IP Datagram Payload

In computer networking, an IP datagram payload refers to the data or message that is carried within an IP packet. An IP packet is a unit of data that is sent across a network, and it consists of a header and a payload. The header contains information about the packet, such as the source and destination IP addresses, the protocol used, and the size of the packet. The payload, on the other hand, contains the actual data or message that is being sent. For example, if you send an email over the internet, the email message itself would be the payload of the IP packet. Similarly, if you were to download a file from a remote server, the contents of the file would be the payload of the IP packet. The size of the payload can vary depending on the type of data being sent. For instance, sending a small text message would have a smaller payload size compared to sending a large video file.

The IP datagram, a fundamental unit of information in network communication, resides in the Internet Layer of the TCP/IP protocol stack. This layer, also known as the network layer, is responsible for the delivery of packets across network boundaries. It handles packet routing, including the logical addressing necessary for transmitting data between networks. Internet Protocol (IP) is a crucial part of this layer, and IP datagrams are the structured packets of information that this protocol operates with.
Each IP datagram comprises a header and payload. The header contains necessary metadata, such as the source and destination IP addresses, the version of IP being used (IPv4 or IPv6), and other control information. The payload carries the actual data to be transmitted, which is typically a segment from the transport layer (TCP or UDP). Thus, the IP datagram operates within the Internet Layer of the TCP/IP protocol stack, playing an essential role in achieving end-to-end data transmission over a network.

Data transmitted over an internet using IP is carried in messages called IP datagrams. Similar to all network protocol messages, IP uses a specific format for its datagrams. We are looking at IP version 4 and we will examine the IPv4 datagram format, which was defined in RFC 791 along with IPv4. The IPv4 datagram is conceptually divided into two pieces:

1. header and
2. the payload.

The header contains addressing and control fields, while the payload carries the actual data to be sent over the internetwork. Unlike some message formats, IP datagrams do not have a footer following the payload.
Even though IP is a relatively simple, connectionless, unreliable protocol, the IPv4 header carries certain information, which makes it somewhat large.