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Subnetwork
Assigning fixed IP addresses makes sense in cases where a
local network has a sufficiently large pool of IP addresses
available, or when a computer is always supposed to be ac-
cessible at a certain address (such as a web server or e-
mail server).
Dynamic IP
Address
A dynamic IP address is an IP address valid only for the du-
ration of one Internet or network session.
Every computer participating in the Internet must have a
uniquely assigned public IP address. Since only a limited
number of such IP addresses is available, they must be
used sparingly. That is why most of the Internet partici-
pants who dial in to the Internet receive a dynamic IP ad-
dress. They are called dynamic because every participant
receives a new public address that has not been assigned
yet each time he or she dials in to the Internet.
By contrast, dynamic addresses are usually used in local IP
networks because they are easy to handle, and because us-
ing them avoids incorrect IP address entries or unintention-
al double assignments. The DHCP service is responsible for
assigning unique dynamic IP addresses.
Subnetwork
A local IP network can consist of one subnetwork or be di-
vided into multiple subnetworks. The division into subnet-
works is performed when the local IP network is configured.
The subnetworks of a local IP network are also IP networks.
Subnet Mask
The subnet mask indicates which part of an IP address is
the network address and which the address of the comput-
er. The network address defines what is called the subnet.
Example 1
IP address:
192.168.178.247
Subnet mask:
255.255.255.0
The assignment of the first three groups of numerals in the sub-
net mask indicates that the first three groups of numerals in the
IP address define the network. The following addresses result:
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