NAT

Problem

Your home contains 30 devices. Your ISP gives your router one public IPv4 address. How can all 30 devices communicate with the Internet?

Solution — NAT/PAT

NAT stands for Network Address Translation; PAT stands for Port Address Translation. The router translates many private connections through its public address.

Laptop 192.168.1.10:51000 ─┐
Phone  192.168.1.11:52000 ─┼→ 84.20.10.5
TV     192.168.1.12:53000 ─┘

It remembers the mappings so replies return to the correct device.

Core idea: many private hosts can share limited public IPv4 addresses.