The Internet Protocol (IP) operates at the Network layer of the OSI model (or the Internet layer in the TCP/IP model). It is responsible for addressing and routing, enabling packets to travel from a source machine to a destination machine across multiple interconnected networks.

IP operates on a best-effort delivery model. It attempts to deliver each packet to its intended destination using the assigned IP address, but it provides no inherent guarantees regarding packet arrival, delivery order, or transmission speed. Reliable delivery mechanisms and error recovery are handled by higher-level protocols running on top of IP.

Internet Protocol and Best-Effort Delivery

An IP address is a logical address used to uniquely locate and route data to devices across different networks. This contrasts with a MAC address, which is a permanent hardware address burned into a network card used only within a local network segment.

IPv4 addresses (formatted like `192.168.1.5`) provide approximately 4 billion possible unique addresses. As the number of connected devices grew globally, available IPv4 address space ran short. To address this limitation, IPv6 was introduced, utilizing much longer addresses to support a vastly larger number of devices across the Internet.

IP Addressing Formats and Exhaustion

When data is transmitted across a network, it is broken down into small, individually addressed units called **packets**. Each packet is labeled with source and destination addresses and transmitted independently.

As packets travel across interconnected networks, intermediary devices known as **routers** inspect the destination IP address on each packet. Routers forward the packet along the best available path toward its ultimate destination, moving it hop by hop across networks. Once all packets reach the receiving destination, they are reassembled in the correct order.

Packet Creation and Hop-by-Hop Routing

University of Michigan - Ann Arbor

Ch.3 Transmission and Routing Protocols - Demystifying Network Architecture: Protocols, Addressing, and Packet Flow @ University of Michigan - Ann Arbor

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