I have understood that real networks have routing changes, leading to out-of-order delivered IP packets. Real networks also have frequent packet loss.
However, what I have not understood is why could a perfectly operating network in addition to out-of-order and lost packets deliver packets as duplicates. What could cause delivery of such duplicate packets?
Could spanning tree protocol (STP) before converging on a spanning tree cause duplicate packets?
Note that I don't currently have a network that would frequently duplicate packets, so this is more of a theoretical question than a practical one.