5 IP ADDRESS CLASSES IN COMPUTER NTEWORKS

classes of IP

1. Class Network ID bitsHost ID bits
Number of
Blocks
(Networks)
Block Size (IPs
per Network)
Usable Host IPs
per Network
A 8 24
2⁷ = 128 (0–127,
but 0 and 127
reserved → 126
usable)
2²⁴ = 16,777,216
2²⁴ - 2 =
16,777,214
B 16 16
2¹⁴ = 16,384
(first two bits
fixed: 10)
2¹⁶ = 65,5362¹⁶ - 2 = 65,534
C 24 8
2²¹ = 2,097,152
(first three bits
fixed: 110)
2⁸ = 256 2⁸ - 2 = 254
D (Multicast) — — — —
Used for
multicast only
E (Experimental) — — — —
Reserved for
research

2. In classful IPv4 addressing:
•Each class (A, B, C) has a fixed block size (number of IP addresses per
network) and a fixed number of such blocks (networks).
•Example:
•Class A → Few networks (128) but very large block size (16,777,216
addresses per network).
•Class B → Moderate networks (16,384) and medium block size (65,536
addresses).
•Class C → Many networks (over 2 million) but small block size (256
addresses).
Number of blocks = how many networks of that class exist.
Block size = how many IPs are in each network.

3. •Pv4 addresses are 32 bits long.
•These 32 bits are divided into Network ID and Host ID parts.
•Class A example: 10.0.0.0
•In Class A,
•Network ID = 8 bits
•Host ID = 24 bits
•That means:
•The first 8 bits (the first number: 10) identify the network.
•The remaining 24 bits identify hosts inside that network.
•So, the total number of addresses per network (block size) = 2²⁴ =
16,777,216
(2^24 possible combinations of host bits)
•Hence, the Class A network 10.0.0.0 includes addresses from
10.0.0.0 to 10.255.255.255.