Internet DRAFT - draft-vyncke-ipv6-traffic-in-p2p-networks
draft-vyncke-ipv6-traffic-in-p2p-networks
Network Working Group M. Defeche
Internet-Draft University of Liege
Intended status: Informational E. Vyncke, Ed.
Expires: September 3, 2012 Cisco Systems
March 2, 2012
Measuring IPv6 Traffic in BitTorrent Networks
draft-vyncke-ipv6-traffic-in-p2p-networks-01
Abstract
This document is a follow-up of a University thesis which aims to
measure the evolution over time of IPv6 traffic and to analyze the
geographical distribution of IPv6 nodes. The first measurements were
done during the Summer 2009 using a specific-purpose program which
connects to the BitTorrent peer-to-peer network and this document
adds measurements done with the same program but in October 2011 and
February 2012.
The study was made in Peer-to-Peer (P2P) networks because they are
responsible for a big part of Internet traffic and because their
structure and functioning permit a rapid discovery of a large number
of nodes from all over the world. In addition, the P2P users are
more likely to be interested by IPv6 as IPv6 does not have the same
NAT problems as IPv4.
Status of this Memo
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Some explanations about BitTorrent . . . . . . . . . . . . . . 3
2.1. Peer Wire Protocol . . . . . . . . . . . . . . . . . . . . 4
2.2. Tracker . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Peer Exchange . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Distributed Hash Table . . . . . . . . . . . . . . . . . . 5
2.5. Local Service Delivery . . . . . . . . . . . . . . . . . . 6
3. Tools used for Measurement . . . . . . . . . . . . . . . . . . 6
4. What was measured . . . . . . . . . . . . . . . . . . . . . . 6
4.1. IPv6 Addresses . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Native IPv6 . . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Teredo . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.3. 6to4 . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1.4. ISATAP . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1.5. Other Addresses . . . . . . . . . . . . . . . . . . . 9
4.2. Traffic Measurements . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
An IPv6 vs. IPv4 measurement was made in Peer-to-Peer (P2P) networks
because they are responsible for most Internet traffic [TFE3] in 2009
and because their structure and functioning permit a rapid discovery
of a large number of nodes from all over the world. In addition, the
P2P users are more likely to be interested by IPv6 as IPv6 does not
have the same NAT problems as IPv4.
The measurements were made in October 2011 and February 2012 re-using
the application developped in October 2009 and presented in
[I-D.defeche-ipv6-traffic-in-p2p-networks]. This was part of the
Master Thesis [THESIS].
Measurements include: number of IPv4 vs. IPv6 nodes, which kind of
IPv6 connectivity and geographical distribution. This measurement is
intended to be run multiple times per year and the results are
displayed on-line [online].
2. Some explanations about BitTorrent
Let's start with some explanations about BitTorrent.
BitTorrent is based on an hybrid decentralized network which is
particularly well suited to the transfer of large files. BitTorrent
generates the largest amount of traffic of all P2P networks and was
installed on 28.20% of PCs in September 2007, and this number is
certainly higher at present. BitTorrent also includes different
protocols to discover peers, namely DHT, PEX and LSD which will be
discussed later. Thanks to these mechanisms BitTorrent can be
completely decentralized. The different clients are all compatible
with the core protocol but some divergences concerning PEX, DHT and
LSD appear between Azureus and the mainline, which represents at
least the BitTorrent and uTorrent clients. Swarming is one of the
basis of the protocol and IPv6 specification exists although it is
not implemented by all clients.
Since BitTorrent is the only protocol that offers in theory a good
support to IPv6, our choice was limited in 2009. But there are other
reasons why BitTorrent is the network protocol that best matches our
needs.
o The number of different copies of the same file(s) is far smaller
than in other networks. This leads to a larger number of peers
sharing the same file(s). Therefore swarming can be more
efficient thanks to a larger number of sources.
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o As BitTorrent is generally used to share large files, peers stay
connected longer, giving us more time to discover them.
o BitTorrent is responsible for the largest part of the P2P traffic
throughout the world.
o BitTorrent is widely used in most regions of the world.
o Thanks to many different extensions like PEX (Section 2.3), DHT
(Section 2.4) and LSD (Section 2.5), the discovery of peers is
improved greatly.
2.1. Peer Wire Protocol
The Peer wire Protocol [TFE5], or PWP, specifies the way peers
communicate in an asynchronous fashion with each other to exchange
data and signalling messages. It is based on TCP connections that
function in Full-Duplex and Pipelining mode to get better
performances. This protocol does not define how to choose pieces to
request, nor how to select peers to download from and to upload to.
Certain algorithms, which are explained below, give some solutions to
attain a good propagation of pieces in the swarm and to make peers
happy with their download rate compared to their upload rate.
2.2. Tracker
The trackers [TFE5] act like servers but do not deal with the
transfer of files ; their only purposes are to manage the swarm and
to respond to periodic client requests for information about peers
sharing the same torrent. Since the transfer of files is completely
supported by peers, the bandwidth requirement is very low and thus a
single tracker can handle many swarms, each one containing a large
number of peers. This protocol commonly called THP is used by
clients to communicate over HTTP with trackers. As a matter of fact,
the trackers run an HTTP server. Peers contact trackers that are
present in the metadata file for the following purposes :
o to enter a swarm
o to leave a swarm
o to inform the tracker that the download is complete
o to periodically give information on the download state and
retrieve information about a random peer set. This time interval
is defined by the tracker. If a peer misses a periodical request
it can be considered as disconnected by the tracker and thus not
present in the swarm any more
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This communication permits trackers to keep track of peers that are
in the swarm and to avoid referencing disconnected peers.
Tracker responses do not support IPv6 peers without this extension
[TFE12] which means that they do not include IPv6 peers in their
responses. This extension adds two new parameters for the tracker
requests:
o ipv6 : the client IPv6 address. It can be added when the client
contacts the tracker over IPv4;
o ipv4 : the client IPv4 address. Conversely, when communication is
made over IPv6.
It permits clients having a dual stack to advertize both its
addresses in the swarm. The port of the additional address is the
same as the primary one.
2.3. Peer Exchange
The Peer Exchange or PEX is a means to discover new peers through
peers that the client is already connected to. As a matter of fact,
peers trade information concerning the peers they are connected to.
Only few initial peers are needed to rapidly find a large number of
peers. This mechanism permits a reduction of the tracker load and an
improvement in the robustness as the tracker dependency is decreased.
2.4. Distributed Hash Table
The DHT technology [TFE13] is a way to store a hash table over a
network, thus in a distributed way, each peers contains a part of it.
Files and nodes are identified by a same length key, which is 20
bytes in BitTorrent. Each peer also maintains a list of different
peers to efficiently route its searches. DHT in BitTorrent is an
implementation of Kademlia which is based on the XOR metric that is
the distance between two nodes or between a node and a file can be
determined by a XOR of their keys.
This technology is used to decentralize the tracking mechanism to
once more decrease the dependence on trackers. Even if the trackers
are down or if no trackers are specified in the metadata file, the
DHT technology permits the discovery of peers sharing the same
torrent thanks to the info key hash as identifier. Conversely to
PEX, no initial peers are needed.
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2.5. Local Service Delivery
The Local Service Discovery or LSD permits the discovery of peers
that are downloading the same torrent in the same local network. The
transfer rate is much higher between two peers in the same local
network than between two peers in different networks since the
bandwidth limitation is that of the local network and not the one of
the Internet connection which is far smaller, especially the upload
stream. Briefly, LSD works as follows : the hash of the info key is
broadcasted in the local network to find out peers sharing the same
torrent.
3. Tools used for Measurement
As millions of pieces of information can be reached, the choice of a
MySQL database came naturally for effectiveness reasons and because
concurrent access is managed. Each program requests, inserts, and/or
updates information in this database.
The computer that holds the database and executes the programs has
native IPv6 and IPv4 connectivity, which will permit a better
evaluation of the two versions than if we use Teredo, for instance.
Our specialized BitTorrent client joins different swarms and
periodically changes to other swarms. While in a swarm we try to get
connected to as many peers as possible thanks to all protocols
supported by BitTorrent. In this way we are able to easily,
automatically and efficiently discover peers. Ideally we should
choose swarms with large numbers of peers in order to effectively
retrieve information. Concerning the legality issue, we can use a
trick to avoid downloading and uploading any files. In fact, we
claim that we are not interested in any pieces so we will not
download anything and we will not upload either since we have nothing
to upload. So we are present in the swarm but without taking part in
the sharing of files.
4. What was measured
The measurements were done in two periods:
o May 2009 to July 2009: 5,000,000 peers were discovered but we were
only able to to establish a BitTorrent connection with 1,500,000
peers;
o 1 day in October 2009: 100,000 peers were discovered;
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o 1 day in October 2011: 180,000 peers were discovered;
o 2 days in February 2012: 664,685 peers were discovered.
4.1. IPv6 Addresses
We will now analyze the distinct IPv6 addresses found via the
different protocols and classify them into different categories. The
next section will explain the utilization of these addresses over the
world in greater detail.
+----------------+--------+--------+--------+--------+--------------+
| | Native | Teredo | 6to4 | ISATAP | Tunnel |
| | | | | | Brokers |
+----------------+--------+--------+--------+--------+--------------+
| Number in 2009 | 1,216 | 99,634 | 41,425 | 24 | 102 |
| Percentage in | 0.85 | 69.72 | 28.99 | 0.02 | 0.08 |
| 2009 | | | | | |
| Number in 2011 | 258 | 1,280 | 636 | 3 | n/a |
| Percentage in | 11.85 | 58.80 | 29.22 | 0.14 | n/a |
| 2011 | | | | | |
| Number in 2012 | 1,466 | 4,483 | 3,582 | 8 | n/a |
| Percentage in | 15.37 | 47.00 | 37.55 | 0.08 | n/a |
| 2012 | | | | | |
+----------------+--------+--------+--------+--------+--------------+
Table 1: Different Types of IPv6 Addresses
The next table describes which weird and plain wrong IPv6 address our
probe has received. It can be expected that a normal BitTorrent
client will try to contact those addresses and therefore will
generate packets whose destination IPv6 address is illegal.
+----------------+-------+---------+-------------+----------+-------+
| | 6bone | Site | IPv4 | IPv4 | Bogon |
| | | Local | Compatible | Mapped | |
+----------------+-------+---------+-------------+----------+-------+
| Number in 2009 | 436 | 24 | 1 | 94 | 74 |
| Percentage in | 0.31 | 0.02 | 0.00 | 0.07 | 0.05 |
| 2009 | | | | | |
| Number in 2011 | 0 | 0 | 0 | 0 | 61 |
| Percentage in | 0 | 0 | 0 | 0 | 100 |
| 2011 | | | | | |
| Number in | 0 | 0 | 0 | 2 | 108 |
| February 2012 | | | | | |
+----------------+-------+---------+-------------+----------+-------+
Table 2: Different Types of IPv6 Addresses (Cont.)
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4.1.1. Native IPv6
In the 2011 study, only 197 distinct native IPv6 addresses were
discovered in 25 different countries during our study. More than 40
% of these addresses came from the French ISP Free.
In the February 2012 study, many native IPv6 addresses have been
discovered 1,466 (15% of all IPv6 addresses). France has still the
highest ratio of native IPv6 addresses vs any addresses with 2.10% of
the French BitTorrent peers using IPv6 (again Free being the largest
followed by SFR). The next countries are:
o Chine with 0.65% (only CERNET)
o Japan with 0.59% (mainly KDDI)
o United-States of America: 0.51% (mainly AT&T but also Comcast,
Hurricane Electric and Verizon)
4.1.2. Teredo
Teredo with 47 % of IPv6 addresses found is clearly the most utilized
way to get IPv6 connectivity. This ratio is also unsually high
compared to other Internet measurements. It is probably linked to:
o users: BiTorrent users are mainly residential and not
professional, therefore Teredo is allowed to traverse the firewall
while most enterprises block all outbound UDP traffic (and
blocking Teredo in the same shot) and the most common Teredo
implementation (Microsoft) also disables Teredo when used in an
Active Directory network;
o application: Teredo is only used by Windows to connect to an IPv6
which does not have any IPv4 address (in other word [RFC3484]
severelly limits the normal use of Teredo), but, with BitTorrent
the peers appear always as single stack (i.e. it appears like
having only an IPv6 address even if it actually have both version
of the IP protocol).
When we analyze the servers employed to configure these addresses we
notice that only four servers represent 99.6 % of the used ones.
Their addresses are as follows (February 2012 but mostly unchanged
compared to 2011):
1. 65.55.158.118 : is deployed by Microsoft (58.80 %);
2. 94.245.115.184 : is deployed by Microsoft ( 1.3 %);
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3. 94.245.121.251 : is deployed by Microsoft (17.20 %);
4. 94.245.121.253 : is deployed by Microsoft (22.30 %);
while in October 2009, three different servers represented 99 % of
the traffic:
1. 213.199.162.214 : is deployed by Microsoft (46.12%);
2. 65.55.158.80 : is also set up by Microsoft (41.33%);
3. 207.46.48.150 : is once more owned by Microsoft (12.41%).
Thus 100 % of the peers that were using Teredo were likely to be
using one of the Microsoft Operating Systems.
4.1.3. 6to4
6to4 is also still broadly used to provide IPv6 connectivity with
37.55% in February 2012, 29.21 % in 2011 and was 28.99 % in 2009 were
created by this transition mechanism. Nevertheless, it is still far
behind Teredo. It must be noted that the proportion of 6to4 nodes
has not decreased as indicated by other measurements, but, the other
measurements count only the web access to dual-stack servers where
happy eye-balls [I-D.ietf-v6ops-happy-eyeballs] and [RFC3484] can
influence the browser behavior in order to avoid all tunneling (this
includes Teredo and 6to4).
4.1.4. ISATAP
We only discovered 8 different peers that used ISATAP ([RFC5214]) to
get IPv6 connectivity in a non IPv6-capable infrastructure. This
mechanism is less common than Teredo ([RFC4380]) and 6to4
([RFC3056]). However, this bad result can be moderated by the fact
that ISATAP is mostly destined to enterprises which often have a
strict control on applications used by their employees. Thus
installing a BitTorrent client is not often possible, and even if it
is the firewall can filter its traffic.
4.1.5. Other Addresses
Although IPv6 addresses with the 6bone prefix should not exist
anymore, in October 2009 we found up to 436 addresses with this
prefix. In fact, all these addresses have the old Teredo prefix
3ffe:831f::/32 which was used in the 6bone network. The 6bone
addresses are no more visible in 2011 and 2012.
In October 2009, we found 94 IPv4-mapped addresses that were all
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discovered by PEX.
The good news is that in February 2012, we found not a single 6bone
address and only 2 IPv4-mapped addresses in our peers.
Bogons are IP blocks that are reserved for private or special uses
plus those that are not yet allocated by the IANA. Thus a bogon is
an illegal IP address that must not appear on the Internet since they
are theoretically unroutable. At present, the IPv6 unicast space is
limited to the 2000::/3 prefix. During our study we discovered up to
1108 bogons via PEX.
4.2. Traffic Measurements
Most of the European countries have at least 1 % of their peers that
can use IPv6 with better results for Latva (3.88%), France (3.02%),
Finland (2.90%), Romania (2.83%). The first non-European country is
Chile with 2.78%. Another surprising fact is that China has only
1.19 % of its peers using IPv6 with 0.65% being native IPv6. This
result may be negatively affected by the filter set up in this
country.
As explained in the analysis of IPv6 addresses section, we only found
few native IPv6 addresses. This analysis confirms what we discussed
previously, which is that Japan and France have the highest rate but
they are now joined by 'newcomers' such as China, USA but also Czech
Republic and Slovenia.
5. IANA Considerations
There are no extra IANA consideration for this document.
6. Security Considerations
This I-D does not describe any specific protocol, so, the security
section is mostly irrelevant. The measures were done with the
specific security issues in mind:
o copyrighted content: only a first fragment is downloaded and never
stored on long term storage, so, it is assumed that even if
copyrighted content is actually received it will never be user or
propagated further to other peers;
o denial of services: timers and rate limiters are used when getting
the list of torrents from our directory, when contacting other
peers, and so on
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7. Acknowledgements
Many thanks to Professor Guy Leduc of the University of Liege and his
research assistants, Cyril Soldani and Sylvain Martin. Martin is
also grateful to Arvid Norberg who implemented the LibTorrent
Rasterbar library [TFE23]. We also exchanged ideas with Nathan Ward.
8. References
8.1. Normative References
[TFE12] Hazel, G., "IPv6 Tracker Extension", May 2008,
<http://www.bittorrent.org/beps/bep_0007.html>.
[TFE13] Maymounkov, P. and D. Mazieres, "Kademlia : A Peer-to-peer
Information System Based on the XOR Metric", 2002, <http:/
/pdos.csail.mit.edu/~petar/papers/
maymounkov-kademlia-lncs.pdf>.
[TFE5] Cohen, B., "The BitTorrent Protocol Specification", 2008,
<http://www.bittorrent.org/beps/bep_0003.html>.
8.2. Informative References
[I-D.defeche-ipv6-traffic-in-p2p-networks]
Defeche, M. and E. Vyncke, "Measuring IPv6 Traffic in
BitTorrent Networks",
draft-defeche-ipv6-traffic-in-p2p-networks-00 (work in
progress), October 2009.
[I-D.ietf-v6ops-happy-eyeballs]
Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", draft-ietf-v6ops-happy-eyeballs-07
(work in progress), December 2011.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
February 2006.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
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March 2008.
[TFE23] Norberg, A., "LibTorrent Rasterbar Library",
<http://www.rasterbar.com/products/libtorrent/>.
[TFE3] Schulze, H., "Internet Study 2008/2009", 2009.
[THESIS] Defeche, M., "Measure and Analysis of IPv6 Traffic in
Peer-to-Peer Networks. Master Thesis", August 2009.
[geoip] Maxmind, "GeoLite Country", 2012,
<http://www.maxmind.com/app/geolitecountry>.
[online] Vyncke, E., "IPv6-enabled BitTorrent Peers",
<http://www.vyncke.org/ipv6status/p2p.php>.
Authors' Addresses
Martin Defeche
University of Liege
Email: martin.defeche@gmail.com
Eric Vyncke (editor)
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Email: evyncke@cisco.com
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