Notes on IP fragmentation: ! The source host or any router in the path between source and destination can fragment an IP packet. ! Reassembly of the packet is done at the destination host since the network treats each fragment as independent unit ! There is no guarantee on the path these fragments will be taking ! The host or the router that fragments a packet must change the values of the 1. Flag field 2. Fragment offset field 3. Total length field All other fields (including the identification field) remain the same. Of course the header checksum need to be calculated for every fragment ! A fragmented IP packet may be fragmented (several times) itself if it passes a network with a smaller "MTU" ! All fragments (and fragments of a fragment) will have the same identification field, which is the same as that used in the original IP packet. The identification number allows the destination to reassemble the packet. Identification numbers for different packets (from the same source) are different
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