The Networking Handbook — 30 Days from Basics to Pro | by Ashwin Sridharan | November 2025

Day 3 — ARP, ICMP and Ping: how your machine finds its neighbors

Why it matters

Every network query, no matter how complex, starts with a simple question:

“Who has this IP address?” »

Whether your server pings a gateway, your pod calls a cluster service, or your VM hits an external API…
Your machine must know the MAC address of the destination (or its gateway) before the departure of a single packet.

Today we will explain the three essential elements of this discovery machinery:

• ARP → IP Cards → MAC
• ICMP → Messaging Protocol for Errors and Discovery
• Ping → ICMP Echo to test connectivity

This is one of the most important foundations of DevOps and SRE troubleshooting.

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Part 1 — ARP: Address Resolution Protocol

ARP answers the question:

“What MAC address does this IP have?” »

If you want to send a package to 192.168.1.20 your machine checks ARP first.

Simple analogy