[ih] order of source and destination address in IP header

[Craig Partridge]

In message <4244C5D8.8050108 at reed.com>, "David P. Reed" writes:

>Good point.   However, you can do fragmentation/reassembly without 
>ambiguity without the source host address... remember that source 
>host/dest host still doesn't provide an unambiguous reassembly (there 
>may be many simultaneous connections between source and dest at the host 
>level.)

That assumes the source doesn't manage identifiers to peers.  If the source
does manage identifiers, then reassembly is unambiguous.  (The problem is
that if the source address is not present, then even if the source uses
unique IDs, there's a chance its ID space will overlap with another
senders).

It may not be ideal, and is quasi-non-deterministic, but if you 
>have a crypto-based authenticator (SHA-1, e.g.) instead of a checksum, 
>you can just deliver all fragments to every destination socket, and then 
>try combining fragments until the authenticator checks correctly...   
>not proposing that for lots of reasons, but just to demonstrate that 
>"source host address" is not the critical element needed for 
>frag/reassembly.

I didn't assert it was -- cf my comment re: a nonce in the first note.

Craig