Learning Objectives

By the end of this chapter, you should be able to:

• Explain why the Address Resolution Protocol (ARP) exists.
• Describe how ARP resolves an IPv4 address into a MAC address.
• Understand how switches build and use CAM (MAC Address) tables.
• Explain what a VLAN is and why it is used.
• Differentiate between broadcast domains and collision domains.
• Understand how Layer 2 technologies are used in enterprise networks and cloud environments.
• Troubleshoot common Layer 2 networking problems.

Introduction

In the previous section, you learned that:

• Devices on a network communicate using Ethernet frames.
• Every Network Interface Card (NIC) has a unique MAC address.
• Switches forward frames based on MAC addresses.

This raises an important question:

If applications communicate using IP addresses, but switches forward traffic using MAC addresses, how does a computer determine the destination MAC address?

This is the problem solved by the Address Resolution Protocol (ARP).

Address Resolution Protocol (ARP)