Internet Engineering Task Force (IETF) J. Arkko
Request for Comments: 6586 A. Keranen
Category: Informational Ericsson
ISSN: 2070-1721 April 2012
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 roadblocks 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 document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 ................................11
5.4. Gaming ....................................................12
5.5. Music Services ............................................13
5.6. Appliances ................................................13
5.7. Other Differences .........................................13
6. Experiences with NAT64 .........................................13
6.1. IPv4 Address Literals .....................................14
6.2. Comparison of Web Access via NAT64 to Other Methods .......15
7. Future Work ....................................................15
8. Conclusions and Recommendations ................................16
9. Security Considerations ........................................18
10. References ....................................................19
10.1. Normative References .....................................19
10.2. Informative References ...................................19
Appendix A. Acknowledgments .......................................21
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, roadblocks and opportunities, as well as a more general
understanding of when such a configuration can be recommended and
what should be taken into account in the network design. Note that
this memo documents our experiences primarily from 2010. As time
goes by, the situation changes with updated software versions, newer
products, and so on.
The networks involved in this setup have been in dual-stack mode for
a 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
[RFC6144] 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
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, Section 8 draws conclusions and makes recommendations on when
and how one should employ IPv6-only networks, and Section 9 discusses
relevant security considerations.
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 [RFC6144], [RFC6145], [RFC6146], [RFC6052], [RFC6147], 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, BSD, Mac OS X, and Microsoft Windows
operating systems. Common uses of the network include email, 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.
In both environments, volunteers had the possibility to opt-in for
the IPv6-only network. The number of users was small: there were
roughly five permanent users and a dozen users who had 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 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. In our case, 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, although many other access points support
this. 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 stateful NAT64 [RFC6146] 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 /63 of address space. This space was easily
available in our networks, as IPv6 allocations are purposefully 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 [RFC6052]
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 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.
Setting up NAT64 and DNS64 by themselves is easy and can be done
quickly by an experienced network manager. However, when duplicate
infrastructure is needed for dual-stack and IPv6-only networks, the
additional switches, cables, access points, etc., will take some
amount of installation effort. In addition, if whitelisting
agreements or IPv6 ISP connectivity is needed, setting these up
requires negotiations with external partners.
3.2. DNS Operation
Router Advertisements are used to carry DNS Configuration options
[RFC6106], 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 6106, 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 also be
reached via IPv6. In principle, this is exactly the same as needing
IPv4-based DNS and DNS discovery in IPv4-only networks. However, in
IPv6, the discovery mechanisms are somewhat more complicated because
there are several alternative techniques.
When a host served by the DNS64 asks for a domain name that does not
have a AAAA (IPv6 address) record, but has an A (IPv4 address)
record, a AAAA record is synthesized from the A record (as defined
for DNS64 in [RFC6147]) 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 [RFC6144]).
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
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
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 the 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 implemented 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 a year and a
half 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 (HTTP and HTTPS) experience. Also,
email, software upgrades, operating system services, many chat
systems, and media streaming work well. On certain Symbian mobile
handsets that we tried, all applications work even on an IPv6-only
network. In another case, with the Android operating system, all the
basic applications worked without problems. In order to make the
latter handset architecture support IPv6-only networks, however, a
small change was needed in the operating system so that it could
discover IPv6-only DNS servers.
However, in general, there is some pain involved and thus IPv6-only
networking 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 environment. These issues fall in
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
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). As our experiment continued, we have seen
improvements in some areas, such as gaming.
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 [RFC6384]. 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 run into it
only a couple of times during real-life web browsing.
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
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 also not been
available to the authors in the IPv4 Internet for a number of years.
It should be noted that the experience with a properly configured set
of ALGs and workarounds 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, Router Advertisement (RA) information is not
automatically updated when the network changes while the computer is
on, and this requires an unnecessary suspend/resume cycle to restore
its proper state. We have also had issues with the rdnssd daemon,
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.
Later, a new version of the Linux distribution that we used solved
these problems, even if some problems still remained. For instance,
in the latest Ubuntu Long-Term Support release (10.04), we have
experienced that the network manager by default returns to an
available IPv4 wireless network even if there is a previously used
IPv6-only network available and the IPv4 network has no global
connectivity before a web-based login is completed.
In Mac OS X (Snow Leopard), the network manager needed to be
explicitly told not to expect IPv4. A more annoying issue was that
in order to switch between an IPv6-only and IPv4-only network, 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 well now, even in
an IPv6-only environment. This change, DNS Discovery Daemon (DDD)
now exists as open source software. Interestingly, all applications
that we have tried so far seem to work without problems with IPv6-
only connectivity, though no exhaustive testing was done, nor did we
try known troublesome applications.
While all these operating systems (or their predecessors) have
already supported IPv6 for a number of years, these kinds 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 a
majority of the commonly used APIs. The Perl programming language
used to be an exception with only partial IPv6 support up to the
version 5.14 (released May 14, 2011). This version finally includes
full IPv6 support, with that in the core libraries and older modules
being updated as well. With previous versions of Perl, 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; thus, many existing Perl
programs using network functionality may not work properly in an
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 instant messaging applications in an IPv6-only
network with NAT64; the test results can be found in Table 1. The
versions used in the tests were the latest versions available in the
summer of 2010.
Facebook on the web (http) OK
Facebook via a client (xmpp) OK
Jabber.org chat service (xmpp) OK
Gmail chat on the web (http) OK
Gmail chat via a client (xmpp) OK
Google Talk client NOT OK
AIM (AOL) NOT OK
ICQ (AOL) NOT OK
Skype NOT OK
MSN NOT OK
Webex NOT OK
Sametime OK (NOW)
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 Google Talk
client is that the software does not support IPv6 connections at this
time. We are continuing our tests with additional applications, and
we have also seen changes over time. For instance, a new version of
Sametime suddenly started working with IPv6-only networks, presumably
due to the new version being more careful with the use of DNS names
as opposed to IPv4 addresses. 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 these 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 regard to
connecting to IPv6 destinations or even IPv6 proxies.
Another class of applications that we tried was games. We tried both
web-based gaming and standalone gaming applications that have
"network", "Internet", or "LAN" gaming modes. The results are shown
in Table 2.
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 results require further verification.
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).
While none of the standalone games we tested in the summer of 2010
were IPv6-capable, the situation improved during the experiment. For
instance, a popular online game, World of Warcraft, now has IPv6
support in its latest version and some of the older games that have
been re-released as open source (e.g., Quake) have been patched IPv6-
capable by the open source community.
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.
There are also problems with different appliances such as webcams.
Many of them do not support IPv6; hence, they 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.
Some networks that advertise IPv6 addresses in their DNS records in
reality have some problems. For instance, a popular short URL
forwarding service has advertised a deprecated IPv4-compatible IPv6
address [RFC4291] in its AAAA record, making it impossible for this
site to be reached unless either IPv4 or NAT64 translation to an IPv4
destination is used.
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
very different from the IPv4 experience, however.
The rest of this section discusses our measurements on specific
issues. These tests and measurements were performed during the year
2011 and present a snapshot of the situation on that time. More up-
to-date measurement information can be found from various online
tools such as [HE-IPv6].
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 cannot 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
surfing. The authors have run into this issue only few times during
the entire experiment. Only two of those cases had a practical
impact (in YouTube, some of the third-party applications for
downloading content did not work and one hotel's web page had a
literal link to its reservation system).
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
(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., [ADD-LITERALS]) can help
to cope with them.
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 average failure rate was calculated over all
of the runs. Separate tests were conducted with an IPv4-only
network, an 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 on 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 from
a NAT44 environment. It would be particularly interesting to measure
delays in the context of dual-stack versus 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
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. Additionally, 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 in time. However, IPv6-only networking can be employed
by early adopters or highly controlled networks. One example of such
a 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
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 in the near future. However, 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 the following:
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 recent standardization of the RA-
based DNS discovery at the IETF will help this happen. Other
operating systems face similar issues. 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.
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.
More work is needed to ensure that IPv6 is supported in equal
manner in various firewall products.
By far, the most important action, at least for our group of
users, would be to bring some key applications (e.g., instant
messaging and VoIP applications and games) to a state where they
can be easily run on IPv6-only networks and behind a NAT64. To
facilitate this, application programmers should use IP-version-
agnostic APIs so that applications automatically use IPv4 or IPv6
depending on what is available. In some cases, it may also be
necessary to add support for new types of ALGs.
The web should be cleaned of IPv4 literals. Also, IPv4 literals
should be avoided in application protocol signaling messages.
Measurements and Analysis
It is also important to continue with testing, measurement, and
analysis of which Internet technologies work in IPv6-only
networks, to what extent, at what speed, and where the remaining
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
By itself, the use of IPv6 instead of IPv4 does not make a big
security difference. The main security requirement is that,
naturally, network security devices need to be able to deal with IPv6
in these networks. This is already required in all dual-stack
networks. As noted, it is important, e.g., to ensure firewall
capabilities. Security considerations for NAT64 and DNS64 are
discussed in [RFC6146] and [RFC6147].
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 and filtering components are not in the
IPv6-only part of the network.
10.1. 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,
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition
Mechanisms for IPv6 Hosts and Routers", RFC 4213,
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS
Configuration", RFC 6106, November 2010.
10.2. 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.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H.
Soliman, "Neighbor Discovery for IP version 6
(IPv6)", RFC 4861, September 2007.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and
X. Li, "IPv6 Addressing of IPv4/IPv6 Translators",
RFC 6052, October 2010.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework
for IPv4/IPv6 Translation", RFC 6144, April 2011.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum,
"Stateful NAT64: Network Address and Protocol
Translation from IPv6 Clients to IPv4 Servers",
RFC 6146, 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, April 2011.
[RFC6384] van Beijnum, I., "An FTP Application Layer Gateway
(ALG) for IPv6-to-IPv4 Translation", RFC 6384,
[ADD-LITERALS] Wing, D., "Coping with IP Address Literals in HTTP
URIs with IPv6/IPv4 Translators", Work in Progress,
[HE-IPv6] Hurricane Electric, "Global IPv6 Deployment Progress
Report", February 2012,
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, Miika
Komu, and Jouni Korhonen have provided useful discussion and comments
on the document.