Private IP
IP address reserved for internal networks and not routable on the public internet.
A private IP address is an IP address used inside local networks — homes, offices and data centers — and is not routable on the public internet. To reach external services, traffic from a private address must usually be translated to a public address through NAT on a router or firewall.
The private ranges are defined by RFC1918 for IPv4: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Because these ranges are not globally routable, the same addresses can be reused independently inside millions of separate networks without conflict.
Private IPs are typically assigned automatically by DHCP running on a home or enterprise router, though servers and infrastructure are often given static private addresses. The use of private addressing has been essential for stretching the limited IPv4 address space.
IPv6 makes it practical for every device to have a globally routable public address, reducing the need for NAT. Private addressing still exists in IPv6 in forms such as Unique Local Addresses (ULA), but typical IPv6 deployments rely far less on translation than IPv4.
Points clés
- Not routable on the public internet
- Common in homes, offices and data centers
- Typically translated through NAT
- Defined by RFC1918 (
10.0.0.0/8,172.16.0.0/12,192.168.0.0/16) - Reusable across isolated networks
- Often assigned automatically by DHCP
- Helps conserve IPv4 address space
- Usually hidden behind routers and firewalls