12 VLANs

This chapter covers

  • How to divide a switch into multiple virtual switches with VLANs
  • How to configure trunk ports to carry traffic in multiple VLANs
  • Routing between VLANs with a router or multilayer switch

In chapter 11, we covered subnetting, which allows us to divide a network into smaller subnets. This is an example of network segmentation—the division of a network into smaller parts. Virtual LANs (VLANs, pronounced “V-LANs”), the topic of this chapter, can be likened to subnets in that they also allow us to divide up a network into smaller parts. With VLANs, we can divide a LAN (a broadcast domain) into smaller LANs, called VLANs. Whereas subnets allow us to segment the network at Layer 3, VLANs allow us to segment the network at Layer 2. In this chapter, we will cover three CCNA exam topics, all related to the topics of switches and VLANs:

  • 1.1.b Layer 2 and Layer 3 switches
  • 2.1 Configure and verify VLANs (normal range) spanning multiple switches
  • 2.2 Configure and verify interswitch connectivity

12.1 Why we need VLANs

To understand a technology, it’s important to understand why that technology exists—to understand the problem it solves. To demonstrate the role VLANs play in segmenting networks, let’s examine a network without segmentation, a network with Layer 3 segmentation, and a network with both Layer 3 and Layer 2 segmentation.

12.1.1 Layer 3 segmentation with subnets

12.1.2 Layer 2 segmentation with VLANs

12.2 Configuring VLANs and access ports

12.2.1 Creating and naming VLANs

12.2.2 Assigning ports to VLANs

12.3 Connecting switches with trunk ports

12.3.1 The IEEE 802.1Q tag

12.3.2 Configuring trunk ports

12.4 Inter-VLAN routing

12.4.1 Router on a stick

12.4.2 Multilayer switching

Summary