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GATE CS 2012 · Computer Networks

Question 23

MCQPrinted as CS Q.231 markWrong answer: −1/3Easy (estimate)

Question

In the IPv4 addressing format, the number of networks allowed under Class C addresses is

Choose one option
Official answer and solution
Official answer
C
From
Official GATE 2012 answer key

Solution

Calculate the total number of network identifiers available in the Class C IPv4 address space.

  1. An IPv4 address comprises 32 bits divided into 4 octets.

  2. In traditional classful addressing, Class C addresses allocate:

  • 24 bits for the Network ID (first 3 octets)
  • 8 bits for the Host ID (last octet)

  1. The leading 3 bits of a Class C network ID are permanently fixed as 110 (defining the first octet range 192 to 223).

  2. Subtracting the 3 fixed prefix bits from the 24 network bits leaves:

24−3=21 variable network bits24 - 3 = 21 \text{ variable network bits}
  1. Therefore, the total number of distinct Class C networks allowed is:
2212^{21}

(Each Class C network can support 28−2=2542^8 - 2 = 254 assignable hosts).

Final answer

C

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper
GATE 2012 Computer Science and Information Technology (CS)
Question
23 of 65, printed as CS Q.23
Section
Computer Science and Information Technology

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