ch03 IP Addressing.pdf - The Cisco Learning Network

26 Chapter 3: IP Addressing
Step 1: Figure Out Network and Host Requirements
In this step, you need to do two things:
■ Determine the number of hosts that do, or will, exist on the largest segment
in your network.
■ Determine the maximum number of segments that you have in your
network--this will tell you how many networks, or subnets, you’ll need.
If you already are dealing with an existing network, then you have a lot of analysis
ahead of you. You’ll need to perform the above two tasks, counting hosts on each
segment, and the number of segments that you have. Remember that when you are
counting hosts, each device with a connection to the segment needs to be counted—
this includes PCs, servers, routers, servers, printers, and other devices. Remember that
a segment could be used in a logical sense, like all the ports off of a switch, or a VLAN.
Switching is discussed in more depth in Chapter 7 and VLANs in Chapter 8. You
might even want to leave some room for growth by taking your final numbers and
adding to them.
To assist with the remaining 5 steps, I’ll create an imaginary network. This
network has 14 segments and the largest segment has 14 devices on it. You’ve
been assigned a single class C network number (192.168.1.0). Now you’re ready
to proceed to step 2.
Step 2: Satisfy Host and Network Requirements
In the second step, you’ll use three formulas:
1. 2 X => number of networks you need (X represents subnet bits)
2. 2 Y
- 2 => number of hosts on your largest segment (Y represents host bits)
3. X + Y