VLSM Part One: IP Addresses

The first part to understanding VLSM is understanding IP addressing itself.

An IP Address is an identifier for a network interface whether it's on a PC or a networking device. The IP address is actually a 32 bit binary series divided into 4 octets. The way we're used to looking at IP addresses is just for ease of use and readability. Let's take a look at an example:

Let's take 192.168.0.1/24 and break it down. The /24 on the right refers to bit notation by the way, meaning 24 bits are being used for subnetting. We'll get to that in a little.

In binary, we would have 11000000.10101000.00000000.0000000 for the IP address. Each one of those binary slots represents 1 bit of information.

Now, let's go back to the subnet. Remember how I said 24 bits were being used for subnetting? That means the first 24 bits of the subnet mask are all '1', meaning they're all part of the network portion of the address. In binary, that would be 11111111.11111111.11111111.00000000, which translates to 255.255.255.0.

That number probably sounds pretty similar to a number you usually see as your subnet mask on your PC or router. That's because most routers default to the RFC1918 Class C private network. 192.168.0.0/24.

Anyway, now we have the IP address and subnet mask all converted to binary, so what now? Guess you'll have to wait for my next post about subnetting.