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Networking Fundamentals · Foundational

Public IP Address

A globally unique, Internet-routable IP address assigned by an ISP or registry.

Definition

Public addresses are allocated from IANA through RIRs and ISPs and must be unique worldwide. Public-facing servers, firewalls and NAT gateways use them. Because IPv4 public space is scarce, organizations often have only a few public IPv4 addresses and rely on NAT for internal hosts.

Example

Searching "what is my IP" shows the public address of your NAT router, not your PC's private address.

Exam tip

If a host's address is outside the RFC 1918, loopback, APIPA and other special ranges, assume it is public.

Don't confuse it with

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