IP address

An IP address is the numeric identifier assigned to each device on a TCP/IP network. Two versions coexist: IPv4 and IPv6.

IPv4: 32-bit address, written as four decimal numbers separated by dots, each 0-255. Example: 192.168.1.1. Total address space: ~4.3 billion addresses, exhausted globally around 2011-2015. Modern networks rely heavily on NAT (Network Address Translation) to share a small pool of public IPv4 addresses across many devices.

IPv6: 128-bit address, written as eight groups of four hex digits separated by colons. Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334 (often abbreviated with :: for consecutive zero groups). Total address space: ~3.4 × 10³⁸ — effectively infinite. Designed in the 1990s to replace IPv4 but adoption has been slow; as of 2026 about 45% of internet traffic uses IPv6.

Reserved address ranges:

• Private (RFC 1918, IPv4): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Used inside home and office networks; never routed on the public internet.
• Loopback: 127.0.0.1 (IPv4), ::1 (IPv6). Refers to “this machine”.
• Link-local (IPv6): fe80::/10. Used for autoconfiguration on a single network segment.

For developers: server logs typically record client IPs. The exact IP your application sees depends on whether traffic passes through proxies/load balancers — check the X-Forwarded-For header if your server isn’t the public-facing edge.