rfc1883.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   contents and semantics of each extension header determine whether or


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   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.

   The exception referred to in the preceding paragraph is the Hop-by-
   Hop Options header, which carries information that must be examined
   and processed by every node along a packet's delivery path, including
   the source and destination nodes.  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.

   If, as a result of processing a header, a 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 2 ("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
           Routing (Type 0)
           Fragment
           Destination Options
           Authentication
           Encapsulating Security Payload

   The first four are specified in this document; the last two are
   specified in [RFC-1826] and [RFC-1827], respectively.








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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 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 [RFC-1827].

           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 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 extensions 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 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.





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4.2  Options

   Two of the currently-defined extension headers -- the Hop-by-Hop
   Options header and the Destination Options header -- carry a variable
   number of type-length-value (TLV) encoded "options", of 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 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
           packets'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 to the
   packet's final destination.  When an Authentication header is present
   in the packet, for any option whose data may change en-route, its
   entire Option Data field must be treated as zero-valued octets when
   computing or verifying the packet's authenticating value.


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      0 - Option Data does not change en-route

      1 - Option Data may change en-route

   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 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 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.


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4.3  Hop-by-Hop Options Header

   The Hop-by-Hop Options header is used to carry optional information
   that must be examined 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, 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 [RFC-1700 et seq.].

   Hdr Ext Len          8-bit unsigned integer.  Length of the
                        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 4.2.

   In addition to the Pad1 and PadN options specified in section 4.2,
   the following hop-by-hop option is defined:

   Jumbo Payload option  (alignment requirement: 4n + 2)

                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |      194      |Opt Data Len=4 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Jumbo Payload Length                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       The Jumbo Payload option is used to send IPv6 packets with
       payloads longer than 65,535 octets.  The Jumbo Payload Length is
       the length of the packet in octets, excluding the IPv6 header but
       including the Hop-by-Hop Options header; it must be greater than
       65,535.  If a packet is received with a Jumbo Payload option
       containing a Jumbo Payload Length less than or equal to 65,535,


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       an ICMP Parameter Problem message, Code 0, should be sent to the
       packet's source, pointing to the high-order octet of the invalid
       Jumbo Payload Length field.

       The Payload Length field in the IPv6 header must be set to zero
       in every packet that carries the Jumbo Payload option.  If a
       packet is received with a valid Jumbo Payload option present and
       a non-zero IPv6 Payload Length field, an ICMP Parameter Problem
       message, Code 0, should be sent to the packet's source, pointing
       to the Option Type field of the Jumbo Payload option.

       The Jumbo Payload option must not be used in a packet that
       carries a Fragment header.  If a Fragment header is encountered
       in a packet that contains a valid Jumbo Payload option, an ICMP
       Parameter Problem message, Code 0, should be sent to the packet's
       source, pointing to the first octet of the Fragment header.

       An implementation that does not support the Jumbo Payload option
       cannot have interfaces to links whose link MTU is greater than
       65,575 (40 octets of IPv6 header plus 65,535 octets of payload).