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24-port NWay Ethernet Switch User’s Guide
Switch Management and Operating Concepts 77
For example, the IP address 10.42.73.210 is a Class A address
(the first number is between 1 and 126), so the first octet (10)
belongs to the network, and the remaining three octets belong to
the node (42.73.210). Since these numbers are not valid IP
addresses, some rules have been developed to make valid (and
unique) IP addresses from the network and note part of an IP
address.
To specify the network address that corresponds to 10.42.73.210,
the first octet – 10 is made into a valid IP address by adding
three octets of zeros to give a network address of 10.0.0.0. This
method is followed for all classes of a classed subnet.
Additional IP addresses for the subnetwork can be similarly
determined. When the remaining octets are set to all binary
ones, the broadcast address for the subnetwork is specified. For
our example, 10.255.255.255 would be the broadcast address for
the subnetwork (remember that eight 1’s in binary form is 255 in
decimal form).
Note that for Class C networks, only the last octet is set to zeros
for the network address, and all ones for the broadcast address.
For Class B networks, the last two octets are set to zeros for the
network address and all ones for the broadcast address.
To specify the network address for a given IP address, the node
section 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 section is set
to all “1”s, the address specifies a broadcast address that is sent
to all hosts on the network. So, 10.255.255.255 is the broadcast
address for the network 10.0.0.0. Note that for a Class C
networks, only the last octet is set to “1”s for the broadcast
address and that for a Class A networks, the last three octets are
set to “1”s for the broadcast address.