What is IP fragmentation?

When data is physically transported on a network, it has to be broken up into MTU (maximum transmission units) because not all equipment can handle large packets. IP fragmentation is when a packet is split into several packets of a specific size (the specified MTU). Once divided, the packets then go on their merry way through the network. This is done so the packet can be routed across a network with equipment that has different specification.

Its not neccesarily a bad thing, or needs to be avoided. It decreases overall speed because of associated overhead, but its unrealistic to have huge packets. It's in fact better to have smaller packets, so at higher levels in the protocol stack, packets can be resent if they're damaged.

If you really wanted to dinker with it, there's settings on your router, and also inside your OS to set the MTU (what a packet will be fragmented into). But, it shouldn't make any perceivable difference.

Ip Packet Fragmentation

The Internet Protocol allows IP fragmentation so that datagrams can be fragmented into pieces small enough to pass over a link with a smaller MTU than the original datagram size.

RFC 1191 describes "Path MTU discovery", a technique for determining the path MTU between two IP hosts, so that IP fragmentation can be avoided.

The details of the fragmentation mechanism, as well as the overall architectural approach to fragmentation, are different in IPv4, the current version of the Internet Protocol, and IPv6, the newer version.

The IP protocol was designed for use on a wide variety of transmission links. Although the maximum length of an IP datagram is 64K, most transmission links enforce a smaller maximum packet length limit, called a MTU. The value of the MTU depends on the type of the transmission link. The design of IP accommodates MTU differences by allowing routers to fragment IP datagrams as necessary. The receiving station is responsible for reassembling the fragments back into the original full size IP datagram.

IP fragmentation involves breaking a datagram into a number of pieces that can be reassembled later. The IP source, destination, identification, total length, and fragment offset fields, along with the "more fragments" and "don't fragment" flags in the IP header, are used for IP fragmentation and reassembly. For more information about the mechanics of IP fragmentation and reassembly

When you send a packet of size XX may be the router has a MTU(Maxium transfer Unit) less then XX. So it breaks the packet into Xa and Xb and sents these two packets forward. This is IP fragmentation. Beacuse of Fragmentation the bandwith might not get fully utilized. As if XX is of size 516KB and MTU is 512KB, then Xa will be of size 512KB but Xb will be of 8KB (4KB payload). Such routers which fragment might become a bottle neck in the network. The solution is to use a Do not Fragment bit in TCP/IP packets. This will tell the router that if fragmentation is required then reject the packet and tell me. The source machine will keep sending packets of smaller size untill a packet is not rejected by router. This way the Fragment size will be found and now the source machine can send all packets of smallest fragement size i.e. 512KB in above case. So the bandwidth is fully utilised.

Breaking an IP datagram (packet) into pieces in order to be sent across a transmission link with a frame size smaller than the datagram. Performed in a router, the header of the original IP packet is replicated with minor changes to each of the fragments. If one of the fragments is dropped, the original datagram must be fragmented again and retransmitted.

IP fragments are problematic. Some firewalls and content switches may not allow them, and they add overhead to routers, which are designed for high-speed packet forwarding, not fragment creation and reassembly. To avoid IP fragmentation, Maximum Segment Size (MSS) messages are sent between two end points to find the maximum frame size that can be transmitted intact.

In a network with multiple data links, the router uses Path Maximum Transmission Unit Discovery (PMTUD) to send error messages back to the sender whenever a link with a smaller frame size is encountered. The host then reduces its TCP packet size and retransmits. PMTUD does not work with UDP, only TCP.

and how to do it you may click on the link and it will open the browser in pdf from there yuo can just save the information and read it and do it

http://ecet.ecs.ru.acad.bg/cst06/Docs/cp/SIII/IIIB...

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What is IP fragmentation?

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