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