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Subnetting, VLANs and routing: hands on with real configs Preview
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Section 1: Subnetting without fear

Why subnetting matters

Video 8 min Lesson 1 of 24 Sample clip Preview

Subnetting means dividing a larger IP network into smaller networks. It can feel like a maths exercise invented to make exams harder, but it solves real problems that every network engineer meets.

Reasons to subnet

  • Organisation: separate departments, floors or device types into their own networks, such as staff laptops, phones, printers, servers and guest Wi-Fi.
  • Security: traffic between subnets passes through a router or firewall, where it can be filtered. Guests should not reach your file server.
  • Performance: broadcasts, such as ARP and DHCP discovery, stay within a subnet. Smaller broadcast domains mean less noise.
  • Efficient use of addresses: give each network the size it needs rather than wasting large ranges.
  • Routing: well planned subnets can be summarised into fewer routes, keeping routing tables small.

Subnets and VLANs together

In modern networks, subnets usually go hand in hand with VLANs: virtual networks on the same physical switches. A typical office might use:

VLAN 10  Staff        192.168.10.0/24
VLAN 20  Voice        192.168.20.0/24
VLAN 30  Printers     192.168.30.0/26
VLAN 99  Management   192.168.99.0/28
VLAN 100 Guest Wi-Fi  10.100.0.0/22

Each VLAN is one broadcast domain and one IP subnet. A router or layer 3 switch connects them and enforces rules between them. You will build exactly this kind of design in the labs.

The skill you need

You should be able to answer, quickly and reliably:

  • How many usable hosts fit in a given prefix?
  • What are the network address, broadcast address and usable range for a given address and mask?
  • What prefix do I need for a subnet with a certain number of hosts?
  • How do I divide a network into several smaller subnets of different sizes?

With practice, most of these take seconds, without a calculator. Online calculators are fine for checking work, but if you depend on them entirely, you will struggle to troubleshoot or design quickly.

How this course approaches it

Section 1 builds subnetting skill from the binary basics to VLSM. Then we set up a lab and configure VLANs, inter VLAN routing, static routing and OSPF, followed by DHCP, NAT and access lists. The course ends with a small office network you design, configure and troubleshoot yourself.

Before the next lesson, write down the subnets you know on your own network, at home or at work, and their prefix lengths.

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