Chapter 4. Layer 2 Fundamentals

This chapter covers the following topics:

• Understanding legacy LAN segment

• Introducing virtual LANs

• Trunking methods

• VLAN Trunking Protocol

• Configuring VTP/VLAN/Trunk

• VLAN pruning

• EtherChannel

• Understanding VLAN 1

• Private VLANs

This chapter explores the intricacies of virtual LAN (VLAN) design and implementation. Prior to the almost universal adoption of IP as the Layer 3 method of communication, most applications were written to rely upon Layer 2-protocols for communication. As a result, users needing to share applications and information needed to be on the same Layer 2 network. Despite the potential shortcomings of Layer 2-only designs, they are still commonly found in production networks. This chapter will also bring to light some of the negative aspects of a Layer 2 network, and why it is generally accepted to move off such infrastructure. It is difficult to replace existing Layer 2 networks because it takes time and manpower. In a lot of cases, the existing Layer 2 hardware is also replaced because, more than likely, the equipment is old. Therefore, the potential monetary cost of moving away from a Layer 2 network can be significant. These factors contribute to the continued existence of Layer 2-only networks.