Network Working Group A. Keranen
Internet-Draft J. Arkko
Intended status: Informational Ericsson
Expires: March 15, 2013 September 11, 2012
Some Measurements on World IPv6 Day from End-User Perspective
draft-keranen-ipv6day-measurements-04
Abstract
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
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This Internet-Draft will expire on March 15, 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
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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 . . . . . . . . . . . . . . . . . . . 7
4.3. TCP Connection Delays . . . . . . . . . . . . . . . . . . 7
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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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 [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
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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
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changes in the DNS records in real-time. The host, and thus the DNS
server, was not part of DNS IPv6 whitelisting agreements.
The local network where the host performing the measurements was has
native IPv6 (dual-stack) connectivity. The IPv6 connectivity to the
local network was provided by an IPv6-over-IPv4 tunnel from the
network's default router to the ISP's IPv6 peering point.
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
information.
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
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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
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.
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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
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
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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
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
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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.
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
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8.1. Normative References
[timediff]
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,
<http://users.piuha.net/akeranen/drafts/v6day/mda.pdf>.
[DNS-top10k]
Keranen, A., "Number of sites with AAAA DNS records in the
top 10,000 most popular sites", June 2011,
<http://users.piuha.net/akeranen/drafts/v6day/
v6sites.pdf>.
[DNS-top100]
Keranen, A., "Number of sites with AAAA DNS records in the
top 100 most popular sites", June 2011, <http://
users.piuha.net/akeranen/drafts/v6day/v6sites-top100.pdf>.
[TCP-fails]
Keranen, A., "TCP connection setup failure ratio (for the
first DNS response)", June 2011, <http://users.piuha.net/
akeranen/drafts/v6day/tcp-fails.pdf>.
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", <http://www.net-dns.org/>.
[IPv6Monitor]
Comcast and University of Pennsylvania, "IPv6 Adoption
Monitor", <http://ipv6monitor.comcast.net>.
[RIPEv6Day]
RIPE NCC, "World IPv6 Day Measurements",
<http://v6day.ripe.net/>.
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[Alexa] Alexa the Web Information Company, "Alexa Top 1,000,000
Sites",
<http://s3.amazonaws.com/alexa-static/top-1m.csv.zip>.
[Labovitz]
Labovitz, C., Iekel-Johnson, S., McPherson, D., Oberheide,
J., and F. Jahanian, "Internet Inter-Domain Traffic",
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
Ericsson
Jorvas 02420
Finland
Email: ari.keranen@ericsson.com
Jari Arkko
Ericsson
Jorvas 02420
Finland
Email: jari.arkko@piuha.net
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