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Network Working Group                                         A. Keranen
Internet-Draft                                                  J. Arkko
Intended status: Informational                                  Ericsson
Expires: January 12, 2012                                  July 11, 2011

     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 service.
   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 as 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 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.

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
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   This Internet-Draft will expire on January 12, 2012.

Copyright Notice

   Copyright (c) 2011 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
   Provisions Relating to IETF Documents

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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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.  Informative References . . . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

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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, and
   unreliable IPv6 connectivity.  Bad IPv6 routing has been behind many
   of the problems.  Among the causes are broken 6to4 tunneling protocol
   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 as 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 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
   makes 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 sufficient capacity to deal with
   the IPv6 traffic and impacts to the operator's IPv4 infrastructure or
   carrier-grade NAT devices as their traffic is reduced.  Network
   owners also wish to understand the extent to which they can expect

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   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 a well-working dual-stack
   connectivity on the measurement end, and then probing the rest of the
   Internet to understand, for instance, how likely it is to have IPv6
   connectivity problems, or what are the delay differences between IPv4
   and IPv6 towards the rest of the Internet.  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 record and the corresponding host
   name 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 module for the DNS queries.

   The measurement script used a bind9 DNS server running on the same
   host that was performing the measurement.  The DNS cache of the
   server was flushed before each measurement run to be able to detect
   the changes in the DNS records in real-time.  The host, and thus the

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   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) at the same time with 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 right 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 have been running since, once
   every three hours.  One test run takes from two to two and a half
   hours to finish.

   The accuracy and generality of the measurement results is limited by
   several factors.  While we run 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.  Also, since one measurement run takes considerably
   long time, the network characteristics and DNS records may have
   changed even during a single run.  The first DNS response was used
   for the TCP connectivity tests and this selection may result in
   selecting un-optimal host; yet, 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 information.

4.  Measurement Results

4.1.  DNS AAAA Records

   The amount of top 10,000 sites with AAAA DNS records before, during,
   and after the World IPv6 Day, is shown in
   <http://users.piuha.net/akeranen/drafts/v6day/v6sites.pdf>.  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%)
   with both A and AAAA record.  During the following days the number of
   sites was slowly increasing, reaching 306 sites at the measurement

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   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 already 383 sites, and the next one
   472 sites.  During the day number of sites with AAAA records peaked
   at 491 (4.91% of the measured 10,000 sites) after 19:30 UTC.

   When the World IPv6 Day was over, also 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 has not
   dropped below 300 since, resulting in over 3% of the top 10,000 sites
   having AAAA records today.

   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., at least for 6 hours).  Also the number of AAAA records
   for the "www" host name dropped steeply after the day and has
   remained 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
   Here, the number of sites with some of the tested host names having
   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 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 was enabling IPv6 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 amount of
   sites with AAAA records before the World IPv6 Day was already higher
   (above 400) and hence the impact of the day was smaller when 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 also 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
   both A and AAAA DNS records.  The fraction of sites for which the

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   first DNS response gave addresses that were not accessible with TCP
   to port 80 over IPv4 or IPv6 is shown in

   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 and 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 failure ratio dropping to
   roughly 20% before the day.  During the day 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 lower level, between 15 and 20 percentage, than before the day.

4.3.  TCP Connection Delays

   For sites that were accessible with both IPv4 and IPv6, we measured
   the time difference it takes to establish 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 average (of the median) over all sites; the result is
   shown in <http://users.piuha.net/akeranen/drafts/v6day/mda.pdf>.

   In general, the delay differences are small: median of medians stays
   less than 3ms off from being equal and even the mean, which is more
   sensitive to outliers, stays most of the time within +/- 5ms; with
   highest spikes reaching to -15ms (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 order of magnitude larger connection
   setup delays.

   Surprisingly the median delay for IPv6 connections is in most of the

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   cases equal or smaller than IPv4 delay, but during the World IPv6
   Day, the IPv6 delays increased slightly and became (on median) slower
   than IPv4 counterparts.  One reason for such effect was that some of
   the sites that enabled IPv6 for the World IPv6 Day, had extremely
   low, less than ten millisecond, 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 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, real impacts
   to end users were 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 was 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 quick 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 what 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

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   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 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.

6.  Security Considerations

   Security issues have not been discussed in this memo.

7.  IANA Considerations

   This memo has no IANA implications.

8.  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.

              Comcast and University of Pennsylvania, "IPv6 Adoption
              Monitor", <http://ipv6monitor.comcast.net>.

              RIPE NCC, "World IPv6 Day Measurements",

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

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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

Authors' Addresses

   Ari Keranen
   Jorvas  02420

   Email: ari.keranen@ericsson.com

   Jari Arkko
   Jorvas  02420

   Email: jari.arkko@piuha.net

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