Both the IPv4 and IPv6 headers contain the source address field. What are the reasons for including this field?
Is it for to trace which who sent this packet if it get's lost?
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The source address fields is required for the destination to know where a packet came from and what connection is belongs to (in combination with the transport-layer port numbers).
Additionally, the source address field is used to report network problems to (via ICMP). However, it is not normally used to report packet loss (due to checksum failure or congestion) - a lost packet either stays lost or it is automatically resent/recreated by the transport layer protocol when acknowledgment is missing.