Skip to main content

Some Measurements on World IPv6 Day from End-User Perspective

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 6948.
Authors Ari Keränen , Jari Arkko
Last updated 2012-08-20 (Latest revision 2012-07-16)
RFC stream Independent Submission
Stream ISE state (None)
Consensus boilerplate Unknown
Document shepherd (None)
IESG IESG state Became RFC 6948 (Informational)
Telechat date (None)
Responsible AD Brian Haberman
IESG note
Send notices to,,,
RFC Editor RFC Editor state ISR-AUTH
Network Working Group                                         A. Keranen
Internet-Draft                                                  J. Arkko
Intended status: Informational                                  Ericsson
Expires: January 17, 2013                                  July 16, 2012

     Some Measurements on World IPv6 Day from End-User Perspective


   During the World IPv6 Day on June 8th, 2011, several key content
   providers enabled their networks to offer both IPv4 and IPv6
   services.  Hundreds of organizations participated in this effort, and
   in the months and weeks leading up to the event worked hard on
   preparing their networks to support this event.  The event was
   largely unnoticed by the general public, which is a good thing since
   it means that no major problems were detected.  For the Internet,
   however, there was a major change on such a small timescale.  This
   memo discusses measurements that the authors made from the
   perspective of an end-user with good IPv4 and IPv6 connectivity.  Our
   measurements include the number of most popular networks providing
   AAAA records for their service as well as delay and connection
   failure statistics.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 17, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal

Keranen & Arkko         Expires January 17, 2013                [Page 1]
Internet-Draft            IPv6 Day Measurements                July 2012

   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation and Goals . . . . . . . . . . . . . . . . . . . . .  3
   3.  Measurement Methodology  . . . . . . . . . . . . . . . . . . .  4
   4.  Measurement Results  . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  DNS AAAA Records . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  TCP Connection Setup . . . . . . . . . . . . . . . . . . .  6
     4.3.  TCP Connection Delays  . . . . . . . . . . . . . . . . . .  7
   5.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

Keranen & Arkko         Expires January 17, 2013                [Page 2]
Internet-Draft            IPv6 Day Measurements                July 2012

1.  Introduction

   Many large content providers participated in World IPv6 Day on June
   8, 2011.  On that day, IPv6 [RFC2460] was enabled by default for 24
   hours on numerous networks and sites that previously supported only
   IPv4.  The aim was to identify any remaining issues with widespread
   IPv6 usage in these networks.  Most of the potential problems
   associated with using IPv6 are, after all, of a practical nature,
   such as: ensuring that the necessary components have IPv6 turned on;
   that configurations are correct; and that any implementation bugs
   have been removed.

   Some content providers have been reluctant to enable IPv6.  The
   reasons for this include delays for applications attempting to
   connect over broken IPv6 links before falling back to IPv4 [RFC6555],
   and unreliable IPv6 connectivity.  Bad IPv6 routing has been behind
   many of the problems.  Among the causes are broken 6to4 tunneling
   protocol [RFC3056] connectivity, experimental IPv6 setups that are
   untested and unmonitored, and configuration problems with firewalls.
   The situation is improving as more users and operators put IPv6 to
   use and fix the problems that emerge.

   World IPv6 Day event was largely unnoticed by the general public,
   which is a good thing since it means that no major problems were
   detected.  Existing IPv4 connectivity was not damaged by IPv6 and
   also new IPv6 connectivity worked as expected in vast majority of
   cases.  For the Internet, however, there was a major change on such a
   small timescale.  This memo discusses measurements that the authors
   made from the perspective of an end-user with well-working IPv4 and
   IPv6 connectivity.  Our measurements include the number of most
   popular networks providing AAAA records for their service as well as
   delay and connection failure statistics.

   The rest of this memo is structured as follows.  Section 2 discusses
   the goals of our measurements, Section 3 describes our measurement
   methodology, Section 4 gives our preliminary results, and Section 5
   draws some conclusions.

2.  Motivation and Goals

   Practical IPv6 deployment plans benefit from accurate information
   about the extent to which IPv6 can be used for communication, and how
   its characteristics differ from those of IPv4.  For instance,
   operators planning to deploy dual-stack networking may wish to
   understand what fraction of their traffic would move to IPv6.  This
   information is useful for estimating the necessary capacity to deal
   with the IPv6 traffic and impacts to the operator's IPv4

Keranen & Arkko         Expires January 17, 2013                [Page 3]
Internet-Draft            IPv6 Day Measurements                July 2012

   infrastructure or carrier-grade NAT devices as their traffic is
   reduced.  Network owners also wish to understand the extent to which
   they can expect different delay characteristics or problems with IPv6
   connectivity.  The goals of our measurements were to help with these
   topics by answering the following questions:

   o  What fraction of most popular Internet sites offer AAAA records?
      How did the World IPv6 Day change the situation?

   o  How do the traffic characteristics differ between IPv4 and IPv6 on
      sites offering AAAA records?  Are the connection failure rates
      similar?  How are RTTs impacted?

   There have been many measurements about some of these aspects from a
   service provider perspective, such as the Google studies on which end
   users have broken connectivity towards them.  Our measurements start
   from a different angle, by assuming good dual-stack connectivity at
   the measurement end, and then probing the rest of the Internet to
   understand, for instance, how likely there are to be IPv6
   connectivity problems, or what the delay differences are between IPv4
   and IPv6.  Similar studies have been performed by the Comcast IPv6
   Adoption Monitor [IPv6Monitor] and RIPE NCC [RIPEv6Day].

3.  Measurement Methodology

   We used the top 10,000 sites of the Alexa 1 million most popular
   sites list [Alexa] from June 1st 2011.  For each domain name in the
   list, we performed DNS queries with different host names.  For IPv4
   addresses (A records) we used host name "www" and also performed a
   query with just the domain name.  For IPv6 addresses (AAAA records)
   we used also different combinations of host names that have been used
   for IPv6 sites, namely "www6", "ipv6", "v6", "ipv6.www", "www.ipv6",
   "v6.www", and "www.v6".

   All DNS queries were initiated in the order listed above (first "www"
   and just the domain name for A-records, then "www", domain name, and
   different IPv6-host names for AAAA records) but the queries were done
   in parallel (i.e., without waiting for the previous query to finish).
   The first response for A and AAAA records and the corresponding host
   names were recorded.  The queries had 3 second re-transmission
   timeout and if there wasn't any response for 10 seconds, all
   remaining queries for the site were canceled.  We used a custom-made
   Perl script and the Net::DNS [net-dns] module for the DNS queries.

   The measurement script used a bind9 DNS server running on the same
   host as was performing the measurement.  The DNS cache of the server
   was flushed before each measurement run in order to detect the

Keranen & Arkko         Expires January 17, 2013                [Page 4]
Internet-Draft            IPv6 Day Measurements                July 2012

   changes in the DNS records in real-time.  The host, and thus the DNS
   server, was not part of DNS IPv6 whitelisting agreements.

   After obtaining IP addresses for the site, if a site had both A and
   AAAA records, a simple C program was used to create TCP connections
   to the port 80 (HTTP) simultaneously using both IPv4 and IPv6 to the
   (first) IP addresses discovered from the DNS.  The connection setup
   was repeated up to 10 times, giving up after the first failed attempt
   (but only after normal TCP re-transmissions).  The connection setup
   delay was measured by recording the time immediately before and after
   the connect system call.  The host used for measurements is a regular
   Linux PC with 2.6.32 version kernel and dual-stack Internet
   connection via Ethernet.

   The measurements were started one week before the World IPv6 Day (on
   Wednesday, June 1st, 17:30 UTC) and were running until July 11th,
   once every three hours.  One test run takes from two to two and a
   half hours to complete.

   The accuracy and generality of the measurement results is limited by
   several factors.  While we ran the tests in three different sites,
   most of the results discussed in this document present snapshots of
   the situation from just one measurement point, the Ericsson Research
   Finland premises, near Helsinki.  Also, since one measurement run
   takes quite a long time, the network characteristics and DNS records
   may change even during a single run.  The first DNS response was used
   for the TCP connectivity tests and this selection may result in
   selection of a non-optimal host; yet, a slight preference is given to
   the "www" and only-domain-name records since their queries were
   started before the others.  While the host performing the
   measurements was otherwise idle, the local network was in regular
   office use during the measurements.  The connectivity setup delay is
   collected in user space, with regular, non real-time, kernel
   implementation, resulting in small inaccuracies in the timing

4.  Measurement Results

4.1.  DNS AAAA Records

   The number of top 10,000 sites with AAAA DNS records before, during,
   and after the World IPv6 Day, is shown in [DNS-top10k].  The
   measurements performed during the World IPv6 Day are shown on the
   light gray background.

   When the measurements began on June 1st, there were 245 sites (2.45%)
   of the top 10,000 sites with both A and AAAA record.  During the

Keranen & Arkko         Expires January 17, 2013                [Page 5]
Internet-Draft            IPv6 Day Measurements                July 2012

   following days the number of such sites slowly increased, reaching
   306 sites at the measurement that was started 22:30 UTC on June 7th,
   the evening before the World IPv6 Day. When the World IPv6 Day
   officially started, the following measurement (1:30 UTC) recorded 383
   sites, and the next one 472 sites.  During the day the number of
   sites with AAAA records peaked at 491 (4.91% of the measured 10,000
   sites) at 19:30 UTC.

   When the World IPv6 Day was over, the number of AAAA records dropped
   nearly as fast as it had increased just 24 hours earlier.  However,
   the number of sites stabilized around 310 and did not drop below 300
   since, resulting in over 3% of the top 10,000 sites still having AAAA
   records at the end of our measurements.

   While 274 sites had IPv6 enabled in their DNS for some of the tested
   host names one day before the World IPv6 Day, only 116 had it for the
   "www" host name that is commonly used when accessing a web site.  The
   number of "www" host names with AAAA records more than tripled during
   the World IPv6 Day reaching 374 sites for 3 consecutive measurement
   runs (i.e., for at least 6 hours).  Also the number of AAAA records
   for the "www" host name dropped steeply after the day and remained at
   around 160 sites since.

   Similar but more pronounced trends can be seen if only top 100 of the
   most popular sites are taken into considerations, as show in
   [DNS-top100].  Here, the number of sites with some of the tested host
   names having an AAAA record was initially 14, jumped to 36 during the
   day, and eventually dropped to 13.  Also, while none of the top 100
   sites apparently had an AAAA record for their "www" host name before
   and after the World IPv6 day, during the day the number peaked at 30.
   Thus, roughly one third of the 100 most popular sites had IPv6
   enabled for the World IPv6 Day.

   Two other test sites in Sweden and Canada experienced similar trends
   with the DNS records.  However, one of the sites used an external DNS
   server that was part of whitelisting agreements.  There the number of
   sites with AAAA records before the World IPv6 Day was already higher
   (above 400) and hence the impact of the day was smaller as the amount
   of sites increased to same numbers as seen by the test site in
   Finland.  With the whitelisted DNS server the level of sites remained
   above 450 after the day.

4.2.  TCP Connection Setup

   To test whether the IP addresses given by the DNS actually provide
   connectivity to the web site, and if there is any difference in the
   connection setup delay and failure rates with IPv4 and IPv6, we
   attempted to create TCP connections for all domains that contained

Keranen & Arkko         Expires January 17, 2013                [Page 6]
Internet-Draft            IPv6 Day Measurements                July 2012

   both A and AAAA DNS records.  The fraction of sites for which the
   first DNS response gave addresses that were not accessible with TCP
   to port 80 over IPv4 or IPv6 is shown in [TCP-fails].

   There is a baseline failure rate with IPv4 around 1-3% that is fairly
   static throughout the test period.  For hosts with AAAA records, the
   fraction of inaccessible sites was much higher: in the beginning up
   to one fourth of the tested hosts did not respond to TCP connection
   attempts.  Much of this was likely due to the various test sites with
   different "IPv6 prefixes" (as discussed in Section 3); in the first
   run more than half of the tested sites with AAAA records used them
   for the first DNS response.  Also, some of the hosts may not even be
   supposed to be accessed with HTTP but provide AAAA records for other
   purposes while some sites had clear configuration errors, such as
   localhost or link-local IPv6 addresses.

   As the World IPv6 Day came closer, the number of inaccessible IPv6
   sites decreased slowly and the number of sites with AAAA records
   increased at the same time, resulting in the failure ratio dropping
   to roughly 20% before the day.  During the day the number of IPv6
   sites increased rapidly but also the number of failures decreased and
   hence, at the end of the day, the failure ratio dropped to just above
   10%.  After the World IPv6 Day when many of the participating IPv6
   hosts were taken off-line, the fraction of failed sites for IPv6
   increased.  However, since there was no increase in the absolute
   number of failed sites, the fraction of inaccessible sites remained
   at a lower level, between 15% and 20%, than before the day.

4.3.  TCP Connection Delays

   For sites that were accessible with both IPv4 and IPv6, we measured
   the time difference between establishing a TCP connection with IPv4
   and IPv6.  We took the median (as defined in Section 11.3 of
   [RFC2330]) of the time differences of all 10 connections, and then
   median and mean (of the median) over all sites; the result is shown
   in [timediff].

   In general, the delay differences are small: median of medians stays
   less than 3ms off from zero (i.e., IPv4 and IPv6 delays being equal)
   and even the mean, which is more sensitive to outliers, stays most of
   the time within +/- 5ms; with the greatest spikes reaching to roughly
   -15ms (i.e., mean of median IPv6 delays being 15ms larger than for
   IPv4 delays).  Closer inspection of the results shows that the spikes
   are often caused by only one or a handful of sites with bad
   connectivity and multiple re-transmissions of TCP SYN and ACK packets
   resulting in connection setup delays an order of magnitude larger.

   Surprisingly the median delay for IPv6 connections is in most cases

Keranen & Arkko         Expires January 17, 2013                [Page 7]
Internet-Draft            IPv6 Day Measurements                July 2012

   equal to or smaller than the IPv4 delay, but during the World IPv6
   Day, the IPv6 delays increased slightly and became (as median) slower
   than their IPv4 counterparts.  One reason for such an effect was that
   some of the sites that enabled IPv6 for the World IPv6 Day, had
   extremely low, less than 10ms, IPv4 delay (e.g., due to Content
   Delivery Network (CDN) provider hosting the IPv4 site), but
   "regular", over hundred millisecond, delay for the IPv6 host.

   More detailed analysis of the TCP connection setup delay differences,
   and the reasons behind them, is left for future work.

5.  Conclusions

   The World IPv6 Day had a very visible impact to the availability of
   content over IPv6, particularly when considering the top 100 content
   providers.  It is difficult to find other examples of bigger one day
   swings in some characteristic of the Internet.  However, the impact
   on end users was small, given that when dual-stack works correctly it
   should not be visible at the user level and that IPv6 availability
   for end users themselves is small.

   The key conclusions are as follows:

   o  The day caused a large jump in the number of content providers
      providing AAAA DNS records on that day.

   o  The day caused a smaller but apparently permanent increase in the
      number of content providers supporting AAAA.

   o  Large and sudden swings in the relative amount of IPv4 vs. IPv6
      traffic are possible merely by supporting a dual-stack access
      network and having a few large content providers offer their
      service either globally or to this particular network over IPv6.

   o  Large fraction of sites that published AAAA records for a name
      under their domain (be it "www" or "www6" or something else) were
      actually not responding to TCP SYN requests on IPv6.  This
      fraction is far higher than that which we've seen in our previous
      measurements, and we are still determining why that is the case.
      Measurement errors or problems on our side of the network cannot
      be ruled out at this stage.  In any case, it is also clear that as
      new sites join, incomplete or in-progress configurations create
      more connectivity problems in the IPv6 Internet than we've seen
      before.  Other measurements are needed to verify what the general
      level IPv6 connectivity is to addresses publicly listed in AAAA

Keranen & Arkko         Expires January 17, 2013                [Page 8]
Internet-Draft            IPv6 Day Measurements                July 2012

   o  Even if the overall level of connection failures was high,
      activities on and around the IPv6 day appear to have caused a
      significant permanent drop in the number of failures.

   o  When IPv6 and IPv4 connectivity were both available, the delay
      characteristics appear very similar.  In other words, most of the
      providers that made IPv6 connectivity available appear to provide
      a production quality network.  TCP connection setup delay
      differences due to RTT differences between IPv4 and IPv6
      connections are in general low.  In the remaining differences in
      our measurements, random packet loss plays a major role.  However,
      some sites can experience considerable differences simply because
      of different content distribution mechanisms used for IPv4 and
      IPv6 content.

   It is promising that the amount of most popular Internet content on
   IPv6 was surprisingly high, roughly one third of top 100 sites
   (during the IPv6 day or with whitelisting enabled).  However, other
   content on the Internet forms a long tail that is harder to move to
   IPv6.  For instance, only 3% of the 10,000 most popular web sites
   provided their content over IPv6 before the IPv6 day.  On a positive
   note, the top 100 sites form a very large part of overall Internet
   traffic [Labovitz] and thus even the top sites moving to IPv6 could
   represent a significant fraction of Internet traffic on IPv6.
   However, this requires that users are enabled to use IPv6 in their
   access networks.  We believe that this should be the goal of future
   global IPv6 efforts.

6.  Security Considerations

   Security issues have not been discussed in this memo.

7.  IANA Considerations

   This memo has no IANA implications.

8.  References

8.1.  Normative References

              Keranen, A., "TCP connection setup delay differences [RFC
              editor: please change the references to the graphs to
              refer to the PDF version of the document]", June 2011,

Keranen & Arkko         Expires January 17, 2013                [Page 9]
Internet-Draft            IPv6 Day Measurements                July 2012

              Keranen, A., "Number of sites with AAAA DNS records in the
              top 10,000 most popular sites", June 2011,

              Keranen, A., "Number of sites with AAAA DNS records in the
              top 100 most popular sites", June 2011, <http://

              Keranen, A., "TCP connection setup failure ratio (for the
              first DNS response)", June 2011, <

8.2.  Informative References

   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              May 1998.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, April 2012.

   [net-dns]  Fuhr, M., "Net::DNS", <>.

              Comcast and University of Pennsylvania, "IPv6 Adoption
              Monitor", <>.

              RIPE NCC, "World IPv6 Day Measurements",

   [Alexa]    Alexa the Web Information Company, "Alexa Top 1,000,000

              Labovitz, C., Iekel-Johnson, S., McPherson, D., Oberheide,
              J., and F. Jahanian, "Internet Inter-Domain Traffic",

Keranen & Arkko         Expires January 17, 2013               [Page 10]
Internet-Draft            IPv6 Day Measurements                July 2012

              Proceedings of ACM SIGCOMM 2010, August 2010.

Appendix A.  Acknowledgments

   The authors would like to thank Suresh Krishnan, Fredrik Garneij,
   Lorenzo Colitti, Jason Livingood, Alain Durand, Emile Aben, Jan
   Melen, and Tero Kauppinen for interesting discussions in this problem
   space.  Thanks also to Tom Petch and Bob Hinden for thorough reviews
   and many helpful comments.

Authors' Addresses

   Ari Keranen
   Jorvas  02420


   Jari Arkko
   Jorvas  02420


Keranen & Arkko         Expires January 17, 2013               [Page 11]