Quiz Entry - updated: 2026.07.14
What are private IP address ranges and when are they used?
Three RFC 1918 blocks — 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — are reserved for internal use and are never routed on the public internet.
These ranges let any organisation address its internal hosts without asking anyone, because internet routers deliberately drop them. The trade-off: a private host can't be reached directly from outside; it gets out via NAT on the router, which swaps its private source address for the router's one public address. This is the main reason IPv4 hasn't fully collapsed despite exhaustion — millions of homes share addresses behind NAT.
| Range | CIDR | Typical use |
|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | Large enterprises |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | Medium networks |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | Home / small office |
Special addresses:
| Address | Purpose |
|---|---|
| 127.0.0.0/8 | Loopback (localhost) |
| 169.254.0.0/16 | Link-local (APIPA) |
| 0.0.0.0 | Default route / "any" |
| 255.255.255.255 | Broadcast |
Why private ranges?
- IPv4 address exhaustion
- Security (not directly reachable from internet)
- Requires NAT to access internet
Home network typical setup:
- Router: 192.168.1.1
- DHCP range: 192.168.1.100-254
- Subnet: 192.168.1.0/24
Go deeper:
RFC 1918 — Address Allocation for Private Internets (IETF) — defines 10/8, 172.16/12, and 192.168/16 as non-routable private blocks.