DevNet Associate DEVASC 200-901 Official Certification Guide by Adrian Iliesiu (z-lib.org)

Addres

s Class

Bit Pattern

of First Byte

First-Byte

Decimal

Range

Host Assignment Range in

Dotted Decimal Format

A 0xxxxxx

x

1 to 127 1.0.0.1 to 127.255.255.254

B 10xxxxx

x

128 to 191 128.0.0.1 to 191.255.255.254

C 110xxxxx 192 to 223 192.0.0.1 to

223.255.255.254

D 1110xxxx 224 to

239

224.0.0.1 to

239.255.255.254

E 11110xxx 240 to

255

240.0.0.1 to

255.255.255.255

Class A uses the first byte for the network ID and the
other 3 bytes (or 24 bits) for the host ID. As you can
imagine, networks with 2 (more than 16 million) hosts
in the same network are nonexistent; technologies such
as classless interdomain routing (CIDR) and variable-
length subnet masking (VLSM) have been developed to
address the wastage of IPv4 addresses with the original
definition of classes of IPv4 addresses. The first bit of the
first byte in a Class A IP address is always 0. This means
that the lowest number that can be represented in the
first byte is 00000000, or decimal 0, and the highest
number is 01111111, or decimal 127. The 0 and 127 Class
A network addresses are reserved and cannot be used as
routable network addresses. Any IPv4 address that has a
value between 1 and 126 in the first byte is a Class A
address.

Class B uses the first 2 bytes for the network ID and the
last 2 bytes for the host ID. The first 2 bits of the first

24