Every device that communicates on the internet needs an IP (Internet Protocol) address, a numerical label that serves as both an identifier and a locator within the global network. IPv4 addresses, the most familiar form, consist of four octets separated by dots (e.g., 203.0.113.42), providing approximately 4.3 billion unique addresses. When the internet was designed in the early 1980s, this seemed like an inexhaustible supply, but the explosive growth of connected devices led to IPv4 address exhaustion, officially declared by IANA in 2011.

Network Address Translation (NAT) became the primary mechanism for stretching the IPv4 address space. NAT allows an entire home or office network to share a single public IP address by translating between private internal addresses (typically in the 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 ranges defined by RFC 1918) and the public address assigned by the ISP. When your computer sends a request to a website, your router replaces the private source address with its public address and records the mapping. When the response arrives, the router reverses the translation and forwards the data to the correct internal device. This is why the IP address visible to internet services differs from the address your device shows in its network settings.

The distinction between public and private IP addresses is fundamental to understanding network architecture. Private addresses are not routable on the public internet and can be reused across millions of separate networks without conflict. Your public IP address, assigned by your Internet Service Provider, is the address that websites, services, and other internet-connected systems see when you connect. Most residential connections use dynamic IP addressing through the Dynamic Host Configuration Protocol (DHCP), meaning your public IP may change periodically when your router reconnects or your DHCP lease expires. Business connections often use static IP addresses that remain constant, essential for hosting servers or services that need a stable address.

IPv6 was developed to solve the address exhaustion problem permanently, expanding the address space to 128 bits and providing approximately 340 undecillion unique addresses. IPv6 addresses are written in hexadecimal notation separated by colons (e.g., 2001:0db8:85a3::8a2e:0370:7334). While IPv6 adoption has grown steadily, with major ISPs and content providers supporting it, the transition from IPv4 is ongoing. Many networks operate in dual-stack mode, supporting both protocols simultaneously, which means a device may have both an IPv4 and an IPv6 public address.