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INFORMATIONAL
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Internet Engineering Task Force (IETF)                           F. GontRequest for Comments: 7872                        SI6 Networks / UTN-FRHCategory: Informational                                       J. LinkovaISSN: 2070-1721                                                   Google                                                                T. Chown                                                                    Jisc                                                                  W. Liu                                                     Huawei Technologies                                                               June 2016Observations on the Dropping of Packetswith IPv6 Extension Headers in the Real WorldAbstract   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; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7872.Gont, et al.                  Informational                     [Page 1]

RFC 7872                 IPv6 Extension Headers                June 2016Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Support of IPv6 Extension Headers in the Internet . . . . . .33.  Security Considerations . . . . . . . . . . . . . . . . . . .64.  References  . . . . . . . . . . . . . . . . . . . . . . . . .64.1.  Normative References  . . . . . . . . . . . . . . . . . .64.2.  Informative References  . . . . . . . . . . . . . . . . .6Appendix A.  Reproducing Our Experiment . . . . . . . . . . . . .8A.1.  Obtaining the List of Domain Names  . . . . . . . . . . .8A.2.  Obtaining AAAA Resource Records . . . . . . . . . . . . .8A.3.  Filtering the IPv6 Address Datasets . . . . . . . . . . .9     A.4.  Performing Measurements with Each IPv6 Address Dataset  .   9A.5.  Obtaining Statistics from Our Measurements  . . . . . . .10Appendix B.  Measurements Caveats . . . . . . . . . . . . . . . .12B.1.  Isolating the Dropping Node . . . . . . . . . . . . . . .12     B.2.  Obtaining the Responsible Organization for the Packet           Drops . . . . . . . . . . . . . . . . . . . . . . . . . .13Appendix C.  Troubleshooting Packet Drops Due to IPv6 Extension                Headers  . . . . . . . . . . . . . . . . . . . . . .14   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .14   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .15Gont, et al.                  Informational                     [Page 2]

RFC 7872                 IPv6 Extension Headers                June 20161.  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   seeAppendix 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 (seeAppendix 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 seeAppendix 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 ASGont, 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.  References4.1.  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 2016Appendix 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 fromAppendix 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.txtGont, 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.txtA.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.txtA.4.  Performing Measurements with Each IPv6 Address DatasetA.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.txtGont, et al.                  Informational                     [Page 9]

RFC 7872                 IPv6 Extension Headers                June 2016A.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.txtA.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.txtA.5.  Obtaining Statistics from Our MeasurementsA.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.txtGont, 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.txtA.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.txtA.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.txtGont, 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.txtAppendix 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 afterGont, 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 inSection 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 2016Appendix 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" (seeAppendix 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 2016Authors' 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.comGont, et al.                  Informational                    [Page 15]

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