D-Link DES-3250TG User Manual page 32

Address Classes
Address classes refer to the range of numbers in the subnet mask. Grouping the subnet masks into
classes makes the task of dividing a network into subnets a bit easier.
There are five address classes. The first four bits in the IP address determine which class the IP address
falls in.
•
Class A addresses begin with 0xxx, or 1 to 126 decimal.
•
Class B addresses begin with 10xx, or 128 to 191 decimal.
•
Class C addresses begin with 110x, or 192 to 223 decimal.
•
Class D addresses begin with 1110, or 224 to 239 decimal.
•
Class E addresses begin with 1111, or 240 to 254 decimal.
Addresses beginning with 01111111, or 127 decimal, are reserved. They are used for internal testing on
a local machine (called loopback). The address 127.0.0.1 can always be pinged from a local node
because it forms a loopback and points back to the same node.
Class D addresses are reserved for multicasting.
Class E Addresses are reserved for future use. They are not used for node addresses.
The part of the IP address that belongs to the network is the part that is 'hidden' by the '1's in the
subnet mask. This can be seen below:
•
Class A
•
Class B
•
Class C
For example, the IP address 10.42.73.210 is a Class A address, so the Network part of the address
(called the Network Address) is the first octet (10.x.x.x). The node part of the address is the last three
octets (x.42.73.210).
To specify the network address for a given IP address, the node part is set to all "0"s. In our example,
10.0.0.0 specifies the network address for 10.42.73.210. When the node part is set to all "1"s, the
address specifies a broadcast address. So, 10.255.255.255 is the broadcast address for the network
10.0.0.0.
Subnet Masking
A subnet mask can be applied to an IP address to identify the network and the node parts of the
address. A bitwise logical AND operation between the IP address and the subnet mask results in the
Network Address.
For example:
00001010.00101010.01001001.11010010
11111111.00000000.00000000.00000000
00001010.00000000.00000000.00000000
The Default subnet masks are:
•
Class A – 11111111.00000000.00000000.00000000
•
Class B – 11111111.11111111.00000000.00000000
•
Class C – 1111111.11111111.11111111.00000000
Additional bits can be added to the default subnet mask for a given Class to further subnet a network.
When a bitwise logical AND operation is performed between the subnet mask and the IP address, the
result defines the Subnet Address.
D-Link DES-3250TG Standalone Layer 2 Switch
NETWORK.node.node.node
NETWORK.NETWORK.node.node
NETWORK.NETWORK.NETWORK.node
10.42.73.210 Class A IP address
255.0.0.0
10.0.0.0
Class A Subnet Mask
Network Address
255.0.0.0
255.255.0.0
255.255.255.0
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