What Is a Private IP Address?

What Is a Private IP Address?

A private IP address is an IP address used within local networks (LANs) that is not routable on the internet. Private IP addresses are defined in RFC 1918 and include ranges: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for IPv4.

Private IPs enable local network communication, allow multiple devices to share single public IP through NAT (Network Address Translation), and conserve public IP address space. Private IP addresses are assigned by routers using DHCP and are not visible outside local network.

Private IPs are essential for home and office networks, enabling multiple devices to connect to internet using single public IP. Learn more about public IP addresses.

Private IP Ranges

RFC 1918 Ranges

Private IP addresses are defined in RFC 1918, specifying three IPv4 address ranges for private use:

• 10.0.0.0/8: 10.0.0.0 to 10.255.255.255 (16.7 million addresses)
• 172.16.0.0/12: 172.16.0.0 to 172.31.255.255 (1 million addresses)
• 192.168.0.0/16: 192.168.0.0 to 192.168.255.255 (65,536 addresses)

Common Private IPs

Common private IP addresses: 192.168.1.1 (router default), 192.168.0.1 (router default), 10.0.0.1 (router default).

IPv6 Private Addresses

IPv6 uses Unique Local Addresses (ULA) for private addressing: fc00::/7 range.

Reserved Ranges

Private IP ranges are reserved and not allocated on internet, ensuring they can be used freely in local networks without conflicts.

Private vs Public IP

Private IP Address

Private IP addresses: used in local networks, not routable on internet, assigned by routers, enable local communication, and shared through NAT.

Public IP Address

Public IP addresses: routable on internet, assigned by ISPs, unique globally, enable internet connectivity, and visible to internet services. Learn more about public IP addresses.

Key Differences

• Private IP: Local network only, not routable on internet
• Public IP: Routable on internet, visible to services
• Private IP: Assigned by router (DHCP)
• Public IP: Assigned by ISP

Relationship

Private and public IPs work together - devices use private IPs locally, router uses NAT to translate to public IP for internet communication.

NAT and Private IP

What Is NAT?

NAT (Network Address Translation) enables multiple devices with private IPs to share single public IP for internet communication.

How NAT Works

NAT works by: router receives data from devices with private IPs, translates private IPs to public IP, sends data to internet using public IP, receives responses, and translates back to private IPs for delivery to devices.

NAT Benefits

NAT benefits: conserves public IP addresses, enables multiple devices to share single public IP, provides network security (hides private IPs), and simplifies network configuration.

NAT Limitations

NAT limitations: can complicate some applications (P2P, gaming), requires port forwarding for incoming connections, and may affect some network protocols.

NAT Types

NAT types: Static NAT (one-to-one mapping), Dynamic NAT (pool of public IPs), and PAT/NAPT (Port Address Translation, multiple private IPs to single public IP).

Private IP Uses

1. Home Networks

Private IPs enable home networks - multiple devices (computers, phones, tablets) connect to router using private IPs, sharing single public IP.

2. Office Networks

Private IPs enable office networks - multiple computers and devices connect using private IPs, sharing public IP for internet access.

3. Local Communication

Private IPs enable local network communication - devices can communicate with each other using private IPs without internet access.

4. Network Security

Private IPs provide network security - devices with private IPs are not directly accessible from internet, protected by NAT and firewall.

5. IP Address Conservation

Private IPs conserve public IP address space - millions of devices can use private IPs while sharing limited public IP addresses.