Public vs. private IP addresses

A public IP address is unique across the entire internet and is assigned to your network by your ISP. A private IP address only has meaning inside a local network - your router hands these out to your phones, laptops, and smart devices, and they're reused on millions of home networks worldwide. The three private ranges (RFC 1918) are:

  • 10.0.0.0 - 10.255.255.255 (a /8 block)
  • 172.16.0.0 - 172.31.255.255 (a /12 block)
  • 192.168.0.0 - 192.168.255.255 (a /16 block)

Other special ranges

  • Loopback (127.0.0.0/8) - always points back to the same device; 127.0.0.1 is "localhost".
  • Link-local / APIPA (169.254.0.0/16) - auto-assigned when a device can't reach a DHCP server. Usually a sign of a network problem.
  • CGNAT (100.64.0.0/10) - carrier-grade NAT, used by ISPs to share a pool of public addresses among many customers.
  • Multicast (224.0.0.0/4) - one-to-many traffic, not assigned to individual hosts.