On Tue, 11 May 2004 13:44:16 +0900
Masataka Ohta <mohta(_at_)necom830(_dot_)hpcl(_dot_)titech(_dot_)ac(_dot_)jp>
wrote:
Mark Smith;
I'm keen to
find out if my understanding of PMTUD purpose and operation
is incorrect.
Read the RFC or my quotation of it.
Ok, well, I haven't got far into it, and it seems to correspond
to what I've understood :
"2. Protocol overview
In this memo, we describe a technique for using the Don't
Fragment (DF) bit in the IP header to dynamically discover the
PMTU of a path. The basic idea is that a source host initially
assumes that the PMTU of a path is the (known) MTU of its first
hop, and sends all datagrams on that path with the DF bit set.
If any of the datagrams are too large to be forwarded without
fragmentation by some router along the path, that router will
discard them and return ICMP Destination Unreachable messages
with a code meaning "fragmentation needed and DF set" [7].
Upon receipt of such a message (henceforth called a "Datagram
Too Big" message), the source host reduces its assumed PMTU for
the path."
I'll continue reading, although I'm happy enough that my original
understanding was correct.
Regards,
Mark.
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