TCP/IP Address Classifications

Class A addresses range from 1.0.0.1 to 126.255.25.254 and can support about 16 million hosts -- each host being a single computer or other networked device.
A Class A network address can support up to 127 networks, and is typically reserved for large companies or Internet service providers.
The 127.0.0.0 address is reserved for loopback testing on the network interface, and is not available for a network

Class B addresses may be from 128.1.0.1 to 191.255.255.254 and support about 65,000 hosts on a network. A Class B network address can support about 16,000 networks. Class B ranges are also typically issued to ISPs or large companies, but may also be used by organizations for internal network organization. When a company does this it typically uses Network Address Translation to hide its private IP address scheme from the world, and it uses a proxy server to manage the connections from the outside to the inside hosts.

Class C IP addresses range from 192.0.1.1 to 223.255.254.254. They can support only 254 hosts on each network, but can have about 2 million networks. Class C address ranges are mostly issued to small companies, which then use NAT to create their own internal address structure, as companies do with Class B addresses.

Class D addresses are reserved for multicast operations, which involves simultaneously sending the same information to all computers in a defined multicast group. This is helpful when large amounts of data must be sent to many hosts at the same time. The Class D range is from 224.0.0.0 to 239.255.255.255.

Class E addresses range from 240.0.0.0 to 254.255.255.254, are reserved for future experimental use, and are currently not documented. You cannot assign Class E addresses to your network interface. The final address of 255.255.255.255 is called the broadcast address, and packets sent to this destination go to every device on the network segment.