Private IPv4 address spaces

The Internet Engineering Task Force (IETF) has directed the Internet Assigned Numbers Authority (IANA) to reserve the following IPv4 address ranges for private networks, as published in RFC 1918:
RFC1918 name
IP address range
number of addresses
classful description
largest CIDR block (subnet mask)
host id size
24-bit block
10.0.0.0 – 10.255.255.255
16,777,216
single class A
10.0.0.0/8 (255.0.0.0)
24 bits
20-bit block
172.16.0.0 – 172.31.255.255
1,048,576
16 contiguous class Bs
172.16.0.0/12 (255.240.0.0)
20 bits
16-bit block
192.168.0.0 – 192.168.255.255
65,536
256 contiguous class Cs
192.168.0.0/16 (255.255.0.0)
16 bits
Classful addressing is obsolete and has not been used in the Internet since the implementation of Classless Inter-Domain Routing (CIDR) starting in 1993. For example, while 10.0.0.0/8 was a single class A network, it is common for organizations to divide it into smaller /16 or /24 networks.

Private network - Wikipedia, the free encyclopedia