Subnetting question

How does one infer how many subnets one can get from an address?

Sample -
172.23.0.0/25

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Comments

Your subnet is 255.255.255.128. So your block size is 128. Your two network addresses are going to be 172.23.0.0 and 172.23.0.128.

So the first usable host in your first subnet will be 172.23.0.1 and your last will be 172.23.0.126. The 172.23.0.127 address will be the broadcast for the that subnet.

In short you need to understand the CIDR notation which is what the /25 is. It tells you that you are using 25 bits for network and 7 for host. I'm not sure what study material your using while going for your degree but I found Todd Lammle's book very easy to learn subnetting with.

rob42

Webmaster has written a very good guide IPv4 Subnetting TechNotes

Also, I'd read the many posts that have been made in this forum on the subject, if I were you. You should find that any questions that you have, have already been answered by many different people, in many different ways. I'm sure that you'll find one that suits your own way of thinking.

I like to approach the subject from a 'binary' perspective, as it suits the way I think. But, everyone is different and no one way is either right or wrong; just different.

If your confused about anything, just ask.