Glossary · Networking

Private vs Public IP Address

A public IP address is reachable on the internet, while a private IP is reserved for local networks and not routed globally.

Updated October 6, 2026

A public IP address is globally unique and routable on the internet, assigned through your ISP. A private IP address belongs to ranges reserved for internal networks, which anyone may reuse and which routers on the internet do not forward.

Why it matters

Private ranges let thousands of home and office networks use the same addresses without clashing, while NAT on the router translates between them and one public address. This conserved IPv4 space. The reserved IPv4 ranges (RFC 1918) are:

  • 10.0.0.0/8
  • 172.16.0.0/12
  • 192.168.0.0/16

Private addresses are not directly reachable from outside, which gives some incidental protection, but that is not a substitute for a firewall. Under CGNAT, even your router's "public" side may be shared.

Example

Your laptop shows 192.168.1.23 (private); a "what is my IP" site shows 203.0.113.45 (public). Two houses may both use 192.168.1.23 inside, yet appear to the internet under different public addresses.

Common mistakes

  • Putting a private address in a public DNS record for a service meant for internet users.
  • Overlapping private ranges on two networks joined by a VPN, which breaks routing.
  • Assuming your device's address is what websites see.

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