Ravindra BagaleCourses & study guides मराठी Track your progress

Chapter 9: Domain Names, DNS and Subdomains

Practice Questions and Lab Exercises

Come on, now practice! Buy a cheap domain or use the hosts file trick, but do every lab by hand.

  1. Label each part of api.shop.example.co.in. (subdomain, second-level, TLD, root).
  2. Explain registrar, registry, name server and web host with one example each.
  3. List eight DNS record types and one use of each.
  4. What is DNS propagation really? How does TTL affect it?
  5. Why can't you use a CNAME at the apex? What do you use instead on Route 53?
  6. Lab: Attach an Elastic IP to your web server and map example.com and www.example.com using GoDaddy DNS (or your registrar). Verify with dig and nslookup.
  7. Lab: Create blog. and api. subdomains: blog as a static site on the same server, api as a reverse proxy to a Node app on port 3000.
  8. Lab: Create a Route 53 public hosted zone, recreate your records, switch the GoDaddy name servers and confirm with dig NS. (Delete the hosted zone afterwards if you don't need it.)
  9. Lab: Secure all names with one certbot command and test renewal with --dry-run.

Got it? Registrar, name servers and EC2 – three separate parts, and dig is your best friend. Now let's move on to dynamic websites – PHP, Python and Node.

Quick Revision

  • Domain parts, right to left: root . → TLD → your domain → subdomains (free, unlimited).
  • Registrar (buy/renew) ≠ name servers (answer DNS) ≠ web host (EC2).
  • Resolution: cache → resolver → root → TLD → authoritative → cached for TTL. "Propagation" = caches expiring.
  • Records: A (IPv4), AAAA, CNAME (alias, not at apex), MX, TXT, NS, SOA, CAA, Route 53 Alias.
  • Setup: website works → Elastic IP (details in 14.1) → GoDaddy DNS: A @ → EIP, CNAME www → @, remove parked records → server_name / ServerName + ServerAlias → reload → dig → certbot.
  • Route 53 option: hosted zone → copy 4 NS → set custom name servers at GoDaddy → recreate MX/TXT first.
  • Subdomain = DNS record + its own server block/vhost (or proxy to an app).
  • Verify: dig +short, dig @8.8.8.8, dig NS, dig +trace, nslookup; flush local cache if needed.

Extended teaching notes

Why this lesson matters

Cloud security is mostly IAM, network exposure, logging and secure defaults. The shared responsibility model means the provider patches the metal; you patch what you configure.

  • No public databases or public admin panels.
  • Roles / OIDC instead of long-lived access keys.
  • CloudTrail / Activity Logs / Audit Logs on and retained.
  • S3/Blob/GCS: Block Public Access; encrypt; least privilege.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.