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Versions: 00 01 02 03 04

6man                                                            J. Leddy
Internet-Draft                                                   Comcast
Intended status: Standards Track                               R. Bonica
Expires: December 13, 2018                              Juniper Networks
                                                           June 11, 2018


 Destination Originates Internet Control Message Protocol (ICMP) Packet
                         Too Big (PTB) Messages
                      draft-leddy-6man-truncate-03

Abstract

   This document defines procedures that enhance Path MTU Discovery
   (PMTUD), so that it no longer relies on the network's ability to
   deliver an ICMP Packet Too Big (PTB) message from a downstream router
   to an IPv6 source node.  According to these procedures, selected
   packets carry a new IPv6 Destination option.  When a downstream
   router cannot forward one of these packets because of MTU issues, it
   truncates the packet, marks it to indicate that it has been
   truncated, and forwards it towards the destination node.

   When the destination node receives a packet that has been truncated,
   it sends an ICMP PTB message to the source node.  The source node
   uses MTU information contained by the ICMP PTB message to update its
   PMTU estimate.

   The destination node also examines the new Destination option to
   determine whether it should discard the truncated packet or deliver
   it to an upper-layer protocol.

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 December 13, 2018.




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Copyright Notice

   Copyright (c) 2018 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Operational Considerations  . . . . . . . . . . . . . . . . .   4
   4.  Reference Topology  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Truncation Option . . . . . . . . . . . . . . . . . . . . . .   6
   6.  PMTU Signaling Procedures . . . . . . . . . . . . . . . . . .   7
   7.  Truncation Considerations . . . . . . . . . . . . . . . . . .   8
   8.  ICMP Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Delivering Truncated Packets  . . . . . . . . . . . . . . . .   9
   10. Backward Compatibility  . . . . . . . . . . . . . . . . . . .  10
   11. Optimizations . . . . . . . . . . . . . . . . . . . . . . . .  11
   12. Upper-Layer Considerations  . . . . . . . . . . . . . . . . .  11
   13. Encapsulating Security Payload Considerations . . . . . . . .  11
   14. Extension Header Considerations . . . . . . . . . . . . . . .  12
   15. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   17. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   18. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     18.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     18.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   An Internet path connects a source node to a destination node.  A
   path can contain links and routers.

   Each link is constrained by the number of bytes that it can convey in
   a single IP packet.  This constraint is called the link Maximum
   Transmission Unit (MTU).  IPv6 [RFC8200] requires every link to have




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   an MTU of 1280 bytes or greater.  This value is called IPv6 minimum
   link MTU.

   Likewise, each Internet path is constrained by the number of bytes
   that it can convey in a IP single packet.  This constraint is called
   the Path MTU (PMTU).  For any given path, the PMTU is equal to the
   smallest of its link MTUs.

   IPv6 allows fragmentation at the source node only.  If an IPv6 source
   node sends a packet whose length exceeds the destination PMTU, the
   packet will be discarded.  In order to avoid this kind of packet
   loss, IPv6 nodes can either:

   o  Refrain from sending packets whose length exceeds the IPv6 minimum
      link MTU.

   o  Maintain a running estimate of the destination PMTU and refrain
      from sending packets whose length exceeds that estimate.

   IPv6 nodes can execute Path MTU Discovery (PMTUD) [RFC8201]
   procedures in order to maintain a running estimate of the destination
   PMTU.  According to these procedures, the source node produces an
   initial PMTU estimate.  This initial estimate is equal to the MTU of
   the first link along the path to the destination node.  It can be
   greater than the actual PMTU.

   Having produced an initial PMTU estimate, the source node sends
   packets to the destination node.  If one of these packets is larger
   than the actual PMTU, a downstream router will not be able to forward
   the packet through the next link along the path.  Therefore, the
   downstream router discards the packet and sends an Internet Control
   Message Protocol (ICMP) [RFC4443] Packet Too Big (PTB) message to the
   source node.  The ICMP PTB message indicates the MTU of the link
   through which the packet could not be forwarded.  The source node
   uses this information to refine its PMTU estimate.

   PMTUD relies on the network's ability to deliver ICMP PTB messages
   from the downstream router to the source node.  If the network cannot
   deliver these messages, a persistent black hole can develop.  In this
   scenario, the source node sends a packet whose length exceeds the
   destination PMTU.  A downstream router discards the packet and sends
   an ICMP PTB message to the source.  However, the network cannot
   deliver the ICMP PTB message to the source.  Therefore, the source
   node does not update its PMTU estimate and it continues to send
   packets whose length exceeds the destination PMTU.  The downstream
   router discards these packets and sends ICMP PTB messages to the
   source.  These ICMP PTB messages are lost, exactly as previous ICMP
   PTB messages were lost.



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   In some operational scenarios (Section 3), networks cannot deliver
   ICMP PTB messages from a downstream router to the source node.
   Therefore, enhanced procedures are required.

   This document defines procedures that enhance PMTUD, so that it no
   longer relies on the network's ability to deliver an ICMP PTB message
   from a downstream router to an IPv6 source node.  According to these
   procedures, selected packets carry a new IPv6 Destination option.
   When a downstream router cannot forward one of these packets because
   of MTU issues, it truncates the packet, marks it to indicate that it
   has been truncated, and forwards it towards the destination node.

   When the destination node receives a packet that has been truncated,
   it sends an ICMP PTB message to the source node.  The source node
   uses MTU information contained by the ICMP PTB message to update its
   PMTU estimate.

   The destination node also examines the new Destination option to
   determine whether it should discard the truncated packet or deliver
   it to an upper-layer protocol.  If the truncated packet is delivered
   to an upper-layer protocol, the upper-layer protocol can infer the
   PMTU between the source node and itself from the packet's length.
   Having inferred the PMTU, the upper-layer protocol can negotiate a
   maximum packet size with its upper-layer peer, thus reducing its
   dependence upon PMTUD and IPv6 fragmentation.

   While packet truncation may facilitate new upper-layer procedures,
   upper-layer procedures are beyond the scope of this document.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Operational Considerations

   The packet truncation procedures described herein make PMTUD more
   resilient when:

   o  The network can deliver ICMP PTB messages from the destination
      node to the source node.

   o  The network cannot deliver ICMP PTB messages from a downstream
      router to the source node.




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   The following are operational scenarios in which packet truncation
   procedures can make PMTUD more resilient:

   o  The destination node has a viable route to the source node, but
      the downstream router does not.

   o  The source node is protected by a firewall that administratively
      blocks all packets except for those from specified subnetworks.
      The destination node resides in one of the specified subnetworks,
      but the downstream router does not.

   o  The source address of the original packet (i.e., the packet that
      elicited the ICMP PTB message) was an anycast address.  Therefore,
      the destination address of the ICMP PTB message is the same
      anycast address.  In this case, an ICMP PTB message from the
      destination node is likely to be delivered to the correct anycast
      instance.  By contrast, an ICMP PTB message from a downstream
      router is less likely to be delivered to the correct anycast
      instance.

   Packet truncation procedures do not make PMTUD more resilient when
   the network cannot reliably deliver any ICMP PTB messages to the
   source node.  The following are operational scenarios where the
   network cannot reliably deliver any ICMP PTB messages to the source
   node:

   o  The source node is protected by a firewall that administratively
      blocks all ICMP PTB messages.

   o  The source node is an anycast instance served by a load-balancer
      as defined in [RFC7690].  The load-balancer does not implement the
      mitigations defined in [RFC7690].

4.  Reference Topology

   -------------          -------------          -------------
   |   Upper   |          |           |          |   Upper   |
   |   Layer   |          |           |          |   Layer   |
   |           |          |           |          |           |
   |    IP     |<-------->|    IP     |<-------->|    IP     |
   |   Layer   |    MTU   |   Layer   |    MTU   |   Layer   |
   -------------   9000   -------------   1500    -------------
       Source                Router               Destination
       Node                                          Node


                                 Figure 1




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   Figure 1 depicts a reference topology that is used in this document.
   The reference topology includes a source node, a router, and a
   destination node.  The link that connects the source node to the
   router has an MTU of 9000 bytes.  The link that connects the router
   to the destination node has an MTU of 1500 bytes.  Therefore, the
   PMTU between the source node and the destination node is 1500 bytes.

5.  Truncation Option

          0                   1                   2
          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  Option Type  |  Opt Data Len |T|D|R| Reserved|
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 2

   Figure 2 depicts the Truncation option.  The IPv6 Destination Options
   header MAY include the Truncation option.  The IPv6 Hop-by-hop header
   MUST NOT include the Truncation option.

   o  Option Type - Truncation option.  Value TBD by IANA.  See Notes
      below.

   o  Opt Data Len - Length of Option Data, measured in bytes.  MUST be
      equal to 1.

   o  T - Indicates that the packet has been truncated.  If the packet
      has not been truncated, it SHOULD be delivered to an upper-layer
      protocol.

   o  D - Indicates that the packet SHOULD be delivered to an upper-
      layer protocol even if it has been truncated.  If the D-bit is set
      to zero, the packet MUST NOT be delivered to an upper-layer
      protocol if it has been truncated.

   o  R - Request to deliver truncated packets.

   A packet MUST NOT contain multiple instances of the Truncation
   option.  If a node receives a packet that contains multiple instances
   of the Truncation option, it processes the first instance and ignores
   all subsequent instances.

   NOTE 1: The highest-order two bits of the Option Type (i.e., the
   "act" bits) are 10.  These bits specify the action taken by a
   destination node that does not recognize Truncation option.  The
   required action is to discard the packet and, regardless of whether
   or not the packet's Destination Address was a multicast address, send



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   an ICMP Parameter Problem, Code 2, message to the packet's Source
   Address, pointing to the unrecognized Option Type.

   NOTE 2: The third highest-order bit of the Option Type (i.e., the
   "chg" bit) is 1.  This indicates that Option Data can be modified
   along the path between the packet's source and its destination.

6.  PMTU Signaling Procedures

   In the Reference Topology (Figure 1), the upper-layer protocol that
   resides on the source node submits a packet to its local IP layer.
   The packet includes a Truncation option (Section 5).  Within the
   Truncation option:

   o  The T-bit is set to zero, indicating that the packet has not been
      truncated.

   o  The D-bit is set to zero, indicating that the packet MUST NOT be
      delivered to an upper-layer protocol if the packet has been
      truncated.

   o  The R-bit is set to zero, indicating that the source node does not
      request delivery of truncated packets

   The packet length is 500 bytes.  Because the packet length is less
   than the destination PMTU, the packet can be delivered without
   encountering MTU issues.

   The IP layer on the source node forwards the packet to the downstream
   router and the downstream router forwards the packet to the
   destination node.  The IP layer on the destination node examines the
   Destination Option header.  Because it recognizes the Truncation
   option, and because the packet has not been truncated, it delivers
   the packet to an upper-layer protocol.

   Now, the upper-layer protocol that resides on the source node submits
   another packet to its local IP layer.  This packet is identical to
   the first, except that the packet length is 2000 bytes.  Because the
   packet length is greater than the destination PMTU, the packet cannot
   be delivered without encountering MTU issues.

   The IP layer on the source node forwards the packet to the downstream
   router but the downstream router cannot forward the packet because
   its length exceeds the MTU of the next-hop link.  Because an MTU
   issue has been encountered, the IP Layer on the downstream router
   examines the Destination Options header, searching for a Truncation
   option.  (Normally, the downstream router would ignore the
   Destination Options header).



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   Because the downstream router finds and recognizes the Truncation
   option, it:

   o  Truncates the packet, so that its new length equals the MTU of the
      next-hop link.

   o  Updates the Payload Length field in the IPv6 header as
      appropriate.

   o  Sets the T-bit in the Truncation option.

   o  Forwards the packet to the destination node.

   The IP layer on the destination node examines the Destination Option
   header.  Because it recognizes the Truncation option, and because the
   packet has been truncated, it sends an ICMP PTB message to the source
   node.  The MTU field in the ICMP PTB message is set to the packet's
   length.

   The IP layer on the destination node then discards the packet because
   the packet has been truncated and the D-bit is set to 0.  It does not
   deliver the packet to an upper-layer protocol.

   As per [RFC8201], the source node updates its PMTU estimate using
   information contained by the ICMP PTB message.

7.  Truncation Considerations

   A packet can be truncated multiple times.

-------------          -------------          -------------          -------------
|    IP     |<-------->|    IP     |<-------->|    IP     |<-------->|    IP     |
|   Layer   |    MTU   |   Layer   |    MTU   |   Layer   |   MTU    |   Layer   |
-------------   9000   -------------   4000   -------------   1500    -------------
    Source                Router1               Router 2              Destination
    Node                                                                 Node


                        Figure 3: Double Truncation

   Figure 3 depicts a network that contains a Source Node, Router1,
   Router2 and a Destination Node.  The link that connects the Source
   Node to Router1 has an MTU of 9000 bytes.  The link that connects
   Router1 to Router2 has an MTU of 4000 bytes, and the link that
   connects Router2 to the Destination Node has an MTU of 1500 bytes.

   Assume that the Source Node sends a packet to the Destination Node.
   The packet is 8000 bytes long.  When Router1 receives this packet, it



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   identifies the next-hop towards the destination.  This is the link
   that connects Router1 to Router2.  Router 1 encounters an MTU issue,
   because the packet length (8000 bytes) is greater than the MTU
   associated with the next-hop link (4000 bytes).  Therefore, Router 1
   truncates the packet to 4000 bytes, sets the T-bit in the Truncation
   Option, and forwards the packet towards Router2.  When Router2
   receives this packet, it identifies the next-hop towards the
   destination.  This is the link that connects Router2 to the
   Destination Node.  Router 2 encounters an MTU issue, because the
   packet length (4000 bytes) is greater than the MTU associated with
   the next-hop link (1500 bytes).  Therefore, Router 2 truncates the
   packet to 1500 bytes, sets the T-bit in the Truncation Option, and
   forwards the packet towards the Destination Node.  The Destination
   Node sends an ICMP PTB packet to the source node.  The MTU field in
   the ICMP PTB field is set to 1500.

   A truncated packet MUST contain the basic IPv6 header, all extension
   headers and the first upper-layer header.  When a router cannot
   forward a packet through the next-hop link due to MTU issues, and the
   total length of the basic IPv6 header, all extension headers, and
   first upper-layer header exceeds the MTU of the next-hop link, the
   router MUST discard the packet and send and ICMP PTB message to the
   source.

   Source nodes MUST NOT emit packets that contain both the Fragment
   Header and Truncation Option.

   Routers MUST NOT truncate packets that include the Fragment header.
   When a router cannot forward a packet through the next-hop link due
   to MTU issues, and the packet includes a Fragment header, the router
   MUST discard the packet and send and ICMP PTB message to the source.

   Routers MUST NOT emit truncated packets whose length is less than the
   IPv6 minimum link MTU.

8.  ICMP Considerations

   When a destination node receives a truncated packet whose length is
   less than the IPv6 minimum link MTU, the destination node MUST
   discard the packet.  It MUST NOT send an ICMP PTB message to the
   packet's source and it MUST NOT deliver the packet to an upper-layer
   protocol.

9.  Delivering Truncated Packets

   A destination node MUST NOT deliver a truncated packet to an upper-
   layer protocol if the D-bit is set to zero.  However, a destination




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   node SHOULD deliver a truncated packet to an upper-layer protocol if
   the D-bit is set to one.

   The upper-layer protocol on the source node determines the D-bit
   value.  The following are possible behaviors:

   o  Some upper-layer protocols never set the D-bit.

   o  Some upper-layer protocols always set the D-bit.

   o  Some upper-layer protocols only set the D-bit when requested to do
      so by the upper-layer protocol on the destination node.  These
      upper-layer protocols interpret the receipt of a Truncation option
      with the R-bit set as a request to set the D-bit on all subsequent
      packets.

10.  Backward Compatibility

   The procedures described in Section 6 of this document assume that
   the source node, downstream router and destination node all
   recognized the Truncation option.  This section explores backwards
   compatibility, where one or more nodes do not recognize the
   Truncation option.

   If the destination node does not recognize the Truncation option, and
   it receives a packet that includes the Truncation option, it discards
   the packet and, regardless of whether or not the packet's Destination
   Address was a multicast address, sends an ICMP Parameter Problem,
   Code 2, message to the packet's Source Address, pointing to the
   unrecognized Option Type.  This behavior is determined by the
   highest-order two bytes of the Option Type.  When the source node
   receives the ICMP Parameter Problem message, it refrains from sending
   packets that contain the Truncation option.

   If the downstream router does not recognize the Truncation option and
   it receives a packet that contains the Truncation option and that
   packets length does not exceed the next-hop MTU, the downstream
   router forwards the packet, without examining the Truncation option
   or any other Destination option.  If the downstream router does not
   recognize the Truncation option and it receives a packet that
   contains the Truncation option and that packets length exceeds the
   next-hop MTU, the downstream discards the packet and sends an ICMP
   PTB message to the source node, as per [RFC8200].

   In all cases mentioned above, PMTUD continues to function as
   specified in [RFC8201].





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11.  Optimizations

   The procedures described in Section 6 of this document can be
   optimized by omitting the Truncation option on packets whose length
   is known to be less than the destination PMTU (e.g., packets whose
   length is less than the IPv6 minimum link MTU).

12.  Upper-Layer Considerations

   The procedures described herein rely upon:

   o  The network's ability to convey packets that contain destination
      options from a source node to a destination node.

   o  The network's ability to convey ICMP Parameter Problem messages in
      the reverse direction.

   Operational experience [RFC7872] reveals that a significant number of
   networks drop packets that contain IPv6 destination options.
   Likewise, many networks drop ICMP Parameter Problem messages.

   [I-D.bonica-6man-unrecognized-opt] describes procedures that upper-
   layer protocols can execute to verify that the above-mentioned
   requirements are satisfied.  Upper-layer protocols can execute these
   procedures before emitting packets that contain the Truncation
   option.

13.  Encapsulating Security Payload Considerations

   An IPv6 packet can contain both:

   o  An Encapsulating Security Payload (ESP) [RFC4303] header.

   o  The Truncation Option.

   In this case, the packet MUST contain a Destination Options header
   that precedes the ESP.  That Destination Options header contains the
   Truncation Option and is not protected by the ESP.  The packet MAY
   also contain another Destination Options header the follows the ESP.
   This Destination Options header is protected by the ESP and MUST NOT
   contain the Truncation Option.

   As per RFC 4303, a packet can contain two Destination Option headers
   one preceding the ESP and one following the ESP.







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14.  Extension Header Considerations

   According to [RFC8201], the following IPv6 extension headers can
   carry options:

   o  The Hop-by-hop Options header.

   o  The Destination Options header.

   The Hop-by-hop Options header is examined by the destination node.
   It can also be examined by intermediate nodes (i.e., nodes along the
   path between the source and the destination), so long as those nodes
   are configured to process Hop-by-hop options.  By contrast, the
   Destination Options header is examined by the destination node only.

   The Truncation option is examined by:

   o  The destination node.

   o  Intermediate nodes, but only on an exception basis (i.e., when the
      intermediate node cannot forward the packet due to MTU issues)

   If performance were not a concern, the Hop-by-hop Options header
   could carry the Truncation Option.  The destination node would
   examine the Truncation option, as would every intermediate node.
   However, the performance impact would not be acceptable.

   By contrast, the Destination Option can carry the truncation option,
   so long as intermediate nodes can examine the Destination Option
   header on an exception basis (e.g., when the packet cannot be
   forwarded due to MTU issues).  [RFC2473] sets a precedent for
   intermediate nodes examining the Destination Options header on an
   exception basis.  (See the Tunnel Encapsulation Limit.)

   Therefore, The IPv6 Destination Options header MAY include the
   Truncation option and the IPv6 Hop-by-hop header MUST NOT include the
   Truncation option.

15.  Security Considerations

   PMTUD is vulnerable to ICMP PTB forgery attacks.  The procedures
   described herein do nothing to mitigate that vulnerability.

   The procedures described herein are susceptible to a new variation on
   that attack, in which an attacker forges a truncated packet.  In this
   case, the attackers cause the destination node to produce an ICMP PTB
   message on their behalf.  To some degree, this vulnerability is
   mitigated, because the destination node will not emit an ICMP PTB



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   message in response to a truncated packet whose length is less than
   the IPv6 minimum link MTU.

16.  IANA Considerations

   IANA is requested to allocate a codepoint from the Destination
   Options and Hop-by-hop Options registry
   (https://www.iana.org/assignments/ipv6-parameters/
   ipv6-parameters.xhtml#ipv6-parameters-2).  This option is called
   "Truncation".  The "act" bits are 10 and the "chg" bit is 1.

17.  Acknowledgements

   Special thanks to Mike Heard, Geoff Huston, Joel Jaegglii, Andy
   Smith, and Jinmei Tatuya who reviewed and commented on this document.

18.  References

18.1.  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>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.




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Internet-Draft       Destination Originates ICMP PTB           June 2018


   [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
              "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
              DOI 10.17487/RFC8201, July 2017,
              <https://www.rfc-editor.org/info/rfc8201>.

18.2.  Informative References

   [I-D.bonica-6man-unrecognized-opt]
              Bonica, R. and J. Leddy, "The IPv6 Unrecognized Option",
              draft-bonica-6man-unrecognized-opt-00 (work in progress),
              June 2018.

   [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>.

   [RFC7690]  Byerly, M., Hite, M., and J. Jaeggli, "Close Encounters of
              the ICMP Type 2 Kind (Near Misses with ICMPv6 Packet Too
              Big (PTB))", RFC 7690, DOI 10.17487/RFC7690, January 2016,
              <https://www.rfc-editor.org/info/rfc7690>.

   [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,
              <https://www.rfc-editor.org/info/rfc7872>.

Authors' Addresses

   John Leddy
   Comcast
   1717 John F Kennedy Blvd.
   Philadelphia, PA  19103
   USA

   Email: john_leddy@comcast.com


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

   Email: rbonica@juniper.net






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