Which device fragments IPv4 packets when necessary?

• A. Routers along the path
• B. End hosts
• C. Switches
• D. DHCP servers

Answer: (A)

Fragmentation in IPv4 happens when a packet is larger than the MTU of the next link. Routers along the path perform this fragmentation when needed, as long as the Don't Fragment flag isn’t set. They split the large packet into smaller fragments that fit the next hop’s MTU, and those fragments are forwarded onward, potentially being fragmented again by subsequent routers until they reach the destination where they’re reassembled. Switches don’t fragment IP packets because they operate at layer 2, and DHCP servers don’t participate in forwarding data in a way that requires IP fragmentation. End hosts can technically fragment if they’re sending packets larger than the path MTU and fragmentation is allowed, but the devices responsible for forward-path fragmentation in normal operation are the routers along the route. Path MTU Discovery helps avoid this by learning the smallest MTU on the path so the sender partitions packets accordingly.