# Networking - Subnetting - Discussion

### Discussion :: Subnetting - Subnetting (Q.No.4)

4.

What is the maximum number of IP addresses that can be assigned to hosts on a local subnet that uses the 255.255.255.224 subnet mask?

 [A]. 14 [B]. 15 [C]. 16 [D]. 30

Explanation:

A /27 (255.255.255.224) is 3 bits on and 5 bits off. This provides 8 subnets, each with 30 hosts. Does it matter if this mask is used with a Class A, B, or C network address? Not at all. The number of host bits would never change.

 Nikhil said: (Feb 8, 2014) 255.255.255.224 i.e Binary of 255 is 11111111 and Binary number of 224 is 11100000. Here 1 Represent On bit and 0 represents Off bit. Then how to calculate Host Id. See Here, Formula Host Id = 2^off bit - 2 i.e 2^5 = 32 - 2 = 30. And Net Id is = 2^on bit = 2^3 = 8. That's why Answer is 30.

 Rahul said: (Mar 11, 2015) Simple. = 256-224 = 32. And here first add is network add and last one is broadcast so we are supposed to subtract these two add from 32. So max host we will connect = 30.

 Pratik said: (Jul 8, 2015) Thanks @Nikhil but can you explain that binary conversions till 255?

 Narsing said: (Jun 16, 2016) Decimal to binary conversion: 255.255.255.255 128 64 32 16 8 4 2 1 2 to the power of 7 = 128. 2 to the power of 6 = 64 . 1 1 1 1 1 1 1 1 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255. 11111111.11111111.11111111.11111111 255 255 255 255 Eg: 192.168.10.10 192-- 128 64 32 16 8 4 2 1 ------> 1 1 0 0 0 0 0 0 168 --> 1 0 1 0 1 0 0 0 10 ---> 0 0 0 0 1 0 1 0 10 ---> 0 0 0 0 1 0 1 0 That means where is the 1 is there will add those numbes, so will get decimal number.

 Sagar said: (Nov 29, 2016) Your answer is easy to understand, Thanks @Nikhil.

 Vasundhra said: (Jan 4, 2017) Not able to perceive, please explain in an easy way. Is there any formula to calculate subnet mask?

 Darth Vader said: (Apr 3, 2017) Convert it to binary: 11111111.11111111.11111111.11100000. You can't use 1s because they are mask bits, you can use 0s as host bits and they can get values between 0 to 31 (total 32 values). 2 of these 32 host values cannot be used as a host IP because one of them belong to broadcast and the other belong to the network address. There is a formula for this host calculation it is 2^(host bits)-2 For this example it is 2^5 - 2 = 32-2 = 30.

 Chaithanya said: (Jun 13, 2017) 24|27 = 3bits on 5 bits off. 2^h-2 h=hostsbits = 5, 32-2 = 30. Or simple total is 256 so 256-224=30.

 Dhananjay said: (Aug 25, 2017) Thanks.

 Seonti said: (Sep 3, 2017) Can anyone explain why it is /27?

 Nishu Kumar said: (Sep 24, 2017) (1)255.255.255.224 128+64+32=224. 2^3 =8, 2^5-2= 32 -2 =30 (2) formula; Block size = 256 - Actual subnet mask, =256 -224, = 32.

 Tara said: (Dec 9, 2017) @Seonti. Here the question is 255.255.255.224. Convert to binary it is 11111111 11111111 11111111 11100000. Count nos of 1 ...it is 27.

 Bijay Kc said: (Apr 5, 2018) Thank you @Nikhil.

 Ankit Chaturvedi said: (Apr 30, 2018) Total host= 2^( use off bits) - 2.

 Nikita said: (Aug 2, 2019) Thank you all for explaining it.

 Melin said: (Apr 30, 2020) Thanks for the explanation.