Jun 112012

In the IPv4 addressing format, The number of networks allowed under the Class C address are:

A) 214         B) 27         C) 221          D) 224

This Question is asked in GATE-2012 (CS) Exam

Every class in IPv4 addressing has fixed format to specify IP – Address. Below is how the addresses are divided among the classes

Class-C IP address will have the following format

  • First 3 bits are fixed as 110.
  • Next 21 bits represent the Network-ID and last 4 bits represent the host-ID.

Since 21 bits are reserved for Network addresses. The total number of unique addresses possible in IPv4 Class-C is 221.

(The total size of Network-ID field is 24 out of which first 3 bits are fixed)

Hence, the correct answer is C)


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