Observations on the Dropping of Packets with IPv6 Extension Headers in the Real World
draft-ietf-v6ops-ipv6-ehs-in-real-world-01

IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Informational                                J. Linkova
Expires: April 17, 2016                                           Google
                                                                T. Chown
                                               University of Southampton
                                                                  W. Liu
                                                     Huawei Technologies
                                                        October 15, 2015

 Observations on the Dropping of Packets with IPv6 Extension Headers in
                             the Real World
               draft-ietf-v6ops-ipv6-ehs-in-real-world-01

Abstract

   This document presents real-world data regarding the extent to which
   packets with IPv6 extension headers are dropped in the Internet (as
   measured in August 2014), and where in the network such dropping
   occurs.  The aforementioned results serve as a problem statement that
   is expected to trigger operational advice on the filtering of IPv6
   packets carrying IPv6 Extension Headers, so that the situation
   improves over time.  This document also explains how the
   aforementioned results were obtained, such that the corresponding
   measurements can be reproduced by other members of the community.

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 April 17, 2016.

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Copyright Notice

   Copyright (c) 2015 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
   (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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Support of IPv6 Extension Headers in the Internet . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Reproducing Our Experiment . . . . . . . . . . . . .   9
     A.1.  Obtaining the List of Domain Names  . . . . . . . . . . .  10
     A.2.  Obtaining AAAA Resource Records . . . . . . . . . . . . .  10
     A.3.  Filtering the IPv6 Address Datasets . . . . . . . . . . .  10
     A.4.  Performing Measurements with Each IPv6 Address Dataset  .  11
     A.5.  Obtaining Statistics from our Measurements  . . . . . . .  12
   Appendix B.  Measurements Caveats . . . . . . . . . . . . . . . .  13
     B.1.  Isolating the Dropping Node . . . . . . . . . . . . . . .  13
     B.2.  Obtaining the Responsible Organization for the Packet
           Drops . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Appendix C.  Troubleshooting Packet Drops due to IPv6 Extension
                Headers  . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   IPv6 Extension Headers (EHs) allow for the extension of the IPv6
   protocol, and provide support for core functionality such as IPv6
   fragmentation.  While packets employing IPv6 Extension Headers have
   been suspected to be dropped in some IPv6 deployments, there was not
   much concrete data on the topic.  Some preliminary measurements have
   been presented in [PMTUD-Blackholes], [Gont-IEPG88] and

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   [Gont-Chown-IEPG89], whereas [Linkova-Gont-IEPG90] presents more
   comprehensive results on which this document is based.

   This document presents real-world data regarding the extent to which
   packets containing IPv6 Extension Headers are dropped in the
   Internet, as measured in August 2014 (pending operational advice in
   this area).  The results presented in this document indicate that in
   the scenarios where the corresponding measurements were performed,
   the use of IPv6 extension headers can lead to packet drops.  We note
   that, in particular, packet drops occurring at transit networks are
   undesirable, and it is hoped and expected that this situation will
   improve over time.

2.  Support of IPv6 Extension Headers in the Internet

   This section summarizes the results obtained when measuring the
   support of IPv6 Extension Headers on the path towards different types
   of public IPv6 servers.  Two sources of information were employed for
   the list of public IPv6 servers: the "World IPv6 Launch Day" site
   (http://www.worldipv6launch.org/) and Alexa's top 1M web sites
   (http://www.alexa.com).  For each list of domain names, the following
   datasets were obtained:

   o  Web servers (AAAA records of the aforementioned list)

   o  Mail servers (MX -> AAAA of the aforementioned list)

   o  Name servers (NS -> AAAA of the aforementioned list)

   Duplicate addresses and IPv6 addresses other than global unicast
   addresses were eliminated from each of those lists prior to obtaining
   the results included in this document.  Additionally, addresses that
   were found to be unreachable were discarded from the dataset (please
   see Appendix B for further details).

   For each of the aforementioned address sets, three different types of
   probes were employed:

   o  IPv6 packets with a Destination Options header of 8 bytes

   o  IPv6 packets resulting in two IPv6 fragments of 512 bytes each
      (approximately)

   o  IPv6 packets with a Hop-by-Hop Options header of 8 bytes

   In the case of packets with a Destination Options Header and the case
   of packets with a Hop-by-Hop Options header, the desired EH size was
   achieved by means of PadN options [RFC2460].  The upper-layer

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   protocol of the probe packets was, in all cases, TCP [RFC0793]
   segments with the Destination Port set to the service port
   [IANA-PORT-NUMBERS] of the corresponding dataset.  For example, the
   probe packets for all the measurements involving web servers were TCP
   segments with the destination port set to 80.

   Besides obtaining the packet drop rate when employing the
   aforementioned IPv6 extension headers, we tried to identify whether
   the Autonomous System (AS) dropping the packets was the same as the
   Autonomous System of the destination/target address.  This is of
   particular interest since it essentially reveals whether the packet
   drops are under the control of the intended destination of the
   packets.  Packets dropped by the destination AS are less of a
   concern, since the device dropping the packets is under the control
   of the same organization as that to which the packets are destined
   (hence, it is probably easier to update the filtering policy if
   deemed necessary).  On the other hand, packets dropped by transit
   ASes are more of a concern, since they affect the deployability and
   usability of IPv6 extension headers (including IPv6 fragmentation) by
   a third-party (the destination AS).  In any case, we note that it is
   impossible to tell whether, in those cases where IPv6 packets with
   extension headers get dropped, the packet drops are the result of an
   explicit and intended policy, or the result of improper device
   configuration defaults, buggy devices, etc.  Thus, packet drops that
   occur at the destination AS might still prove to be problematic.

   Since there is some ambiguity when identifying the autonomous system
   to which a specific router belongs (see Appendix B.2), each of our
   measurements results in two different values: one corresponding to
   the "best-case scenario", and one corresponding to the "worst-case
   scenario".  The "best-case scenario" is that in which, when in doubt,
   the packets are assumed to be dropped by the destination AS, whereas
   the "worst-case scenario" is that in which, when in doubt, the
   packets are assumed to be dropped by a transit AS (please see
   Appendix B.2 for details).  In the following tables, the values shown
   within parentheses represent the possibility that, when a packet is
   dropped, the packet drop occurs in an AS other than the destination
   AS (considering both the best-case scenario and the worst-case
   scenario).

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   +-------------+-----------------+-----------------+-----------------+
   |   Dataset   |       DO8       |       HBH8      |      FH512      |
   +-------------+-----------------+-----------------+-----------------+
   |  Webservers |      11.88%     |      40.70%     |      30.51%     |
   |             | (17.60%/20.80%) | (31.43%/40.00%) |  (5.08%/6.78%)  |
   +-------------+-----------------+-----------------+-----------------+
   | Mailservers |      17.07%     |      48.86%     |      39.17%     |
   |             |  (6.35%/26.98%) | (40.50%/65.42%) |  (2.91%/12.73%) |
   +-------------+-----------------+-----------------+-----------------+
   | Nameservers |      15.37%     |      43.25%     |      38.55%     |
   |             | (14.29%/33.46%) | (42.49%/72.07%) |  (3.90%/13.96%) |
   +-------------+-----------------+-----------------+-----------------+

   Table 1: WIPv6LD dataset: Packet drop rate for different destination
    types, and estimated percentage of dropped packets that were deemed
          to be dropped in a different AS (lower, in parentheses)

      NOTE: As an example, we note that the cell describing the support
      of IPv6 packets with DO8 for webservers (containing the value
      "11.88% (17.60%/20.80%)") should be read as: "when sending IPv6
      packets with DO8 to public webservers, 11.88% of such packets get
      dropped.  Among those packets that get dropped, 17.60%/20.80%
      (best case / worst case) of them get dropped at an AS other than
      the destination AS".

   +--------+------------------+-------------------+-------------------+
   |   EH   |    Webservers    |    Mailservers    |    Nameservers    |
   |  Type  |                  |                   |                   |
   +--------+------------------+-------------------+-------------------+
   |  DO8   |      11.88%      |       17.07%      |       15.37%      |
   |        | (17.60%/20.80%)  |   (6.35%/26.98%)  |  (14.29%/33.46%)  |
   +--------+------------------+-------------------+-------------------+
   |  HBH8  |      40.70%      |       48.86%      |       43.25%      |
   |        | (31.43%/40.00%)  |  (40.50%/65.42%)  |  (42.49%/72.07%)  |
   +--------+------------------+-------------------+-------------------+
   | FH512  |      30.51%      |       39.17%      |       38.55%      |
   |        |  (5.08%/6.78%)   |   (2.91%/12.73%)  |   (3.90%/13.96%)  |
   +--------+------------------+-------------------+-------------------+

    Table 2: WIPv6LD dataset: Packet drop rate for different EH types,
    and estimated percentage of dropped packets that were deemed to be
             dropped in a different AS (lower, in parentheses)

      NOTE: This table contains the same information as Table 1, but
      makes it easier to obtain the drop rates for each EH type.  Each
      cell should be read in exactly the same way as each cell in
      Table 1.

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   +-------------+-----------------+-----------------+-----------------+
   |   Dataset   |       DO8       |       HBH8      |      FH512      |
   +-------------+-----------------+-----------------+-----------------+
   |  Webservers |      10.91%     |      39.03%     |      28.26%     |
   |             | (46.52%/53.23%) | (36.90%/46.35%) | (53.64%/61.43%) |
   +-------------+-----------------+-----------------+-----------------+
   | Mailservers |      11.54%     |      45.45%     |      35.68%     |
   |             |  (2.41%/21.08%) | (41.27%/61.13%) |  (3.15%/10.92%) |
   +-------------+-----------------+-----------------+-----------------+
   | Nameservers |      21.33%     |      54.12%     |      55.23%     |
   |             | (10.27%/56.80%) | (50.64%/81.00%) |  (5.66%/32.23%) |
   +-------------+-----------------+-----------------+-----------------+

   Table 3: Alexa's top 1M sites dataset: Packet drop rate for different
    destination types, and estimated percentage of dropped packets that
    were deemed to be dropped in a different AS (lower, in parentheses)

   +--------+------------------+-------------------+-------------------+
   |   EH   |    Webservers    |    Mailservers    |    Nameservers    |
   |  Type  |                  |                   |                   |
   +--------+------------------+-------------------+-------------------+
   |  DO8   |      10.91%      |       11.54%      |       21.33%      |
   |        | (46.52%/53.23%)  |   (2.41%/21.08%)  |  (10.27%/56.80%)  |
   +--------+------------------+-------------------+-------------------+
   |  HBH8  |      39.03%      |       45.45%      |       54.12%      |
   |        | (36.90%/46.35%)  |  (41.27%/61.13%)  |  (50.64%/81.00%)  |
   +--------+------------------+-------------------+-------------------+
   | FH512  |      28.26%      |       35.68%      |       55.23%      |
   |        | (53.64%/61.43%)  |   (3.15%/10.92%)  |   (5.66%/32.23%)  |
   +--------+------------------+-------------------+-------------------+

   Table 4: Alexa's top 1M sites dataset: Packet drop rate for different
      EH types, and estimated percentage of dropped packets that were
      deemed to be dropped in a different AS (lower, in parentheses)

      NOTE: This table contains the same information as Table 3, but
      makes it easier to obtain the drop rates for each EH type.  Each
      cell should be read in exactly the same way as each cell in
      Table 3.

   There are a number of observations to be made based on the results
   presented above.  Firstly, while it has been generally assumed that
   it is IPv6 fragments that are dropped by operators, our results
   indicate that it is IPv6 extension headers in general that result in
   packet drops.  Secondly, our results indicate that a significant
   percentage of such packet drops occurs in transit Autonomous Systems;
   that is, the packet drops are not under the control of the same
   organization as the final destination.

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3.  IANA Considerations

   There are no IANA registries within this document.  The RFC-Editor
   can remove this section before publication of this document as an
   RFC.

4.  Security Considerations

   This document presents real-world data regarding the extent to which
   IPv6 packets employing extension headers are dropped in the Internet.
   As such, this document does not introduce any new security issues.

5.  Acknowledgements

   The authors would like to thank (in alphabetical order) Mikael
   Abrahamsson, Mark Andrews, Fred Baker, Brian Carpenter, Gert Doering,
   C.  M.  Heard, Nick Hilliard, Joel Jaeggli, Tatuya Jinmei, Merike
   Kaeo, Warren Kumari, Ted Lemon, Mark Smith, Ole Troan, and Eric
   Vyncke, for providing valuable comments on earlier versions of this
   document.  Additionally, the authors would like to thank participants
   of the v6ops and opsec working groups for their valuable input on the
   topics discussed in this document.

   The authors would like to thank Fred Baker for his guidance in
   improving this document.

   Fernando Gont would like to thank Jan Zorz / Go6 Lab
   <http://go6lab.si/>, and Jared Mauch / NTT America, for providing
   access to systems and networks that were employed to produce some of
   the measurement results presented in this document.  Additionally, he
   would like to thank SixXS <https://www.sixxs.net> for providing IPv6
   connectivity.

6.  References

6.1.  Normative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <http://www.rfc-editor.org/info/rfc793>.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <http://www.rfc-editor.org/info/rfc1034>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

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   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", RFC 4443,
              DOI 10.17487/RFC4443, March 2006,
              <http://www.rfc-editor.org/info/rfc4443>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
              <http://www.rfc-editor.org/info/rfc6145>.

   [RFC6946]  Gont, F., "Processing of IPv6 "Atomic" Fragments",
              RFC 6946, DOI 10.17487/RFC6946, May 2013,
              <http://www.rfc-editor.org/info/rfc6946>.

6.2.  Informative References

   [blackhole6]
              blackhole6, , "blackhole6 tool manual page",
               <http://www.si6networks.com/tools/ipv6toolkit>, 2014.

   [Gont-Chown-IEPG89]
              Gont, F. and T. Chown, "A Small Update on the Use of IPv6
              Extension Headers", IEPG 89. London, UK. March 2, 2014,
              <http://www.iepg.org/2014-03-02-ietf89/
              fgont-iepg-ietf89-eh-update.pdf>.

   [Gont-IEPG88]
              Gont, F., "Fragmentation and Extension header Support in
              the IPv6 Internet",  IEPG 88. Vancouver, BC, Canada.
              November 13, 2013, <http://www.iepg.org/2013-11-ietf88/
              fgont-iepg-ietf88-ipv6-frag-and-eh.pdf>.

   [IANA-PORT-NUMBERS]
              IANA, "Service Name and Transport Protocol Port Number
              Registry", <http://www.iana.org/assignments/
              service-names-port-numbers/
              service-names-port-numbers.txt>.

   [IPv6-Toolkit]
              "SI6 Networks' IPv6 Toolkit",
              <http://www.si6networks.com/tools/ipv6toolkit>.

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   [Linkova-Gont-IEPG90]
              Linkova, J. and F. Gont, "IPv6 Extension Headers in the
              Real World v2.0",  IEPG 90. Toronto, ON, Canada. July 20,
              2014, <http://www.iepg.org/2014-07-20-ietf90/
              iepg-ietf90-ipv6-ehs-in-the-real-world-v2.0.pdf>.

   [path6]    path6, , "path6 tool manual page",
               <http://www.si6networks.com/tools/ipv6toolkit>, 2014.

   [PMTUD-Blackholes]
              De Boer, M. and J. Bosma, "Discovering Path MTU black
              holes on the Internet using RIPE Atlas", July 2012,
              <http://www.nlnetlabs.nl/downloads/publications/
              pmtu-black-holes-msc-thesis.pdf>.

   [RFC5927]  Gont, F., "ICMP Attacks against TCP", RFC 5927,
              DOI 10.17487/RFC5927, July 2010,
              <http://www.rfc-editor.org/info/rfc5927>.

   [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
              with IPv6 Neighbor Discovery", RFC 6980,
              DOI 10.17487/RFC6980, August 2013,
              <http://www.rfc-editor.org/info/rfc6980>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,
              <http://www.rfc-editor.org/info/rfc7045>.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,
              <http://www.rfc-editor.org/info/rfc7113>.

   [RFC7123]  Gont, F. and W. Liu, "Security Implications of IPv6 on
              IPv4 Networks", RFC 7123, DOI 10.17487/RFC7123, February
              2014, <http://www.rfc-editor.org/info/rfc7123>.

Appendix A.  Reproducing Our Experiment

   This section describes, step by step, how to reproduce the experiment
   with which we obtained the results presented in this document.  Each
   subsection represents one step in the experiment.  The tools employed
   for the experiment are traditional UNIX-like tools (such as gunzip),
   and the SI6 Networks' IPv6 Toolkit [IPv6-Toolkit].

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A.1.  Obtaining the List of Domain Names

   The primary data source employed was Alexa's Top 1M web sites,
   available at: <http://s3.amazonaws.com/alexa-static/top-1m.csv.zip>.
   The file is a zipped file containing the list of the most popular web
   sites, in CSV format.  The aforementioned file can be extracted with
   "gunzip < top-1m.csv.zip > top-1m.csv".

   A list of domain names (i.e., other data stripped) can be obtained
   with the following command of [IPv6-Toolkit]: "cat top-1m.csv |
   script6 get-alexa-domains > top-1m.txt".  This command will create a
   "top-1m.txt" file, containing one domain name per line.

      NOTE: The domain names corresponding to the WIPv6LD dataset is
      available at: <http://www.si6networks.com/datasets/wipv6day-
      domains.txt>.  Since the corresponding file is a text file
      containing one domain name per line, the steps produced in this
      subsection need not be performed.  The WIPv6LD data set should be
      processed in the same way as the Alexa Dataset, starting from
      Appendix A.2.

A.2.  Obtaining AAAA Resource Records

   The file obtained in the previous subsection contains a list of
   domain names that correspond to web sites.  The AAAA records for such
   domain names can be obtained with:

   $ cat top-1m.txt | script6 get-aaaa > top-1m-web-aaaa.txt

   The AAAA records corresponding to the mailservers of each of the
   aforementioned domain names can be obtained with:

   $ cat top-1m.txt | script6 get-mx | script6 get-aaaa > top-1m-mail-
   aaaa.txt

   The AAAA records corresponding to the nameservers of each of the
   aforementioned domain names can be obtained with:

   $ cat top-1m.txt | script6 get-ns | script6 get-aaaa > top-1m-dns-
   aaaa.txt

A.3.  Filtering the IPv6 Address Datasets

   The lists of IPv6 addresses obtained in the previous step could
   possibly contain undesired addresses (i.e., non-global unicast
   addresses) and/or duplicate addresses.  In order to remove both
   undesired and duplicate addresses, each of the three files from the
   previous section should be filtered accordingly:

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   $ cat top-1m-web-aaaa.txt | addr6 -i -q -B multicast -B unspec -k
   global > top-1m-web-aaaa-unique.txt

   $ cat top-1m-mail-aaaa.txt | addr6 -i -q -B multicast -B unspec -k
   global > top-1m-mail-aaaa-unique.txt

   $ cat top-1m-dns-aaaa.txt | addr6 -i -q -B multicast -B unspec -k
   global > top-1m-dns-aaaa-unique.txt

A.4.  Performing Measurements with Each IPv6 Address Dataset

A.4.1.  Measurements with web servers

   In order to measure DO8 with the list of webservers:

   # cat top-1m-web-aaaa-unique.txt | script6 trace6 do8 tcp 80 > top-
   1m-web-aaaa-do8-m.txt

   In order to measure HBH8 with the list of webservers:

   # cat top-1m-web-aaaa-unique.txt | script6 trace6 hbh8 tcp 80 > top-
   1m-web-aaaa-hbh8-m.txt

   In order to measure FH512 with the list of webservers:

   # cat top-1m-web-aaaa-unique.txt | script6 trace6 fh512 tcp 80 > top-
   1m-web-aaaa-fh512-m.txt

A.4.2.  Measurements with mail servers

   In order to measure DO8 with the list of mailservers:

   # cat top-1m-mail-aaaa-unique.txt | script6 trace6 do8 tcp 25 > top-
   1m-mail-aaaa-do8-m.txt

   In order to measure HBH8 with the list of webservers:

   # cat top-1m-mail-aaaa-unique.txt | script6 trace6 hbh8 tcp 25 > top-
   1m-mail-aaaa-hbh8-m.txt

   In order to measure FH512 with the list of webservers:

   # cat top-1m-mail-aaaa-unique.txt | script6 trace6 fh512 tcp 25 >
   top-1m-mail-aaaa-fh512-m.txt

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A.4.3.  Measurements with DNS servers

   In order to measure DO8 with the list of mameservers:

   # cat top-1m-dns-aaaa-unique.txt | script6 trace6 do8 tcp 53 > top-
   1m-dns-aaaa-do8-m.txt

   In order to measure HBH8 with the list of webservers:

   # cat top-1m-dns-aaaa-unique.txt | script6 trace6 hbh8 tcp 53 > top-
   1m-dns-aaaa-hbh8-m.txt

   In order to measure FH512 with the list of webservers:

   # cat top-1m-dns-aaaa-unique.txt | script6 trace6 fh512 tcp 53 > top-
   1m-dns-aaaa-fh512-m.txt

A.5.  Obtaining Statistics from our Measurements

A.5.1.  Statistics for Web Servers

   In order to compute the statistics corresponding to our measurements
   of DO8 with the list of webservers:

   $ cat top-1m-web-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
   web-aaaa-do8-stats.txt

   In order to compute the statistics corresponding to our measurements
   of HBH8 with the list of webservers:

   $ cat top-1m-web-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-1m-
   web-aaaa-hbh8-stats.txt

   In order to compute the statistics corresponding to our measurements
   of FH512 with the list of webservers:

   $ cat top-1m-web-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
   1m-web-aaaa-fh512-stats.txt

A.5.2.  Statistics for Mail Servers

   In order to compute the statistics corresponding to our measurements
   of DO8 with the list of mailservers:

   $ cat top-1m-mail-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
   mail-aaaa-do8-stats.txt

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   In order to compute the statistics corresponding to our measurements
   of HBH8 with the list of mailservers:

   $ cat top-1m-mail-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-
   1m-mail-aaaa-hbh8-stats.txt

   In order to compute the statistics corresponding to our measurements
   of FH512 with the list of mailservers:

   $ cat top-1m-mail-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
   1m-mail-aaaa-fh512-stats.txt

A.5.3.  Statistics for Name Servers

   In order to compute the statistics corresponding to our measurements
   of DO8 with the list of nameservers:

   $ cat top-1m-dns-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
   dns-aaaa-do8-stats.txt

   In order to compute the statistics corresponding to our measurements
   of HBH8 with the list of mailservers:

   $ cat top-1m-dns-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-1m-
   dns-aaaa-hbh8-stats.txt

   In order to compute the statistics corresponding to our measurements
   of FH512 with the list of mailservers:

   $ cat top-1m-dns-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
   1m-dns-aaaa-fh512-stats.txt

Appendix B.  Measurements Caveats

   A number of issues have needed some consideration when producing the
   results presented in this document.  These same issues should be
   considered when troubleshooting connectivity problems resulting from
   the use of IPv6 Extension headers.

B.1.  Isolating the Dropping Node

   Let us assume that we find that IPv6 packets with EHs are being
   dropped on their way to the destination system 2001:db8:d::1, and
   that the output of running traceroute towards such destination is:

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      1. 2001:db8:1:1000::1
      2. 2001:db8:2:4000::1
      3. 2001:db8:3:4000::1
      4. 2001:db8:3:1000::1
      5. 2001:db8:4:4000::1
      6. 2001:db8:4:1000::1
      7. 2001:db8:5:5000::1
      8. 2001:db8:5:6000::1
      9. 2001:db8:d::1

   Additionally, let us assume that the output of EH-enabled traceroute
   to the same destination is:

      1. 2001:db8:1:1000::1
      2. 2001:db8:2:4000::1
      3. 2001:db8:3:4000::1
      4. 2001:db8:3:1000::1
      5. 2001:db8:4:4000::1

   For the sake of brevity, let us refer to the last-responding node in
   the EH-enabled traceroute ("2001:db8:4:4000::1" in this case) as "M".
   Assuming that packets in both traceroutes employ the same path, we'll
   refer to "the node following the last responding node in the EH-
   enabled traceroute" ("2001:db8:4:1000::1" in our case), as "M+1",
   etc.

   Based on traceroute information above, which node is the one actually
   dropping the EH-enabled packets will depend on whether the dropping
   node filters packets before making the forwarding decision, or after
   making the forwarding decision.  If the former, the dropping node
   will be M+1.  If the latter, the dropping node will be "M".

   Throughout this document (and our measurements), we assume that those
   nodes dropping packets that carry IPv6 EHs apply their filtering
   policy, and only then, if necessary, forward the packets.  Thus, in
   our example above the last responding node to the EH-enabled
   traceroute ("M") is "2001:db8:4:4000::1", and therefore we assume the
   dropping node to be "2001:db8:4:1000::1" ("M+1").

   Additionally, we note that when isolating the dropping node we assume
   that both the EH-enabled and the EH-free traceroutes result in the
   same paths.  However, this might not be the case.

B.2.  Obtaining the Responsible Organization for the Packet Drops

   In order to identify the organization operating the dropping node,
   one would be tempted to lookup the ASN corresponding to the dropping
   node.  However, assuming that M and M+1 are two peering routers, any

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   of these two organizations could be providing the address space
   employed for such peering.  Or, in the case of an Internet eXchange
   Point (IXP), the address space could correspond to the IXP AS, rather
   than to any of the participating ASes.  Thus, the organization
   operating the dropping node (M+1) could be the AS for M+1, but it
   might as well be the AS for M+2.  Only when the ASN for M+1 is the
   same as the ASN for M+2 we have certainty about who the responsible
   organization for the packet drops is (see slides 21-23 of
   [Linkova-Gont-IEPG90]).

   In the measurement results presented in Section 2, the aforementioned
   ambiguity results in a "best-case" and a "worst-case" scenario
   (rather than a single value): the lowest percentage value means that,
   when in doubt, we assume the packet drops occur in the same AS as the
   destination; on the other hand, the highest percentage value means
   that, when in doubt, we assume the packet drops occur at different AS
   than the destination AS.

   We note that the aforementioned ambiguity should also be considered
   when troubleshooting and reporting IPv6 packet drops, since
   identifying the organization responsible for the packet drops might
   probe to be a non-trivial task.

   Finally, we note that a specific organization might be operating more
   than one Autonomous System.  However, our measurements assume that
   different Autonomous System Numbers imply different organizations.

Appendix C.  Troubleshooting Packet Drops due to IPv6 Extension Headers

   Isolating IPv6 blackholes essentially involves performing IPv6
   traceroute for a destination system with and without IPv6 extension
   headers.  The EH-free traceroute would provide the full working path
   towards a destination, while the EH-enabled traceroute would provide
   the address of the last-responding node for EH-enabled packets (say,
   "M").  In principle, one could isolate the dropping node by looking-
   up "M" in the EH-free traceroute, with the dropping node being "M+1"
   (see Appendix B.1 for caveats).

   At the time of this writing, most traceroute implementations do not
   support IPv6 extension headers.  However, the path6 tool [path6] of
   [IPv6-Toolkit] provides such support.  Additionally, the blackhole6
   tool [blackhole6] of [IPv6-Toolkit] automates the troubleshooting
   process and can readily provide information such as: dropping node's
   IPv6 address, dropping node's Autonomous System, etc.

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Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com

   J. Linkova
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA 94043
   USA

   Email: furry@google.com

   Tim Chown
   University of Southampton
   Highfield
   Southampton , Hampshire   SO17 1BJ
   United Kingdom

   Email: tjc@ecs.soton.ac.uk

   Will(Shucheng) Liu
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: liushucheng@huawei.com

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