Test by Bikram | Computer Networks | Test 1 | Question: 18

Question

Number of subnets can be formed by using the subnet mask $255.255.248.0$ in a class B network _________

Answer 1

There are 16bits in NID and 16bits in HID  in Class B network. 

Now 248 in binary is  11111 000

5 number of  1  in HID part

So $2^5 = 32$ total subnets are there .

http://www.ietf.org/rfc/rfc1878.txt
 

Hence number of subnets are 32.

Comments

Why we subtracted 2 here 32 subnets are possible.We subtract in case of host but 32 subnets are possible here.

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yes , you are correct .We should not subtract .

Earlier we used to but now we dont waste them , 

"This practice is obsolete! Modern software will be able to utilize all definable networks"

this is exact line mentioned in this RFC 

http://www.ietf.org/rfc/rfc1878.txt