[6man] #11 (rfc2460bis): HBH header handling

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#11: HBH header handling

 2460bis relaxes the must to a should. And incorporates a paragraph from
 7045 giving performance considerations.
 The use of a _should_ process combined with a _may_ drop is not elegant.
 The second paragraph can also be read as a licence to drop.

 After having thought about the text in draft-ietf-6man-hbh-header-
 handling, I propose the following instead:

 OLD:
   The exception referred to in the preceding paragraph is the Hop-by-
   Hop Options header, which carries information that should 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.

   It should be noted that due to performance restrictions nodes may
   ignore the Hop-by-Hop Option header, drop packets containing a hop-
   by-hop option header, or assign packets containing a hop-by-hop
   option header to a slow processing path.  Designers planning to use a
   hop-by-hop option need to be aware of this likely behaviour.

 NEW:
   The exception referred to in the preceding paragraph is the Hop-by-
   Hop Options header, which carries information that may be examined
   and processed by nodes 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.

   NOTE: While RFC2460 required that all nodes must process the Hop-by-
   Hop Options header, it is now expected that nodes only process the
   Hop-by-Hop Options header if explicitly configured to do so.


 In short replace the should we a may, making HBH options header purely
 optional. Note that section 4.8 in 2460bis already uses a may.
 I also suggest we remove the 7045 paragraph on performance considerations,
 that's highly subjective.

 3. Section 4.3 HBH
 OLD:
  The Hop-by-Hop Options header is used to carry optional information
   that should 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:

 NEW:
   The Hop-by-Hop Options header is used to carry optional information
   that may 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:

 Same change as above.

-- 
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 Reporter:  [e-mail]  |      Owner:
     Type:  defect                |     Status:  new
 Priority:  major                 |  Milestone:
Component:  rfc2460bis            |    Version:
 Severity:  In WG Last Call       |   Keywords:
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Ticket URL: <https://tools.ietf.org/wg/6man/trac/ticket/11>
6man <https://tools.ietf.org/wg/6man/>