Reserved address space

As defined in RFC 1918, reserved address spaces are IP ranges that have been reserved for internal Intranets. These addresses are:

10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

Users who've setup their own home networks are more than likely familiar with the 192.168 addresses as 192.168.1.1 is commonly used on home network routers and internal addresses often start at: 192.168.1.100 and continue with: .101 .102 .103, etc.

Also see: Intranet, IP, Localhost, Network definitions