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.
