Configure TCP/IP - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 396

A Class B network has 2 bytes to use for node addresses. This is 2 16 minus the two
patterns in the reserved-exclusive club (all 0s and all 1s in the node bits) for a total of
65,534 possible node addresses for each Class B network.
Class C Networks
The first 3 bytes of a Class C network are dedicated to the network portion of the address,
with only 1 byte remaining for the node address. The format is Network.Network.
Network.Node.
In the example IP address 198.21.74.102, the network address is 198.21.74, and the
node address is 102.
In a Class C network, the first three bit positions are always binary 110. Three bytes,
or 24 bits, minus 3 reserved positions leaves 21 positions. There are therefore 2 21 (or
2,097,152) possible Class C networks.
The lead bit pattern of 110 equates to decimal 192 and runs through 223. Remembering
our handy easy-recognition method, this means you can always spot a Class C address if
the first byte is in the range 192-223, regardless of the values of the second and third bytes
of the IP address.
Each unique Class C network has 1 byte to use for node addresses. This leads to 2 8 , or
256, minus the two special patterns of all 0s and all 1s, for a total of 254 node addresses
for each Class C network.
Class D networks, used for multicasting only, use the address range
224.0.0.0 to 239.255.255.255 and are used, as in broadcasting, as
destination addresses only. Class E networks (reserved for future use at
this point) cover 240.0.0.0 to 255.255.255.255. Addresses in the Class E
range are considered within the experimental range.
Subnetting a Network
If an organization is large and has lots of computers or if its computers are geographically
dispersed, it makes good sense to divide its colossal network into smaller ones connected
by routers. These smaller networks are called subnets . The benefits of using subnets are as
follows:
Reduced Network Traffic We all appreciate less traffic of any kind, and so do networks.
Without routers, packet traffic could choke the entire network. Most traffic will stay on the
local network—only packets destined for other networks will pass through the router and
to another subnet. This traffic reduction also improves overall performance.
Simplified Management It's easier to identify and isolate network problems in a group of
smaller networks connected together than within one gigantic one.