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
draft-keranen-ipv6day-measurements-01
Abstract
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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 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
Keranen & Arkko Expires January 12, 2012 [Page 1]
Internet-Draft IPv6 Day Measurements July 2011
(http://trustee.ietf.org/license-info) 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. Informative References . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Keranen & Arkko Expires January 12, 2012 [Page 2]
Internet-Draft IPv6 Day Measurements July 2011
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
Keranen & Arkko Expires January 12, 2012 [Page 3]
Internet-Draft IPv6 Day Measurements July 2011
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
Keranen & Arkko Expires January 12, 2012 [Page 4]
Internet-Draft IPv6 Day Measurements July 2011
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
Keranen & Arkko Expires January 12, 2012 [Page 5]
Internet-Draft IPv6 Day Measurements July 2011
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
<http://users.piuha.net/akeranen/drafts/v6day/v6sites-top100.pdf>.
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
Keranen & Arkko Expires January 12, 2012 [Page 6]
Internet-Draft IPv6 Day Measurements July 2011
first DNS response gave addresses that were not accessible with TCP
to port 80 over IPv4 or IPv6 is shown in
<http://users.piuha.net/akeranen/drafts/v6day/tcp-fails.pdf>.
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
Keranen & Arkko Expires January 12, 2012 [Page 7]
Internet-Draft IPv6 Day Measurements July 2011
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
records.
Keranen & Arkko Expires January 12, 2012 [Page 8]
Internet-Draft IPv6 Day Measurements July 2011
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.
[IPv6Monitor]
Comcast and University of Pennsylvania, "IPv6 Adoption
Monitor", <http://ipv6monitor.comcast.net>.
[RIPEv6Day]
RIPE NCC, "World IPv6 Day Measurements",
<http://v6day.ripe.net/>.
[Alexa] Alexa the Web Information Company, "Alexa Top 1,000,000
Sites",
<http://s3.amazonaws.com/alexa-static/top-1m.csv.zip>.
Keranen & Arkko Expires January 12, 2012 [Page 9]
Internet-Draft IPv6 Day Measurements July 2011
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.
Authors' Addresses
Ari Keranen
Ericsson
Jorvas 02420
Finland
Email: ari.keranen@ericsson.com
Jari Arkko
Ericsson
Jorvas 02420
Finland
Email: jari.arkko@piuha.net
Keranen & Arkko Expires January 12, 2012 [Page 10]