Networking Guide
Chapter 1, Networking overview

The Internet Protocol (IP)

The Internet Protocol (IP)

The Internet Protocol defines a data delivery system wherein the sending and receiving machines are not necessarily directly connected. IP splits data into packets of a given size, which are then forwarded to the receiving machine via the network. These individual packets of data (often called ``datagrams'') are routed through different machines on the Internet to the destination network and receiving machine. A particular set of data, such as a file, can be broken up into several datagrams that are sent separately.

A datagram consists of header information and a data segment. The header contains information about routing and processing the datagram. Datagrams can be further fragmented into smaller pieces, depending on the physical requirements of the networks they cross. For example, when a gateway sends a datagram to a network that cannot accommodate the datagram as a single packet, the datagram must be split into pieces that are small enough for transmission. The datagram fragment headers contain the information necessary to reassemble the fragments into the complete datagram. Fragments do not necessarily arrive in order; the software module implementing the IP protocol on the destination machine must reassemble the fragments into the original datagram. If any fragments are lost, the entire datagram is discarded.

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