In a message from Steven Bellovin, sie said...
> 
> The spec permits one IPid sequence per <src,dst,protocol> triple,
> since those parameters are used in matching fragments.  The downside
> is implementation complexity; it won't break anything anywhere on
> the net.  You also don't need to consume IPid space -- or at least,
> you don't need to worry about preventing duplicates -- on packets
> that have  set.

Without wanting to advocate change for the sake of change, how much
sense does it make to go a step further and use a constant value in
the ID field (say 0?) for all "do not fragment" packets ?

Darren