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Chapter 0 About 3–4 hours 42 questions total Graded in-browser Saved locally

Table of Contents

A beginner course that uses diagrams to grasp the flow, with short exercises and numeric questions inside each chapter so you can follow DNS behavior yourself. 42 questions in total, graded in-browser, saved locally.

Start with Chapter 1Jump to the comprehensive review

A beginner course where you grasp the flow through diagrams and then follow DNS behavior yourself through short exercises placed inside each chapter. Rather than formulas, the questions let you check the real moving parts of DNS — the delegation path, the remaining cache lifetime, and how many queries fly.

The goal is not just being able to configure A / AAAA / CNAME / MX, but being able to trace "who is holding that answer right now, and how many seconds until the picture changes" in both words and numbers. In the final Chapter 7, along with 8 case questions, you can also review all 42 questions from the whole course.

Overall diagram of DNS where the browser, stub, recursive resolver, and authoritative servers cooperate
First, it helps to grasp DNS as a chain of navigation with divided responsibilities. It is not one all-powerful server, but a baton relay between servers with different roles.

What makes this course different

1. Short exercises inside each chapter

You solve 1–3 questions right after reading the text, which makes it hard to get away with only "feeling like you understood."

2. More numeric questions than usual

You count remaining TTL, number of misses, the number of steps in MX resolution, and the wait time for negative caching by hand.

3. Graded in-browser

All 42 questions are graded in-browser, and your correctness is saved only in localStorage.

4. Comprehensive review at the end

Chapter 7 adds 8 case questions and also shows a review list of questions you have not yet solved.

Five viewpoints we keep reusing in this course

1. Who are you asking?
stub / recursive / authority
The party the user talks to is not the same as the one that holds the final answer.
2. Kind of response
referral / authoritative / cached / negative
A DNS response is not always "the final answer."
3. Type of question
A / AAAA / MX / TXT / ...
Same name, different type — different answer.
4. Remaining cache lifetime
expires_at = fetched_at + TTL
TTL decides when an update becomes visible.
5. Delegation boundary
Where is the zone cut?
The zone cut is the boundary where delegation splits responsibility between parent and child zones. In trouble, going back to "which zone is authoritative here" sorts things out.

Chapter overview

  • Chapter 1 Introduction
    The entry point — thinking of DNS as "name + type."5 questions
  • Chapter 2 Hierarchy and delegation
    Sort out domains, zones, zone cut, and glue.5 questions
  • Chapter 3 Recursive resolution
    Count the flow root → TLD → authority, and count cache hits.6 questions
  • Chapter 4 Record types
    Read A / AAAA / CNAME / MX / TXT / NS / SOA by their use cases.6 questions
  • Chapter 5 Cache and TTL
    Compute TTL and negative caching by hand, in seconds.6 questions
  • Chapter 6 dig and DNSSEC
    How to read dig output, layered caches, and the scope of DNSSEC.6 questions
  • Chapter 7 Comprehensive review
    8 case questions + full review of all questions.8 questions

    • Tips for studying

    1. Go in the order text → the short exercise right below it. It sticks faster than just reading.
    2. Do not skim the numeric questions in your head — write out expires_at / remaining TTL / time of miss on paper.
    3. Make sure you try both the recursive resolution simulator in Chapter 3 and the TTL simulator in Chapter 5.
    4. When the review in Chapter 7 surfaces a question you got wrong, go back to that chapter and review it for one or two passes.

    Prerequisites

    • Some experience touching web apps or APIs is enough.
    • If you have seen the terms IP address, URL, and server before, you can follow along.
    • Deep networking theory or cryptography theory is not required. We cover DNSSEC only as far as needed.
    • No external libraries — this runs on static HTML / CSS / JavaScript only.