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

Question

A class B address has the subnet mask of $255.255.224.0$. what will be the IP address of the second host in the second sub network of the main network address $132.55.0.0$?

• A. $132.55.0.1$
• B. $132.55.32.2$
• C. $132.55.64.1$ 
• D. $132.55.64.2$

Comments

@Bikram Sir

If 5 bits from host are left then we can have maximum 30 usable hosts because

$\textbf{1. One will be used for subnet id i.e. 132.55.64.0}$

$\textbf{1. One will be used for broadcast address of that subnet i.e. 132.55.64.255}$

Please look at this example from cisco

Answer 1

We know class B default NetWork mask : 255.255.0.0 ..But subnet mask is 255.255.224.0..

So 3 1's have been borrowed from host bits which will now become subnet bit.

for subnets there are 8 subnets ( 2³ = 8 ) possible like 000, 001, 010 , 011 and so on .....  the first subnet is 000, second subnet 001, third 010 and fourth 011

Hence subnet no of 2nd subnet = 001 and second host will be : 00000   00000010..which can be written in dotted decimal notation as : 32.2. ( 001 00000  00000 010 )

The first 2 octets will remain undisturbed as they are part of network id.

So  B) is the correct answer..

Comments

@Nitesh

Read the best chosen answer, and plz read all the discussion before make any comment https://gateoverflow.in/1265/gate2007-67-isro2016-72

we discussed a lot , and for that geeksforgeeks link they follow old standards .

In GATE exam number of hosts always 2^h-2 and two times this types of question came and in both questions host we calculate using 2^h-2 

Now number of subnet is 2ⁿ in new standard , in GATE last time they ask this question in 2007, that time they follow old standard which is evident from their options.

Now coming to GATE 2007 question, the correct answer is 64, 1022 but as No option matches we have to select 62,1022 which is option C .

---

@ Nitesh Choudhary   

I made a poll here , just see the result .

https://www.facebook.com/groups/gateoverflow/permalink/652856628252884/

I hope you are convinced now , what convention to follow .

---

Sir 2^n subnets are possible in case of classless addressing but not for classful so 2nd address would be 010

Answer 2

I think for making it unambiguous question it should be like

what is the first valid ip of second subnet?

Answer 3

Option B.

Hope this is clear enough :)