The following IP addresses are reserved as private address space, specified in the RFC 1918. This means everybody can set up an internal network using addresses in these blocks, but packets originating from those addresses should never appear on the internet.
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)
To allow these addresses to access the Internet you must NAT (Network Address Translate) these numbers via one or more public addresses which are provided by your ISP.