IPv6 Extension Headers in the Real World
draft-gont-v6ops-ipv6-ehs-in-real-world-00

IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Informational                                J. Linkova
Expires: February 8, 2015                                         Google
                                                                T. Chown
                                               University of Southampton
                                                                  W. Liu
                                                     Huawei Technologies
                                                          August 7, 2014

                IPv6 Extension Headers in the Real World
               draft-gont-v6ops-ipv6-ehs-in-real-world-00

Abstract

   IPv6 Extension Headers allow for the extension of the IPv6 protocol,
   and provide support for some core functionality such as IPv6
   fragmentation.  However, IPv6 Extension Headers are deemed to present
   a challenge to IPv6 implementations and networks, and are known to be
   intentionally filtered in some existing IPv6 deployments.  This
   summarizes the issues associated with IPv6 extension headers, and
   presents real-world data regarding the extent to which packets with
   IPv6 extension headers are filtered in the public Internet, and where
   in the network such filtering occurs.  Additionally, it provides some
   guidance to operators in troubleshooting IPv6 blackholes resulting
   from the use of IPv6 extension headers.  Finally, this document
   provides some advice to protocol designers, and discusses areas where
   further work might be needed.

Status of This Memo

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   This Internet-Draft will expire on February 8, 2015.

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Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Previous Work on IPv6 Extension Headers . . . . . . . . . . .   3
   3.  Operational Implications  . . . . . . . . . . . . . . . . . .   4
     3.1.  Performance Issues  . . . . . . . . . . . . . . . . . . .   4
     3.2.  Security Implications . . . . . . . . . . . . . . . . . .   4
   4.  Support of IPv6 Extension Headers in the Public Internet  . .   5
   5.  Implications of Widespread IPv6 Extension Header Filtering  .   7
     5.1.  Advice to Protocol Designers  . . . . . . . . . . . . . .   8
     5.2.  A possible attack vector  . . . . . . . . . . . . . . . .   8
     5.3.  Possible Future Work  . . . . . . . . . . . . . . . . . .   8
   6.  Troubleshooting Packet Drops due to IPv6 Extension Headers  .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Measurements Caveats . . . . . . . . . . . . . . . .  12
     A.1.  Isolating the Dropping Node . . . . . . . . . . . . . . .  12
     A.2.  Obtaining the Responsible Organization for the Packet
           Drops . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   IPv6 Extension Headers (EHs) allow for the extension of the IPv6
   protocol, and provide support for core functionality such as IPv6
   fragmentation.  However, IPv6 Extension Headers have been deemed to
   present a challenge to IPv6 implementations and networks, and have
   been assumed/known to be intentionally filtered in some existing IPv6
   deployments.

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   Discussions over the operational implications of IPv6 extension
   headers and their usability in the public Internet come up over and
   over again at both in IETF circles and other venues, and not
   infrequently some key aspects involving IPv6 extension headers are
   overlooked.

   This document tries raise awareness about the operational
   implications of IPv6 Extension Headers, and their usability in the
   public Internet.  Additionally, it provides some guidance in
   troubleshooting IPv6 blackholes resulting from the filtering of
   packets that employ IPv6 extension headers.  Finally, it aims to
   raise awareness about the operational reality of IPv6 extension
   headers to protocol designers, and trigger discussion within the IETF
   community regarding areas where future work might be required.

   Section 2 of this document summarizes the work that has been done in
   the area of IPv6 extension headers.  Section 3 discusses the
   operational implications of IPv6 Extension Headers.  Section 4
   presents real-world data regarding the extent to which IPv6 Extension
   Headers are usable in the public Internet.  Section 5 provides advise
   to protocol designers regarding the use of IPv6 extension headers,
   and aims to raise awareness about the possible interoperability
   implications on existing protocols.  Finally, Section 6 provides some
   guidance in troubleshooting of problems that may arise as a result of
   filtering packets that employ IPv6 Extension Headers.

2.  Previous Work on IPv6 Extension Headers

   Some of the implications of IPv6 Extension Headers have been
   discussed in IETF circles.  For example, [I-D.taylor-v6ops-fragdrop]
   discusses a rationale for which operators filter IPv6 fragments.
   [I-D.wkumari-long-headers] discusses possible issues arising from
   "long" IPv6 header chains.  [RFC7045] clarifies how intermediate
   nodes should deal with IPv6 extension headers.  [RFC7112] discusses
   the issues arising in a specific case where the IPv6 header chain is
   fragmented into two or more fragments (and formally forbids such
   case).  [RFC6980] analyzes the security implications of employing
   IPv6 fragmentation with Neighbor Discovery for IPv6, and formally
   recommends against such usage.  Finally, [RFC7123] discusses how some
   popular RA-Guard implementations are subject to evasion by means of
   IPv6 extension headers.

   While packets employing IPv6 Extension Headers have been "known" 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
   Section 4 of this document is based.

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3.  Operational Implications

3.1.  Performance Issues

   Many IPv6 router implementations suffer from a negative performance
   impact when IPv6 Extension Headers are employed.

   In the most trivial case, a packet that includes a Hop-by-Hop Options
   header will typically go through the slow forwarding path, and be
   processed by the router's CPU.  Another case is that in which a
   router that has been configured to enforce an ACL based on upper-
   layer information (e.g., upper layer protocol or TCP Destination
   Port).  In such case, the router will need to process the entire IPv6
   header chain in order to find the required information, and this may
   cause the packet to be processed in the slow path [Cisco-EH-Cons].

   Processing a large amounts of traffic in the slow patch may cause the
   router to be unable to handle the same traffic loads when compared to
   normal packets, and may result in Denial of Service (DoS) scenarios.

   We note that, for obvious reasons, the aforementioned performance
   issues may also affect other devices such as firewalls, Network
   Intrusion Detection Systems (NIDS), etc.  [Zack-FW-Benchmark].

3.2.  Security Implications

   The security implications of IPv6 Extension Headers generally fall
   into one or more of these categories:

   o  Evasion of security controls

   o  DoS due to processing requirements

   o  DoS due to implementation errors

   o  Extension Header-specific issues

   Different from IPv4, where the upper-layer protocol can be found
   after the variable-length IPv4 header, the structure of IPv6 packets
   is both more flexible and complex.  Namely, finding the upper-layer
   information may imply processing the (daisy-chain like) entire IPv6
   header chain.  This has been often overlooked, and a number of
   security devices have been found to be trivially evasible by
   inserting one or more IPv6 Extension Headers between the main IPv6
   header and the upper layer protocol.  [RFC7113] describes this issue
   for the RA-Guard case, but same same techniques can be employed for
   circumventing e.g. some IPv6 firewalls.  Additionally,
   inconsistencies in how some packets may be processed may result in

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   evasion of security controls [I-D.kampanakis-6man-ipv6-eh-parsing]
   [Atlasis2014].

   As noted in Section 3.1, packets that employ IPv6 Extension Headers
   may have a negative performance impact on the handling devices.
   Unless appropriate mitigations are put in place (e.g., packet
   filtering and/or rate-limiting), an attacker could simply send a
   large amount of IPv6 traffic employing IPv6 Extension Headers with
   the purpose of performing a Denial of Service (DoS) attack.

   IPv6 implementations, as virtually every piece of software, tend to
   mature over time.  While the IPv6 protocol itself (and many
   implementations) have been around for a long time already, bugs in
   IPv6 Extension Header processing have been recently found in a number
   of implementations.  Because there is currently almost no reliance on
   IPv6 Extension headers, the corresponding code paths are rarely
   exercised, and there is the potential that bugs still remain to be
   discovered in some implementations.

   Besides the general implications of IPv6 Extension Headers, each
   Extension Header tends to its own specific implications.  One
   particular case is that of the Fragment Header, which is employed to
   provide the fragmentation function in IPv6.  While many of the
   security implications of the fragmentation/reassembly mechanism are
   known from the IPv4 world, many of the related issues have creeped
   into IPv6 implementations.  They range from Denial of Service attacks
   to information leakage (see e.g.
   [I-D.ietf-6man-predictable-fragment-id], [Bonica-NANOG58],
   [Atlasis2012]).

4.  Support of IPv6 Extension Headers in the Public 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)

   Duplicate and unreachable addresses were eliminated from each of
   those lists prior to obtaining the results below.

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

   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
   concern, since they can be assumed to be the result of an explicit
   policy of the organization to which the packets are destined (who can
   make its own decision regarding what kind of traffic is
   "acceptable").  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)
   regardless of the intent of the communicating end-points.  Thus, when
   packet drops do occur, the "best-case scenario" is that in which the
   packets are dropped by the destination AS, whereas the "worst-case
   scenario" is that in which the packets are dropped by a transit AS.
   Since there is some ambiguity when identifying the autonomous system
   to which a specific router belongs (see Appendix A.2, our
   measurements result in a percentage *range*: the lowest percentage
   value represents the "best case scenario" (where, when in doubt, we
   assume the packet drops occur in the same AS as the destination AS),
   and the highest percentage value represents the "worst case scenario"
   (where, when in doubt, we assume the packet drops occur at different
   AS than the destination AS).

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   +--------------+-----------------+-----------------+----------------+
   |   Dataset    |       DO8       |       HBH8      |     FH512      |
   +--------------+-----------------+-----------------+----------------+
   |     Web      |      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%) |
   +--------------+-----------------+-----------------+----------------+
   | Namerservers |      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

   +-------------+-----------------+-----------------+-----------------+
   |   Dataset   |       DO8       |       HBH8      |      FH512      |
   +-------------+-----------------+-----------------+-----------------+
   |     Web     |      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%) |
   +-------------+-----------------+-----------------+-----------------+
   | Namerserver |      21.33%     |      54.12%     |      55.23%     |
   |      s      | (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

   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 are
   dropped.  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.

5.  Implications of Widespread IPv6 Extension Header Filtering

   The results presented in Section 4 indicate that at least for part of
   the public Internet, communication employing IPv6 extension headers
   is unreliable.  The following subsections discuss specific
   implications arising from this conclusion.

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5.1.  Advice to Protocol Designers

   New protocols that are to operate in the public Internet should
   consider the effect of widespread filtering of IPv6 extension headers
   in the public Internet.  If IPv6 extension headers are at all
   employed, a fall-back mechanism that does not rely on IPv6 extension
   headers should be considered.

5.2.  A possible attack vector

   The widespread filtering of IPv6 packets employing IPv6 Extension
   Headers could, in some scenarios, be exploited for malicious
   purposes: if packets employing IPv6 EHs are known to be filtered on
   the path from one system (say, "A") to another (say, "B"), an
   attacker could cause packets sent from A to B to be dropped by
   sending a forged an ICMPv6 Packet Too Big [RFC4443] error message to
   A (with a Next-Hop MTU smaller than 1280), such that subsequent
   packets from A to B include a fragment header (i.e., they result in
   atomic fragments [RFC6946]).

   A problem with this attack scenario is that a node cannot simply
   "filter/drop all incoming ICMPv6 Packet Too Big error messages", or
   else it might not be able to properly reduce the assumed path MTU
   when communicating with other IPv6 nodes.

   Possible mitigations for this issue include:

   o  Filtering incoming ICMPv6 Packet Too Big (PTB) error messages that
      advertise a Next-Hop MTU smaller than 1280 bytes.

   o  Artificially reducing the MTU to 1280 bytes and filter incoming
      ICMPv6 PTB error messages

   Filtering only those ICMPv6 PTB messages that advertise a Next-Hop
   MTU smaller than 1280 would prevent the generation of IPv6 atomic
   fragments without breaking Path-MTU Discovery.  However, such
   filtering would require deep packet inspection, and such
   functionality (if at all desirable) might not be available.

5.3.  Possible Future Work

   The impact of widespread filtering of IPv6 EHs on existing protocols
   should be considered.  In particular, the effect of widespread
   filtering of IPv6 fragments on the Domain Name System (DNS) [RFC1034]
   should be evaluated (particularly when it is expected that reliance
   on IPv6 transport will increase over time).

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6.  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 A.1 for caveats).

   At the time of this writing, most traceroute implementations do not
   support IPv6 extension headers.  However, the path6 tool [path6] and
   RIPE Atlas [RIPE-Atlas] provide 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.

7.  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.

8.  Security Considerations

   The security implications of IPv6 extension headers are discussed in
   Section 3.2.  This document does not introduce any new security
   issues.

9.  Acknowledgements

   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.

10.  References

10.1.  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.

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   [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.

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

   [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.

   [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
              Oversized IPv6 Header Chains", RFC 7112, January 2014.

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

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

10.2.  Informative References

   [Atlasis2012]
              Atlasis, A., "Attacking IPv6 Implementation Using
              Fragmentation", BlackHat Europe 2012. Amsterdam,
              Netherlands. March 14-16, 2012,
              <https://media.blackhat.com/bh-eu-12/Atlasis/bh-eu-12-
              Atlasis-Attacking_IPv6-Slides.pdf>.

   [Atlasis2014]
              Atlasis, A., "A Novel Way of Abusing IPv6 Extension
              Headers to Evade IPv6 Security Devices", May 2014,
              <http://www.insinuator.net/2014/05/a-novel-way-of-abusing-
              ipv6-extension-headers-to-evade-ipv6-security-devices/>.

   [Bonica-NANOG58]
              Bonica, R., "IPv6 Extension Headers in the Real World
              v2.0", NANOG 58. New Orleans, Louisiana, USA. June 3-5,
              2013, <https://www.nanog.org/sites/default/files/
              mon.general.fragmentation.bonica.pdf>.

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   [Cisco-EH-Cons]
              Cisco, , "IPv6 Extension Headers Review and
              Considerations", October 2006,
              <http://www.cisco.com/en/US/technologies/tk648/tk872/
              technologies_white_paper0900aecd8054d37d.pdf>.

   [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>.

   [I-D.ietf-6man-predictable-fragment-id]
              Gont, F., "Security Implications of Predictable Fragment
              Identification Values", draft-ietf-6man-predictable-
              fragment-id-01 (work in progress), April 2014.

   [I-D.kampanakis-6man-ipv6-eh-parsing]
              Kampanakis, P., "Implementation Guidelines for parsing
              IPv6 Extension Headers", draft-kampanakis-6man-ipv6-eh-
              parsing-01 (work in progress), August 2014.

   [I-D.taylor-v6ops-fragdrop]
              Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
              M., and T. Taylor, "Why Operators Filter Fragments and
              What It Implies", draft-taylor-v6ops-fragdrop-02 (work in
              progress), December 2013.

   [I-D.wkumari-long-headers]
              Kumari, W., Jaeggli, J., and R. Bonica, "Operational
              Issues Associated With Long IPv6 Header Chains", draft-
              wkumari-long-headers-02 (work in progress), October 2013.

   [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>.

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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>.

   [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>.

   [RIPE-Atlas]
              RIPE, , "RIPE Atlas", <https://atlas.ripe.net/>.

   [Zack-FW-Benchmark]
              Zack, E., "Firewall Security Assessment and Benchmarking
              IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
              Berlin, Germany. June 30, 2013,
              <http://www.ipv6hackers.org/meetings/ipv6-hackers-1/zack-
              ipv6hackers1-firewall-security-assessment-and-
              benchmarking.pdf>.

   [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.  Measurements Caveats

   A number of issues have needed some consideration when producing the
   results presented in Section 4.  These same issues should be
   considered when troubleshooting connectivity problems resulting from
   the use of IPv6 Extension headers.

A.1.  Isolating the Dropping Node

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

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      1. 2001:db8:1:1000::1
      2. 2001:db8:2:2000::4
      3. 2001:db8:2:4000::1
      4. 2001:db8:3:4000::1
      5. 2001:db8:3:1000::1
      6. 2001:db8:4:4000::1
      7. 2001:db8:4:1000::1
      8. 2001:db8:5:5000::1
      9. 2001:db8:5:6000::1
      10. 2001:db8:d::1

   and the output of EH-enabled traceroute to the same destination is:

      1. 2001:db8:1:1000::1
      2. 2001:db8:2:2000::4
      3. 2001:db8:2:4000::1
      4. 2001:db8:3:4000::1
      5. 2001:db8:3:1000::1
      6. 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 on ingress or the egress.  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 nodes
   perform ingress-filtering.  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 "node" 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.

A.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 4, the aforementioned
   ambiguity results in "percentage ranges" (rather than a specific
   ratio).  This same ambiguity should be considered when
   troubleshooting and reporting IPv6 packet drops.

   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.

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

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

   Email: liushucheng@huawei.com

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