Internet DRAFT - draft-smith-6man-in-flight-eh-insertion-harmful

draft-smith-6man-in-flight-eh-insertion-harmful







Internet Engineering Task Force                                 M. Smith
Internet-Draft
Intended status: Best Current Practice                     N. Kottapalli
Expires: May 6, 2020
                                                               R. Bonica
                                                        Juniper Networks
                                                                 F. Gont
                                                            SI6 Networks
                                                              T. Herbert
                                                              Quantonium
                                                        November 3, 2019


      In-Flight IPv6 Extension Header Insertion Considered Harmful
           draft-smith-6man-in-flight-eh-insertion-harmful-01

Abstract

   In the past few years, as well as currently, there have and are a
   number of proposals to insert IPv6 Extension Headers into existing
   IPv6 packets while in-flight.  This contradicts explicit prohibition
   of this type of IPv6 packet proccessing in the IPv6 standard.  This
   memo describes the possible failures that can occur with EH
   insertion, the harm they can cause, and the existing model that is
   and should continue to be used to add new information to an existing
   IPv6 and other packets.

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 May 6, 2020.








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Copyright Notice

   Copyright (c) 2019 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  In-Flight Extension Header Insertion Defined  . . . . . . . .   3
     3.1.  In-Flight Insertion . . . . . . . . . . . . . . . . . . .   3
     3.2.  In-Flight Removal . . . . . . . . . . . . . . . . . . . .   4
     3.3.  In-Flight Insertion Without Removal . . . . . . . . . . .   4
   4.  EH Removal Failure Causes . . . . . . . . . . . . . . . . . .   4
     4.1.  Implementation Bugs . . . . . . . . . . . . . . . . . . .   4
     4.2.  Partial Node Failure  . . . . . . . . . . . . . . . . . .   5
     4.3.  Operator Configuration Error  . . . . . . . . . . . . . .   5
   5.  Single Point of Failure . . . . . . . . . . . . . . . . . . .   5
   6.  MUST Remove is Aspirational . . . . . . . . . . . . . . . . .   6
   7.  Harm  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Violates RFC8200 and All Of Its Ancestors.  . . . . . . .   6
     7.2.  Ignores Source Address Field Semantics  . . . . . . . . .   6
     7.3.  Breaks ICMPv6 . . . . . . . . . . . . . . . . . . . . . .   6
       7.3.1.  Breaks PMTUD  . . . . . . . . . . . . . . . . . . . .   6
     7.4.  Breaks IPsec  . . . . . . . . . . . . . . . . . . . . . .   6
     7.5.  May Cause Faults in Subsequent Transit Networks . . . . .   6
     7.6.  Incorrect Destination Host Processing . . . . . . . . . .   6
     7.7.  Implementation Complexity . . . . . . . . . . . . . . . .   7
     7.8.  Costly Troubleshooting  . . . . . . . . . . . . . . . . .   8
   8.  Be conservative in what you send, ... . . . . . . . . . . . .  10
   9.  Solution: Encapsulation . . . . . . . . . . . . . . . . . . .  10
     9.1.  IPv6 Tunnelling . . . . . . . . . . . . . . . . . . . . .  11
     9.2.  MPLS  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   10. Reducing Tunneling Overhead . . . . . . . . . . . . . . . . .  12
     10.1.  ROHC . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.2.  Skinny IPv6-in-IPv6 Tunneling  . . . . . . . . . . . . .  12
   11. In-Flight Insertion Considered Harmful  . . . . . . . . . . .  13



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   12. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   14. Change Log [RFC Editor please remove] . . . . . . . . . . . .  13
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     15.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Terminology

   o  In-Flight - the state of a packet while it is travelling throught
      the network between its original source IPv6 and final destination
      IPv6 hosts.  The packet will be being forwarded along a series of
      hops along a set of IPv6 routers interconnecting the source and
      destination IPv6 hosts.

3.  In-Flight Extension Header Insertion Defined

3.1.  In-Flight Insertion

   At a point somewhere along the path an IPv6 [RFC8200] packet travels
   between the packet's source IPv6 host, identified in the packet's
   Source Address field, and the packet's final IPv6 destination host,
   identified in the packet's Destination Address field, the packet is
   split apart after the IPv6 fixed header and before the packet
   payload.  Then, one or more new Extension Headers (EHs) [RFC8200] are
   inserted between those two existing packet parts.  The new EH or EHs
   may be the sole EH or EHs in the packet after insertion, or it, or
   they, may be inserted at the start, within, or after the packet's set
   of original EHs.

   Importantly, note that the packet's original source and Destination
   Address field values are left unchanged when EH insertion takes
   place.  It is likely that other immutable fields of the IPv6 header
   are also left unchanged, with possible exception to the immutable
   Next Header field [RFC8200] if the inserted EH or EHs are inserted
   directly after the IPv6 fixed header.

   For IPv6 tunnel packets [RFC2473], where they may be two or more
   instances of an IPv6 fixed header throughout the packet, EH insertion



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   could be occurring between any of the IPv6 fixed headers and their
   respective following payloads, although it is most likey to occur
   after the first of the IPv6 fixed header, commonly known as the
   (outer) tunnel header.

   An example of where this in-flight EH insertion may take place is
   when a packet enters a transit BGP autonomous system network
   [RFC4271] along its path across the Internet.

3.2.  In-Flight Removal

   At some later point along the IPv6 packet's path towards its final
   destination, the packet is somehow determined to need to have the
   prevously inserted EH removed, independently of the Destination
   Address of the packet.  The packet is again split apart, at the point
   where the one or more inserted EHs exists, and then the inserted EH
   or EHs are removed.  The packet is then reassembled, and sent further
   towards its final destination.

   Again, the packet's original source and Destination Address field
   values are left unchanged when EH removal takes place.  As with
   insertion, the likely only IPv6 fixed header field modified during EH
   removal would be the immutable Next Header field.

   An example of where this in-flight EH removal would take place is
   when a packet leaves a transit BGP autonomous system network that has
   previously inserted one or more EHs.

3.3.  In-Flight Insertion Without Removal

   A possibility is that in-flight insertion of the EH occurs without
   the intention that it is subsequently removed while the packet is in-
   flight.

   In this instance, the device that is intended to process the inserted
   EH is the IPv6 host identified in the packet's (unchanged)
   Destination Address field.

4.  EH Removal Failure Causes

4.1.  Implementation Bugs

   Despite being configured to remove the inserted one or more EHs, an
   implementation bug could cause some or all packets not to have the
   inserted EH or EHs removed.






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4.2.  Partial Node Failure

   Even though the software or firmware that is to perform EH removal is
   bug free, it is possible that a hardware fault could cause EH removal
   to not occur, while packets are still sent towards their final
   destinaton.  This could occur because the hardware fault that does
   not cause the node to entirely fail, only partially performing some
   of its functions..

4.3.  Operator Configuration Error

   Due to human error, the function to remove the inserted EH or EHs may
   be misconfigured.  Consequently, the inserted EH or EHs may not be
   removed for some or all packets.

   When the packets to have the EH(s) removed are transit packets,
   meaning these packets are likely leaving the operator's own network,
   and entering another operator's network, it is less likely that the
   packets leaving are inspected to ensure the EH removal function has
   been configured correctly.  It is common to assume that if traffic is
   leaving the local network in the expected volumes, then the traffic
   is being processed correctly by the egress network device.  This can
   be because the equipment, time and effort to validate this egressing
   traffic can be very expensive when traffic volumes are in the 10s or
   perhaps 100s of gigabits per second.

   The receiving network will also not detect or be able to detect that
   the inserted EHs have not been removed, as the inserted EH or EHs
   will appear to have been placed in the packet by the IPv6 host
   identified in the packet's Source Address field.

5.  Single Point of Failure

   When functions that inspect or modify packets beyond standard IP
   packet forwarding are performed at the edge of a network, such as a
   network firewall or a Network Address Translation, it is typical for
   there to only be one device performing that will perform this
   function at the packets' exit from the network.  It is rare to have
   two devices in-line or in series that are performing this same
   inspection or modification, providing redundancy for the function
   should it fail to be performed correctly at the first function
   instance.

   In a scenario where EHs are to be removed, it is likely that the
   device that is to perform EH removal will be a single point of
   failure.





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6.  MUST Remove is Aspirational

   RFCs/IDs say the inserted EH MUST be removed at the EH insertion
   boundary, and then use that to say it is a safe operation.  This is
   ignoring the reality of all of the above possible causes of an
   inserted EH failing to be removed.  Such a MUST statement is no more
   than aspirational - it is a theoretically true statement in 100% of
   cases, but in practice cannot ever be assured to be true in 100% of
   cases, due to the removal failure causes, described previously.

7.  Harm

7.1.  Violates RFC8200 and All Of Its Ancestors.

   (RFC8200 EH processing text quote)

   RFC 2460 and ancestors back to RFC 1883 text quote.

7.2.  Ignores Source Address Field Semantics

7.3.  Breaks ICMPv6

7.3.1.  Breaks PMTUD

7.4.  Breaks IPsec

7.5.  May Cause Faults in Subsequent Transit Networks

   If an in-flight inserted EH is not removed, and the packet travels
   into another subsequent transit network, that subsequent transit
   network may have an alternative interpretation of the inserted EH,
   causing a fault.

   The subsequent transit network, if using EH insertion, would likely
   blindly insert another instance of the EH, resulting in a packet with
   two EHs.  At network egress, the incorrect EH may removed, which
   would also still leave a remaining inserted EH to travel into further
   subsequent networks.  A directly subsequent network that is also
   performing EH insertion is unlikely to act as a sanitser for EHs that
   were inserted by previous upstream networks.

7.6.  Incorrect Destination Host Processing

   Should an in-flight inserted EH fail to be removed, the receiving
   IPv6 host may process it incorrectly.  Incorrect processing could
   involve discarding the packet when it should be further processed, or
   processing the packet when it should be discarded.




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   An failed to be removed, in-flight inserted EH is less likely to be
   understood by a typical receiving IPv6 host, as the inserted EH is
   being used for a network function.

   If an IPv6 host receives an EH that it doesn't understand, how to
   process the EH is encoded in the highest order two bits of the EH
   type [RFC8200].  If the highest order bits are all zeros, skip this
   EH and continue processing the header.  If the highest order bits are
   01, discard the packet.  If the highest order bits are 10 or 11, then
   discard the packet, and either universally generate and send an ICMP
   Parameter Problem for all Destination Address types, or for the
   latter value, generate and send an ICMP Parameter Problem for only
   non-multicast Destination Addresses.

   A failed to be removed, in-flight inserted EH may not have these
   highest order bits set correctly to best suit the application's and
   its end-user's goals.

   For example, if the packet was carrying a streaming video
   application's data, then an unknown inserted EH, yet failed to be
   removed network function EH may be harmless to the application and
   its end-user if it can be skipped over by the receiving IPv6 host.
   However, if the inserted yet not-removed EH has non-zero highest
   order bits, the packet would be discarded, causing the video data not
   to be displayed to the end-user, despite there being no harm in doing
   so.

   Alternatively, there could be cases where the inserted, yet failed to
   be removed EH should cause a packet to be discarded by the host with
   the Destination Address, perhaps for security reasons.  However, if
   the inserted EH has highest order two bits that are all zero, meaning
   ignore the unknown EH and continue processing the header, the packet
   will instead by further processed by the receiving IPv6 host.
   Perhaps the packet will be further processed in a way that violates a
   security policy that should be being enforced when the inserted, yet
   failed to be removed EH is being processed.

7.7.  Implementation Complexity

   IPv6 uses a packet's Destination Address to determine the point where
   forwarding across the network stops, and processing up the protocol
   stack at a destination host starts.

   In other words, the Destination Address of a packet identifies the
   point in the network where processing of the packet starts going
   beyond the IPv6 fixed header, and where the intention of the packet
   processing stops being limited to forwarding towards the packet's
   destination.



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   This is the fundamental distinction between an IPv6 router and a
   host; an IPv6 router forwards packets with non-local addresses
   [RFC8200], while an IPv6 host, with that holds address that matches a
   packet's Destination Address, processes the packet locally, with
   processing occuring beyond the IPv6 packet's fixed header.  Note that
   these definitions of IPv6 router and host are functional; a router as
   a device implements both IPv6 router and host functions - the
   device's forwarding plane implementing the IPv6 router function, and
   the device's control plane implementing IPv6 host functions.

   This means that all IPv6 addresses that appear in an IPv6 packet's
   Source Address and Destination Address field are, without exception,
   host addresses.

   The decision as to whether to process the packet beyond the fixed
   header or not is binary and simple - does the current node holding
   the packet possess the IPv6 address recorded in the Destination
   Address field of the packet?

   Identifying packets that have had EH's inserted, to then remove and
   process the EH, is much more complex than the simple, Destination
   Address match selector.  The EH chain inside each packet has to be
   processed to find the EH that was inserted, should it exist.

7.8.  Costly Troubleshooting

   The lack of attribution of which device inserted the EH could incur
   high costs during troubleshooting, in terms of time, effort and
   financially for a commercially operated network, should EH removal
   fail.

   Imagine a scenario where there is a popular streaming video on demand
   (SVOD) content service on the Internet providing content to large
   number of customers at a residential "eyeball" ISP.  Between the SVOD
   network and the ISP network, there are 8 different transit networks.

   One or more of those transit networks decides to implement a local
   function using EH insertion.  Unfortunately, EH removal at the egress
   of one or possibly more of these transit networks fails, due to one
   of the possible causes mentioned previously.  This or these failures
   occurs somewhere in the path from the SVOD network to the ISP
   network.

   As the Destination Address of this packet is as it was when the SVOD
   network sent the packet, prior to when the EH was inserted while in
   transit, this packet will continue to be forwarded and then delivered
   to the destination host at the ISP network.




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   When the packet arrives at the destination host, the host is required
   to process the Extension Headers in order [RFC8200].  Should an
   Extension Header be encountered that the host does not recognise, the
   host may discard the packet based on the two highest order bits of
   the EH type.  The packet's video data will not be available to the
   video application and will not be displayed to the end-user.

   As the transit network(s) that inserted the EH, yet failed to remove
   it may be carrying the SVOD traffic for 100s or 1000s of customers at
   the residential ISP, 100s or 1000s of customers will fail to receive
   their SVOD service.  These customers will either contact the support
   helpdesk of the ISP or the support helpdesk of the SVOD service to
   report the fault.

   In either case, the network operators trying to resolve this faul
   will have no indication which of the 8 transit networks is inserting
   the EH yet failing to remove it.

   Consequently, the only way to troubleshoot this is through a brute-
   force process of elimination.  It would be necessary to contact all
   of the 8 transit networks, and ask them if they're inserting EHs
   while packets are in-flight.  If they are, then it may be necessary
   to convince them that their inserted EHs are failing to be removed at
   the egress of their network, as they may be sceptical, since there
   are no local effects of the fault.  Providing a packet capture with
   the inserted EH that is causing the fault does not provide any
   supporting evidence to show that a specific transit network is
   failing to remove inserted EHs.

   Once the operator or operators of the networks that are inserting EHs
   are convinced that their network may not be removing EHs, those
   operators will now have to arrange to inspect the traffic leaving
   their network, after it has been sent by their network's egress
   device.

   Organising and executing this traffic inspection is likely to be time
   and possibly resource intensive.  The egress transit link attached to
   the device that is failing to remove the inserted EHs may be carrying
   10s or perhaps 100 or more Gbps of transit traffic.  Inserting a
   traffic inspection device within the link will cause this traffic to
   shift to other links if available, either when the link is broken, or
   in preparation for breaking the link.

   As this will be a service impacting event, it will likely need to go
   through change management procedures for review.  Given the event's
   severity, service impact notification may involve a number of days,
   prior the event being executed.




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   Once the faulty device has been identified, it needs to be rectified.
   This may involve rectification by the device's vendor if the fault
   cause is a software or firmware bug.

   Given the above troubleshooting process, the amount of parties
   involved, and the time it could take to perform the troubleshooting
   and rectification steps, in this scenario, troubleshooting and
   rectification would likely take in the order of at least a week, if
   not a number of weeks.  This will have a very significant business
   impact on either or both of the SVOD provider or the residential ISP,
   both in terms of market preception and lost customers, frustrated
   with how long this fault is taking to resolve to the point where they
   cancel their service.

8.  Be conservative in what you send, ...

   i.e. Postel's law

   "Be conservative in what you send, ..." is saying try to avoid
   sending anything that the receiver may not be expecting and that may
   confuse the receiver.  The "be liberal in what you accept" is
   advising robustness to attempt to tolerate a sender that has failed
   to be conservative.

   In-flight EH insertion violates the conservative sender part, because
   [RFC8200] compliant receivers are not expecting to receive EHs in a
   packet that were not placed there by the device identified in the
   packet's Source Address field.  A device performing in-flight EH
   insertion is intentionally not being conservative with what it is
   sending, in comparison to the scope of what an [RFC8200] compliant
   receiver expects to receive.

9.  Solution: Encapsulation

   In the Internet Protocol Architecture [RFC1122][RFC6272], adding new
   information to an existing protocol data unit is achieved through
   encapsulation.  The new information is recorded in a new header and
   possibly a new trailer, which are then used to surround or enclose
   the existing protocol data unit, similar to how an envelope is used
   to enclose the contents of a letter in the physical mail system.

   In addition to other new information, the new encapsulation header
   records the source of that new information.  For the link-layer that
   is the source node's link-layer address; for the IP layer it is
   either the IPv4 or IPv6 source host's address; and for the transport
   layer, it is the source transport layer port, or some other transport
   layer source entity identifier.




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   The new encapsulation also records the destination entity or entities
   that is or are intended to receive and process the new information.
   For the link-layer, the destination node's link-layer address, or a
   single group address that identifies a set of link-layer nodes; for
   the IP layer, the IPv4 or IPv6 destination host, or a single group
   address that identifies a set of hosts; and for the transport layer,
   the destination transport layer port or other transport layer
   destination entity identifier.

   The source and destination entity identification in the encapsulation
   header provides unambiguous and explicit identification of both which
   entity created and sent the new information, and which entity or
   entities are to process the new information.

9.1.  IPv6 Tunnelling

   If additional IPv6 information is to be added to an existing IPv6
   packet while it is in-flight, such as a new Extenstion Header, then a
   new IPv6 header is required.  This new IPv6 header will unambiguously
   record the identity of the IPv6 host that has added the new IPv6
   information in the Source Address field, and will unambigously record
   the identity of the IPv6 host (or group of hosts) that is to process
   the added IPv6 information in the Destination Address field.  A new
   IPv6 packet is created using the new IPv6 header, followed by the new
   supplimentary information, followed by the existing IPv6 packet,
   appearing in the payload field of the new packet.  IPv6-in-IPv6
   encapsulation is commonly known as "tunneling", and is specified in
   [RFC2473], which includes showing how new information added via
   Extension Headers occurs. [intarea-tunnels] provides more discussion
   of IP tunneling in the context of the Internet Architecture.

   Conceptually, IPv6-in-IPv6 tunneling is a form of link-layer
   encapsulation from the perspective of the existing (and eventually
   inner) IPv6 packet.  It just happens to be a coincidence that the
   outer link-layer encapsulation header and other new information (i.e.
   Extension Headers) has the same protocol format and field sematics as
   the existing, inner IPv6 packet.

9.2.  MPLS

   Despite using terms such as "label imposition" or "label swapping",
   MPLS [RFC3031] also follows this encapsulation model to add new
   information, via labels, to an existing in-flight protocol data unit,
   such as an IPv6 packet.  In-flight insertion of MPLS labels never
   occurs.

   At each hop through the MPLS network where labels are processed, at
   devices known as Label Switching Routers (LSRs), upon egress from the



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   LSR, a new link-layer header is created that both unambiguously
   identifies the current LSR in the link-layer Source Address field,
   and unambiguously identifies the next LSR (or set of LSRs) that is to
   process the set of labels that are encoded in the link-layer protocol
   data unit sent by the current LSR.  The labels are encoded following
   this new header, and then the original packet follows in the link-
   layer payload field.

   If in-flight MPLS label insertion were to be actually occurring, then
   it would mean that as a packet was label switched across a set of
   LSRs along a Label Switched Path (LSP), the link-layer header Source
   Address would not change across the LSP - it would remain as the
   Source Address of the LSR at the head end of the LSP, regardless of
   how many subsequent LSRs the packet is label switched through.

   In-flight MPLS label insertion would also mean that the Destination
   Address in the link-layer header would also not change as the packet
   is label switched along the LSP.  It would remain unchanged
   regardless of how many LSRs the packet traverses, and would likely
   identify the final LSR at the tail end of the LSP.

   If MPLS had used an in-flight insertion model, then MPLS would have
   likely suffered from problems similar to those described above that
   can occur with IPv6 EH insertion.

10.  Reducing Tunneling Overhead

   As a tunnel is creating a virtual link layer, link-layer compression
   of the inner IPv6 header and its payload can be used to effectively
   reduce the tunneling overhead.

10.1.  ROHC

   "The Robust Header Compression (ROHC) protocol provides an efficient,
   flexible, and future-proof header compression concept.  It is
   designed to operate efficiently and robustly over various link
   technologies with different characteristics."  [RFC5795]

10.2.  Skinny IPv6-in-IPv6 Tunneling

   Skinny-IPv6-in-IPv6 tunnelling [SKINNYV6V6] is a stateless form of
   tunnelling compression that leverages two charateristics of IPv6 and
   IPv6 networks:

   o  The common semantics between the inner IPv6 and outer IPv6 tunnel
      packet's headers.  While the inner IPv6 packet is in flight over
      the IPv6 tunnel, the large majority of its header field values are




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      carried and proxied by the outer IPv6 tunnel header's
      corresponding fields.

   o  The availability of many /64 prefixes within an IPv6 network,
      using /64s rather than /128s to identify IPv6 tunnel end-points.
      This allows the inner packet's 64 bit IIDs to be carried in the
      outer IPv6 tunnel packet's IID fields while the inner packet is
      carried over the IPv6 tunnel.

11.  In-Flight Insertion Considered Harmful

   More generally, insertion within an existing, in-flight packet at any
   location within the packet is considered harmful.  EH insertion, as
   described and discussed previously, is a more specific instance of a
   harmful practise.

12.  Security Considerations

13.  Acknowledgements

   Review and comments were provided by YOUR NAME HERE!

   This memo was prepared using the xml2rfc tool.

14.  Change Log [RFC Editor please remove]

   draft-smith-6man-in-flight-eh-insertion-harmful-00, initial version,
   2019-09-09

   draft-smith-6man-in-flight-eh-insertion-harmful-01, update,
   2019-11-03

   o  Added co-authors

   o  Link-layer compression section

   o  Costly troubleshooting scenario section

15.  References

15.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.





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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

15.2.  Informative References

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <https://www.rfc-editor.org/info/rfc2473>.

   [RFC5795]  Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
              Header Compression (ROHC) Framework", RFC 5795,
              DOI 10.17487/RFC5795, March 2010,
              <https://www.rfc-editor.org/info/rfc5795>.

   [SKINNYV6V6]
              "Skinny IPv6 in IPv6 Tunnelling",
              <https://datatracker.ietf.org/doc/draft-smith-skinny-ipv6-
              in-ipv6-tunnelling/>.

Authors' Addresses

   Mark Smith
   PO Box 521
   Heidelberg, VIC  3084
   AU

   Email: markzzzsmith@gmail.com


   Naveen Kottapalli

   Email: naveen.sarma@gmail.com


   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20171
   USA

   Email: rbonica@juniper.net








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   Fernando Gont
   SI6 Networks
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires
   Argentina

   Email: fgont@si6networks.com


   Tom Herbert
   Quantonium
   Internet Road
   Santa Clara, CA
   USA

   Email: tom@quantonium.net



































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