(This is IPv4)
Network Layer
the PDU created by IP, and is IP header + Payload
A packet needs to know the route, or path, to reach the final destination because not every Network is directly connected. A packet can take one of many routes to a different network. A packet should take the most efficient route among the different networks between a packet’s source and destination.
Stale
A packet is stale when it has been delay for so long that the timeout has been reached.