I apologize if this is a too simple question for the people here, but this is my problem:

I am tasked to determine the subnetmask (binary), subnet mask (decimal) and the Prefix notation for a set amount of hosts. All I have is the number of hosts.

Can anyone explain how I go about determining this for for example 75 hosts? I don't know how to start and hours of googling has gotten me nowhere.

edit: this is different from other similar posts because I don't have anything other to go from than the number of hosts.

  • You need to understand what a subnet mask is and what it does. Once you understand that, the rest is easy.
    – Ron Trunk
    Mar 13 '19 at 12:21
  • Hi CUPA and welcome ... the concept of "borrowing bits" is normally rather unhelpful. I'd suggest you read the section "Total IPv4 Network Host Addresses" and "Total Usable IPv4 Network Host Addresses" in Cown's linked answer networkengineering.stackexchange.com/a/53994
    – jonathanjo
    Mar 13 '19 at 12:30

if your subnet needs to be as big a net for 75 hosts you cleary need a single /25 subnet.

How do I know that?
The answer is quite simple:
Within a /24 net you can store 255 IP adresses minus 2 adresses for host- and broadcast adresses which are the first and the last adress in your adress space.
Within a /25 net you can store half (128) of the amout of a /24 net (minus 2 adresses = 126).
Within a /26 net you can store a quarter (64) of a /24 net and a half of a /25 net (minus 2 adresses = 62).
So basically a /26 doesn't fit your needs because it's too small.

Furthermore you should read Cown's linked answer which might help you: https://networkengineering.stackexchange.com/a/53994

Best regards.

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