45. Practice Exercises with Hints
45.2 Networking Foundations – Quick Fire
Chapters 1–3 revise: private vs public IP, CIDR idea, well-known ports, TCP 3-way, UDP use-cases, OSI vs TCP/IP mapping for security.
| Exercise | Task | Hint |
|---|---|---|
| E1 | Is 10.0.5.20 public or private? Why does NAT matter for attackers? |
RFC 1918 private; NAT hides many hosts behind one public IP – scan public face first |
| E2 | Port 22 vs 80 vs 443 vs 3306 – service + risk one-liner each | SSH / HTTP / HTTPS / MySQL; never expose 3306 to 0.0.0.0/0 |
| E3 | Explain SYN flood idea in two lines – defence angle only | Half-open sockets; SYN cookies / rate limits / firewall – no attack recipe |
| E4 | Map "DNS" and "TLS" to OSI-ish layers students mix up | DNS often app/related; TLS encrypts above transport – interview: be clear, not pedantic |
| E5 | Sahyadri Traders Pune office: which ports must stay closed on the public Elastic IP? | DB, RDP if unused, random high admin panels; allow 443 (+22 from your IP only) |
| E6 | TCP vs UDP for DNS – when does each appear? | UDP 53 common queries; TCP 53 for large / zone transfers – restrict zone transfer |
| Red team (attacker) does | Blue team (defender) detects / stops |
|---|---|
| Port-scans public EIP looking for 22/3389/3306 open | Security group least privilege; alert on mass SYN; close unused ports |
| Abuses open DNS zone transfer | Disable AXFR to world; monitor; split DNS |
Ravindra Bagale's Tip
Students rattle off "OSI layer numbers" but forget that "port 3306 open to the public = disaster". In interviews, risk language > layer bingo. Got it?
Ravindra Bagale's Tip – मराठी
Students "OSI layer number" पटापट सांगतात पण "port 3306 public = disaster" विसरतात. Interview मध्ये risk language > layer bingo. समजले का?
Ravindra Bagale's Tip – हिंदी
Students "OSI layer number" फटाफट बोल देते हैं पर "port 3306 public = disaster" भूल जाते हैं. Interview में risk language > layer bingo. समझ आया?
Lab
On OWN EC2: sudo yum install nmap (Amazon Linux) if needed; from Kali host-only or your laptop against your EIP only: nmap -sS -T2 -p 22,80,443,3306 <YOUR_EIP>. Expect 3306 filtered/closed. Screenshot SG rules.
Real incident: Equifax breach (2017)
Public reporting (US congressional / company statements and major press) described attackers exploiting a known vulnerability in a web component (Apache Struts – patch available before the intrusion window, as reported) and then accessing large volumes of personal data. Weakness themes: unpatched internet-facing software + detection lag. Defence mindset for this exercise set: know your public ports, patch edge apps, monitor. Source: Equifax public statements and contemporaneous major reporting (verify; say "reported" for record counts – no invented numbers here).
Extended teaching notes
Why this lesson matters
Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.
Apply the fix across stacks
Same class of bug, same idea in every language.
Java / Spring Boot
Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.
ASP.NET Core
EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.
Node.js / Express
helmet, parameterised SQL, npm audit, avoid eval and shell concat.
Python / Django / Flask / FastAPI
ORM, autoescape, pip-audit, Bandit; never shell=True with user input.
PHP / Laravel
PDO/Eloquent, Blade escaping, composer audit.
Go / Ruby
database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.
nginx / Apache / Tomcat
Hide versions, TLS, security headers, least-open ports.
MySQL / PostgreSQL / MongoDB / Redis
Private networks, auth on, least-privilege users, no 0.0.0.0/0.
AWS / Azure / GCP
Roles not long-lived keys, private data stores, cloud audit logs on.
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)
- Write the lesson title, date and the exact lab target you are allowed to use.
- List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
- Run one safe check from the lesson on a lab system only. Paste the command and output.
- Write a two-sentence fix you would give a teammate.
- 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.