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Aolynk DR811/DR814 ADSL2+Broadband Router
6 IP Addresses, Network Masks, and Subnets
58
Table 6-1
IP Address structure
Class
Field1
Field2
Field3
Field4
Class A
Network ID
Host ID
Class B
Network ID
Host ID
Class C
Network ID
Host ID
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)
6.1.2 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 Internet's 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.
Here are 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)
●
A host ID can have any value except all fields set to 0 or all fields set to 255, as
those values are reserved for special uses.
6.2 Subnet Masks