Format of an IP Datagram

The format of data that can be recognized by IP is called an IP datagram. It consists of two components, namely, the header and data, which need to be transmitted. The fields in the datagram, except the data, have specific roles to perform in the transmission of data. Every field in the IP datagram has a fixed size except for the IP Options field, which can be 20–60 bytes in length. The sending computer sends a message to the protocol in the same layer on the destination computer by using the header. The format of an IP datagram is displayed in Figure 3.3.

Figure 3.3. The fields in the IP datagram are used for transmitting data.

In the sections that follow, the fields in an IP datagram are discussed in detail. ...

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