User`s manual

IP Address, Network Masks, and Subnets RX3042H User's Manual
106
Table 11.1. IP Address Structure
Field 1 Field 2 Field 3 Field 4
Network ID Host ID
Network ID Host ID
Network ID Host ID
Class A
Class B
Class C
Here are some examples of valid IP addresses:
Class A: 10.30.6.125 (network = 10, host = 30.6.125)
Class B: 129.88.16.49 (network = 129.88, host = 16.49)
Class C: 192.60.201.11 (network = 192.60.201, host = 11)
11.2 Network classes
The three commonly used network classes are A, B, and C. (There
is also a class D but it has a special use beyond the scope of this
discussion.) These classes have different uses and characteristics.
Class A networks are the Internetʼs largest networks, each with
room for over 16 million hosts. Up to 126 of these huge networks
can exist, for a total of over 2 billion hosts. Because of their huge
size, these networks are used for WANs and by organizations at
the infrastructure level of the Internet, such as your ISP.
Class B networks are smaller but still quite large, each able to hold
over 65,000 hosts. There can be up to 16,384 class B networks
in existence. A class B network might be appropriate for a large
organization such as a business or government agency.
Class C networks are the smallest, only able to hold 254 hosts at
most, but the total possible number of class C networks exceeds 2
million (2,097,152 to be exact). LANs connected to the Internet are
usually class C networks.
Some important notes regarding IP addresses:
The class can be determined easily from field1:
field1 = 1-126: Class A
field1 = 128-191: Class B
field1 = 192-223: Class C
(field1 values not shown are reserved for special uses)