I'm a student taking the cisco beginners course, but I'm running into some problems with subnetting.

When you have this network setup below, what are the valid number of hosts, and how does one calculate that. If I just take the host bits (n = 11) and apply 2^n then I get 121 as outcome. Which ofcourse is wrong. Could anyone tell me what I'm doing wrong here?

Network address:
Subnet mask:
Network address in binary: 00001010.00000000.00000000.00000000
Subnet mask in binary:     11111111.11111111.11111000.00000000


  • 3
    2^11 = 2048, 11^2 = 121. You've just messed up the order of operations. Commented Dec 7, 2015 at 15:34

2 Answers 2


How is 2^11 = 121? Firstly, 2^11 = 2048. The formula for finding the number of valid hosts are (2^n)-2 which is 2046. The 2 being the broadcast address and network address.

In the example you've given, is given as the network ID. Since the mask is a one, it means that the hosts jump in terms of 8 hosts, and will have 32 subnets. The broadcast ID of the first network will be

So the network ID of the next subnet will be, while it's broadcast ID will be and so on. You're not clear with your logic of subnetting. Please watch a few videos on how to subnet. I suggest this one and the rest of their series.


I made a video for my class to explain a simple way to understand the concept. If you need help understanding Class A subnetting, you should watch https://www.youtube.com/watch?v=tzyRGqLqiao

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