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broadcast 
address
. Anything that's sent to the broadcast address is effectively sent to every IP 
in the block, so we can't really use it for anything but broadcasts. In summary, keep 
in mind that an IP address ending in 
.0
 can't be used, and neither can an IP address 
that ends in 
.255
.
The following is a list of common CIDR values and their impact on the number of 
available IP addresses:
CIDR
Total Usable IP Addresses
/32
1
/24
254
/16
65,534
/8
16,777,214

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Chapter 11
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 277 
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Going back to the example IP layout mentioned earlier in this section, I set aside 
a group of IP addresses starting with 
192.168.1.1
 through 
192.168.1.10
 for use 
by network appliances. Typical 
devices that would fit into this category would be 
managed switches, routers, wireless access points, and so on. These devices typically 
have an integrated web console for remote management, so it would be best to have 
a static IP address assignment. That way, I'll have an IP address available that I can 
use to access these devices. I like to set up network appliances as the first devices 
so that they all get the lowest numbers when it comes to the last number of each IP 
address. This is just personal preference.
Next in the example layout, we define IP addresses 
192.168.1.11
 through 
192.168.1.99
 for servers. This may seem like quite a few addresses for servers, and 
it is. However, with the rise of virtualization and how simple it has become to spin 
up a server, this block could get used up faster than you'd think. Feel free to adjust 
accordingly.
Now we have our DHCP pool, which consists of addresses 
192.168.1.101
 through 
192.168.1.240
. These IP addresses are assignable to any devices that connect to our 
network. Typically, I like to have these assignments expire in one day to prevent 
one-off devices from claiming and holding onto an IP address for too long, which 
can lead to devices fighting over a DHCP lease. In this situation, you'd have to clear 
your DHCP leases to reset everything, and I find that to be too much of a hassle. 
When we get to the section on setting up a DHCP server, I'll show you how to set the 
expiration time.
Finally, we have addresses 
192.168.1.241
 through 
192.168.1.254
 for the purposes 
of DHCP reservations. I generally refer to reserved DHCP addresses as 
static leases
, 
but both terms mean the same thing. These addresses will be assigned by DHCP, but 
each device with a static lease will be given the same IP address each time. You don't 
have to separate these into their own pool, since DHCP will not assign the same 
address twice. It may still be a good idea to separate them though, if only to be able 
to tell from looking at an IP address that it's a static lease, due to it being within a 
particular hypothetical block. Static leases are good for devices that aren't necessarily 
a server, but still need a predictable IP address. An example of this may be an 
administrator's desktop PC. Perhaps they want to be able to connect to the office via 
VPN and be able to easily find their computer on the network and connect to it. If 
the IP was dynamically assigned instead of statically assigned, it would be harder for 
them to find it.
After you carve up your IP addresses, the next thing is to make sure that they're 
accurately documented. If you don't focus on documentation now while designing 
services, you will definitely regret it later. You can consider setting up a private Wiki 
server, for example. 

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Setting Up Network Services