15.3 IP ADDRESSING AND SUBNETTING

A communication network can only deliver information if every device can be uniquely identified. Within a single Local Area Network (LAN), this role is performed by Media Access Control (MAC) addresses, which identify individual network interfaces. However, MAC addresses are suitable only for communication within a single network segment. Once communication extends across multiple interconnected networks, a more scalable addressing system is required.

The Internet addresses this problem through the Internet Protocol (IP), which assigns every device a logical network address. Unlike MAC addresses, which are tied to particular network hardware, IP addresses are organized hierarchically so that routers can determine the most appropriate path through an internetwork. This hierarchical structure enables the Internet to scale from small local networks to a global system interconnecting billions of devices.

IP addresses serve two complementary purposes. First, they uniquely identify the destination device. Second, they indicate the network to which that device belongs. Routers use the network portion of the address to determine where packets should be forwarded, while the remaining portion identifies the individual host within that network.

Two versions of the Internet Protocol are currently in widespread use. Internet Protocol Version 4 (IPv4) has formed the foundation of the Internet since the early 1980s and remains the dominant protocol today. However, the enormous growth of the Internet eventually exhausted the available IPv4 address space. To overcome this limitation, Internet Protocol Version 6 (IPv6) was developed, providing a vastly larger address space together with several architectural improvements that simplify packet forwarding and support future Internet growth.

Although IPv4 and IPv6 use different address formats, they perform exactly the same fundamental function: providing logical addressing that enables routers to forward packets between independent networks. The following sections examine the structure of both addressing schemes and the techniques used to organize addresses into efficient routing hierarchies.