Netmask - NETGEAR RT338 Reference Manual

This addressing structure lets IP uniquely identify each physical network and each node on each
physical network.
For each unique value of the network portion of the address, the base address of the range (host
address of all zeros) is known as the network address and is not usually assigned to a host. The top
address of the range (host address of all ones) is not assigned but is used as the broadcast address
for sending a packet simultaneously to all hosts with the same network address.

Netmask

In each of the above address classes, the size of the two parts (network address and node address)
is implied by the class. This partitioning scheme can also be expressed by a netmask associated
with the IP address. A netmask is a 32-bit quantity that, when logically ANDed with an IP address,
yields the network address. For instance, the netmasks for Class A, B, and C addresses are
255.0.0.0, 255.255.0.0, and 255.255.255.0, respectively.
For example, the address 192.168.170.237 is a Class C IP address, where the network portion is
the upper 24 bits. When ANDed with the Class C netmask, as shown here, only the network
portion of the address remains:
11000000 10101000
ANDed with:
11111111 11111111
Equals:
11000000 10101000
As a shorter alternative to dotted-decimal notation, the netmask may also be expressed in terms of
the number of ones from the left. This number is appended to the IP address, following a backward
slash ( / ), as "/n." In the example, the address could be written as 192.168.170.237/24, indicating
that the netmask is 24 ones followed by 8 zeros.
Introduction
Reference Guide for the Model RT338 ISDN Router
10101010 11101101 (192.168.170.237)
11111111 00000000 (255.255.255.0)
10101010 00000000 (192.168.170.0)
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