I know that UDP is an unreliable protocol where things can arrive out of order, fail to arrive completely, etc.
I'm also aware that when using UDP for something like traceroute, packets that arrive at routers with TTL=1 and packets that arrive at end hosts destined for non-open ports generate ICMP error messages which are transmitted back to the sender.
My question is - does the sender have any way of knowing if a standard packet was dropped? I know the protocol is unreliable, but is any kind of "ack" sent back by the receiver in the UDP protocol whatsoever to allow the sender to know about the dropped packet?
This is a straight up protocol question for basic UDP, I don't want to know about what I "can do". I've read through a few things now and while I'm basically 100% sure the answer is no, you can't tell, I read a couple things which made me uneasy about it.