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Versions: 00 01 02 draft-ietf-v6ops-ipv6-ehs-in-real-world

IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Informational                                J. Linkova
Expires: September 9, 2015                                        Google
                                                                T. Chown
                                               University of Southampton
                                                                  W. Liu
                                                     Huawei Technologies
                                                           March 8, 2015


          Observations on IPv6 EH Filtering in the Real World
               draft-gont-v6ops-ipv6-ehs-in-real-world-02

Abstract

   This document presents real-world data regarding the extent to which
   packets with IPv6 extension headers are filtered in the Internet (as
   measured in August 2014), and where in the network such filtering
   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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 September 9, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (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 . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   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  . . . . . . . . . . .   9
     A.2.  Obtaining AAAA Resource Records . . . . . . . . . . . . .   9
     A.3.  Filtering the IPv6 Address Datasets . . . . . . . . . . .  10
     A.4.  Performing Measurements with Each IPv6 Address Dataset  .  10
     A.5.  Obtaining Statistics from our Measurements  . . . . . . .  11
   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  . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

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
   [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
   IPv6 Extension Headers are filtered in the Internet, as measured in
   August 2014 (pending operational advice in this area).



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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 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 such list)

   o  Name servers (NS -> AAAA of such list)

   IPv6 addresses other than global unicast addresses and duplicate
   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 performed:

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



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   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, our measurements result in a
   percentage *range* (see Appendix B.2).  In the following tables, the
   values shown within parentheses represent the estimated range of
   possibility that when a packet is dropped, the packet drop occurs in
   an AS other than the destination AS.

   +-------------+-----------------+-----------------+-----------------+
   |   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, between 17.60%-
      20.80% of them get dropped at an AS other than the destination
      AS".







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   +--------+------------------+-------------------+-------------------+
   |   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.

   +-------------+-----------------+-----------------+-----------------+
   |   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)












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   +--------+------------------+-------------------+-------------------+
   |   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 occur in transit Autonomous Systems;
   that is, the packet drops are not under the control of the same
   organization as the final destination.

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 filtered in the
   Internet.  As such, this document does not introduce any new security
   issues.







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5.  Acknowledgements

   The authors would like to thank (in alphabetical order) Mark Andrews,
   Fred Baker, Brian Carpenter and Tatuya Jinmei 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 and Go6 Lab
   <http://go6lab.si/> 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, September 1981.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

   [RFC6946]  Gont, F., "Processing of IPv6 "Atomic" Fragments", RFC
              6946, May 2013.







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6.2.  Informative References

   [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>.

   [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>.

   [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, July 2010.

   [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
              with IPv6 Neighbor Discovery", RFC 6980, August 2013.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045, December 2013.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113, February 2014.





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   [RFC7123]  Gont, F. and W. Liu, "Security Implications of IPv6 on
              IPv4 Networks", RFC 7123, February 2014.

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

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

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].

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 an 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
   domains can be obtained with:

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





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   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:

   $ 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




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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

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:





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   $ 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

   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



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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:

      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 both 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 filtering packets that carry IPv6 EHs apply their filtering
   policy, and only then, if necessary, forward the packets.  Thus, in



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   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
   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 "percentage ranges" (rather than a specific
   ratio): 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



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   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] automates the troubleshooting process and can
   readily provide information such as: dropping node's IPv6 address,
   dropping node's Autonomous System, etc.

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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