UDP is &#x27;spray and pray&#x27;. If a packet is fragmented (goes out on the wire as more than one IP frame), several things can happen. Frames can jitter (arrive with different timing); they can be reordered (e.g. packets sent 1,2,3 but arrive 2,1,3 or 3,1,2 etc) and a frame can be dropped (e.g. arrive 1,3 or 2,3).<p>UDP has no feedback from the receiver to the source. If a packet is dropped, the IP stack on the receiver will never complain and the IP stack on the sender will never resend. SO the receiver will silently drop the whole packet.<p>Notice it can be hard to tell if a packet is dropped, or is reordered. You receive 2,3 - maybe 1 is still coming but reordered?  So detecting dropped packets is a heuristic, depending on timing.  Various algorithms will use a timer to say when to give up on a packet, or drop a packet if a frame from a subsequent packet is received, or tolerate one frame from a subsequent packet (maybe the last frame of the previous packet was reordered with the first of the next) and so on. But all the work is on the receiver. The sender is not involved.<p>Unless there is some application-layer protocol that notices packets arriving with a gap, and sends something back (that might also not arrive) like &quot;I got packet a,b,d but missed c&quot;. Etc.  Notice the application cannot resend frames; only packets because it is unaware of fragmentation&#x2F;reassembly which happens in the IP stack.