Lesson 3

Planning an IP Addressing and Subnetting Strategy

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Lesson 3: Planning an IP Addressing and Subnetting Strategy

Once you have determined what types of IP addresses your network will use and have

decided how many LANs you are going to create and how you’re going to connect

them, you can begin the process of calculating the network’s IP addresses, subnet

masks, and default gateway addresses. You can also plan how the network administra-

tors are actually going to perform the TCP/IP configuration tasks.

After this lesson, you will be able to

■ Understand how to subnet a network

■ Calculate a subnet mask

■ Calculate IP addresses on subnetted networks

Estimated lesson time: 30 minutes

Obtaining Network Addresses

In Lesson 1 of this chapter, you learned about the circumstances under which to use

registered and unregistered IP addresses, and you have presumably used this informa-

tion to design a network infrastructure in which the computers use the appropriate

address types. If some or all of your computers require registered IP addresses, you can

obtain them in one of two forms, depending on how many addresses you need.

Planning

If you need only a few registered addresses, you can obtain them singly from your

ISP along with an appropriate subnet mask, although you will almost certainly have to pay an

extra monthly fee for them. If the computers requiring the registered address are all on the

same LAN and must communicate with each other, be sure that you obtain addresses in the

same subnet. If you need a large number of registered IP addresses, you can obtain a net-

work address from the ISP and use it to create as many host addresses as you need.

A network address is the network identifier portion of an IP address plus a subnet

mask. For example, if your ISP were to assign you the network address 192.168.65.0,

with a subnet mask of 255.255.255.0, you can assign IP addresses ranging from

192.168.65.1 to 192.168.65.254 to your computers. The network address you receive

from the ISP depends on the class of the address and on the number of computers you

have requiring registered addresses.

Off the Record

In practice, the network address your ISP assigns you will not be part of

the private address range used in this example. Also, it will probably be more complex than

the address shown here, because the ISP will be assigning you only a small portion of the

addresses assigned to them.