Why is fragmentation required

Applications relying on UDP can only deal with this at the application layer. A number of protocols such as the real-time transport protocol RTP and Session Initiation Protocol SIP can be used to establish a session state and help minimise or avoid the issues caused by IP fragmentation.

RTP Actually has its own fragmentation mechanism. A common simplistic approach is to just use a small packet size. All IPv4 hosts including routers should be capable of accepting byte packets for instance. To express this in table form as we did earlier:. With IPv4 things are more complicated; an initial timeout of 15 seconds is suggested when the first fragment is received.

The TTL field value of each subsequent fragment received is then used to reset the timer value, as long as it is higher than the current value. This allows for a gap of up to 4. Should the timer expire, all fragments are discarded. If fragment zero is not available, no message is sent. The last of four children of the seventies, Steve was born in London and has never been too far from a shooting, bombing or riot.

He's now grateful to live in a small town in East Yorkshire in the north east of England. He's worked in the IT industry for over 25 years in a variety of roles, predominantly in data centre environments. More recently he's widened his skill set to embrace DevOps, Linux, containers, automation, orchestration, cloud and more.

Details of his F5 related books can be found here. You can find him on Twitter: sjiveson. Amazing article. Helped me to truly understand the process of fragmentation, which is not clearly portrayed anywhere else! Fragmentation allows for; Transport layer protocols to be ignorant of the underlying network architecture, reducing overheads.

IP And higher layer protocols to work across variable and diverse network paths and mediums without the need and overhead of a path discovery protocol but see the PMTUD section. Only the first fragment contains the high layer headers which can cause issues with firewalls, middle-boxes and routers i.

NAT functionality that rely on inspecting those headers. Fragmentation may result in out of order packet delivery and the need for reordering especially if only some packets are fragmented or if link aggregation or other path splitting technologies are in use.

This does not mean the same ID should be used when fragmenting packets where the source, destination and protocol are the same but that the same ID could be used when they are not. Unlike the original packet, all but the last fragment will have the third bit of the field, More Fragments MF , set to 1.

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Pamela Weaver. Application Security Latest Articles. App Security Edge Security It is done by the network layer at the destination side and is usually done at routers.

Source side does not require fragmentation due to wise good segmentation by transport layer i. Receiver identifies the frame with the identification 16 bits field in the IP header. Each fragment of a frame has the same identification number. Receiver identifies the sequence of frames using the fragment offset 13 bits field in the IP header Overhead at the network layer is present due to the extra header introduced due to fragmentation.

Fields in IP header for fragmentation — Identification 16 bits — use to identify fragments of the same frame. Fragment offset 13 bits — use to identify the sequence of fragments in the frame. It generally indicates a number of data bytes preceding or ahead of the fragment. Reassembly of Fragments — It takes place only at the destination and not at routers since packets take an independent path datagram packet switching , so all may not meet at a router and hence a need of fragmentation may arise again.

The fragments may arrive out of order also. Skip to content. Change Language. Related Articles.