Every machine on the Internet has a unique identifying number, called an IP Address
. A typical IP address looks like this: 220.127.116.11
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.
- 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.
- 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