IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                              SI6 Networks
Intended status: Informational                               N. Hilliard
Expires: January 26, 2021                                           INEX
                                                              G. Doering
                                                             SpaceNet AG
                                                               W. Kumari
                                                               G. Huston
                                                           July 25, 2020

    Operational Implications of IPv6 Packets with Extension Headers


   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 https://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 January 26, 2021.

Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

Gont, et al.            Expires January 26, 2021                [Page 1]

Internet-Draft           IPv6 Extension Headers                July 2020

   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.  Disclaimer  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Previous Work on IPv6 Extension Headers . . . . . . . . . . .   3
   4.  Security Implications . . . . . . . . . . . . . . . . . . . .   4
   5.  Operational Implications  . . . . . . . . . . . . . . . . . .   6
     5.1.  Requirement to process required layer-3/layer-4
           information . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Route-Processor Protection  . . . . . . . . . . . . . . .   8
     5.3.  Inability to Perform Fine-grained Filtering . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   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, common implementation limitations suggest
   that EHs present a challenge for IPv6 packet routing equipment, and
   evidence exists that IPv6 packets with EHs may be intentionally
   dropped in 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 in
   other fora), and have noticed that the security and operational
   implications associated with IPv6 EHs 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.

Gont, et al.            Expires January 26, 2021                [Page 2]

Internet-Draft           IPv6 Extension Headers                July 2020

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

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

   Section 3 of this document summarizes the previous work that has been
   carried out in the area of IPv6 extension headers.  Section 4 briefly
   discusses the security implications of IPv6 Extension Headers, while
   Section 5 discusses their operational implications.

2.  Disclaimer

   This document analyzes the operational challenges represented by
   packets that employ IPv6 Extension Headers, and documents some of the
   operational reasons for which these packets may be dropped in the
   public Internet.  This document IS NOT a recommendation to drop such
   packets, but rather an analysis of why they're dropped.

3.  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.
   [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.  [I-D.ietf-opsec-ipv6-eh-filtering] analyzes
   the security implications of IPv6 EHs, and the operational
   implications of dropping packets that employ IPv6 EHs and associated
   options.  [RFC6980] analyzes the security implications of employing
   IPv6 fragmentation with Neighbor Discovery for IPv6, and formally
   recommends against such usage.  Finally, [RFC7113] discusses how some
   popular RA-Guard implementations are subject to evasion by means of
   IPv6 extension headers.  [I-D.ietf-intarea-frag-fragile] analyzes the
   fragility introduced by IP fragmentation.

   A number of recent RFCs have discussed issues related to IPv6
   extension headers, specifying updates to a previous revision of the
   IPv6 standard ([RFC2460]), which have now been incorporated into the
   current IPv6 core standard ([RFC8200]).  Namely,

Gont, et al.            Expires January 26, 2021                [Page 3]

Internet-Draft           IPv6 Extension Headers                July 2020

   o  [RFC5095] discusses the security implications of Routing Header
      Type 0 (RTH0), and deprecates it.

   o  [RFC5722] analyzes the security implications of overlapping
      fragments, and provides recommendations in this area.

   o  [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).

   o  [RFC6946] discusses a flawed (but common) processing of the so-
      called IPv6 "atomic fragments", and specified improved processing
      of such packets.

   o  [RFC8021] deprecates the generation of IPv6 atomic fragments.

   o  [RFC8504] allows hosts to enforce limits on the number of options
      included in IPv6 EHs.

   o  [RFC7739] discusses the security implications of predictable
      fragment Identification values, and provides recommendations for
      the generation of these values.

   Additionally, [RFC8200] has relaxed the requirement that "all nodes
   examine and process the Hop-by-Hop Options header" from [RFC2460], by
   specifying that only to nodes that have been explicitly configured to
   process the Hop-by-Hop Options header are required to do so.

   A number of studies have measured the extent to which packets
   employing IPv6 extension headers are filtered in the public Internet.
   Some preliminary measurements regarding the extent to which packet
   containing IPv6 EHs are dropped in the public Internet were presented
   in [PMTUD-Blackholes], [Gont-IEPG88], [Gont-Chown-IEPG89], and
   [Linkova-Gont-IEPG90].  [RFC7872] presents more comprehensive results
   and documents the methodology for obtaining the presented results.
   [Huston-2017] measures packet drops resulting from IPv6 fragmentation
   when communicating with DNS servers.

4.  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

Gont, et al.            Expires January 26, 2021                [Page 4]

Internet-Draft           IPv6 Extension Headers                July 2020

   o  Extension Header-specific issues

   Unlike IPv4 packets where the upper-layer protocol 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,
   and may represent a challenge for devices that need to find this
   information, since 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) have been found to be trivially evasible 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 5 for
   further details).

      In the most trivial case, a packet that includes a Hop-by-Hop
      Options header might 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), causing the
      packet to be processed in the slow path [Cisco-EH-Cons].  We note
      that, for obvious reasons, the aforementioned performance issues
      may affect other devices such as firewalls, Network Intrusion
      Detection Systems (NIDS), etc.  [Zack-FW-Benchmark].  The extent
      to which these devices are affected is typically implementation-

   IPv6 implementations, like all other software, tend to mature with
   time and wide-scale deployment.  While the IPv6 protocol itself has
   existed for over 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

Gont, et al.            Expires January 26, 2021                [Page 5]

Internet-Draft           IPv6 Extension Headers                July 2020

   potential for bugs that still remain to be discovered in some

   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, as
   discussed in [RFC7739], [Bonica-NANOG58] and [Atlasis2012]).

5.  Operational Implications

5.1.  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

5.1.1.  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] and [APNIC-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 but the packet lookup engine may not be able to
   inspect far enough into a packet to determine how it should be

      For example, current high-end routers can use up to 192 bytes of
      header (Cisco ASR9000 Typhoon) or 384 bytes of header (Juniper MX

   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

Gont, et al.            Expires January 26, 2021                [Page 6]

Internet-Draft           IPv6 Extension Headers                July 2020

   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.

5.1.2.  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 normally 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.

   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.

   While support of [RFC6437] is currently widespread for all popular
   host implementations, there is no existing data regarding the extent
   to which the Flow Label has superseded the use of transport protocol
   port numbers for ECMP.

Gont, et al.            Expires January 26, 2021                [Page 7]

Internet-Draft           IPv6 Extension Headers                July 2020

5.1.3.  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.

5.1.4.  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

   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 traditional [RFC5635] source-based real-time black hole
   mechanisms useless.  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.

5.2.  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.
   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.

Gont, et al.            Expires January 26, 2021                [Page 8]

Internet-Draft           IPv6 Extension Headers                July 2020

   The Hop-by-Hop Options header has been particularly challenging
   since, in most (if not all) implementations, it has typically caused
   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.

5.3.  Inability to Perform Fine-grained Filtering

   Some router implementations lack 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").

6.  IANA Considerations

   There are no IANA registries within this document.  The RFC-Editor
   can remove this section before publication of this document as an

7.  Security Considerations

   The security implications of IPv6 extension headers are discussed in
   Section 4.  This document does not introduce any new security issues.

8.  Acknowledgements

   The authors would like to thank (in alphabetical order) Mikael
   Abrahamsson, Fred Baker, Brian Carpenter, Tom Herbert, 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 Jan Zorz / Go6 Lab
   <http://go6lab.si/>, Jared Mauch, and Sander Steffann
   <http://steffann.nl/>, for providing access to systems and networks
   that were employed to perform experiments and measurements involving
   packets with IPv6 Extension Headers.

Gont, et al.            Expires January 26, 2021                [Page 9]

Internet-Draft           IPv6 Extension Headers                July 2020

9.  References

9.1.  Normative References

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              DOI 10.17487/RFC5095, December 2007,

   [RFC5722]  Krishnan, S., "Handling of Overlapping IPv6 Fragments",
              RFC 5722, DOI 10.17487/RFC5722, December 2009,

   [RFC6946]  Gont, F., "Processing of IPv6 "Atomic" Fragments",
              RFC 6946, DOI 10.17487/RFC6946, May 2013,

   [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
              with IPv6 Neighbor Discovery", RFC 6980,
              DOI 10.17487/RFC6980, August 2013,

   [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
              Oversized IPv6 Header Chains", RFC 7112,
              DOI 10.17487/RFC7112, January 2014,

   [RFC8021]  Gont, F., Liu, W., and T. Anderson, "Generation of IPv6
              Atomic Fragments Considered Harmful", RFC 8021,
              DOI 10.17487/RFC8021, January 2017,

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

   [RFC8504]  Chown, T., Loughney, J., and T. Winters, "IPv6 Node
              Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
              January 2019, <https://www.rfc-editor.org/info/rfc8504>.

Gont, et al.            Expires January 26, 2021               [Page 10]

Internet-Draft           IPv6 Extension Headers                July 2020

9.2.  Informative References

              Scudder, J., "Modern router architecture and IPv6",  APNIC
              Blog, June 4, 2020, <https://blog.apnic.net/2020/06/04/

              Atlasis, A., "Attacking IPv6 Implementation Using
              Fragmentation",  BlackHat Europe 2012. Amsterdam,
              Netherlands. March 14-16, 2012,

              Atlasis, A., "A Novel Way of Abusing IPv6 Extension
              Headers to Evade IPv6 Security Devices", May 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-

              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/

              Cisco, "IPv6 Extension Headers Review and Considerations",
              October 2006,

              Gont, F. and T. Chown, "A Small Update on the Use of IPv6
              Extension Headers", IEPG 89. London, UK. March 2, 2014,

Gont, et al.            Expires January 26, 2021               [Page 11]

Internet-Draft           IPv6 Extension Headers                July 2020

              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/

              Huston, G., "Dealing with IPv6 fragmentation in the
              DNS",  APNIC Blog, 2017,

              Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
              and F. Gont, "IP Fragmentation Considered Fragile", draft-
              ietf-intarea-frag-fragile-17 (work in progress), September

              Gont, F. and W. LIU, "Recommendations on the Filtering of
              IPv6 Packets Containing IPv6 Extension Headers", draft-
              ietf-opsec-ipv6-eh-filtering-06 (work in progress), July

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

              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.

              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.

              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/

Gont, et al.            Expires January 26, 2021               [Page 12]

Internet-Draft           IPv6 Extension Headers                July 2020

              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-

              De Boer, M. and J. Bosma, "Discovering Path MTU black
              holes on the Internet using RIPE Atlas", July 2012,

   [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,

   [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,

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
              March 2011, <https://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,

   [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,

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,

Gont, et al.            Expires January 26, 2021               [Page 13]

Internet-Draft           IPv6 Extension Headers                July 2020

   [RFC7739]  Gont, F., "Security Implications of Predictable Fragment
              Identification Values", RFC 7739, DOI 10.17487/RFC7739,
              February 2016, <https://www.rfc-editor.org/info/rfc7739>.

   [RFC7872]  Gont, F., Linkova, J., Chown, T., and W. Liu,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", RFC 7872,
              DOI 10.17487/RFC7872, June 2016,

              Zack, E., "Firewall Security Assessment and Benchmarking
              IPv6 Firewall Load Tests",  IPv6 Hackers Meeting #1,
              Berlin, Germany. June 30, 2013,

Authors' Addresses

   Fernando Gont
   SI6 Networks
   Segurola y Habana 4310, 7mo Piso
   Villa Devoto, Ciudad Autonoma de Buenos Aires

   Email: fgont@si6networks.com
   URI:   https://www.si6networks.com

   Nick Hilliard
   4027 Kingswood Road
   Dublin  24

   Email: nick@inex.ie

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

   Email: gert@space.net

Gont, et al.            Expires January 26, 2021               [Page 14]

Internet-Draft           IPv6 Extension Headers                July 2020

   Warren Kumari
   1600 Amphitheatre Parkway
   Mountain View, CA  94043

   Email: warren@kumari.net

   Geoff Huston

   Email: gih@apnic.net
   URI:   http://www.apnic.net

Gont, et al.            Expires January 26, 2021               [Page 15]