Internet Protocols Questions Long
IP fragmentation is a process used in computer networks to transmit data packets that are larger than the maximum transmission unit (MTU) size allowed by the underlying network. When a packet is too large to be transmitted in its entirety, it is divided into smaller fragments at the sender's end and reassembled at the receiver's end.
The process of IP fragmentation involves the following steps:
1. Packet Division: When a packet is larger than the MTU size of the network, the sender's IP layer divides it into smaller fragments. Each fragment contains a portion of the original packet's data and a fragment header. The fragment header includes information such as the identification number, flags, offset, and checksum.
2. Fragmentation Header: The fragment header contains the identification number, which is a unique value assigned to the original packet. This identification number is used by the receiver to identify and reassemble the fragments correctly. The flags field indicates whether the fragment is the last fragment or if there are more fragments to follow. The offset field specifies the position of the fragment within the original packet.
3. Fragmentation Process: The sender's IP layer determines the maximum size of the fragments based on the MTU of the network. It then creates multiple fragments by copying the necessary data from the original packet into each fragment. The size of each fragment, except the last one, is equal to the MTU size. The last fragment may be smaller if the remaining data does not fill an entire MTU.
4. Transmission: The fragments are then individually encapsulated into separate IP packets and transmitted over the network. Each fragment is treated as an independent packet and can take different paths to reach the destination.
5. Reassembly: At the receiver's end, the IP layer receives the fragments and uses the identification number to identify which fragments belong to the same original packet. The receiver uses the offset field to determine the correct order of the fragments.
6. Fragment Reassembly: The receiver collects all the fragments belonging to the same original packet and reassembles them in the correct order. It uses the offset field to determine the position of each fragment within the original packet. The receiver also performs a checksum calculation to verify the integrity of the reassembled packet.
7. Delivery: Once the reassembly process is complete, the reassembled packet is passed to the higher layers of the network stack for further processing and delivery to the intended recipient.
It is important to note that IP fragmentation and reassembly introduce additional overhead and can impact network performance. Therefore, it is generally preferred to avoid fragmentation whenever possible by adjusting the packet size or using techniques such as Path MTU Discovery to determine the maximum size allowed by the network.