Network Working Group
Internet Engineering Task Force (IETF)                        S. Deering
Internet-Draft
Request for Comments: 8200                                       Retired
Obsoletes: 2460 (if approved)
STD: 86                                                        R. Hinden
Intended status: Standards Track
Obsoletes: 2460                                     Check Point Software
Expires: November 20, 2017                                  May 19,
Category: Standards Track                                      July 2017
ISSN: 2070-1721

           Internet Protocol, Version 6 (IPv6) Specification
                     draft-ietf-6man-rfc2460bis-13

Abstract

   This document specifies version 6 of the Internet Protocol (IPv6).
   It obsoletes RFC2460 RFC 2460.

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

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   This Internet-Draft will expire on November 20, 2017.
   http://www.rfc-editor.org/info/rfc8200.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4   5
   3.  IPv6 Header Format  . . . . . . . . . . . . . . . . . . . . .   5   6
   4.  IPv6 Extension Headers  . . . . . . . . . . . . . . . . . . .   6   7
     4.1.  Extension Header Order  . . . . . . . . . . . . . . . . .   8  10
     4.2.  Options . . . . . . . . . . . . . . . . . . . . . . . . .   9  11
     4.3.  Hop-by-Hop Options Header . . . . . . . . . . . . . . . .  12  13
     4.4.  Routing Header  . . . . . . . . . . . . . . . . . . . . .  12  14
     4.5.  Fragment Header . . . . . . . . . . . . . . . . . . . . .  14  15
     4.6.  Destination Options Header  . . . . . . . . . . . . . . .  21  23
     4.7.  No Next Header  . . . . . . . . . . . . . . . . . . . . .  22  24
     4.8.  Defining New Extension Headers and Options  . . . . . . .  22  24
   5.  Packet Size Issues  . . . . . . . . . . . . . . . . . . . . .  23  25
   6.  Flow Labels . . . . . . . . . . . . . . . . . . . . . . . . .  24  26
   7.  Traffic Classes . . . . . . . . . . . . . . . . . . . . . . .  24  26
   8.  Upper-Layer Protocol Issues . . . . . . . . . . . . . . . . .  24  27
     8.1.  Upper-Layer Checksums . . . . . . . . . . . . . . . . . .  25  27
     8.2.  Maximum Packet Lifetime . . . . . . . . . . . . . . . . .  26  28
     8.3.  Maximum Upper-Layer Payload Size  . . . . . . . . . . . .  27  29
     8.4.  Responding to Packets Carrying Routing Headers  . . . . .  27  29
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27  29
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  28
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  30
   12.
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     12.1.  32
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     12.2.  32
     11.2.  Informative References . . . . . . . . . . . . . . . . .  31  33
   Appendix A.  Formatting Guidelines for Options  . . . . . . . . .  33  36
   Appendix B.  Changes Since RFC2460 RFC 2460 . . . . . . . . . . . . . . .  36
     B.1.  Change History Since RFC2460  39
   Acknowledgments . . . . . . . . . . . . . .  39 . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45  42

1.  Introduction

   IP version 6 (IPv6) is a new version of the Internet Protocol (IP),
   designed as the successor to IP version 4 (IPv4) [RFC0791]. [RFC791].  The
   changes from IPv4 to IPv6 fall primarily into the following
   categories:

      o  Expanded Addressing Capabilities

         IPv6 increases the IP address size from 32 bits to 128 bits, to
         support more levels of addressing hierarchy, a much greater
         number of addressable nodes, and simpler auto-configuration autoconfiguration of
         addresses.  The scalability of multicast routing is improved by
         adding a "scope" field to multicast addresses.  And a new type
         of address called an "anycast address" is defined, defined; it is used
         to send a packet to any one of a group of nodes.

      o  Header Format Simplification

         Some IPv4 header fields have been dropped or made optional, to
         reduce the common-case processing cost of packet handling and
         to limit the bandwidth cost of the IPv6 header.

      o  Improved Support for Extensions and Options

         Changes in the way IP header options are encoded allows for
         more efficient forwarding, less stringent limits on the length
         of options, and greater flexibility for introducing new options
         in the future.

      o  Flow Labeling Capability

         A new capability is added to enable the labeling of sequences
         of packets that the sender requests to be treated in the
         network as a single flow.

      o  Authentication and Privacy Capabilities

         Extensions to support authentication, data integrity, and
         (optional) data confidentiality are specified for IPv6.

   This document specifies the basic IPv6 header and the initially- initially
   defined IPv6 extension headers and options.  It also discusses packet
   size issues, the semantics of flow labels and traffic classes, and
   the effects of IPv6 on upper-layer protocols.  The format and
   semantics of IPv6 addresses are specified separately in [RFC4291].
   The IPv6 version of ICMP, which all IPv6 implementations are required
   to include, is specified in [RFC4443] [RFC4443].

   The data transmission order for IPv6 is the same as for IPv4 as
   defined in Appendix B of [RFC0791]. [RFC791].

   Note: As this document obsoletes [RFC2460], any document referenced
   in this document that includes pointers to RFC2460, RFC 2460 should be
   interpreted as referencing this document.

2.  Terminology

   node         a device that implements IPv6.

   router       a node that forwards IPv6 packets not explicitly
                addressed to itself.  [See  (See Note below]. below.)

   host         any node that is not a router.  [See  (See Note below]. below.)

   upper layer  a protocol layer immediately above IPv6.  Examples are
                transport protocols such as TCP and UDP, control
                protocols such as ICMP, routing protocols such as OSPF,
                and internet internet-layer or lower-layer protocols being
                "tunneled" over (i.e., encapsulated in) IPv6 such as IPX,
                Internetwork Packet Exchange (IPX), AppleTalk, or IPv6
                itself.

   link         a communication facility or medium over which nodes can
                communicate at the link layer, i.e., the layer
                immediately below IPv6.  Examples are Ethernets (simple
                or bridged); PPP links; X.25, Frame Relay, or ATM
                networks; and internet (or higher) layer internet-layer or higher-layer "tunnels",
                such as tunnels over IPv4 or IPv6 itself.

   neighbors    nodes attached to the same link.

   interface    a node's attachment to a link.

   address      an IPv6-layer identifier for an interface or a set of
                interfaces.

   packet       an IPv6 header plus payload.

   link MTU     the maximum transmission unit, i.e., maximum packet size
                in octets, that can be conveyed over a link.

   path MTU     the minimum link MTU of all the links in a path between
                a source node and a destination node.

   Note: it is possible for a device with multiple interfaces to be
   configured to forward non-self-destined packets arriving from some
   set (fewer than all) of its interfaces, interfaces and to discard non-self-
   destined packets arriving from its other interfaces.  Such a device
   must obey the protocol requirements for routers when receiving
   packets from, and interacting with neighbors over, the former
   (forwarding) interfaces.  It must obey the protocol requirements for
   hosts when receiving packets from, and interacting with neighbors
   over, the latter (non-forwarding) interfaces.

3.  IPv6 Header Format

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version| Traffic Class |           Flow Label                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Payload Length        |  Next Header  |   Hop Limit   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                         Source Address                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Destination Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Version             4-bit Internet Protocol version number = 6.

      Traffic Class       8-bit traffic class Traffic Class field.  See section Section 7.

      Flow Label          20-bit flow label.  See section Section 6.

      Payload Length      16-bit unsigned integer.  Length of the IPv6
                          payload, i.e., the rest of the packet
                          following this IPv6 header, in octets.  (Note
                          that any extension headers [Section 4] (see Section 4)
                          present are considered part of the payload,
                          i.e., included in the length count.)
      Next Header         8-bit selector.  Identifies the type of header
                          immediately following the IPv6 header.  Uses
                          the same values as the IPv4 Protocol field
                          [IANA-PN].

      Hop Limit           8-bit unsigned integer.  Decremented by 1 by
                          each node that forwards the packet.  When
                          forwarding, the packet is discarded if Hop
                          Limit was zero when received or is decremented
                          to zero.  A node that is the destination of a
                          packet should not discard a packet with hop
                          limit Hop
                          Limit equal to zero, zero; it should process the
                          packet normally.

      Source Address      128-bit address of the originator of the
                          packet.  See [RFC4291].

      Destination Address 128-bit address of the intended recipient of
                          the packet (possibly not the ultimate
                          recipient, if a Routing header is present).
                          See [RFC4291] and section Section 4.4.

4.  IPv6 Extension Headers

   In IPv6, optional internet-layer information is encoded in separate
   headers that may be placed between the IPv6 header and the upper-
   layer header in a packet.  There is a small number of such extension
   headers, each one identified by a distinct Next Header value.

   Extension Headers headers are numbered from IANA IP Protocol Numbers
   [IANA-PN], the same values used for IPv4 and IPv6.  When processing a
   sequence of Next Header values in a packet, the first one that is not
   an Extension Header extension header [IANA-EH] indicates that the next item in the
   packet is the corresponding upper-layer header.  A special "No Next
   Header" value is used if there is no upper-layer header.

   As illustrated in these examples, an IPv6 packet may carry zero, one,
   or more extension headers, each identified by the Next Header field
   of the preceding header:

   +---------------+------------------------
   |  IPv6 header  | TCP header + data
   |               |
   | Next Header = |
   |      TCP      |
   +---------------+------------------------

   +---------------+----------------+------------------------
   |  IPv6 header  | Routing header | TCP header + data
   |               |                |
   | Next Header = |  Next Header = |
   |    Routing    |      TCP       |
   +---------------+----------------+------------------------

   +---------------+----------------+-----------------+-----------------
   |  IPv6 header  | Routing header | Fragment header | fragment of TCP
   |               |                |                 |  header + data
   | Next Header = |  Next Header = |  Next Header =  |
   |    Routing    |    Fragment    |       TCP       |
   +---------------+----------------+-----------------+-----------------

   Extension headers (except for the Hop-by-Hop Options header) are not
   processed, inserted, or deleted by any node along a packet's delivery
   path, until the packet reaches the node (or each of the set of nodes,
   in the case of multicast) identified in the Destination Address field
   of the IPv6 header.

   The Hop-by-Hop Options header is not inserted or deleted, but may be
   examined or processed by any node along a packet's delivery path,
   until the packet reaches the node (or each of the set of nodes, in
   the case of multicast) identified in the Destination Address field of
   the IPv6 header.  The Hop-by-Hop Options header, when present, must
   immediately follow the IPv6 header.  Its presence is indicated by the
   value zero in the Next Header field of the IPv6 header.

   NOTE: While [RFC2460] required that all nodes must examine and
   process the Hop-by-Hop Options header, it is now expected that nodes
   along a packet's delivery path only examine and process the Hop-by-
   Hop
   Hop-by-Hop Options header if explicitly configured to do so.

   At the Destination destination node, normal demultiplexing on the Next Header
   field of the IPv6 header invokes the module to process the first
   extension header, or the upper-layer header if no extension header is
   present.  The contents and semantics of each extension header
   determine whether or not to proceed to the next header.  Therefore,
   extension headers must be processed strictly in the order they appear
   in the packet; a receiver must not, for example, scan through a
   packet looking for a particular kind of extension header and process
   that header prior to processing all preceding ones.

   If, as a result of processing a header, the destination node is
   required to proceed to the next header but the Next Header value in
   the current header is unrecognized by the node, it should discard the
   packet and send an ICMP Parameter Problem message to the source of
   the packet, with an ICMP Code value of 1 ("unrecognized Next Header
   type encountered") and the ICMP Pointer field containing the offset
   of the unrecognized value within the original packet.  The same
   action should be taken if a node encounters a Next Header value of
   zero in any header other than an IPv6 header.

   Each extension header is an integer multiple of 8 octets long, in
   order to retain 8-octet alignment for subsequent headers.  Multi-
   octet fields within each extension header are aligned on their
   natural boundaries, i.e., fields of width n octets are placed at an
   integer multiple of n octets from the start of the header, for n = 1,
   2, 4, or 8.

   A full implementation of IPv6 includes implementation of the
   following extension headers:

      Hop-by-Hop Options
      Fragment
      Destination Options
      Routing
      Authentication
      Encapsulating Security Payload

   The first four are specified in this document; the last two are
   specified in [RFC4302] and [RFC4303], respectively.  The current list
   of IPv6 extension headers can be found at [IANA-EH].

4.1.  Extension Header Order

   When more than one extension header is used in the same packet, it is
   recommended that those headers appear in the following order:

      IPv6 header
      Hop-by-Hop Options header
      Destination Options header (note 1)
      Routing header
      Fragment header
      Authentication header (note 2)
      Encapsulating Security Payload header (note 2)
      Destination Options header (note 3)
      upper-layer
      Upper-Layer header

      note 1: for options to be processed by the first destination that
              appears in the IPv6 Destination Address field plus
              subsequent destinations listed in the Routing header.

      note 2: additional recommendations regarding the relative order of
              the Authentication and Encapsulating Security Payload
              headers are given in [RFC4303].

      note 3: for options to be processed only by the final destination
              of the packet.

   Each extension header should occur at most once, except for the
   Destination Options header header, which should occur at most twice (once
   before a Routing header and once before the upper-layer header).

   If the upper-layer header is another IPv6 header (in the case of IPv6
   being tunneled over or encapsulated in IPv6), it may be followed by
   its own extension headers, which are separately subject to the same
   ordering recommendations.

   If and when other extension headers are defined, their ordering
   constraints relative to the above listed headers must be specified.

   IPv6 nodes must accept and attempt to process extension headers in
   any order and occurring any number of times in the same packet,
   except for the Hop-by-Hop Options header header, which is restricted to
   appear immediately after an IPv6 header only.  Nonetheless, it is
   strongly advised that sources of IPv6 packets adhere to the above
   recommended order until and unless subsequent specifications revise
   that recommendation.

4.2.  Options

   Two of the currently-defined currently defined extension headers defined specified in this
   document -- the Hop-by-Hop Options header and the Destination Options
   header -- carry a variable number of type-length-value (TLV) encoded
   "options", of "options" that are type-length-
   value (TLV) encoded in the following format:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
      |  Option Type  |  Opt Data Len |  Option Data
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

      Option Type         8-bit identifier of the type of option.

      Opt Data Len        8-bit unsigned integer.  Length of the Option
                          Data field of this option, in octets.

      Option Data         Variable-length field.  Option-Type-specific
                          data.

   The sequence of options within a header must be processed strictly in
   the order they appear in the header; a receiver must not, for
   example, scan through the header looking for a particular kind of
   option and process that option prior to processing all preceding
   ones.

   The Option Type identifiers are internally encoded such that their
   highest-order two 2 bits specify the action that must be taken if the
   processing IPv6 node does not recognize the Option Type:

      00 - skip over this option and continue processing the header.

      01 - discard the packet.

      10 - discard the packet and, regardless of whether or not the
           packet's Destination Address was a multicast address, send an
           ICMP Parameter Problem, Code 2, message to the packet's
           Source Address, pointing to the unrecognized Option Type.

      11 - discard the packet and, only if the packet's Destination
           Address was not a multicast address, send an ICMP Parameter
           Problem, Code 2, message to the packet's Source Address,
           pointing to the unrecognized Option Type.

   The third-highest-order bit of the Option Type specifies whether or
   not the Option Data of that option can change en-route en route to the
   packet's final destination.  When an Authentication header is present
   in the packet, for any option whose data may change en-route, en route, its
   entire Option Data field must be treated as zero-valued octets when
   computing or verifying the packet's authenticating value.

       0 - Option Data does not change en-route en route

       1 - Option Data may change en-route en route

   The three high-order bits described above are to be treated as part
   of the Option Type, not independent of the Option Type.  That is, a
   particular option is identified by a full 8-bit Option Type, not just
   the low-order 5 bits of an Option Type.

   The same Option Type numbering space is used for both the Hop-by-Hop
   Options header and the Destination Options header.  However, the
   specification of a particular option may restrict its use to only one
   of those two headers.

   Individual options may have specific alignment requirements, to
   ensure that multi-octet values within Option Data fields fall on
   natural boundaries.  The alignment requirement of an option is
   specified using the notation xn+y, meaning the Option Type must
   appear at an integer multiple of x octets from the start of the
   header, plus y octets.  For example:

      2n     means any 2-octet offset from the start of the header.
      8n+2   means any 8-octet offset from the start of the header, plus
             2 octets.

   There are two padding options which that are used when necessary to align
   subsequent options and to pad out the containing header to a multiple
   of 8 octets in length.  These padding options must be recognized by
   all IPv6 implementations:

   Pad1 option (alignment requirement: none)

      +-+-+-+-+-+-+-+-+
      |       0       |
      +-+-+-+-+-+-+-+-+

      NOTE! the format of the Pad1 option is a special case -- it does
            not have length and value fields.

      The Pad1 option is used to insert one 1 octet of padding into the
      Options area of a header.  If more than one octet of padding is
      required, the PadN option, described next, should be used, rather
      than multiple Pad1 options.

   PadN option (alignment requirement: none)

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
      |       1       |  Opt Data Len |  Option Data
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

      The PadN option is used to insert two or more octets of padding
      into the Options area of a header.  For N octets of padding, the
      Opt Data Len field contains the value N-2, and the Option Data
      consists of N-2 zero-valued octets.

   Appendix A contains formatting guidelines for designing new options.

4.3.  Hop-by-Hop Options Header

   The Hop-by-Hop Options header is used to carry optional information
   that may be examined and processed by every node along a packet's
   delivery path.  The Hop-by-Hop Options header is identified by a Next
   Header value of 0 in the IPv6 header, header and has the following format:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Next Header  |  Hdr Ext Len  |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
    |                                                               |
    .                                                               .
    .                            Options                            .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header         8-bit selector.  Identifies the type of header
                          immediately following the Hop-by-Hop Options
                          header.  Uses the same values as the IPv4
                          Protocol field [IANA-PN].

      Hdr Ext Len         8-bit unsigned integer.  Length of the Hop-by-
                          Hop
                          Hop-by-Hop Options header in 8-octet units,
                          not including the first 8 octets.

      Options             Variable-length field, of length such that the
                          complete Hop-by-Hop Options header is an
                          integer multiple of 8 octets long.  Contains
                          one or more TLV-encoded options, as described
                          in section Section 4.2.

   The only hop-by-hop options defined in this document are the Pad1 and
   PadN options specified in section Section 4.2.

4.4.  Routing Header

   The Routing header is used by an IPv6 source to list one or more
   intermediate nodes to be "visited" on the way to a packet's
   destination.  This function is very similar to IPv4's Loose Source
   and Record Route option.  The Routing header is identified by a Next
   Header value of 43 in the immediately preceding header, header and has the
   following format:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Next Header  |  Hdr Ext Len  |  Routing Type | Segments Left |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                       type-specific data                      .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header         8-bit selector.  Identifies the type of header
                          immediately following the Routing header.
                          Uses the same values as the IPv4 Protocol
                          field [IANA-PN].

      Hdr Ext Len         8-bit unsigned integer.  Length of the Routing
                          header in 8-octet units, not including the
                          first 8 octets.

      Routing Type        8-bit identifier of a particular Routing
                          header variant.

      Segments Left       8-bit unsigned integer.  Number of route
                          segments remaining, i.e., number of explicitly
                          listed intermediate nodes still to be visited
                          before reaching the final destination.

      type-specific data  Variable-length field, of format determined by
                          the Routing Type, and of length such that the
                          complete Routing header is an integer multiple
                          of 8 octets long.

   If, while processing a received packet, a node encounters a Routing
   header with an unrecognized Routing Type value, the required behavior
   of the node depends on the value of the Segments Left field, as
   follows:

      If Segments Left is zero, the node must ignore the Routing header
      and proceed to process the next header in the packet, whose type
      is identified by the Next Header field in the Routing header.

      If Segments Left is non-zero, the node must discard the packet and
      send an ICMP Parameter Problem, Code 0, message to the packet's
      Source Address, pointing to the unrecognized Routing Type.

   If, after processing a Routing header of a received packet, an
   intermediate node determines that the packet is to be forwarded onto
   a link whose link MTU is less than the size of the packet, the node
   must discard the packet and send an ICMP Packet Too Big message to
   the packet's Source Address.

   The currently defined IPv6 Routing Headers and their status can be
   found at [IANA-RH].  Allocation guidelines for IPv6 Routing Headers
   can be found in [RFC5871].

4.5.  Fragment Header

   The Fragment header is used by an IPv6 source to send a packet larger
   than would fit in the path MTU to its destination.  (Note: unlike
   IPv4, fragmentation in IPv6 is performed only by source nodes, not by
   routers along a packet's delivery path -- see section Section 5.)  The
   Fragment header is identified by a Next Header value of 44 in the
   immediately preceding header, header and has the following format:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  |   Reserved    |      Fragment Offset    |Res|M|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Identification                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header         8-bit selector.  Identifies the initial header
                          type of the Fragmentable Part of the original
                          packet (defined below).  Uses the same values
                          as the IPv4 Protocol field [IANA-PN].

      Reserved            8-bit reserved field.  Initialized to zero for
                          transmission; ignored on reception.

      Fragment Offset     13-bit unsigned integer.  The offset, in
                          8-octet units, of the data following this
                          header, relative to the start of the
                          Fragmentable Part of the original packet.

      Res                 2-bit reserved field.  Initialized to zero for
                          transmission; ignored on reception.

      M flag              1 = more fragments; 0 = last fragment.

      Identification      32 bits.  See description below.

   In order to send a packet that is too large to fit in the MTU of the
   path to its destination, a source node may divide the packet into
   fragments and send each fragment as a separate packet, to be
   reassembled at the receiver.

   For every packet that is to be fragmented, the source node generates
   an Identification value.  The Identification must be different than
   that of any other fragmented packet sent recently* with the same
   Source Address and Destination Address.  If a Routing header is
   present, the Destination Address of concern is that of the final
   destination.

      *  "recently" means within the maximum likely lifetime of a
         packet, including transit time from source to destination and
         time spent awaiting reassembly with other fragments of the same
         packet.  However, it is not required that a source node knows
         the maximum packet lifetime.  Rather, it is assumed that the
         requirement can be met by implementing an algorithm that
         results in a low identification reuse frequency.  Examples of
         algorithms that can meet this requirement are described in
         [RFC7739].

   The initial, large, unfragmented packet is referred to as the
   "original packet", and it is considered to consist of three parts, as
   illustrated:

   original packet:

   +------------------+-------------------------+---//----------------+
   |  Per-Fragment    | Extension & Upper-Layer |   Fragmentable      |
   |    Headers       |       Headers           |      Part           |
   +------------------+-------------------------+---//----------------+

      The Per-Fragment Headers headers must consist of the IPv6 header plus any
      extension headers that must be processed by nodes en route to the
      destination, that is, all headers up to and including the Routing
      header if present, else the Hop-by-Hop Options header if present,
      else no extension headers.

      The Extension Headers headers are all other extension headers that are not
      included in the Per-Fragment headers part of the packet.  For this
      purpose, the Encapsulating Security Payload (ESP) is not
      considered an extension header.  The Upper-Layer Header header is the
      first upper-layer header that is not an IPv6 extension header.
      Examples of upper-layer headers include TCP, UDP, IPv4, IPv6,
      ICMPv6, and as noted ESP.

      The Fragmentable Part consists of the rest of the packet after the
      upper-layer header or after any header (i.e., initial IPv6 header
      or extension header) that contains a Next Header value of No Next
      Header.

   The Fragmentable Part of the original packet is divided into
   fragments.  The lengths of the fragments must be chosen such that the
   resulting fragment packets fit within the MTU of the path to the
   packets'
   packet's destination(s).  Each complete fragment, except possibly the
   last ("rightmost") one, being is an integer multiple of 8 octets long.

   The fragments are transmitted in separate "fragment packets" as
   illustrated:

   original packet:

   +-----------------+-----------------+--------+--------+-//-+--------+
   |  Per-Fragment   |Ext & Upper-Layer|  first | second |    |  last  |
   |    Headers      |    Headers      |fragment|fragment|....|fragment|
   +-----------------+-----------------+--------+--------+-//-+--------+

   fragment packets:

   +------------------+---------+-------------------+----------+
   |  Per-Fragment    |Fragment | Ext & Upper-Layer |  first   |
   |    Headers       | Header  |   Headers         | fragment |
   +------------------+---------+-------------------+----------+

   +------------------+--------+-------------------------------+
   |  Per-Fragment    |Fragment|    second                     |
   |    Headers       | Header |   fragment                    |
   +------------------+--------+-------------------------------+
                         o
                         o
                         o
   +------------------+--------+----------+
   |  Per-Fragment    |Fragment|   last   |
   |    Headers       | Header | fragment |
   +------------------+--------+----------+

   The first fragment packet is composed of:

      (1)  The Per-Fragment Headers headers of the original packet, with the
           Payload Length of the original IPv6 header changed to contain
           the length of this fragment packet only (excluding the length
           of the IPv6 header itself), and the Next Header field of the
           last header of the Per-Fragment Headers headers changed to 44.

      (2)  A Fragment header containing:

              The Next Header value that identifies the first header
              after the Per-Fragment Headers headers of the original packet.

              A Fragment Offset containing the offset of the fragment,
              in 8-octet units, relative to the start of the
              Fragmentable Part of the original packet.  The Fragment
              Offset of the first ("leftmost") fragment is 0.

              An M flag value of 1 as this is the first fragment.

              The Identification value generated for the original
              packet.

      (3)  Extension Headers, headers, if any, and the Upper-Layer header.  These
           headers must be in the first fragment.  Note: This restricts
           the size of the headers through the Upper-Layer header to the
           MTU of the path to the packets' packet's destinations(s).

      (4)  The first fragment.

   The subsequent fragment packets are composed of:

      (1)  The Per-Fragment Headers headers of the original packet, with the
           Payload Length of the original IPv6 header changed to contain
           the length of this fragment packet only (excluding the length
           of the IPv6 header itself), and the Next Header field of the
           last header of the Per-Fragment Headers headers changed to 44.

      (2)  A Fragment header containing:

              The Next Header value that identifies the first header
              after the Per-Fragment Headers headers of the original packet.

              A Fragment Offset containing the offset of the fragment,
              in 8-octet units, relative to the start of the
              Fragmentable part Part of the original packet.

              An M flag value of 0 if the fragment is the last
              ("rightmost") one, else an M flag value of 1.

              The Identification value generated for the original
              packet.

      (3)  The fragment itself.

   Fragments must not be created that overlap with any other fragments
   created from the original packet.

   At the destination, fragment packets are reassembled into their
   original, unfragmented form, as illustrated:

   reassembled original packet:

   +---------------+-----------------+---------+--------+-//--+--------+
   | Per-Fragment  |Ext & Upper-Layer|  first  | second |     | last   |
   |    Headers    |     Headers     |frag data|fragment|.....|fragment|
   +---------------+-----------------+---------+--------+-//--+--------+

   The following rules govern reassembly:

      An original packet is reassembled only from fragment packets that
      have the same Source Address, Destination Address, and Fragment
      Identification.

      The Per-Fragment Headers headers of the reassembled packet consists of all
      headers up to, but not including, the Fragment header of the first
      fragment packet (that is, the packet whose Fragment Offset is
      zero), with the following two changes:

         The Next Header field of the last header of the Per-Fragment
         Headers
         headers is obtained from the Next Header field of the first
         fragment's Fragment header.

         The Payload Length of the reassembled packet is computed from
         the length of the Per-Fragment Headers headers and the length and
         offset of the last fragment.  For example, a formula for
         computing the Payload Length of the reassembled original packet
         is:

            PL.orig = PL.first - FL.first - 8 + (8 * FO.last) + FL.last

            where
            PL.orig  =  Payload Length field of reassembled packet.
            PL.first =  Payload Length field of first fragment packet.
            FL.first =  length of fragment following Fragment header of
                        first fragment packet.
            FO.last  =  Fragment Offset field of Fragment header of last
                        fragment packet.
            FL.last  =  length of fragment following Fragment header of
                        last fragment packet.

         The Fragmentable Part of the reassembled packet is constructed
         from the fragments following the Fragment headers in each of
         the fragment packets.  The length of each fragment is computed
         by subtracting from the packet's Payload Length the length of
         the headers between the IPv6 header and fragment itself; its
         relative position in Fragmentable Part is computed from its
         Fragment Offset value.

         The Fragment header is not present in the final, reassembled
         packet.

         If the fragment is a whole datagram (that is, both the Fragment
         Offset field and the M flag are zero), then it does not need
         any further reassembly and should be processed as a fully
         reassembled packet (i.e., updating Next Header, adjust Payload
         Length, removing the Fragmentation Header, Fragment header, etc.).  Any other
         fragments that match this packet (i.e., the same IPv6 Source
         Address, IPv6 Destination Address, and Fragment Identification)
         should be processed independently.

   The following error conditions may arise when reassembling fragmented
   packets:

      o  If insufficient fragments are received to complete reassembly
         of a packet within 60 seconds of the reception of the first-
         arriving fragment of that packet, reassembly of that packet
         must be abandoned and all the fragments that have been received
         for that packet must be discarded.  If the first fragment
         (i.e., the one with a Fragment Offset of zero) has been
         received, an ICMP Time Exceeded -- Fragment Reassembly Time
         Exceeded message should be sent to the source of that fragment.

      o  If the length of a fragment, as derived from the fragment
         packet's Payload Length field, is not a multiple of 8 octets
         and the M flag of that fragment is 1, then that fragment must
         be discarded and an ICMP Parameter Problem, Code 0, message
         should be sent to the source of the fragment, pointing to the
         Payload Length field of the fragment packet.

      o  If the length and offset of a fragment are such that the
         Payload Length of the packet reassembled from that fragment
         would exceed 65,535 octets, then that fragment must be
         discarded and an ICMP Parameter Problem, Code 0, message should
         be sent to the source of the fragment, pointing to the Fragment
         Offset field of the fragment packet.

      o  If the first fragment does not include all headers through an
         Upper-Layer header, then that fragment should be discarded and
         an ICMP Parameter Problem, Code 3, message should be sent to
         the source of the fragment, with the Pointer field set to zero.

      o  If any of the fragments being reassembled overlaps overlap with any
         other fragments being reassembled for the same packet,
         reassembly of that packet must be abandoned and all the
         fragments that have been received for that packet must be
         discarded
         discarded, and no ICMP error messages should be sent.

         It should be noted that fragments may be duplicated in the
         network.  Instead of treating these exact duplicate fragments
         as overlapping fragments, an implementation may choose to
         detect this case and drop exact duplicate fragments while
         keeping the other fragments belonging to the same packet.

   The following conditions are not expected to occur frequently, frequently but are
   not considered errors if they do:

      The number and content of the headers preceding the Fragment
      header of different fragments of the same original packet may
      differ.  Whatever headers are present, preceding the Fragment
      header in each fragment packet, are processed when the packets
      arrive, prior to queueing the fragments for reassembly.  Only
      those headers in the Offset zero fragment packet are retained in
      the reassembled packet.

      The Next Header values in the Fragment headers of different
      fragments of the same original packet may differ.  Only the value
      from the Offset zero fragment packet is used for reassembly.

      Other fields in the IPv6 header may also vary across the fragments
      being reassembled.  Specifications that use these fields may
      provide additional instructions if the basic mechanism of using
      the values from the Offset zero fragment is not sufficient.  For
      example, Section 5.3 of [RFC3168] describes how to combine the
      Explicit Congestion Notification (ECN) bits from different
      fragments to derive the ECN bits of the reassembled packet.

4.6.  Destination Options Header

   The Destination Options header is used to carry optional information
   that need be examined only by a packet's destination node(s).  The
   Destination Options header is identified by a Next Header value of 60
   in the immediately preceding header, header and has the following format:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Next Header  |  Hdr Ext Len  |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
    |                                                               |
    .                                                               .
    .                            Options                            .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header         8-bit selector.  Identifies the type of header
                          immediately following the Destination Options
                          header.  Uses the same values as the IPv4
                          Protocol field [IANA-PN].

      Hdr Ext Len         8-bit unsigned integer.  Length of the
                          Destination Options header in 8-octet units,
                          not including the first 8 octets.

      Options             Variable-length field, of length such that the
                          complete Destination Options header is an
                          integer multiple of 8 octets long.  Contains
                          one or more TLV-encoded options, as described
                          in section Section 4.2.

   The only destination options defined in this document are the Pad1
   and PadN options specified in section Section 4.2.

   Note that there are two possible ways to encode optional destination
   information in an IPv6 packet: either as an option in the Destination
   Options header, header or as a separate extension header.  The Fragment
   header and the Authentication header are examples of the latter
   approach.  Which approach can be used depends on what action is
   desired of a destination node that does not understand the optional
   information:

      o  If the desired action is for the destination node to discard
         the packet and, only if the packet's Destination Address is not
         a multicast address, send an ICMP Unrecognized Type message to
         the packet's Source Address, then the information may be
         encoded either as a separate header or as an option in the
         Destination Options header whose Option Type has the value 11
         in its highest-order two 2 bits.  The choice may depend on such
         factors as which takes fewer octets, or which yields better
         alignment or more efficient parsing.

      o  If any other action is desired, the information must be encoded
         as an option in the Destination Options header whose Option
         Type has the value 00, 01, or 10 in its highest-order two 2 bits,
         specifying the desired action (see section Section 4.2).

4.7.  No Next Header

   The value 59 in the Next Header field of an IPv6 header or any
   extension header indicates that there is nothing following that
   header.  If the Payload Length field of the IPv6 header indicates the
   presence of octets past the end of a header whose Next Header field
   contains 59, those octets must be ignored, ignored and passed on unchanged if
   the packet is forwarded.

4.8.  Defining New Extension Headers and Options

   Defining new IPv6 extension headers is not recommended, unless there
   are no existing IPv6 extension headers that can be used by specifying
   a new option for that IPv6 extension header.  A proposal to specify a
   new IPv6 extension header must include a detailed technical
   explanation of why an existing IPv6 extension header can not be used
   for the desired new function.  See [RFC6564] for additional
   background information.

   Note: New extension headers that require hop-by-hop behavior must not
   be defined because, as specified in Section 4 of this document, the
   only Extension Header extension header that has hop-by-hop behavior is the Hop-by-Hop
   Options header.

   New hop-by-hop options are not recommended because nodes may be
   configured to ignore the Hop-by-Hop Option Options header, drop packets
   containing a hop-by-hop Hop-by-Hop Options header, or assign packets containing
   a hop-
   by-hop Hop-by-Hop Options header to a slow processing path.  Designers
   considering defining new hop-by-hop options need to be aware of this
   likely
   behaviour. behavior.  There has to be a very clear justification why any
   new hop-by-hop option is needed before it is standardized.

   Instead of defining new Extension Headers, extension headers, it is recommended that the
   Destination Options header is used to carry optional information that
   must be examined only by a packet's destination node(s), because they
   provide better handling and backward compatibility.

   If new Extension Headers extension headers are defined, they need to use the following
   format:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Next Header  |  Hdr Ext Len  |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
    |                                                               |
    .                                                               .
    .                  Header Specific                  Header-Specific Data                         .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Next Header           8-bit selector.  Identifies the type of
                            header immediately following the extension
                            header.  Uses the same values as the IPv4
                            Protocol field [IANA-PN].

      Hdr Ext Len           8-bit unsigned integer.  Length of the
                            Destination Options header in 8-octet units,
                            not including the first 8 octets.

      Header Specific Data  Variable-length field.  Fields specific to
                            the extension header.

5.  Packet Size Issues

   IPv6 requires that every link in the internet Internet have an MTU of 1280
   octets or greater.  This is known as the IPv6 minimum link MTU.  On
   any link that cannot convey a 1280-octet packet in one piece, link-
   specific fragmentation and reassembly must be provided at a layer
   below IPv6.

   Links that have a configurable MTU (for example, PPP links [RFC1661])
   must be configured to have an MTU of at least 1280 octets; it is
   recommended that they be configured with an MTU of 1500 octets or
   greater, to accommodate possible encapsulations (i.e., tunneling)
   without incurring IPv6-layer fragmentation.

   From each link to which a node is directly attached, the node must be
   able to accept packets as large as that link's MTU.

   It is strongly recommended that IPv6 nodes implement Path MTU
   Discovery [RFC1981], [RFC8201], in order to discover and take advantage of path
   MTUs greater than 1280 octets.  However, a minimal IPv6
   implementation (e.g., in a boot ROM) may simply restrict itself to
   sending packets no larger than 1280 octets, and omit implementation
   of Path MTU Discovery.

   In order to send a packet larger than a path's MTU, a node may use
   the IPv6 Fragment header to fragment the packet at the source and
   have it reassembled at the destination(s).  However, the use of such
   fragmentation is discouraged in any application that is able to
   adjust its packets to fit the measured path MTU (i.e., down to 1280
   octets).

   A node must be able to accept a fragmented packet that, after
   reassembly, is as large as 1500 octets.  A node is permitted to
   accept fragmented packets that reassemble to more than 1500 octets.
   An upper-layer protocol or application that depends on IPv6
   fragmentation to send packets larger than the MTU of a path should
   not send packets larger than 1500 octets unless it has assurance that
   the destination is capable of reassembling packets of that larger
   size.

6.  Flow Labels

   The 20-bit Flow Label field in the IPv6 header is used by a source to
   label sequences of packets to be treated in the network as a single
   flow.

   The current definition of the IPv6 Flow Label can be found in
   [RFC6437].

7.  Traffic Classes

   The 8-bit Traffic Class field in the IPv6 header is used by the
   network for traffic management.  The value of the Traffic Class bits
   in a received packet or fragment might be different from the value
   sent by the packet's source.

   The current use of the Traffic Class field for Differentiated
   Services and Explicit Congestion Notification is specified in
   [RFC2474] and [RFC3168].

8.  Upper-Layer Protocol Issues

8.1.  Upper-Layer Checksums

   Any transport or other upper-layer protocol that includes the
   addresses from the IP header in its checksum computation must be
   modified for use over IPv6, to include the 128-bit IPv6 addresses
   instead of 32-bit IPv4 addresses.  In particular, the following
   illustration shows the TCP and UDP "pseudo-header" for IPv6:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                         Source Address                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Destination Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Upper-Layer Packet Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      zero                     |  Next Header  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      o  If the IPv6 packet contains a Routing header, the Destination
         Address used in the pseudo-header is that of the final
         destination.  At the originating node, that address will be in
         the last element of the Routing header; at the recipient(s),
         that address will be in the Destination Address field of the
         IPv6 header.

      o  The Next Header value in the pseudo-header identifies the
         upper-layer protocol (e.g., 6 for TCP, TCP or 17 for UDP).  It will
         differ from the Next Header value in the IPv6 header if there
         are extension headers between the IPv6 header and the upper-
         layer header.

      o  The Upper-Layer Packet Length in the pseudo-header is the
         length of the upper-layer header and data (e.g., TCP header
         plus TCP data).  Some upper-layer protocols carry their own
         length information (e.g., the Length field in the UDP header);
         for such protocols, that is the length used in the pseudo-
         header.  Other protocols (such as TCP) do not carry their own
         length information, in which case the length used in the
         pseudo-header is the Payload Length from the IPv6 header, minus
         the length of any extension headers present between the IPv6
         header and the upper-layer header.

      o  Unlike IPv4, the default behavior when UDP packets are
         originated by an IPv6 node is that the UDP checksum is not
         optional.  That is, whenever originating a UDP packet, an IPv6
         node must compute a UDP checksum over the packet and the
         pseudo-header, and, if that computation yields a result of
         zero, it must be changed to hex FFFF for placement in the UDP
         header.  IPv6 receivers must discard UDP packets containing a
         zero checksum, checksum and should log the error.

      o  As an exception to the default behaviour, behavior, protocols that use UDP
         as a tunnel encapsulation may enable zero-checksum mode for a
         specific port (or set of ports) for sending and/or receiving.
         Any node implementing zero-checksum mode must follow the
         requirements specified in "Applicability Statement for the Use
         of IPv6 UDP Datagrams with Zero Checksums" [RFC6936].

   The IPv6 version of ICMP [RFC4443] includes the above pseudo-header
   in its checksum computation; this is a change from the IPv4 version
   of ICMP, which does not include a pseudo-header in its checksum.  The
   reason for the change is to protect ICMP from misdelivery or
   corruption of those fields of the IPv6 header on which it depends,
   which, unlike IPv4, are not covered by an internet-layer checksum.
   The Next Header field in the pseudo-header for ICMP contains the
   value 58, which identifies the IPv6 version of ICMP.

8.2.  Maximum Packet Lifetime

   Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
   lifetime.  That is the reason the IPv4 "Time to Live" "Time-to-Live" field was
   renamed "Hop Limit" in IPv6.  In practice, very few, if any, IPv4
   implementations conform to the requirement that they limit packet
   lifetime, so this is not a change in practice.  Any upper-layer
   protocol that relies on the internet layer (whether IPv4 or IPv6) to
   limit packet lifetime ought to be upgraded to provide its own
   mechanisms for detecting and discarding obsolete packets.

8.3.  Maximum Upper-Layer Payload Size

   When computing the maximum payload size available for upper-layer
   data, an upper-layer protocol must take into account the larger size
   of the IPv6 header relative to the IPv4 header.  For example, in
   IPv4, TCP's MSS Maximum Segment Size (MSS) option is computed as the
   maximum packet size (a default value or a value learned through Path
   MTU Discovery) minus 40 octets (20 octets for the minimum-length IPv4
   header and 20 octets for the minimum-length TCP header).  When using
   TCP over IPv6, the MSS must be computed as the maximum packet size
   minus 60 octets, because the minimum-length IPv6 header (i.e., an
   IPv6 header with no extension headers) is 20 octets longer than a
   minimum-length IPv4 header.

8.4.  Responding to Packets Carrying Routing Headers

   When an upper-layer protocol sends one or more packets in response to
   a received packet that included a Routing header, the response
   packet(s) must not include a Routing header that was automatically
   derived by "reversing" the received Routing header UNLESS the
   integrity and authenticity of the received Source Address and Routing
   header have been verified (e.g., via the use of an Authentication
   header in the received packet).  In other words, only the following
   kinds of packets are permitted in response to a received packet
   bearing a Routing header:

      o  Response packets that do not carry Routing headers.

      o  Response packets that carry Routing headers that were NOT
         derived by reversing the Routing header of the received packet
         (for example, a Routing header supplied by local
         configuration).

      o  Response packets that carry Routing headers that were derived
         by reversing the Routing header of the received packet IF AND
         ONLY IF the integrity and authenticity of the Source Address
         and Routing header from the received packet have been verified
         by the responder.

9.  IANA Considerations

   RFC2460

   RFC 2460 is referenced in a number of IANA registries.  These
   include:

      o  Internet Protocol Version 6 (IPv6) Parameters [IANA-6P]

      o  Assigned Internet Protocol Numbers [IANA-PN]
      o  ONC RPC Network Identifiers (netids) [IANA-NI]

      o  Technical requirements for authoritative name servers [IANA-NS]

      o  Network Layer Protocol Identifiers (NLPIDs) of Interest
         [IANA-NL]

      o  Protocol Registries [IANA-PR]

      o  Structure of Management Information (SMI) Numbers (MIB Module
         Registrations) [IANA-MI]

   The IANA should update has updated these references to point to this document.

10.  Security Considerations

   IPv6, from the viewpoint of the basic format and transmission of
   packets, has security properties that are similar to IPv4.  These
   security issues include:

      o  Eavesdropping, On-path where on-path elements can observe the whole
         packet (including both contents and metadata) of each IPv6
         datagram.
      o  Replay, where the attacker records a sequence of packets off of
         the wire and plays them back to the party which that originally
         received them.
      o  Packet insertion, where the attacker forges a packet with some
         chosen set of properties and injects it into the network.
      o  Packet deletion, where the attacker remove removes a packet from the
         wire.
      o  Packet modification, where the attacker removes a packet from
         the wire, modifies it, and re-injects reinjects it into the network.
      o  Man in the Middle  Man-in-the-middle (MITM) attacks, where the attacker subverts
         the communication stream in order to pose as the sender to
         receiver and the receiver to the sender.
      o  Denial of Service Attacks,  Denial-of-service (DoS) attacks, where the attacker sends large
         amounts of legitimate traffic to a destination to overwhelm it.

   IPv6 packets can be protected from eavesdropping, replay, packet
   insertion, packet modification, and man in the middle MITM attacks by use of the
   "Security Architecture for the Internet Protocol" [RFC4301].  In
   addition, upper-layer protocols such as TLS Transport Layer Security
   (TLS) or SSH Secure Shell (SSH) can be used to protect the application application-
   layer traffic running on top of IPv6.

   There is not any mechanism to protect against "denial of service
   attacks". DoS attacks.  Defending
   against these type of attacks is outside the scope of this
   specification.

   IPv6 addresses are significantly larger than IPv4 address addresses making it
   much harder to scan the address space across the Internet and even on
   a single network link (e.g., Local Area Network).  See [RFC7707] for
   more information.

   IPv6 addresses of nodes are expected to be more visible on the
   Internet as compared with IPv4 since the use of address translation
   technology is reduced.  This creates some additional privacy issues
   such as making it easier to distinguish endpoints.  See [RFC7721] for
   more information.

   The design of IPv6 extension headers header architecture, while adding a lot
   of flexibility, also creates new security challenges.  As noted
   below, issues relating to the fragment Fragment extension header have been
   resolved, but it's clear that for any new extension header designed
   in the future, the security implications need to be examined
   throughly,
   thoroughly, and this needs to include how the new extension header
   works with existing extension headers.  See [RFC7045] for more
   information.

   This version of the IPv6 specification resolves a number of security
   issues that were found with the previous version [RFC2460] of the
   IPv6 specification.  These include:

      o  Revised the text to handle the case of fragments that are whole
         datagrams (i.e., both the Fragment Offset field and the M flag
         are zero).  If received received, they should be processed as a
         reassembled packet.  Any other fragments that match should be
         processed independently.  The Fragment creation process was
         modified to not create whole datagram fragments (Fragment
         Offset field and the M flag are zero).  See [RFC6946] and
         [RFC8021] for more information.

      o  Removed the paragraph in Section 5 that required including a
         Fragment header to outgoing packets if an ICMP Packet Too Big
         message reporting a Next-Hop MTU is less than 1280.  See
         [RFC6946] for more information.

      o  Changed the text to require that IPv6 nodes must not create
         overlapping fragments.  Also, when reassembling an IPv6
         datagram, if one or more of its constituent fragments is
         determined to be an overlapping fragment, the entire datagram
         (and any constituent fragments) must be silently discarded.
         Includes clarification that no ICMP error message should be
         sent if overlapping fragments are received.  See [RFC5722] for
         more information.

      0

      o  Revised the text to require that all headers through the first
         Upper-Layer Header
         upper-layer header are in the first fragment.  See [RFC6946]
         for more information.

      o  Removed the paragraph in Section 5 that required including a
         fragment header to outgoing packets if a ICMP Packet Too Big
         message reporting a Next-Hop MTU less than 1280.  See [RFC7112]
         for more information.

      o  Incorporated the updates from [RFC5095] and [RFC5871] to remove
         the description of the RH0 Routing Header, Header type 0 (RH0), that the
         allocations guidelines for routing Routing headers are specified in RFC5871, RFC
         5871, and removed RH0 Routing Header from the list of required extension
         headers.

   Security issues relating to other parts of IPv6 including addressing,
   ICMPv6, Path MTU Discovery, etc., are discussed in the appropriate
   specifications.

11.  Acknowledgments

   The authors gratefully acknowledge the many helpful suggestions of
   the members of the IPng working group, the End-to-End Protocols
   research group, and the Internet Community At Large.

   The authors would also like to acknowledge the authors of the
   updating RFCs that were incorporated in this version of the document
   to move the IPv6 specification to Internet Standard.  They are Joe
   Abley, Shane Amante, Jari Arkko, Manav Bhatia, Ronald P.  Bonica,
   Scott Bradner, Brian Carpenter, P.F.  Chimento, Marshall Eubanks,
   Fernando Gont, James Hoagland, Sheng Jiang, Erik Kline, Suresh
   Krishnan, Vishwas Manral, George Neville-Neil, Jarno Rajahalme, Pekka
   Savola, Magnus Westerlund, and James Woodyatt.

12.  References

12.1.

11.1.  Normative References

   [RFC0791]

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <http://www.rfc-editor.org/info/rfc791>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <http://www.rfc-editor.org/info/rfc2474>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <http://www.rfc-editor.org/info/rfc3168>.

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

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

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

12.2.

11.2.  Informative References

   [Err2541]  RFC Errata, Erratum ID 2541, RFC 2460.

   [Err4279]  RFC Errata, Erratum ID 4279, RFC 2460.

   [Err4657]  RFC Errata, Erratum ID 4657, RFC 2460.

   [Err4662]  RFC Errata, Erratum ID 4662, RFC 2460.

   [IANA-6P]  IANA, "Internet Protocol Version 6 (IPv6) Parameters",
              <https://www.iana.org/assignments/ipv6-parameters/
              ipv6-parameters.xhtml>.
              <https://www.iana.org/assignments/ipv6-parameters>.

   [IANA-EH]  IANA, "IPv6 Extension Header Types",
              <https://www.iana.org/assignments/ipv6-parameters/ipv6-
              parameters.xhtml#extension-header>.

   [IANA-MI]  "Structure of Management Information (SMI) Numbers (MIB
              Module Registrations)", < http://www.iana.org/assignments/
              smi-numbers/smi-numbers.xhtml>.
              <https://www.iana.org/assignments/ipv6-parameters>.

   [IANA-NI]  IANA, "ONC RPC Network Identifiers (netids)",
              <http://www.iana.org/assignments/rpc-netids/
              rpc-netids.xhtml>.
              <https://www.iana.org/assignments/rpc-netids>.

   [IANA-NL]  IANA, "Network Layer Protocol Identifiers (NLPIDs) of
              Interest",
              <http://www.iana.org/assignments/nlpids/nlpids.xhtml>.

   [IANA-NS]  "Technical requirements for authoritative name servers",
              <https://www.iana.org/help/nameserver-requirements>. <https://www.iana.org/assignments/nlpids>.

   [IANA-PN]  "Assigned Internet Protocol  IANA, "Protocol Numbers",
              <https://www.iana.org/assignments/protocol-numbers/
              protocol-numbers.xhtml>.
              <https://www.iana.org/assignments/protocol-numbers>.

   [IANA-PR]  IANA, "Protocol Registries", <https://www.iana.org/protocols>. <https://www.iana.org/
              protocols>.

   [IANA-RH]  "IANA Routing Types Parameter Registry",
              <https://www.iana.org/assignments/ipv6-parameters/
              ipv6-parameters.xhtml#ipv6-parameters-3>.  IANA, "Routing Types", <https://www.iana.org/assignments/
              ipv6-parameters>.

   [RFC1661]  Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
              STD 51, RFC 1661, DOI 10.17487/RFC1661, July 1994,
              <http://www.rfc-editor.org/info/rfc1661>.

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
              1996, <http://www.rfc-editor.org/info/rfc1981>.

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

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <http://www.rfc-editor.org/info/rfc4301>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <http://www.rfc-editor.org/info/rfc4302>.

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

   [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,
              <http://www.rfc-editor.org/info/rfc5095>.

   [RFC5722]  Krishnan, S., "Handling of Overlapping IPv6 Fragments",
              RFC 5722, DOI 10.17487/RFC5722, December 2009,
              <http://www.rfc-editor.org/info/rfc5722>.

   [RFC5871]  Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
              the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871,
              May 2010, <http://www.rfc-editor.org/info/rfc5871>.

   [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
              M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
              RFC 6564, DOI 10.17487/RFC6564, April 2012,
              <http://www.rfc-editor.org/info/rfc6564>.

   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, DOI 10.17487/RFC6936, April 2013,
              <http://www.rfc-editor.org/info/rfc6936>.

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

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

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

   [RFC7707]  Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
              <http://www.rfc-editor.org/info/rfc7707>.

   [RFC7721]  Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              RFC 7721, DOI 10.17487/RFC7721, March 2016,
              <http://www.rfc-editor.org/info/rfc7721>.

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

   [RFC8021]  Gont, F., Liu, W., and T. Anderson, "Generation of IPv6
              Atomic Fragments Considered Harmful", RFC 8021,
              DOI 10.17487/RFC8021, January 2017,
              <http://www.rfc-editor.org/info/rfc8021>.

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

Appendix A.  Formatting Guidelines for Options

   This appendix gives some advice on how to lay out the fields when
   designing new options to be used in the Hop-by-Hop Options header or
   the Destination Options header, as described in section Section 4.2.  These
   guidelines are based on the following assumptions:

      o  One desirable feature is that any multi-octet fields within the
         Option Data area of an option be aligned on their natural
         boundaries, i.e., fields of width n octets should be placed at
         an integer multiple of n octets from the start of the Hop-by-
         Hop
         Hop-by-Hop or Destination Options header, for n = 1, 2, 4, or
         8.

      o  Another desirable feature is that the Hop-by-Hop or Destination
         Options header take up as little space as possible, subject to
         the requirement that the header be an integer multiple of 8
         octets long.

      o  It may be assumed that, when either of the option-bearing
         headers are present, they carry a very small number of options,
         usually only one.

   These assumptions suggest the following approach to laying out the
   fields of an option: order the fields from smallest to largest, with
   no interior padding, then derive the alignment requirement for the
   entire option based on the alignment requirement of the largest field
   (up to a maximum alignment of 8 octets).  This approach is
   illustrated in the following examples:

   Example 1

   If an option X required two data fields, one of length 8 octets and
   one of length 4 octets, it would be laid out as follows:

                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   | Option Type=X |Opt Data Len=12|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                         8-octet field                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Its alignment requirement is 8n+2, to ensure that the 8-octet field
   starts at a multiple-of-8 offset from the start of the enclosing
   header.  A complete Hop-by-Hop or Destination Options header
   containing this one option would look as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                         8-octet field                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Example 2

   If an option Y required three data fields, one of length 4 octets,
   one of length 2 octets, and one of length 1 octet, it would be laid
   out as follows:

                                                   +-+-+-+-+-+-+-+-+
                                                   | Option Type=Y |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Opt Data Len=7 | 1-octet field |         2-octet field         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Its alignment requirement is 4n+3, to ensure that the 4-octet field
   starts at a multiple-of-4 offset from the start of the enclosing
   header.  A complete Hop-by-Hop or Destination Options header
   containing this one option would look as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Opt Data Len=7 | 1-octet field |         2-octet field         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | PadN Option=1 |Opt Data Len=2 |       0       |       0       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Example 3

   A Hop-by-Hop or Destination Options header containing both options X
   and Y from Examples 1 and 2 would have one of the two following
   formats, depending on which option appeared first:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=3 | Option Type=X |Opt Data Len=12|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                         8-octet field                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | PadN Option=1 |Opt Data Len=1 |       0       | Option Type=Y |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Opt Data Len=7 | 1-octet field |         2-octet field         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | PadN Option=1 |Opt Data Len=2 |       0       |       0       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=3 | Pad1 Option=0 | Option Type=Y |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Opt Data Len=7 | 1-octet field |         2-octet field         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | PadN Option=1 |Opt Data Len=4 |       0       |       0       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       0       |       0       | Option Type=X |Opt Data Len=12|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         4-octet field                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                         8-octet field                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Appendix B.  Changes Since RFC2460 RFC 2460

   This memo has the following changes from RFC2460. RFC 2460.

   o  Removed IP Next Generation from the Abstract.

   o  Added text in Section 1 that the Data Transmission Order data transmission order is the
      same as IPv4 as defined in RFC791. RFC 791.

   o  Clarified the text in Section 3 about decrementing the hop limit. Hop Limit.

   o  Clarification  Clarified that extension headers (except for the hop-by-hop
      options Hop-by-Hop
      Options header) are not processed, inserted, or deleted by any
      node along a packet's delivery path.

   o  Changed requirement for the Hop-by-Hop Options header to a may, "may",
      and added a note to indicate what is expected regarding the Hop-
      by-Hop
      Hop-by-Hop Options header.

   o  Added a paragraph to Section 4 to clarify how Extension Headers extension headers
      are numbered and which are upper-layer headers.

   o  Add  Added a reference to the end of Section 4 to IPv6 the "IPv6 Extension
      Header Types" IANA registry.

   o  Incorporate  Incorporated the updates from RFC5095 RFCs 5095 and RFC5871 5871 to remove the
      description of the RH0 Routing Header, RH0, that the allocations guidelines for routing
      headers are specified in RFC5871, RFC 5871, and removed RH0 Routing Header from the list
      of required extension headers.

   o  Revised Section 4.5 on IPv6 Fragmentation fragmentation based on updates from
      RFC5722, RFC6946 RFC7112,
      RFCs 5722, 6946, 7112, and RFC8021. 8021.  This include: includes:

      -  Revised the text to handle the case of fragments that are whole
         datagrams (i.e., both the Fragment Offset field and the M flag
         are zero).  If received received, they should be processed as a
         reassembled packet.  Any other fragments that match should be
         processed independently.  The revised Fragment creation process
         was modified to not create whole datagram fragments (Fragment
         Offset field and the M flag are zero).

      -  Changed the text to require that IPv6 nodes must not create
         overlapping fragments.  Also, when reassembling an IPv6
         datagram, if one or more its constituent fragments is
         determined to be an overlapping fragment, the entire datagram
         (and any constituent fragments) must be silently discarded.
         Includes a clarification that no ICMP error message should be
         sent if overlapping fragments are received.

      -  Revised the text to require that all headers through the first
         Upper-Layer Header header are in the first fragment.  This changed the
         text describing how packets are fragmented and reassembled, reassembled and
         added a new error case.

      -  Added text to the Fragment Header header process on handling exact
         duplicate fragments.

      -  Updated the Fragmentation header text to correct the inclusion
         of AH an Authentication Header (AH) and note no next header noted No Next Header case.

      -  Change  Changed terminology in the Fragment header section from
         "Unfragmentable Headers" to "Per-Fragment Headers". headers".

      -  Removed the paragraph in Section 5 that required including a
         fragment
         Fragment header to outgoing packets if a an ICMP Packet Too Big
         message reporting reports a Next-Hop MTU less than 1280.

      -  Changed the text to clarify MTU restriction and 8-byte
         restrictions, and noting noted the restriction on headers in the first
         fragment.

   o  In Section 4.5 4.5, added clarification noting that some fields in the
      IPv6 header may also vary across the fragments being reassembled reassembled,
      and that other specifications may provide additional instructions
      for how they should be reassembled.  For  See, for example, Section 5.3
      of [RFC3168].

   o  Incorporated the update from RFC6564 RFC 6564 to add a new Section 4.8
      that describes recommendations for defining new Extension extension headers
      and options.

   o  Added text to Section 5 to define "IPv6 minimum link MTU".

   o  Simplify  Simplified the text in Section 6 about Flow Labels and remove removed
      what was Appendix A, A ("Semantics and instead point Usage of the Flow Label
      Field"); instead, pointed to the current specifications of the
      IPv6 Flow Label field as defined in [RFC6437] and the Traffic Class as defined field in
      [RFC2474] and [RFC3168].

   o  Incorporate  Incorporated the update in made by RFC6935 "UDP RFC 6935 ("IPv6 and UDP Checksums
      for Tunneled Packets" Packets") in Section 8.  Added an exception to the
      default
      behaviour behavior for the handling of handling UDP packets with zero
      checksums for tunnels.

   o  Add  Added instruction to Section 9 9, "IANA Considerations" Considerations", to change
      references to RFC2460 RFC 2460 to this document document.

   o  Revised and expanded Section 10 10, "Security Considerations".

   o  Add  Added a paragraph to the acknowledgement Acknowledgments section acknowledging the
      authors of the updating documents documents.

   o  Update  Updated references to current versions and assign assigned references to
      normative and informative.

   o  Changes  Made changes to resolve the open Errata errata on RFC2460. RFC 2460.  These are:

         Errata ID: 2541:

         Erratum ID 2541 [Err2541]: This errata erratum notes that RFC2460 RFC 2460
         didn't update
         RFC2205 RFC 2205 when the length of the Flow Label flow label was
         changed from 24 to 20 bits from RFC1883. RFC 1883.  This issue was
         resolved in RFC6437 RFC 6437 where the Flow Label flow label is defined.  This draft
         specification now references
         RFC6437. RFC 6437.  No change is required.

         Errata ID: 4279:

         Erratum ID 4279 [Err4279]: This errata erratum noted that the
         specification doesn't handle the case of a forwarding node
         receiving a packet with a zero Hop Limit.  This is fixed in
         Section 3 of this
         draft.

         Errata ID: 2843: This errata is marked rejected.  No change was
         made.

B.1.  Change History Since RFC2460

   NOTE TO RFC EDITOR: Please remove this subsection prior to RFC
   Publication specification.

         Erratum ID 4657 [Err4657]: This section describes change history made in each Internet Draft
   that went into producing this version.  The numbers identify the
   Internet-Draft version in which the change was made.

   Working Group Internet Drafts

      13)  Added link to reference to RFC6564 in Section 4.8.

      13)  Added erratum proposed text to Section 5 to define "IPv6 minimum link MTU".

      13)  Editorial changes.

      12)  Editorial changes (remove old duplicate paragraph).

      11)  In Section 4.5 added clarification noting that some fields in
           the IPv6 header may also vary across the fragments being
           reassembled and that other specifications may provide
           additional instructions for how they should be reassembled.
           For example, Section 5.3 of [RFC3168].

      11)  In Section 4 restructured text including separated behaviors
           of
         extension headers and the hop-by-hop option header,
           removed "examine" from first paragraph about extension
           headers, and removed reference to RFC7045 because "examine"
           was removed (RFC7045 is referenced in Security
           Considerations).  Also removed "including the source and
           destination nodes" from paragraph about the hop-by-hop
           options header.

      11)  Revised Section 4.8 to make it closer to the update done must never be inserted by
           RFC6554 that updated it and reordered the paragraphs.

      11)  Reordered items in Appendix B "Changes Since RFC2460" to
           match any node other than
         the order source of the document.

      11)  Editorial changes.

      10)  Revised and expanded Security Consideration Section based on
           IESG Discuss comments.

      10)  Editorial changes.

      09)  Based on results of IETF last call, changed text packet.  This was resolved in Section 4
           to add clarification 4,
         "IPv6 Extension Headers".

         Erratum ID 4662 [Err4662]: This erratum proposed text that
         extension headers headers, with one exception, are not examined,
         processed, modified, inserted, or deleted by any node along a
         packet's delivery path.

      09)  Changed reference from draft-ietf-6man-rfc4291bis to RFC4291
           because the bis draft won't be advanced as the same time.

      09)  Revised "Changes since RFC2460" Section to have a summary of
           changes since RFC2460 and a separate subsection with a change
           history of each Internet Draft.  This subsection will be
           removed when the RFC is published.

      09)  Editorial changes.

      08)  Revised header insertion text in Section 4 based on the
           results of w.g. survey that concluded to describe the
           problems with header insertion.

      08)  Editorial changes.

      07)  Expanded Security Considerations section to include both
           IPsec and encryption at higher levels in the protocol stack
           as ways to mitigate IP level security issues.

      07)  Added paragraph to Section 4 to clarify how Extension Headers
           are numbered and which are upper-layer headers.

      07)  Moved the text regarding network duplicated fragments to the
           received fragment error section.

      07)  Added clarification that no ICMP error message should be sent
           if overlapping fragments are received.

      07)  Revised the text in Section 4.8 regarding new hop-by-hop
           options and new Extension headers to be closer to the -05
           version.

      07)  Added additional registries to the IANA Considerations
           section that IANA needs to update.

      07)  Editorial changes.

      06)  Added the Routing Header to the list required extension
           headers that a full implementation includes.

      06)  Moved the text in Section 4.5 regarding the handling of
           received overlapping fragments to the list of error
           conditions

      06)  Rewrote the text in Section 4.8 "Defining New Extension
           Headers and Options" to be clearer and remove redundant text.

      06)  Editorial changes.

      05)  Changed requirement for the Hop-by-Hop Options header from a
           should to a may, and added a note to indicate what is
           expected.

      05)  Corrected reference to point to draft-ietf-6man-rfc4291bis
           instead of draft-hinden-6man-rfc4291bis.

      05)  Change to text regarding not inserting extension headers to
           cite using encapsulation as an example.

      04)  Changed text discussing Fragment ID selection to refer to
           RFC7739 for example algorithms.

      04)  Editorial changes.

      03)  Clarified the text about decrementing the hop limit.

      03)  Removed IP Next Generation from the Abstract.

      03)  Add reference to the end of Section 4 to IPv6 Extension
           Header IANA registry.

      03)  Editorial changes.

      02)  Added text to Section 4.8 "Defining New Extension Headers and
           Options" clarifying why no new hop by hop extension headers
           should be defined.

      02)  Added text to Fragment Header process on handling exact
           duplicate fragments.

      02)  Editorial changes.

      01)  Added text that Extension headers must never be inserted by
           any node other than the source of the packet.

      01)  Change "must" to "should" in Section 4.3 on the Hop-by-Hop
           header.

      01)  Added text that the Data Transmission Order is the same as
           IPv4 as defined in RFC791.

      01)  Updated the Fragmentation header text to correct the
           inclusion of AH and note no next header case.

      01)  Change terminology in Fragment header section from
           "Unfragmentable Headers" to "Per-Fragment Headers".

      01)  Removed paragraph in Section 5 that required including a
           fragment header to outgoing packets if a ICMP Packet Too Big
           message reporting a Next-Hop MTU less than 1280.  This is
           based on the update in RFC8021.

      01)  Changed to Fragmentation Header section to clarify MTU
           restriction and 8-byte restrictions, and noting the
           restriction on headers in first fragment.

      01)  Editorial changes.

      00)  Add instruction to the IANA to change references to RFC2460
           to this document

      00)  Add a paragraph to the acknowledgement section acknowledging
           the authors of the updating documents

      00)  Remove old paragraph in Section 4 that should have been
           removed when incorporating the update from RFC7045.

      00)  Editorial changes.

   Individual Internet Drafts
      07)  Update references to current versions and assign references
           to normative and informative.

      07)  Editorial changes.

      06)  The purpose of this draft is to incorporate the updates
           dealing with Extension headers as defined in RFC6564,
           RFC7045, and RFC7112.  The changes include:

              RFC6564: Added new Section 4.8 that describe
              recommendations for defining new Extension headers and
              options

              RFC7045: The changes were to add a reference to RFC7045,
              change the requirement for processing the hop-by-hop
              option to a should, and added a note that due to
              performance restrictions some nodes won't process the Hop-
              by-Hop Option header.

              RFC7112: The changes were to revise the Fragmentation
              Section (Section 4.5) to require that all headers through
              the first Upper-Layer Header are in the first fragment.
              This changed the text describing how packets are
              fragmented and reassembled and added a new error case.

      06)  Editorial changes.

      05)  The purpose of this draft is to incorporate the updates
           dealing with fragmentation as defined in RFC5722 and RFC6946.
           Note: The issue relating to the handling of exact duplicate
           fragments identified on the mailing list is left open.

      05)  Fix text in the end of Section 4 to correct the number of
           extension headers defined in this document.

      05)  Editorial changes.

      04)  The purpose of this draft is to update the document to
           incorporate the update made by RFC6935 "UDP Checksums for
           Tunneled Packets".

      04)  Remove Routing (Type 0) header from the list of required
           extension headers.

      04)  Editorial changes.

      03)  The purpose of this draft is to update the document for the
           deprecation of the RH0 Routing Header as specified in RFC5095
           and the allocations guidelines for routing headers as
           specified in RFC5871.  Both of these RFCs updated RFC2460.

      02)  The purpose of this version of the draft is to update the
           document to resolve the open Errata on RFC2460.

              Errata ID: 2541: This errata notes that RFC2460 didn't
              update RFC2205 when the length of the Flow Label was
              changed from 24 to 20 bits from RFC1883.  This issue was resolved in RFC6437 where the Flow Label is defined.  This
              draft now references RFC6437.  No change is required.

              Errata ID: 4279: This errata noted that the specification
              doesn't handle the case of a forwarding node receiving a
              packet with a zero Hop Limit.  This is fixed in Section 3
              of this draft.  Note: No change was made regarding host
              behaviour.

              Errata ID: 4, "IPv6
         Extension Headers".

         Erratum ID 2843: This errata erratum is marked rejected. "Rejected".  No change is required.

      02)  Editorial changes to the Flow Label and Traffic Class text.

      01)
         was made.

Acknowledgments

   The purpose authors gratefully acknowledge the many helpful suggestions of this version
   the members of the draft is to update IPng Working Group, the
           document to point End-to-End Protocols
   research group, and the Internet community at large.

   The authors would also like to acknowledge the current specifications authors of the IPv6
           Flow Label field as defined in [RFC6437] and the Traffic
           Class as defined
   updating RFCs that were incorporated in [RFC2474] and [RFC3168].

      00)  The purpose of this version is to establish a baseline from
           RFC2460.  The only intended changes are formatting (XML is
           slightly different from .nroff), differences between an RFC
           and Internet Draft, fixing a few ID Nits, and updates document to move the
           authors information.  There should not be any content changes
   IPv6 specification to the specification. Internet Standard.  They are Joe Abley, Shane
   Amante, Jari Arkko, Manav Bhatia, Ronald P. Bonica, Scott Bradner,
   Brian Carpenter, P.F. Chimento, Marshall Eubanks, Fernando Gont,
   James Hoagland, Sheng Jiang, Erik Kline, Suresh Krishnan, Vishwas
   Manral, George Neville-Neil, Jarno Rajahalme, Pekka Savola, Magnus
   Westerlund, and James Woodyatt.

Authors' Addresses

   Stephen E. Deering
   Retired
   Vancouver, British Columbia
   Canada

   Robert M. Hinden
   Check Point Software
   959 Skyway Road
   San Carlos, CA  94070
   USA
   United States of America

   Email: bob.hinden@gmail.com