IP Classes Commonly Used Explained | Generated by AI
Question: In IP address classification, the leftmost one or more binary bits are usually used to specify the network type. The commonly used IP address classes are:
A. 3 classes
B. 4 classes
C. 5 classes
D. 6 classes
The correct answer is A, but you chose B. Please explain the error.
Answer:
The correct answer is A. 3 classes.
Detailed explanation:
Traditional classful IPv4 addressing divides IP addresses into five classes (A, B, C, D, E) based on the first few bits of the address:
- Class A: 0xxxxxxx (first bit = 0) → 1.0.0.0 – 126.255.255.255
- Class B: 10xxxxxx (first two bits = 10) → 128.0.0.0 – 191.255.255.255
- Class C: 110xxxxx (first three bits = 110) → 192.0.0.0 – 223.255.255.255
- Class D: 1110xxxx (first four bits = 1110) → multicast addresses
- Class E: 1111xxxx (first four bits = 1111) → reserved (experimental)
However, in actual network usage and most textbooks/exams (especially in China), when people talk about “commonly used IP address classes”, they usually refer only to Class A, Class B, and Class C — because:
- Class D is used only for multicast
- Class E is reserved and not used in normal networks
Therefore, the commonly used IP address classes are three classes (A, B, C).
That’s why the correct answer is A. 3 classes.
Your choice B. 4 classes is incorrect because although there are technically five classes in total, the question specifically asks about “commonly used” classes, and the standard answer in most educational contexts (especially in certification exams like HCIA, CCNA introductory materials in Chinese) is three classes.
References:
- None (this is standard IPv4 classful addressing knowledge)