The process of dividing an IP datagram into small pieces when they must travel across a network that cannot handle the original datagram size. Each fragment has the same format as a datagram; fields in the IP header specify whether a datagram is a fragment. IP software at the receiving end must reassemble fragments to produce the original datagram. See Identifier, Flags, and Fragment Offset.

Fragmentation is also a designation for a type of munition. It indicates that the munition (or warhead, shell, grenade, whatever) is designed to do damage primarily by ejecting fragments away from the detonation at high speed. These fragments can be part of the munition casing, such as in the original 'pineapple' grenade of World War II, or can be additional objects added to the device as in the modern variant of the hand grenade. Surface-to-air missiles and air-to-air missiles tend towards this type of warhead, since the fragility of their targets means the lethal radius of the warhead is increased significantly over a simple blast warhead (although recent SAMs favor the continuous-rod warhead instead).

In computer disk terminology, fragmentation is the process or condition of files that are composed of more than one extent. Fragmentation of this sort is bad, as it will increase the amount of head motion needed to read the file, and thus slow things down. Poorly optimized operating systems occasionally need to be defragmented to increase performance.

Alternately, in the BSD fast filesystem (also in UFS), a fragment is a block that has been subdivided to hold tail ends of several files that would otherwise each take up an entire block. This kind of fragmentation is a Good Thing.

Just to be confusing, both meanings of fragmentation are used when refering to unix filesystems.

In p2p (peer to peer) networks, fragmentation is a result of a design flaw in the network protocol. It results in seperate segments of the network not being able to communicate with each other, this again results in poor network performance.

The gnutella network is an example of a network that has problems with network fragmentation.

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