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Commonly confused · Networking Fundamentals

Public vs Private IP Address: What's the Difference?

A public IP address is globally unique and routable on the Internet, while a private IP address comes from RFC 1918 ranges reserved for internal networks and is not routed on the Internet. Private hosts reach the Internet through NAT, which translates them to a public address.

Public IP Address

Full definition
vs

Private IP Address

Full definition
Public IP AddressPrivate IP Address
Routable on InternetYesNo
UniquenessGlobally unique, assigned through ISPs and RIRsUnique only within the local network; reused everywhere
IPv4 rangesEverything not reserved10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
CostLeased from an ISPFree to use internally
Internet accessDirectRequires NAT/PAT at the edge
Typical exampleWeb server facing the InternetOffice PCs, printers, home devices
Remember it

Private addresses are like extension numbers; public addresses are the company's main phone line.

Exam tip

Know the three RFC 1918 ranges cold, especially that 172.16.0.0/12 covers 172.16.x.x through 172.31.x.x. Do not confuse them with APIPA (169.254.0.0/16) or loopback (127.0.0.0/8).

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