Learning Objectives

By the end of this section, you will be able to:

• Explain what routing is and why it is essential.
• Understand the purpose of a default gateway.
• Read and interpret routing tables.
• Distinguish between static and dynamic routing.
• Explain how ICMP supports network diagnostics.
• Review the role of NAT at Layer 3.
• Apply a structured Layer 3 troubleshooting methodology.

What Is Routing?

Imagine you are driving from Lagos, Nigeria, to Accra, Ghana.

You don't drive in a straight line. Instead, you follow a series of roads, highways, and intersections chosen to get you to your destination.

The Internet works in much the same way.

When your computer sends data to another device, the packet usually passes through multiple routers before reaching its destination.

The process of selecting the path that packets take across interconnected networks is called routing.

Without routing, devices could communicate only with others on the same local network.

How Routing Works

Suppose your laptop has the following IP address: