Configure TCP/IP - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 416

(256 - 240 = 16) as your incremental value in the third octet. The third octet must start
with 0 for the first subnet, the second subnet will have 16 in the third octet, and so on.
This means that some of your valid subnets are as follows (not in order):

Subnet Hosts Broadcast

x.0-255.0.0 x.0-255.0.1 through x.0-255.15.254 x.0-255.15.255

x.0-255.16.0 x.0-255.16.1 through x.0-255.31.254 x.0-255.31.255

x.0-255.32.0 x.0-255.32.1 through x.0-255.47.254 x.0-255.47.255

x.0-255.48.0 x.0-255.48.1 through x.0-255.63.254 x.0-255.63.255

They go on in this way for the remaining third-octet values through 224 in the subnet
column.

Working with Classless Inter-Domain Routing

Microsoft uses an alternate way to write address ranges, called Classless Inter-Domain
Routing ( CIDR ; pronounced “cider”). CIDR is a shorthand version of the subnet mask.
For example, an address of 131.107.2.0 with a subnet mask of 255.255.255.0 is listed in
CIDR as 131.107.2.0/24 because the subnet mask contains 24 1s. An address listed as
141.10.32.0/19 would have a subnet mask of 255.255.224.0, or 19 1s (the default subnet
mask for Class B plus 3 bits). This is the nomenclature used in all Microsoft exams
(see Figure 8.12).

fIgure 8.12 Subnet mask represented by 1s

Subnet mask in binary: 111 111111111 111111111111 00000000 . . .

Subnet mask in decimal: 255 . 255 . 255 . 0

(The spaces in the above example are only for illustrative purposes.
The subnet mask in decimal would actually appear as 255.255.255.0.)

Let's say an Internet company has assigned you the following Class C address and CIDR
number: 192.168.10.0/24. This represents the Class C address of 192.168.10.0 and a subnet
mask of 255.255.255.0.
Again, CIDR represents the number of 1s turned on in a subnet mask. For example, a
CIDR number of /16 stands for 255.255.0.0 (11111111.11111111.00000000.00000000).
The following is a list of all of the CIDR numbers (starting with a Class A default subnet
mask) and their corresponding subnet masks: