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+17 votes

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

  1. $2^{14}$
  2. $2^{7}$
  3. $2^{21}$
  4. $2^{24}$
asked in Computer Networks by Veteran (355k points)
edited by | 2.9k views

2 Answers

+28 votes
Best answer

Answer is (c)

Class Leading
Size of network
 bit field
Size of rest
bit field
of networks
per network
Total addresses
in class
Start address End address
Class A     0     8     24     128 (27)     16,777,216 (224)     2,147,483,648 (231)
Class B     10     16     16     16,384 (214)     65,536 (216)     1,073,741,824 (230)
Class C     110     24     8     2,097,152 (221)     256 (28)     536,870,912 (229)
Class D (multicast)     1110     not defined     not defined     not defined     not defined     268,435,456 (228)
Class E (reserved)     1111     not defined     not defined     not defined     not defined     268,435,456 (228)

We have $32\text{ bits}$ in the $\text{IPV4}$ network

Class A $=\text{ 8 network bits + 24 Host bits}$

Class B $=\text{ 16 network bits + 16 Host bits}$

Class C $=\text{ 24 network bits + 8 host bits}$

Now for Class C we have $3\text{ bits}$ reserved for the network id...
Hence remaining bits are $21.$ Therefore total number of networks possible are $2^{21}$.

Similarly in Class B we have $2\text{ bits}$ reserved...
Hence total number of networks in Class B are $2^{14}$.

And we have $1\text{ bit}$ reserved in Class A, therefore there are $2^7$ networks.

And a better reasoning for the bit reservation is given here. have a look. 


answered by Boss (19.7k points)
edited by

Isnt the correct answer be 221-2, because first and last network IDs are not used as Network ID of any network

@anchitjindal07 the question asks for the number of networks "allowed" in class C network, and therefore base address and broadcast address are also allowed in it.
0 votes
ans c)
answered by Active (5.2k points)

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