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For example, perhaps a user not only has a laptop (which itself can have both a 
wired and wireless interface, both consuming an IP address), but perhaps they 
also have a mobile phone (which likely features Wi-Fi), and a 
Voice over IP
 (
VoIP
) 
phone (there goes another address). If that user somehow manages to convince their 
supervisor that they also need a desktop computer as well as their laptop, there will 
be a total of five IP addresses for that one user. Suddenly, 254 addresses doesn't 
seem like all that many.
Perhaps a really good real-world example of this is a small restaurant in a busy 
city that offers free Wi-Fi to its customers. The person designing the guest network 
for their customers may assume that a 
/24
 network is more than enough, if they 
only have a hundred customers or so each day. While that logic may seem sound, 
consider that if the restaurant is next to a busy street, people that have Wi-Fi enabled 
on their phone may snag an address as they pass by, and if the DHCP addresses are 
configured to expire in 24 hours, then there will often be no available IP addresses 
at all most of the time. If you've ever attempted to connect to a restaurant Wi-Fi 
network and found yourself unable to access the internet after connecting, this 
could be a real-world example of a pain-point of not designing a network layout 
effectively.
The obvious answer to this problem is splitting up your network into 
subnets
. 
Although I won't go into the details of how to subnet your network (which would 
be beyond the scope of this book), I mention it here because it's definitely something 
you should take into consideration. In the next section, I'll explain how to set up 
your own DHCP server with a single network. However, if you need to expand your 
address space, you can easily do so by updating your DHCP configuration. When 
coming up with an IP address layout, always assume the worst and plan ahead. 
While it may be a simple task to expand your DHCP server, planning a new IP 
scheme rollout is very time consuming, and to be honest, annoying.
When I set up a new network, I like to divide the address space into several 
categories. First, I'll usually set aside a group of IP addresses specifically for DHCP. 
These addresses will get assigned to clients as they connect, and I'll usually have 
them expire and need to be renewed in about one day. Then, I'll set aside a block of 
IP addresses for network appliances, another block for servers, and so on. In the case 
of a typical 
/24
, I might decide on a scheme such as the following (assuming it's a 
small office with no growth planned):
Network: 192.168.1.0/24 
Network equipment: 192.168.1.1 - 192.168.1.10 
Servers: 192.168.1.11 - 192.168.1.99 
DHCP: 192.168.1.100 - 192.168.1.240 
Reservations: 192.168.1.241 - 192.168.1.254 

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Setting Up Network Services