IP Packet Fragmentation

IP packets may be up to about 65000 octets long. Since the networks over which IP operates often have a limited packet size, the IP protocol will break large packets into smaller fragments, and route each of them separately over the Internet.

Fragments may be fragmented again if they reach a network with a smaller MTU (Maximum Transfer Unit).

All fragments are eventually re-assembled only at the target machine. This machine needs to collect the set of fragments until all of them arrive, and them re-assemble the original packet. it may also discard the fragments if it encounters any problem (e.g. full queues).