Almost every home and office network uses RFC 1918 addresses internally, then NATs to one public IP on the way out. They're globally non-unique by design — millions of networks share the same 192.168.1.0/24.
IPv6's rough equivalent is ULAs (fc00::/7), but ULAs are designed to be globally unique even though they aren't routed.
See also
- NATRewriting the source/destination IP (and usually port) of packets as they cross a network boundary.
- CGNATA second layer of NAT operated by an ISP, sharing one public IP between many customers because IPv4 ran out.
- IPv4The original 32-bit IP addressing scheme — addresses look like 203.0.113.42 and there are ~4.3 billion of them.
- IPv6The 128-bit successor to IPv4 — addresses look like 2001:db8::1 and there are 2^128 of them.