According to RFC 1918, you can use the following IP networks for private nets which will never be connected to the Internet.
# Private IPv4 Ranges
According to RFC 1918, you can use the following IP networks for private nets which will never be connected to the Internet:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255