Q18

The fragmentation of an $\text{IP}$ datagram is performed only at the source of the datagram

The fragmentation of an $\text{IP}$ datagram is performed at any $\text{IP}$ router which finds that the size of the datagram to be transmitted exceeds the $\text{MTU}$

The reassembly of fragments is performed only at the destination of the datagram

The reassembly of fragments is performed at all intermediate routers along the path from the source to the destination