IP address
Numeric identifier for a device on a TCP/IP network. IPv4: 32 bits (4.3 billion, practically exhausted). IPv6: 128 bits (340 undecillion, plenty).
IPv4 notation: 192.168.1.1 (4 octets). IPv6: 2001:db8::1 (8 16-bit blocks, hex). CIDR notation: /24 = 256 addresses. RFC 1918 reserves private ranges (10.0.0.0/8, 172.16/12, 192.168/16). NAT translates private ↔ public. IPv4 exhaustion events: IANA empty 2011, RIPE 2019. IPv6 adoption ~45% globally (Google measurement 2024). The whole web is hosted on extremely few public IPv4 addresses via load balancers + reverse proxies + CDN.