networkheader

Networkheader is a term used to describe the metadata portion of a network packet that is added by protocol layers to enable delivery, routing, and error detection. A header is prepended to the payload and interpreted by devices and software along the path, including routers, switches, firewalls, and end hosts. Headers encode instructions and context that control how the payload should be handled.

Headers are structured by protocol. At the network layer, Internet Protocol (IP) headers carry addressing and routing information. An IPv4 header includes version, header length, total length, identification, flags, fragment offset, time to live, protocol, header checksum, and source and destination addresses. IPv6 uses a fixed 40-byte header with fields for version, traffic class, flow label, payload length, next header, hop limit, and addresses.

At the transport layer, headers like TCP and UDP provide port numbers and control information. The TCP header additionally carries sequence and acknowledgment numbers, data offset, flags, window size, and a checksum. UDP uses a simpler header with source port, destination port, length, and checksum. Link-layer headers, such as Ethernet, frame the data with destination and source MAC addresses and an EtherType field.

The header serves multiple purposes: identifying the packet's origin and destination, indicating the protocol and how to process the payload, enabling segmentation or reassembly, and supporting features such as quality of service and security. Header size contributes to protocol efficiency and can affect throughput, particularly on small-packet networks or in header compression schemes.