Wednesday, September 25, 2002, 2:12:13 PM, you wrote:
the following distinction : "a datagram is the data unit before
fragmentation" ; "a packet is a piece of a fragmented datagram".
A fragment of a datagram is itself a datagram; after you re-assemble them,
the result is still a datagram.
Yes, I agree, though the definition has - in common habit and use -
quite fuzzy contours. In theory, theory would be like pratice; but in
practice, pratice isn't theory. ;)
A datagram is self-describing; full source and destination. A fragment
(IPv4 fragment) may not be.
Don't be misled by the word fragment: in the IP case, it retains src
and dst info as well. No RFC needs to be read to confirm that ;), a little
that: how could it be routed at layer 3 on an internet, otherwise?
In the fragmentation process a datagram/packet may "lose" in its "self
contained unit" ULP information, like TCP ports, but that's not matter