Classful addressing (Class A, B, C) in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Classful addressing in IP networks?

Classful addressing is an early method of dividing IP addresses into fixed classes (A, B, C, D, E) based on the first few bits, to organize networks by size and purpose.

beginner

What is the range of the first octet for Class A IP addresses?

Class A IP addresses have a first octet range from 1 to 126. They are designed for very large networks with many hosts.

intermediate

How many networks and hosts does Class B addressing support?

Class B supports 16,384 networks and up to 65,534 hosts per network, suitable for medium-sized networks.

beginner

What is the default subnet mask for Class C addresses?

The default subnet mask for Class C is 255.255.255.0, allowing up to 254 hosts per network.

intermediate

Why is Classful addressing considered inefficient today?

Classful addressing wastes IP addresses because fixed class sizes don't fit all network sizes well, leading to unused addresses and poor scalability.

Which class of IP address starts with a first octet between 192 and 223?

A Class C

B Class A

C Class B

D Class D

Class C addresses have their first octet in the range 192 to 223.

What is the default subnet mask for Class B addresses?

A 255.0.0.0

B 255.255.255.0

C 255.255.0.0

D 255.255.255.255

Class B uses the default subnet mask 255.255.0.0.

Which class is designed for the largest number of hosts per network?

A Class D

B Class A

C Class C

D Class B

Class A supports the largest number of hosts per network, up to over 16 million.

What is the main limitation of Classful addressing?

A It wastes IP addresses due to fixed class sizes

B It supports unlimited hosts

C It uses variable-length subnet masks

D It is used only for IPv6

Classful addressing wastes IP addresses because fixed class sizes don't fit all network sizes well.

Which class is typically used for small networks with fewer than 254 hosts?

A Class D

B Class B

C Class A

D Class C

Class C is used for small networks, supporting up to 254 hosts.

Explain the differences between Class A, B, and C IP addresses in terms of their range and typical use.

Think about how many hosts each class supports and their first octet ranges.

Why did the networking community move away from Classful addressing to Classless addressing?

Consider the problem of wasted IP addresses and how modern methods solve it.