IP Fragmentation Overview

Fragmentation is the process of segmenting a large IP datagram into several smaller pieces. Fragmentation is required when IP must transmit a large packet through a network that transmits smaller packets, or when the maximum transmission unit (MTU) size of the other network is smaller.

By default, the router does not fragment the packet if the don’t-fragment bit (DF bit) is set in the IP header. You can specify that the router not consider the DF bit before determining whether to fragment a packet.

Note: Lower-layer protocols can also set the MTU value. If MTU values set in lower layers differ from the one set at the IP layer, the router always uses the MTU lower-layer value.