IP Fundamentals

Public vs Private IP Addresses & RFC 1918

Understand the difference between globally routable public IPs and reserved RFC 1918 private IPv4 ranges.

Key Technical Takeaways

  • •Class A Private Range: 10.0.0.0 to 10.255.255.255 (10.0.0.0/8 prefix, 16.7M hosts)
  • •Class B Private Range: 172.16.0.0 to 172.31.255.255 (172.16.0.0/12 prefix, 1M hosts)
  • •Class C Private Range: 192.168.0.0 to 192.168.255.255 (192.168.0.0/16 prefix, 65k hosts)
  • •Carrier-Grade NAT (CGNAT): 100.64.0.0/10 prefix used by ISPs to share public IPv4 addresses across subscriber pools.

Public IP addresses are globally unique and routable on the public internet, assigned by regional internet registries (RIRs) to ISPs and enterprises. Private IP addresses are reserved for internal local area networks (LANs) and cannot be routed across the public internet without Network Address Translation (NAT).

Interactive IP & Network Tools

Private vs Public IP Checker →CIDR Calculator →