A private IP address is one reserved for use inside local networks. RFC 1918 sets three ranges aside for this, and every home and office network in the world draws from the same three — which is why your laptop's 192.168.1.23 also exists, right now, on millions of unrelated networks. Private addresses are never routed on the public internet: no registrar, ISP, country or owner is attached to them, and nothing about the number says whose network you are on.
| Range | Addresses | Typically found in |
|---|---|---|
| 10.0.0.0/8 | 16,777,216 | corporate and campus networks, ISP equipment, VPN pools, container platforms — and some home ISP gateways |
| 172.16.0.0/12 | 1,048,576 | mid-size business networks, lab setups, Docker's default bridge network |
| 192.168.0.0/16 | 65,536 | nearly every home router, mobile hotspot and small-office access point |
A common trap with the middle range: only 172.16.x.x through 172.31.x.x is private. A 172.x address outside that window — say 172.67.1.1 — is ordinary public internet space.
Your router performs network address translation (NAT): every device inside uses a private address, and the router rewrites their traffic to go out under the single public address your ISP assigned. From the internet's point of view your whole household is one address; from inside, every device has its own. This is also why a website can see your public address but never your laptop's private one — and why the same private ranges can be reused by everyone without collision.
Many ISPs add a second layer, carrier-grade NAT, using the dedicated 100.64.0.0/10 range between your router and the internet. If your router's "WAN address" starts with 100.64 through 100.127, you are behind CGN — technically not RFC 1918 space, but not publicly reachable either, which is what breaks naive port forwarding on such lines.
127.0.0.1 — loopback. It never leaves your own device; it is how a machine talks to itself, not a network address.
169.254.x.x — link-local. A device gives itself one of these when it asked for an address and no router answered; seeing one usually means DHCP failed and the network is misconfigured.
Everything else is public space: allocated to a network operator, routed globally, and carrying a whois record, an origin network and a geolocation.
For public addresses, the lookup pages show exactly that record — owner, network, country and abuse history: see a public address lookup.
Manufacturers ship every router with a factory address inside these ranges — that address is the door to its admin panel, and because it is private, it only opens from inside your own network. Find yours — or start from the most common factory values: 192.168.1.1, 192.168.0.1, 10.0.0.1.
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