A Brief Review of Public and Private IPv4 Addresses

ImagePrivate vs. Public IPv4 Addresses

In the history of IPv4 addressing, the world started out with a plan that gave every single host a globally unique public IPv4 address. However, as discussed in several places already, the IPv4 address space had too few addresses. So, in the 1990s, companies started using addresses from the private IPv4 address range, as defined in RFC 1918. These companies either simply did not connect to the Internet, or to connect to the Internet, they used NAT, sharing a few public globally unique IPv4 addresses for all host connections into the Internet.

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