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DF (Don’t Fragment) and FM (Fragment More) flags are important in IT networking because they are used in the IP (Internet Protocol) header to control the fragmentation of packets when they are sent over a network.
The DF flag is used to indicate whether a packet can be fragmented or not. When the DF flag is set to 0, it means that the packet can be fragmented if necessary. Conversely, when the DF flag is set to 1, it means that the packet should not be fragmented. If a router receives a packet with the DF flag set to 1 and it needs to be fragmented to be transmitted over a network with a smaller Maximum Transmission Unit (MTU), the router will discard the packet and send an ICMP (Internet Control Message Protocol) “Fragmentation Needed” message back to the sender.
The FM flag is used to indicate whether there are more fragments following the current fragment. When the FM flag is set to 0, it means that the current fragment is the last fragment. Conversely, when the FM flag is set to 1, it means that there are more fragments to follow. This allows the receiving host to reassemble the fragments in the correct order.
By using the DF and FM flags, network devices can ensure that packets are properly transmitted across networks with different MTUs and that they can be reassembled correctly at the destination. This helps to optimize network performance and reliability.