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rfc:rfc7872

Internet Engineering Task Force (IETF) F. Gont Request for Comments: 7872 SI6 Networks / UTN-FRH Category: Informational J. Linkova ISSN: 2070-1721 Google

                                                              T. Chown
                                                                  Jisc
                                                                W. Liu
                                                   Huawei Technologies
                                                             June 2016
              Observations on the Dropping of Packets
           with IPv6 Extension Headers in the Real World

Abstract

 This document presents real-world data regarding the extent to which
 packets with IPv6 Extension Headers (EHs) are dropped in the Internet
 (as originally measured in August 2014 and later in June 2015, with
 similar results) 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 EHs so that the situation improves over time.  This
 document also explains how the results were obtained, such that the
 corresponding measurements can be reproduced by other members of the
 community and repeated over time to observe changes in the handling
 of packets with IPv6 EHs.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7872.

Gont, et al. Informational [Page 1] RFC 7872 IPv6 Extension Headers June 2016

Copyright Notice

 Copyright (c) 2016 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Support of IPv6 Extension Headers in the Internet . . . . . .   3
 3.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
 4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
   4.2.  Informative References  . . . . . . . . . . . . . . . . .   6
 Appendix A.  Reproducing Our Experiment . . . . . . . . . . . . .   8
   A.1.  Obtaining the List of Domain Names  . . . . . . . . . . .   8
   A.2.  Obtaining AAAA Resource Records . . . . . . . . . . . . .   8
   A.3.  Filtering the IPv6 Address Datasets . . . . . . . . . . .   9
   A.4.  Performing Measurements with Each IPv6 Address Dataset  .   9
   A.5.  Obtaining Statistics from Our Measurements  . . . . . . .  10
 Appendix B.  Measurements Caveats . . . . . . . . . . . . . . . .  12
   B.1.  Isolating the Dropping Node . . . . . . . . . . . . . . .  12
   B.2.  Obtaining the Responsible Organization for the Packet
         Drops . . . . . . . . . . . . . . . . . . . . . . . . . .  13
 Appendix C.  Troubleshooting Packet Drops Due to IPv6 Extension
              Headers  . . . . . . . . . . . . . . . . . . . . . .  14
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

Gont, et al. Informational [Page 2] RFC 7872 IPv6 Extension Headers June 2016

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 EHs 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
 packets containing IPv6 EHs are dropped in the Internet, as measured
 in August 2014 and later in June 2015 with similar results (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 EHs 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 EHs 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" site
 <http://www.worldipv6launch.org> and Alexa's list of the Top
 1-Million 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 records of the aforementioned list)
 o  Name servers (NS -> AAAA records 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;

Gont, et al. Informational [Page 3] RFC 7872 IPv6 Extension Headers June 2016

 o  IPv6 packets resulting in two IPv6 fragments of 512 bytes each
    (approximately); and
 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
 protocol of the probe packets was, in all cases, TCP [RFC793] 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 EHs, we tried to identify whether the Autonomous
 System (AS) dropping the packets was the same as the AS 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 EHs (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 EHs 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 AS 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).

Gont, et al. Informational [Page 4] RFC 7872 IPv6 Extension Headers June 2016

 +----------+------------------+------------------+------------------+
 | Dataset  |       DO8        |       HBH8       |      FH512       |
 +----------+------------------+------------------+------------------+
 |   Web    |      11.88%      |      40.70%      |      30.51%      |
 | servers  | (17.60%/20.80%)  | (31.43%/40.00%)  |  (5.08%/6.78%)   |
 +----------+------------------+------------------+------------------+
 |   Mail   |      17.07%      |      48.86%      |      39.17%      |
 | servers  |  (6.35%/26.98%)  | (40.50%/65.42%)  |  (2.91%/12.73%)  |
 +----------+------------------+------------------+------------------+
 |   Name   |      15.37%      |      43.25%      |      38.55%      |
 | servers  | (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 (Best-Case / Worst-Case) Percentage of Packets
                  That Were Dropped in a Different AS
    NOTE: In the tables above and below, "HBH8" stands for "packets
    with a Hop-By-Hop Options extension header of 8 bytes", "DO8"
    stands for "packets with a Destination Options extension header of
    8 bytes", and "FH512" stands for "IPv6 packets with a Fragment
    Header of 512 bytes".
    NOTE: As an example, we note that the cell describing the support
    of IPv6 packets with DO8 for web servers (containing the value
    "11.88% (17.60%/20.80%)") should be read as: "when sending IPv6
    packets with DO8 to public web servers, 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".
 +----------+------------------+------------------+------------------+
 | Dataset  |       DO8        |       HBH8       |      FH512       |
 +----------+------------------+------------------+------------------+
 |   Web    |      10.91%      |      39.03%      |      28.26%      |
 | servers  | (46.52%/53.23%)  | (36.90%/46.35%)  | (53.64%/61.43%)  |
 +----------+------------------+------------------+------------------+
 |   Mail   |      11.54%      |      45.45%      |      35.68%      |
 | servers  |  (2.41%/21.08%)  | (41.27%/61.13%)  |  (3.15%/10.92%)  |
 +----------+------------------+------------------+------------------+
 |   Name   |      21.33%      |      54.12%      |      55.23%      |
 | servers  | (10.27%/56.80%)  | (50.64%/81.00%)  |  (5.66%/32.23%)  |
 +----------+------------------+------------------+------------------+
 Table 2: Alexa's Top 1M Sites Dataset: Packet Drop Rate for Different
 Destination Types, and Estimated (Best-Case / Worst-Case) Percentage
            of Packets That Were Dropped in a Different AS

Gont, et al. Informational [Page 5] RFC 7872 IPv6 Extension Headers June 2016

 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 EHs in general that result in packet drops.
 Secondly, our results indicate that a significant percentage of such
 packet drops occurs in transit ASes; that is, the packet drops are
 not under the control of the same organization as the final
 destination.

3. Security Considerations

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

4. References

4.1. Normative References

 [RFC793]   Postel, J., "Transmission Control Protocol", STD 7,
            RFC 793, DOI 10.17487/RFC0793, September 1981,
            <http://www.rfc-editor.org/info/rfc793>.
 [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>.

4.2. Informative References

 [Gont-Chown-IEPG89]
            Gont, F. and T. Chown, "A Small Update on the Use of IPv6
            Extension Headers", IEPG meeting before IETF 89, March
            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 meeting before IETF 88, November
            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>.

Gont, et al. Informational [Page 6] RFC 7872 IPv6 Extension Headers June 2016

 [IPv6-Toolkit]
            SI6 Networks, "SI6 Networks' IPv6 Toolkit v2.0 (Guille)",
            <http://www.si6networks.com/tools/ipv6toolkit>.
 [Linkova-Gont-IEPG90]
            Linkova, J. and F. Gont, "IPv6 Extension Headers in the
            Real World v2.0", IEPG Meeting before IETF 90, July 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>.

Gont, et al. Informational [Page 7] RFC 7872 IPv6 Extension Headers June 2016

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 v2.0 (Guille) [IPv6-Toolkit].
 Throughout this appendix, "#" denotes the command-line prompt for
 commands that require superuser privileges, whereas "$" denotes the
 prompt for commands that do not require superuser privileges.

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 Comma-Separated Value (CSV) format.  The aforementioned
 file can be extracted with
 $ gunzip < top-1m.csv.zip > top-1m.csv
 A list of domain names (i.e., with other data stripped) can be
 obtained with the following command [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 dataset 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

Gont, et al. Informational [Page 8] RFC 7872 IPv6 Extension Headers June 2016

 The AAAA records corresponding to the mail servers 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 name servers 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 (e.g., 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 web servers:
 # 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 web servers:
 # 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 web servers:
 # cat top-1m-web-aaaa-unique.txt | script6 trace6 fh512 tcp 80 >
 top-1m-web-aaaa-fh512-m.txt

Gont, et al. Informational [Page 9] RFC 7872 IPv6 Extension Headers June 2016

A.4.2. Measurements with Mail Servers

 In order to measure DO8 with the list of mail servers:
 # 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 mail servers:
 # 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 mail servers:
 # cat top-1m-mail-aaaa-unique.txt | script6 trace6 fh512 tcp 25 >
 top-1m-mail-aaaa-fh512-m.txt

A.4.3. Measurements with Name Servers

 In order to measure DO8 with the list of name servers:
 # 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 name servers:
 # 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 name servers:
 # 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 web servers:
 $ cat top-1m-web-aaaa-do8-m.txt | script6 get-trace6-stats >
 top-1m-web-aaaa-do8-stats.txt

Gont, et al. Informational [Page 10] RFC 7872 IPv6 Extension Headers June 2016

 In order to compute the statistics corresponding to our measurements
 of HBH8 with the list of web servers:
 $ 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 web servers:
 $ 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 mail servers:
 $ 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 mail servers:
 $ 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 mail servers:
 $ 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 name servers:
 $ 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 mail servers:
 $ cat top-1m-dns-aaaa-hbh8-m.txt | script6 get-trace6-stats >
 top-1m-dns-aaaa-hbh8-stats.txt

Gont, et al. Informational [Page 11] RFC 7872 IPv6 Extension Headers June 2016

 In order to compute the statistics corresponding to our measurements
 of FH512 with the list of mail servers:
 $ 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 EHs.

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 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

Gont, et al. Informational [Page 12] RFC 7872 IPv6 Extension Headers June 2016

 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 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 Autonomous System Numbers (ASNs)
 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 do 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 a 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
 prove to be a non-trivial task.
 Finally, we note that a specific organization might be operating more
 than one AS.  However, our measurements assume that different ASNs
 imply different organizations.

Gont, et al. Informational [Page 13] RFC 7872 IPv6 Extension Headers June 2016

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 EHs.  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 EHs.  However, the path6 tool of [IPv6-Toolkit] provides
 such support.  Additionally, the blackhole6 tool of [IPv6-Toolkit]
 automates the troubleshooting process and can readily provide
 information such as: dropping node's IPv6 address, dropping node's
 AS, etc.

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 draft 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 of Go6 Lab
 <http://go6lab.si/> and Jared Mauch of 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.
 Fernando Gont would like to thank Nelida Garcia and Guillermo Gont
 for their love and support.

Gont, et al. Informational [Page 14] RFC 7872 IPv6 Extension Headers June 2016

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
 United States
 Email: furry@google.com
 Tim Chown
 Jisc
 Lumen House, Library Avenue
 Harwell Oxford, Didcot  OX11 0SG
 United Kingdom
 Email: tim.chown@jisc.ac.uk
 Will (Shucheng) Liu
 Huawei Technologies
 Bantian, Longgang District
 Shenzhen  518129
 China
 Email: liushucheng@huawei.com

Gont, et al. Informational [Page 15]

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