CABLE OVERVIEW
Version 1.0, 05/2015. Copyright 2012 Hitron Technologies
22
Version 1.0, 05/2015. Copyright 2015 Hitron Technologies
22
CDA3-35 User’s Guide
In order to define the extent of a subnet, and to differentiate it from the main network,
a subnet mask is used. This “masks” the part of the IP address that refers to the main
network, leaving the part of the IP address that refers to the sub-network.
Each subnet mask has 32 bits (binary digits), as does each IP address:
A binary value of 1 in the subnet mask indicates that the corresponding bit in the
IP address is part of the main network.
A binary value of 0 in the subnet mask indicates that the corresponding bit in the
IP address is part of the sub-network.
For example, the following table shows the IP address of a computer (192.168.1.1)
expressed in decimal and binary (each cell in the table indicates one octet):
The following table shows a subnet mask that “masks” the first twenty-four bits of the
IP address, in both its decimal and binary notation.
This shows that in this subnet, the first three octets (192.168.100.1, in the example IP
address) define the main network, and the final octet (1, in the example IP address)
defines the computer’s address on the subnet.
The decimal and binary notations give us the two common ways to write a subnet
mask:
Decimal: the subnet mask is written in the same fashion as the IP address:
255.255.255.0, for example.
Binary: the subnet mask is indicated after the IP address (preceded by a forward
slash), specifying the number of binary digits that it masks. The subnet mask
255.255.255.0 masks the first twenty-four bits of the IP address, so it would be
written as follows: 192.168.1.1/24.
Table 5: IP Address: Decimal and Binary
192 168 0 1
11000000 10101000 00000000 00000001
Table 6: Subnet Mask: Decimal and Binary
255 255 255 0
11111111 11111111 11111111 00000000
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