Subnets

Question

Given an IP address 156.233.42.56 with a subnet mask of 7 bits. How many hosts and Subnets are Possible ?

• A. 126 hosts and 510 subnet
• B. 128 host and 512 subnet
• C. 510 hosts and 126 subnet
• D. 512 hosts and 128 Subnet

Comments

@Soumya :)

Read the comment very above by Bikram sir, The question was ambiguous and this convention is not standard we will not subtract 2 from subnets according to RFC,IEEE :)

---

We will follow the RFC,IEEE standard always so 2^n will be used.

---

@Na462 yes we should follow 2^n for subnetting but Gate is following 2^n-1 you can reffer previous year question also .

Answer 1

Since its class B then total number of bits for the host are 16. The mask is give of 7 bits. This means that the subnets in the autonomous system will be taking 7 bits and the rest  16-7 = 9 bits are for the hosts per subnet.

Hence option C is correct

Answer 2

Class B network has the form N: N: H: H, the default subnet mask is 16 bits long.

There are an additional 7 bits to the default subnet mask. the total number of bits in 
the subnet are 16+7 = 23.

This leaves us with 32-23 = 9 bits for assigning to hosts.

7 bits of subnet mask corresponds to 2^7-2 = 128-2 = 126 subnets.

9 bits belonging to host addresses correspond to 2^9-2 = 512-2 = 510 hosts.
so, the answer will be 510 hosts and 128 subnets