90
GigaX3112 Series Layer 3 Managed Switch
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 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, e.g. your ISP.
Class B networks are smaller but still quite large, each being 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)
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
A mask looks like a regular IP address, but contains a pattern of
bits that tells what parts of an IP address are the network ID and
what parts are the host ID: bits set to 1 mean “this bit is part of the
network ID” and bits set to 0 mean “this bit is part of the host ID.”
Subnet masks are used to define subnets (what you get after dividing a network
into smaller pieces). A subnetʼs network ID is created by “borrowing” one or
more bits from the host ID portion of the address. The subnet mask identifies
these host ID bits.
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