IPv6の仕様（ホップバイホップオプションヘッダ）

   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,
       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).