Private IP Basics
A Private IP Address is an address used exclusively within a confined space like a home, office, or school Local Area Network (LAN), and is not recognized on the public internet.
Since these addresses are not routable on the external internet, they must be translated into a Public IP via NAT (Router/Gateway) to communicate with the outside world.
1. Private IP Address Ranges (RFC 1918 Standard)
There are three designated address ranges reserved for private use that anyone can use freely.
| Class | Private IP Address Range | Target Scale | Characteristics |
|---|---|---|---|
| Class A | 10.0.0.0 ~ 10.255.255.255 | Large Networks | Used by large enterprises requiring a vast number of IPs. |
| Class B | 172.16.0.0 ~ 172.31.255.255 | Medium Networks | Commonly used in schools or medium-sized businesses. |
| Class C | 192.168.0.0 ~ 192.168.255.255 | Small Networks | The most familiar range, often the default for home Wi-Fi routers. |
Note: You may have seen
192.168.0.1on router configuration pages; this is because home routers typically default to the Class C private range.
2. Reasons for Using Private IPs
- IPv4 Conservation: A single Public IP can support hundreds of internal devices via a router (NAT), significantly delaying IPv4 exhaustion.
- Enhanced Security: External hackers cannot directly access devices with Private IPs, providing a basic layer of security.
3. Public IP vs. Private IP Comparison
| Feature | Public IP | Private IP |
|---|---|---|
| Scope | Global Internet (WAN) | Internal Network (LAN) |
| Uniqueness | Must be globally unique | Must be unique only within the LAN (Can be duplicated across different LANs) |
| Assigned By | ISP (Internet Service Provider) | Router/Gateway (DHCP) or Administrator |
| Accessibility | Directly accessible from outside | Not directly accessible from outside (Requires NAT) |