What happens if the Don't Fragment (DF) flag is set?

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Multiple Choice

What happens if the Don't Fragment (DF) flag is set?

Explanation:
When the Don't Fragment flag is set, routers are instructed not to break the packet into smaller pieces. If the next link’s MTU can accommodate the whole packet, it passes through unchanged. If the packet is larger than the MTU and fragmentation would be required, the router cannot fragment it due to this flag, so it drops the packet and sends back an ICMP message indicating that fragmentation is needed (and DF was set). This behavior is also why Path MTU Discovery works. In short, the packet is not fragmented by routers; it may be dropped if it would require fragmentation.

When the Don't Fragment flag is set, routers are instructed not to break the packet into smaller pieces. If the next link’s MTU can accommodate the whole packet, it passes through unchanged. If the packet is larger than the MTU and fragmentation would be required, the router cannot fragment it due to this flag, so it drops the packet and sends back an ICMP message indicating that fragmentation is needed (and DF was set). This behavior is also why Path MTU Discovery works. In short, the packet is not fragmented by routers; it may be dropped if it would require fragmentation.

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