation Code Sizes ......................... 10
      3.5. Typical Deployment and Traffic Volume Considerations ... 10
         3.5.1. Deployment Possibilities .......................... 10
         3.5.2. Cellular Networks with 464XLAT .................... 10
      3.6. Load Sharing ........................................... 11
      3.7. Logging ................................................ 11
   4. Performance Comparison ...................................... 11
   5. Security Considerations ..................................... 12
   6. IANA Considerations ......................................... 12
   7. Conclusions ................................................. 12

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   8. References .................................................. 13
      8.1. Normative References ................................... 13
      8.2. Informative References ................................. 14
   9. Acknowledgments ............................................. 15

1. Introduction

   IETF has standardized a high number of IPv6 transition technologies
   [Len2017] and occupied a neutral position trusting the selection to
   the market. In the upcoming years, several network operators would
   like to get rid of the burden of maintaining IPv4 in their access
   and/or core networks. This document deals with five different
   solutions, each of which can be used to provide an IPv4 service
   using an IPv6-only access/core network. The following IPv6
   transition technologies are covered: 464XLAT [RFC6877], DS-Lite
   (Dual Stack Lite) [RFC6333], lw4o6 (Lightweight 4over6) [RFC7596],
   MAP-E [RFC7597] and MAP-T [RFC7599].

2. High-level Architectures and their Consequences

2.1. Service Provider Network Traversal

   As for the high-level solution of IPv6 service provider network
   traversal, MAP-T use double translation. First at the CE from IPv4
   to IPv6 (NAT46), and then from IPv6 to IPv4 (NAT64), at the service
   provider network.

   464XLAT may use double translation (stateless NAT46 + stateful
   NAT64) or single translation (stateful NAT64), depending on
   different factors, such as the use of DNS by the applications and
   the availability of a DNS64 function (in the host or in the service
   provider network). For deployment guidelines, please refer to [I-

   DS-Lite, lw4o6 and MAP-E encapsulate the IPv4 packets into IPv6

   Each solution has its own advantages and drawbacks. Double
   translation results in only 20 bytes overhead (the difference in the
   minimum header size between IPv4 and IPv6), whereas the overhead of
   the encapsulation is 40 bytes (because both, the IPv4 and IPv6
   headers are included). The difference may be significant in the case
   of small packet sizes or when the overhead results in fragmentation.

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   The first step of the double translation cases is a stateless NAT
   from IPv4 to IPv6 implemented as SIIT (Stateless IP/ICMP Translation
   Algorithm) [RFC7915], which does not translate IPv4 options and/or
   multicast IP/ICMP packets, whereas with encapsulation-based
   technologies these remain intact.

   On the other hand, single and double translation results in "normal"
   IPv6 traffic which can be inspected, e.g., by hashing algorithms,
   and firewalls, whereas encapsulation results in IPv4-embedded IPv6
   packets and their interpretation requires special software/hardware
   for looking further into the packet.

   The worst case is DS-Lite, which is also doing double stateful
   translation (NAT44 at the CE and NAT44 at the AFTR).

   Another consequence is that the solutions using double translation
   can carry only TCP, UDP or ICMP over IP, when they are used with
   IPv4 address sharing (please refer to section 3.3 for more details),
   whereas the solutions using encapsulation can carry any other
   protocols over IP, too.

   We also note that none of the five solutions support "native" IPv4
   multicast. Please refer to Section 4 of [I-D.draft-ietf-v6ops-
   transition-ipv4aas] for the planned requirements for CE routers.

2.2. IPv4 Address Sharing

   All five technologies support IPv4 address sharing, which has severe
   consequences described in [RFC6269].

   The efficiency of the address sharing of the five technologies is
   significantly different, it is discussed in section 3.2.

   We note that lw4o6, MAP-E and MAP-T can also be configured without
   IPv4 address sharing, see the details in Section 3.3. However in
   that case, there is no advantage in terms of public IPv4 address

3. Detailed Analysis

3.1. Architectural Differences

3.1.1. 464XLAT

   When 464XLAT is used, in the simplest case, CLAT performs a
   stateless translation from IPv4 to IPv6 [RFC7915]. It uses IPv4-

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   embedded IPv6 addresses [RFC6052] for both source address and
   destination address. PLAT performs stateful NAT64 [RFC6146].

   Alternatively, when a dedicated /64 is not available for
   translation, the CLAT device uses a stateful NAT44 translation
   before the stateless NAT46 translation.

   Note that we generally do not see state close to the end-user as
   equally problematic as state in the middle of the network.

   In typical deployments, 464XLAT is used together with DNS64, see
   Section 3.1.2 of [I-D.draft-ietf-v6ops-nat64-deployment]. When an
   IPv6-only client communicates with an IPv4-only server, the DNS64
   server returns the IPv4-embedded IPv6 address of the IPv4-only
   server. In this case, the IPv6-only client sends out IPv6 packets,
   thus CLAT functions as an IPv6 router and the PLAT performs a
   stateful NAT64 for these packets.

   Alternatively, one can say that the DNS64 + stateful NAT64 is used
   to carry the traffic of the IPv6-only client and the IPv4-only
   server, and the CLAT is used only for the IPv4 traffic from
   applications or devices that use literal IPv4 addresses or non-IPv6
   compliant APIs.

3.1.2. DS-Lite

   The B4 (Basic Bridging BroadBand) element performs a stateful NAT44
   and encapsulates the IPv4 packets into IPv6 packets. The AFTR
   (Address Family Transition Router) de-encapsulates the IPv4 packets
   from the IPv6 packets and performs stateful NAPT (Network Address
   and Port Translation).

3.1.3. Lw4o6

   Lightweight 4over6 is a variant of DS-Lite. The difference is, that
   the stateful NAPT is moved from the AFTR to the lwB4 element, so a
   single stateful NAT44 is performed. It uses a provisioning mechanism
   to determine the size of the limited port-set per user. The AFTR
   becomes a lwAFTR.

   Alternatively, one can say that lw4o6 is a subset of MAP-E, as it
   uses the same provisioning, the same port mapping algorithm, and is
   indistinguishable from MAP-E when used without IPv4 address sharing.

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3.1.4. MAP-E

   The CE (Customer-Edge) router first performs a stateful NAPT44
   [RFC2663] to transform the source addresses and source port numbers
   of the IPv4 packets into a predefined range, the size of which is a
   design parameter. The CE router then encapsulates the IPv4 packet in
   an IPv6 packet [RFC2473]. MAP defines a special stateless mapping
   algorithm, which encodes the relevant IPv4 address[es] into the IPv6
   address, either wholly or partially depending on the BMR.
   Optionally, when used with IPv4 address sharing, port set bits may
   also be encoded in to the IPv6 source address. This transformation
   may be fine-tuned by the mapping rules. Packets destined outside of
   the MAP domain must traverse a MAP BR to be de-encapsulated. Packets
   destined for another CE router within the MAP domain may be
   forwarded directly with an appropriate FMR, and de-encapsulated by
   the destination CE router.

3.1.5. MAP-T

   MAP-T works very similarly to MAP-E, with the difference that it
   uses double translation instead of encapsulation. It can also be
   compared to 464XLAT when there is a double translation.

   After performing the above mentioned stateful NAPT44, the CE router
   performs stateless translation from IPv4 to IPv6 [RFC7915], which
   also translates the IPv4 address and port set ID into the IPv6
   address space, based on the BMR. The MAP BR (Border Relay) performs
   stateless translation from IPv4 to IPv6 [RFC7915].

   Using translation instead of encapsulation also allows IPv4-only
   nodes to correspond directly with IPv6 nodes in the MAP-T domain
   that have IPv4-embedded IPv6 addresses.

3.1.6. Basic Comparison

   The five IPv4aaS technologies can be classified into 2x2=4
   categories on the basis of two aspects:

   .  Technology used for service provider network traversal. It can be
      single/double translation or encapsulation.

   .  Presence or absence of state in the operator network.

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   State in the    | Service provider network traversal technology

   operator        |  single/double  |    encapsulation/

   network         |   translation   |    de-encapsulation


   Present         |     464XLAT     |        DS-Lite


   Absent          |      MAP-T      |      MAP-E, lw4o6

3.2. Tradeoff between Port Number Efficiency and Stateless Operation

   464XLAT and DS-Lite use stateful NAPT at the PLAT and AFTR devices,
   respectively. This may cause scalability issues. Lw4o6, MAP-E and
   MAP-T avoid using NAPT in the service provider network. Its cost is
   that they have to limit the port numbers available for a user.

   Although the number of ports available for a user is limited with
   all five technologies, when used with address sharing, the stateful
   technologies, such as 464XLAT and DS-Lite, allow for dynamic and
   centrally adjustable port allocations, whereas port ranges are
   predetermined and fixed with the three A+P (Address plus Port) based
   technologies, lw4o6, MAP-E, and MAP-T.

   Determining the optimal size of the fixed port set is not an easy
   task, but may also be impacted by local regulatory law, which may
   define a maximum number of users per IP address, and consequently a
   minimum number of ports per user.

   On the one hand, the "lack of ports" situation may cause serious
   problems in the operation of certain applications. For example,
   Miyakawa has demonstrated the consequences of the session number
   limitation due to port number shortage on the example of Google Maps
   [Miy2010]. When the limit was 15, several blocks of the map were
   missing, and the map was unusable. This study also provided several
   examples for the session numbers of different applications (the
   highest one was iTunes: 230-270 ports).

   The port number consumption of different applications is highly
   varying and e.g. in the case of web browsing it depends on several
   factors, including the choice of the web page, the web browser, and

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   sometimes even the operating system [Rep2014]. For example, under
   certain conditions, 120-160 ports were used (URL:, browser:
   Firefox under Ubuntu Linux), and in some other cases it was only 3-
   12 ports (URL:, browser: Iceweasel under Debian Linux).

   There may be several users behind a CE router, especially in the
   broadband case (e.g. Internet is used by different members of a
   family simultaneously), so sufficient ports must be allocated to
   avoid impacting user experience.

   However, on the other hand, assigning too many ports per CE router
   will result in waste of public IPv4 addresses, which is a scarce and
   expensive resource.

   We note that common CE router NAT44 implementations utilizing
   Netfilter, use a 3-tuple (source address, destination address, and
   destination port) approach for source port allocation; external
   source ports will be reused for unique internal source and
   destination address and port flows.  It is also noted, that
   Netfilter cannot currently make use of multiple source port ranges,
   this may influence the design when using stateless technologies.

   Stateful technologies, 464XLAT and DS-Lite (and also NAT444) can
   therefore be much more efficient in terms of port allocation and
   thus public IP address saving. The price is the stateful operation
   in the service provider network, which is allegedly does not scale
   up well. It should be noticed that in many cases, all those factors
   may depend on how it is actually implemented.


   We note that these CGN-type solutions can allocate ports dynamically
   "on the fly". Depending on configuration, this can result in the
   same customer being allocated ports from different source addresses.
   This can cause operational issues for protocols and applications
   that expect multiple flows to be sourced from the same address.
   E.g., ECMP hashing, STUN, gaming, content delivery networks.
   However, it should be noticed that this is the same problem when a
   network has a NAT44 with multiple public IPv4 addresses, or even
   when applications in a dual-stack case, behave wrongly if happy
   eyeballs is flapping the flow address between IPv4 and IPv6.

   The consequences of IPv4 address sharing [RFC6269] may impact all
   five technologies. However, when ports are allocated dynamically,
   more customers may get ports from the same public IPv4 address,
   which may results in negative consequences with higher probability,
   e.g. many applications and service providers (Sony PlayStation

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   Network, OpenDNS, etc.) permanently black-list IPv4 ranges if they
   detect that they are used for address sharing.

   Both cases are, again, implementation dependent.

   We note that although it is not of typical use, one can do
   deterministic stateful NAT and reserve a fixed set of ports for each
   customer, too.

3.3. Support for Server Operation

   Lw4o6, MAP-E and MAP-T may be configured without IPv4 address
   sharing, allowing exclusive use of all ports, and non-port-based
   layer 4 protocols. Thus, they may also be used to support
   server/services operation. However, when public IPv4 addresses are
   assigned to the CE router without address sharing, obviously there
   is no advantage in terms of IPv4 public addresses saving.

   It is also possible to configure specific ports mapping in
   464XLAT/NAT64 using EAMT [RFC7757], which means that only those
   ports are "lost" from the pool of addresses, so there is a higher
   maximization of the total usage of IPv4/port resources.

   We note that MAP-E and MAP-T may also provide more than one IP
   address (that is a complete prefix) to the customers.

3.4. Support and Implementations

3.4.1. OS Support

   As for 464XLAT, client support (CLAT) exists in Windows 10, Linux
   (including Android), Windows Mobile, Chrome OS and iOS, but it is
   missing from MacOS. For the other four solutions, we are not aware
   of any OS support.

3.4.2. Support in Cellular and Broadband Networks

   Several cellular networks use 464XLAT, whereas we are not aware of
   any deployment of the four other technologies in cellular networks,
   as they are not supported.

   In broadband networks, there are some deployments of 464XLAT, MAP-E
   and MAP-T. Both, lw4o6 and DS-Lite have more deployments, having
   been up now DS-Lite the most used one, but lw4o6 taking over in the
   last years.

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3.4.3. Implementation Code Sizes

   As for complexity hint, the code size reported from OpenWRT
   implementation is 17kB, 35kB, 15kB, 35kB, and 48kB for 464XLAT,
   lw4o6, DS-Lite, MAP-E, MAP-T, and lw4o6, respectively

   We note that the support for all five technologies requires much
   less code size than the total sum of the above quantities, because
   they contain a lot of common functions (data plane is shared among
   several of them).

3.5. Typical Deployment and Traffic Volume Considerations

3.5.1. Deployment Possibilities

   Theoretically, all five covered IPv4aaS technologies could be used
   together with DNS64 + stateful NAT64, as it is done in 464XLAT. In
   this case the CE router would treat the traffic between an IPv6-only
   client and IPv4-only server as normal IPv6 traffic, and the stateful
   NAT64 gateway would do a single translation, thus offloading this
   kind of traffic from the IPv4aaS technology. The cost of this
   solution would be the need for deploying also DNS64 + stateful

   However, this has not been implemented in clients or actual
   deployments, so only 464XLAT always uses this optimization and the
   other four solutions do not use it at all.

3.5.2. Cellular Networks with 464XLAT

   Actual figures from existing deployments, show that the typical
   traffic volumes in an IPv6-only cellular network, when 464XLAT
   technology is used together with DNS64, are:

   .  75% of traffic is IPv6 end-to-end (no translation)

   .  24% of traffic is uses DNS64 + NAT64 (1 translation)

   .  Less than 1% of traffic use the CLAT in addition to NAT64 (2
      translations), due to an IPv4 socket and/or IPv4 literal.

   Without using DNS64, 25% of the traffic would undergo double

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3.6. Load Sharing

   If multiple network-side devices are needed as PLAT/AFTR/BR for
   capacity, then there is a need for a load sharing technology. ECMP
   (Equal-Cost Multi-Path) load sharing can be used for all
   technologies, however stateful technologies will be impacted by
   changes in network topology or device failure.

   Technologies utilizing DNS64 can also distribute load across
   PLAT/AFTR devices, evenly or unevenly, by using different prefixes.
   Different network specific prefixes can be distributed for
   subscribers in appropriately sized segments (like split-horizon DNS,
   also called DNS views).

   Stateless technologies, due to the lack of flow tracking, can make
   use of anycast routing for load sharing and resiliency across
   network-devices, both ingress and egress; flows can take asymmetric
   paths through the network, i.e., in through one lwAFTR/BR and out
   via another.

3.7. Logging

   In the case of 464XLAT and DS-Lite, it varies with time who uses a
   given public IPv4 address and port combination, therefore, logging
   is necessary to be able to investigate possible abuses.

   Configurations that dynamically assign ports "on the fly", will have
   a much higher capacity requirement for logging, than those that
   assign port blocks or ranges.

   Stateless technologies that algorithmically assign addresses and
   ports, e.g., lw4o6, MAP-T, MAP-E, may require additional support
   tools to assist in resolving assignments, but require no additional

4. Performance Comparison

   We plan to compare the performances of the most prominent free
   software implementations of the five IPv6 transition technologies
   using the methodology described in "Benchmarking Methodology for
   IPv6 Transition Technologies" [RFC8219].

   On the one hand, the Dual DUT Setup of RFC8219 makes it possible to
   use the existing "Benchmarking Methodology for Network Interconnect
   Devices" [RFC2544] compliant measurement devices, however, this
   setup has the drawback that the performances of the CE and of the
   ISP side device (e.g. the CLAT and the PLAT of 464XLAT) are measured

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   together. In order to measure the performance of only one of them,
   we need to ensure that the desired one is the bottleneck.

   On the other hand, the Single DUT Setup of [RFC8219] makes it
   possible to benchmark the selected device separately, however, no
   [RFC8219] compliant testers available yet. A DPDK-based software
   Tester for stateless NAT64 is currently under development and it is
   expected to be available this autumn as a free software. XXX FROM

   Any volunteers for developing [RFC8219] compliant measurement

5. Security Considerations

   According to the simplest model, the number of bugs is proportional
   to the number of code lines. Please refer to section 3.4.3 for code
   sizes of CE implementations.

   For all five technologies, the CE device should contain a DNS proxy.
   However, the user may change DNS settings. If it happens and lw4o6,
   MAP-E and MAP-T are used with significantly restricted port set,
   which is required for an efficient public IPv4 address sharing, the
   entropy of the source ports is significantly lowered (e.g. from 16
   bits to 10 bits, when 1024 port numbers are assigned to each
   subscriber) and thus these technologies are theoretically less
   resilient against cache poisoning, see [RFC5452]. However, an
   efficient cache poisoning attack requires that the subscriber
   operates an own caching DNS server and the attack is performed in
   the service provider network. Thus, we consider the chance of the
   successful exploitation of this vulnerability as low.

   An in-depth security analysis of all five IPv6 transition
   technologies and their most prominent free software implementations
   according to the methodology defined in [Len2018] is planned.

6. IANA Considerations


7. Conclusions


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8. References

8.1. Normative References

   [RFC2544] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
             Network Interconnect Devices", RFC 2544, DOI
             10.17487/RFC2544, March 1999, <http://www.rfc-

   [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
             IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
             December 1998, <>.

   [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
             Translator (NAT) Terminology and Considerations", RFC
             2663, DOI 10.17487/RFC2663, August 1999, <http://www.rfc-

   [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
             Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
             DOI 10.17487/RFC6052, October 2010, <http://www.rfc-

   [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
             NAT64: Network Address and Protocol Translation from IPv6
             Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
             April 2011, <

   [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
             Beijnum, "DNS64: DNS extensions for Network Address
             Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
             DOI 10.17487/RFC6147, April 2011.

   [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
             Roberts, "Issues with IP Address Sharing", RFC 6269, DOI
             10.17487/RFC6269, June 2011, <http://www.rfc-

    [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,

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

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   [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, <>.

   [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, <http://www.rfc-

   [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, <>.

   [RFC7915] Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
             "IP/ICMP translation algorithm", RFC 7915, DOI:
             10.17487/RFC7915, June 2016, <http://www.rfc-

   [RFC7757] Anderson, T., and A. Leiva Popper "Explicit Address
             Mappings for Stateless IP/ICMP Translation", RFC 7757, DOI
             10.17487/RFC7757, February 2016, <http://www.rfc-

   [RFC8219] Georgescu, M., Pislaru, L., and G. Lencse, "Benchmarking
             Methodology for IPv6 Transition Technologies", IETF RFC
             8219, DOI: 10.17487/RFC8219, Aug. 2017, <http://www.rfc-

8.2. Informative References

   [I-D.draft-ietf-v6ops-nat64-deployment]  J. Palet, "NAT64/464XLAT
             Deployment Guidelines in Operator and Enterprise
             Networks", draft-ietf-v6ops-nat64-deployment-03, (work in
             progress), October 2018.

   [I-D.draft-ietf-v6ops-transition-ipv4aas] Palet, J., Liu, H., and M.
             Kawashima, "Requirements for IPv6 Customer Edge Routers to
             Support IPv4 Connectivity as-a-Service", draft-ietf-v6ops-
             transition-ipv4aas-10, (work in progress), October 2018.

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   [Len2017] Lencse, G., and Y. Kadobayashi, "Survey of IPv6 Transition
             Technologies for Security Analysis", IEICE Communications
             Society Internet Architecture Workshop, Tokyo, Japan, Aug.
             28, 2017, IEICE Tech. Rep., vol. 117, no. 187, pp. 19-24.

   [Len2018] Lencse, G., and Y. Kadobayashi, "Methodology for the
             identification of potential security issues of different
             IPv6 transition technologies: Threat analysis of DNS64 and
             stateful NAT64", Computers & Security (Elsevier), vol. 77,
             no. 1, pp. 397-411, August 1, 2018, DOI:

   [Miy2010] Miyakawa, S., "IPv4 to IPv6 transformation schemes", IEICE
             Trans. Commun., vol.E93-B, no.5, pp.1078-1084, May 2010.

   [Rep2014] Repas, S., Hajas, T., and G. Lencse, "Port number
             consumption of the NAT64 IPv6 transition technology",
             Proc. 37th Internat. Conf. on Telecommunications and
             Signal Processing (TSP 2014), Berlin, Germany, pp.66-72,
             Jul. 1-3, 2014. DOI: 10.1109/TSP.2015.7296411

9. Acknowledgments

   The authors would like to thank Ole Troan for his thorough review of
   this draft and acknowledge the inputs of Ole Troan, Mark Andrews,
   Edwin Cordeiro, Fred Baker, Alexandre Petrescu, Cameron Byrne, Tore
   Anderson, Alexandre Petrescu, Mikael Abrahamsson, Gert Doering,
   Satoru Matsushima, and TBD.

   This document was prepared using

   Copyright (c) 2018 IETF Trust and the persons identified as authors
   of the code. All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, is permitted pursuant to, and subject to the license
   terms contained in, the Simplified BSD License set forth in Section
   4.c of the IETF Trust's Legal Provisions Relating to IETF Documents

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Authors' Addresses

   Gabor Lencse
   Budapest University of Technology and Economics
   Magyar Tudosok korutja 2.
   H-1117 Budapest, Hungary


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


   Lee Howard
   9940 Main St., Suite 200
   22031, USA

   Richard Patterson
   Sky UK
   1 Brick Lane
   London, E1 6PU
   United Kingdom


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