Every machine on the Internet has a unique identifying number, called an IP Address. A typical IP address looks like this: 18.104.22.168
The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Those numbers are called octets, because they each have eight positions when viewed in binary form. The octets serve a purpose other than simply separating the numbers.
They are used to create classes of IP addresses.
* Class A – This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class.
* Class B – Class B is used for medium-sized networks. A good example is a large college campus. IP addresses with a first octet from 128 to 191 are part of this class.
* Class C – Class C addresses are commonly used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class.
* Class D – Used for multicasts (where a node sends a packet addressed to a special group address.). For multicasts, the first octet has a value of 224.
* Class E with the first octet of 225 is used for experimental purposes only.
Loopback – The IP address 127.0.0.1 is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing.
Broadcast – Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address 255.255.255.255.