Private IP Addresses

The following blocks of IP addresses are reserved for private or local area (LAN) networks:

  • 10.0.0.0 – 10.255.255.255 ( 10.0.0.0/8 )
  • 172.16.0.0 – 172.31.255.255 ( 172.16.0.0/12 )
  • 192.168.0.0 – 192.168.255.255 ( 192.168.0.0/16 )

IP addresses from the reserved ranges are called “Private IP Addresses” and used by many companies and organizations within their private networks. Private IP addresses should not appear on the public Internet.

Sometimes private IP addresses are recorded in the header of an e-mail message. This indicates that the message has passed through the e-mail forwarding hosts on the local network before reaching the Internet.

Other Specialy Assigned IP Address Blocks

  • 0.0.0.0/8 - addresses in this block refer to source hosts on "this" network.
  • 127.0.0.0/8 - internal host loopback addresses.
  • 169.254.0.0/16 - “link local“ block. Hosts obtain these addresses by auto-configuration, such as when a DHCP server may not be found.

See also
RFC1918 Address Allocation for Private Internets.
RFC3330 Special-Use IPv4 Addresses.