[tptacek]

You could design a network protocol that fragments by capturing a variable number of bytes from the next header, and ICMP already does something like that.

(None of this would fix the real problem with fragmentation, which is that you can't efficiently segment out a large frame without having some kind of reliability layer).

[raggi]

If I was revisiting, I'd probably eradicate the layer and pick a fixed number of flow types with distinct headers and state machines. The layers were a reasonable choice given the understanding of the time, but in hindsight I think you can make a strong case they're cut at the wrong places.