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IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Informational                               N. Hilliard
Expires: September 12, 2016                                         INEX
                                                              G. Doering
                                                             SpaceNet AG
                                                                  W. Liu
                                                     Huawei Technologies
                                                               W. Kumari
                                                                  Google
                                                          March 11, 2016


    Operational Implications of IPv6 Packets with Extension Headers
               draft-gont-v6ops-ipv6-ehs-packet-drops-03

Abstract

   This document summarizes the security and operational implications of
   IPv6 extension headers, and attempts to analyze reasons why packets
   with IPv6 extension headers may be dropped in the public Internet.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 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



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   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.  Previous Work on IPv6 Extension Headers . . . . . . . . . . .   3
   3.  Security Implications . . . . . . . . . . . . . . . . . . . .   4
   4.  Operational Implications  . . . . . . . . . . . . . . . . . .   5
     4.1.  Requirement to process required layer-3/layer-4
           information . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Route-Processor Protection  . . . . . . . . . . . . . . .   7
     4.3.  Inability to Perform Fine-grained Filtering . . . . . . .   8
   5.  A Possible Attack Vector  . . . . . . . . . . . . . . . . . .   8
   6.  Future Work . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   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.  However, common implementation limitations suggest
   that EHs present a challenge for IPv6 packet routing equipment, and
   evidence exists to suggest that IPv6 packets with EHs may be
   intentionally dropped on the public Internet in some network
   deployments.

   The authors of this document have been involved in numerous
   discussions about IPv6 extension headers (both within the IETF and
   outside of it), and have noticed that a number of security and
   operational issues were unknown to the larger audience participating
   in these discussions.

   This document has the following goals:

   o  Raise awareness about the security and operational implications of
      IPv6 Extension Headers, and presents reasons why some networks
      intentionally drop packets containing IPv6 Extension Headers.




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   o  Highlight areas where current IPv6 support by networking devices
      maybe sub-optimal, such that the aforementioned support is
      improved.

   o  Highlight operational issues associated with IPv6 extension
      headers, such that those issues are considered in IETF
      standardization efforts.

   Section 2 of this document summarizes the previous work that has been
   done in the area of IPv6 extension headers.  Section 3 briefly
   discusses the security implications of IPv6 Extension Headers, while
   Section 4 discusses their operational implications.  Finally,
   Section 6 proposes an action plan for improving the state of affairs
   of 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 drop 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 fragmentation case where the IPv6
   header chain is fragmented into two or more fragments (and formally
   forbids such fragmentation case).
   [I-D.kampanakis-6man-ipv6-eh-parsing] describes how inconsistencies
   in the way IPv6 packets with extension headers are parsed by
   different implementations may result in evasion of security controls,
   and presents guidelines for parsing IPv6 extension headers with the
   goal of providing a common and consistent parsing methodology for
   IPv6 implementations.  [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.

   Some preliminary measurements regarding the extent to which packet
   containing IPv6 EHs are dropped in the public Internet have been
   presented in [PMTUD-Blackholes], [Gont-IEPG88], [Gont-Chown-IEPG89],
   and [Linkova-Gont-IEPG90].  [I-D.ietf-v6ops-ipv6-ehs-in-real-world]
   presents more comprehensive results and documents the methodology for
   obtaining the presented results.








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3.  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

   Unlike IPv4 packets where the upper-layer protocols can be trivially
   found by means of the "IHL" ("Internet Header Length") IPv4 header
   field, the structure of IPv6 packets is more flexible and complex.
   Locating upper-layer protocol information requires that all IPv6
   extension headers be examined.  This has presented implementation
   difficulties, and packet filtering mechanisms that require upper-
   layer information (even if just the upper layer protocol type) on
   several security devices can be trivially evaded by inserting IPv6
   Extension Headers between the main IPv6 header and the upper layer
   protocol.  [RFC7113] describes this issue for the RA-Guard case, but
   the same techniques can be employed to circumvent other IPv6 firewall
   and packet filtering mechanisms.  Additionally, implementation
   inconsistencies in packet forwarding engines may result in evasion of
   security controls [I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014]
   [BH-EU-2014].

   Packets that use IPv6 Extension Headers may have a negative
   performance impact on the handling devices.  Unless appropriate
   mitigations are put in place (e.g., packet dropping 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 (see Section 4 for
   further details).

   NOTE:
      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 possible case might
      be 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), needs to process the entire IPv6 header
      chain (in order to find the required information) and this causes
      the packet to be processed in the slow path [Cisco-EH-Cons].  We
      note that, for obvious reasons, the aforementioned performance
      issues may also affect other devices such as firewalls, Network



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      Intrusion Detection Systems (NIDS), etc.  [Zack-FW-Benchmark].
      The extent to which these devices are affected will typically be
      implementation-dependent.

   IPv6 implementations, like all other software, tend to mature with
   time and wide-scale deployment.  While the IPv6 protocol itself has
   existed for almost 20 years, serious bugs related to IPv6 Extension
   Header processing continue to be discovered.  Because there is
   currently little operational 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.

   IPv6 Fragment Headers are employed to allow fragmentation of IPv6
   packets.  While many of the security implications of the
   fragmentation / reassembly mechanism are known from the IPv4 world,
   several related issues have crept into IPv6 implementations.  These
   range from denial of service attacks to information leakage, for
   example [I-D.ietf-6man-predictable-fragment-id], [Bonica-NANOG58] and
   [Atlasis2012]).

4.  Operational Implications

4.1.  Requirement to process required layer-3/layer-4 information

   Intermediate systems and middleboxes that need to find the layer-4
   header must process the entire IPv6 extension header chain.  When
   such devices are unable to obtain the required information, they may
   simply drop the corresponding packets.  The following subsections
   discuss some of reasons for which such layer-4 information may be
   needed by an intermediate systems or middlebox, and why packets
   containing IPv6 extension headers may represent a challenge in such
   scenarios.

4.1.1.  Packet Forwarding Engine Constraints

   Most modern routers use dedicated hardware (e.g.  ASICs or NPUs) to
   determine how to forward packets across their internal fabrics (see
   [IEPG94-Scudder] for details).  One of the common methods of handling
   next-hop lookup is to send a small portion of the ingress packet to a
   lookup engine with specialised hardware (e.g. ternary CAM or RLDRAM)
   to determine the packet's next-hop.  Technical constraints mean that
   there is a trade-off between the amount of data sent to the lookup
   engine and the overall performance of the lookup engine.  If more
   data is sent, the lookup engine can inspect further into the packet,
   but the overall performance of the system will be reduced.  If less
   data is sent, the overall performance of the router will be increased




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   but the packet lookup engine may not be able to inspect far enough
   into a packet to determine how it should be handled.

   NOTE:
      For example, current high-end routers at the time of authorship of
      this document can use up to 192 bytes of header (Cisco ASR9000
      Typhoon) or 384 bytes of header (Juniper MX Trio)

   If a hardware forwarding engine on a modern router cannot make a
   forwarding decision about a packet because critical information is
   not sent to the look-up engine, then the router will normally drop
   the packet.  Historically, some packet forwarding engines punted
   packets of this form to the control plane for more in-depth analysis,
   but this is unfeasible on most current router architectures as a
   result of the vast difference between the hardware forwarding
   capacity of the router and processing capacity of the control plane
   and the size of the management link which connects the control plane
   to the forwarding plane.

   If an IPv6 header chain is sufficiently long that its header exceeds
   the packet look-up capacity of the router, then it may be dropped due
   to hardware inability to determine how it should be handled.

4.1.2.  ECMP and Hash-based Load-Sharing

   In the case of ECMP (equal cost multi path) load sharing, the router
   on the sending side of the link needs to make a decision regarding
   which of the links to use for a given packet.  Since round-robin
   usage of the links is usually avoided in order to prevent packet
   reordering, forwarding engines need to use a mechanism which will
   consistently forward the same data streams down the same forwarding
   paths.  Most forwarding engines achieve this by calculating a simple
   hash using an n-tuple gleaned from a combination of layer-2 through
   to layer-4 packet header information.  This n-tuple will typically
   use the src/dst MAC address, src/dst IP address, and if possible
   further layer-4 src/dst port information.  As layer-4 port
   information increases the entropy of the hash, it is highly desirable
   to use it where possible.

   We note that in the IPv6 world, flows are expected to be identified
   by means of the IPv6 Flow Label [RFC6437].  Thus, ECMP and Hash-based
   Load-Sharing would be possible without the need to process the entire
   IPv6 header chain to obtain upper-layer information to identify
   flows.  However, we note that for a long time many IPv6
   implementations failed to set the Flow Label, and ECMP and Hash-based
   Load-Sharing devices also did not employ the Flow Label for
   performing their task.




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   Clearly, widespread support of [RFC6437] would relieve middle-boxes
   from having to process the entire IPv6 header chain, making Flow
   Label-based ECMP and Hash-based Load-Sharing [RFC6438] feasible.

4.1.3.  Enforcing infrastructure ACLs

   Generally speaking, infrastructure ACLs (iACLs) drop unwanted packets
   destined to parts of a provider's infrastructure, because they are
   not operationally needed and can be used for attacks of different
   sorts against the router's control plane.  Some traffic needs to be
   differentiated depending on layer-3 or layer-4 criteria to achieve a
   useful balance of protection and functionality, for example:

   o  Permit some amount of ICMP echo (ping) traffic towards the
      router's addresses for troubleshooting.

   o  Permit BGP sessions on the shared network of an exchange point
      (potentially differentiating between the amount of packets/seconds
      permitted for established sessions and connection establishment),
      but do not permit other traffic from the same peer IP addresses.

4.1.4.  DDoS Management and Customer Requests for Filtering

   The case of customer DDoS protection and edge-to-core customer
   protection filters is similar in nature to the infrastructure ACL
   protection.  Similar to infrastructure ACL protection, layer-4 ACLs
   generally need to be applied as close to the edge of the network as
   possible, even though the intent is usually to protect the customer
   edge rather than the provider core.  Application of layer-4 DDoS
   protection to a network edge is often automated using Flowspec
   [RFC5575].

   For example, a web site which normally only handled traffic on TCP
   ports 80 and 443 could be subject to a volumetric DDoS attack using
   NTP and DNS packets with randomised source IP address, thereby
   rendering useless traditional [RFC5635] source-based real-time black
   hole mechanisms.  In this situation, DDoS protection ACLs could be
   configured to block all UDP traffic at the network edge without
   impairing the web server functionality in any way.  Thus, being able
   to block arbitrary protocols at the network edge can avoid DDoS-
   related problems both in the provider network and on the customer
   edge link.

4.2.  Route-Processor Protection

   Most modern routers have a fast hardware-assisted forwarding plane
   and a loosely coupled control plane, connected together with a link
   that has much less capacity than the forwarding plane could handle.



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   Traffic differentiation cannot be done by the control plane side,
   because this would overload the internal link connecting the
   forwarding plane to the control plane.

   The Hop-by-Hop Options header is particularly challenging since, in
   most (if not all) implementations, it causes the corresponding packet
   to be punted to a software path.  As a result, operators usually drop
   IPv6 packets containing this extension header.  Please see [RFC6192]
   for advice regarding protection of the router control plane.

4.3.  Inability to Perform Fine-grained Filtering

   Some routers lack of fine-grained filtering of IPv6 extension
   headers.  For example, an operator may want to drop packets
   containing Routing Header Type 0 (RHT0) but may only be able to
   filter on the extension header type (Routing Header).  As a result,
   the operator may end up enforcing a more coarse filtering policy
   (e.g. "drop all packets containing a Routing Header" vs. "only drop
   packets that contain a Routing Header Type 0").

5.  A Possible Attack Vector

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

   Possible scenarios where this attack vector could be exploited
   include (but are not limited to):

   o  Communication between any two systems through the public network
      (e.g., client from/to server or server from/to server), where
      packets with IPv6 extension headers are dropped by some
      intermediate router

   o  Communication between two BGP peers employing IPv6 transport,
      where these BGP peers implement ACLs to drop IPv6 fragments (to
      avoid control-plane attacks)

   The aforementioned attack vector is exacerbated by the following
   factors:






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   o  The attacker does not need to forge the IPv6 Source Address of his
      attack packets.  Hence, deployment of simple BCP38 filters will
      not help as a counter-measure.

   o  Only the IPv6 addresses of the IPv6 packet embedded in the ICMPv6
      payload need to be forged.  While one could envision filtering
      devices enforcing BCP38-style filters on the ICMPv6 payload, the
      use of extension headers (by the attacker) could make this
      difficult, if not impossible.

   o  Many implementations fail to perform validation checks on the
      received ICMPv6 error messages, as recommended in Section 5.2 of
      [RFC4443] and documented in [RFC5927].  It should be noted that in
      some cases, such as when an ICMPv6 error message has (supposedly)
      been elicited by a connection-less transport protocol (or some
      other connection-less protocol being encapsulated in IPv6), it may
      be virtually impossible to perform validation checks on the
      received ICMPv6 error messages.  And, because of IPv6 extension
      headers, the ICMPv6 payload might not even contain any useful
      information on which to perform validation checks.

   o  Upon receipt of one of the aforementioned ICMPv6 "Packet Too Big"
      error messages, the Destination Cache [RFC4861] is usually updated
      to reflect that any subsequent packets to such destination should
      include a Fragment Header.  This means that a single ICMPv6
      "Packet Too Big" error message might affect multiple communication
      instances (e.g.  TCP connections) with such destination.

   o  A router or other middlebox cannot simply drop all incoming ICMPv6
      Packet Too Big error messages, as this would create a PMTUD
      blackhole.

   Possible mitigations for this issue include:

   o  Dropping incoming ICMPv6 Packet Too Big error messages that
      advertise an MTU smaller than 1280 bytes.

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

   Both of these mitigations come at the expense of possibly preventing
   communication through SIIT [RFC6145], that relies on IPv6 atomic
   fragments (see [I-D.ietf-6man-deprecate-atomfrag-generation]), and
   also implies that the filtering device has the ability to filter ICMP
   PTB messages based on the contents of the MTU field.

   [I-D.ietf-6man-deprecate-atomfrag-generation] documents while the
   generation of IPv6 atomic fragments is considered harmful, and



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   documents why this functionality is being removed from the upcoming
   revision of the core IPv6 protocol [I-D.ietf-6man-rfc2460bis].  Thus,
   any of the above mitigations would eliminate the attack vector
   without any interoperability implications.

6.  Future Work

   Based on the discussion provided in this document, we recommend the
   following (*non*-mutually exclusive) actions to improve the state of
   affairs of IPv6 extension headers:

   o  Vendors must allow for better granularity in the specification of
      filters for IPv6 extension headers, such that filters for specific
      EH types and subtypes (e.g.  RHT0 vs. RHT2) can be specified
      wthout affecting other extension header types/subtypes
      unnecessarily (please see Section 4.3).

   o  Provide advice on the filtering of IPv6 packets that contain IPv6
      extension headers (as in [I-D.ietf-opsec-ipv6-eh-filtering]).

   o  The IETF should evaluate the possibility of enforcing a cap on the
      maximum length of an IPv6 EH chain (e.g., as proposed in
      [I-D.wkumari-long-headers]).  If not at the protocol specification
      level (i.e., "Standards Track"), such a cap could be recommended
      as operational advice of the form "IPv6 implementations are
      expected to support EH chains as long as the they fit in the Path-
      MTU for the corresponding packets (see [RFC7112]).  However, given
      current technology constraints, we specifically note that all
      implementations MUST support EH chains of at least X bytes, and
      MUST be able to process such EH chains (where necessary), without
      negative performance impact".

   We explicitly note that the authors of this document do not (in any
   way) suggest or propose to depracate IPv6 extension headers and that,
   on the contrary, they propose actions to improve their state of
   affairs.

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.  A specific attack vector that could leverage the
   widespread dropping of packets with IPv6 EHs (along with possible



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   countermeasures) is discussed in Section 5.  This document does not
   introduce any new security issues.

9.  Acknowledgements

   The authors would like to thank (in alphabetical order) Mikael
   Abrahamsson, Fred Baker, Brian Carpenter, Lee Howard, Sander
   Steffann, Eric Vyncke, and Andrew Yourtchenko, for providing valuable
   comments on earlier versions of this document.  Additionally, the
   authors would like to thank participants of the v6ops working group
   for their valuable input on the topics that led to the publication of
   this document.

   Fernando Gont would like to thank Sander Steffann, who took the time
   to meet to discuss this document, even while higher priority events
   were in place.

   Fernando Gont would like to thank Jan Zorz / Go6 Lab
   <http://go6lab.si/>, and Jared Mauch / NTT America, for providing
   access to systems and networks that were employed to perform
   experiments and measurements involving packets with IPv6 Extension
   Headers.  Additionally, he would like to thank SixXS
   <https://www.sixxs.net> for providing IPv6 connectivity.

10.  References

10.1.  Normative References

   [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>.

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

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

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





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

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/>.

   [BH-EU-2014]
              Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High-
              End IDPS Devices at the IPv6 Era",  BlackHat Europe 2014,
              2014, <https://www.ernw.de/download/eu-14-Atlasis-Rey-
              Schaefer-briefings-Evasion-of-HighEnd-IPS-Devices-wp.pdf>.

   [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>.

   [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>.



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   [I-D.ietf-6man-deprecate-atomfrag-generation]
              Gont, F., LIU, S., and T. Anderson, "Generation of IPv6
              Atomic Fragments Considered Harmful", draft-ietf-6man-
              deprecate-atomfrag-generation-05 (work in progress),
              January 2016.

   [I-D.ietf-6man-predictable-fragment-id]
              Gont, F., "Security Implications of Predictable Fragment
              Identification Values", draft-ietf-6man-predictable-
              fragment-id-10 (work in progress), October 2015.

   [I-D.ietf-6man-rfc2460bis]
              Deering, S. and B. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", draft-ietf-6man-rfc2460bis-03 (work
              in progress), January 2016.

   [I-D.ietf-opsec-ipv6-eh-filtering]
              Gont, F., LIU, S., and R. Bonica, "Recommendations on
              Filtering of IPv6 Packets Containing IPv6 Extension
              Headers", draft-ietf-opsec-ipv6-eh-filtering-00 (work in
              progress), March 2015.

   [I-D.ietf-v6ops-ipv6-ehs-in-real-world]
              Gont, F., Linkova, J., Chown, T., and S. LIU,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", draft-ietf-v6ops-
              ipv6-ehs-in-real-world-02 (work in progress), December
              2015.

   [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., Bonica, R., and J. Linkova,
              "Operational Issues Associated With Long IPv6 Header
              Chains", draft-wkumari-long-headers-03 (work in progress),
              June 2015.






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   [IEPG94-Scudder]
              Petersen, B. and J. Scudder, "Modern Router Architecture
              for Protocol Designers",  IEPG 94. Yokohama, Japan.
              November 1, 2015, <http://www.iepg.org/2015-11-01-ietf94/
              IEPG-RouterArchitecture-jgs.pdf>.

   [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>.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <http://www.rfc-editor.org/info/rfc5575>.

   [RFC5635]  Kumari, W. and D. McPherson, "Remote Triggered Black Hole
              Filtering with Unicast Reverse Path Forwarding (uRPF)",
              RFC 5635, DOI 10.17487/RFC5635, August 2009,
              <http://www.rfc-editor.org/info/rfc5635>.

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

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
              March 2011, <http://www.rfc-editor.org/info/rfc6192>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <http://www.rfc-editor.org/info/rfc6437>.

   [RFC6438]  Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
              for Equal Cost Multipath Routing and Link Aggregation in
              Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
              <http://www.rfc-editor.org/info/rfc6438>.






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

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

   [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
              Oversized IPv6 Header Chains", RFC 7112,
              DOI 10.17487/RFC7112, January 2014,
              <http://www.rfc-editor.org/info/rfc7112>.

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

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

   [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>.

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





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   Nick Hilliard
   INEX
   4027 Kingswood Road
   Dublin  24
   IE

   Email: nick@inex.ie


   Gert Doering
   SpaceNet AG
   Joseph-Dollinger-Bogen 14
   Muenchen  D-80807
   Germany

   Email: gert@space.net


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

   Email: liushucheng@huawei.com


   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: warren@kumari.net

















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