I'm puzzled by something in RFC1981, which discusses PMTUD and IPv6. It contains these two paragraphs towards the end of Section 4:
A node MUST NOT reduce its estimate of the Path MTU below the IPv6
minimum link MTU.
Note: A node may receive a Packet Too Big message reporting a
next-hop MTU that is less than the IPv6 minimum link MTU. In that
case, the node is not required to reduce the size of subsequent
packets sent on the path to less than the IPv6 minimun link MTU,
but rather must include a Fragment header in those packets [IPv6-
SPEC].
What does that mean - "insert a Fragment header"? And it may not be
*required* to reduce the size of subsequent packets, but does that mean
it *can* if it wants to? And isn't inserting a whole new header a bit
counterproductive if someone is telling your your packets are too big
already? All in all I have this strong feeling I'm missing something
obvious. Any clues gratefully received.
Regards, K.
PS: [IPv6-SPEC]" refers to RFC1883, "Internet Protocol, Version 6 (IPv6)
Specification". I've read it again, especially the section on the
Fragment header, but am none the wiser.
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