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Every machine on the Internet has a
unique identifying number, called an IP Address. A typical IP
address looks like this: 216.27.61.137
To make it easier for us humans to remember, IP addresses are
normally expressed in decimal format as a "dotted decimal
number" like the one above. But computers communicate in binary
form. Look at the same IP address in binary:
11011000.00011011.00111101.10001001 The four numbers in an IP
address are called octets, because they each have eight
positions when viewed in binary form. If you add all the
positions together, you get 32, which is why IP addresses are
considered 32-bit numbers. Since each of the eight positions can
have two different states (1 or 0) the total number of possible
combinations per octet is 28 or 256. So each octet can contain
any value between 0 and 255. Combine the four octets and you get
232 or a possible 4,294,967,296 unique values!
Out of the almost 4.3 billion possible combinations, certain
values are restricted from use as typical IP addresses. For
example, the IP address 0.0.0.0 is reserved for the default
network and the address 255.255.255.255 is used for broadcasts.
The octets serve a purpose other than simply separating the
numbers. They are used to create classes of IP addresses that
can be assigned to a particular business, government or other
entity based on size and need. The octets are split into two
sections: Net and Host. The Net section always contains the
first octet. It is used to identify the network that a computer
belongs to. Host (sometimes referred to as Node) identifies the
actual computer on the network. The Host section always contains
the last octet. There are five IP classes plus certain special
addresses:
Default Network - The IP address of 0.0.0.0 is used for the
default network.
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. The other
three octets are used to identify each host. This means that
there are 126 Class A networks each with 16,777,214 (224 -2)
possible hosts for a total of 2,147,483,648 (231) unique IP
addresses. Class A networks account for half of the total
available IP addresses. In Class A networks, the high order bit
value (the very first binary number) in the first octet is
always 0. Net Host or Node 115. 24.53.107
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.
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 B addresses
also include the second octet as part of the Net identifier. The
other two octets are used to identify each host. This means that
there are 16,384 (214) Class B networks each with 65,534 (216
-2) possible hosts for a total of 1,073,741,824 (230) unique IP
addresses. Class B networks make up a quarter of the total
available IP addresses. Class B networks have a first bit value
of 1 and a second bit value of 0 in the first octet. Net Host or
Node 145.24. 53.107
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 C addresses also include the
second and third octets as part of the Net identifier. The last
octet is used to identify each host. This means that there are
2,097,152 (221) Class C networks each with 254 (28 -2) possible
hosts for a total of 536,870,912 (229) unique IP addresses.
Class C networks make up an eighth of the total available IP
addresses. Class C networks have a first bit value of 1, second
bit value of 1 and a third bit value of 0 in the first octet.
Net Host or Node 195.24.53. 107
Class D - Used for multicasts, Class D is slightly different
from the first three classes. It has a first bit value of 1,
second bit value of 1, third bit value of 1 and fourth bit value
of 0. The other 28 bits are used to identify the group of
computers the multicast message is intended for. Class D
accounts for 1/16th (268,435,456 or 228) of the available IP
addresses. Net Host or Node 224. 24.53.107
Class E - Class E is used for experimental purposes only.
Like Class D, it is different from the first three classes. It
has a first bit value of 1, second bit value of 1, third bit
value of 1 and fourth bit value of 1. The other 28 bits are used
to identify the group of computers the multicast message is
intended for. Class E accounts for 1/16th (268,435,456 or 228)
of the available IP addresses. Net Host or Node 240. 24.53.107
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. |
