Q. What are private IP addresses?
A. The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets (local networks):
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
Also, IP addresses in the range of 169.254.0.0 -169.254.255.255 are reserved for Automatic Private IP Addressing.
These IP's should not be used on the Internet.
I usually use 192.168.0.1, 192.168.0.2, etc. and a subnet mask of 255.255.255.0 when assigning static IP addresses to computers on a small Local Area Networks (LANs). If a DHCP server is also on the LAN it's scope (range of IP addresses that it can assign to computers on the LAN set to obtain their IP addresses automatically) should be adjusted so it does not interfere with locally assigned static IP addresses.