Private IP addresses are reserved for use inside local networks and are not routed across the public internet. Homes and organizations can reuse the same ranges without requesting a globally unique address for every device.
RFC 1918 private IPv4 ranges
| Range | CIDR block | Address count |
|---|---|---|
10.0.0.0 - 10.255.255.255 | 10.0.0.0/8 | 16,777,216 |
172.16.0.0 - 172.31.255.255 | 172.16.0.0/12 | 1,048,576 |
192.168.0.0 - 192.168.255.255 | 192.168.0.0/16 | 65,536 |
Only 172.16.0.0 through 172.31.255.255 is private. Other addresses beginning with 172 can be public.
How private addressing works
A router or DHCP server normally assigns private addresses to laptops, phones, printers, servers, and other local devices. When those devices access the internet, network address translation (NAT) maps their connections to a public address. Reply traffic is then returned to the correct internal device.
NAT conserves public IPv4 addresses and hides the internal numbering scheme, but it is not a substitute for a firewall, secure Wi-Fi, or access control.
Ranges often confused with RFC 1918
127.0.0.0/8is loopback traffic for the same host.169.254.0.0/16is link-local addressing, often assigned when DHCP fails.100.64.0.0/10is shared address space used by carriers; it is not an RFC 1918 range.fc00::/7identifies IPv6 unique local addresses, a separate IPv6 concept.
Security and troubleshooting
- Use a firewall and avoid unnecessary port forwarding from the public internet.
- Change default router credentials and keep router firmware updated.
- Use WPA2 or WPA3 and place untrusted IoT devices on a separate network.
- Plan different private subnets for sites and VPNs to prevent overlapping routes.
- Do not treat a private source address as proof that traffic is trusted; compromised internal devices also use private addresses.
To identify an address correctly, compare the complete address with the CIDR range rather than checking only its first number.