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1. Hi Rene,
Very Good article for Beginners.

Thanks,
Srini

2. Hi,
Under Class A subnetting section, the subnet mask should be 255.240.0.0 instead of 255.0.0.0.
Typo I guess.

3. Hi George,

Let's walk through this example together, that might help...

First we need to figure out the network address and to do that, we need to take a close look at the subnet mask:

255.255.255.248

The subnet mask defines how large each subnet is. You can do this in binary but I'll use decimal since it's faster. A quick method is to take the number 256 minus the subnet mask. We are looking at the 4th octet so that's 248:

256 - 248 = 8

We now know that each subnet has 8 addresses. Let's start counting from 0 to show you how it works:

Subnet #1 120.48.7.0
Subnet #2 120.48.7.8
Subnet #3 120.48.7.16
Subnet #4 120.48.7.24
Subnet #5 120.48.7.32
etc.

These are all "steps" of 8 addresses. If you keep counting then you'll end up at the subnet where you 120.48.7.104 address belongs to:

Subnet: 120.48.7.104
Subnet: 120.48.7.112
Subnet: 120.48.7.120

As you can see, your 120.48.7.104 is a network address. The next subnet starts with 120.48.7.112.

Finding the broadcast address is easy now, it's the last address in the subnet: 120.48.7.111.

Finding the first and last usable host addresses is also easy now...the first address is 120.48.7.105 and the last one is 120.48.7.110 (one before the broadcast address).

Does this help?

Rene

4. Hi Rene,

You are doing a good Job. I wanted to ask, in your example you have said 120.48.7.104 is the first address for that block? I thought .104 is the network and the first usable address will start from 105? If you could clarify that for me. Thanks

5. Ali,
You are correct, and I have corrected the error. Nice catch.

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