IP Address Classes
There are 5 classes of the IPv4 address space; A,B,C,D and E, each of which contain a contiguous subset of the overall. Mostly the case is that the leftmost four bits of the address determine its class (for instance; All Class C addresses, for example, have the leftmost three bits set to '110', but each of the remaining 29 bits may be set to either '0' or '1' independently (as represented by an x in these bit positions):
110xxxxx xxxxxxxx xxxxxxxx xxxxxxxx
When converting it to dotted decimal notation, it goes without saying that the address falls in the class C range from 192.0.0.0 through 18.104.22.168.
Class E is a reserved class, hence it will not be used on IP networks. They are mostly experimental addresses and so far testing has produced unsuccessful results.
There is also a special limited broadcast IP address; 255.255.255.255. It is used for indicating that all other nodes on a LAN should pick up the transmission, however it is limited and does not extend to all nodes on the internet.
Basically IP reserves the range of addresses from 255.0.0.0 through 255.255.255.255 for broadcast (class E is excluded from this range).
Class D addresses are reserved for multicast, which is the process used for indicating groups of nodes and sending IP messages to those group instead of to each node or to a unicast.
It is popular with research oriented networks, however are still in an experimental stage so should be used with wariness on nodes on the internet.
The three widely used classes of IP networks are classes A, B and C.