Network Working Group                                           J. Arkko
Internet-Draft                                                A. Keranen
Intended status: Informational                                  Ericsson
Expires: April 29, 2011                                 October 26, 2010

                 Experiences from an IPv6-Only Network


   This document discusses our experiences from moving a small number of
   users to an IPv6-only network, with access to the IPv4-only parts of
   the Internet via a NAT64 device.  The document covers practical
   experiences as well as road blocks and opportunities for this type of
   a network setup.  The document also makes some recommendations about
   where such networks are applicable and what should be taken into
   account in the network design.  The document also discusses further
   work that is needed to make IPv6-only networking applicable in all

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 29, 2011.

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   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Technology and Terminology . . . . . . . . . . . . . . . . . .  4
   3.  Network Setup  . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  The IPv6-Only Network  . . . . . . . . . . . . . . . . . .  5
     3.2.  DNS Operation  . . . . . . . . . . . . . . . . . . . . . .  6
   4.  General Experiences  . . . . . . . . . . . . . . . . . . . . .  7
   5.  Experiences with IPv6-Only Networking  . . . . . . . . . . . .  9
     5.1.  Operating Systems  . . . . . . . . . . . . . . . . . . . .  9
     5.2.  Programming Languages and APIs . . . . . . . . . . . . . . 10
     5.3.  Instant Messaging and VoIP . . . . . . . . . . . . . . . . 10
     5.4.  Gaming . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.5.  Music Services . . . . . . . . . . . . . . . . . . . . . . 12
     5.6.  Appliances . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.7.  Other Differences  . . . . . . . . . . . . . . . . . . . . 12
   6.  Experiences with NAT64 . . . . . . . . . . . . . . . . . . . . 12
     6.1.  IPv4 Address Literals  . . . . . . . . . . . . . . . . . . 13
     6.2.  Comparison of Web Access via NAT64 to Other Methods  . . . 13
   7.  Future Work  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  Conclusions and Recommendations  . . . . . . . . . . . . . . . 15
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

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1.  Introduction

   This document discusses our experiences from moving a small number of
   users to an IPv6-only network, with access to the IPv4-only parts of
   the Internet via a NAT64 device.  This arrangement has been done with
   a permanent change in mind rather than as a temporary experiment,
   involves both office and home users, heterogeneous computing
   equipment, and varied applications.  We have learned both practical
   details, road blocks and opportunities, as well as more general
   understanding of when such a configuration can be recommended and
   what should be taken into account in the network design.

   The networks involved in this setup have been in dual stack mode for
   considerable amount of time, in one case for over ten years.  Our
   IPv6 connectivity is stable and in constant use with no significant
   problems.  Given that the IETF is working on technology such as NAT64
   [I-D.ietf-behave-v6v4-framework] and several network providers are
   discussing the possibility of employing IPv6-only networking, we
   decided to take our network beyond the "comfort zone" and make sure
   that we understand the implications of having no IPv4 connectivity at
   all.  This also allowed us to test a NAT64 device that is being
   developed by Ericsson.

   The main conclusion is that it is possible to employ IPv6-only
   networking, though there are a number of issues such as lack of IPv6
   support in some applications and bugs in untested parts of code.  As
   a result, dual-stack [RFC4213] remains as our recommended model for
   general purpose networking at this time, but IPv6-only networking can
   be employed by early adopters or highly controlled networks.  The
   document also suggests actions to make IPv6-only networking
   applicable in all environments.  In particular, resolving problems
   with a few key applications would have a significant impact for
   enabling IPv6-only networking for large classes of users and
   networks.  It is important that the Internet community understands
   these deployment barriers and works to remove them.

   The rest of this document is organized as follows.  Section 2
   introduces some relevant technology and terms, Section 3 describes
   the network setup, Section 4 discusses our general experiences,
   Section 5 discusses experiences related to having only IPv6
   networking available, and Section 6 discusses experiences related to
   NAT64 use.  Finally, Section 7 presents some of our ideas for future
   work and Section 8 draws conclusions and makes recommendations on
   when and how one should employ IPv6-only networks.

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2.  Technology and Terminology

   In this document, the following terms are used.  "NAT44" refers to
   any IPv4-to-IPv4 network address translation algorithm, both "Basic
   NAT" and "Network Address/Port Translator (NAPT)", as defined by

   "Dual Stack" refers to a technique for providing complete support for
   both Internet protocols -- IPv4 and IPv6 -- in hosts and routers

   "NAT64" refers to a Network Address Translator - Protocol Translator
   defined in [I-D.ietf-behave-v6v4-framework],
   [I-D.ietf-behave-v6v4-xlate], [I-D.ietf-behave-v6v4-xlate-stateful],
   [I-D.ietf-behave-address-format], [I-D.ietf-behave-dns64], and

3.  Network Setup

   We have tested IPv6-only networking in two different network
   environments: office and home.  In both environments all hosts had
   normal dual stack native IPv4 and IPv6 Internet access already in
   place.  The networks were also already employing IPv6 in their
   servers and DNS records.  Similarly, the network was a part of
   whitelisting arrangement to ensure that IPv6-capable content
   providers would be able to serve their content to the network over

   The office environment has heterogeneous hardware with PCs, laptops,
   and routers running Linux, Mac OS X, and Microsoft Windows operating
   systems.  Common uses of the network include e-mail, Secure Shell
   (SSH), web browsing, and various instant messaging and Voice over IP
   (VoIP) applications.  The hardware in the home environment consists
   of PCs, laptops and a number of server, camera, and sensor
   appliances.  The primary operating systems in this environment are
   Linux and Microsoft Windows operating systems.  Common applications
   include web browsing, streaming, instant messaging and VoIP
   applications, gaming, file storage, and various home control
   applications.  Both environments employ extensive firewalling
   practices, and filtering is applied for both IPv4 and IPv6 traffic.
   However, firewall capabilities, especially with older versions of
   firewall software, dictate some differences between the filtering
   applied for IPv4 and IPv6 since some features commonly supported for
   IPv4 were not yet implemented for IPv6.  In addition, in the home
   environment the individual devices are directly accessible from the
   Internet on IPv6 (on select protocols such as SSH) but not on IPv4
   due to lack of available public IPv4 addresses.

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   In both environments, volunteers had the possibility to opt-in for
   the IPv6-only network.  The number of users is small: there are
   roughly five permanent users and a dozen users who have been in the
   network at least for some amount of time.  Each user had to connect
   to the IPv6-only wired or wireless network, and depending on their
   software, possibly configure their computer by indicating that there
   is no IPv4 and/or setting DNS server addresses.  The users were also
   asked to report their experiences back to the organizers.

3.1.  The IPv6-Only Network

   The IPv6-only network was provided as a parallel network on the side
   of the already existing dual stack network.  It was important to
   retain the dual stack network for the benefit of those users who did
   not decide to opt-in and also because we knew that there were some
   IPv4-only devices in the network.  A separate wired access network
   was created using Virtual Local Area Networks (VLANs).  This network
   had its own IPv6 prefix.  A separate wireless network, bridged to the
   wired network, was also created.  With the devices that were used in
   our environment the new wireless network required additional access
   point hardware in order to accommodate advertising multiple wireless
   networks.  The simple access point model that we employed in these
   networks did not allow this on a single device.  All the secondary
   infrastructure resulted in some additional management burden and
   cost, however.  An added complexity was that the home network already
   employed two types of infrastructure, one for family members and
   another one for visitors.  In order to duplicate this model for the
   IPv6-only network there are now four separate networks, with several
   access points on each.

   A NAT64 with integrated DNS64 was installed on the edge of the IPv6-
   only networks.  No IPv4 routing or Dynamic Host Configuration
   Protocol (DHCP) was offered on these networks.  The NAT64 device
   sends Router Advertisements (RAs) [RFC4861] from which the hosts
   learn the IPv6 prefix and can automatically configure IPv6 addresses
   for them.  Each new IPv6-only network needed one new /64 prefix to be
   used in these advertisements.  In addition, each NAT64 device needed
   another /64 prefix to be used for the representation of IPv4
   destinations in the IPv6-only network.  As a result, one IPv6-only
   network requires an additional /63 of address space.  This space was
   easily available in our networks, as IPv6 allocations are on purpose
   made in sufficiently large blocks.  Additional address space needs
   can be accommodated from the existing block without registry
   involvement.  Another option would have been to use the Well-Known
   Prefix [I-D.ietf-behave-address-format] for the representation of
   IPv4 destinations in the IPv6-only network.  In any case, the
   prefixes have to be listed in the intra-domain routing system so that
   they can be reached.  In one case the increase from one block to

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   multiple also made it necessary to employ an improved routing
   configuration.  In addition to routing, the new prefixes have to be
   listed in the appropriate firewall rules.

3.2.  DNS Operation

   The RAs are also used to carry DNS Configuration options [RFC5006],
   listing the DNS64 as the DNS server the hosts should use.  In
   addition, aliases were added to the DNS64 device to allow it to
   receive packets on the well-known DNS server addresses that Windows
   operating systems use (fec0:0:0:ffff::1, fec0:0:0:ffff::2, and fec0:
   0:0:ffff::3).  At a later stage support for stateless DHCPv6
   [RFC3736] was added.  We do recommend enabling RFC 5006, well-known
   addresses, and stateless DHCPv6 in order to maximize the likelihood
   of different types of IPv6-only hosts being able to use DNS without
   manual configuration.  DNS server discovery was never a problem in
   dual stack networks, because DNS servers on the IPv4 side can easily
   provide IPv6 information (AAAA records) as well.  With IPv6-only
   networking, it becomes crucial that the local DNS server can be
   reached via IPv6 as well.

   When a host served by the DNS64 asks for a domain name that does not
   have an AAAA (IPv6 address) record, but has an A (IPv4 address)
   record, an AAAA record is synthesized from the A record (as defined
   for DNS64 in [I-D.ietf-behave-dns64]) and sent in the DNS response to
   the host.  IP packets sent to this synthesized address are routed via
   the NAT64, translated to IPv4 by the NAT64, and forwarded to the
   queried host's IPv4 address; return traffic is translated back from
   IPv4 to IPv6 and forwarded to the host behind the NAT64 (as described
   in [I-D.ietf-behave-v6v4-framework]).  This allows the hosts in the
   IPv6-only network to contact any host in the IPv4 Internet as long as
   the hosts in the IPv4 Internet have DNS address records.

   The NAT64 devices have standard dual stack connectivity and their
   DNS64 function can use both IPv4 and IPv6 when requesting information
   from DNS.  A destination that has both an A and AAAA records is not
   treated in any special manner, because the hosts in the IPv6-only
   network can contact the destination over IPv6.  Destinations with
   only an A record will be given a synthesized AAAA record as explained
   above.  However, in one of our open visitor networks that is sharing
   the infrastructure with the home network we needed a special
   arrangement.  Currently, the home network obtains its IPv6
   connectivity through a tunnel via the office network, and it is
   undesirable to allow outsiders using the visitor network to generate
   traffic through the office network, even if the traffic is just
   passing by and forwarded to the IPv6 Internet.  As a result, in the
   visitor network there is a special IPv6-only to IPv4-only
   configuration where the DNS64 never asks for AAAA records and always

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   generates synthesized records.  Therefore no traffic from the visitor
   network, even if it is destined to the IPv6 Internet, is routed via
   the office network but traffic from the home network can still use
   the IPv6 connectivity provided by the office network.

      Note: This configuration may also be useful for other purposes.
      For instance, one drawback of standard behavior is that if a
      destination publishes AAAA records but has bad IPv6 connectivity,
      the hosts in the IPv6-only network have no fallback.  In the dual
      stack model a host can always try IPv4 if the IPv6 connection
      fails.  In the special configuration IPv6 is only used internally
      at the site but never across the Internet, eliminating this
      problem.  This is not a recommended mode of operation, but it is
      interesting to note that it may solve some issues.

   Note that in NAT64 (unlike in its older variant [RFC4966]) it is
   possible to decouple the packet translation, IPv6 routing, and DNS64
   functions.  Since clients are configured to use a DNS64 as their DNS
   server, there is no need for having an Application Layer Gateway
   (ALG) on the path sniffing and spoofing DNS packets.  This decoupling
   possibility was used by one of our users, as he is outside of our
   physical network and wants to communicate directly on IPv6 where it
   is possible without having to go through our central network
   equipment.  His DNS queries go to our DNS64 and to establish
   communications to an IPv4 destination our central NAT64 is used.  If
   there is a need to translate some packets, these packets find the
   translator device through normal IPv6 routing means since the
   synthesized addresses have our NAT64's prefix.  However, for non-
   synthesized IPv6 addresses the packets are routed directly to the

4.  General Experiences

   Based on our experiences, it is possible to live (and work) with an
   IPv6-only network.  For instance, at the time of this writing, one of
   the authors has been in an IPv6-only network for about six months and
   has had no major problems.  Most things work well in the new
   environment; for example, we have been unable to spot any practical
   difference in the web browsing experience.  Also e-mail, software
   upgrades, operating system services, many chat systems and media
   streaming work well.  On certain mobile handsets that we tried all
   applications work flawlessly even on an IPv6-only network.

   However, there is some pain involved and thus it is not suitable for
   everyone just yet.  Switching IPv4 off does break many things as
   well.  Some of the users in our environment left due to these issues,
   as they missed some key feature that they needed from their computing

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   environment.  These issues fall in several categories:


      We saw many issues that can be classified as bugs, likely related
      to so few people having tried the software in question in an IPv6-
      only network.  For instance, some operating system facilities
      support IPv6 but have annoying problems that are only uncovered in
      IPv6-only networking.

   Lack of IPv6 Support

      We also saw many applications that do not support IPv6 at all.
      These range from minor, old tools (such as the Unix dict(1)
      command) to major applications that are important to our users
      (such as Skype) and even to entire classes of applications (many
      games have issues).

   Protocol, Format, and Content Problems

      There are many protocols that carry IP addresses in them, and
      using these protocols through a translator can lead to problems.
      In our current network setup we did not employ any ALGs except for
      FTP [I-D.ietf-behave-ftp64].  However, we have observed a number
      of protocol issues with IPv4 addresses.  For instance, some
      instant messaging services do not work due to this.  Finally,
      content on some web pages may refer to IPv4 address literals
      (i.e., plain IP addresses instead of host and domain names).  This
      renders some links inaccessible in an IPv6-only network.  While
      this problem is easily quantifiable in measurements, the authors
      have only run into it once during real-life web browsing.

   Firewall Issues

      We also saw a number of issues related to lack of features in IPv6
      support in firewalls.  In particular, while we did not experience
      any Maximum Transmission Unit (MTU) and fragmentation problems in
      our networks, there is potential for generating problems, as the
      support for IPv6 fragment headers is not complete in all firewalls
      and the NAT64 specifications call for use of the fragment header
      (even in situations where fragmentation has not yet occurred,
      e.g., if an IPv4 packet that is not a fragment does not have the
      Don't Fragment (DF) bit set).

   In general, most of the issues relate to poor testing and lack of
   IPv6 support in some applications.  IPv6 itself and NAT64 did not
   cause any major issues for us, once our setup and NAT64 software was
   stable.  In general, the authors feel that with the exception of some

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   applications, our experience with translation to reach the IPv4
   Internet has been equal to our past experiences with NAT44-based
   Internet access.  While translation implies loss of end-to-end
   connectivity, in practice direct connectivity has not been available
   to the authors in the IPv4 Internet either for a number of years.

   It should be noted that the experience with a properly configured set
   of ALGs and work-arounds such as proxies may be different.  Some of
   the problems we encountered can be solved through these means.  For
   instance, a problematic application can be configured to use a proxy
   that in turn has both IPv4 and IPv6 access.

5.  Experiences with IPv6-Only Networking

   The overall experience was as explained above.  The remainder of this
   section discusses specific issues with different operating systems,
   programming languages, applications, and appliances.

5.1.  Operating Systems

   Even operating systems have some minor problems with IPv6.  For
   example, in Linux RA information was not automatically updated when
   the network changes while the computer is on and required an
   unnecessary suspend/resume cycle to restore its proper state.  We
   have also had issues with the rdnssd deamon, which first does not
   come as a default feature in Ubuntu and does not always appear to
   work reliably.  To resolve these issues we had to configure the
   network manager to use a specific server address.

   In Mac OS X the network manager needed to be explicitly told to not
   expect IPv4.  A more annoying issue was that in order to switch
   between an IPv6-only and IPv4-only networks, these settings had to be
   manually changed, making it undesirable for Mac OS X users to employ
   IPv6-only networks.

   Also on Microsoft Windows 7 we experienced problems when relying on
   default, well-known DNS server addresses: without manual
   configuration, the host was unable to use the DNS addresses, even
   though the system displays them as current DNS server addresses.

   Latest versions of the Android operating system support IPv6 on its
   wireless LAN interface, but due to lack of DNS discovery mechanisms,
   this does not work in IPv6-only networks.  We corrected this,
   however, and prototype phones in our networks work now well even in
   an IPv6-only environment.  Interestingly, all applications that we
   have tried so far seem to work without problems with IPv6-only

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   While all these operating systems (or their predecessors) have
   supported IPv6 already for a number of years, these kind of small
   glitches seem to imply that they have not been thoroughly tested in
   networks lacking IPv4 connectivity.  At the very least their
   usability leaves something to be desired.

5.2.  Programming Languages and APIs

   For applications to be able to support IPv6, they need access to the
   necessary APIs.  Luckily, IPv6 seems to be well supported by majority
   of the commonly used APIs, but there is one notable exception: the
   Perl programming language (current version 5.12) does not yet have
   support for IPv6 sockets in its core libraries.  While IPv6 socket
   support is available as an extension module, it may not be possible
   to install this module without administrative rights.  This has also
   resulted in other networking core libraries (such as FTP and SMTP)
   not being able to fully support IPv6 and thus Perl programs using
   network functionality may not work in an IPv6-only environment.

5.3.  Instant Messaging and VoIP

   By far the biggest complaint from our group of users was that Skype
   stopped working.  In some environments even Skype can be made to work
   through a proxy configuration, and this was verified in our setting
   but not used as a permanent solution.  More generally, we tested a
   number of instance messaging applications in an IPv6-only network
   with NAT64 and the test results can be found from Table 1.

     SYSTEM                                 STATUS

     Facebook on the web (http)               OK
     Facebook via a client (xmpp)             OK chat service (xmpp)           OK
     Gmail chat on the web (http)             OK
     Gmail chat via a client (xmpp)           OK
     Gtalk client                           NOT OK
     AIM (AOL)                              NOT OK
     ICQ (AOL)                              NOT OK
     Skype                                  NOT OK
     MSN                                    NOT OK

   Table 1. Instant Messaging Applications in an IPv6-Only Network

   Packet tracing revealed that the issues in AIM, ICQ, and MSN appear
   to be related to passing literal IPv4 addresses in the protocol.  It
   remains to be determined whether this can be solved through
   configuration, proxies, or ALGs.  The problem with the Gtalk client

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   is that the software does not support IPv6 connections at this
   moment.  We are continuing our tests with additional applications
   such as Webex and Sametime, but have either not completed the work or
   have so far inconclusive results.  One problem in running these tests
   is to ensure that we can distinguish IPv6 and NAT64 issues from other
   issues, such as a generic issue on a given operating system platform.

   Some of this problems are solvable, however.  For instance, we used
   localhost as a proxy for Skype, and then used SSH to tunnel to an
   external web proxy, bypassing Skype's limitations with regards to
   connecting to IPv6 destinations or even IPv6 proxies.

5.4.  Gaming

   Another class of applications that we tried was games.  We tried both
   web-based gaming and standalone gaming applications that have a
   "network" / "Internet" or "LAN" gaming modes.  The results are shown
   in Table 2.

     SYSTEM                                           STATUS

     Web-based (e.g. armorgames)                        OK
     Runescape (on the web)                           NOT OK
     Flat out 2                                       NOT OK
     Battlefield                                      NOT OK
     Secondlife                                       NOT OK
     Guild Wars                                       NOT OK
     Age of Empires                                   NOT OK
     Star Wars: Empire at War                         NOT OK
     Crysis                                           NOT OK
     Lord of the Rings: Conquest                      NOT OK
     Rome Total War                                   NOT OK
     Lord of the Rings: Battle for Middle Earth 2     NOT OK

   Table 2. Gaming Applications in an IPv6-Only Network

   Most web-based games worked well, as expected from our earlier good
   general web experience.  However, we were also able to find one web-
   based game that failed to work (Runescape).  This particular game is
   a Java application that fails on an attempt to perform a HTTP GET
   request.  The reason remains unclear, but a likely theory is the use
   of an IPv4-literal in the application itself.

   The experience with standalone games was far more discouraging.
   Without exception all games failed to enable either connections to
   ongoing games in the Internet or even LAN-based connections to other
   computers in the same IPv6-only LAN segment.  This is somewhat
   surprising, and the result require further verification.

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   Unfortunately, the games provide no diagnostics about their
   operation, so it is hard to guess what is going on.  It is possible
   that their networking code employs older APIs that cannot use IPv6
   addresses [RFC4038].  The inability to provide any LAN-based
   connectivity is even more surprising, as this must mean that they are
   unable to use IPv4 link local connectivity, which should have been
   available to the devices (IPv4 was not blocked; just that no DHCP
   answers were provided on IPv4).

5.5.  Music Services

   Most of the web-based music services appear to work fine, presumably
   because they employ TCP and HTTP as a transport.  One notable
   exception is Spotify, which requires communication to specific IPv4
   addresses.  A proxy configuration similar to the one we used for
   Skype makes it possible to use Spotify as well.

5.6.  Appliances

   There are also problems with different appliances such as webcams.
   Many of them do not support IPv6 and hence will not work in an IPv6-
   only network.  Also not all firewalls support IPv6.  Or even if they
   do, they may still experience issues with some aspects of IPv6 such
   as fragments.

   Some of these issues are easily solved when the appliance works as a
   server, such as what most webcams and our sensor gateway devices do.
   We placed the appliance in the IPv4 part of the network (in this
   case, in private address space), added its name to the local DNS, and
   simply allowed devices from the IPv6-only network reach it through

5.7.  Other Differences

   One thing that becomes simplified in an IPv6-only network is source
   address selection [RFC3484].  As there is no IPv4 connectivity, the
   host only needs to consider its IPv6 source address.  For global
   communications there is typically just one possible source address.

6.  Experiences with NAT64

   After correcting some initial bugs and stability issues, the NAT64
   operation itself has been relatively problem free.  There have been
   no unexplained DNS problems or lost sessions.  With the exception of
   the specific applications mentioned above and IPv4 literals, the user
   experience has been in line with using IPv4 Internet through a NAT44
   device.  These failures with the specific applications are clearly

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   very different from the IPv4 experience, however.

   The rest of this section discusses our measurements on specific

6.1.  IPv4 Address Literals

   While browsing in general works, IPv4 literals embedded in the HTML
   code may break some parts of the web pages when using IPv6-only
   access.  This happens because the DNS64 can not synthesize AAAA
   records for the literals since the addresses are not queried from the
   DNS.  Luckily, the IPv4 literals seem to be fairly rarely
   encountered, at least so that they would be noticed, with regular web

   We have attempted to measure the likelihood of running into an IPv4
   literal in the web.  To do this, we took the top 1,000 and 10,000 web
   sites from the Alexa popular web site list.  With 1,000 top sites,
   0.2% needed an IPv4 literal to render all components in their top
   page (e.g., images, videos, JavaScript, and Cascading Style Sheet
   (CSS) files).  With 10,000 top sites, this number increases to 2%.

   However, it is not clear what conclusions can be made about this.  It
   is often the case that there are unresolvable or inaccessible
   components on a web page anyway for various reasons, and to
   understand the true impact we would have to know how "important" a
   given page component was.  Also, we did not measure the number of
   links with IPv4 literals on these pages, nor did we attempt to search
   the site in any thorough manner for these literals.

   As noted, personal anecdotal evidence says that IPv4 literals are not
   a big problem.  But clearly, cleaning the most important parts of the
   web from IPv4 literals would be useful.  With tools such as the
   popular web site list, some user pressure, and co-operation from the
   content providers the most urgent part of the problem could hopefully
   be solved as a one-time effort.  While IPv4 literals still exist in
   the web, using a suitable HTTP proxy (e.g.,
   [I-D.wing-behave-http-ip-address-literals]) can help to cope with

6.2.  Comparison of Web Access via NAT64 to Other Methods

   We also compared how well the web works behind a NAT64 compared to
   IPv4-only and native IPv6 access.  For this purpose, we used wget to
   go through the same top web site lists as described in Section 6.1,
   again downloading everything needed to render their front page.  The
   tests were repeated and an average was calculated over all of the
   runs.  Separate tests were conducted with an IPv4-only network, an

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   IPv6-only network, and an IPv6-only network with NAT64.

   When accessed with the IPv4-only network, our tests show that 1.9% of
   the sites experienced some sort of error or failure.  The failure
   could be that the whole site was not accessible, or just that a
   single image (e.g., an advertisement banner) was not loaded properly.
   It should also be noted that access through wget is somewhat
   different from a regular browser: some web sites refuse to serve
   content to wget, browsers typically have DNS heuristics to fill in
   "www." in front of a domain name where needed, and so on.  In
   addition to missing advertisement banners, temporary routing glitches
   and other mistakes, these differences also help to explain the reason
   for the high baseline error rate in this test.  It should also be
   noted that variations in wget configuration options produced highly
   different results, but we believe that the options we settled on bear
   closest resemblance to real world browsing.

   When we tried to access the same sites with native IPv6 (without
   NAT64), 96% of the sites failed to load correctly.  This was as
   expected, given that most of the Internet content is not available on
   IPv6.  The few exceptions included, for instance, sites managed by

   When the sites were accessed from the IPv6-only network via a NAT64
   device, the failure rate increased to 2.1%.  Most of these failures
   appear to be due to IPv4 address literals, and the increased failure
   rate matches that of IPv4 literal occurrence in the same set of top
   web sites.  With the top 10,000 sites the failure rate with NAT64
   increases similarly to our test on IPv4 address literals.

7.  Future Work

   One important set of measurements remains for future work.  It would
   be useful to understand the effect of DNS64 and NAT64 to response
   time and end-to-end communication delays.  Some users have anecdotal
   reports of slow web browsing response times, but we have been unable
   to determine if this was due to the IPv6-only network mechanisms or
   for some other reason.  Measurements on pure DNS response times and
   packet round-trip delays does not show a significant difference to a
   NAT44 environment.  It would be particularly interesting to measure
   delays in the context of dual stack vs. NAT64-based IPv6-only
   networking.  When using dual stack, broken IPv6 connectivity can be
   repaired by falling back to IPv4 use.  With NAT64, this is not always
   possible as discussed in Section 3.2.

   Also more programs, especially VoIP and Peer-to-Peer (P2P)
   applications should be tested with NAT64.  In addition, tunneling and

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   mobility protocols should be tested and especially Virtual Private
   Network (VPN) protocols and applications would deserve more thorough

8.  Conclusions and Recommendations

   The main conclusion is that it is possible to employ IPv6-only
   networking.  For large classes of applications there are no downsides
   or the downsides are negligible.  We have been unable to spot any
   practical difference in the web browsing experience, for instance.
   And IPv6 usage -- be it in dual stack or IPv6-only form -- comes with
   inherent advantages, such as enabling direct end-to-end connectivity.
   In our case, we employed this by enabling direct connectivity to
   devices in a home network from anywhere in the (IPv6) Internet.
   There are, however, a number of issues as well, such as lack of IPv6
   support in some applications or bugs in untested parts of the code.

   Our experience with IPv6-only networking confirms that dual stack
   should still be our recommended model for general purpose networking
   at this point of time.  However, IPv6-only networking can be employed
   by early adopters or highly controlled networks.  One example of such
   controlled network is a mobile network with operator-driven selection
   of handsets.  For instance, on some handsets that we tested, we were
   unable to see any functional difference between IPv4 and IPv6, today.

   Our recommendations apply at the present time.  With effort and time,
   deployment barriers can be removed and IPv6-only networking becomes
   applicable in all networking situations.

   Some of the improvements are already in process in the form of new
   products and additional IPv6 support.  For instance, we expect that
   the handset market will have a much higher number of IPv6-capable
   devices next year.  But some of the changes do not come without the
   community spending additional effort.  We have identified a number of
   actions that should be taken to improve the state of IPv6-only
   networking.  These include:

   DNS Discovery

      The state of DNS discovery continues to be one of the main
      barriers for easy adoption of IPv6-only networking.  Since DNS
      discovery is not a problem in dual stack networking, there has
      been too little effort in testing and deploying the necessary
      components.  For instance, it would be useful if RA-based DNS
      discovery came as a standard feature and not as an option in Linux
      distributions.  Our hope is that ongoing standardization of the
      RA-based DNS discovery at the IETF will help this happen.  Similar

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      issues face other operating systems.  The authors believe that at
      this time, prudent operational practices call for maximizing the
      number of offered automatic configuration mechanisms on the
      network side.  It might be useful for an IETF document to provide
      guidance on operating DNS in IPv6-only networks.

   Network Managers

      Other key software components are the various network management
      and attachment tools in operating systems.  These tools generally
      have the required functionality, but do not always appear to have
      been tested very extensively on IPv6, or let alone IPv6-only
      networks.  Further work is required here.

   Application Support

      But by far the most important action, for at least our group of
      users, would be to bring some key applications (e.g., instant
      messaging and VoIP applications and also games) to a state where
      they can be easily run on IPv6-only networks and behind a NAT64.
      In some cases, it may also be necessary to add support for new
      types of ALGs.

   IPv4 Literals

      The web should be cleaned from IPv4 literals.

   Measurements and Analysis

      It is also important to continue with testing, measurements, and
      analysis of what Internet technology works in IPv6-only networks,
      to what extent, at what speed, and where the remaining problems


      It is also useful to provide guidance for network administrators
      and users on how to turn on IPv6-only networking.

   As can be seen from the above list, there are only minor things that
   can be done through standardization.  Most of the effort is practical
   and centers around improving various implementations.

9.  Security Considerations

   The use of IPv6 instead of IPv4 by itself does not make a big
   security difference.  The main security requirement is that,

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   naturally, network security devices need to be able to deal with IPv6
   in these networks.  This is though already required in all dual-stack
   networks.  As noted, it is important, e.g., to ensure firewall

   In our experience many of the critical security functions in a
   network end up being on the dual stack part of the network anyway.
   For instance, our mail servers obviously still have to be able to
   communicate with both the IPv4 and IPv6 Internet, and as a result
   they and the associated spam & filtering components are not in the
   IPv6-only part of the network.

10.  IANA Considerations

   This document has no IANA implications.

11.  References

11.1.  Normative References

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, April 2004.

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

   [RFC5006]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Option for DNS Configuration",
              RFC 5006, September 2007.

11.2.  Informative References

   [RFC4038]  Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
              Castro, "Application Aspects of IPv6 Transition",
              RFC 4038, March 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

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   [RFC4966]  Aoun, C. and E. Davies, "Reasons to Move the Network
              Address Translator - Protocol Translator (NAT-PT) to
              Historic Status", RFC 4966, July 2007.

              Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation",
              draft-ietf-behave-v6v4-framework-10 (work in progress),
              August 2010.

              Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators",
              draft-ietf-behave-address-format-10 (work in progress),
              August 2010.

              Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
              "DNS64: DNS extensions for Network Address Translation
              from IPv6 Clients to IPv4 Servers",
              draft-ietf-behave-dns64-11 (work in progress),
              October 2010.

              Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", draft-ietf-behave-v6v4-xlate-23 (work in
              progress), September 2010.

              Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers",
              draft-ietf-behave-v6v4-xlate-stateful-12 (work in
              progress), July 2010.

              Beijnum, I., "An FTP ALG for IPv6-to-IPv4 translation",
              draft-ietf-behave-ftp64-05 (work in progress),
              September 2010.

              Wing, D., "Coping with IP Address Literals in HTTP URIs
              with IPv6/IPv4 Translators",
              draft-wing-behave-http-ip-address-literals-02 (work in
              progress), March 2010.

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Appendix A.  Acknowledgments

   The authors would like to thank the many people who have engaged in
   discussions around this topic, and particularly the people who were
   involved in building some of the new tools used in our network, our
   users who were interested in going where only few had dared to
   venture before, or people who helped us in this effort.  In
   particular, we would like to thank Martti Kuparinen, Tero Kauppinen,
   Heikki Mahkonen, Jan Melen, Fredrik Garneij, Christian Gotare, Teemu
   Rinta-Aho, Petri Jokela, Mikko Sarela, Olli Arkko, Lasse Arkko, and
   Cameron Byrne.  Also Marcelo Braun, Iljitsch van Beijnum, and Miika
   Komu have provided useful discussion and comments on the document.

Authors' Addresses

   Jari Arkko
   Jorvas  02420


   Ari Keranen
   Jorvas  02420


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