What is a subnet?

Introduction

This posts covers subnetting, and provides a few tutorials and practices for anyone beginning to learn subnetting. This posts also talks about some concepts and logic behind subnetting, and the importance of subnets in IT.

subnetting and networking

What is a subnet?

A subnet is a division of an IP space, used to segment your network, provide better security, and better allocate IP address space based on usage. You can also use subnets to create VLANs. This a deeper subject that focuses on logic instead of physical traditional networks but will not be covered within this post.

First Exercise

Lets say we want to do a /26.

Think of a subnet as a pie, /24 is the whole pie (complete subnet of 255). Then go ahead and divide this pie in half (now you have two halves of 128/128. This is a /25). Now go ahead and cut the pie again (now you have 4 equal slices of 64/64/64/64, this is a/26).

Each slice represents a new subnet, and when you add all the subnets back together you will always get 255.

Second Exercise

We have a network address of 10.10.1.0/24.

We want to create a subnet for 3 networks. One for printers, one for PCs, and one for Wireless Devices.

There are roughly:

• 50 PCs
• 40 Printers
• 60 Wireless Devices

How would you divide this address to accommodate these networks?

In this example I would use a /26 (each subnet has64 addresses, with 62 usable addresses). This is more than enough to accommodate each of these networks. Though most of the time in life, networks could vary in subnets. Meaning, to best manage IP address usage, and make sure that we are efficient. We can use a smaller subnet to save space.

Example, if we had only 20 Wireless Devices, and we used a /26 subnet. We would be wasting more than 40 addresses. A better solution would be to use a /27 which has 32 addresses, with 30 usable addresses.

Extra Information

After completing these exercises you might still be very confused on this topic. So lets add take aways. First misconception is subnetting does not give you extra IPs, it only gives you the ability to strategically slice an IP space you already have.

Second, Subnetting gives you a degree of network security due to Network Segmentation. By nature subnets are not able to communicate with each other unless you allow it through Firewall Zoning, ACL, or by creating subinterfaces on a switch (if you are using VLANs).

The Last thing is, with subnetting you are able to keep your network more organized. From a security standpoint, your offices from receiving will not have access to anything on your finance offices before you even configure a Firewall/ACL rule. Not only that but your network environment will look extremely organized.