IP addresses & packets

Its job in the system

IP is the common layer that allows diverse networks to interconnect. A packet carries addressing and other control information along with its payload. Routers use the destination address to move packets towards a network that can deliver them. The payload can belong to many different applications without each intermediate network needing to understand that application.

How it works

An IP address identifies a network interface or addressing destination within the protocol’s scheme; it is not a permanent identity card for a person. IPv4 and IPv6 use different address formats and rules. IPv6 has a much larger address space. The two versions coexist, with deployment and transition arrangements varying between networks.

IP forwarding offers best-effort delivery: a packet can be lost, delayed, duplicated, or arrive out of order. IP by itself does not promise that a complete page will arrive. Higher layers provide the behaviours an application needs. A hop limit, or its IPv4 counterpart, helps prevent a packet from circulating indefinitely through routing loops.

What it connects to

The sending host places transport data into IP packets, and local link mechanisms carry each packet to the next hop. At another link the local framing changes, while the IP layer provides continuity across the route. Routers, transport protocols, and DNS each solve a different part of getting useful data to the right application.

Different places, different designs

Public addressing, private IPv4 networks, address translation, IPv6, tunnels, and enterprise policies create different deployments. A home may share one externally visible IPv4 address among several devices. These variations are deliberately collapsed in the overview, which focuses on communication roles rather than a full configuration.