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IPv6 Operations                                               M. Defeche
Internet-Draft                                       University of Liege
Intended status:  Informational                                E. Vyncke
Expires:  April 19, 2010                                   Cisco Systems
                                                        October 16, 2009


             Measuring IPv6 Traffic in BitTorrent Networks
          <draft-defeche-ipv6-traffic-in-p2p-networks-00.txt>

Status of this Memo

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Copyright Notice

   Copyright (c) 2009 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
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This document summarizes a University thesis which aims to measure
   the evolution over time of IPv6 traffic, to analyze the geographical
   distribution of IPv6 nodes and to compare the two Internet Protocol
   versions on many different criteria (RTT, latency, MTU).  The
   measurements were done during the Summer 2009 using a specific-
   purpose program which connects to the BitTorrent peer-to-peer
   network.

   The study was made in Peer-to-Peer (P2P) networks because they are
   responsible for most 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.





























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Some explanations about BitTorrent . . . . . . . . . . . . . .  4
     2.1.  Peer Wire Protocol . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Tracker  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Peer Exchange  . . . . . . . . . . . . . . . . . . . . . .  6
     2.4.  Distributed Hash Table . . . . . . . . . . . . . . . . . .  6
     2.5.  Local Service Delivery . . . . . . . . . . . . . . . . . .  6
   3.  Tools used for Measurement . . . . . . . . . . . . . . . . . .  7
   4.  What was measured  . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  IPv6 BitTorrent Clients  . . . . . . . . . . . . . . . . .  8
     4.2.  IPv6 Addresses . . . . . . . . . . . . . . . . . . . . . .  8
       4.2.1.  Native IPv6  . . . . . . . . . . . . . . . . . . . . .  9
       4.2.2.  Teredo . . . . . . . . . . . . . . . . . . . . . . . .  9
       4.2.3.  6to4 . . . . . . . . . . . . . . . . . . . . . . . . . 10
       4.2.4.  Tunnel Brokers . . . . . . . . . . . . . . . . . . . . 10
       4.2.5.  ISATAP . . . . . . . . . . . . . . . . . . . . . . . . 11
       4.2.6.  Other Addresses  . . . . . . . . . . . . . . . . . . . 11
       4.2.7.  Summary about IPv6 Addresses . . . . . . . . . . . . . 12
     4.3.  Traffic Measurements . . . . . . . . . . . . . . . . . . . 12
     4.4.  Comparaison IPv4 vs. IPv6  . . . . . . . . . . . . . . . . 12
     4.5.  Round-Trip Time  . . . . . . . . . . . . . . . . . . . . . 13
     4.6.  Comparaison of Hops  . . . . . . . . . . . . . . . . . . . 14
     4.7.  MTU Comparaison  . . . . . . . . . . . . . . . . . . . . . 14
     4.8.  Monthly Evolution  . . . . . . . . . . . . . . . . . . . . 15
     4.9.  Protocols Used to Discover Peers . . . . . . . . . . . . . 15
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18

















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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] 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 May, June, July and October 2009 to get
   an idea of the evolution within a couple of months.  The intend is to
   run the same measurements every month for a couple of years.

   Measurements include:  number of IPv4 vs. IPv6 nodes, which kind of
   IPv6 connectivity, comparing the MTU, RTT between the two versions of
   IP and geographical distribution.


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 [micro]Torrent 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 is limited.  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.

   o  As BitTorrent is generally used to share large files, peers stay
      connected longer, giving us more time to discover them.




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   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

   This communication permits trackers to keep track of peers that are
   in the swarm and to avoid referencing disconnected peers.



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   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.

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



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   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 and because this
   information is retrieved and handled by five different programs, 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 runs
   the operating system Debian GNU/Linux 5.0 and has native IPv6 and
   IPv4 connectivity, which will permit a better evaluation of the two
   versions than if we use Teredo, for instance.

   All our programs evolved constantly to better match our needs and to
   improve their performance.  Most of them where rethought several
   times to achieve our goals.  A long time was spent to debug the
   LibTorrent Rasterbar library to get a full IPv6-capable BitTorrent
   client and to identify problems that The Pirate Bay had with IPv6.

   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.

   As we are interested in the number of routers on the path between us
   and the remote peer we must discover the value of the Time-To-Live or
   Hop Limit depending on the IP version.  Since the TTL or Hop Limit is
   initially set depending on the operating system, for instance 64 for
   Linux, and because the number of routers on the path should not
   exceed 32 we can easily calculate the number of times the field was
   decremented.

   Ping and ping6 commands are used to measure the latency to all



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   discovered peers.  Tracepath and tracepath6 commands are used to
   measure the TTL and the MTU between peers.  Of course, when the IPv6
   connectivity of a peer is through a transition mechanism such as 6to4
   or Teredo, then it is easy to extract the IPv4 address of the peer
   from its IPv6 address and comparaison can be done.


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.

   The number of peers to which we managed to establish a BitTorrent
   connection may seem low in comparison with the number of discovered
   peers but is not.  In fact, certain peers are already disconnected
   when we obtain information about them.  The study made by Tribler on
   PEX clearly indicated that information retrieved by PEX is mostly
   garbage.  Furthermore, when a BitTorrent client has reached its
   maximum number of connections, it rejects connection attempts made by
   remote peers and stops initiating new connections.  These are the two
   principal reasons that explain the difference between the number of
   discovered peers and peers we were connected to.

4.1.  IPv6 BitTorrent Clients

   Among the 621,625 peers whose client is known to us, 542,537 of them
   utilized one which supports IPv6, that is 87.28%.  We could adjust
   the percentage of peers having IPv6 connectivity with this
   information.  However, the IPv6 results will not be adjusted with
   this value since it has no influence on the different proportion
   analyzed.  And among the 542,537 peers that used a BitTorrent client
   that supports IPv6, 53,828 were using IPv6, that is 9.92%.

4.2.  IPv6 Addresses

   We will now analyze the 142,904 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.







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    +------------+--------+--------+--------+--------+----------------+
    |            | Native | Teredo | 6to4   | ISATAP | Tunnel Brokers |
    +------------+--------+--------+--------+--------+----------------+
    | Number     | 1,216  | 99,634 | 41,425 | 24     | 102            |
    | Percentage | 0.85   | 69.72  | 28.99  | 0.02   | 0.08           |
    +------------+--------+--------+--------+--------+----------------+

                Table 1: Different Types of IPv6 Addresses

   +------------+-------+----------+---------------+-----------+-------+
   |            | 6bone | Site     | IPv4          | IPv4      | Bogon |
   |            |       | Local    | Compatible    | Mapped    |       |
   +------------+-------+----------+---------------+-----------+-------+
   | Number     | 436   | 24       | 1             | 94        | 74    |
   | Percentage | 0.31  | 0.02     | 0.00          | 0.07      | 0.05  |
   +------------+-------+----------+---------------+-----------+-------+

            Table 2: Different Types of IPv6 Addresses (Cont.)

4.2.1.  Native IPv6

   Only 1,216 distinct native IPv6 addresses were discovered in 28
   different countries during our study.  More than 73% of these
   addresses came from the French ISP Free.  Even if we downloaded
   torrents whose names contained either FRENCH or VOSTFR we were not
   connected to more French peers than Italian peers, for instance.  As
   the high number of native IPv6 addresses from France is not due to
   the high number of peers from France, this phenomenon can be
   explained principally because Free seems to be the only large ISP
   that proposes IPv6 connectivity.  We also noticed that many
   Universities and institutes around the world offer IPv6 connectivity
   especially in Portugal where there are nine of them, which is more
   than any other country.

4.2.2.  Teredo

   Teredo with 69.72% 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);

   o  application:  Teredo is only used by Windows to connect to an IPv6
      which does not have any IPv4 address (in other word [RFC3484]



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      severelly limits the normal use of Teredo), but, with BitTorrent
      the peers appear always as single stack.

   When we analyze the servers employed to configure these addresses we
   notice that only three servers represent more than 99% of the
   utilized ones.  Their addresses are as follows :

   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 more than 99% of the peers that were using Teredo were likely to
   be using one of the Microsoft Operating Systems.  A test on my
   personal computer showed that Miredo, which is a type of Teredo IPv6
   tunneling software for Linux, does not use one of the Microsoft
   Teredo servers.

4.2.3.  6to4

   6to4 is also broadly used to provide IPv6 connectivity as 28.99% of
   the addresses found were created by this transition mechanism.
   Nevertheless, it is still far behind Teredo.  As 6to4 is designed to
   provide IPv6 connectivity to many hosts with a single public IPv4
   address, we checked if many 6to4 hosts were using the same 6to4
   router.  The result is not very satisfactory since 99.47% of the 6to4
   hosts employ a distinct 6to4 router.  However, we noticed that 9
   hosts were using the same 6to4 router which is quite high.  It seems
   that the 6to4 mechanism is mostly used for small LAN and not by large
   sites.

   6to4 is more commonly used than native IPv6.  We found 6to4 users in
   almost every country in Europe.  The USA has far more 6to4 users than
   other countries.

4.2.4.  Tunnel Brokers

   We can determine, via the list of Tunnel Brokers of the SixXS service
   [[TFE28]] and IPv6 Task Force [[TFE29]] websites, whether an ISP is a
   tunnel broker.  Unfortunately, these lists are not exhaustive so we
   may have missed a peer using a Tunnel Broker.  However, as we are
   aware of the largest Tunnel Broker, those we missed should be small
   and thus cannot really influence the result.  No dynamic
   identification of the Tunnel Broker was implemented due to the
   difficulty of identifying them all.  The Tunnel Brokers in Table 3
   that we discovered represent only 0.08% of the IPv6 addresses found.




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        +--------------------+-------------+--------+------------+
        | Tunnel Broker      | Region      | Number | Percentage |
        +--------------------+-------------+--------+------------+
        | Hurricane Electric | Worldwide   | 25     | 24.51      |
        | Internode          | Australia   | 2      | 1.96       |
        | Hexago             | Canada      | 22     | 21.57      |
        | SixXs              | Worldwide   | 49     | 48.04      |
        | XS4ALL             | Netherlands | 4      | 3.92       |
        +--------------------+-------------+--------+------------+

                      Table 3: List of Tunnel Brokers

   Only 5 different Tunnel Brokers were found.  The most widely used one
   is SixXS with 48.04% of the total Tunnel Broker utilization.  We
   noticed that 61% of the peers that were using this Tunnel Broker came
   from the Czech Republic.  Hexago is rather popular for a Tunnel
   Broker that operates only in Canada.

4.2.5.  ISATAP

   We only discovered 24 different peers that used ISATAP ([RFC4212]) to
   get IPv6 connectivity in a non IPv6-capable infrastructure.  Half of
   these addresses have a global unicast prefix and the other half have
   a 6to4 prefix.  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.

4.2.6.  Other Addresses

   Although IPv6 addresses with the 6bone prefix should not exist
   anymore 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.

   We found 94 IPv4-mapped addresses that were all discovered by PEX.

   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
   74 bogons via PEX, most of which had the b524::/16 prefix.

   We found 24 site-local addresses via PEX.  These addresses came from
   peers that were connected to other peers in their site that they



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   found via LSD.  These addresses are obviously useless to us since we
   are not in the same site.

4.2.7.  Summary about IPv6 Addresses

   The most impressive results are those of Teredo and 6to4 that
   represent together 98.71% of IPv6 addresses discovered.  The native
   IPv6 addresses form only a very small fraction of the total.

   Another important conclusion is that PEX is not ideally implemented
   in many BitTorrent clients since they exchange data that cannot be
   used by the remote peers like bogons or addresses reserved for the
   private-use networks.  Filtering the addresses to send via PEX avoids
   wasting processing time to initiate connections that cannot be
   established and limits the number of addresses to send which saves
   bandwidth.

4.3.  Traffic Measurements

   Most of the European countries have at least 3% of their peers using
   IPv6 with better results for Sweden, Portugal and Latvia.  Another
   surprising fact is that China has only 2.64% of its peers using IPv6
   which seems strange since China is one of the leading countries in
   IPv6 deployment.  This result may be negatively affected by the
   filter set up in this country.  Even if they have many free IPv4
   block left, the USA still has more than 4.8% of their peers using
   IPv6 which is more than their current policy supposes.

   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 with
   1.09% and 0.65% respectively.  China with 0.65%, has a good
   percentage in comparison with other countries.  This is explained by
   its interest to widely deploy native IPv6.  Thus China has
   particularly poor results concerning 6to4 and Teredo traffic.

4.4.  Comparaison IPv4 vs. IPv6

   In this section we will compare the two IP versions with different IT
   statistics to find out whether the new version is really better.  Of
   course, we must take into account the fact that IPv6 transition
   mechanisms have a structure that can considerably influence certain
   statistics.  We will thus treat the IPv6 peers differently according
   to the mechanism they use, if they use one at all.







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4.5.  Round-Trip Time

   First of all, even if we tried to obtain RTT statistics about each
   peer we did not get it all because some were disconnected when we did
   the test and others were not reachable via ICMP as many routers do
   not forward this type of ICMP message.  We obtained this information
   for approximately 36% of the IPv4 peers and 18% of the IPv6 ones.

   As we tested it for IPv4 addresses embedded in IPv6 ones we will
   compare the two results.  We have the RTT information of 32% of the
   embedded IPv4 addresses, most of which come from 6to4.  As a matter
   of fact, many NAT devices block the ICMP traffic which explains why
   we have so little RTT information about IPv4 addresses embedded in
   Teredo ones.

   Table 4 indicates at first sight that IPv4 is two times faster than
   IPv6.  This global result is not representative of the new IP version
   speed as it is greatly influenced by the transition mechanisms that
   are normally much slower than native connectivity.  The standard
   deviation average concerns the average of the standard deviation of
   all peers made thanks to the three different attempts.

                  +--------------------+-------+-------+
                  | Global             | IPv4  | IPv6  |
                  +--------------------+-------+-------+
                  | Average            | 324.8 | 812.8 |
                  | Standard Deviation | 403.6 | 890.8 |
                  +--------------------+-------+-------+

                  Table 4: Global RTT Information in msec

   Table 5 shows the results of the native IPv6 peers in comparison with
   those of the IPv6 (all kind of connectivity) and IPv4 peers.  We can
   immediately see that the IPv6 RTT average is clearly smaller than the
   global IPv6 RTT average.  However, the IPv6 RTT average is still
   higher than that of IPv4 but this difference can be explained by the
   current structure of the Internet:  where even if the peer has native
   IPv6 connectivity, it does not mean that the IPv6 peering agreements
   of his/her ISP are as good as their IPv4 ones.  This inconvenience
   should be reduced by the IPv6 deployment evolution.  The average of
   the standard deviation of IPv6 peers is particularly high which
   implies that different attempts gave highly different results.









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   +-----------------+--------------------+--------------------+-------+
   |                 | Native IPv6        | All IPv6           | IPv4  |
   |                 | connectivity       | connectivity       |       |
   +-----------------+--------------------+--------------------+-------+
   | Average         | 493.1              | 812.8              | 324.8 |
   | Standard        | 646.3              | 890.8              | 403.6 |
   | Deviation       |                    |                    |       |
   +-----------------+--------------------+--------------------+-------+

               Table 5: Native IPv6 RTT Information in msec

4.6.  Comparaison of Hops

   We will analyze the TTL and Hop Limit on the path from the remote
   peers to us for which we obtained more than 1,300,000 statistics
   about IPv4 peers and more than 90,000 about IPv6 peers.  We observe
   in Table 6 that the number of routers on the path from IPv4 peers is
   superior to the number of routers from IPv6 peers but not to that of
   native IPv6 which is quite coherent.  As a matter of fact, as the Hop
   Limit is not decremented in the tunnel, its value arrives higher at
   the destination.  The fact that there is a higher number of routers
   between native IPv6 peers and us also seems logical as the number of
   interconnections in the IPv6 Internet is smaller than in the IPv4
   Internet and that may result in a longer path.

                +-----------+-------+-------+-------------+
                | Hop count | IPv4  | IPv6  | Native IPv6 |
                +-----------+-------+-------+-------------+
                | Average   | 15.10 | 11.93 | 18.12       |
                +-----------+-------+-------+-------------+

               Table 6: Native IPv6 RTT Information in msec

4.7.  MTU Comparaison

   We obtained more than 190,000 MTU statistics about IPv6 peers and
   more than 1,800,000 about IPv4 peers, which gives us a sufficient
   sample.

   Table 7 shows the different MTU results depending on the IP version
   and whether the path MTU discovery reached the destination.
   Unsurprisingly, the global IPv6 MTU is far smaller than the IPv4 one
   as more than 98% of the addresses where formed thanks to a tunneling
   mechanism.  The results of the native IPv6 peers are much higher but
   are still inferior to those of IPv4.






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               +---------+---------+---------+-------------+
               | MTU     | IPv4    | IPv6    | Native IPv6 |
               +---------+---------+---------+-------------+
               | Average | 1,497.6 | 1,288.9 | 1,468.0     |
               +---------+---------+---------+-------------+

               Table 7: Native IPv6 RTT Information in msec

4.8.  Monthly Evolution

   The monthly analysis done in 2009, shown in Table 8, allows us to see
   this decrease more clearly with 1.7% lost between the month of June
   and July.  As July is a holiday month, the sharing habits may be
   different.  As a matter of fact, most downloaders are students.
   However, this hypothesis does not explain why the IPv6 traffic
   decreases.  The fact that Universities, which may have IPv6
   connectivity, may be closed during the holidays and thus prevent
   students from using their bandwidth cannot explain this reduction as
   the percentage of IPv6 traffic coming from Universities is very low.
   Nevertheless, this decline from the Universities exists as IPv6
   traffic in July diminished by more than three times when compared to
   results in June.

   Once more the peers that were solely discovered via DHT are not taken
   into account in the IPv6 evolution analysis.

   +-----------------+----------+-----------+-----------+--------------+
   |                 | May 2009 | June 2009 | July 2009 | October 2009 |
   +-----------------+----------+-----------+-----------+--------------+
   | %-age of IPv6   | 4.50     | 4.79      | 3.10      | 2.30         |
   | peers           |          |           |           |              |
   +-----------------+----------+-----------+-----------+--------------+

             Table 8: Monthly Evolution of IPv6 vs IPv4 peers

4.9.  Protocols Used to Discover Peers

   In this section we will look at the effectiveness of the different
   protocols to discover peers.  As we can see in Table 9, PEX is
   globally far more effective to find peers than other means.  It is
   even more efficient for IPv6 in comparison with the performance of
   trackers.









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               +---------+-----------+---------+-----------+
               | Source  | IPv4      | IPv6    | Total     |
               +---------+-----------+---------+-----------+
               | Tracker | 1,550,023 | 37,745  | 1,587,768 |
               | PEX     | 3,558,648 | 167,606 | 3,726,254 |
               | DHT     | 843,353   | 0       | 843,353   |
               | LSD     | 0         | 0       | 0         |
               +---------+-----------+---------+-----------+

           Table 9: Number of Valid Peers Discovered by Protocol

   Concerning DHT, we have never been able to get IPv6 peers by this
   means because of incompatibilities between BitTorrent clients and
   because of problems in the LibTorrent Rasterbar library.  But if we
   look at the Table 9, the DHT results are not as good as the other
   means.

   The good performance of PEX can be explained by its exponential way
   of functioning.  As a matter of fact, via a small number of peers a
   large number of peers can be reached.  However, as already explained,
   the proportion of disposable information is very important.

   We did not receive any peers via LSD either since no other computer
   was running a BitTorrent client in the local network.  Nevertheless,
   it was functioning during all our study.


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., "Kademlia : A Peer-to-peer Information
              System Based on the XOR Metric".

   [TFE28]    SixXs, "List of Tunnel Brokers",
              <http://www.sixxs.net/tools/aiccu/brokers/>.

   [TFE29]    IPv6 Task Force, "List of Tunnel Brokers", <http://
              www.ipv6tf.org/index.php?page=using/connectivity/test>.

   [TFE5]     Cohen, B., "The BitTorrent Protocol Specification", 2008,
              <http://www.bittorrent.org/beps/bep_0003.html>.

8.2.  Informative References

   [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.

   [RFC4212]  Blinov, M. and C. Adams, "Alternative Certificate Formats
              for the Public-Key Infrastructure Using X.509 (PKIX)
              Certificate Management Protocols", RFC 4212, October 2005.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

   [TFE23]    Norberg, Arvid., "LibTorrent Rasterbar Library",
              <http://www.rasterbar.com/products/libtorrent/>.

   [TFE3]     Schulze, H., "Internet Study 2008/2009", 2009.



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   [THESIS]   Defeche, M., "Measure and Analysis of IPv6 Traffic in
              Peer-to-Peer Networks. Master Thesis", August 2009.


Authors' Addresses

   Martin Defeche
   University of Liege
   Institut Montefiore
   Bat. B28 Reseaux informatiques
   Grande Traverse 10
   Liege  4000
   Belgium

   Email:  martin.defeche@gmail.com


   Eric Vyncke
   Cisco Systems
   De Kleetlaan 6a
   Diegem  1831
   Belgium

   Phone:  +32 2 778 4677
   Email:  evyncke@cisco.com


























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