byte in a Class B IPv4 address are always 10. The lowest
number that can be represented in the first byte is
10000000, or decimal 128, and the highest number that
can be represented is 10111111, or decimal 191. Any IPv4
address that has a value between 128 and 191 in the first
byte is a Class B address.
Class C uses the first 3 bytes for the network ID and the
last byte for the host ID. Each Class C network can
contain up to 254 hosts. A Class C network always begins
with 110 in the first byte, meaning it can represent
networks from 11000000, or decimal 192, to 11011111, or
decimal 223. If an IP address contains a number in the
range 192 to 223 in the first byte, it is a Class C address.
The role of the address mask is to identify which portion
of the IP address is the network ID part and which
portion is the host ID. Similarly to IPv4 addresses,
address masks are also 32 bits long and use dotted
decimal notation. IPv4 addresses and address masks go
together hand in hand. Address masks specify the
network ID portion of an IP address by turning the
corresponding bit into a 1 and the host ID portion of the
IP address by turning the corresponding address mask
bit into a 0. The default address masks for the first three
classes of IPv4 addresses are as follows:
Class A: The default address mask is 255.0.0.0 or /8, indicating that
the first 8 bits of the address contain the network ID, and the other 24
bits contain the host ID.
Class B: The default address mask is 255.255.0.0 or /16, indicating
that the first 16 bits of the address contain the network ID, and the last
16 bits contain the host ID.
Class C: The default address mask is 255.255.255.0 or /24, indicating
that the first 24 bits of the address contain the network ID, and the last
8 bits contain the host ID.In each IP network, there are two reserved addresses.
The IP address where all the host ID bits are 0 is
reserved and is used to identify the network itself. For
example, the Class C network address 192.16.1.0 cannot