On 9/26/02, Lloyd Wood wrote:
On Wed, 25 Sep 2002, Fred Baker wrote:
At 01:12 PM 9/25/2002 +0100, Lloyd Wood wrote:
A datagram is self-describing; full source and
destination. A fragment (IPv4 fragment) may not be.
you sure? take a GOOD look at RFC 791... It is
completely self-describing in terms of getting itself
there and where it belongs in the reassembled datagram.
If the other bits and pieces don't arrive, there is
another matter, but it is at that point a host issue,
not a forwarding issue.
I'm not sure that following fragments relying on a bit in
another fragment saying 'following fragment' is truly
self-describing.
(Not having port nos in following fragments would only be
a host issue if routers and firewalls never peeked at
ports en route.)
So, as originally proposed an IP fragment is a fully
self-routed L3 datagram.
However, in the de facto world of merged L3/L4 routing
(with NATs, load balancers, etc.) it is dependent on state
information and hence is not a datagram.
However, the term was applied before L3/L4 "routing" came
into existence. So the term 'datagram' was correct. And of
course nobody would change the term ex post facto. This is
why these terms are indeed fluid and nebulous.