Public vs Private Addresses
A public IP address is unique on the internet and reachable from anywhere (unless a firewall blocks it). A private IP address is reserved for use inside networks. The same private addresses are reused in millions of homes and offices, so they are never routed on the internet.
The Private IPv4 Ranges
RFC 1918 defines three private blocks:
| Range | CIDR | Typical use |
|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | Companies, cloud networks |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | Companies, Docker networks |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | Home routers |
Other Special Ranges
- 127.0.0.0/8 – loopback; 127.0.0.1 is the machine itself.
- 169.254.0.0/16 – link-local; a device assigns itself such an address when it gets no address from DHCP. Seeing one usually means the network connection failed.
- 100.64.0.0/10 – shared address space used by internet providers for carrier-grade NAT.
- IPv6:
fc00::/7(unique local) andfe80::/10(link-local) play similar roles.
How Private Networks Reach the Internet: NAT
Your router has one public address and gives private addresses to your devices. When a device connects to a website, the router replaces the private source address with its public one and keeps track of the connection. This is Network Address Translation (NAT). Websites see the router’s public address, not your device’s private one.
Many providers now add a second layer, carrier-grade NAT (CGNAT), so that many customers share one public address. That affects hosting services at home and IP geolocation — see how accurate IP geolocation is.
Reading CIDR Notation
The number after the slash says how many leading bits are fixed. /24 fixes the first 24 bits, leaving 8 bits (256 addresses) for hosts, for example 192.168.1.0/24 = 192.168.1.0 to 192.168.1.255. A smaller number means a larger block: /16 holds 65,536 addresses, /8 about 16.7 million.
Why Private Addresses Matter in Tools
- A private address cannot be geolocated; our IP Location tool tells you when you enter one.
- A public domain that resolves to a private address is a configuration error — or a sign of DNS filtering, as in our Iran blocking guide.
- Private addresses in the first hops of a traceroute are normal.