Well DA-300N, User Manual

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User’s Guide IP Addresses, Network Masks, and Subnets
scope of this discussion.) These classes have different uses
with
ver 16 million hosts. Up to 126 of these huge
can exist, for a total of over 2 billion hosts. Because of
their huge size, these networks are used for WANs and by
e infrastructure level of the Internet, such as
your ISP.
ppropriate
lues not shown are reserved for special uses)
alue except all fields set to 0 or all
ial
and characteristics.
Class A networks are the Internet's largest networks, each
room for o
networks
organizations at th
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 a
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 va

A host ID can have any v
fields set to 255, as those values are reserved for spec
uses.
Subnet masks
A rn of
mask
looks like a regular IP address, but contains a patte
bit and s that tells what parts of an IP address are the network ID
Definition
mask
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
ding a network into smaller pieces). A subnet's network ID divi is
created by "borrowing" one or more bits from the host ID portion
of the address. The subnet mask identifies these host ID bits.
For example, consider a class C network 192.168.1. To split this
into two subnets, you would use the subnet mask:
55.255.
as hat's happening if w is in binary:
1111. 111 00000
1 through
mask
e this
wo
ual
C address).
k
2 255.128
It's e ier to see w e write th
1111 11111. 11111111.100
As with any class C address, all of the bits in field
field3 are part of the network ID, but note how the
specifies that the first bit in field4 is also included. Sinc
extra bit has only two values (0 and 1), this means there are t
subnets. Each subnet uses the remaining 7 bits in field4 for its
host IDs, which range from 1 to 126 hosts (instead of the us
0 to 255 for a class
Similarly, to split a class C network into four subnets, the mas
is:
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