IP addresses have a network part and a host-part, hosts in the same subnet can reach each other directly. To reach a host on another subnet you need a gateway (router) to the other network.

IPv4 Address classes

Class	Address starting bits	First Byte less than	Comment
A	0	127
B	10	192	127 is reserved for loopback interfaces
C	110	224
D	1110	240	240 – 255 is reserved for experimental usage

Some address ranges are private, this means they are not routed. You can never reach a host with such an address outside your network directly.

• 10.0.0.0 through 10.255.255.255 (10.0.0.0/8, 1 Class A network)
• 172.16.0.0 through 172.31.255.255 (172.16.0.0/12, 16 Class B networks)
• 192.168.0.0 through 192.168.255.255 (192.168.0.0/16, 65025 Class C networks)