What is mean by Fragmented Packet?

Answer 1

Background: everything that is sent over the internet is sent as small messages, known as Internet Protocol (or IP) packets, that are in a common format regardless of the kind of link over which the packet is currently being transmitted.

In version 4 of the Internet Protocol (which is the version that is most widely used today) a packet may be too big for the kind of link over which it is about to be sent. For instance, traditional Ethernet imposes a maximum size for IP packets of 1500 bytes. If a packet that is about to be sent over an Ethernet link is bigger than that, the router which is about to send the packet over that link will fragment the packet. What this means is that the router will split the packet up into smaller messages (known as fragments) that are each small enough to be transmitted over the link. When the fragments arrive at their destination (the computer to which they are being sent), that computer can reassemble the fragments to recover the original message - assuming none of the messages are lost in transit.

IP version 4 also has a "don't fragment" option which tells routers to not fragment packets that have that option set. If this option is set, and the router wants to send the packet over a link for which the packet is too large, the router will not send the packet at all. Instead, the router will send a message back to the sender of the packet that was too large. The sending computer can then respond to this by sending out smaller packets. This is known as "path MTU discovery" because it enables the sending computer to determine the largest packet size that will work for the path between sender and receiver. (MTU stands for maximum transmission unit.)

For best efficiency the sending computer would like to send out packets that are as large as possible, but not so large that any of the packets will be fragmented.

Fragmentation is of dubious value because it slows down routers, and because none of the fragments will be useful to the receiver computer unless all of the fragments arrive there intact. Path MTU discovery is generally considered preferable to fragmentation. However there are problems with Path MTU discovery. One is that many sites (for no good reason) filter the messages that are sent back to the senders when a packet is too large for a link. Another is that path MTU discovery is inefficient for short conversations consisting of just a packet or two in each direction. Yet another problem is that the path between sender and receiver can change during a conversation in a way that renders the old path MTU obsolete.

Internet Protocol version 4 (IPv4) is in the process of being supplanted by Internet Protocol version 6 (IPv6). In IPv6, routers do not fragment packets, and path MTU discovery is mandatory.

Answer 2

It optimizes transmission of information over network. You can vary size of fragment and you have to acknowledge only whole fragment. It allows to reduce load on NIC due to fewer number of requests.