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A.2 Subnet
Mask
At this point, one may start to wonder how to identify the node address and the network
address from the four number segments. Sadly, with only the IP address, no one can
meaningfully separate the node address from the network address, not even computers.
What is needed in addition to IP address is the Address Delimiter – The Subnet Mask. A
Subnet Mask has the same format as the IP address (XXX.XXX.XXX.XXX); however,
the segments are usually filled with either 255 or 0.
Ex.
Here are some valid subnet masks:
255.255.255.0
(Class C Subnet Mask)
255.255.0.0 (Class B Subnet Mask)
A.3 IP Address and Subnet Mask Couple
When combining IP address with Subnet Masks, the node address can be separated from
the network address in this way: (1) the node address is the IP address segment that maps
to the Subnet Mask segment(s) that is/are filled with 0; (2) the network address is the IP
address segment that maps to the Subnet Mask segment(s) that is/are filled with 255.
Ex.
Illustration of IP address / Subnet Mask mapping rule:
IP
address
192.168.2.3
Subnet
Mask
255.255.255.0
Solution
This IP address couple gives you:
Node
Address
3
Network
Address
192.168.2
Note:
The IP address/Subnet Mask mapping rule introduced above is generally true for most of
the TCP/IP networking applications; in some specialized networks, network
administrators can enter numbers other than 255 or 0 in the Subnet Mask segments for
network customizations. However, this advance TCP/IP application is beyond the scope
of this tutorial.