Technology / Networking

How to Set Up Multiple Subnets

by Jon Welling
How to Set Up Multiple Subnets picture: A
Published on August 8, 2022

What is a subnet? If you landed on this post, you are most likely wondering what a subnet is, why to use subnets, and how to configure subnets. We'll answer those questions for you and more — like how to set up multiple subnets. So, let's get into it.

Ready to Learn How to Subnet?

Understanding how to subnet is crucial to being a successful network technician or administrator. Once you get the hang of it, subnetting is pretty easy. But at first, it can be a little challenging. If you’re wanting to learn how to subnet, CBT Nuggets has got you covered. Trainer Keith Barker has several subnetting training courses that are designed to get learners up to speed. There’s his IPv4 Subnetting training, as well as this IP Addressing and Subnetting one. Start becoming a subnetting pro today!

What is a Subnet?

A subnet is a carved-out piece of a network. It's that simple. Subnets are nothing more than individual pieces of anetwork grouped together and separated from other pieces of a network.

Let's use your home as an example. Most people only have one network in their home (unless they are an uber-geek IT tech). Is that the best option, however? I ask because consumers should also start being aware of IT security trends.

Here's a common scenario. Your home only has one network in it. That network has everything on it. That includes your Apple TV or Roku devices, laptops, desktops, smartphones, Amazon Echos, smart doorbells, and other fancy gadgets you own.

There's a growing security concern revolving around IoT devices, though. So much so that various government entities are starting to regulate things like your smart doorbell or Amazon Echo. Those security issues have become that serious.

So, how do you manage those IoT devices? One option is to create multiple networks in your home. Another option is to put those IoT devices on a different subnet.

Another example we all have become intimately familiar with over the past two years is working from home. Whether you are employed by an organization or run your own business out of your house, it's not a good idea to have business information flowing through the same network as your personal data. This is another good scenario where you might want to create different subnets.

Keep in mind, these are only examples. There are other ways of managing both scenarios above (like creating different VLANs on your network). So, if you are one of those Uber-geek IT people cringing at the moment, it's okay. These are only examples.

We're turning a single network into two networks with the examples above. Even though those 'networks' use the same hardware, radio signals, and wires, they act as two different networks. This is the idea behind subnetting.

How to Set Up Multiple Subnets

Creating multiple subnets on your network is typically easy. Of course, that all depends on the network equipment you are using and the network architecture of your organization. With that said, there is a lot of background information that you need to understand to create subnets, too.

So, first, we will discuss the tl;dr version of creating a subnet. Then we will discuss a little more of the technical aspects of creating subnets. This can be a complicated subject, so we highly encourage you to do more research after reading this article. It's tough to fit every piece of information (even from a high-level perspective) into a thousand-word article on this subject.

Let's use your home as an example again. Most homes typically only have one network. Most home routers aren't even capable of creating multiple subnets, but we will assume you have a really nice home router that can.

Your router will only have 254 usable network addresses on a typical home network. Most routers have a network IP address of 192.168.1.xxx. Otherwise, you can use any IP address between 192.168.1.2 through 192.168.1.255. Any IP address that falls into that network range uses one of those 254 IP addresses.

If we were to create a subnet, we would create a new IP address space. In this case, that IP address space might use the 192.168.2.xxx address space.  Otherwise, any IP address between 192.168.2.2 through 192.168.2.255 is usable.

Now we have two subnets on our network. Unless we specifically create network routes (think of a network route like a bridge that connects two networks), any device using a 192.168.1.xxx address can't communicate with a device using a 192.168.2.xxx address in the same 'network.' This is true even though both networks are using the same pieces of hardware, radio waves, and cables.

Note that in both examples above, we are assuming your router is using the 192.168.1.1 or 192.168.1.2 IP addresses. Otherwise, you could use those addresses as well.

That's essentially what creating a subnet is. Of course, this is way more complicated. So, let's dig into this more.

Each IP address is a 32-bit set of information. Each IP address includes four octets of data, typically displayed as four sets of three-digit numbers. Those are the numbers between each decimal point.

Each of those sets of numbers can be as large as 255. That's the base-10 representation of an octet of information. It's getting super Mathy up in here!

So, it would make sense that a network could contain way more IP addresses than the 254 we mentioned above.

That's because a network can be divided in multiple different ways. In the examples above, we created a /24 network space.  That means the first three numbers of the IP address specify which network, or subnet, in this case, your IP address belongs to. That's why simply changing from 192.168.1.xxx to 192.168.2.xxx created a new subnet.

We can create subnets where only the first two numbers designate the subnet your IP address belongs to. These networks have access to way more than 254 IP addresses. Likewise, simply changing your IP address from 192.168.1.xxx to 192.168.2.xxx wouldn't change which subnet your device belongs to.

What is a Subnet Mask?

Finally, each network address assignment also has a subnet mask.  Subnet masks were very confusing to me for a long time. I didn't understand why you needed them.

Let me explain what finally made sense to me. A subnet mask is a way for an internal network address to know which subnet it belongs to.  It doesn't identify subnets, though.

For example, let's say you have two of those bright orange buckets from Home Depot. Each bucket is large enough to hold every IP address you could ever have on a network. However, the IP address assigned to you doesn't have any information on which bucket it belongs to.

In this case, your computer is assigned the IP address 192.168.1.35.  With that information alone, your computer has no idea if the 192.168.2.35 IP address is in the same subnet as your IP address.

Why does that matter? Depending on which subnet your computer belongs to, it may not be able to communicate with another IP address. It may have to send information along different paths to get to it.

That's why the subnet mask is essential. That subnet mask tells your computer how many IP addresses are on the same subnet your laptop belongs to through the power of math. With that information, your computer can determine whether the IP address to which you need to send data is also on the same subnet.

Wrapping Up

We covered a lot of information in this article. Yet, we hardly scratched the surface. Networking has a lot of different components, and subnets are much more complicated than what we can cover in a thousand words. Consider this article a primer for subnets.

If you made it this far through the article, you are most likely hungry to learn more. We've got you covered!

Consider looking into a Cisco CCNA course online. The Cisco CCNA certification is the most widely recognized IT certification in the industry. It's a must for any IT pro.

There's also the CompTIA Network+ certification. CBT Nuggets has a variety of online Network+ courses for all skill levels. The CompTIA Network+ certification is an excellent way to learn networking since CompTIA is a vendor-neutral organization.

Those aren't the only courses CBT Nuggets offers, however. If you are just hungry for knowledge and don't care about certifications, there are many IT skill courses available, too. Have you ever wondered how to reverse engineer a subnet? We have you covered. Learn all about subnetting right now!


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