The Internet Protocol: IPV4 Packet Fragmentation & Reassembly

Why Fragmentation?

Although IPv4 packets can be as big as 64kB, few data link layer technologies can send a 64 KB IPv4 packet inside a frame.

Furthermore, as in the figure below, if the host on the FDDI network abides by its own data link layer’s maximum packet size of $4478$ bytes, the resulting data link layer frame would violate the maximum frame size of the Ethernet between routers R1 and R2. Hence, a host may end up sending a packet that is too large for a data link layer technology used by (an) intermediate router(s).