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I want to know that how can we calculate the Subnet prefix and CIDR, when the given information is only IP address and required No of hosts. For example: Suppose we have:
IP Address= 198.1.1.0 and Required No of hosts= 60
what will be the subnet prefix and CIDR?

I know how to calculate CIDR from NETMASK, but what if there is no netmask given ?? I have been trying to solve it for hours. Please give a clue or something as I am new to this subject.

Tom
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1 Answers1

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Ok if you know how to calculate CIDR from NETMASK this will be easy...

/30 = 4-2=2 hosts
/29 = 8-2=6 hosts
/28 = 16-2=14 hosts
/27 = 32-2=30 hosts
/26 = 64-2=62 hosts

basically, 

/x is 2^(32-x)-2 hosts

and if you have n hosts, you can use a /x with 

x=floor(32-LOG2(n+2))

you can remove one more host if you want an ip for the gateway

So in your example, you want 60 hosts : 

32-log2(60+2)=26.04... so /26
198.1.1.0 is ok as a prefix for a /26 (see others posts on the topic)

so 198.1.1.0/26 = 198.1.1.0/255.255.255.192

Golgot
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